The curative effects of cysteamine, cysteine, and dithiocarb in experimental paracetamol poisoning.

Abstract

In a curative test (i.p. injection 1 hr after administration of paracetamol) cysteamine (100 mg/kg), cysteine (200 mg/kg), and dithiocarb (100 mg/kg) reduced the death rate from paracetamol poisoning (1.5g/kg p.o.) in male mice from 67 to 10, 15 or 10%, respectively. A reduction of mortality rate to 30 or 35% was induced by glutathione (100 mg/kg) and thiazolidine carboxylic acid (50 mg per kg), respectively, whereas penicillamine, thioctic acid, silymarin, and dimercaprol were ineffective. When given 2 or 4 hrs after paracetamol, cysteine, unlike cysteamine, had a curative effect on paracetamol toxicity. Hepatotoxic activity of paracetamol (0.5 g/kg p.o.) was evident by high increases in the levels of serum enzymes (GOT, GPT, GLDH, SDH). Paracetamol-induced enzyme elevations were prevented completely by treatment with cysteamine (50 mg/kg) or cysteine (100 mg/kg) and partially by treatment with dithiocarb (100 mg/kg) 1 hr after paracetamol. LD50 values (i.p. injection) were 450 mg per kg for cysteamine, 660 mg/kg for cysteine, and 1800 mg/kg for dithiocarb. With regard to the therapeutic index cysteamine, cysteine, and dithiocarb can be recommended as antidotes for paracetamol poisoning. A nearly total depletion of hepatic glutathione occurred after paracetamol (0.5 g/kg p.o.). Administration of cysteine (100 mg/kg), one hr after paracetamol, induced a complete repletion of liver glutathione whereas cysteamine (100 or 200 mg/kg) and dithiocarb (100 mg/kg) induced a partial repletion. Glutathione repletion probably accounts for the antidote efficiency of cysteine, cysteamine, and dithiocarb. Its mechanism, however, remains obscure.