The invention relates to a device, a kit, and a method for delivering a dose of a medicament comprising activated carbon particles for the treatment of rectal and anal fistulae.

Background

A fistula is an abnormal conduit or connection between bodily organs or vessels that do not usually connect. Fistulas or fistulae can form in many parts of the body. Anal fistula and rectal fistula are conditions in which tubes form between a sufferer's rectum and intestines, or other internal organs, or between a sufferer's rectum and the external skin adjacent to the sufferer's anus. For example, fistulas situated high in the anus (high anal fistula) may connect with the urinary tract, and fistulas situated low in the anus (low anal fistula) may, in women, pass into the vagina. In addition to significant pain, rectal and anal fistulas commonly become infected and accumulate pus.

Furthermore, such fistulas can allow the leakage of fecal matter from the rectum.

Anal and rectal fistulas may form as a result of disease or infection. For example, anal fistulas may arise if a sufferer's anal glands become blocked, thereby forming an abscess that points through from the rectum to the skin surface in the anal region. The growth of fistulas may be accelerated, and fistulas themselves may be maintained, by a local build up of toxins in the rectum.

Anal and rectal fistulas may be treated by surgical procedures. Such procedures are undesirable, however. One potential side-effect of the surgical procedure to treat fistula is an increased probability that a patient will develop anal incontinence in the years following the surgery.

Activated carbon has the ability to adsorb chemicals such as unwanted toxins and has been proposed for use in the treatment of rectal and anal fistulas. However, there are a number of problems associated with the use of activated carbon for this purpose. Activated carbon is typically supplied as an extremely fine powder having a high surface area. The European Pharmacopoeia describes activated carbon as a black, light powder free from grittiness. There are, however, problems associated with handling such a powder as the fine scale of the powder particles means that the particles easily become airborne and the activated carbon tends to contaminate its immediate surroundings with a fine dust of activated carbon. These fine powders of activated carbon may have particles sizes predominately smaller than 170 mesh (predominantly smaller than 89 μηη), i.e. they may be powders in which most of the particles in the powder would pass through a sieve of mesh size 170 mesh and in which the average particle size is considerably smaller than this. The inventor of the present application investigated a typical sample of activated carbon powder using a microscope and found that the particles were smaller than 20 μηη in diameter. Such a fine powder is, therefore, inherently dirty and difficult to handle.

A fine powder also does not flow easily, and it is difficult to administer a dry dose of activated carbon. A dry dose of activated carbon is a dose of activated carbon that has been maintained in dry conditions until the point of delivery.

Handling problems and poor flowability of fine activated carbon powders also present difficulties in production. For example, it may be difficult to fill a device with a metered dose of fine carbon powder. To alleviate some of the handling problems, activated carbon has previously been prepared for oral administration. However, orally administered activated carbon must pass through a patient's entire digestive system before it reaches the rectal region and in doing so a large, and unpredictable, proportion of the carbon will have absorbed various chemicals and lost its activity. The activity retained by a dose of activated carbon may vary depending on the food in the patient's digestive system. There may also be a natural variation in the activity retained by a dose of orally administered carbon from patient-to-patient, and even from day-today in the same patient. By increasing the dose of orally administered activated carbon it may be possible to increase the proportion of carbon that reaches the rectum in an activated state. However, activated carbon absorbs many essential chemicals and nutrients on passing through the patient's digestive system and it is undesirable to take large oral doses of activated carbon over a prolonged period of time for this reason.

Activated carbon has been prepared for rectal administration by pre-mixing to form a suspension with a liquid such as propylene glycol (PG). The problem with such suspensions is that the carbon loses its activity very quickly.

Suspensions, therefore, need to be used shortly after preparation and have little practical shelf-life.

Activated carbon has also been coated to allow it to survive through a patient's digestive system when taken orally. It may be difficult to prepare a coating that accurately dissolves to release the activated carbon only once it has passed into a patient's rectum. Furthermore, such coating may reduce the activity of the carbon in the same manner as described above for activated carbon suspensions and thereby may reduce the effectiveness of such coated particles for the treatment of rectal and anal fistulas.

Summary of Invention

The invention provides a device, a method, and a kit for delivering a dose of a medicament comprising activated carbon particles into a patient's rectal cavity as defined in the appended independent claims, to which reference is now being made. Preferred or advantageous features of the invention are set out in various dependent sub-claims.

In a first aspect, a device for delivering a dose of a medicament comprising activated carbon particles into a patient's rectal cavity comprises a rectally- insertable cannula having a proximal opening, a distal opening, and a cavity defined through a body of the cannula between the proximal opening and the distal opening for containing the dose of medicament. An openable closure acts to close the proximal opening of the cannula. For example, a one-way valve may act to close the proximal opening of the cannula, or alternatively a suitable closure means such as a frangible seal that ruptures on the application of pressure may be used. A frangible seal, or similar ruptureable closure, could only be used one time, and would need to be replaced if the cannula is to be re-used.

