Phenothiazine

New Zealand Journal of Agriculture, Volume 63, Issue 3, 15 September 1941, Page 189

Phenothiazine

A New Drug for the Control of Internal Parasites

;uuiiiini,i,uißy

L. K. WHITTEN

E Veterinary Parasitologist, e |/ Animal Research. Station,. e e Wallaceville. E

THE control of internal parasites of I domestic stock has’ been a problem' studied by scientists for many years. Numerous drugs have been introduced, but each one, if effective at all, can be used against only a few species of parasites. Copper sulphate alone or with other drugs was proved to be effective against the large stomach worm of sheep and cattle. Oil of Chenopodium has been used for many years in the treatment of parasites of man, horses, and pigs. Later, carbon tetrachloride was used against hookworms in man and dogs, the large stomach worm and the liver fluke in sheep and redworms in horses. Tetrachlorethylene was introduced by American workers for the treatment of hookworms in man and dogs, and more recently : hookworms, stomach worms, and small intestinal worms in sheep and cattle. A mixture of copper sulphate and nicotine sulphate has been useful in the control of stomach and intestinal. worms of sheep and cattle, and in recent years has been very widely used. Most of the drugs used against stomach and intestinal worms of ruminants must pass directly to the fourth stomach to be effective. ’ When they pass into the first or second stomach they become greatly diluted, and have little or no effect on the parasites. In normal circumstances drenches pass to the fourth stomach in approximately 50 per cent, of cases, but copper sulphate has the property of causing reflex closure of the oesophageal groove, so that other drugs mixed with it or, given immediately afterwards pass to the fourth stomach in approximately 80 per cent, of cases. Two drugs, how-

ever, are effective, irrespective of whether they are swallowed into the first, second, or fourth stomach —carbon tetrachloride and phenothiazine.

Discovery of Phenothiazine

Phenothiazine was first synthesised in 1885, but it was not until 1934 that it was investigated as a possible substitute for lead arsenate in the control of codlin moth. In 1938 it was found

that when given in small doses to cattle it prevented the development of hornfly larvae in their faeces, and in the same year was used against worms in pigs with promising results. , In the following years much work has been done in U.S.A., Australia, Canada, and Great Britain, and has shown that it is the most effective. drug yet discovered for the treatment of many of the more important parasites of sheep, cattle, horses, and pigs. In sheep and cattle it is highly effective against large stomach worms (Haemonchus contortus) , small stomach worms (Ostertagia circumcincta) , small intestinal worms (Trichostrongylus spy.), hookworms (Bunostomum trigonacephalum), and large bowel parasites Chabertia and Oesophagostomum spp. Although very little data is avail-

able, it is probably only partially effective against Cooperia and Nematodirus, while it is ineffective against fluke, tapeworms, whipworms, lungworms, and Strongyloides spp. In horses it is highly effective against redworms (Strongylus and Trichonema), partially effective against large roundworms (.Ascaris)- and pinworms (OxyUris'), but is ineffective against bots and tapeworms. The drug is effective against ' roundworms and nodule worms in pigs, but in poultry only the caecal worm Heterakis is susceptible. In dogs it is practically useless.

Methods of Administration

Phenothiazine itself is a bulky, lightgreen or yellow powder, which is in-

soluble in water and practically tasteless. Its physical properties make it very difficult to obtain an even suspension of the powder in water, and for this reason it is generally sold mixed with a small percentage of a wetting agent. In the case of animals which are fed individually the dose can be administered mixed with the feed; with horses this proves very convenient, and most animals readily take the drug in their chaff or mash. This method should not be used where two or more animals are fed from the one manger. Where animals are to be dosed, methods of administration differ from those used with other drenches because of the bulkiness and insolubility of the drug. It can be suspended in water to form a thin paste, which can

be delivered through a simple syringe type of instrument if the plunger is kept well oiled and cleaned regularly. Automatic guns and syringes involving the use of ball valves are unsatisfactory, because the powder causes clogging of the valves. An alternative is to use a more fluid suspension with an old-fashioned drenching funnel or bottle. Dosing with the powder or in the form of pills or capsules is possible but less satisfactory, and is more time-consuming than in liquid form.

Dose Rates

The dose rates which are recommended are as follows: — Grams. Lambs.— 6 weeks to 5 months . . 15 Sheep s months to 12 months . 20 Sheep— Over 12 months 25 Calves— 6 months to 12 months 25-30 Cattle — Over 12 months 30-40 Horses months to 12 months 20-30 Horses — 12 months 30-40 Pigs Up to 25 lb. liveweight ... 5 25-50 lb 9 50-100 lb 12 100-200 lb. 20 Over 200 lb 30 Animals need not be starved before or treatment, but a short fast may ensure that the whole dose is consumed when exhibited in the feed. Doses greatly in excess of those recommended can be given without ill-effects, but care should be taken with weak and anaemic horses, as a few reports from overseas suggest that such subjects may react severely with larger doses. Repeated doses in calves and pigs may occasionally prove toxic, although such ill-effects are rare. - For a few days after dosing the urine t of some animals becomes' dark red when exposed to air for some minutes, due to the presence of oxidation products of phenothiazine, but, apart from a slight staining of the wool, it is of no consequence, although it may be mistaken for blood and cause some concern. Because of its high efficiency against such a wide range of internal parasites and its wide margin of safety, phenothiazine, which is now available in New Zealand, is welcomed as one of the greatest contributions made in recent years in the field of parasite control. The present price of the drug is high, but a greater demand, manufacture on a large scale and improved methods will doubtless result in a reduction in cost and permit its more, widespread use in reducing loss from internal parasitism.