Cilomilast: pharmacokinetic and pharmacodynamic interactions with digoxin

Cilomilast is an orally active, selective phosphodiesterase 4 inhibitor currently in clinical development for the treatment of chronic obstructive pulmonary disease.

The purpose of this study was to examine the tolerability and steady-state pharmacokinetics of cilomilast and digoxin when coadministered at standard therapeutic doses in healthy adults.

In an initial, open-label phase, healthy young adults received cilomilast 15 mg BID for 5 days. After a 7-day washout period, subjects entered a double-blind, crossover phase during which they received oral digoxin (375 microg once daily) for 2 consecutive 14-day periods with no intervening washout period. Cilomilast 15 mg BID or placebo was coadministered during the first 14-day period. Subjects then crossed over to the alternative treatment for the second 14-day period. Blood and urine samples were collected at appropriate times for evaluation of digoxin and cilomilast steady-state pharmacokinetic parameters. The size of the study was sufficient to achieve 90% power to correctly exclude an effect of cilomilast.

Twelve of the 16 subjects enrolled completed the study. There were 4 withdrawals--1 due to noncompliance, 1 due to a positive drug screening, and 2 due to adverse events. At steady state, cilomilast 15 mg BID had no significant effect on the steady-state pharmacokinetic parameters of digoxin, with 90% CIs for both primary end points--area under the plasma concentration-time curve (AUC) over a 24-hour dosing interval and minimum plasma concentration--completely contained within the specified interval for equivalence (0.80-1.25). A mean reduction in maximum observed plasma concentration of digoxin of 11% was observed during coadministration with cilomilast, and time to maximum concentration was delayed by a median of 1 hour, suggesting a small reduction in the rate of digoxin absorption. Digoxin did not appear to markedly affect cilomilast steady-state pharmacokinetics. The most frequently reported adverse event was headache.

Cilomilast 15 mg BID had no clinically significant effect on steady-state AUC or on predose trough plasma concentrations of digoxin (375 microg once daily). The steady-state pharmacokinetics of cilomilast 15 mg BID were similar whether administered alone or with digoxin at steady state (375 microg once daily).