Development and pharmacology of fluvastatin

Fluvastatin is the first synthetic 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase inhibitor to be approved for clinical use, and has been studied extensively in humans since 1986. It is structurally distinct from the other currently available HMGCoA reductase inhibitors (lovastatin, simvastatin, and pravastatin), leading to unique biopharmaceutical properties relative to the other agents of this class. Absorption of fluvastatin is virtually complete across all species, including man, and is not affected by the presence of food. Systemic exposure is limited, as fluvastatin is subject to first-pass metabolism, and the plasma half-life of the drug is approximately 30 minutes. Some 95% of a single dosage of fluvastatin is excreted via the biliary route, with less than 2% of this being the parent compound. Additionally, there is no evidence of circulating active metabolites or accumulation during chronic dosing. Studies of the effect of food on the pharmacokinetics of fluvastatin have demonstrated marked reductions in the rate of bioavailability--from 40% to 60%; however, a comparison of fluvastatin administration with the evening meal or at bedtime has revealed no significant differences in the extent of bioavailability (area under the curve) of these two regimens. Furthermore, no significant difference in pharmacodynamic effect (reduction in low-density lipoprotein cholesterol levels) could be ascertained between mealtime dosing and bedtime dosing. The pharmacokinetics of fluvastatin have also been assessed in various demographic groups. Relative to the general population, plasma concentrations of fluvastatin do not vary as a function of either age or gender. In addition, administration to a patient population with hepatic insufficiency resulted in a 2.5-fold increase in both the rate and extent of bioavailability relative to controls. Also, although minimal alterations of fluvastatin clearance in patients with renal insufficiency are anticipated due to limited renal excretion (5%), a study in this patient group is currently underway to examine this further. Interaction studies have been performed with fluvastatin and several drugs with which it might be coadministered. Cholestyramine, an anionic-binding resin, has a considerable effect in lowering the rate and extent of fluvastatin bioavailability. Although this effect was noted even when cholestyramine was given 4 hours prior to fluvastatin, this regimen did not result in diminished efficacy. Further, no effects on either warfarin levels or prothrombin times were observed in a study involving concomitant administration of warfarin and fluvastatin. Moreover, additional interaction studies with niacin and propranolol have not demonstrated any effect on fluvastatin plasma levels, and administration to a patient population chronically receiving digoxin resulted in no difference in the extent of bioavailability of digoxin relative to control data. The results generated to date in clinical pharmacokinetic studies with fluvastatin thus support its use in a broad population of hypercholesterolaemic patients.