Phentermine and topiramate

Table 5 displays clinically significant drug interactions with phentermine and topiramate extended-release capsules. Table 5. Clinically Significant Drug Interactions with Phentermine and Topiramate Extended-Release Capsules Monoamine Oxidase Inhibitors Clinical Impact Concomitant use of phentermine with monoamine oxidase inhibitors (MAOIs) increases the risk of hypertensive crisis. Intervention Concomitant use of phentermine and topiramate extended-release capsules are contraindicated during MAOI treatment and within 14 days of stopping an MAOI.

Oral Contraceptives Clinical Impact Co-administration of multiple-dose phentermine and topiramate extended-release capsules 15 mg/92 mg once daily with a single dose of oral contraceptive containing 35 µg ethinyl estradiol (estrogen component) and 1 mg norethindrone (progestin component), in obese otherwise healthy volunteers, decreased the exposure of ethinyl estradiol by 16% and increased the exposure of norethindrone by 22% [see Clinical Pharmacology (12.3) ] .

Although this interaction is not anticipated to increase the risk of pregnancy, irregular bleeding (spotting) may occur more frequently due to both the increased exposure to the progestin and lower exposure to the estrogen, which tends to stabilize the endometrium. Intervention Inform patients not to discontinue their combination oral contraceptive if spotting occurs, but to notify their health care provider if the spotting is troubling to them.

CNS Depressants Including Alcohol Clinical Impact The concomitant use of alcohol or CNS depressant drugs (e.g., barbiturates, benzodiazepines, and sleep medications) with phentermine or topiramate may potentiate CNS depression such as dizziness or cognitive adverse reactions, or other centrally mediated effects of these agents. Intervention Advise patients not to drive or operate machinery until they have gained sufficient experience on phentermine and topiramate extended-release capsules to gauge whether it adversely affects their mental performance, motor performance, and/or vision.

Caution patients against excessive alcohol intake when taking phentermine and topiramate extended-release capsules. Consider phentermine and topiramate extended-release capsules dosage reduction or discontinuation if cognitive dysfunction persists [see Warnings and Precautions (5.5) ] Non-Potassium Sparing Diuretics Clinical Impact Concurrent use of phentermine and topiramate extended-release capsules with non-potassium sparing diuretics may potentiate the potassium-wasting action of these diuretics. Concomitant administration of hydrochlorothiazide alone with topiramate alone has been shown to increase the C max and AUC of topiramate by 27% and 29%, respectively.

Intervention When phentermine and topiramate extended-release capsules are used concomitantly with non-potassium-sparing diuretics, measure potassium before and during phentermine and topiramate extended-release capsules treatment [see Warnings and Precautions (5.12) and Clinical Pharmacology (12.3) ] . Antiepileptic Drugs Clinical Impact Concomitant administration of phenytoin or carbamazepine with topiramate in patients with epilepsy, decreased plasma concentrations of topiramate by 48% and 40%, respectively, when compared to topiramate given alone [see Clinical Pharmacology (12.3) ] .

Concomitant administration of valproic acid and topiramate has been associated with hyperammonemia with and without encephalopathy. Concomitant administration of topiramate with valproic acid in patients has also been associated with hypothermia (with and without hyperammonemia). Intervention Consider measuring blood ammonia in patients in whom the onset of hypothermia or encephalopathy has been reported [see Clinical Pharmacology (12.3) ] . Carbonic Anhydrase Inhibitors Clinical Impact Concomitant use of topiramate with any other carbonic anhydrase inhibitor may increase the severity of metabolic acidosis and may also increase the risk of kidney stone formation.

Intervention Avoid the use of phentermine and topiramate extended-release capsules with other drugs that inhibit carbonic anhydrase. If concomitant use of phentermine and topiramate extended-release capsules with another carbonic anhydrase inhibitor is unavoidable, monitor patient for the appearance or worsening of metabolic acidosis [see Warnings and Precautions (5.7 , 5.10) ] . Pioglitazone Clinical Impact A decrease in the exposure of pioglitazone and its active metabolites were noted with the concurrent use of pioglitazone and topiramate in a clinical trial. The clinical relevance of these observations is unknown.

Intervention Consider increased glycemic monitoring when using pioglitazone and phentermine and topiramate extended-release capsules concomitantly [see Clinical Pharmacology (12.3) ] . Amitriptyline Clinical Impact Some patients may experience a large increase in amitriptyline concentration in the presence of topiramate. Intervention Any adjustments in amitriptyline dose when used with phentermine and topiramate extended-release capsules should be made according to the patient's clinical response and not on the basis of amitriptyline levels [see Clinical Pharmacology (12.3) ] .

Oral Contraceptives : Altered exposure of progestin and estrogen may cause irregular bleeding, but not increased risk of pregnancy. Advise patients not to discontinue oral contraceptives if spotting occurs ( 7 ). CNS Depressants Including Alcohol : May potentiate CNS depressant effects. Avoid excessive use of alcohol ( 7 ). Non-potassium Sparing Diuretics : May potentiate hypokalemia. Measure potassium before and during treatment ( 7 ).

8.1 Pregnancy Risk Summary Phentermine and topiramate extended-release capsules are contraindicated in pregnant patients. The use of phentermine and topiramate extended-release capsules can cause fetal harm, and weight loss offers no clear clinical benefit to a pregnant patient (see Clinical Considerations ) . Available data from pregnancy registries and epidemiologic studies indicate an increased risk of major congenital malformations, including but not limited to cleft lip and/or cleft palate (oral clefts), and of being SGA in infants exposed in utero to topiramate (see Data ) .

When phentermine and topiramate were co-administered to rats at doses of 3.75 and 25 mg/kg, respectively [approximately 2 times the maximum recommended human dose (MRHD) based on area under the curve (AUC)], or at the same dose to rabbits (approximately 0.1 times and 1 time, respectively, the clinical exposures at the MRHD based on AUC), there were no drug-related malformations. However, structural malformations, including craniofacial defects and reduced fetal weights occurred in offspring of multiple species of pregnant animals administered topiramate at clinically relevant doses (see Data ) . Advise pregnant women of the potential risk to a fetus.

Clinical Considerations Disease Associated Maternal and/or Embryo/Fetal Risk Weight loss during pregnancy may result in fetal harm. Appropriate weight gain based on pre-pregnancy weight is currently recommended for all pregnant patients, including those who are already overweight or obese, due to the obligatory weight gain that occurs in maternal tissues during pregnancy. Maternal obesity increases the risk for congenital malformations, including neural tube defects, cardiac malformations, oral clefts, and limb reduction defects. Fetal/Neonatal Adverse Reactions Phentermine and topiramate extended-release capsules can cause metabolic acidosis [see Warnings and Precautions (5.7) ] .

The effect of topiramate-induced metabolic acidosis has not been studied in pregnancy; however, metabolic acidosis in pregnancy (due to other causes) can cause decreased fetal growth, decreased fetal oxygenation, and fetal death, and may affect the fetus' ability to tolerate labor. Data Human Data Data evaluating the risk of major congenital malformations, oral clefts, and being SGA with topiramate exposure during pregnancy is available from the North American Antiepileptic Drug (NAAED) Pregnancy Registry and from several larger retrospective epidemiologic studies. Major Congenital Malformations The NAAED Pregnancy Registry indicates an increased risk…