There is a recognised need for a reliable, chemically- based reversible contraceptive for men (i. e. a"male contraceptive") analogous to the oestrogen-based orally administered"pill"available to women. However, even in high doses, testosterone ester-based treatments (which are the male hormone equivalent of the oestrogen-based contraceptives for women) induce azoospermia in only about 65% of male subjects (see, for example, World Health Organisation Task Force on Methods for the Regulation of Male Fertility "Contraceptive efficacy of testosterone-induced azoospermia in normal men", Lancet 336: 955-959; Bagatell C J et al.,"Metabolic and behavioural effects of high-dose, exogenous testosterone in healthy men" Journal of Clinical Endocrinology and Metabolism 79: 561-567,1994; Behre H M et al.,"Potential of testosterone buciclate for male contraception: endocrine differences between responders and nonresponders"Journal of Clinical Endocrinology and

Metabolism 80: 2394-2403,1995; Aribarg A et al., "Rates of testosterone-induced suppression to severe oligospermia or azoospermia in 2 multinational clinical studies"International Journal of Andrology 18: 157- 165,1995; and Wu F C"Male contraception", Baillieres Clinical Obstetrics and Gynaecology 10: 1-23,1996).

An alternative approach for a male contraceptive combined a testosterone ester or an anti-androgen with a progestin (see, for example, Meriggiola M C et al., "A combined regimen of cyproterone acetate and testosterone enanthate as a potentially highly effective male contraceptive", Journal of Endocrinology and Metabolism 81: 3018-3023,1996; and Bebb R A et al.,"Combined administration of levenorgestrel and testosterone induces a more rapid and effective suppression of spermatogenesis than testosterone alone: a promising male contraceptive approach", Journal of Clinical Endocrinology and Metabolism 87: 757-762, 1996). Whilst these treatments appeared promising in the small studies reported (eg 5 men in each group), the results remain unconfirmed in larger studies.

Bellis et al., noted (see IV European Congress of Endocrinology, Abstract P1-296,9-13 May 1998) that prolactin levels increased as a result of administering a combination of testosterone enanthate and desogestrel (a progestin).

The pituitary produced lactogenic hormone prolactin (also known as luteotrophin) is known to be one of the major hormones affecting male reproductive function.

Whilst the gonadotrophins luteinizing hormone (LH) and follicle stimulating hormone (FSH) both stimulate spermatogenesis, it is generally accepted that elevated prolactin is inhibitory to normal reproductive function in both men and women (see Huhtaniemi et al.,

"Combination of a GnRH agonist with an antiandrogen or bromocriptine in the treatment of prostatic cancer; slight potentiation of antigonal effects", Int. J. of Andrology 14: 374-386,1991). Thus, patients having abnormally high levels of prolactin (hyperprolactinemia) suffer reduced fertility and impotence. In these patients suppression of prolactin secretion by means of a prolactin inhibitor (eg NORPROLAC (TM) of Sandoz Pharmaceuticals) readily restores normality. Paradoxically, abnormally low levels of prolactin (hypoprolactinemia) also leads to low fertility; Ufearo and Orisakwe reported (in their article entitled"Restoration of normal sperm characteristics in hypoprolactineamic infertile men treated with metoclopromide and exogenous prolactin", Clinical Pharmacology and Therapeutics 58: 354-359, 1995) that administration of exogenous prolactin to these patients readily restored normal sperm characteristics. However, whilst the low level of endogenous prolactin in the hypoprolactinemic patients was identified as being a likely cause of their infertility, simple administration of a prolactin inhibitor on its own to normal males is unlikely to be successful as a contraceptive since spermatogenesis will not be totally suppressed in the presence of normal amounts of gonadotrophin.

The present invention provides a male contraceptive, said contraceptive comprising: i) a prolactin inhibitor; and ii) a sex steroid.

