Effect of lead exposure on plasma phenylbutazone levels in rats.

The effect of lead exposure on phenylbutazone kinetics was studied in rats. The biological half-life (t1/2) of phenylbutazone was determined from the plasma level versus time curve in 3 groups of rats given (i) 10 mg/kg lead orally for 8 weeks (ii) 100 mg/kg single oral dose and (iii) no lead, after oral administration of 100 mg/kg phenylbutazone to all rats. The t1/2 of the drug was found to be 33% lower on chronic lead exposure and 46% higher on acute exposure than in unexposed control rats. This variation in the t1/2 values of the two different groups of rats indicates that probably phenylbutazone metabolism varies with the period of lead exposure.