phentermine

History

Phentermine is one of two drugs in the Fen-phen anti-obesity medication, the other being fenfluramine or dexfenfluramine. Fenfluramine was withdrawn from the U.S. market in 1997 after reports of valvular heart disease and pulmonary hypertension.

Phentermine is still available by itself in most countries, including the U.S. However, because it is an amphetamine, individuals may develop an addiction to it. Hence, it is classified as a controlled substance in many countries. Internationally, phentermine is a schedule IV drug under the Convention on Psychotropic Substances (PDF file). In the United States, it is classified as a Schedule IV controlled substance under the Controlled Substances Act.

Mechanism of action

Phentermine, like many other prescription drugs, works with neurotransmitters in the brain. It is a centrally-acting stimulant and is a constitutional isomer of methamphetamine. It stimulates neuron bundles to release a particular group of neurotransmitters known as catecholamines; these include dopamine, epinephrine (also known as adrenalin), and norepinephrine (noradrenaline). The anorectic activity seen with these compounds would thus seem likely due to this effect on the central nervous system, which is consistent with current knowledge about central nervous system systems and feeding behavior. This is the same mechanism of action as other stimulant appetite suppressants such as diethylpropion, and phendimetrazine.

The neurotransmitters signal a fight-or-flight response in the body which, in turn, puts a halt to the hunger signal. As a result, it causes a loss in appetite because the brain does not receive the hunger message.

Clinical use

Generally, it is recommended by the Food and Drug Administration (FDA) that phentermine should be used short-term (usually interpreted as 'up to 12 weeks'), while following nonpharmacological approaches to weight loss such as healthy dieting and exercise. However, recommendations limiting its use for short-term treatment may be controversial. One reason given behind limiting its use to 12 weeks is drug tolerance, whereby phentermine loses its appetite-suppressing effects after the body adjusts to the drug. On the contrary, it has been shown that phentermine did not lose effectiveness in a 36-week trial (PMID 11054601). Due to the risk of insomnia, it is generally recommended that the drug be taken either before breakfast or 1-2 hours after breakfast.

Contraindications

Phentermine should generally be avoided in patients with:

• Agitation
• Allergy/Hypersensitivity to other sympathomimetic amines
• Atherosclerosis
• Cardiovascular disease
• Glaucoma
• High blood pressure
• Hyperthyroidism
• History of drug abuse

Additionally, this drug should not be used at the same time or within 14 days following the use of monoamine oxidase inhibitors.

See also

• Obesity
• Anti-obesity drug
• Amphetamine
• Methamphetamine

External links

• MedLine Plus - Phentermine
• International Programme on Chemical Safety - Phentermine
• TOXNET
• DrugBank:Phentermine

• Link page to external chemical sources.

References and end notes