Lovastatin and extended-release (ER) niacin in a fixed dose combination (Advicor 1 ) is approved for the treatment of dyslipidemia. Since both drugs are extensively metabolized, this study investigated the bioavailability and pharmacokinetics of their co-administration following single-dose administration. In a 4-way crossover study 40 subjects received: two 1000/20 Advicor tablets (ADV), two 1000 mg niacin ER tablets (NSP), two 20 mg lovastatin tablets (Mevacor 1 ; MEV), and two niacin ER 1000 mg tablets with two lovastatin 20 mg tablets (NSP ΓΎ MEV). Plasma was assayed for niacin, nicotinuric acid (NUA), lovastatin, lovastatin acid and HMGCoA reductase inhibition. Urine was assayed for niacin and its metabolites, NUA, N-methylnicotinamide and N-methyl-2pyridone-5-carboxamide. Least square mean ratios and 90% confidence intervals for C max and AUC (0Γt) were determined for NSP ΓΎ MEV versus MEV or NSP, ADV versus MEV or NSP, and ADV versus NSP ΓΎ MEV. Co-administration of niacin and lovastatin did not significantly influence C max and AUC (0Γt) of lovastatin, niacin, NUA and total urinary recovery of niacin and metabolites. A 22 to 25% decrease in lovastatin acid C max was observed while lovastatin acid AUC (0Γt) was not affected. The HMGCoA reductase inhibition C max and AUC (0Γt) were not affected indicating that the difference in lovastatin acid C max was not clinically relevant.