PREPARATIONS: Tablets: 4, 8, 16, 24, and 32 mg. Injectable suspension: 20, 40, and 80 mg/ml. Powder for Injection: 40, 125, 500, 1000, and 2000 mg.
DRUG INTERACTIONS: Troleandomycin (TAO), an infrequently used macrolide antibiotic, reduces the liver's ability to metabolize methylprednisolone (and possibly other corticosteroids). This interaction can result in higher blood levels of methylprednisolone and a higher probability of side effects. Erythromycin and clarithromycin (Biaxin) are likely to share this interaction, and ketoconazole (Nizoral) also inhibits the metabolism of methylprednisolone. Estrogens, including birth control pills, can increase the effect of corticosteroids by 50% by mechanisms that are not completely understood. For all of the above interactions, the dose of methylprednisolone may need to be lowered. Cyclosporine reduces the metabolism of methylprednisolone while methylprednisolone reduces the metabolism of cyclosporine. When given together, the dose of both drugs may need to be reduced to avoid increased side effects. Methylprednisolone may increase or decrease the effect of blood thinners, for example, warfarin (Coumadin). Blood clotting should be monitored and therapy adjusted in order to achieve the desired level of blood thinning (anti-coagulation).
Phenobarbital, phenytoin (Dilantin), and rifampin (Rifadin, Rimactane) may increase the metabolism of methylprednisolone and other corticosteroids, resulting in lower blood levels and reduced effects. Therefore, the dose of methylprednisolone may need to be increased if treatment with phenobarbital is begun. Combining corticosteroids with potassium depleting drugs (for example, diuretics, amphotericin B) may result in low blood potassium (hypokalemia), resulting in heart failure.
Combining corticosteroids with anticholinesterase drugs (for example, physostigmine) can result in severe weakness in patients with myasthenia gravis.
Live vaccines or inactivated vaccines may not be as effective in patients receiving prolonged corticosteroid therapy because steroids depress the immune system. Vaccines should be administered after corticosteroid therapy is completed.
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