By Rania Gollakner, BS, DVM, MPH

What is methazolamide?

Methazolamide (brand names: Neptazane®, GlaucTabs®, Glaumetax®, MZM) is a carbonic anhydrase inhibitor used to treat open angle glaucoma. Its use, in many cases, has been replaced with topical medications since they have fewer systemic side effects.

Its use in cats and dogs to treat glaucoma is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their direction may be significantly different from those on the label.

How is methazolamide given?

Methazolamide is given by mouth in the form of a tablet. It may be given with or without food; however, if vomiting occurs when dosed on an empty stomach, give future doses with food. It may also be compounded into a liquid form; measure liquid doses carefully.

This medication should take effect within 1 to 2 hours; however, effects may not be visibly obvious and therefore laboratory tests may need to be done to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects may include vomiting, diarrhea, lack of appetite, sleepiness, disorientation, or excitement. Serious side effects include heavy panting, decreased blood cell counts (characterized by abnormal bleeding, bruising, or infections), kidney problems or blood sugar imbalances (characterized by increased drinking and urination), liver problems (characterized by yellowing of the skin, eyes, or gums), low electrolytes that can cause muscle weakness or abnormal heart rhythms, muscle tremors or seizures, skin rash, persistent vomiting, bloody diarrhea or persistent lack of appetite.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Do not use in pets that are allergic to it, pets that have significant liver, kidney, or adrenal disease, or pets that have electrolyte imbalances. Do not use in pets with severe obstructive lung disease, or with closed angle glaucoma. Use caution in pregnant or lactating pets, or in pets using topical eye drugs for glaucoma.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with methazolamide: tricyclic antidepressants, aspirin, digoxin, insulin, methenamine compounds, potassium and drugs affecting potassium, phenobarbital, primidone, or quinidine.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Your veterinarian will monitor eye pressures regularly to be sure that the medication is working. Electrolyte levels, and blood cell counts may be monitored by your veterinarian as well. Monitor your pet for serious side effects.

How do I store methazolamide?

Store the tablets at room temperature in a tight container and protect from light. For compounded medications, follow the storage directions on the label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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