Phentermine: A Systematic Review for Plastic & Reconstructive Surgeons

Purpose: Phentermine is the most prescribed prescription anti-­obesity drug in America, with 2.43 million consumers reported in 2011. Case reports have suggested there are anesthetic risks, such as hypotension, involved with its perioperative use. This is an important patient safety issue for plastic surgeons because phentermine is taken by many aesthetic surgery patients. Still, there is no published data regarding the prevalence of phentermine use among plastic surgery patients.

Methods: A systematic review of the pharmacology of phentermine and the anesthetic risks involved with its perioperative use was undertaken using the search engines PubMed/MEDLINE, Embase, and Scopus.

Results: A total of 251 citations were reviewed, yielding four articles which discussed perioperative phentermine use and complications with anesthesia. One was a review article, two were case reports, and one was a letter. Complications upon induction of general or sedation anesthesia included hypotension, hypertension, hypoglycemia, hyperthermia, bradycardia, cardiac depression, and acute pulmonary edema. There were no deaths reported due to exclusive phentermine use.

Conclusions: The relationship between phentermine and anesthesia, if any, is unclear. Blood pressure lability is the most reported complication related to perioperative phentermine use. Specifically, phentermine induced hypotension may be unresponsive to vasopressors that increase catecholamine release, such as ephedrine. Therefore, the decision to perform surgery, especially elective surgery, in a patient taking phentermine should be made with caution. Due to the half-­life of phentermine, we recommend discontinuing phentermine for at least four days prior to surgery. The patient should be made aware of the increased risk of surgery, and a skilled anesthesiologist should closely monitor intraoperative blood pressure and body temperature for signs of autonomic derailment.