A study was conducted to determine the intrapulmonary and systemic pharmacokinetics of aerosolized pentamidine prophylaxis (APP) in patients infected with human immunodeficiency virus (HIV). 151 patients received high-dose (300 mg twice a month or 600 mg once a month) APP as part of a previously published clinical trial, and 29 additional patients received standard-dose (300 mg once a month) APP. Serial blood samples were obtained from the first cohort: 577 samples were obtained from 76 patients in the group given 600 mg once a month, and 554 blood samples were obtained from 75 patients in the group given 300 mg twice a month. In 9 of the 151 patients, bronchoscopy and tri-lobar (right upper, middle, and lower lobe) bronchoalveolar lavage (BAL) were performed 6 and 12 months after initiation of APP. Unilobar (right middle lobe) BAL was performed in the 29 patients infected with HIV who underwent bronchoscopy for diagnostic purposes. Pentamidine was measured using a chromatographic (HPLC) assay. The concentrations (mean +/- SD) of pentamidine in plasma in the groups given 300 mg twice a month and 600 mg once a month were 5.3 +/- 6.1 ng/mL and 8.8 +/- 9.6 ng/mL, respectively, and accumulation did not occur. The BAL supernatant and alveolar cell pentamidine concentrations were not significantly different in the 3 lobes and ranged from 16.5 +/- 7.7 ng/mL to 29.2 +/- 19.5 ng/mL and 1255 +/- 1142 ng/mg protein to 1572 +/- 1161 ng/mg protein in the group given 300 mg twice a month; and from 5.5 +/- 2.9 ng/mL to 9.4 +/- 7.7 ng/mL and 339 +/- 201 ng/mg protein to 571+/- 681 ng/mg protein in the group given 600 mg once a month. The intropulmonary concentrations of pentamidine at 6 and 12 months were not significantly different. In 18 of the 29 patients who received 1 to 7 prior monthly doses of standard APP, drug concentrations in BAL increased linearly (y = 2.05x) with the number of doses administered before bronchoscopy. These data indicate that intrapulmonary drug concentrations continue to increase for approximately 6 months after the initiation of APP, at which time steady state is achieved, and that administration of high dose APP is probably safe.