Cyclosporine (Neoral®) and Tacrolimus (Prograf®, FK506) belong to a class of drugs called calcineurin inhibitors. They block the action of immune cells in the blood which normally detect and attack your transplanted organ leading to rejection. These medications may have side effects that are unpleasant and can cause other medical problems. Many medications, including over-the counter and herbal medications, may unfavorably interact with cyclosporine and tacrolimus, increasing your risk of drug toxicities. Monitoring of drug levels regularly and taking all prescribed medications as directed can lower the risk of side effects.

Both cyclosporine and tacrolimus can reduce blood flow to the kidney which decreases the ability of the kidneys to function. Swelling of the hands and feet, unusual weight gain, or less than normal output when urinating may be signs of kidney toxicity. A reduction in the drug dosage or temporary discontinuation of the drug may be necessary to overcome this side effect.

In some instances, other medications may be required to treat the side effects from cyclosporine or tacrolimus. For example, a decrease in magnesium level and an increase in potassium level in the blood may occur requiring treatment. Also, some transplant patients develop high blood pressure with the use of these drugs which may be treated with calcium-channel blockers (e.g. Norvasc®). Both cyclosporine and less commonly tacrolimus may elevate blood sugar. Dry mouth, increased thirst, or increased urination may be signs of diabetes. For patients who develop diabetes, oral medications that lower blood sugar may be required, but insulin may be necessary in some extreme instances. Lipid levels may be raised by these drugs. A class of medications called "statins" (e.g. Lipitor®, Pravachol®) can be used to lower lipid levels without unfavorably interacting with anti-rejection drugs.

Other side effects of cyclosporine and tacrolimus include headache, tremor and occasionally seizures. Patients taking tacrolimus may also notice a worsening of their handwriting. Diarrhea and nausea can also occur especially with tacrolimus, but usually decrease with time. Some side effects that may occur with cyclosporine, but not with tacrolimus, include excess hair growth or swelling of gums. Patients taking cyclosporine should have regular dental visits and practice good oral hygiene.