The device further comprises an actuation means for driving a volume of fluid, such as a liquid, through the one-way valve (or alternative closure means) and the cavity to flush the dose of medicament out of the cavity through the distal opening of the cannula. A gas, such as air or an inert gas, may be used as a driving fluid, particularly where the particle size of the medicament is low. For example gas may be a preferable driving fluid for medicament particles having a particle size of between 0.02 mm and 0.2 mm, for example particles between 0.05 mm and 0.15 mm. It is preferred, however, that the driving fluid is a liquid, particularly for larger particle sizes. A liquid may provide fewer uncomfortable side effects and may assist in distributing the medicament within the rectal cavity.

The actuation means or actuator may comprise a suitable volume of liquid or may be loadable with a suitable volume of liquid for flushing the cavity. For example, the actuation means or actuator may have a chamber for holding a volume of liquid that may be filled with a suitable liquid prior to use of the device. A suitable liquid is preferably a liquid that does not influence the adsorptive capacity of the carbon and may be water or a medical solution, for example a saline solution. The skilled person will be aware of suitable liquids that can safely be injected into a patient's rectum. By containing the medicament within the cavity of the cannula, the activated carbon can be maintained separately from the liquid until the point of delivery. As the activated carbon can be stored in a dry condition it does not lose its activity for a considerable period of time and, therefore, the activity of the carbon particles is high as they are injected into the patient. Preferably, a driving liquid is used that does not mix to a great extent with the activated carbon during delivery but merely forces the activated carbon out of the distal opening of the cannula and into a patient's rectum. The function of the liquid is to act like a piston to drive the carbon into the patient, and the liquid may therefore be referred to as a driving liquid or a propellant. Some liquids that are suitable for rectal injection may react with activated carbon and lower its potential efficacy. However, as it is preferred that the activated carbon does not mix with the driving liquid to any great extent, such liquids are not excluded from use as the driving fluid.

It may be advantageous if the volume of the cannula cavity is predetermined to provide a single dose of the medicament. Thus, a dose may be readily metered by filling the entire cavity with the medicament.

It is particularly preferable that the cavity is shaped to facilitate the entire dose of medicament being delivered to the patient by a single actuation of the actuation means. For example, it is preferred that the volume of liquid driven through the openable closure will flush substantially the entire dose of medicament out through the distal opening of the cannula with minimal backwash and/or retention of medicament within the cannula. It may, therefore, be advantageous that the internal cavity is shaped to be long, but narrow, to restrict the opportunity for internal turbulence as the volume of liquid is flushed through the cavity. By allowing substantially 100 % of the medicament to be delivered, the patient can be confident that they are receiving a consistent dose time-after-time. A further benefit is the lack of waste of un-delivered medicament.

The volume of medicament that can be delivered may be determined by the volume of the internal cavity of the cannula. Different cannulas may be provided having the same external dimensions, but different internal dimensions to provide a device or devices that can deliver different volumes of medicament.

The flow rate of liquid passing through the cannula cavity may be important in delivering the medication effectively. If the flow rate is too slow, for example, the liquid can infiltrate into the carbon particles and may not act as an effective propellant. Although the flow rate within the cannula is partially determined by the actuation means and the pressure that the actuation means is capable of generating, the internal shape and dimensions of the cavity may be important for the delivery of the medicament. Preferably, the cavity should be able to contain a sufficient amount of the medicament for delivery to the patient (although multiple deliveries may be required if a large dose of medicament needs to be administered), but be dimensioned to deliver the dose using a minimal volume of the driving liquid.

Characteristics that can be used to define particulate materials include the average particle size and particle size distribution. One common means for determining average particle sizes and particle size distributions is to separate the particles by passing the particles through a series of sieves. A standard method for determining the particle size of granular activated carbon is provided in ASTM D2862.

Preferably, the medicament consists of particles of activated carbon having an average particle size greater than 0.02 mm or more preferably greater than 0.05 mm. For example, if the particle size is determined by sieving a portion of powder through a graded series of sieves, the average particles size determined in this way is preferably greater than 0.02 mm or 0.05 mm. If the average particle size is lower than 0.02 mm then the medicament may be difficult to handle, as it will be prone to forming an airborne dust. Such fine particles are difficult to wet and may also clump or agglomerate during storage. Therefore, such particles may not flush from the cannula easily. The inventor of the present invention carried out experiments in which he attempted to flush a typical, fine activated carbon powder (particle size predominantly smaller than 89 μηι and average particle size likely to be lower than 20 μηι ) out of a cannula. In these experiments, between 20% and 50% of the fine activated carbon powder was not ejected from the cannula. Thus, it is difficult to administer an accurate dose of the carbon in this manner if the particle size of the activated carbon is too small.

