Kinetic interactions between 4-methylpyrazole and ethanol in healthy humans.

4-Methylpyrazole (4-MP), a potent inhibitor of alcohol dehydrogenase activity, is a candidate to replace ethanol as the antidote for methanol and ethylene glycol intoxications, because it has a longer duration of action and apparently fewer adverse effects. To study a probable mutual inhibitory effect between ethanol and 4-MP on their elimination, two studies were performed in healthy human volunteers using double-blind crossover designs. In study A1 4-MP in the presumed therapeutic dose range of 10 to 20 mg/kg caused a 40% reduction in the rate of elimination of ethanol in 12 subjects given 0.5 to 0.7 g/kg of ethanol. These data suggest that such doses of 4-MP inhibit alcohol dehydrogenase activity in humans in vivo and would be effective at blocking methanol or ethylene glycol metabolism. In study B, ethanol (0.6 g/kg followed by 0.2 g/kg twice) significantly decreased the rate of elimination of 4-MP (5 mg/kg, given intravenously to four subjects). These moderate doses of ethanol also inhibited the rate of urinary excretion of 4-carboxypyrazole, the primary metabolite of 4-MP in humans. Data suggest that ethanol inhibits 4-MP metabolism, thereby increasing the duration of therapeutic blood levels of 4-MP in the body. This mutual interaction may have clinical implications, because most self-poisoned patients have also ingested ethanol. Theoretically, methanol and ethylene glycol might also show such interactions with 4-MP.

Effects of 4-methylpyrazole, methanol/ethylene glycol antidote, in healthy humans.

4-Methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase, may be useful for the treatment of methanol and ethylene glycol intoxications. A placebo-controlled, double blind, multiple dose, sequential, ascending-dose study has been performed to determine the tolerance of 4-MP in healthy volunteers. Oral loading doses of 4-MP were followed by supplemental doses every 12 h through 5 days, producing plasma levels in the therapeutic range. A slight, transient elevation in one or both serum transaminase values was observed in 6 of the 15 subjects treated with 4-MP. This effect was not dose related nor apparently mediated through a hypersensitivity reaction. Serum triglyceride levels were increased in 30% of 4-MP treated subjects, but also in 25% of the placebo subjects. 4-MP treatment did not produce any other significant changes in objective clinical parameters nor in subjective side effects. The results suggest that a mild, transient increase in liver function tests might be observed in some subjects treated with multiple doses of 4-MP. Nevertheless, the slower elimination rate and lesser degree of toxicity of 4-MP would make it preferable to ethanol in therapy of these poisonings.

Non-linear kinetics of 4-methylpyrazole in healthy human subjects.

In order to evaluate the pharmacokinetic profile of the alcohol dehydrogenase inhibitor 4-methylpyrazole 4-MP, a placebo-controlled, double-blind, single-dose, randomized, sequential, ascending-dose "Phase-I study" was performed in healthy male volunteers at dose levels of 10 (n = 4), 20 (n = 4), 50 (n = 4) and 100 mg.kg-1 (n = 3). In the 10 and 20 mg.kg-1 group, the elimination of 4-MP from the plasma followed non-linear kinetics with mean rates of concentration decline of 3.66 and 5.05 mumol.l-1.h-1, respectively. In the two highest dose groups, the elimination also appeared to be non-linear although the patterns were not followed long enough to confirm this. The mean rates of concentration decline at the higher doses were significantly increased, up to 14.9 mumol.l-1.h-1 at 100 mg.kg-1. The average renal clearance of 4-MP was low, 0.016 ml.min-1.kg-1, and only 3% of the administered dose was excreted unchanged in the urine, indicating metabolism as the major route of elimination. Because of the apparently unusual kinetics following single dose treatment, thorough multiple dose studies need to be carried out to determine a safe dosage regimen for 4-MP.