Investigational drugs for eating disorders

What potential role is there for medication treatment in anorexia nervosa?

OBJECTIVE

To review selected issues regarding the development of drug treatments for anorexia nervosa (AN).

METHOD

The existing pharmacotherapy literature for AN is reviewed, and the theoretical and practical considerations are discussed.

RESULTS

A very wide variety of drugs have been examined in AN, generally with negative results. There are a number of potential reasons for this finding, including compliance, nutritional deficits, selection of the wrong targets or the wrong outcome measures, use of monotherapy, lack of animal models, or factors intrinsic to AN.

CONCLUSION

Pharmacotherapy provides little benefit in the treatment of AN at present. Several strategies might lead to the identification of more effective agents, including new measurement strategies, identification of novel pharmacologic targets, and consideration of a clinical trials network.

Emerging drugs for eating disorder treatment

Anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED) comprise the currently recognised eating disorders. Although distinct diagnostic entities, they share certain forms of comorbid psychopathology, particularly anxiety and mood disorders. BN and BED have been studied most intensively as targets for pharmacotherapy. The list of drugs tested in eating disorders is substantial; however, the number of therapeutic classes of medications tested in these conditions is relatively modest. Antidepressant medications, including tricyclic antidepressants, selective serotonin re-uptake inhibitors, as well as some of the novel antidepressants, have shown evidence of some therapeutic value in both BN and BED. Their efficacy in AN, however, has been disappointing. The pharmacological options for AN are very limited. The number of controlled trials that have been conducted is small, and the research that has been successfully completed has generally failed to demonstrate medication efficacy. Patients with BN typically show reduced binge eating and purging frequency in medication trials, but rarely attain abstinence. In BED, patients often measure the value of their medication therapy by its ability to stimulate weight loss, which is another area on which future pharmacotherapy may improve. Novel pharmacological interventions are needed for each of these conditions. Peptide hormones are increasingly being evaluated for eating disorder treatment, including ghrelin agonists, neuropeptide Y1 and -5 antagonists, orexin receptor antagonists, corticotropin-releasing factor receptor 2 antagonists, histamine 3 antagonists, melanocortin 4 receptor antagonists, beta3-adrenoceptor agonists, 5-hydroxytryptamine-2A antagonists and growth hormone agonists. Although these compounds are in early phases of clinical testing for eating disorder treatments, data from these studies will be instructive in the quest for effective pharmacotherapy for these conditions. An overview of the current pharmacotherapy options for eating disorders is presented with a discussion of the emerging potential treatments.

Assessment of pharmacology and potential anti-obesity properties of H3receptor antagonists/inverse agonists

Histamine is a key neurotransmitter that alters central nervous system functions in both behavioural and homeostatic contexts through its actions on the histamine (H) subreceptors H(1), H(2) and H(3) G-protein-coupled receptors. H(3)receptors have a diverse central nervous system distribution where they function as both homo- and hetero-receptors to modulate the synthesis and/or release of several neurotransmitters. H(3) receptors are constitutively active, which implies that antagonists of H(3) receptors may also function as inverse agonists to alter the basal state of the receptor and uncouple constitutive receptor-G-protein interactions. Reference H(3) antagonists such as thioperamide and ciproxifan, administered either centrally or systemically, have been shown to cause changes in food consumption and/or body weight in proof-of-concept studies. More recently, several non-imidazole-based H(3) antagonists/inverse agonists have also been described with efficacy in at least one animal model of human obesity. Considerable preclinical effort remains necessary before such compounds achieve therapeutic success or failure. Moreover, ongoing research in a number of laboratories has shed new insights into the effects of H(3) ligands in the control of feeding, appetite and body weight, which offer different results and conclusions. The goal of this review is to appraise these findings and forecast whether any H(3) antagonists/inverse agonists will provide clinical utility to treat human obesity.