Anorectic Agents

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Chapter: Essential pharmacology : Adrenergic System and Drugs

Because of adverse central effects, the use of amphetamines to suppress appetite cannot be justified. A number of related drugs have been developed which inhibit feeding centre (like amphetamine) but have little/no CNS stimulant action or abuse liability.


ANORECTIC AGENTS

 

Because of adverse central effects, the use of amphetamines to suppress appetite cannot be justified. A number of related drugs have been developed which inhibit feeding centre (like amphetamine) but have little/no CNS stimulant action or abuse liability. All of them act by inhibiting the reuptake of NA/DA or 5HT, enhancing monoaminergic transmission in the brain. Accordingly they may be grouped into:

 

Noradrenergic agents: Phentermine, phenylpropanolamine (PPA), diethylpropion, mazindol.

 

Serotonergic agents: Fenfluramine, dexfenfluramine.

 

Noradrenergic/serotonergic agent:     Sibutramine.

 

 

The noradrenergic agents primarily affect the appetite centre, while the serotonergic ones primarily affect the satiety centre. The noradrenergic agents activate hypothalamic adrenergic/ dopaminergic receptors and have residual stimulatory effects; interfere with sleep. None is marketed in India (PPA is included only in decongestant formulations).

 

Fenfluramine and dexfenfluramine reduce food seeking behaviour by enhancing serotonergic transmission in the hypothalamus. However, tolerance to the anorectic action develops in 2–3 months. They have tranquillising rather than stimulant property, and were extensively used by slimming centres.

 

In the late 1990s ecocardiographic abnormalities, valvular defects, pulmonary hypertension and sudden deaths were related to the use of a combined preparation of fenfluramine + phentermine. Similar valvular lesions are known to occur in carcinoid. The USFDA recommended discontinuation of fenfluramine, dexfenfluramine and their combinations. These are now banned in India and most other countries.

 

Sibutramine

 

This recently introduced antiobesity drug inhibits the reuptake of both NA as well as 5HT, but does not have clinically useful antidepressant property. It suppresses appetite in a manner similar to fenfluramine and appears to stimulate thermogenesis by indirectly activating β3 system in adipose tissue. It can cause loss of 3–9 kg weight, but many subjects regain the same when therapy is discontinued. Side effects include dry mouth, constipation, anxiety, insomnia, mood swings, chest pain and a mild increase in BP and HR. A number of serious adverse reaction reports including cardiovascular events and deaths have been received by the USFDA and drug committees in Europe. An ongoing study is assessing its impact on longterm morbidity and mortality.

 

Dose: Start with 10 mg OD, increase to 15 mg OD if tolerated. OBESTAT, SIBUTREX 5 mg, 10 mg caps.

 

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