Pharmacokinetic interaction of sparfloxacin and digoxin

Sparfloxacin, a broad-spectrum, oral fluoroquinolone antimicrobial agent, has a long elimination half-life that permits once-daily administration. Antibiotics may increase the oral bioavailability of digoxin, leading to increases in its plasma concentration. Since patients treated with sparfloxacin may be receiving concurrent treatment with digoxin, the possibility of an interaction between sparfloxacin and digoxin was examined in a double-masked, placebo-controlled, multiple-dose, two-way crossover study in 24 healthy male volunteers between 20 and 49 years of age. All subjects were given digoxin 0.3 mg once daily throughout the 20-day study. Sparfloxacin (or placebo) was given as a 400-mg loading dose on day 1, followed by single 200-mg daily doses for 9 days, with crossover to the alternate treatment on days 11 through 20. Plasma levels of digoxin were analyzed by validated radioimmunoassay, and plasma levels of sparfloxacin were analyzed by validated high-performance liquid chromatography. Concomitant administration of sparfloxacin and digoxin was generally well tolerated. Mean values for steady-state area under the concentration-time curve over 24 hours for the 2 treatments were virtually identical: 28.4 ng/h per mL(-1) for digoxin administered with placebo and 28.9 ng/h per mL(-1) for digoxin administered concomitantly with sparfloxacin. Mean steady-state maximum plasma concentrations were 3.91 and 3.59 ng/mL for digoxin with placebo and digoxin with sparfloxacin, respectively. Mean steady-state trough plasma digoxin concentrations for the 2 treatments were 0.87 and 0.89 ng/mL, respectively. Mean times to steady-state maximum plasma concentrations were identical at 0.89 hours for both treatments. Mean steady-state oral clearance was 10.6 L/h for digoxin alone and 10.4 L/h for digoxin with sparfloxacin. Thus administration of sparfloxacin in combination with digoxin did not alter the pharmacokinetics of digoxin in healthy male volunteers aged 20 to 49 years. Steady-state plasma sparfloxacin concentrations were consistent with those obtained in other multiple-dose phase I studies, suggesting that digoxin does not alter the steady-state pharmacokinetics of sparfloxacin.