The prolactin inhibitor will preferably inhibit prolactin secretion, but may alternatively operate by preventing the activity of prolactin in the testis.

One example of a suitable prolactin inhibitor is

quinagolide, sold under the trade name NORPROLAC (TM) of Sandoz Pharmaceuticals, but other Dopamine D2 receptor agonists are also acceptable. Commercially available agonists include Bromocriptine and Cabergoline.

The sex steroid, which is preferably a male sex steroid or androgen, will inhibit gonadotrophin secretion whilst enabling normal male behaviour to be maintained.

Any sex steroid hormone which reduces gonadotrophin secretion will be suitable and the term"sex steroid" as used herein encompasses not only naturally occurring sex steroid compounds (such as testosterone), but includes also precursors therefor (eg. androstenedione), but also synthetic analogues thereof which may be especially desirable for oral administration. Testosterone esters are especially suitable. The sex steroid may be administered by injection, as a transdermal patch, as a sub-cutaneous implant or orally, for example by capsule. With a testosterone implant an acceptable dosage for a period 4 months can be sustained. Suitable compositions are available commercially for injection or for implant administration. Examples of suitable testosterone esters include testosterone enanthanate, testosterone propionate, testosterone phenylpropionate, testosterone isocaproate, testosterone decanoate or the like.

Thus, the prolactin inhibitor and sex steroid may be administered by the same or different routes and at the same or different times. Whilst a composition comprising both active ingredients in admixture is convenient, especially when adapted for oral administration, this is by no means essential for the present invention which merely requires that levels of sex steroid are elevated whilst endogenous levels of

prolactin are suppressed or prolactin activity otherwise reduced. For ease of administration sequential administration of the two active ingredients may be preferred: In a further aspect, the present invention thus also provides a kit for male contraception comprising i) a prolactin inhibitor, and packaged separately thereto ii) a sex steroid.

Whilst we do not wish to be bound by theoretical considerations, we believe that the current invention is based upon the recognition that, unlike for female contraception, it is necessary to inhibit prolactin as well as the classical gonadotrophins to induce infertility in 100% of men. We believe that prolactin acts in the brain through an inhibitory mechanism to regulate the secretion of gonadotrophins and sexual behaviour, and also acts in the testis through a stimulatory mechanism to regulate spermatogenesis and fertility. Thus, to produce complete cessation of sperm production it is necessary to remove all endocrine support to the testis. Administration of the sex steroid (androgen) suppresses production of the classical gonadotrophins (LH and FSH) and administration of the prolactin inhibitor either suppresses the secretion of prolactin and hence the action of prolactin at the testis or reduces the activity of prolactin in the testis.

The combination of prolactin inhibitor and testosterone (or equivalent) as a male contraceptive has the following potential advantages: 1. To remove prolactin which acts within the testis

to stimulate spermatogenesis.

2. To block the stimulatory effect of sex steroids on prolactin secretion which promotes spermatogenesis. Note, giving testosterone as a contractive results in increased prolactin concentrations.

3. To remove any inhibitory effect of prolactin on sexual behaviour thus allowing the combined testosterone to be fully effective.

4. To remove the stimulatory action of prolactin on the prostate and other male accessary sex glands which may result in hyperplasia and cancer. Note, in the rat prolactin acts along with sex steroids to maintain the function of the prostate.

The contraceptive according to the present invention may have the following advantages: 1. More effective at inducing complete azoospermia, both in time from onset of treatment (normally takes 3-4 months), and in the percentage of subjects successfully treated.

2. Possibility of reducing the daily dose of sex steroid/androgen while maintaining azoospermia in the long-term, thus limiting associated unwanted side-effects (weight-gain, acne, increase in lipoproteins etc). Prolactin normally acts in the testis synergistically with LH and FSH to maintain both steroidogenesis and spermatogenesis, thus lowering prolactin will reduce these effects.

