Pharmacokinetics and absorption of foscarnet after intravenous and oral administration to patients with human immunodeficiency virus

Six patients with human immunodeficiency virus were given foscarnet in oral solution, 4000 mg every 6 hours for 3 days, followed by a washout period for 2 days and continuous intravenous infusion of 16,000 mg/24 hr over 72 hours. After oral foscarnet, plasma concentrations were less than 33 μmol/L in four patients; two had occasional concentrations of 35 to 50 μmol/L. The extent of absorption varied between 12% and 22%. During intravenous infusion, plasma concentrations ranged between 75 and 265 μmol/L. The disposition of foscarnet was triphasic, with mean half-lives of 0.45, 3.3, and 18 hours. Excretion data suggested elimination was by tubular secretion and glomerular filtration. Renal clearance was 176 ml/min 1.73 m2. The apparent nonrenal clearance, 40 ml/min 1.73 m2, probably reflects sequestration of foscarnet into bone. Ten percent to 28% of the cumulative dose may have been deposited in bone 2 days after infusion. A slight increase in serum calcium levels and changes in serum phosphate values may reflect the uptake of foscarnet in bone. Five patients had diarrhea (oral) and two had thrombophlebitis (intravenous). Clinical Pharmacology and Therapeutics (1988) 44, 65–73; doi:10.1038/clpt.1988.114