Overview of human pharmacokinetics of naltrexone.

Experimental data on 3H labelled naltrexone obtained from the Research Triangle Institute were analyzed. Both plasma and urine curves were resolved into their exponential components. Mean total clearance of unconjugated naltrexone was 3510 (300) ml/min, and its mean urinary clearance was 76.0 (6.8) ml/min. Fraction of dose excreted through urine was between 55 and 60%. Orally administered drug is completely absorbed into plasma. Plasma curve resulting from intravenous administration contained three exponentials: 1.9 (.5)/min, 0.18 (.07)/min and 0.00106 (.00008)/min. Distribution volumes were 7.6 (.7) liters, 60 (12) liters and 164 (16) liters. After oral administration there were two exponentials: 0.012 (.002/min and 0.00122 (.00009)/min. The faster exponential corresponds to gastrointestinal absorption with a half life of about 1 hour.