The effect of acetaminophen on methemoglobin and blood glutathione parameters in the cat.

Acetaminophen (APAP) was given orally to 6 mature cats (3 male and 3 female) in single progressive doses of 20 (low), 60 (medium), or 120 (high) mg APAP/kg body weight, each 3 weeks apart. Methemoglobin (MHB), reduced blood glutathione (GSH) and APAP blood concentrations, and blood NADH methemoglobin reductase and NADPH glutathione reductase activities were measured periodically for 8 days after dosing. A statistically significant increase in MHB formation (21.7% and 45.5%, respectively) occurred following the medium and high doses. NADH methemoglobin reductase activity at the high dose decreased significantly. Red blood cell GSH concentrations decreased significantly during the first 24 h after the high APAP dose and returned to normal by 192 h. NADPH glutathione reductase activity decreased significantly following the high dose, but not after the lower APAP doses.