cyclosporine and fluconazole

Fluconazole is an inhibitor of CYP3A4, the cytochrome P450 enzyme responsible for the metabolism of cyclosporine. Inhibition of CYP3A4 reduces the hepatic clearance of cyclosporine, leading to increased plasma concentrations and systemic exposure. The interaction is pharmacokinetic, involving enzyme inhibition rather than a pharmacodynamic effect.

Elevated cyclosporine levels increase the risk of cyclosporine-associated toxicity, including nephrotoxicity, neurotoxicity (e.g., tremor, headache), and hypertension. The interaction is clinically relevant in transplant recipients and patients with autoimmune conditions, especially when cyclosporine is used at therapeutic doses. The magnitude of the effect varies, but significant increases in cyclosporine exposure have been reported.

If co-administration is necessary, monitor cyclosporine trough concentrations before starting fluconazole and then at frequent intervals (e.g., twice weekly) during therapy and after discontinuation of fluconazole. Adjust the cyclosporine dose according to the measured levels and clinical response. Monitor renal function and serum creatinine. Consider an alternative antifungal with less CYP3A4 inhibition, such as an echinocandin, but fluconazole may be used with careful monitoring and dose adjustment.

The interaction is well established through clinical case reports, pharmacokinetic studies, and is documented in standard drug interaction databases. The effect size varies among patients, but the potential for clinically significant toxicity is widely recognized.