Certain drugs such as troleandomycin (TAO), erythromycin ( Ery-Tab , EryPed 200), and clarithromycin ( Biaxin ) and ketoconazole ( Nizoral ) can reduce the ability of the liver to metabolize (breakdown) corticosteroids and this may lead to an increase in the levels and side effects of corticosteroids in the body. On the other hand, phenobarbital, ephedrine , phenytoin ( Dilantin ), and rifampin ( Rifadin , Rimactane ) may reduce the blood levels of corticosteroids by increasing the breakdown of corticosteroids by the liver. This may necessitate an increase of corticosteroid dose when they are used in combination with these drugs.
In each study, TOBI-treated patients experienced significant improvement in pulmonary function. Improvement was demonstrated in the TOBI group in Study 1 by an average increase in FEV 1 % predicted of about 11% relative to baseline (Week 0) during 24 weeks compared to no average change in placebo patients. In Study 2, TOBI-treated patients had an average increase of about 7% compared to an average decrease of about 1% in placebo patients. Figure 1 shows the average relative change in FEV 1 % predicted over 24 weeks for both studies.
In a small study in healthy volunteers, the slightly less potent CYP3A inhibitor ketoconazole increased the exposure of fluticasone propionate after a single inhalation by 150%. This resulted in a greater reduction of plasma cortisol as compared with fluticasone propionate alone. Co-treatment with other potent CYP3A inhibitors, such as itraconazole and cobicistat-containing products, and moderate CYP3A inhibitors, such as erythromycin, is also expected to increase the systemic fluticasone propionate exposure and the risk of systemic side effects. The combination should be avoided unless the benefit outweighs the increased risk of systemic corticosteroid side-effects, in which case patients should be monitored for systemic corticosteroid side-effects.