Preferably the medicament consists of activated carbon particles having an average particle size of greater than 0.02 mm, for example between 0.05 mm and 1 mm, for example between 0.1 mm and 0.5 mm, particularly preferably between about 0.2 mm and about 0.3 mm. It may be particularly preferred that 85% or more of the activated carbon particles have diameter in the range from 0.089 mm to 0.3 mm, when measured by a sieve analysis. The activated carbon may be activated carbon wherein 85% or more of the activated carbon particles have diameter in the range from 0.104 mm to 0.297 mm. The activated carbon may be activated carbon wherein 85% or more of the activated carbon particles have diameter in the range from 0.125 mm to 0.297 mm. A particularly preferred activated carbon is activated carbon wherein 85% or more of the activated carbon particles have diameter in the range from 0.152 mm to 0.297 mm.

In addition to the preferred particle size ranges stated above, it is preferred that the activated carbon has a bulk density or apparent density of between 0.4 g/cm ³ and 0.5 g/cm ³ , preferably about 0.44 g/cm ³ or 0.45 g/cm ³ . Bulk density may be calculated according to the standard procedure set out in ASTM D2854. It is preferred that the activated carbon particles are formed by grinding carbon material to the desired size. Ground activated carbon has an irregular particle shape and this irregular shape may be particularly suited to being cleanly delivered from a device according to an embodiment of the invention. Loading a cannula with the medicament may be an action undertaken by a patient. However, it may be convenient if the device is preloaded with the medicament. The medicament may, therefore, be loaded into the cannula cavity under controlled conditions and sealed at one end by the openable closure and at the other end by a sealing means. Such sealing means may, for example, be a removable seal that is removed by the user before delivery or a frangible seal that breaks on actuation. A suitable sealing means may be a cap or sheath that protects the external surface of the cannula, or at least of an insertable portion of the cannula. The sealing means may even be a oneway valve that allows passage of the contents of the cavity to pass out of the cannula when the device is actuated.

In order to facilitate the flushing of the medicament from the cannula cavity it is preferable that the cannula cavity has a length extending longitudinally along the cannula between the distal opening and the proximal opening. It is preferable that the ratio of cavity length to cavity diameter (taken perpendicular to the length) is greater than 5:1 , preferably greater than 7:1 . The ratio of cavity length to cavity diameter may be as much as 20:1 or 50:1.

It is preferable that the diameter of the distal opening is between about 2 mm and about 5 mm. It is noted that the opening need not be circular and the cannula cavity need not have a circular cross-section. Where the distal opening is not circular the term diameter refers to the maximum dimension of the opening. The relatively large diameter of the distal opening facilitates the egress of the medicament from the cavity during actuation of the device. If the opening is too small, there is a risk that the full dose of medicament may not be delivered in a single actuation of the device.

Preferred doses of activated carbon may be in the range of 0.5 grams to 10 grams. A preferred single delivery of activated carbon weighs about 1 gram or 1.2 grams. Assuming that the activated carbon has a bulk density of between 0.4 g/cm ³ and 0.5 g/cm ³ , the volume defined by the internal cavity of the cannula is preferably in the range of 1 cm ³ to about 25 cm ³ . Preferred ranges are between 1 .25 cm ³ and 20 cm ³ , or between 1.5 cm ³ and 5 cm ³ , for example between 1 .75 cm ³ and 4 cm ³ or between 2 cm ³ and 3 cm ³ . Particularly preferred volumes are between 2.2 cm ³ and 2.75 cm ³ , for example 2.5 cm ³ or 2.6 cm ³ .

The internal cavity of the cannula preferably has a substantially circular cross- section. It may be advantageous to define a proximal cross-section, i.e. the cross-section of the cavity at its proximal end, a maximum cross-section, i.e. the maximum cross-section of the cavity, and a distal cross-section, i.e. the cross-section of the cavity at its distal end.

Preferably, the maximum cross-section is greater than the proximal cross- section and the proximal cross-section is greater than the distal cross-section.

Preferably, the proximal cross-section has a diameter of between 5 mm and 8 mm, for example between 5.5 mm and 7.5 mm, or between 6 mm and 7 mm. Preferably, the maximum cross-section is between 6 mm and 10 mm, for example between 7 mm and 9 mm, or between 7.5 mm and 8 mm.

Preferably, the distal cross-section is between 1.5 mm and 4 mm, for example between 2 mm and 3.5 mm, or between 2.5 mm and 3 mm.

Preferably, the length of the cavity is between 140 mm and 90 mm, for example between 100 mm and 125 mm, or between 1 10 mm and 120 mm.

The cannula may be made from any suitable material, for example from medical grade polyethylene or polypropylene. It may be advantageous if at least a portion of the cannula is transparent. This would allow patients to check whether or not a full dose of medicament has been delivered.

