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Drug interactions between Effexor XR and phentermine

Results for the following 2 drugs:
Effexor XR (venlafaxine)
phentermine

Interactions between your drugs

Major

phentermine ↔ venlafaxine

Applies to:phentermine and Effexor XR (venlafaxine)

GENERALLY AVOID: Several case reports suggest that serotonin reuptake inhibitors may potentiate the pharmacologic response to sympathomimetic agents. The exact mechanism of interaction is unclear. In one case report, a patient experienced jitteriness, racing thoughts, stomach cramps, dry eyes, palpitations, tremors, and restlessness following a single dose of phentermine ingested approximately a week after she had discontinued fluoxetine. Because of the long half-life of fluoxetine and its metabolite, an interaction with fluoxetine is possible. Similar toxic reactions have been reported when fluoxetine was used concomitantly with amphetamine or phenylpropanolamine. Additionally, some sympathomimetic agents such as amphetamines may possess serotonergic activity and should generally not be administered with serotonin reuptake inhibitors because of the additive risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5-HT1A and 2A receptors. The interaction was suspected in a patient treated with dexamphetamine who developed symptoms consistent with the serotonin syndrome approximately 2 weeks after the addition of venlafaxine. The medications were discontinued and the patient was given cyproheptadine for suspected serotonin syndrome, whereupon symptoms promptly resolved. A second episode occurred when dexamphetamine was subsequently resumed and citalopram added. The patient improved following cessation of citalopram on his own, and residual symptoms were successfully treated with cyproheptadine.

MANAGEMENT: In general, amphetamines and other sympathomimetic appetite suppressants should not be combined with selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). Close monitoring for enhanced sympathomimetic effects and possible serotonin syndrome is recommended if these agents must be used together. Symptoms of the serotonin syndrome may include mental status changes such as irritability, altered consciousness, confusion, hallucinations, and coma; autonomic dysfunction such as tachycardia, hyperthermia, diaphoresis, shivering, blood pressure lability, and mydriasis; neuromuscular abnormalities such as hyperreflexia, myoclonus, tremor, rigidity, and ataxia; and gastrointestinal symptoms such as abdominal cramping, nausea, vomiting, and diarrhea.

References

  1. Fauci AS, Braunwald E, Isselbacher KJ, Wilson JD, Martin JB, Kasper DL, Hauser SL, Longo DL, eds. "Harrison's Principles of Internal Medicine. 14th ed." New York, NY: McGraw-Hill Health Professionals Division (1998):
  2. Prior FH, Isbister GK, Dawson AH, Whyte IM "Serotonin toxicity with therapeutic doses of dexamphetamine and venlafaxine." Med J Aust 176 (2002): 240-1
  3. Barrett J, Meehan O, Fahy T "SSRI and sympathomimetic interaction." Br J Psychiatry 168 (1996): 253
  4. Walters AM "Sympathomimetic-fluoxetine interaction." J Am Acad Child Adolesc Psychiatry 31 (1992): 565-6
  5. Bostwick JM, Brown TM "A toxic reaction from combining fluoxetine and phentermine." J Clin Psychopharmacol 16 (1996): 189-90
  6. Martin TG "Serotonin syndrome." Ann Emerg Med 28 (1996): 520-6
View all 6 references

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Drug and food interactions

Moderate

phentermine food

Applies to: phentermine

GENERALLY AVOID: Alcohol may potentiate the central nervous system and cardiovascular effects of centrally-acting appetite suppressants. In one study, concurrent administration of methamphetamine (30 mg intravenously) and ethanol (1 gm/kg orally over 30 minutes) increased heart rate by 24 beats/minute compared to methamphetamine alone. This increases cardiac work and myocardial oxygen consumption, which may lead to more adverse cardiovascular effects than either agent alone. Subjective effects of ethanol were diminished in the eight study subjects, but those of methamphetamine were not affected. The pharmacokinetics of methamphetamine were also unaffected except for a decrease in the apparent volume of distribution at steady state.

MANAGEMENT: Concomitant use of centrally-acting appetite suppressants and alcohol should be avoided if possible, especially in patients with a history of cardiovascular disease. Patients should be counselled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

References

  1. Mendelson J, Jones RT, Upton R, Jacob P 3rd "Methamphetamine and ethanol interactions in humans." Clin Pharmacol Ther 57 (1995): 559-68
  2. "Product Information. Didrex (benzphetamine)" Pharmacia and Upjohn, Kalamazoo, MI.
  3. "Product Information. Suprenza (phentermine)." Akrimax Pharmaceuticals, Cranford, NJ.

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Moderate

venlafaxine food

Applies to: Effexor XR (venlafaxine)

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

References

  1. Gilman AG, Rall TW, Nies AS, Taylor P, eds. "Goodman and Gilman's the Pharmacological Basis of Therapeutics. 8th ed." New York, NY: Pergamon Press Inc. (1990):
  2. "Product Information. Fycompa (perampanel)." Eisai Inc, Teaneck, NJ.
  3. Warrington SJ, Ankier SI, Turner P "Evaluation of possible interactions between ethanol and trazodone or amitriptyline." Neuropsychobiology 15 (1986): 31-7
  4. "Product Information. Rexulti (brexpiprazole)." Otsuka American Pharmaceuticals Inc, Rockville, MD.
View all 4 references

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Therapeutic duplication warnings

No therapeutic duplications were found for your selected drugs.

Drug Interaction Classification

The classifications below are a guideline only. The relevance of a particular drug interaction to a specific patient is difficult to determine using this tool alone given the large number of variables that may apply.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No information available.

Do not stop taking any medications without consulting your healthcare provider.

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