What is the recommended dosing for Qsymia (phentermine/topiramate) in an adult patient with obesity?

Qsymia Dosing for Adult Obesity

Start Qsymia at 3.75 mg/23 mg once daily for 14 days, then increase to 7.5 mg/46 mg daily, with a target dose of 15 mg/92 mg daily if tolerated, as this higher dose demonstrates superior efficacy. 1

Initial Titration Schedule

• Days 1-14: Begin with 3.75 mg phentermine/23 mg topiramate once daily 1, 2
• Day 15 onward: Increase to 7.5 mg/46 mg once daily (standard maintenance dose) 1, 2
• Take early in the day to minimize insomnia risk 1

Dose Escalation Protocol

At 12 weeks, assess weight loss response: 1, 2

• If <3% weight loss: Consider discontinuation OR escalate dose (depending on tolerance and adverse effects) 1
• For dose escalation: Increase to 11.25 mg/69 mg daily for 14 days, then advance to maximum dose of 15 mg/92 mg daily 1, 2
• Target the 15 mg/92 mg dose as the goal, since it shows significantly better efficacy than the 7.5 mg/46 mg dose 1

Discontinuation Criteria

Stop Qsymia if <5% weight loss after 12 weeks at maximum dose (15 mg/92 mg) 1, 2

Safe Discontinuation Method

• Taper gradually: Take 1 capsule every other day for at least 1 week before stopping completely 1
• This taper is mandatory to minimize seizure risk from abrupt topiramate withdrawal 1

Absolute Contraindications

• Pregnancy or women of childbearing potential without reliable contraception (teratogenic risk: cleft lip/palate) 1, 3, 2
• History of cardiovascular disease 1, 3
• Uncontrolled hypertension 1, 3
• Current or recent (within 14 days) MAOI use 1, 3
• Untreated hyperthyroidism (arrhythmia and seizure risk) 1

Critical Monitoring Requirements

Mandatory Counseling for Women

• Counsel all women of childbearing age about teratogenic risks before prescribing 1, 3, 2
• Topiramate reduces oral contraceptive efficacy—women must use reliable non-hormonal contraception or backup methods 3
• Consider monthly pregnancy testing during treatment 1

Cardiovascular Monitoring

• Monitor blood pressure and heart rate at baseline and periodically, especially during titration 1, 3
• Blood pressure generally declines, but heart rate may increase modestly at higher doses 1

Metabolic Monitoring

• Check serum bicarbonate periodically (topiramate causes metabolic acidosis via carbonic anhydrase inhibition) 1, 3, 2
• Monitor for kidney stone risk, especially in patients with history of nephrolithiasis 1, 3

Perioperative Management

• Discontinue at least 4 days before procedures requiring general anesthesia due to perioperative complication risk 2

Common Adverse Effects

• Paresthesias (tingling): Most common side effect (4-23% of patients) 3, 4
• Cognitive impairment and concentration difficulties: Particularly at higher doses 1, 3
• Dry mouth: 0-19% of patients 3, 4
• Constipation: 3-10% of patients 1, 3, 4
• Insomnia: 5-10% of patients 1, 3, 4
• Dysgeusia (taste changes): Common 1, 4
• Irritability and mood changes: Monitor for depression and anxiety 1, 4

Special Clinical Considerations

Preferred Patient Populations

• Consider in patients with obesity and migraines (topiramate provides additional migraine prophylaxis benefit) 1
• May be useful in patients attempting smoking cessation (though this applies more to naltrexone-bupropion) 1

Avoid in Geriatric Patients

• Limited high-quality data for use in patients >70 years 1

Drug Interactions

• Strong CYP3A inhibitors (itraconazole, ketoconazole, clarithromycin, protease inhibitors) may require dose adjustment 2
• Insulin/sulfonylureas: Increased hypoglycemia risk—adjust diabetes medications and monitor glucose closely 2

Controlled Substance Status

• Schedule IV controlled substance due to phentermine component (abuse/dependence potential) 1