How long should phentermine be held prior to surgery?

Phentermine Discontinuation Prior to Surgery

Phentermine should be discontinued at least 4 days before a procedure requiring anesthesia to minimize perioperative cardiovascular complications. 1

Rationale for Discontinuation

• Phentermine is a sympathomimetic medication that can cause significant perioperative complications due to its effects on the cardiovascular system 1
• As a norepinephrine reuptake inhibitor, phentermine can lead to both hyperadrenergic effects and paradoxical refractory hypotension during surgery 1
• Perioperative complications associated with phentermine include:
  • Hypertension and hypotension 2
  • Bradycardia 2
  • Hyperthermia 2
  • Cardiac depression 2
  • Acute pulmonary edema 2

Timing of Discontinuation

• The American Gastroenterological Association (AGA) clinical practice guideline specifically recommends discontinuing phentermine and phentermine-containing medications at least 4 days before procedures requiring anesthesia 1
• This recommendation is based on the half-life of phentermine and the need to allow sufficient time for the drug to be eliminated from the body 2
• This 4-day recommendation differs from the classic 2-week discontinuation period that was previously recommended for "fen-phen" combinations 2

Mechanism of Perioperative Risk

• Phentermine's sympathomimetic properties can cause hyperadrenergic effects that become hazardous during anesthesia 1
• Paradoxically, phentermine can also lead to refractory hypotension during surgery, possibly due to catecholamine depletion and autonomic dysfunction 1
• Hypotension induced by phentermine may be unresponsive to vasopressors that rely on catecholamine release, such as ephedrine 2

Special Considerations

• The decision to perform elective surgery in a patient taking phentermine should be made with caution 2
• Patients should be informed about the increased risks associated with phentermine use in the perioperative period 2
• For emergency surgeries where the 4-day washout period is not possible, anesthesiologists should be specifically informed about the patient's phentermine use to monitor for potential complications 2
• Skilled anesthesia monitoring of intraoperative blood pressure and body temperature is essential to detect signs of autonomic instability 2

Comparison with Other Medications

• Unlike some other medications that may be continued until the day of surgery, phentermine requires this specific washout period due to its sympathomimetic effects 1
• This differs from medications like butorphanol and nalbuphine, which can be continued preoperatively 1
• Other medications with sympathomimetic properties, such as ergotamine, also require discontinuation (at least 2 days prior to surgery) 1