Controlled Substance Schedule IV
Pregnancy Risk Category NR
How supplied
Tablets: 8 mg, 30 mg, 37.5 mg
Capsules: 15 mg, 18.75 mg, 30 mg, 37.5 mg
Capsules (resin complex, sustained-
release): 15 mg, 30 mg
Action
Unknown. Drug probably promotes nerve impulse transmission by releasing stored norepinephrine from nerve terminals in the brain. Main sites of activity appear to be the cerebral cortex and the reticular activating system.
Indications & dosage
Short-term adjunct in exogenous obesity--
Adults: 8 mg P.O. t.i.d. 30 minutes before meals. Or, 15 to 30 mg (resin complex) or 15 to 37.5 mg (phentermine hydrochloride) P.O. daily as a single dose in the morning.
Adverse reactions
CNS: overstimulation, headache, euphoria, dysphoria, dizziness, insomnia.
CV: palpitations, tachycardia, increased blood pressure.
GI: dry mouth, dysgeusia, constipation, diarrhea, other GI disturbances.
GU: impotence.
Skin: urticaria.
Other: altered libido.
Interactions
Drug-drug. Acetazolamide, antacids, sodium bicarbonate: increased renal reabsorption. Monitor for enhanced effects.
Ammonium chloride, ascorbic acid: decreased plasma levels and increased renal excretion of phentermine. Monitor for decreased phentermine effects.
Haloperidol, phenothiazines, tricyclic antidepressants: altered CNS effects. Avoid concomitant use.
Insulin, oral antidiabetics: may alter antidiabetic requirements. Monitor blood glucose levels.
MAO inhibitors: may cause severe hypertension, possibly hypertensive crisis. Don't use together or within 14 days of discontinuation of MAO inhibitor therapy.
Drug-food. Caffeine: may increase CNS stimulation. Avoid concomitant use.
Effects on diagnostic tests
None reported.
Contraindications
Contraindicated in patients with hypersensitivity or idiosyncrasy to sympathomimetic amines and in those with hyperthyroidism, moderate to severe hypertension, advanced arteriosclerosis, symptomatic CV disease, or glaucoma; also contraindicated within 14 days of MAO inhibitor therapy and in agitated patients.
Nursing considerations
Patient teaching
*Liquid contains alcohol. **May contain tartrazine. †Canada ‡Australia §U.K. OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING