Pitavastatin

Pitavastatin competitively inhibits HMG-CoA reductase, the rate-limiting enzyme in the biosynthesis of cholesterol, and inhibits cholesterol synthesis in the liver. As a result the expression of LDL receptors in the liver is increased, promoting the uptake of circulating LDL from the blood, decreasing total cholesterol (TC) and LDL-cholesterol (LDL-C) concentrations in the blood. Its sustained inhibition of hepatic cholesterol synthesis reduces VLDL secretion into the blood, reducing plasma triglyceride (TG) levels.

Pharmacodynamic Effects

Pitavastatin reduces elevated LDL-C, total cholesterol and triglycerides and increases HDL-cholesterol (HDL-C). It reduces Apo-B, and produces variable increases in Apo-A1 (see Table 1). It also reduces non-HDL-C and elevated TC/HDL-C, and Apo-B/Apo-A1 ratios.

Table 1. Dose response in patients with primary hypercholesterolaemia (Adjusted mean percent change from baseline over 12 weeks):

* unadjusted

Absorption

Pitavastatin is rapidly absorbed from the upper gastrointestinal tract and peak plasma concentrations are achieved within one hour after oral administration. Absorption is not affected by food. Unchanged drug undergoes enterohepatic circulation and is well absorbed from the jejunum and ileum. The absolute bioavailability of pitavastatin is 51%.

Distribution

Pitavastatin is more than 99% protein bound in human plasma, mainly to albumin and alpha 1-acid glycoprotein, and the mean volume of distribution is approximately 133 L. Pitavastatin is actively transported into hepatocytes, the site of action and metabolism, by multiple hepatic transporters including OATP1B1 and OATP1B3. Plasma AUC is variable with an approximately 4- fold range between the highest and lowest values. Studies with SLCO1B1 (the gene which encodes OATP1B1) suggests that polymorphism of this gene could account for much of the variability in AUC. Pitavastatin is not a substrate for p-glycoprotein.

Biotransformation

Unchanged pitavastatin is the predominant drug moiety in plasma. The principal metabolite is the inactive lactone which is formed via an ester-type pitavastatin glucuronide conjugate by UDP glucuronosyltransferase (UGT1A3 and 2B7). In vitro studies, using 13 human cytochrome P450 (CYP) isoforms, indicate that the metabolism of pitavastatin by CYP is minimal; CYP2C9 (and to a lesser extent CYP2C8) is responsible for the metabolism of pitavastatin to minor metabolites.

Elimination

Unchanged pitavastatin is rapidly cleared from the liver in the bile, but undergoes enterohepatic recirculation, contributing to its duration of action. Less than 5% of pitavastatin is excreted in the urine. The plasma elimination half-life ranges from 5.7 hours (single dose) to 8.9 hours (steady state) and the apparent geometric mean oral clearance is 43.4 L/h after single dose. Effect of food: The maximum plasma concentration of pitavastatin was reduced by 43% when it was taken with a high-fat meal, but AUC was unchanged.

Special populations

Elderly

In a pharmacokinetic study which compared healthy young and elderly (≥65 years) volunteers, pitavastatin AUC was 1.3-fold higher in elderly subjects. This has no effect on the safety or efficacy of pitavastatin in elderly patients in clinical trials.

Gender

In a pharmacokinetic study which compared healthy male and female volunteers, pitavastatin AUC was increased 1.6-fold in women. This has no effect on the safety or efficacy of pitavastatin in women in clinical trials.

Race

There was no difference in the pharmacokinetic profile of pitavastatin between Japanese and Caucasian healthy volunteers when age and body weight was taken into account. Paediatric population: There are limited pharmacokinetic data in children and adolescents. In study NK-104-4.01EU sparse sampling revealed a dose-dependent effect on pitavastatin plasma concentrations at 1 hour post dose. There was also indication that concentration at 1 hour post dose were (inversely) related to body weight and may be higher in children than adults.

Renal insufficiency

For patients with moderate renal disease and those on haemodialysis increases in AUC values were 1.8-fold and 1.7-fold respectively.

Hepatic insufficiency

For patients with mild (Child-Pugh A) hepatic impairment AUC was 1.6 times that in healthy subjects, while for patients with moderate (Child-Pugh B) hepatic impairment AUC was 3.9-fold higher. Dose restrictions are recommended in patients with mild and moderate hepatic impairment. Pitavastatin is contraindicated in patients with severe hepatic impairment.

Non-clinical data reveal no special hazard for humans based on results from conventional studies of safety pharmacology, repeated dose toxicity, genotoxicity carcinogenic potential, toxicity to reproduction. Indications of renal toxicity were seen in monkeys at exposures greater than those reached in adult humans administered the maximum daily dose of 4mg and urinary excretion plays a far greater role in the monkey than in other animal species. In vitro studies with liver microsomes indicate that a monkey-specific metabolite may be implicated. The renal effects observed in monkeys are unlikely to have clinical relevance for humans, however the potential for renal adverse reactions cannot be completely excluded.

Pitavastatin had no effect on fertility or reproductive performance and there was no evidence of teratogenic potential. However, maternal toxicity was observed at high doses. A study in rats indicated maternal mortality at or near term accompanied by fetal and neonatal deaths at doses of 1 mg/kg/day (approximately 4 fold greater than the highest dose in humans on an AUC basis). No studies have been conducted in juvenile animals.