Overview
11 DESCRIPTION Phentermine hydrochloride USP has the chemical name of α,α,-Dimethylphenethylamine hydrochloride. The structural formula is as follows: Phentermine hydrochloride is a white, odorless, hygroscopic, crystalline powder which is soluble in water and lower alcohols, slightly soluble in chloroform and insoluble in ether.
Mechanism of Action
12 CLINICAL PHARMACOLOGY 12.1 Mechanism of Action Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, amphetamine (d- and d / l-amphetamine). Drugs of this class used in obesity are commonly known as "anorectics" or "anorexigenics." It has not been established that the primary action of such drugs in treating obesity is one of appetite suppression since other central nervous system actions, or metabolic effects, may also be involved. 12.2 Pharmacodynamics Typical actions of amphetamines include central nervous system stimulation and elevation of blood pressure. Tachyphylaxis and tolerance have been demonstrated with all drugs of this class in which these phenomena have been looked for. 12.
Indications
- 1 INDICATIONS AND USAGE Phentermine hydrochloride is indicated as a short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity for patients with an initial body mass index ≥ 30 kg/m 2 , or ≥ 27 kg/m 2 in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia). Below is a chart of body mass index (BMI) based on various heights and weights.
Common Doses
- 15 mg
- 29 mL
- 37.5 mg
- 18.75 mg
Dosage
2 DOSAGE AND ADMINISTRATION Dosage should be individualized to obtain an adequate response with the lowest effective dose. (2.1) Late evening administration should be avoided (risk of insomnia). (2.1) Phentermine hydrochloride tablets can be taken with or without food. (2.1) Limit the dosage to 15 mg daily for patients with severe renal impairment (eGFR 15 to 29 mL/min/1.73 m 2 ) (2.2) 2.1 Exogenous Obesity Dosage should be individualized to obtain an adequate response with the lowest effective dose. The usual adult dose is one tablet (37.
Contraindications
- 4 CONTRAINDICATIONS History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension) During or within 14 days following the administration of monoamine oxidase inhibitors Hyperthyroidism Glaucoma Agitated states History of drug abuse Pregnancy [ see Use in Specific Populations (8.1) ] Nursing [ see Use in Specific Populations (8.3) ] Known hypersensitivity, or idiosyncrasy to the sympathomimetic amines History of cardiovascular disease (e.g.
Side Effects
- 6 ADVERSE REACTIONS The following adverse reactions are described, or described in greater detail, in other sections: Primary pulmonary hypertension [ see Warnings and Precautions (5.2) ] Valvular heart disease [ see Warnings and Precautions (5.3) ] Effect on the ability to engage in potentially hazardous tasks [ see Warnings and Precautions (5.5) ] Withdrawal effects following prolonged high dosage administration [ see Drug Abuse and Dependence (9.
Interactions
- 7 DRUG INTERACTIONS Monoamine oxidase inhibitors: Risk of hypertensive crisis. ( 4 , 7.1 ) Alcohol: Consider potential interaction. ( 7.2 ) Insulin and oral hypoglycemics: Requirements may be altered. ( 7.3 ) Adrenergic neuron blocking drugs: Hypotensive effect may be decreased by phentermine. ( 7.4 ) 7.1 Monoamine Oxidase Inhibitors Use of phentermine is contraindicated during or within 14 days following the administration of monoamine oxidase inhibitors because of the risk of hypertensive crisis . 7.