The Efficacy and Safety of Short Term S-ketamine Infusion as an Adjunctive Therapy in Patients With Fibromyalgia

Inclusion Criteria: * Patients between ages over 18 years with proper cognitive function and language skills for the study; * Patients diagnosed with FM as defined by the ACR FM diagnostic criteria; * Patients who have experienced insufficient symptom relief with non-pharmacological treatments and have not previously received recommended pharmacological treatment for FM; * A score of ≥ 4 on the average pain intensity over 7 days on the numeric rating scale (NRS) at baseline. Exclusion criteria: * Patient refusal; * Inability to sign informed consent; * Had other secondary FM, this is, hypothyroidism, nutritional deficiency, diabetes mellitus, connective tissue disorder; * Had psychiatric disorder, this is, schizophrenia and other psychotic disorder, bipolar disorder, or personality disorder; * Obstructive sleep apnea syndrome or a STOP-Bang score ≥ 3; * History of treatment with pregabalin and/or venlafaxine for any disease; * History of treatment with intravenous ketamine or ESK for chronic pain; * Presence of other painful ailments such as inflammatory rheumatic disease; * Uncontrolled diabetes, refractory hypertension, malignancies, narrow-angle glaucoma, hyperthyroidism, severe cardiovascular disease or any other contraindications to esketamine; * History of prescription drug abuse, alcoholism or illicit drug use; * Pregnant or lactating women; * Allergic to any of the study drugs.