Hospital-Compounded Oral Ketamine as Maintenance Therapy After Intravenous Induction for Fibromyalgia: A Retrospective Real-World Study, Off-Label Pharmacotherapy

This retrospective study evaluated real-world use of hospital-compounded oral ketamine in fibromyalgia patients following a course of intravenous (IV) ketamine induction. Fifty-three patients with fibromyalgia first underwent a 3-day IV ketamine infusion (1.44 mg/kg/day) in hospital and then transitioned to oral ketamine, compounded by the hospital pharmacy. Patients were categorized as complete, partial, or non-responders based on clinical outcomes after 3 months. Of the 53 patients, 41.5% were complete responders, 15% partial responders, and 43.5% non-responders. Complete responders continued oral ketamine for a mean of 15.6 months. Overall, 58.5% discontinued ketamine (23 patients within 3 months, 8 after more prolonged use), most commonly due to lack of efficacy (12 patients) or side effects (11 patients). Side effects were generally mild; significant adverse events occurred in only two patients (3.8%: one with hypertension, one with atrial fibrillation), and one patient had a isolated elevation in a liver enzyme (gamma-GT). These findings suggest sequential IV induction followed by oral ketamine maintenance can be a safe, potentially effective off-label therapy for some fibromyalgia patients refractory to standard treatments. The tolerability and sustained use observed in responders highlight the need for further prospective studies to clarify ketamine's role in chronic fibromyalgia pain management.