Therapeutic Dose Monitoring for Linezolid in a Patient with MRSA Pneumonia with Bacteremia in Diabetes Insipidus

INTRODUCTION: Few studies have investigated the effect of increased creatinine clearance (CrCl) on linezolid (LZD) concentration. Herein, we report the pharmacokinetic/pharmacodynamic (PK/PD) profile of LZD used in the management of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia with concomitant bacteremia in a patient with high CrCl caused by diabetes insipidus (DI). CASE REPORT: A 19-year-old man was admitted to the intensive care unit following a traumatic brain injury. After admission, he underwent a craniotomy for the severe brain injury. However, he developed DI after the operation. Despite treatment with vasopressin, his urine output reached 5–6 L/day as a result of the DI, and his CrCl increased to 180–278 mL/min. We were required to administer 6–7 L of fluid a day to compensate for the high urinary fluid output. On day 55, MRSA pneumonia with sepsis was suspected and, consequently, LZD was administrated intravenously (600 mg every 12 h). He was treated with LZD for 14 days. The patient has since successfully recovered from MRSA pneumonia with concomitant bacteremia, and was transferred to the general ward on day 82. Blood LZD levels from days 60–68, which were measured after the patient’s transfer to the general ward, showed that the trough levels were lower than the threshold level of detection. The blood 24-h area under the plasma LZD concentration–time curve (AUC)(24)/minimum inhibitory concentration (MIC) was 69.3. CONCLUSION: In spite of the low level of LZD AUC(24)/MIC caused by the high CrCl with DI, MRSA pneumonia with concomitant bacteremia was successfully treated with LZD. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s40121-015-0100-z) contains supplementary material, which is available to authorized users.