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The cardboard packaging of two medications used to treat obesity. Orlistat is shown above under the brand name Xenical in a white package with the Roche logo in the bottom right corner ( the Roche name within a hexagon). Sibutramine is below under the brand name Meridia. The package is white on the top and blue on the bottom separated by a measuring tape. The A of the Abbott Laboratories logo is on the bottom half of the package.
The two most commonly used medications to treat obesity: orlistat (Xenical) and sibutramine (Meridia)

Anti-obesity medication or weight loss drugs refer to all pharmacological agents that reduce or control weight. These drugs alter one of the fundamental processes of the human body, weight regulation, by either altering appetite, metabolism, or absorption of calories. It is common for them to be tried and if there is little or no benefit from them to discontinue treatment.[1] The main treatment modalities for overweight and obesity are dieting and physical exercise.

Because of potential side effects, it is recommended that anti-obesity drugs only be prescribed for obesity where it is hoped that the benefits of the treatment outweigh its risks.[2][3]

Contents

Mechanisms of action

Anti-obesity drugs operate through one or more of the following mechanisms:

  • Suppression of the appetite. Catecholamines and their derivatives (such as amphetamine-based drugs) are the main tools used for this. Drugs blocking the cannabinoid receptors may be a future strategy for appetite suppression.
  • Increase of the body's metabolism.
  • Interference with the body's ability to absorb specific nutrients in food. For example, Orlistat (also known as Xenical and Allī) blocks fat breakdown and thereby prevents fat absorption. The OTC fiber supplements glucomannan and guar gum have been used for the purpose of inhibiting digestion and lowering caloric absorption

Anorectics are primarily intended to suppress the appetite, but most of the drugs in this class also act as stimulants (dexedrine, e.g.), and patients have abused drugs "off label" to suppress appetite (e.g. digoxin).

Anti-obesity drugs

If diet and exercise are ineffective alone, anti-obesity drugs are a choice for some patients. Some prescription weight loss drugs are stimulants, which are recommended only for short-term use, and thus are of limited usefulness for extremely obese patients, who may need to reduce weight over months or years.

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Orlistat

Orlistat (Xenical) reduces intestinal fat absorption by inhibiting pancreatic lipase. Originally available only by prescription, it was approved by the FDA for over-the-counter sale in February 2007. [1] Orlistat may cause frequent, oily bowel movements (steatorrhea), but if fat in the diet is reduced, symptoms often improve.

Sibutramine

Sibutramine (Reductil or Meridia) is an anorectic or appetite suppressant, reducing the desire to eat. Both drugs have side effects. Sibutramine may increase blood pressure and may cause dry mouth, constipation, headache, and insomnia.

Rimonabant

Rimonabant (Acomplia) is a recently developed anti-obesity medication. It is cannabinoid (CB1) receptor antagonist that acts centrally on the brain thus decreasing appetite.[4] It may also act peripherally by increasing thermogenesis and therefore increasing energy expenditure.[4] These drugs not only cause weight loss, but prevent or reverse the metabolic effects of obesity, such as insulin resistance and hyperlipidemia.

Weight loss with Rimonabant however has not been shown to be greater than other available weight-loss medication.[4] Due to safety concerns, primarily pyschiatric in nature, the drug has not received approval in the United States or Canada, either as an anti-obesity treatment or as a smoking-cessation drug.

Sanofi-Aventis has received approval to market Rimonabant as a prescription anti-obesity drug in the European Union, subject to some restrictions, however, in October 2008, the European Medicines Agency (EMEA) recommended that Acomplia no longer be available in UK. One month later, Sanofi-Aventis decided it would no longer study rimonabant for any indication.

Metformin

In people with Diabetes mellitus type 2, the drug metformin (Glucophage) can reduce weight.[5]

Exenatide

Exenatide (Byetta) is a long-acting analogue of the hormone GLP-1, which the intestines secrete in response to the presence of food. Among other effects, GLP-1 delays gastric emptying and promotes a feeling of satiety. Some obese people are deficient in GLP-1, and dieting reduces GLP-1 further.[6] Byetta is currently available as a treatment for Diabetes mellitus type 2. Some, but not all, patients find that they lose substantial weight when taking Byetta. Drawbacks of Byetta include that it must be injected twice daily, and that it causes severe nausea in some patients, especially when therapy is initiated. Byetta is recommended only for patients with Type 2 Diabetes. A somewhat similar drug, Symlin, is currently available for treating diabetes and is in testing for treating obesity in non-diabetics.

