Most patients who take cyclosporine and tacrolimus lose 20 to 30 percent of their renal function in the first year. If blood levels of the drugs are carefully managed, renal function then stabilizes, with only mild progressive loss of renal function thereafter. On occasion, severe neurologic complications develop, including psychosis, seizures, and apraxia. Much more commonly seen are headaches, tremors, and severe musculoskeletal pains. Hypertension, which is common in patients using either cyclosporine or tacrolimus, is thought to result from peripheral and renal vasoconstriction.
Patients receiving either drug can develop hyperkalemia and hyperuricemia.
Cyclosporine, but not tacrolimus, is associated with gingival hyperplasia and excessive hair growth, particularly on the arms and face. Both cyclosporine and tacrolimus are extensively metabolized in the liver, primarily via the cytochrome P-450 IIIA enzyme. As a result, both drugs are prone to numerous drug-drug interactions. The most dramatic examples include interactions with ketoconazole and phenytoin. Ketoconazole inhibits the P-450 IIIA enzyme and can result in dramatic increases in circulating levels of cyclosporine and tacrolimus.