3. Possibility of reducing the risk of hyperstimulation of androgen target tissues including the prostate (and the potential risk of prostatic cancer). Prolactin normally acts in

these tissues to promote responsiveness to androgens, thus lowering prolactin will reduce this effect.

4. Possibility of maintaining full sexual behaviour with a relatively low dose of sex steroid/androgen. High prolactin secretion is associated with impotence in men, thus lowering prolactin should favour normal sexual behaviour.

5. The avoidance of the use of anti-androgens which may have unknown long-term side-effects, eg on the liver, and progestins which could markedly affect behaviour as in the female, would be an advantage over alternative methods.

In a further aspect, the present invention provides a method of inducing azoospermia in mammalian males (preferably human males), said method comprising: a) administering an effective dose of a prolactin inhibitor; and b) administering an effective dose of a sex steroid.

Optionally, the sex steroid may be administered by subcutaneous implant (usually an implant 400 to 1500 mg, preferably 600 to 1200 mg of sex steroid) which provides an effective dose over a sustained period eg 4 months or longer. Alternatively, the sex steroid may be administered by injection and a single weekly dose of between 50 mg to 300 mg, preferably 150 to 200 mg, should be suitable. An example of a commercially available formulation for injection is SUSTANON 250 (TM) of Organon Laboratories Ltd. A daily dose of testosterone may also be taken for example orally in tablet or capsule form and a dose of 5 to 40 mg may be suitable.

The prolactin inhibitor is preferably a non-ergot D2 receptor agonist, such as quinagolide (NORPROLAC).

Conventionally the prolactin inhibitor may be taken daily, by the oral route, at a suitable dose. A suitable daily dose may be 25 Ug/day to 200 yg/day, preferably 50 Ug/day to 150 Hg/day, for example 60 yg/day to 100 Ug/day. 75 Hg/day should be suitable.

It could also be administered as a long-acting injection or implant.

In a further aspect, the present invention provides the use of a prolactin inhibitor in the manufacture of a medicament which in combination with exogenously administered sex steroid is effective in treating fertile males to reduce their fertility.

In a yet further aspect, the present invention provides the use of exogenous sex steroid in the manufacture of a medicament which in conjunction with exogenously administered prolactin inhibitor is effective in treating fertile males to reduce their fertility.

Other potential uses of the contraceptive include: i) Treatment of hyperprolactinemia where replacement therapy with sex steroids/androgens is required. ii) Alleviate the problems of androgen stimulation at puberty (eg severe acne). iii) Treatment of skin disorders associated with the actions of prolactin and androgens (eg psoriasis). iv) Therapy for other disorders influenced by the pattern of prolactin and androgen secretion (benign prostatic hyperplasia) eg prostate cancer. v) Hormonal replacement in old age (50 years +) where it may be desirable to reduce prolactin secretion but supplement androgens.

The present invention will now be made fully described with reference to the following, non-limiting, example and figure in which: Figure 1 shows schematically the experimental protocol followed in the example.

Example Objectives This study will investigate the effects of prolactin inhibition on testicular function when combined with testosterone in healthy adult male volunteers.

Prolactin inhibition will be achieved by the daily treatment with an orally active, non-ergot, dopamine D2 receptor agonist, Quinagolide (Norprolac: Sandoz Pharmaceuticals) and gonadotrophin inhibition will be induced by the simultaneous administration of subcutaneous testosterone implants (Organon Laboratories).

Experimental design Each male volunteer will be randomly allocated to either of three treatment groups: (i) Testosterone implant only (high T control); (ii) Testosterone implant (high T) plus Norprolac (NOR) administered for 24 weeks (high T+NOR); (iii) Testosterone implant (low T) plus Norprolac for 24 weeks (low T+NOR part). The study will extend over a total of 9 months defined as 1 month pre-treatment, 4 months treatment and 4 months recovery (see Figure 1). The protocol is designed to establish whether prolactin inhibition combined with exogenous testosterone produces a more rapid and complete induction of azoospermia compared to testosterone alone, and whether prolactin inhibition delays the recovery of normal testicular function after

withdrawal of testosterone. Each subject will be studied in four phases:- Screening Potential subjects will be fully informed about the nature of the study by means of both oral and written information. After written informed consent has been granted, each subjects will undergo a detailed general medical history and physical examination so as to satisfy the inclusion-exclusion criteria.

