Abstract: The invention provides methods for predicting toxicity related to calcineurin inhibition therapy by measuring the peak concentration of drug and the trough concentration of the drug, calculating a peak-trough fluctuation, and comparing this peak-trough fluctuation to known values to predict if the patient will exhibit calcineurin-inhibition therapy-related toxicity. The invention also provides methods for monitoring drug levels to ensure that a patient receiving calcineurin inhibition therapy remains within a therapeutic window which maximizes the efficacy and minimizes the toxicity of the calcineurin inhibitor. The invention also provides dosage methods which maximize the peak concentration, minimize the trough concentration, and maximize the fluctuation between peak and trough concentration of calcineurin inhibitors, to maximize the efficacy of the calcineurin inhibition therapy, and minimize the risk of developing calcineurin-inhibition therapy-realted toxicity.