The sirolimus test is ordered to measure the amount of drug in the blood to determine whether concentrations have reached therapeutic levels and are below toxic levels. If someone is taking both sirolimus and cyclosporine (or tacrolimus), then both drug concentrations will be measured. Other tests may also be periodically ordered to evaluate organ function and the body’s blood cell counts because sirolimus may decrease a person’s platelet count, increase their blood lipids, and, when taken long-term with other immunosuppressants, affect kidney function.

Sirolimus is ordered frequently at the start of therapy. Because of its long half-life, sirolimus concentrations may take some time to reach equilibrium in the blood. Patients may not be tested for a week or two after a dosage change. Once dosages have been established and shown to be well tolerated, then the frequency of sirolimus testing may decrease. The test is performed whenever there is a change in dose, a change in other medications, or whenever patients have symptoms that suggest side effects, toxicity, or organ rejection. Monitoring is necessary as long as the patient is taking sirolimus.

Concentrations that are higher than the established therapeutic range may cause symptoms associated with toxicity. Concentrations that are too low may lead to rejection of the transplanted organ.

If the person is also taking other immunosuppressants or medications, then patients should work closely with their doctor and transplant team to ensure that there is no potential interaction between the medications.

Drugs that inhibit or accelerate the metabolism of sirolimus may affect blood levels. Drugs that can increase sirolimus blood levels include antifungal medications, clarithromycin, erythromycin, isoniazid, protease inhibitors, and quinidine. Those that can decrease sirolimus levels include carbamazepine, phenobarbitol, phenytoin, rifampin and nafcillin. Grapefruit juice and herbal supplements such as St. John’s Wort must be avoided while taking sirolimus.

Patients should not alter their dose or the time that they take their dose without consulting their doctor. Sirolimus should be taken consistently with respect to meals. Women should not become pregnant while taking sirolimus. Those considering pregnancy should talk to their doctor about associated risks.

Patients taking sirolimus should also talk to their doctor before getting any vaccines.

Patients may have side effects and experience complications such as infections and slow healing even when taking sirolimus properly. Side effects may include:

Anemia

Constipation

Diarrhea

Fever

Headache

Hypertension

Insomnia

Nausea

Sensitivity to sunlight

Weight gain