The means for actuation or actuator may be directly coupled to the cannula, with the one-way valve (or any other suitable closure) disposed between the actuation means and the cannula cavity. Close proximity of the actuation means and the cannula may provide certain difficulties if self-delivery of the medicament is required, however. For example, it may be awkward to self- administer a dose of activated carbon particles if the actuation means is directly attached to a rectally-insertable cannula as there may be difficulties in reaching the activation means. Thus, it may be advantageous that the device further comprises a length of flexible tubing disposed between the one-way valve closing the proximal opening of the cannula and the actuation means. A length of flexible tubing may be particularly advantageous where the actuation means is a manual actuation means such as a syringe or a bellows. Such an arrangement may allow the actuation means to be placed in a more convenient position for delivery of the dose of medicament following insertion of the cannula. Thus, it is preferable that the flexible tubing is between 30 cm and 60 cm in length.

The actuation means may be a manually-operated actuator for example a syringe or a bellows or a bulb. The manually-operated actuator is preferably capable of being filled with a driving liquid from a source of such liquid. For example, if the driving liquid is water then it may be supplied as water for injection in a container, such as a flask or a vial. This water may then be transferred to an actuation means, such as a syringe, prior to use of the device. It is preferable, therefore, that the actuation means is removably coupleable from the device to allow it to be filled or loaded with the driving liquid and then coupled to the device in a suitable arrangement for forcing the driving liquid through the openable closure into the cannula cavity.

It may be advantageous for the actuation means to be an automatic actuator that delivers a volume of a driving liquid on, for example, the press of a button. For example, the actuation means may be a motorised actuator that is operable to drive liquid from a source of liquid through the openable closure and the cannula cavity to deliver the dose of particular medicament.

There may be a number of advantages to the use of an automatic actuator. For example, the driving liquid may be forced through the cannula cavity at a flow rate that is optimised for both clean delivery of the medicament and patient comfort. Manual operation, for example of a syringe actuator, may be too hesitant, thereby failing to deliver the full dose of medicament, or may be too enthusiastic, causing patient discomfort.

As stated above, it is desirable that the flow rate of the driving liquid is not too slow. It is preferred that the minimal flow rate of driving liquid within the cannula cavity is at least about 0.08 m/s, preferably at least 0.09 m/s or 0.1 m/s. As the preferred internal shape of the cannula is tapered towards its distal end, the exit flow rate of the driving liquid is greater than the minimal flow rate within the cavity. Thus, the driving liquid may be driven such that it passes through the distal opening of the cannula and into the patient at a flow rate of greater than 0.6 m/s, often greater than 0.8 m/s. It is possible to envisage the exit flow rates of the driving liquid as being up to 2 m/s.

It may be undesirable to insert the cannula too deeply into a patient's rectum. Overly deep penetration may result in a risk that the patient may be injured by the cannula. Thus, it may be advantageous that the device comprises a flange or collar that extends radially outwards from an external surface of the cannula at a predetermined distance from the distal opening to determine the correct depth of insertion of the cannula into the patient's rectum. In a preferred usage, the cannula is inserted into the rectal ampulla so that the medicament may be delivered to the rectum's mucus lining. Such a flange or collar presents a physical barrier that prevents or hinders a portion of the cannula proximal to the flange or collar from easily being inserted through a patient's anus. The flange or collar may also help provide a user with purchase on the cannula to allow the application of insertion force in the direction of a longitudinal axis of the cannula. For example, a user may apply a force on a proximal surface of a flange or collar in order to insert the cannula to a depth at which a distal surface of the flange or collar abuts the patient's anus.

It is desirable to deliver the medicament to an appropriate position within the rectal cavity. The anal channel is typically between 2 and 3 cm in length, and the insertable portion of the cannula needs to be longer than this. Preferably, the device is insertable to a depth of between 5 cm and 10 cm, preferably between 6 cm and 8 cm, for example about 7 cm. Thus, if the device comprises a flange or collar, then the insertable portion of the cannula may be defined as that extending between the distal end and the flange or collar.

The device may additionally comprise a second flange or collar extending radially outwards from the external surface of the cannula to facilitate the application of an insertion force in a direction along a longitudinal axis of the cannula. In this optional arrangement the second flange would be located closer to the proximal opening of the cannula than a first flange used for determining the maximum depth of insertion.

Without the first or second flange/collar for facilitating the application of an insertion force, it may be difficult for some patients to grip the cannula and insert a cannula to an appropriate depth for delivery of the medicament.

