Drug Interactions between methimazole and Predicort-50

MONITOR: The clearance of prednisolone may be increased when coadministered with some antithyroid agents, such as carbimazole and methimazole. The mechanism for this interaction has not been delineated, but may involve induction of CYP450-mediated metabolism of prednisolone. In one study, 6 hours after a 540 mcg/kg IV dose of prednisolone, the prednisolone plasma levels in patients receiving methimazole or carbimazole were approximately 10% of those in healthy subjects and were undetectable after 8 hours. In the healthy subjects, who had not taken methimazole or carbimazole, total and unbound prednisolone levels were higher and measurable over the entire 10-hour study period. It is unknown if other corticosteroids are affected similarly.

MANAGEMENT: Patients should be closely monitored for altered efficacy and safety while achieving a euthyroid state or when carbimazole or methimazole are added, discontinued, or the dosage is changed. Prednisolone dosage adjustments may be required. Patients should be advised to notify their clinician if they experience a worsening or change in their symptoms.