Phentermine / Topiramate Dosage

Medically reviewed by Drugs.com. Last updated on Sep 6, 2024.

Applies to the following strengths: 3.75 mg-23 mg; 7.5 mg-46 mg; 11.25 mg-69 mg; 15 mg-92 mg

Usual Adult Dose for Weight Loss

Initial Dose: Phentermine 3.75 mg-topiramate 23 mg orally once a day for 14 days, then phentermine 7.5 mg-topiramate 46 mg orally once a day

After 12 weeks of phentermine 7.5 mg-topiramate 46 mg: Weight loss should be evaluated; if less than 3% of baseline body weight has been lost, the dosage should be increased.

Dose Escalation: Phentermine 11.25 mg-topiramate 69 mg orally once a day for 14 days, then phentermine 15 mg-topiramate 92 mg orally once a day

After 12 weeks of phentermine 15 mg-topiramate 92 mg: Weight loss should be evaluated; if less than 5% of baseline body weight has been lost, this drug should be discontinued.

Maintenance Dose: Phentermine 7.5 mg-topiramate 46 mg OR phentermine 15 mg-topiramate 92 mg orally once a day

Phentermine 3.75 mg-topiramate 23 mg and phentermine 11.25 mg-topiramate 69 mg are for titration purposes only.

Comments:

Selection of patients for treatment with this drug should be based on BMI; the patient's BMI should be determined by dividing weight (in kg) by height (in meters) squared.
The manufacturer product information should be consulted for a BMI conversion table based on height (inches or cm) and weight (pounds or kg).
If a patient has not lost at least 5% of baseline body weight after 12 weeks of therapy with phentermine 15 mg-topiramate 92 mg, it is unlikely that the patient will achieve and sustain clinically meaningful weight loss with continued therapy.
Phentermine 15 mg-topiramate 92 mg should be discontinued gradually by taking phentermine 15 mg-topiramate 92 mg orally every other day for at least 1 week before stopping therapy altogether, due to the possibility of triggering a seizure.

Use: As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in patients with an initial BMI of 30 kg/m2 or greater (obese), or 27 kg/m2 or greater (overweight) with at least 1 weight-related comorbidity (e.g., hypertension, type 2 diabetes mellitus, dyslipidemia)

Usual Pediatric Dose for Weight Loss

12 YEARS AND OLDER:
Initial Dose: Phentermine 3.75 mg-topiramate 23 mg orally once a day for 14 days, then phentermine 7.5 mg-topiramate 46 mg orally once a day

After 12 weeks of phentermine 7.5 mg-topiramate 46 mg: Weight loss should be evaluated; if less than 3% of baseline BMI has been reduced, the dosage should be increased.

Dose Escalation: Phentermine 11.25 mg-topiramate 69 mg orally once a day for 14 days, then phentermine 15 mg-topiramate 92 mg orally once a day

After 12 weeks of phentermine 15 mg-topiramate 92 mg: Weight loss should be evaluated; if less than 5% of baseline BMI has been reduced, this drug should be discontinued.

Maintenance Dose: Phentermine 7.5 mg-topiramate 46 mg OR phentermine 15 mg-topiramate 92 mg orally once a day

Phentermine 3.75 mg-topiramate 23 mg and phentermine 11.25 mg-topiramate 69 mg are for titration purposes only.

95TH PERCENTILE BMI VALUES BY AGE AND SEX:

Age 12 years: Male 24.2 kg/m2, female 25.3 kg/m2
Age 12.5 years: Male 24.7 kg/m2, female 25.8 kg/m2
Age 13 years: Male 25.2 kg/m2, female 26.3 kg/m2
Age 13.5 years: Male 25.6 kg/m2, female 26.8 kg/m2
Age 14 years: Male 26 kg/m2, female 27.3 kg/m2
Age 14.5 years: Male 26.5 kg/m2, female 27.7 kg/m2
Age 15 years: Male 26.8 kg/m2, female 28.1 kg/m2
Age 15.5 years: Male 27.2 kg/m2, female 28.5 kg/m2
Age 16 years: Male 27.6 kg/m2, female 28.9 kg/m2
Age 16.5 years: Male 27.9 kg/m2, female 29.3 kg/m2
Age 17 years: Male 28.3 kg/m2, female 29.6 kg/m2
Age 17.5 years: Male 28.6 kg/m2, female 30 kg/m2

Comments:

Selection of patients for treatment with this drug should be based on BMI percentile.
If a patient has not had a reduction of at least 5% of baseline BMI after 12 weeks of therapy with phentermine 15 mg-topiramate 92 mg, it is unlikely that the patient will achieve and sustain clinically meaningful weight loss with continued therapy.
Rate of weight loss should be monitored; if weight loss exceeds 0.9 kg/week, dosage reduction should be considered.
Phentermine 15 mg-topiramate 92 mg should be discontinued gradually by taking phentermine 15 mg-topiramate 92 mg orally every other day for at least 1 week before stopping therapy altogether, due to the possibility of triggering a seizure.