Preferably a device as defined herein is used to deliver a dose of medicament comprising or consisting of activated carbon for the treatment of fistulas for example rectal and/or anal fistulas. It may be particularly advantageous for the cannula to be preloaded with medicament in a controlled environment. In such circumstances, the loaded cannula may be conveniently supplied as a disposable component containing a preloaded quantity of medicament. Such a preloaded cannula could be attached to a device, the device could be activated to deliver the medicament, and then the spent cannula could be removed from the device and disposed of. Thus, in a second aspect the invention may provide a rectally-insertable cannula having a proximal opening, a distal opening, and a cavity containing a dose of a particular medicament defined within a body of the cannula between the proximal opening and the distal opening, in which the proximal opening is closed by an openable closure such as a one-way valve or frangible seal for allowing passage of liquid into the cannula cavity and the distal opening is closed by a seal, for example a removable seal, or a frangible seal, or a cap. The distal opening may be closed by a displaceable plug, for example a plug of petroleum jelly. The rectally insertable cannula further comprises a coupling for allowing the cannula to be coupled to an actuation means for driving liquid through the openable closure and the cannula cavity to flush to particular medicament out of the cavity through the distal opening. Advantageously, the coupling may be a standard luer-lock fitting.

Preferably the rectally-insertable cannula is loaded with a particulate medicament comprising, or consisting of, activated carbon particles.

A rectally-insertable cannula as described herein may be a separate, disposable component-part of a device as described above in relation to the first aspect of the invention.

It may be convenient for a patient suffering from anal or rectal fistula to be supplied with a kit of parts for treatment of the disease comprising a device as described above. Thus, a third aspect of the invention may provide a kit for the treatment of anal and rectal fistula comprising a device as described above in relation to the first aspect of the invention, a supply of activated carbon particles, and a source of liquid for flushing the activated carbon particles through the device. The liquid for flushing the activated carbon particles could be any suitable liquid. Preferably, the liquid is a liquid that does not influence the adsorptive properties of the activated carbon particles and is safe for injection into a patient's rectum. The skilled person will be aware of many such suitable liquids but as an example the liquid may be sterile water, for example water for injection or a salt solution.

As described above, it may be advantageous for the activated carbon particles to be preloaded into disposable, rectally-insertable, cannulas. Thus, the invention may further provide a kit for the treatment of anal and rectal fistula comprising a disposable, rectally-insertable, cannula as described above in relation to the second aspect of the invention, and an activation means that can be filled or loaded with a volume of driving liquid. The disposable cannula is removably-coupleable to the activation means such that the activation means is capable of driving a volume of the liquid through the openable closure of the cannula and the cannula cavity to flush the dose of activated carbon out of the cannula cavity through the distal opening of the cannula. The kit may also comprise a supply of the driving liquid. Preferably, the kit comprises a plurality of rectally-insertable cannulas, each cannula being removably-coupleable to the activation means and each cannula being loaded with a single dose of activated carbon.

In a further aspect, the invention may provide a method for delivering a dose of medicament comprising particles of activated carbon into a patient's rectum. The method comprises the steps of inserting a distal end of a cannula into the patient's rectum, the cannula having a proximal opening at a proximal end of the cannula, a distal opening at the distal end of the cannula, and a cavity containing the dose of medicament defined within a body of a cannula between the proximal opening and the distal opening. The proximal opening is closed by an openable closure such as a one-way valve or a frangible seal for allowing passage of liquid into the cannula cavity. The method further comprises the step of driving a volume of fluid, preferably a liquid, into the cavity through the openable closure to flush the dose of medicament out of the cavity through the distal opening of the cannula and into the patient's rectum. The method may be carried out using any device or kit as described above.

The method may comprise the further step of loading particles of activated carbon into the cannula cavity. Such a step would be required where the patient is supplied with the medicament in a form that is not preloaded into the cannula.

The method may further comprise the step of coupling the cannula to an activation means for driving the volume of liquid into the cavity through the openable closure. The activation means may be coupled to a source of liquid for driving the liquid into the cavity or may be loaded with the liquid in a separate method step.

Specific Embodiments of the Invention

Specific embodiments of the invention will now be described with reference to the Figures in which;

Figure 1 illustrates a device for delivering a dose of a medicament comprising activated carbon particles according to an embodiment of the invention;

Figure 2 illustrates a rectally-insertable cannula for use as a component part of the device illustrated in Figure 1 ;

Figure 3 illustrates a longitudinal cross-section of the rectally-insertable cannula of Figure 2;

Figure 4 illustrates a kit of parts for the treatment of rectal and anal fistulas comprising a device according to the embodiment of Figure 1 and a source of sterile water;

Figures 5 to 10 illustrate method steps involved in using the kit of Figure 4; and

Figure 1 1 is a schematic diagram illustrating the positioning of the device according to the embodiment of figure 1 for use in delivering a medicament.

Figure 1 illustrates a device 10 for delivering a dose of a medicament comprising activated carbon particles into a patient's rectal cavity. The device comprises a rectally-insertable cannula 20, a syringe 30, and a length of flexible tubing 40 coupling the syringe 30 to the cannula 20.

