Effect of neomycin on the bioavailability of spironolactone: a single-dose study

The effect of oral neomycin sulfate on the bioavailability of oral spironolactone in humans was studied. A 100-mg spironolactone tablet was administered alone or with two 500-mg neomycin sulfate tablets to 12 healthy, fasting men in a randomized crossover fashion. Levels of canrenone (an active spironolactone metabolite) in plasma and urine samples collected for 32 and 48 hours after dosing, respectively, were measured fluorimetrically. Neomycin significantly decreased the peak plasma canrenone concentration, significantly increased the time to reach peak concentration of canrenone, and significantly decreased the urinary excretion of canrenone over the first four hours (p less than 0.05). There were no significant differences between treatment groups in elimination half-life, area under the plasma curves or 48-hour urinary excretion of canrenone. Single doses of neomycin appear to delay the rate but not reduce the extent of spironolactone absorption. Thus, neomycin may not interfere with the clinical efficacy of spironolactone.