Pre-treatment (4 weeks) Two fasting blood samples will be collected for routine haematology (haemoglobin, haematocrit and white cell count) and biochemistry-electrolytes, urea, creatinine, liver function tests (albumin, AST, ALT, GGT, alkaline phosphatase), glucose, lipids (total cholesterol, LDL and HDL cholesterol) and baseline hormone analyses (LH, FSH, testosterone). Two semen samples will be analysed at least two weeks apart.

Subjects and their partners will also be asked to complete a diary/questionnaire to evaluate sexual function, mood, and well-being.

Treatment phase (16 weeks) Subjects will only commence this phase when all parameters in the previous 4 weeks are confirmed to be normal. The treatment phase is initiated at testosterone implant with or without starting Norprolac simultaneously. Each subject will have a medical review, physical examination, blood and semen analyses at 4 weekly intervals. Diaries/questionnaires will be completed weekly.

Recovery phase (approx 16 All subjects will be followed until they attain the

recovery criteria. Recovery is defined as (a) when the geometric mean pre-treatment sperm density is reached or (b) 3 consecutive specimens show sperm density>20 million/ml. Medical review, physical examination, semen analyses and blood sampling will be carried out at 4 weekly intervals until the recovery phase terminates.

Diaries/questionnaires will be completed weekly.

Subjects Healthy adult men from the general community will be recruited into the three study groups each comprising 16 subjects making a total of 48.

Subject inclusion criteria -Healthy male aged 19-50 years -Both pre-treatment semen samples have sperm densities >20 million/ml -Both pre-treatment semen samples have sperm motility >40% -Both pre-treatment semen samples have sperm morphologies >40% -Pre-treatment hormone, biochemical and haematological screening tests normal -Men with sexual relationship (or partner) must be willing to use their current or another form of contraception for the duration of study -Willing to adhere to monitoring procedures Subject exclusion criteria -Past or present disturbance of liver function -Hyperlipoproteinaemia -Diabetes mellitus or carbohydrate intolerance -Cardiac diseases -Hypertension (Diastolic >90 mm/Hg) -Prostatic disease -Genitourinary infection -Psychiatric illness

-Alcohol abuse -Drug abuse -Use of one or more of the following medications: sex steroids, hydantoins, barbiturates, primidone, carbemazapine, rifampicin, griseofulvin.

Description of Drugs & Procedures Quinagolide (Norprolac) Norprolac will be administered as a daily oral tablet taken at bedtime (75pg/day, Norprolac, Sandoz; Product Licence No. PL0101/0382). This treatment has been found to effectively suppress prolactin secretion in patients with hyperprolactinemia and is well tolerated (Brownell et al.,"The treatment of hyperprolactinemia from bromocriptine to Norprolac", In Norprolac (quinagolide): an update. Ed J. Brownell pp 7-11, Medical Forum Int. The Netherlands, 1996). A short pilot study with 6 volunteers will be carried out to confirm the effectiveness of this treatment at suppressing prolactin secretion in normal men. Side effects may include nausea, vomiting, headache, dizziness and fatigue, occasionally abdominal pain, constipation or diarrhoea, insomnia, oedema, nasal congestion and hypotension. Side effects are transient, dose-related and unlikely to be a problem at the relatively low dose of 75 Ug/day and with the precaution of gradual dose increment using a starter pack of 25,50 and 75 yg/day over 1-2 weeks. Any side effects are reversible upon discontinuation.

Testosterone.

