Phentermine
Adipex-P®, Fastin®, Ionamin®, Obenix®, Obephen®, Obermine®, Obestin®, Phentamine®, Phentride®, T-Diet®, Zantryl® | Atti-Plex P™ | Kraft-Obese™ | Phentercot™ | Pro-Fast™ HS | Pro-Fast™ SA | Pro-Fast™ SR | Tara-8™
Classification:
Autonomic Agents
Psychotropic Agents
NOTE: Phentermine is a schedule C-IV controlled substance.
Description: Phentermine is an oral sympathomimetic amine used as an adjunct for short-term (e.g., 8-12 weeks) treatment of exogenous obesity. Phentermine is available as the hydrochloride salt (various brand names) or as the resin complex (Ionamin®) and is structurally and chemically related to the amphetamines. The pharmacologic effects of phentermine are also similar to amphetamines. Phentermine resin complex was approved by the FDA in 1959 and phentermine hydrochloride was FDA approved in 1973. In the mid-90s, there was renewed interest in phentermine in combination with another anorectic, fenfluramine, for the treatment of obesity and substance abuse, however, little scientific data support this practice. On July 8, 1997, the FDA issued a ‘Dear Health Care Professional’ letter warning physicians about the development of valvular heart disease in women receiving the combination of fenfluramine and phentermine. On 9/8/97, the use of phentermine in combination with fenfluramine was banned in Florida.
Mechanism of Action: Limited data are available in reference texts regarding the mechanism of action of this drug. Similar to amphetamines, phentermine increases the release of norepinephrine and dopamine from nerve terminals and inhibits their reuptake. Thus, phentermine is classified as an indirect sympathomimetic. Clinical effects include CNS stimulation and elevation of blood pressure. Appetite suppression is believed to occur through direct stimulation of the satiety center in the hypothalamic and limbic region.
Tolerance to the anorexiant effects of phentermine usually develops within a few weeks of starting therapy. The mechanism of tolerance appears to be pharmacodynamic in nature; higher doses of phentermine are required to produce the same response. When tolerance develops to the anorexiant effects, it is generally recommended that phentermine be discontinued rather than the dose increased.
Pharmacokinetics: Phentermine is administered orally as a hydrochloride salt or as a resin complex. Limited data exist on the pharmacokinetics of phentermine. Following oral administration, most absorption of phentermine occurs from the small intestine. The duration of action following administration of the 8 mg capsules or tablets is about 4 hours and 12-14 hours after administration of the 30 mg capsules, 37.5 mg tablets, or the resin capsules. Phentermine is primarily excreted by the kidneys. The elimination half-life ranges 19-24 hours and is influenced by urinary pH. Because the pKa of phentermine is 9.84, the elimination half-life decreases to about 7-8 hours under acidic urinary conditions.
[1 of 14 - Click here to see more photos]
[ Revised 11/10/2004 4:22:00 PM ]
Related entries
Syndicate
|
