Toxicity and interaction of topical organophosphate insecticide dichlorvoscrotoxyphos and phenothiazine anthelmintic in sheep previously exposed to both drugs.

Toxicity and interaction of topical application of dichlorvoscrotoxyphos (D-C) insecticide and phenothiazine anthelmintic (PTZ) given in the diet were studied in 4 groups of 4-5 lambs each that had had prior drug exposure. In a study reported previously each lamb in groups 1 and 2 was sprayed with 3 biweekly topical applications of 1550 ml of 0.25% D-C emulsion. Groups 1 and 3 were treated with PTZ (12.5 g/sheep initially and 4 days later with 6.25 g every 3 days for 9 treatments). Group 4 was the control. Following termination of that study the animals were given a 30-day nonmedicated period and reused in the present study as described below. Each lamb in group 1 and 3 was challenged with PTZ given in the diet (1g/sheep/day for 3 days). On the third day of PTZ administration, each lamb in group 1 and 2 was sprayed with 1 gallon of 0.25% D-C emulsion. The 4th group served as a control. Following D-C spray, clinical signs of toxicosis were seen within 17 min in 56% of the exposed lambs regardless of concurrent PTZ treatment. The erythrocyte acetylcholinesterase (EACE) activities of the D-C exposed groups were significantly (P less than 0.05) depressed on post-treatment days (PTD) 1 and 3 regardless of the PTZ treatment. The base-line EACE values were reestablished on PTD 18. The PTZ alone was not toxic and did not inhibit EACE activity.(ABSTRACT TRUNCATED AT 250 WORDS)