Brit. J. Pharmacol. (1953), 8, 230. THE EVALUATION OF " MYSOLINE "-A NEW ANTICONVULSANT DRUG BY J. YULE BOGUE AND H. C. CARRINGTON From Imperial Chemical Industries Limited, Research and Biological Laboratories, Blackley, Manchester, 9 (RECEIVED JANUARY 27, 1953) Mysoline* is a new anticonvulsant which was vative of phenobarbitone, formula I, in which the first prepared and evaluated by us and subse- oxygen in the urea grouping of the barbituric acid quently subjected to clinical trial (Handley and is replaced by two atoms of hydrogen. Indeed, Stewart, 1952). This paper describes some of the among the methods by which it may be prepared methods by which the drug was evaluated. (B.P.666,027, W. R. Boon, H. C. Carrington, C. H. The drugs commonly used for the treatment of Vasey, and I.C.I., 6.2.52) are the electrolytic reduc- epilepsy generally belong to the same chemical tion of phenobarbitone itself, and the catalytic classes as the hypnotics and sedatives, but the desulphurization of the corresponding 2-thio- hypnotic and anticonvulsant activities do not barbituric acid. necessarily go together. In the barbiturate series, Ph CO.NH Ph CO.NH phenobarbitone is both a hypnotic and an anti- convulsant, but many other powerful hypnotic C\ CO \ H2 barbiturates are almost devoid of anticonvulsant Et CO.NH Et CO.NH action. The hydantoins, too, have both types of (I) (1I) activity, but they are weaker hypnotics than the barbiturates, and in recent years several members Mysoline is a colourless, remarkably stable, of the series with little or no hypnotic action have crystalline substance which melts at 281-282° C. been introduced as anticonvulsants. These include It is sparingly soluble in water (60 mg./100 ml. 5: 5-diphenylhydantoin (phenytoin) and 5-ethyl-3- at 370 C.) and in most organic solvents, and, un- methyl-5-phenylhydantoin (mesantoin, methoin). like the parent barbiturate, it has no acidic pro- It is unfortunate that the hydantoins in general perties. are rather toxic substances. 5-Ethyl-5-phenyl- METHODS hydantoin (nirvanol), which was introduced many Seizures Induced by Electrical Shock.-A standard years ago for the treatment of chorea, fell out of convulsion was produced in rats by electrical stimula- use after a short time because of its toxicity. Com- tion, and the effects of drugs on the inhibition of these have also been made of convulsions were measured. plaints of toxic side-effects The method chosen was a modification of that de- both phenytoin and methoin. With the latter scribed by Kozelka, Hine, and Grieber (1942) and this is not surprising in view of recent evidence Alles, Ellis, Feigen, and Redman (1947) in that time that in the animal body it is metabolized to nir- rather than current was the variable. The electrical vanol (Butler, 1952). circuit was similar to that used by Tainter, Tainter, The barbiturates are less liable to produce Lawrence, Neuru, Lackey, Luduena, Kirtland, and chronic toxic effects than the hydantoins. It is Gonzales (1943). Seizures were induced by passing therefore rather surprising that more effort has a 7.5-mA. 50-cycle sinusoidal waveform current by not been made to obtain non-hypnotic anti- means of padded ear clips. A timing switch was convulsants in this series. The only analogue of incorporated in the circuit and set so that the maxi- wide use in mal duration of the shock did not exceed 10 seconds. phenobarbitone which has found Within a period of 2-7 seconds the normal rat epilepsy is phemitone (5-ethyl-l-methyl-5-phenyl- exhibited the characteristic tonic extension of the hind barbituric acid), which has somewhat less hypnotic legs. When this was attained the current was switched and anticonvulsant activity. off and the elapsed time recorded. Mysoline (5-ethyl-5-phenylhexahydropyrimidine- Albino rats of both sexes within a weight range of 4: 6-dione), formula II, may be considered as a deri- 85-105 g. were used. The initial threshold in terms of the energy required to produce the tonic extensor * " Mysoline " is the registered trade-mark of Imperial Chemical (Pharmaceuticals) Ltd. component of the electrically induced seizure was " MYSOLINE"-A NEW ANTICONVULSANT 231 determined for each animal, which then served as its TABLE I own control. Only those which exhibited the tonic THE ACTIVITY OF MYSOLINE AND OTHER ANTICONVUL- extensor component a of 23-34 SANTS AGAINST ELECTRICALLY INDUCED SEIZURES IN after shock intensity RATS milliampere seconds or 600-800 mW. sec. (shock dura- tion 3-4.5 seconds) were selected for anticonvulsant No. of Rats in a Group of 10 in assay. Each assay of a drug at the chosen dose level which the Tonic Extensor Com- Oral ponent was Abolished was carried out on a group of 10 rats. Anticonvulsant Dose On the day after the initial threshold determina- mg./kg. Hours After Dosing tion the drug was administered orally. The maximum 1 3 6 24 48 72 dose never exceeded 500 mg. /kg.; all doses were Mysoline 500 6 10 10 10 10 1 10/ 10 given in a volume of 0.5 ml./ 100 g. body weight. 