Pharmacokinetics of beta-methyldigoxin in subjects with normal and impaired renal function

Role of Organic Anion Transporting Polypeptide 2 in Pharmacokinetics of Digoxin and β-Methyldigoxin in Rats

Recently, we found that potent P-glycoprotein (P-gp) inhibitors, such as verapamil and cyclosporin A, markedly modulated the pharmacokinetics of digoxin in rats, whereas they did not affect beta-methyldigoxin pharmacokinetics significantly. Digoxin is also a substrate of rat organic anion transporting polypeptide 2 (Oatp2). Here, we compared the magnitude of Oatp2-mediated drug interaction of digoxin and beta-methyldigoxin using amiodarone as an Oatp2 inhibitor in rats. Amiodarone (20 mg/kg) given intravenously significantly increased plasma levels and decreased biliary excretion, liver distribution, and intestinal distribution of digoxin administered intravenously at a dose of 10 mug/kg. Amiodarone also significantly decreased biliary excretion and liver distribution of beta-methyldigoxin, but the change in plasma levels of beta-methyldigoxin was quite small. These findings may give a clue in selecting these cardiac glycosides in clinical pharmacotherapy for patients receiving multiple drugs towards escape from Oatp2-mediated drug interactions.

Standardized structure and modular design of a pharmacokinetic database

BACKGROUND

The accumulated knowledge on drugs can be used for an individual drug dosage adjustment if it is placed at our disposal in an informatically structured form.

THEORY AND METHODS

We have started building up a pharmacokinetic database aimed at adjusting drug dosages, in exemplary form, to patients with renal impairment. Parameters needed for the three dosage adjustment rules (Dettli, Kunin, Holford) and the most general concept of pharmacokinetics constituted the theoretical basis.

TWO PROCESSES PERTAIN TO ALL DRUGS

Distribution and elimination. Total drug clearance and at least two parameters representing distribution and elimination processes are closely interdependent in mathematical terms (clearance = volume of distribution*rate of elimination). This relation yields the unifying concept that serves as a prerequisite for a structured recording of 30 assigned pharmacokinetic and pharmacodynamic parameters within an informatic database.

SOLUTIONS AND RESULTS

The information is retrieved and referenced from 2383 original publications by means of a standardized input module. The complete database at present contains 15,397 records for 1573 drugs. A programmed meta-analytic algorithm is used to calculate the statistical measures for the central value and variance--as available--from the pooled values of primary records. The statistically standardized parameters are extracted for 6601 pharmacokinetic parameters, and placed at the users disposal with the output module.

PRACTICAL UTILITY

Following meta-analysis, published pharmacokinetics can be used as statistical estimates of population parameters. The statistical estimates with variances permit an individual drug dosage adjustment by applying the Bayesian approach or neural networks.