Inhibition of methylprednisolone elimination in the presence of clarithromycin therapy

Background: Macrolide antibiotics have long been used as steroid-sparing agents in patients with severe steroid-dependent asthma. Their efficacy and their propensity to potentiate glucocorticoid adverse effects have been attributed in part to their ability to delay glucocorticoid clearance. Objective: We sought to determine whether clarithromycin, a newer macrolide antibiotic, can alter the pharmacokinetic profile of oral glucocorticoids and thereby increase the risk of steroid-induced adverse effects. Methods: An open-label study in a paired design (before and after treatment) was conducted in a hospital-based outpatient clinic. Participants were 6 adult patients (mean age, 30 years) with mild-to-moderate asthma. Prednisone (40 mg/1.73 m(2)) and methylprednisolone (40 mg/1.73 m(2)) were given as single randomized doses on consecutive study days before and on days 8 and 9 of a clarithromycin (500 mg twice daily) course. Twelve-hour pharmacokinetic profiles with measurement of plasma methylprednisolone and prednisolone levels were taken before and after clarithromycin therapy. Results: Clarithromycin therapy resulted in a 65% reduction of methylprednisolone clearance and significantly higher mean plasma methylprednisolone concentrations compared with preclarithromycin concentrations but had no significant effect on prednisolone clearance or mean prednisolone plasma concentrations. Conclusions: Clinicians must be aware of potential drug interactions that could place patients at increased risk for steroid-induced adverse effects. Such an effect has been demonstrated between clarithromycin and methylprednisolone, two drugs that may be administered concomitantly in asthma. To avoid potential steroid-enhancing effects, prednisone should be substituted for methylprednisolone during prolonged courses of clarithromycin therapy.