Disposition of hydrochlorothiazide (Hct) during phenytoin (Ph) treatment.

Plasma levels and urinary recovery of Hct were determined in seven healthy male volunteers. 75 mg Hct were administered as a tablet in a randomised fashion with or without phenytoin pretreatment (300 mg/d). Bioavailability of Hct showed considerable intra- and interindividual variation (32--87% and 42--77% respectively), but phenytoin did not influence the disposition parameters of the diuretic.