200 7 10 10 9 1 _ 10/10 A control group of 10 rats was included in each 100 5 10 10 5 0 - 10/10 50 3 9 10 4 - - 10/10 experiment and was given the same volume of 20 1 9 10 I 0 - 10/10 diluent or dispersing agent as was used for the drug 10 1 8 10 0 - - 10/10 10 2 7 8 1 - - 9/10 under test. Unless otherwise stated, mysoline and 5 1 6 5 0 - - 7/10 other insoluble drugs were administered as an aqueous Phenobarbitone 20 5 10 10 1 - - 10/10 dispersion in Dispersol OG and LN. This dispersing sodium 10 3 5 8 1 - - 8/10 agent was a mixture of polyglyceryl ricinoleate (OG) 10 1 6 3 0 - - 6/10 and the disodium salt of a disulphonate of dinaphthyl 5 0 0 2 0 - - 2/10 methane (LN). 5: 5-Diphenyl- 200 9 10 10 2 10/10 hydantoin 100 9 10 10 0 - - 10/10 Seizures were induced at intervals of 1, 3, 6, and 50 4 5 4 1 - - 7/10 24 hours after dosing and thereafter at 24-hour inter- Methoin (Mesan- 50 9 10 10 0 - - 10/10 vals until the rats returned to within the normal toin; 5-ethyl-3- 20 3 9 8 0 - - 9/10 threshold range. The maximum shock intensity de- methyl-5-phenyl- 10 1 2 0 0 - - 2/10 livered to a protected animal was 75 mA. sec. or 2,000 mW. sec. (a 10-second shock). Troxidone (Trid- 500 2 6 2 0 - - 6/10 ione; 3: 5: 5-tri- 100 0 0 0 0 - - 0/10 Anticonvulsant activity was assessed in terms of methyloxazoli- the dose of drug required to abolish the tonic extensor dine-2: 4-dione component of the seizure at this maximal intensity. Phenylacetylurea 100 10 10 10 1 - - 10/10 Toman, Swinyard, and Goodman (1946), Tomnan (Phenurone) 50 8 8 5 0 - - 9/10 and Goodman (1948), and Toman, and 20 0 4 0 0 - - 4/10 Goodman, 10 0 1 0 0 - - 1/10 Swinyard (1949) have criticized the use of currents of relatively long duration. One of their assay * The last column includes all rats which did not exhibit the tonic methods is based on the ability of anticonvulsant extensor component at one or more of the test times. agents to modify the different phases of the seizure pattern elicited by supramaximal shocks of very short RESULTS duration (150 mA. for 0.2 sec.). They were able to study these phases independently of the effects of Electrical Seizures.-Table I summarizes the drugs on the energy threshold required to produce results obtained with mysoline and compares them maximal seizures. They found that long periods of with those found with phenobarbitone, 5:5- stimulation concealed the occurrence of drug-modified diphenylhydantoin, methoin (mesantoin), troxidone seizures. Nevertheless, the method as used by us (tridione), and phenylacetylurea (phenurone). has never failed to show the anticonvulsant activity At 5 mg./kg. mysoline was found to be more of clinically recognized anti-epileptic agents or of active than phenobarbitone at the same dose level. other compounds reported in the literature. We were The tonic extensor component was abolished in not, of course, able to follow the five components of the supramaximal induced seizure described by not less than 6 out of 10 animals as compared with Toman, Swinyard, and Goodman (1946). 2 out of 10 with phenobarbitone. At 10 mg./kg. mysoline protected 9 or 10 out of 10 as compared Leptazol (Metrazol) Seizures.-A standard dose of with 6 to 8 with phenobarbitone. This activity 90 mg. /kg. made from a crystalline preparation of was not approached by the other anticonvulsants leptazol was given intraperitoneally to our own strain until 50 or 100 mg./kg. was given. At doses from of albino rats at 160-180 g. At this dose all un- 50 mg. /kg. upwards mysoline showed a pro- treated rats exhibited maximal seizures followed by longation of the duration of activity. Mysoline collapse, with not less than four deaths out of a appeared to be slowly absorbed and reached its group of six. Comparative anticonvulsant activity maximum at 3-6 hours after adminis- was assessed in terms of the dose required to prevent activity maximal seizures and death. Treatment varied from tration at low or moderate dosage. At high 1-6 hours before leptazol injection. Two groups of dosage (500 mg./kg.) the duration of protection 6 treated and 6 control animals were used at each exceeded 48 hours, but there was marked ataxia dose level.