Pramlintide

Pramlintide (Symlin) is a synthetic analogue of the hormone Amylin, which in normal people is secreted by the pancreas in response to eating. Among other effects, Amylin delays gastric emptying and promotes a feeling of satiety. Many diabetics are deficient in Amylin. Currently, Symlin is only approved to be used along with insulin by Type 1 and Type 2 diabetics. However, Symlin is currently being tested in non-diabetics as a treatment for obesity. A drawback is that Symlin must be injected at mealtimes.

Other drugs

Lorcaserin, a serotonin-blocking drug, is undergoing FDA trials, as of 2009.

Other weight loss drugs have also been associated with medical complications, such as fatal pulmonary hypertension and heart valve damage due to Redux and Fen-phen, and hemorrhagic stroke due phenylpropanolamine.[7][8] Many of these substances are related to amphetamine.

Unresearched nonprescription products or programs for weight loss are heavily promoted by mail and print advertising and on the internet. The US Food and Drug Administration recommends caution with use of these products,[9] since many of the claims of safety and effectiveness are unsubstantiated.[10] Individuals with anorexia nervosa and some athletes try to control body weight with laxatives, diet pills or diuretic drugs, although these generally have no impact on body fat.[11] Products that work as a laxative can cause the blood's potassium level to drop, which may cause heart and/or muscle problems. Pyruvate is a popular product that may result in a small amount of weight loss. However, pyruvate, which is found in red apples, cheese, and red wine, has not been thoroughly studied and its weight loss potential has not been scientifically established.[12]

Alternative medicine

Alternative medicine has insufficient evidence to support or oppose its use.[13]

Side effects

Some anti-obesity drugs have severe or life-threatening side effects, fen-phen being a famous example. These side effects are often associated with their mechanism of action. In general, stimulants carry a risk of high blood pressure, faster heart rate, palpitations, closed-angle glaucoma, drug addiction, restlessness, agitation, and insomnia.

Another drug, orlistat, blocks absorption of dietary fats, and as a result may cause oily spotting bowel movements (steatorrhea), oily stools, stomach pain, and flatulence. A similar medication, designed for patients with Type 2 diabetes, is Acarbose which partially blocks absorption of carbohydrates in the small intestine, and produces similar side effects including stomach pain, and flatulence.

Limitations of current knowledge

The limitation of drugs for obesity is that we do not fully understand the neural basis of appetite and how to modulate it. Appetite is clearly a very important instinct to promote survival. Arguably any drug that would abolish appetite may carry a high mortality risk and may be unsuitable for clinical use.

Because the human body uses various chemicals and hormones to protect its stores of fat (a reaction probably useful to our ancestors when food was scarce in the past,) there has not yet been found a 'silver bullet', or a way to completely circumvent this natural habit of protecting excess food stores. Because of this, anti-obesity drugs are not a practical long-term solution for people who are overweight.

In order to circumvent the number of feedback mechanisms that prevent most monotherapies from producing sustained large amounts of weight loss, it has been hypothesized that combinations of drugs may be more effective by targeting multiple pathways and possibly inhibiting feedback pathways that work to cause a plateau in weight loss. This was evidenced by the success of the combination of phentermine and fenfluramine or dexfenfluramine, popularly referred to phen-fen, in producing significant weight loss but fenfluramine and dexfenfluramine were pulled from the market due to safety fears regarding a potential link to heart valve damage. The damage was found to be a result of activity of fenfluramine and dexfenfluramine at the 5-HT2B serotonin receptor in heart valves. Newer combinations of SSRIs and phentermine, known as phenpro, have been used with equal efficiency as fenphen with no known heart valve damage due to lack of activity at this particular serotonin receptor due to SSRIs. There has been a recent resurgence in combination therapy clinical development with the development of 3 combinations: Qnexa (topiramate + phentermine), Empatic (bupropion + zonisamide) and Contrave (bupropion + naltrexone).

Future developments

Other classes of drugs in development include lipase inhibitors, similar to orlistat. Another lipase inhibitor, called GT 389-255, is being developed by Peptimmune[14] (licensed from Genzyme). This is a novel combination of an inhibitor and a polymer designed to bind the undigested triglycerides therefore allowing increased fat excretion without side effects such as oily stools that occur with orlistat. The development seems to be stalled as Phase 1 trials were conducted in 2004 and there has been no further human clinical development since then.

