Insight into phentermine for sustained weight management 

Many anti-obesity medications can enhance response rates and result in meaningful weight loss.

It is generally accepted that treatment of obesity is most effective if it includes some form of lifestyle intervention, which can result in a 5%-10% weight loss over the course of six months. However, nearly a third of patients don't respond to this course of treatment, and it is common for patients to simply regain the weight post-lifestyle intervention.

Research indicates that multiple mechanisms maintain body weight and could partly explain the high rate of weight regain after weight loss through lifestyle intervention. For example, energy expenditure decreases with weight loss, which may contribute to weight regain.

Weight loss leads to changes in the neuroendocrine system that promote weight regain, including; decreased levels of leptin, peptide YY, cholecystokinin, and insulin; and increased levels of ghrelin and pancreatic polypeptide.

 One of the prime drivers behind the development of anti-obesity medications is filling the great clinical need for medications that can manage the long-term weight loss journey as part of a holistic approach to weight loss incorporating diet, exercise, behaviour modification and anti-obesity medications.

Many anti-obesity medications can enhance response rates and result in meaningful weight loss. Maintaining weight loss over the long term is often the challenging part. Even with ongoing lifestyle interventions, weight regain can be mitigated but not completely prevented.

WHEN IS LONG-TERM USE INDICATED?

Generally, pharmacotherapy for obesity is an adjunct for managing exogenous obesity, alongside a weight loss plan involving exercise, lifestyle modification and calorie restriction.  It is intended for patients with:

• An initial BMI of at least 30 kg/m²
• At least 27 kg/m² with other risk factors like hypertension, diabetes, or hyperlipidaemia.

Long-term use of pharmacotherapy is recommended if weight loss cannot be maintained by any other method at the clinician’s discretion. According to a study by Calderon et al, weight regain is the norm in up to 95% of patients 12 months after discontinuing their medication.

PHENTERMINE

Phentermine, the most widely prescribed weight-loss medicine in South Africa, acts by suppressing appetite. Phentermine is a sympathomimetic amine with significant anorectic activity.  Its appetite suppressant effect is generally considered to be exerted through the hypothalamus, but it is not certain that this is the only effect related to weight loss. Phentermine has major effects on the dopaminergic and noradrenergic nervous systems.

Anorectic medicines act mainly on the satiety centre in the hypothalamus where apatite is controlled. Phentermine reduces the perception of hunger by increasing the amount of noradrenaline in the hypothalamus (made up of multiple nuclei including the lateral hypothalamic nucleus, arcuate nucleus, and ventromedial nucleus). Appetite suppression is coordinated by various nuclei within the hypothalamus, notably the lateral hypothalamic nucleus, arcuate nucleus, and ventromedial nucleus.

Local health professional prescriptions of phentermine mirror the medication’s popularity in the United States. In 2012, the FDA approved phentermine/topiramate ER as the first combination drug for long-term obesity management.