Chemical Abstracts Service Registry Number: 106650-56-0. (Hydrochloride anhydrous form 84485-00-7; Hydrochloride monohydrate form 125494-59-9)
Formal Names: Meridia, Reductil
Type: Stimulant (anorectic class). See page 15
Federal Schedule Listing: Schedule IV (DEA no. 1675)
USA Availability: Prescription
Pregnancy Category: C
Uses. This weight control medicine appears to work by making people feel more full while eating a meal, thereby reducing appetite. People using sibu-tramine eat less regardless of whether they are trying to lose weight. In rats the drug increases the rate at which the body consumes stored energy, burning off calories. A similar action has been measured in humans. Sibutramine has also been used for treating nerve pain caused by diabetes. One research study found that the drug improved attention and muscular coordination.
A given dose of the drug tends to produce higher drug levels in women than in men, but the difference is not considered significant enough to affect calculation of dosage. Blood levels from a given dose also tend to be higher in blacks than in whites, but again the difference is considered insignificant.
Drawbacks. The drug elevates heart rate and blood pressure. Headache, insomnia, dry mouth, and constipation are typical unwanted effects. The medicine may promote bleeding. Sibutramine is not recommended for persons suffering from narrow-angle glaucoma or for persons who have had seizures.
Abuse factors. Although chemical details are highly technical, sibutramine operates in ways fundamentally different from the weight-loss drugs fenfluramine and dextroamphetamine, differences that may make abuse of sibutra-mine less likely. Volunteers with a history of drug abuse were paid to participate in a study. They found sibutramine unpleasant (causing confusion, unease, and loss of energy), so unpleasant that in order to avoid a high dose they were willing to accept reduction in the fee. In another study, examining how recreational stimulant users react to sibutramine, researchers concluded the drug had no more appeal than a placebo.
Drug interactions. Sibutramine should normally be avoided if a person is taking a monoamine oxidase inhibitor (MAOI—found in some antidepressants and other medicine). The drug is a "serotonin reuptake inhibitor," meaning it can interact with various medicines (including dextromethorphan, fentanyl, meperidine, and pentazocine) to cause "serotonin syndrome," a serious condition that can involve hyperactivity, confusion, and influenzalike symptoms. Sibutramine should be used cautiously if a person is taking ephedrine, contained in some cold and allergy remedies.
Cancer. Mice experiments involving blood plasma levels similar to normal human dosage found no evidence that sibutramine causes cancer. In experimentation producing levels of sibutramine metabolites (breakdown products) many times higher than those seen in humans, female rats showed no evidence of cancer; but male rats developed tumors that are commonly caused by hormone changes. Typical laboratory tests used to measure a chemical's cancer potential show none for sibutramine, though its breakdown products produced ambiguous results in one test.
Pregnancy. Rat studies involving doses strong enough to produce metabolite blood levels 43 times higher than normal human levels yielded no observable birth defects. Some rabbit studies involving doses high enough to be poisonous have produced birth defects, but other testing at a poisonous dosage level has not. Sibutramine's potential for causing human congenital abnormalities is unknown, and pregnant women are advised to avoid the drug. Its potential for transfer into milk is unknown, so nursing mothers are advised to avoid the drug.
Additional information. The hydrochloride anhydrous form of sibutramine was tested as an antidepressant in the 1980s, but medical literature has reported little about this form of the drug since then. The hydrochloride monohydrate form became available in the 1990s to help people lose weight.
Additional scientific information may be found in:
Cole, J.O., et al. "Sibutramine: A New Weight Loss Agent without Evidence of the Abuse Potential Associated with Amphetamines." Journal of Clinical Psychophar-macology 18 (1998): 231-36. James, W.P., et al. "Effect of Sibutramine on Weight Maintenance after Weight Loss:
A Randomised Trial." Lancet 356 (2000): 2119-25. Lean, M.E. "Sibutramine—A Review of Clinical Efficacy." International Journal of Obesity and Related Metabolic Disorders 21 (1997, Suppl. 1): S30-S36. Luque, C.A., and J.A. Rey. "Sibutramine: A Serotonin-Norepinephrine Reuptake-Inhibitor for the Treatment of Obesity." Annals of Pharmacotherapy 33 (1999): 968-78.
Schuh, L.M., et al. "Abuse Liability Assessment of Sibutramine, a Novel Weight Control
Agent." Psychopharmacology 147 (2000): 339-46. "Sibutramine for Obesity." Medical Letter on Drugs and Therapeutics 40 (1998): 32.
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