What is the recommended dosing of phentermine (Phentermine) and topiramate (Topamax) for weight loss?

From the Guidelines

Phentermine and topiramate (Topamax) should be used together for weight loss under medical supervision, with a typical starting dose of 3.75 mg phentermine/23 mg topiramate extended-release daily for 14 days, then increasing to 7.5 mg/46 mg daily, and potentially up to 15 mg/92 mg daily if needed and tolerated. The combination of phentermine and topiramate works by suppressing appetite and reducing food cravings, with phentermine activating the sympathetic nervous system to decrease food intake and increase resting energy expenditure 1. The recommended dosage of phentermine is 15–37.5 mg orally once daily, but dosage should be individualized to achieve adequate response with the lowest effective dose 1. For the combination of phentermine and topiramate, it is recommended to initiate treatment with the starter dose of 3.75 mg/23 mg taken once daily for 14 days, followed by a maintenance dose of 7.5 mg/46 mg daily, with potential escalation to 15 mg/92 mg daily if the patient has not lost at least 3% of their body weight after 12 weeks 1. Common side effects include dry mouth, constipation, insomnia, and tingling sensations, and the medication combination is contraindicated in pregnancy, glaucoma, hyperthyroidism, and in patients taking MAOIs. Regular monitoring of heart rate, blood pressure, and electrolytes is necessary, and the medications should be tapered rather than stopped abruptly to avoid withdrawal effects. Key considerations for the use of phentermine-topiramate ER include caution in patients with a history of cardiovascular disease or uncontrolled hypertension, avoidance in patients treated with or within 14 days of monoamine oxidase inhibitors, and counseling of female patients with child-bearing potential on the risks of teratogenicity and consistent use of reliable contraception 1. The potential benefits of phentermine-topiramate ER for patients with migraine headaches should also be considered, and the medication should be taken early in the day to minimize the risk of insomnia. Overall, the use of phentermine and topiramate for weight loss should be carefully considered and monitored by a healthcare professional to minimize potential risks and maximize benefits. Some of the key points to consider when prescribing phentermine and topiramate include:

• Starting with a low dose and gradually increasing as needed and tolerated
• Monitoring for common side effects such as dry mouth, constipation, and insomnia
• Avoiding use in patients with certain medical conditions, such as pregnancy, glaucoma, and hyperthyroidism
• Counseling patients on the risks of teratogenicity and consistent use of reliable contraception
• Regularly monitoring heart rate, blood pressure, and electrolytes to minimize potential risks.

From the Research

Phentermine and Topamax Dosing for Weight Loss

• The combination of phentermine and topiramate extended release (ER) has been approved by the FDA for chronic weight management in obese adults and overweight adults with weight-related co-morbidities 2.
• The recommended dosing for phentermine and topiramate ER is phentermine 15 mg/topiramate ER 92 mg, which has been shown to result in an average weight loss of 10% of initial weight 3.
• Clinical trials have demonstrated that the combination of phentermine and topiramate ER is effective for weight loss, with a mean weight loss of at least 10% of baseline achieved and sustained for up to 2 years in over 50% of subjects treated 4.
• The placebo-subtracted weight reduction (%) for phentermine/topiramate has been reported to be 6.8% for at least 12 months 5.
• Phentermine and topiramate ER has been shown to be safe and effective for weight loss, but it must be used with caution in women of child-bearing age due to an increased risk to infants of oral cleft, and it is associated with increased heart rate, the clinical significance of which is being investigated in an FDA-required CVD outcomes study 3.

Efficacy of Phentermine and Topamax

• The combination of phentermine and topiramate ER has been shown to produce significant weight loss and improved cardiometabolism 5, 2.
• Phentermine and topiramate ER has been demonstrated to be effective in reducing the risk of developing type 2 diabetes and improving CVD risk factors 3.
• The medication has been shown to be effective in achieving and sustaining weight loss, with a mean weight loss of at least 10% of baseline achieved and sustained for up to 2 years in over 50% of subjects treated 4.

Safety and Precautions

• Phentermine and topiramate ER must be used with caution in women of child-bearing age due to an increased risk to infants of oral cleft 3.
• The medication is associated with increased heart rate, the clinical significance of which is being investigated in an FDA-required CVD outcomes study 3.
• Phentermine and topiramate ER should be initiated in obese individuals after weighing its benefits and risks, and it should be tailored for specific patients depending on their chronic conditions, comorbidities, and preferences 5.