Phentermine


Concise Prescribing Info
Indications/Uses
Anorectic in short-term treatment of moderate to severe obesity.
Dosage/Direction for Use
Adult : PO As phentermine HCl: 15-37.5 mg once daily. As modified-release ion-exchange resin complex: 15-30 mg once daily.
Dosage Details
Oral
Anorectic in short-term treatment of moderate to severe obesity
Adult: As phentermine HCl: 15-37.5 mg once daily in the morning; higher dose of 37.5 mg may be given in 2 divided doses. Individualise to achieve adequate response w/ lowest effective dose. As modified-release ion-exchange resin complex: 15-30 mg once daily in the morning.
Contraindications
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.
Special Precautions
Patient w/ HTN, DM, seizure disorder, Tourette's syndrome. Avoid abrupt withdrawal. Renal impairment.
Adverse Reactions
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.
Patient Counseling Information
May impair ability to drive or operate machinery.
MonitoringParameters
Monitor wt, waist circumference and BP.
Overdosage
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.
Drug Interactions
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.
Food Interaction
Increased CNS effects (e.g. dizziness, confusion) w/ alcohol.
Lab Interference
False-positive result w/ urine detection of amphetamine/methamphetamine.
Action
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.
Chemical Structure

Chemical Structure Image
Phentermine

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

Storage
Store between 20-25°C.
MIMS Class
ATC Classification
A08AA01 - phentermine ; Belongs to the class of centrally acting antiobesity products. Used in the treatment of obesity.
References
Anon. Phentermine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 07/07/2016.

Buckingham R (ed). Phentermine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 07/07/2016.

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.

Disclaimer: This information is independently developed by MIMS based on Phentermine from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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