The cannula 20 is illustrated in greater detail in Figures 2 and 3. The cannula 20 has a generally elongated shape and has a proximal end 25 and a distal end 26. A cavity 22 is defined within a body 23 of the cannula 20, the cavity having a proximal opening 21 at the proximal end of the cannula leading into the cavity 22 and a distal opening 24 at the distal end of the cannula leading out of the cavity 22. The cavity 22 extends longitudinally between the proximal opening 21 and the distal opening 24.

The body 23 of the cannula 20 further defines a radially-extending flange or collar 27, which extends around a circumference of the cannula body 23 between the proximal end 25 and the distal end 26. A portion of the cannula body extending from the radially-extending flange toward the proximal end of the cannula may be termed a proximal portion 25a of the cannula body 23. Likewise, a portion of the cannula body 23 extending from the radially- extending flange 27 to the distal end 26 may be termed a distal portion 26a of the cannula. The distal portion 26a may also be termed the insertable portion.

In the specific embodiment described herein, the cannula is formed as a two- piece construction. Thus, the distal portion of the cannula body 26a and the proximal portion of the cannula body 25a are formed as separate polyethylene components and then joined together to form the cannula 20. The radially- extending flange is formed as part of the proximal portion of the cannula 25a, but could clearly be formed as part of the distal portion of the cannula 26a. The cannula may also be formed as a single component.

The distal portion 26a of the cannula is externally-sized and shaped to be inserted through a human anus into a human rectum in order to deliver the medicament beyond the anal channel and into the patient's rectal ampulla. Accordingly, the distal or insertable portion 26a has a length of 7 cm and has a substantially circular external cross-section. The distal portion 26a is tapered at an angle of about 2° and has an outer diameter of 6.5 mm at the distal end 26. The radially-extending flange 27 has a substantially circular cross- section and a diameter of 3 cm. The proximal portion 25a of the cannula body 23 is also of substantially circular cross-section and tapers from an outer diameter of about 15.5 mm adjacent to the radially-extending flange to an outer diameter of about 8.7 mm at the proximal end 25 of the cannula.

The cavity 22 defined within the cannula body 23 extends longitudinally through the cannula body from the proximal end 25 to the distal end 26. At the distal end 26, the cavity terminates at the distal opening 24. The distal opening is of substantially circular cross-section and has a diameter of 2.8 mm. At the proximal end of the cannula the cavity 22 is spanned by a one-way valve 50 (shown schematically in Figure 3). The diameter of the cannula cavity at the proximal end is 6.3 mm. The one-way valve 50 is actuatable to allow liquids to enter the cavity 22 through the proximal opening 21 of the cannula, but does not allow the passage of material contained within the cavity 22 of the cannula out of the cavity through the proximal opening 21 . The cavity is about 120 mm in total length from the proximal opening to the distal opening. The cavity has a maximum diameter in the region of the radially-extending flange, where the internal cavity diameter is 7.7 mm. The volume of the cavity is about 2.6 cm ³ , and the cannula is designed to be loaded with about 1 .2 gram of activated carbon particles having a bulk density of about 0.45 g/cm ³ .

An upper surface 27a of the radially-extending flange 27 acts as a stop to prevent the cannula from being inserted too far into a patient's rectum. As the cannula is inserted to its maximum penetration depth, the upper surface 27a of the radially-extending flange abuts the patient's anus and prevents inadvertent over-penetration. It is clear that the radially-extending flange does not need to extend around the entire circumference of the cannula in order to perform this function. Any radially-extending projection that hinders passage of the cannula through the anus may be used if over-penetration is a concern.

A lower surface 27b of the radially-extending flange 27a may act as a lug that allows a user to apply an insertion-force in the direction of the distal end 26 of the cannula to facilitate its insertion. The proximal end 25 of the cannula body 23 defines an internal cavity 28 in which a thread linkage is pressed so as to allow the cannula to be coupled to a source of driving liquid. The thread on the thread linkage is compatible with luer fittings as are well known in the medical profession. Luer fittings are commonly used to attach tubing and syringes and needles for medical use.

The internal surface of the cavity 22 is substantially cylindrical in cross-section and does not comprise any sudden changes in cross-section in order to minimise turbulence when a liquid is forced through the cavity 22.

In use, a medicament comprising activated carbon particles is contained within the cavity 22. The cavity 22 and the distal opening 24 are sized and shaped to optimise delivery of activated carbon particles having an average particle size of between 0.15 mm and 0.3 mm. Particles of this size range are easier to handle compared with fine activated carbon particles previously used for medical treatments and do not stick or agglomerate within the cavity to a great extent, which would hinder their delivery. As the particles are loaded within an elongated cavity that has a wide opening, the water entering the cavity through the one-way valve effectively acts to push the particles out of this opening. Preferably the water does not mix with the particles within the cavity (although some mixing is inevitable) but rather the front of the water entering through the valve pushes the cavity full of activated carbon particles ahead of it.

