Chlorothiazide or Hydrochlorothiazide

By Rania Gollakner, BS, DVM, MPH

What is chlorothiazide/hydrochlorothiazide?

Chlorothiazide (brand names: Diuril®, Azide®, Saluric®) and hydrochlorothiazide (brand names: HydroDiuril®, Microzide®, Esidrix®, Urozide®) are thiazide diuretics used to treat nephrogenic diabetes insipidus (different from diabetes mellitus), high blood pressure, abdominal fluid retention, heart failure, and elevated magnesium levels. Hydrochlorothiazide in particular has been used to prevent the recurrence of calcium oxalate urinary stones.

Its use in cats and dogs to treat nephrogenic diabetes insipidus, high blood pressure, fluid retention, or certain electrolyte imbalances 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 directions may be significantly different from those on the label.

How is chlorothiazide/hydrochlorothiazide given?

Chlorothiazide/hydrochlorothiazide is given by mouth in the form of a tablet, capsule, or liquid suspension (commercially produced or compounded at a pharmacy). Chlorothiazide may also be given as an injection in the hospital setting. These medications may be given with or without food, however, if your pet vomits when dosed on an empty stomach, give future doses with food. Measure liquid forms carefully. Because these medications can cause increased urination, try to give the medication at least a few hours prior to bedtime to reduce disruptions in sleep. Always allow your pet to have to have access to water.

This medication should take effect within 1 to 2 hours and gradual improvements are usually noticeable after a few days; 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?

The most common side effect is low potassium levels and increased need to urinate. Other side effects include electrolyte and nutrient imbalances, vomiting, or diarrhea. Severe side effects include skin rash, elevated blood sugar, weakness, collapse, seizures, head tilt, lack of urination, pale gums, or a racing heartbeat.

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 chlorothiazide or hydrochlorothiazide in pets that are allergic to these medications or sulfa drugs, or in pets that are not able to make urine. Do not use in lactating animals or use a milk replacer if use of this medication is required. These medications should be used with extreme caution in pets with kidney disease, electrolyte imbalances, liver disease, lupus (SLE), hyperuricemia, or diabetes.

Chlorothiazide or hydrochlorothiazide should be used cautiously in pregnant pets or those that have a condition that may lead to abnormal electrolyte levels, such as vomiting or diarrhea.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with chlorothiazide or hydrochlorothiazide: amphotericin B, corticosteroids, corticotropin, diazoxide, digoxin, insulin, lithium, methenamine, myelosuppressive agents, non-steroidal anti-inflammatory drugs (NSAIDs), neuromuscular blocking agents, probenecid, quinidine, vitamin D, or calcium salts.

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

Chlorothiazide/hydrochlorothiazide can interact with many laboratory tests including the following: amylase, cortisol, urinary estrogen, histamine, parathyroid-function tests, phentolamine tests, and tyramine tests.


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

Electrolytes, kidney values, blood sugar levels, hydration, blood pressure, and general blood cell counts will likely be monitored by your veterinarian. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor your pet at home for serious side effects.

How do I store chlorothiazide/hydrochlorothiazide?

These medications should be stored at room temperature, protected from light. The liquid suspension should be protected from freezing. For compounded forms of the medication, follow 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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