Severe prolonged tacrolimus overdose with minimal consequences.

A 59-year-old man inadvertently received a 10-fold increase in his twice-daily oral dose of tacrolimus 1 mg that resulted in trough blood levels above 90 ng/ml for over a week. The patient had end-stage renal disease secondary to diabetes mellitus and had received a kidney transplant from his daughter 3 months earlier. Despite the numerous adverse effects commonly reported with tacrolimus, such as mild nephrotoxicity, nausea, tremors, and elevated liver enzyme levels, our patient's acute but prolonged overdose resulted in minimal signs and symptoms of toxicity. Nevertheless, education regarding the importance of accurate dosing, close monitoring, potential drug interactions, and the various capsule colors should be provided to all patients who receive tacrolimus, as well as their physicians, nurses, and pharmacists, in order to prevent as many errors as possible.