Mistaken Administration of Hydroxyurea Instead of Tacrolimus in a Pediatric Kidney Transplant Recipient: A Case Report

Tacrolimus is a core medication of anti-rejection regimens for pediatric kidney transplant recipients. It is well known to have a narrow therapeutic window, affected by multiple factors, including absorption differences that influence drug concentrations in the body. Genetic polymorphisms of metabolizing enzymes, drug interactions, and intercurrent illnesses can impact drug clearance. This case report discusses a unique situation where a 12-year-old kidney transplant recipient experienced undetectable concentrations of tacrolimus in whole blood that were initially thought to result from excessive clearance due to severe diarrhea. Our nurse case manager investigated potential pharmacy errors by recommending that we test the home medication bottle, which revealed the absence of tacrolimus. Instead, the patient was given hydroxyurea, an anti-metabolite commonly used for oncologic and hematologic indications and can cause diarrhea, thrombocytopenia, and neutropenia. The patient experienced borderline rejection. The cause of this pharmacy error was multifactorial. However, confusion and complexities in the compounding process of liquid formulations likely played a role. This report underscores the importance of considering pharmacy errors as a potential cause of variations in tacrolimus drug concentrations. It emphasizes the role of nurses and interdisciplinary collaboration in identifying and addressing medication errors. It also underscores the need for standardization in the pharmaceutical compounding process and advocates for pharmaceutical industries to produce pediatric-appropriate formulations to reduce such errors.