Suspected serotonin syndrome induced by fentanyl

Abstract

A 64-year-old male lung cancer patient with bone metastasis received oxycodone hydrochloride prolonged-release tablets for pain in right shoulder and back and bilateral hypochondrium. The initial dose was 10 mg twice daily and was increased to 80 mg twice daily gradually. Because of poor analgesic effect, the first fentanyl transdermal patch 4.2 mg was applied and kept pasted for 48 hours. On the third day, the second patch 8.4 mg was given and kept pasted for 72 hours. On the 5th day, the patient developed severe mental symptoms such as agitation and delirium, accompanied by fever and increased heart rate. Midazolam, diazepam, olanzapine, meropenem, and indomethacin suppository were given, but his symptoms were not improved. It was considered that combined use of high dose oxycodone and fentanyl induced delirium. Then, oxycodone hydrochloride prolonged-release tablet was changed to morphine sulfate sustained-release tablet. However, because morphine sulfate sustained-release tablets could not be taken by mouth due to the patient′s agitation, fentanyl was increased to 2 patches (16.8 mg). On the second day, the patient presented with hematuria and serum creatine phosphokinase (CK) increased from 26 U/L 6 days ago to 1 511 U/L. Serotonin syndrome and rhabdomyolysis induced by fentanyl were considered. Fentanyl transdermal patches were removed immediately and continuous intravenous pumping of morphine 2 mg/h was applied. After fentanyl transdermal patch withdrawal, his mental symptoms and hematuria gradually disappeared, body temperature and heart rate returned to normal. Serum creatine phosphokinase decreased to 82 U/L 8 days after fentanyl withdrawal. Key words: Fentanyl; Serotonin syndrome; Analgesics