Laboratory monitoring of cyclosporine levels: guidelines for the dermatologist.

The following guidelines are recommended for laboratory monitoring of circulating levels of cyclosporine in dermatology patients. Measurements should be determined as trough levels in whole blood, not plasma or serum. The measurements should be performed with an assay that is specific for the parent cyclosporine compound (e.g., a high-performance liquid chromatography method or a specific monoclonal immunoassay). The results of nonspecific immunoassays that detect cyclosporine as well as its metabolites are difficult to interpret and cannot readily be compared among different studies or laboratories. In psoriasis patients, the circulating concentration of cyclosporine does not correlate reliably with the therapeutic response. Some patients may achieve an excellent response with blood levels in the range of 50 ng/ml; others may show little or no response despite blood levels as high as 200 ng/ml. In patients with a poor clinical response, monitoring of cyclosporine levels may be useful to confirm that the drug has been taken and may provide an estimate of the degree of absorption and metabolism of the parent compound. Because an upper limit of safety for the circulating concentration of cyclosporine has not been clearly defined, one should attempt to achieve a therapeutic response with the lowest possible dose. Clinicians must carefully monitor patients for signs of cyclosporine toxicity, regardless of the circulating concentration of the drug. Whole blood levels exceeding 250 ng/ml should be avoided.