Methazolamide-d6 is intended for use as an internal standard for the quantification of methazolamide by GC- or LC-MS. Methazolamide is a carbonic anhydrase inhibitor. It reduces intraocular pressure and cerebrospinal fluid flow in a rat model of glaucoma. Methazolamide reduces electroshock-induced seizures in rats with an ED50 value of 19.2 mg/kg. It also inhibits production of reactive oxygen species (ROS) in a primary cortical neuron (PCN) cellular model of subarachnoid hemorrhage (SAH) and reduces cerebral edema in a mouse model of SAH.3 Methazolamide is larvicidal, with a 50% larvicidal concentration (LC50) value of 724 ppm, but has no activity when administered in the diet to adult A. aegypti. Formulations containing methazolamide have been used in the treatment of glaucoma.