DP70: NO PRESSURE: DOES TIMING REALLY MATTER FOR PHENTERMINE DISCONTINUATION?
Tachy V Hernandez Romero, MD; Maria F Acevedo Kury; Zulma D Sosa Carcamo, MD; Ridwan Ahmad, MBBS; Adam Jacob, MD; Joan M Irizarry Alvarado, MD
Mayo Clinic
BACKGROUND: Phentermine is a sympathomimetic amine commonly prescribed for weight loss. Due to its long half-life (~20 hours), current guidelines recommend discontinuing phentermine at least four days prior to surgery to minimize the risk of intraoperative hypotension. However, these recommendations are based on an outdated systematic review of a review article, two case reports and a letter1. These studies involved phentermine with fluphenazine, rather than current formulations of phentermine alone or with topiramate.
OBJECTIVE: We hypothesized that intraoperative hypotension would not differ significantly between patients who continued phentermine through the day of surgery and those who discontinued it four or more days preoperatively.
METHODS: In this retrospective cohort study, we identified 1,362 adults (≥18 years) who underwent elective, non-cardiac surgery under general, neuraxial, or peripheral regional anesthesia at all Mayo Clinic locations (Rochester, Florida, Arizona) from January 1, 2019-December 31, 2023, and were prescribed phentermine or phentermine-topiramate. We grouped patients by timing of last dose (≤1 day vs ≥4 days preoperatively). We collected baseline demographics, surgical and anesthetic factors, and intraoperative hemodynamic variables (i.e., MAP, use of pressors, colloids and crystalloids). Hypotension was defined as MAP <65 mmHg.
RESULTS: Patients who discontinued phentermine less than four days before surgery had a significantly lower likelihood of experiencing intraoperative hypotension compared to those who discontinued it four or more days prior (p = 0.0035). Similarly, discontinuation less than seven days before surgery was associated with lower vasopressor use (p = 0.0145). Intraoperative MAP was not statistically significant in patients who discontinued phentermine less than 7 days. Furthermore, the use of pressors was statistically more significant in those patients who held phentermine more than 7 days before surgery.
CONCLUSIONS: Findings suggest that phentermine is unlikely to be the sole cause of hypotension risk. Other underlying factors (e.g., comorbidities, physiological responses, intraoperative events) may contribute, thus warranting further investigation.