The present invention relates to a carba ic acid ester for use as a drug. The invention also relates to a preparation for treatment of addiction to alcohol, and to the use of the carbamic acid ester for producing a preparation for treatment of addiction to alcohol. Disulfiram (Antabuse ^® ) is widely used as a drug for treatment of addiction to alcohol. If a person takes disulfiram and then drinks alcohol, he experiences the unpleasant disulfiram/alcohol reaction which is charac- terised by nausea, a ruddy complexion, palpitation of the heart, low blood pressure, vomiting, and a pulsating headache.

Theoretically, treatment with disulfiram should make an alcoholic abstain from drinking alcohol. However, it has been found, in actual practice, that treatment with disulfiram frequently fails because the patient stops taking disulfiram and then resumes his drinking. The reason is that disulfiram can only be administered orally in the form of tablets or as a mixture and there- fore requires daily administration.

In view hereof, there is need of a different form of administration by which disulfiram can be taken sys¬ tematically in the form of .a depot drug from which the substance is slowly released. For many years, the so-called "implantation tech¬ nique" has been tried, by which disulfiram tablets are inserted under the skin by operative surgery. However, experience has shown that this treatment has no effect because disulfiram is released so slowly that the patient experiences no disulfiram/alcohol reaction when consuming alcohol .

In course of time, several injection drugs containing disulfiram have been proposed. USSR patent specification

390,206 proposes a solution of disulfiram in benzyl benzoate and vegetable oil. M. Phillips, in US patent specification 4,678,809, has proposed the intramuscular injection of disulfiram as an aqueous suspension, or operated into a matrix of poly(lactic acid-co-glycolic acid). The specification of EP 0,169,618 proposes in¬ jecting disulfiram in a uniform microcrystalline form suitable for absorption by the reticulo-endothelial system. However, none of these forms of administration has found to be useful in actual practice. The reason is that disulfiram mainly acts by an irreversible blocking of a liver enzyme, acetaldehyde dehydrogenase. Alcohol is metabolised mainly in the liver. The first step of this metabolism is an enzymatic oxidation to acetaldehyde which is then oxidised by another enzyme system called acetaldehyde dehydrogenase which is the enzyme irrevers- ably blocked by disulfiram.

When a patient undergoing disulfiram treatment consumes alcohol, an accumulation of acetaldehyde occurs which leads to the above-mentioned toxic reactions in the disulfiram/alcohol reaction.

If disulfiram is taken perorally, it will, like other drugs, after intestinal absorption be immediately carried to the liver via the portal vein system.

It is known that disulfiram, besides being very sparingly soluble in water, is metabolised very quickly in blood at a t /2 of but 4 min. It may therefore be ^: assumed that disulfiram can be administered only perorally because this is the only way in which it can affect the liver enzyme acetaldehyde dehydrogenase to a suffi¬ cient degree. If disulfiram is given parenterally, for example in the form of an injected local depot in a muscle, it will never reach the liver in such quantities that a therapeutical effect is obtained.

This shows that there is a definite need of novel compounds which have the therapeutical effect of di-

sulfira , but whose physicochemical properties are better suited for parenteral administration so that suitable depot formulations can be prepared from these compounds. Substituted S-alkyl esters of thiocarbamic acid have been known for many years. For example, H. Tilles (JACS 81, page 174, 1959) has prepared 256 thiocarbamic acid esters with different substituents on the N atom for the purpose of developing novel herbicides.

GB patent specification 868,111 discloses 140 thio- carbamic acid esters with herbicidal activity. Many of the thiocarbamic acid esters here described have since then found widespread use as vermicidal agents. For environmental reasons, these thiocarbamic acid esters have been thoroughly investigated in respect of toxicity, but there are no reports on effects showing that sub¬ stances of this type are capable of blocking the enzyme acetaldehyde dehydrogenase, thereby to produce a di¬ sulfiram/alcohol reaction.

The invention relates to substituted carbamic acid esters of the general formula I

wherein X is -CH.. or -CH_CH ₃ ,

R and R ₁ which may be the same or different, are hydrogen, C- _c alkyl or a group of the formula

wherein n is 0, 1 or 2, and R ₂ , R ₃ and R ₄ are H, OH, OCH CH.., NO_ or halogen, and wherein R and R ₁ together with the nitrogen atom can form a saturated ring system having 4-6 atoms selected among C, N, 0 or S, and

wherein A is sulphur or oxygen.

In a special embodiment, the invention relates to substituted thiocarbamic acid esters of the general formula II

wherein X is -CH.. or -CH-CH., ,

R and R- which may be the same or different, are hydrogen, C, _c alkyl or a group of the formula

wherein n is 0, 1 or 2, and R_, R- and R. are H, OH, OCR.. CH- NO_ or halogen, and wherein R and R. together with the nitrogen atom can form a saturated ring system having 4-6 atoms selected among C, N or S.