The activated carbon particles can be produced by known methods from organic materials, such as wood or coconut shells, and ground to the desired particle size, for example a particle size of between 0.15 mm and 0.3 mm.

When loaded within the cavity 22, the activated carbon particles are prevented from escaping through the proximal opening 21 by means of the one-way valve 50 that spans the proximal opening. The distal opening 24 may also be closed by a closure means in order to retain the particles within the cavity 22. For example, the device may comprise a displaceable plug, a removable seal or a frangible seal spanning the distal opening 24. Alternatively or additionally, the device may comprise a cap that acts to close the distal opening 24 and, thereby retain any medicament within the cavity 22 until it is desired to use the device.

The cannula body is formed in sections by an injection moulding process from polyethylene. Polyethylene is a substantially inert material that is commonly used in medical devices. It is noted that the cannula may be formed from any suitable medical material and that the person skilled in the art would be aware of such material. For example, the cannula may be made from a

polypropylene, a polycarbonate, or some other convenient medical grade polymer.

The syringe is a standard syringe having a liquid capacity of 12 ml, and comprises a plunger 31 that is slidable within a barrel 32. The syringe has a threaded luer-type connection 33, which allows the syringe to be coupled to the flexible tubing 40. The syringe acts as an actuation means of the device for driving a volume of liquid through the cannula cavity 22 to flush a dose of medicament contained within the cannula cavity.

The flexible tubing 40 is formed from a flexible medical-grade polyvinyl chloride (PVC) and has an internal diameter of 2.6 mm, a length of 45 cm, and a capacity (i.e. the volume defined by the lumen of the tubing) of 2.4 ml. Each end of the flexible tubing terminates in a luer-type connection 41 , 42. A first luer connection 41 allows the flexible tubing to be connected to the proximal end of the cannula 20 while a second luer connection 42, at the opposite end of the flexible tubing to the first luer connection 41 , allows the flexible tubing to be connected to the syringe 30.

It may be particularly convenient to supply a patient with both the device and any further elements that they need to self-administer a dose of a medicament comprising activated carbon particles. Thus, it may be advantageous to supply component elements of a device for delivering a dose of medicament and other materials in the form of a kit. An embodiment of such a kit is illustrated in Figure 4. This kit includes component parts of a device as described above, i.e. a rectally insertable cannula 20, a syringe 30, and a length of flexible tubing 40 for connecting the syringe to the cannula (the flexible tubing is shown connected to the cannula). The kit also comprises a container filled with water for injection 60. The water for injection is used as a driving fluid to expel the medicament through the cannula and into the patient.

The kit may comprise other components. For example, the kit may include a supply of activated carbon for loading into the cannula. The kit may comprise a plurality of cannulas, each one pre-loaded with a dose of activated carbon.

In Figures 3 and 4, the cannula 20 is shown with its distal portion 26a sheathed within a cap 29. The cap comprises a stopper or bung 29a and a downwardly depending sheath 29b, and both sheaths the distal portion of the cannula 26a and closes the distal opening 24 thereby retaining medicament within the cannula. It is noted that, in any embodiment of a device, a waxy lubricant such as petroleum jelly (e.g. Vaseline®) may be pre-applied to the cannula beneath the cap. The lubricant may, advantageously, act as a plug to close the distal opening of the cannula in addition to, or instead of a stopper portion of the cap. If the distal opening is closed by an application of a lubricant (such as petroleum jelly or Vaseline®) the lubricant may act to retain carbon within the cannula during handling immediately prior to application of a dose, but is removed by the force of the carbon particles once the device is activated.

The cannula is supplied pre- loaded with a medicament consisting of particles of activated carbon. The kit illustrated in Figure 4 may be used to deliver a dose of a medicament comprising activated carbon particles as described below.

Figures 5 to 10 illustrate a method of using the kit as illustrated in Figure 4 in order to deliver a dose of activated carbon particles into a patient's rectal cavity. The individual component parts of the kit are removed from packaging in which they are supplied and set out before the user. The plunger 31 of the syringe 30 is withdrawn to the 1 1 ml marking on the barrel 32 of the syringe (as illustrated in Figure 5). The user then removes a sealing cork 61 that acts to seal the container of water for injection 60 (illustrated in Figure 6). The container of water 60 is maintained in an upright position so that its contents are not spilled. The syringe 30 is coupled to the water container 60 in order to charge the syringe with water. The threaded luer connection 33 of the syringe engages with a corresponding mating thread in the neck 62 of the water container 60 (illustrated in Figure 7).

The water container 60, with the syringe now affixed, is inverted (illustrated in Figure 8). The plunger 31 of the syringe 30 is then depressed to the 3 mm mark. This action causes air within the barrel of the syringe to be forced into the water container 60, which pressurises the container. The plunger is then withdrawn again. On withdrawal of the plunger, the water for injection passes into the barrel of the syringe. If required, the plunger can be repeatedly depressed and withdrawn. After these steps the barrel of the syringe should be filled with water for injection from the container of water 60 (this is illustrated in Figure 9). Clearly, any technique for filling the syringe with the water may be used.