Another potential long-term approach to anti-obesity medication is through the development of ribonucleic acid interference (RNAi). Animal studies have illustrated that the deletion of the RIP140 gene in mice by genetic knockdown results in the lack of fat accumulation, even when mice are fed a high fat diet[15]. Experiments conducted by Professor Malcolm Parker of Imperial College show that by silencing RIP 140, a nuclear hormone co-repressor which regulates fat accumulation, animal models exhibit a lean profile throughout their life, are resistant to diet-induced obesity, and show an enhanced metabolic rate. CytRx Corporation is developing RNAi therapeutics against this drug target for the treatment of obesity and type 2 diabetes. Similarly, another nuclear hormone receptor co-repressor, SMRT, has demonstrated an opposing effect in genetically engineered mice. Dr. Russell Nofsinger and Dr. Ronald Evans of the Salk Institute showed that disruption of the molecular interaction between SMRT and their nuclear hormone receptor partners leads to increased adiposity and a decreased metabolic rate[16]. These studies suggest that new drugs targeting the molecular interaction between nuclear hormone receptors and their regulatory cofactors could provide a useful new category of therapeutic targets to be developed in an effort to control obesity.

Luigi Ambrosio, a lead researcher at the National Research Council's Institute for Composite and Biomedical Materials in Naples is testing a new hydrogel diet pill. The pill, which is undergoing clinical trials at Rome's Policlinico Gemelli hospital, is made from biodegradable polycellulose that soaks up to 1,000 times its weight in water, which the body flushes out in a few hours while giving dieters a sense of satiety. Because there are no active ingredients, successful safety trials could put this hydrogel pill on the market without a long delay.

History

The first described attempts at producing weight loss are those of Soranus of Ephesus, a Greek physician, in the second century AD. He prescribed elixirs of laxatives and purgatives, as well as heat, massage, and exercise. This remained the mainstay of treatment for well over a thousand years. It was not until the 1920s and 1930s that new treatments began to appear. Based on its effectiveness for hypothyroidism, thyroid hormone became a popular treatment for obesity in otherwise healthy people. It had a modest effect but produced the symptoms of hyperthyroidism as a side effect, such as palpitations and difficulty sleeping. Dinitrophenol (DNP) was introduced in 1933; this worked by uncoupling the biological process of oxidative phosphorylation in mitochondria, causing them to produce heat instead of ATP. The most significant side effect was a dramatic rise in body temperature, frequently causing death. By the end of the 1930s DNP had fallen out of use.[17]

Amphetamines (marketed as Benzedrine) became popular for weight loss during the late 1930s. They worked primarily by suppressing appetite, and had other beneficial effects such as increased alertness. Use of amphetamines increased over the subsequent decades, culminating in the "rainbow pill" regime. This was a combination of multiple pills, all thought to help with weight loss, taken throughout the day. Typical regimens included stimulants, such as amphetamines and thyroid hormone, diuretics, digitalis, laxatives, and often a barbiturate to suppress the side effects of the stimulants. In 1967/1968 a number of deaths attributed to diet pills triggered a Senate investigation and the gradual implementation of greater restrictions on the market. This culminating in 1979 with the FDA banning the use of amphetamines, then the most effective of the diet drugs, in diet pills.[17]

Meanwhile, phentermine had been FDA approved in 1959 and fenfluramine in 1973. The two were no more popular then other drugs until in 1992 a researcher reported that the two caused a 10% weight loss which was maintained for over two years.[18] Fen-phen was born and rapidly became the most commonly prescribed diet medication. Dexfenfluramine (Redux) was developed in the mid-1990s as an alternative to fenfluramine with less side-effects, and received regulatory approval in 1996. However, this coincided with mounting evidence that the combination could cause valvular heart disease in up to 30% of those who had taken it, leading to withdrawal of Fen-phen and dexfenfluramine from the market in September 1997.[17]

Ephedra was removed from the US market in 2004 over concerns that it raises blood pressure and could lead to strokes and death.[19]

Research

A number of drug are in clinical trials including as of October 2009 Cetilistat.[20]