It has now surprisingly been found that carbamic acid esters of the above-mentioned type are highly potent inhibitors of acetaldehyde dehydrogenase, as is evidenced by the following tests.

METHOD FOR INHIBITING ALDEHYDE DEHYDROGENASE

Fractionation of rat liver homogenates was performed according to Tottmar et al, Biochem. J. 1973:135:577. The aldehyde dehydrogenase activity in the homogenate after incubation for 1 h with different thiocarbamic acid esters (see Table 1) was measured spectrophotometrical- ly in 50 μl aliquots by following the reduction of NAD to NADH at 340 nm at 37°C in the presence of the substrate acetaldehyde 0.025 μmol/litre, as described by Tottmar and Marcher (Acta Pharmacol, et Toxicol. 1976:38:366). These tests gave the results indicated in Table 1.

TABLE 1

In vitro inhibition of aldehyde dehydrogenase of low Km with different thiocarbamic acid esters of the general formula

Measured on bov ne ver

The values are X ± SD of double determinations, on the one hand in homogenates from 4 rats and, on the other hand, in bovine liver (last two values in Table 1). The concentration = 2760 μmol/litre for all co - pounds, except the last two compounds for which the concentration was 3.0 mmol/litre.

Method of assessing the "Antabuse ^® -alcohol" reaction on rats by tonometry These measurements were performed on a selected compound. The substance employed is diethyl thiocarbamic acid-S-methyl ester (referred to as DTSM hereinafter). Male rats having a body weight of 300-400 g were anaesthetised with urethane 1.25 g/kg i.p. On a group of 4 rats, a catheter filled with heparin-salt water was inserted by operative surgery in one carotid artery, and the blood pressure was recorded before and after intraperitoneal injection of ethanol (1 g/kg, 10 ml/kg of 10% v/v ethanol in water). Two other groups of 3 rats each were treated intraperitoneally with DTSM for 1 and 2 hours, respectively, whereupon ethanol (1 g/kg, 10 ml/kg of 10% v/v ethanol in water) was injected intra¬ peritoneally. The blood pressure was measured before the injection of ethanol and for 30 min. after injection, after which time the blood pressure has usually stabilised itself (Hellstrδm and Tottmar: Pharmacology Biochemistry and Behaviour 1982:17:1103.).

The results are shown in Table 2.

TABLE 2 Diastolic blood pressure of rats 30 min. after ethanol injection

Pretreatment % of own ref. value* p value and time X ± SD (N) > (Student's test)

Salt water 92.5 ± 5.2 (4) 1 hour

DTSM 30 mg/kg 77.1 ± 3.6 (3) < 0.01 i.p. 1 hour

DTSM 30 mg/kg 57.6 ± 28 (3) < 0.05 i.p. 2 hours

* measured before ethanol injection

Substituted thiocarbamic acid esters according to the invention can be prepared in per se known manner. The techniques stated in "Houben-Weyl , Methoden der Organische Chemie", Vol. 9, pp 834-37, are eminently suitable for preparing the compounds according to the present invention.

The carbamic acid esters of formula I wherein A is oxygen, can also be prepared in per se known manner, for example in accordance with R.O. House in "Modern synthetic reactions", W.A. Benjamin, INC, California, 1972, pp 602-604. By this technique, for example 1- piperidine carboxymethyl ester can be prepared from piperidine and chloroformylmethyl ester. The substituted carbamic acid esters here referred to are solid or liquid substances that can be taken like a conventional drug in the form of capsules, tablets or a mixture. However, they are especially suitable for parenteral administration, in particular as consti- tuents of a depot preparation of prolonged release.

The compounds according to the invention can thus be taken in a vegetable oil, in a fat emulsion, or as

micel les .

The following Examples illustrate the possibilities of using the compounds, but must not be regarded as restrictive Examples.

EXAMPLE 1

8 g diethyl thiocarbamic acid-S-methyl ester is dissolved in 90 g peanut oil. 2 g benzyl alcohol is added as a preservative. The mixture is poured into 5 ml glass ampoules which are then sterilised at 120°C for 20 min.

EXAMPLE 2

16 g dimethyl thiocarbamic acid-S-methyl ester is dissolved in 80 g soybean oil. 5 g egg lecithin,

10 g glycerol and 100 ml sterile water are added, and from this mixture a stable emulsion is prepared which is heat-treated and then poured aseptically into 5 ml stoppered tubes.

EXAMPLE 3

30 g egg lecithin, 20 g sodium glycocholate and 30 g N-(para-hydroxyphenetyl )-carbamic acid-S-methyl ester are dissolved in 100 ml ethanol. The solution is evaporated to dryness in a rotary evaporator. Adding an aqueous phosphate buffer gives a limpid micelle solu¬ tion which is poured aseptically into ampoules.

EXAMPLE 4 8 g diethyl thiocarbamic acid-S-ethyl eter is dis¬ solved in 80 g glycerol monooleate to which 12 g egg lecithin is added. The mixture is sterilised by heat treatment and poured into 5 ml ampoules.