Phentermine

Oral
Anorectic in short-term treatment of moderate to severe obesity

Hyperthyroidism, history of CV disease (e.g. coronary artery disease, arrhythmias, CHF, uncontrolled HTN), glaucoma, history of alcohol/drug abuse, agitated states. Pregnancy and lactation. Concomitant or w/in 14 days of MAOI use.

Patient w/ HTN, DM, seizure disorder, Tourette's syndrome. Avoid abrupt withdrawal. Renal impairment.

Urticaria, palpitation, tachycardia, elevation of BP, ischaemic events, overstimulation, restlessness, dizziness, insomnia, euphoria, tremor, headache, dry mouth, unpleasant taste, diarrhoea, vomiting, constipation, impotence, change in libido. Rarely, psychotic episodes, cardiac valvular disease.
Potentially Fatal: Rarely, primary pulmonary HTN.

PO: X

May impair ability to drive or operate machinery.

Monitor wt, waist circumference and BP.

Symptoms: Restlessness, tremor, hyperreflexia, rapid respiration, confusion, assaultiveness, hallucination, panic states, fatigue, depression, arrhythmia, HTN or hypotension, circulatory collapse, nausea, vomiting, diarrhoea, abdominal cramps, insomnia. Chronic intoxication: Irritability, severe dermatoses, psychosis, hyperactivity. Management: Supportive and symptomatic treatment. Administer activated charcoal and perform gastric lavage w/in 1 hr of ingestion. Diazepam (preferably PO, cautiously by IV inj) may be given to control excitement and convulsions. Urine acidification may increase phentermine excretion.

Primary pulmonary HTN or valvular heart disease may occur when phentermine is used concurrently w/ fenfluramine or dexfenfluramine. May decrease hypotensive effect of adrenergic neuron blocking drugs (e.g. guanethidine, clonidine, methyldopa). CNS stimulant effect may be increased by thyroid hormones.
Potentially Fatal: Increased risk of hypertensive crisis w/ MAOI.

Increased CNS effects (e.g. dizziness, confusion) w/ alcohol.

False-positive result w/ urine detection of amphetamine/methamphetamine.

Description: Phentermine is a sympathomimetic amine that exerts its appetite suppressant effect through a mechanism which appears to be secondary to CNS effects, including stimulation of the hypothalamus to release norepinephrine.
Pharmacokinetics:
Absorption: Readily absorbed from the GI tract. Time to peak plasma concentration: Approx 3-4.4 hr.
Distribution: Volume of distribution: 348 L. Plasma protein binding: 17.5%.
Metabolism: Hepatically metabolised via p-hydroxylation and N-oxidation, mainly by CYP3A4 isoenzyme.
Excretion: Via urine (62-85% as unchanged drug). Elimination half-life: Approx 20 hr.

Source: National Center for Biotechnology Information. PubChem Database. Phentermine, CID=4771, https://pubchem.ncbi.nlm.nih.gov/compound/Phentermine (accessed on Jan. 31, 2020)

Store between 20-25°C.

Anti-Obesity Agents

A08AA01 - phentermine ; Belongs to the class of centrally acting antiobesity products. Used in the treatment of obesity.

Anon. Phentermine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 07/07/2016.

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McEvoy GK, Snow EK, Miller J et al (eds). Phentermine Hydrochloride. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 07/07/2016.

Phentermine Hydrochloride Capsule (Eon Labs, Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 07/07/2016.

Phentermine Hydrochloride Capsule (Epic Pharma, LLC) . DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 07/07/2016.