Drug Interactions between brinzolamide ophthalmic and Qsymia

MONITOR: Coadministration with topiramate may increase the plasma concentrations of phentermine. The exact mechanism of interaction has not been established. When a single 15 mg dose of phentermine was administered with a 92 mg dose of topiramate, phentermine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 13% and 42%, respectively, compared to phentermine administered alone. No significant changes were observed in the pharmacokinetics of topiramate.

MANAGEMENT: Caution is advised when phentermine is used in combination with topiramate. Patients should be monitored for potentially increased adverse effects of phentermine such as dizziness, restlessness, insomnia, tremor, headache, euphoria, dysphoria, palpitation, tachycardia, and blood pressure elevation.

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GENERALLY AVOID: Following ophthalmic administration, brinzolamide and dorzolamide are systemically absorbed and may have additive pharmacologic effects with other, systemically administered carbonic anhydrase inhibitors. Specific data are not available regarding coadministration with topiramate or zonisamide, which are anticonvulsants with some carbonic anhydrase inhibiting activity. Theoretically, adverse effects such as drowsiness, paresthesia, tinnitus, electrolyte imbalance, metabolic acidosis, and gastrointestinal disturbances may be increased. Carbonic anhydrase inhibition can also promote kidney stone formation by reducing urinary citrate excretion and increasing urinary pH, and cause oligohidrosis or hyperthermia by altering electrolyte and fluid balance. Oligohidrosis and hyperthermia are sometimes associated with serious sequelae but may be preventable by prompt recognition of symptoms and appropriate treatment.

MANAGEMENT: The concomitant use of ocular and systemic carbonic anhydrase inhibitors is not recommended. Patients treated with topiramate or zonisamide should be advised to increase fluid intake to enhance urinary output, which lowers the concentration of substances involved in stone formation. Patients should be monitored closely for evidence of decreased sweating and increased body temperature, especially in warm or hot weather. Proper hydration before and during vigorous activities or exposure to warm temperatures is recommended. Patients should contact their doctor immediately if they develop signs or symptoms of kidney stones such as sudden back pain, abdominal pain, blood in the urine and/or painful urination, or if they experience a rise in body temperature or decreased sweating.

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