The cannula 20, which is preloaded with the medicament, is coupled to the flexible tubing by screwing in the luer connections on the flexible tubing with equivalent connections on the cannula. Likewise, the flexible tubing is also connected to the syringe filled with water by coupling the luer connections on the flexible tubing and on the syringe (Figure 10).

Immediately prior to use the cover or cap 29 is removed from the cannula 20. This opens the distal opening 24 such that the medicament can be forced out. If desired, the external surfaces of the distal portion 26a of the cannula may be lubricated, for example with petroleum jelly. Such lubrication may improve a patient's comfort on inserting the cannula. In some embodiments the distal portion of the cannula may be pre-lubricated. As mentioned above, a lubricant may also act to block the distal opening and prevent egress of carbon particles from the cannula until the device is activated. The distal portion 26a of the cannula 20 is then inserted carefully through the patient's anus so that the distal end 26 and the distal opening 24 enter the patient's rectal cavity. The cannula should be inserted until the radially-extending flange 27 abuts the anus and prevents further insertion. Figure 1 1 is a schematic illustration showing a cross-section of a patient's rectum showing the presence of rectal and anal fistulae 1 100 leading from the rectum 1200 or anal canal 1 150 to the patient's skin. A cannula 20 is schematically shown in the correct, inserted, position for delivery of activated carbon. To be effective, it is desirable that the activated carbon is delivered to the internal surfaces of the upper rectum. It is thought that the carbon may then act to remove toxins that would otherwise prevent the healing of the fistulae 1 100. Thus, it can be seen that, when correctly positioned the distal portion of the cannula is able to deliver a portion of medicament beyond the anal canal 1 150 and to the rectum 1200.

With the cannula in place, the plunger 31 of the syringe 30 is pressed quickly. The plunger should preferably travel to its full extent over a period of no longer than 2 seconds. The water for injection contained within the barrel of the syringe is forced out of the syringe and through the flexible tubing 40, through the one-way valve 50 that closes the proximal opening 21 of the cannula and into the cannula cavity. On entering the cannula cavity 22, the flow of water forces the medicament that is contained within the cavity out of the cavity through the distal opening 24 and into the patient's rectal cavity.

After delivery of the medicament the cannula is removed from the patient's rectum. The cannula may then be cleaned, if it is to be re-used, or disposed of, if the device is only intended for one-time-use.

The device, kit, and method of using the device and kit as described herein refer to a specific embodiment. It is clear that many factors may be varied without changing the nature of the invention. For example, the embodiment described in detail above utilises a syringe as an actuation means for driving a volume of liquid through the cannula cavity. Any suitable actuation means may be used instead. For example, it may be possible to use a bellows or a bulb as an alternative to a syringe. In particular, it may be possible to replace the syringe with an automatic or motorised injection means for driving the volume of liquid. The actual volume of liquid injected, and therefore the size of the syringe, may be varied. For example, such variation may be desirable if the volume of the cannula cavity is larger or smaller than the embodiment described above, or if the length of flexible tubing is longer or shorter. The volume of liquid should be sufficient to drive the entire contents of the cannula into the patient's rectum without delivering an excessive volume of liquid to the patient. With regard to volume, a Pentasa ® (mesalazine) enema typically uses 100 ml of water. Thus, it would be expected that the maximum driving volume for a dose of activated carbon, delivered from a device according to an embodiment of the invention, may be at least 100 ml if required. In practice, the delivery of 100 ml of fluid into a patient's rectal cavity is likely to bring on a strong urge to defecate. Thus, it is preferable that the volume of driving liquid is lower than 100 ml, for example lower than 50 ml. The design of the internal cavity is such that it should be possible to deliver the desired volume of medicament with minimal driving liquid. Thus, preferred embodiments of a device use about 10 ml of driving liquid, for example between 8 ml and 12 ml of liquid.

Although the embodiment described above uses flexible tubing disposed between the syringe and the cannula, other embodiments may dispense with the flexible tubing and provide a direct connection between the cannula and syringe or other means for driving the volume of liquid.

The size and shape of the cannula may be varied from the dimensions described in the embodiment above. Different sized cannulas may, for example, allow different volumes of medicament to be dispensed to a patient.

The device may be used with a gas such as air used as a driving fluid rather than a liquid driving fluid. In one experiment, activated carbon of particle size 0.05 to 0.15 mm (mesh size 100x270 US mesh) was administered using air (instead of water) as the propellant/fluid. The applicants found that

administration was effectively administered rectally, with air as the propellant. The applicants also found that activated carbon of particle size 0.05 to 0.15 mm (mesh size 100x270 US mesh) was effectively administered using water as the propellant/fluid.