Pharmacokinetic and Pharmacodynamic Actions of Enalapril in Humans: Effect of Probenecid Pretreatment

The pharmacokinetic and pharmacodynamic profiles of oral enalapril (20 mg), in absence and in presence of probenecid pretreatment (1 g twice daily for 5 days), were investigated in 12 healthy volunteers on normal salt intake (150 mmol/24 hr). Mean peak serum concentration of enalapril rose from 158 +/- 7 to 216 +/- 1 ng/ml (P less than .01), whereas that of its metabolite, enalaprilat, rose from 62 +/- 6 to 84 +/- 8 ng/ml (P less than .01) in the presence of probenecid pretreatment. Area under the curve of both enalapril and enalaprilat increased by 50% (P less than .001), which was accompanied by a reduction in renal excretion of both compounds. The renal clearance of enalapril decreased from 229 +/- 19 to 61 +/- 4 ml/min (P less than .001) and that of enalaprilat from 108 +/- 4 to 66 +/- 2 ml/min (P less than .001). The total drug recovery fell from 48 +/- 3 to 38 +/- 2% (P less than .01) of the administered dose with no accompanying changes in plasma elimination half-lives of the parent drug or metabolite. The pharmacodynamic response of enalapril such as fractional excretions of sodium, calcium, magnesium and urate were enhanced by probenecid pretreatment. Absolute urinary excretion of sodium increased from 51 +/- 5 to 91 +/- 8 mmol/6 hr (P less than .001) after enalapril and from 55 +/- 4 to 113 +/- 13 mmol/6 hr (P less than .01) after enalapril in presence of probenecid pretreatment, despite a significant decrease in the renal excretion of enalapril and enalaprilat over the same interval.(ABSTRACT TRUNCATED AT 250 WORDS)