Use: As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in patients with an initial BMI in the 95th percentile or greater standardized for age and sex

Renal Dose Adjustments

Mild renal dysfunction (CrCl 50 to less than 80 mL/min): No adjustment recommended
Moderate or severe renal dysfunction (CrCl less than 50 mL/min): The maximum recommended dosage is phentermine 7.5 mg-topiramate 46 mg orally once a day.

Comments:

CrCl calculated using the Cockcroft-Gault equation with actual body weight

Liver Dose Adjustments

Mild liver dysfunction (Child-Pugh score 5 to 6): No adjustment recommended
Moderate liver dysfunction (Child-Pugh score 7 to 9): The maximum recommended dosage is phentermine 7.5 mg-topiramate 46 mg orally once a day.
Severe liver dysfunction (Child-Pugh score 10 to 15): Not recommended

Precautions

The US FDA requires a Risk Evaluation and Mitigation Strategy (REMS) for this drug. It includes a medication guide, elements to assure safe use, and implementation system. For additional information: www.accessdata.fda.gov/scripts/cder/rems/index.cfm

CONTRAINDICATIONS:

Pregnancy
Glaucoma
Hyperthyroidism
Coadministration with or within 14 days of stopping a monoamine oxidase inhibitor
Known hypersensitivity to either active component or to any of the ingredients, or idiosyncrasy to the sympathomimetic amines

Safety and efficacy have not been established in patients younger than 12 years.

Consult WARNINGS section for additional precautions.

US Controlled Substance: Schedule IV

Dialysis

ESRD on dialysis: Not recommended

Other Comments

Administration advice:

Before starting this drug and monthly during therapy, obtain a negative pregnancy test in patients of childbearing potential; this drug is contraindicated during pregnancy.
Before starting this drug and periodically during therapy, obtain a blood chemistry profile that includes bicarbonate, creatinine, and potassium in all patients, and glucose in patients with type 2 diabetes on antidiabetic medication.
Administer once a day in the morning with or without food; do not administer in the evening due to possible insomnia.

Storage requirements:

Store at 20C to 25C (68F to 77F); excursions permitted to 15C to 30C (59F to 86F).
Keep container tightly closed and protect from moisture.

General:

Limitations of Use:
The effect of this drug on cardiovascular morbidity and mortality has not been established.
Safety and efficacy of this drug in combination with other products intended for weight loss (including prescription drugs, over-the-counter drugs, herbal preparations) have not been established.
This drug is available through a limited program under the REMS; for further information: qsymiarems.com or 1-888-998-4887
This product contains FD&C Yellow 5 (tartrazine) which may cause allergic-type reactions (including bronchial asthma) in certain susceptible patients.

Monitoring:

Cardiovascular: Resting heart rate in all patients, especially those with cardiac or cerebrovascular disease (when starting or increasing dosage); blood pressure in patients being treated for hypertension (before starting and during therapy)
Dermatologic: For decreased sweating (during physical activity, especially in hot weather)
General: Pregnancy testing (before starting and monthly during therapy); for increased body temperature (during physical activity, especially in hot weather)
Metabolic: Electrolytes including serum bicarbonate (before starting and during therapy); blood glucose levels in patients with type 2 diabetes on antidiabetic medication (before starting and during therapy); potassium (before and during therapy)
Musculoskeletal: Height velocity in pediatric patients
Psychiatric: For emergence/worsening of depression, suicidal thoughts/behavior, and/or any unusual changes in mood/behavior in all patients
Renal: Serum creatinine (before starting and during therapy)

Patient advice:

Read the US FDA-approved patient labeling (Medication Guide).
Avoid getting pregnant during therapy.
Patients of childbearing potential:
Use effective contraception during therapy.
Notify health care provider if spotting occurs while taking a combined oral contraceptive.
Stop this drug immediately and notify health care provider for a known/suspected pregnancy.
Inform health care provider of palpitations or feelings of a racing heartbeat while at rest during therapy.
Inform health care provider immediately if mood changes, depression, or suicidal ideation occur.
Immediately report symptoms of severe and persistent eye pain or significant changes in your vision to health care provider.
Inform health care provider about any changes in attention, concentration, memory, difficulty finding words, or other cognitive functions.
Do not to drive or operate machinery until you have gained sufficient experience on this drug to gauge whether it adversely affects your mental performance, motor performance, and/or vision.
Avoid excessive alcohol intake while taking this drug.
Inform health care provider about any factors that can increase the risk of acidosis (e.g., prolonged diarrhea, surgery, high protein/low carbohydrate diet, concomitant medications [such as carbonic anhydrase inhibitors]).
Patients with type 2 diabetes mellitus on antidiabetic therapy: Monitor your blood glucose levels and report symptoms of hypoglycemia to health care provider.
Report symptoms of hypotension (e.g., dizziness, lightheadedness, syncope) to health care provider.
Do not to abruptly stop this drug without first talking to health care provider.
Increase fluid intake to increase urinary output, which can decrease the concentration of substances involved in kidney stone formation; report symptoms of severe side/back pain and/or blood in your urine to health care provider.
Monitor for decreased sweating and increased body temperature during physical activity (especially in hot weather).
Report signs of skin reaction to health care provider.
Do not breastfeed during therapy.
If a dose is missed, wait until the next morning to take the usual dose; do not double the dose.