Prospective Pharmacogenetic Cohort Study of CYP2D6 Metabolizer Phenotype, Analgesic Failure, and Adverse Effects in Postoperative Patients Receiving Tramadol by Elastomeric Infusion Pump

Inclusion Criteria: * Elective surgery followed by the institution's standardized tramadol-containing elastomeric analgesia pump. * Ability to report pain on a 0-to-10 numeric rating scale. * Provision of a blood or buccal sample for CYP2D6 genotyping before or immediately after surgery. * Written informed consent for genetic testing, storage of genotype data, and clinical follow-up. Exclusion Criteria: * Known tramadol allergy or contraindication. * Chronic opioid therapy, opioid use disorder, or opioid tolerance requiring an individualized regimen. * Severe renal or hepatic dysfunction outside the standardized pump eligibility criteria. * Concomitant medication or condition that requires deviation from the standard pump before the first outcome assessment. * Pregnancy or breastfeeding. * Inability to provide reliable pain scores or complete 72-hour monitoring.