Testosterone will be administered using slow-release, release subcutaneous testosterone implants given on one occasion at the start of the study (4x200mg or 6x200mg testosterone, Testosterone implant, Organon Laboratories Ltd; Product Licence No. 0065/5084R).

Testosterone implants have been used for over 30 years in clinical practice as a standard form of androgen substitution for treatment of male hypogonadism. It is remarkably free from side-effects. Extrusion of pellets, and local infection occurs in less than 5% of cases but are seldom a problem in experienced hands.

The dose (800 mg or 1200mg) used in this study is higher than the standard replacement of dose of 600-800 mg. However, testosterone implant in doses up to 1200mg has been shown to cause no side effects for up to 6 months (Handelsman et al.,"Establishing the minimum effective dose and additive effects of depot progestin in suppression of human spermatogenesis by a testosterone depot", Journal of Clinical Endocrinology and Metabolism 81: 4113-4121,1996). Weight-gain, acne and changes in behaviour and lipoproteins are possible undesirable effects of higher doses of testosterone compared to that used in this study.

Testosterone implant The implant procedure is carried out by aseptic technique under local lignocaine anaesthesia through a 1-2 cm surgical incision of the anterior abdominal wall. A metal trocar and cannula are used to introduce the four or six testosterone pellets into the subcutaneous fatty tissue. The incision is closed by non-absorbable sutures (2-0 black silk) which are removed after 4 days. The discomfort of the implant procedure is minimal and well-tolerated.

Venepuncture Venous blood will be obtained from an arm vein by venepuncture through a 21G needle. Between 20-30mol of blood is collected on each occasion.

Semen collection Ejaculated semen is collected by masturbation after a period of abstinence of 2-5 days, The sample can be produced in the Subfertility Laboratory Donor Rooms or at home within 60 minutes of analysis.

Samples analyses Blood samples obtained every 4 weekly will be analysed for changes in hormonal parameters (LH, FSH, prolactin, testosterone, dihydrotestosterone, oestradiol, sex- hormone binding globulin) by radioimmuno-assay.

Blood samples every 8 weeks will be analysed for general biochemistry, liver functions, glucose, HbAlc, lipid profiles, glucose and full blood count.

Semen collection and analysis of volume, count, motility, morphology will be carried out according to the WHO Laboratory Manual For The Examination of Human Semen and Semen-Cervical Mucus Interaction, 3rd Edition (1992) at 4-weekly intervals.

Data analysis Power analysis has been used to assess the minimum group size necessary to detect a significant effect of the treatments and should be adequate to demonstrate any major differences in clinical response. Given that the principle pharmacodynamic endpoint (sperm density) have a between subject variability of 2 million/ml, 16 complete time-courses for each group would allow an 80% power to detect group differences of 8 million/ml for main effects at the 95% level of significance. The data will be analysed by repeated measure ANOVA.

Treatment Testosterone has been used by the WHO Task Force on Male Fertility Regulation in clinical trials involving over 700 healthy men. In these studies,

supraphysiological doses of testosterone had been delivered by weekly injections of testosterone enanthate. In this study, testosterone is delivered by a single administration of testosterone pellet implants which not only contain a lower total dose but produce stable rather than fluctuating levels of testosterone compared to weekly injections. Testosterone implants have been used for over 30 years in clinical practice as a standard form of androgen substitution for treatment of male hypogonadism. It is remarkably free from side-effects. Extrusion of pellets, and local infection occurs in less than 5% of cases but are seldom a problem in experienced hands. The implant procedure carried out under local anaesthesia is well- tolerated.

Quinalgolide (Norprolac) is an approved oral dopamine agonist for the treatment of hyperprolactinaemia. Its main indication is in patients who are unable to tolerate the side effects of the more established drug, Bromocriptine. Norprolac is believed to produce less side effects because it is, unlike its predecessors, a (the first to be marketed) non-ergot dopamine agonist.