Liraglutide, which was first used to treat type 2 diabetes, centrally exploits the hypothalamic target for appetite suppression and delay gastric emptying. Semaglutide is a genetically engineered glucagon-like peptide-1 receptor agonist, which has shown sustained glycaemic control and weight loss benefits in trials.12,13 As a peptide, it has to be given as a weekly subcutaneous injection. It is available on the PBS for the treatment of type 2 diabetes but it is not approved by the TGA or subsidised on the PBS for weight loss.
Combination therapies include phentermine and topiramate (combination not approved for use in Australia), which combines a weight loss drug with an antiepileptic drug for a greater weight loss effect, but tolerability limits its use.14 Buproprion/naltrexone therapy combines naltrexone HCl, which is more commonly used to treat substance abuse conditions, and bupropion HCl, which is an antidepressant. These two medications work together in the brain to help downregulate hunger signalling.
Pharmacotherapies used in weight loss management and their mechanisms of action are listed in Table 1. Patient responses to these therapies vary for clinically meaningful weight loss (more than 5% body weight loss after 12 weeks of therapy).
At a patient management and therapeutic level, bariatric surgery (also known as weight loss surgery) is increasingly being relied on as the most effective way to enable significant durable weight loss in patients with severe obesity who fail to respond to genuine efforts with dietary, exercise and lifestyle measures. The 2011 review of surgical interventions for the treatment of obesity from the Australian Government Department of Health supports this approach.15 The new term ‘metabolic surgery’ recognises the physiological benefits of these procedures (chief among them, reversal of diabetes risk).16
Bariatric operations have traditionally been categorised according to the mechanism by which weight loss ensues as:
- restrictive procedures (limit intake)
- malabsorptive procedures (interfere with digestion and absorption)
- combination of the above procedures.
Selection of patients for bariatric surgery
Although some patients with obesity have success with early intervention and modifications to diet and lifestyle, many are unable to achieve adequate sustained weight loss. The National Health and Medical Research Council guidelines state that people with obesity can be selected for bariatric surgery if they have failed sustained efforts with dietary and lifestyle therapies.17 Bariatric surgery should be discussed with motivated patients who have a BMI of 35 kg/m2 or greater and one or more obesity-associated comorbidities. Reflecting the low success rates with nonsurgical approaches, bariatric surgery can also be considered in patients with morbid obesity (BMI of 40 kg/m2 or more) even in the apparent absence of obesity-related comorbid disease. The indications and contraindications for bariatric surgery are listed in Box 1.
The GP’s role
Work up for patients with obesity who are considering bariatric surgery is important (Box 2).18 This is often performed by the GP although patients are increasingly being referred to an endocrinologist with an interest in obesity treatment, a surgeon who performs bariatric surgery or a multidisciplinary clinic with specialist physician, surgeon, dietitian, exercise physiologist and psychologist expertise available.