References

  1. ^ National Institute for Health and Clinical Excellence. Clinical guideline 43: Obesity: The prevention, identification, assessment and management of overweight and obesity in adults and children. London, 2006.
  2. ^ Snow V, Barry P, Fitterman N, Qaseem A, Weiss K (2005). "Pharmacologic and surgical management of obesity in primary care: a clinical practice guideline from the American College of Physicians". Ann. Intern. Med. 142 (7): 525–31. PMID 15809464. http://www.annals.org/cgi/content/full/142/7/525.  
  3. ^ Cooke D, Bloom S (2006). "The obesity pipeline: current strategies in the development of anti-obesity drugs". Nature reviews. Drug discovery 5 (11): 919–31. doi:10.1038/nrd2136. PMID 17080028. http://www.nature.com/nrd/journal/v5/n11/abs/nrd2136.html.  
  4. ^ a b c Akbas F, Gasteyger C, Sjödin A, Astrup A, Larsen TM (January 2009). "A critical review of the cannabinoid receptor as a drug target for obesity management". Obes Rev 10 (1): 58–67. doi:10.1111/j.1467-789X.2008.00520.x. PMID 18721231.  
  5. ^ George A. Bray and Frank L. Greenway (1999). "Current and Potential Drugs for Treatment of Obesity: Table 19: Clinical trials with metformin for the treatment of obese diabetics". Endocrine Reviews 20 (6): 805–87. doi:10.1210/er.20.6.805. PMID 10605627. http://edrv.endojournals.org/cgi/content/full/20/6/805/T19. Retrieved 2006-08-07.  
  6. ^ de Luis DA, Gonzalez Sagrado M, Conde R, Aller R, Izaola O (2007). "Decreased basal levels of glucagon-like peptide-1 after weight loss in obese subjects". Ann. Nutr. Metab. 51 (2): 134–8. doi:10.1159/000103273. PMID 17536190.  
  7. ^ Abenhaim L, Moride Y, Brenot F, et al (August 1996). "Appetite-suppressant drugs and the risk of primary pulmonary hypertension. International Primary Pulmonary Hypertension Study Group". N. Engl. J. Med. 335 (9): 609–16. doi:10.1056/NEJM199608293350901. PMID 8692238. http://content.nejm.org/cgi/pmidlookup?view=short&pmid=8692238&promo=ONFLNS19.  
  8. ^ Alfred P. Fishman, MD (1999). "Aminorex to Fen/Phen: An Epidemic Foretold". Circulation 99 (1): 156–161. PMID 9884392. http://circ.ahajournals.org/cgi/content/full/99/1/156. Retrieved 2006-07-24.  
  9. ^ U. S. Food and Drug Administration: The Facts About Weight Loss Products and Programs
  10. ^ Committee on Governmental Affairs, United States Senate (2002-10-08). "Prepared Statement of the Federal Trade Commission on the Marketing of Dietary Supplements". Press release. http://www.ftc.gov/os/2002/10/dietary_testimony.htm. Retrieved 2006-08-07.  
  11. ^ Martin M, Schlabach G, Shibinski K (1998). "The Use of Nonprescription Weight Loss Products Among Female Basketball, Softball, and Volleyball Athletes from NCAA Division I Institutions: Issues and Concerns". J Athl Train 33 (1): 41–44. PMID 16558483.  
  12. ^ George A. Bray and Frank L. Greenway (1999). "Current and Potential Drugs for Treatment of Obesity: Postabsorptive modifiers of nutrient metabolism". Endocrine Reviews 20 (6): 805–87. doi:10.1210/er.20.6.805. PMID 10605627. http://edrv.endojournals.org/cgi/content/full/20/6/805#SEC4.  
  13. ^ Lau DC, Douketis JD, Morrison KM, Hramiak IM, Sharma AM, Ur E (April 2007). "2006 Canadian clinical practice guidelines on the management and prevention of obesity in adults and children [summary"]. CMAJ 176 (8): S1–13. doi:10.1503/cmaj.061409. PMID 17420481.  
  14. ^ Peptimmune homepage
  15. ^ Leonardsson G, Steel JH, Christian M, Pocock V, et al. (2004). "Nuclear receptor corepressor RIP140 regulates fat accumulation". Proc. Natl. Acad. Sci. U.S.A. 101 (22): 8437–42. doi:10.1073/pnas.0401013101. PMID 15155905.  
  16. ^ Nofsinger RR, Li P, Hong SH, Jonker JW, Barish GD, Ying H, Cheng SY, Leblanc M, Xu W, Pei L, Kang YJ, Nelson M, Downes M, Yu RT, Olefsky JM, Lee CH, Evans RM. (2008). "SMRT repression of nuclear receptors controls the adipogenic set point and metabolic homeostasis". Proc. Natl. Acad. Sci. U.S.A. 105 (50): 20021–6. doi:10.1073+pnas.0811012105 (inactive 2009-10-29). PMID 19066220.  
  17. ^ a b c Pool, Robert (2001). Fat: Fighting the Obesity Epidemic. Oxford, UK: Oxford University Press. ISBN 0-19-511853-7.  
  18. ^ Weintraub M (May 1992). "Long-term weight control: The National Heart, Lung, and Blood Institute funded multimodal intervention study". Clin. Pharmacol. Ther. 51 (5): 581–5. PMID 1445528.  
  19. ^ Kolata,Gina (2007). Rethinking thin: The new science of weight loss - and the myths and realities of dieting. Picador. ISBN 0-312-42785-9.  
  20. ^ "Alizyme - Cetilistat". http://www.alizyme.com/alizyme/products/cetilistat/.  

Further reading

Boss, Olivier; Karl G. Hofbauer (2004). Pharmacotherapy of obesity: options and alternatives. Boca Raton: CRC Press. ISBN 0-415-30321-4.  

External links


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