Chlorothiazide or Hydrochlorothiazide

What is chlorothiazide or 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 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 (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. 

“Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they 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.
• Measure liquid forms carefully.
• Chlorothiazide/hydrochlorothiazide may be given with or without food.
• If your pet vomits when dosed on an empty stomach, give future doses with food.
• These medications can cause increased urination, so try to give the medication at least a few hours prior to bedtime to reduce disruptions in sleep.
• Always allow your pet 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 noted outwardly, and laboratory tests may be needed to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Chlorothiazide or hydrochlorothiazide may cause the following side effects:

• Low potassium levels
• Increased need to urinate
• Electrolyte and nutrient imbalances
• Vomiting
• Diarrhea

Serious adverse reactions may occur. If any of the following signs develop, stop giving chlorothiazide or hydrochlorothiazide and contact your veterinarian immediately:

• Skin rash
• Elevated blood sugar
• Weakness
• Collapse
• Seizures
• Head tilt
• Lack of urination
• Pale gums
• Racing heartbeat

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately.  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
• Are not able to make urine
• Are lactating (use a milk replacer if the medication is required)

USE WITH EXTREME CAUTION in pets with:

• Kidney disease
• Electrolyte imbalances
• Liver disease
• Lupus (SLE)
• Hyperuricemia
• Diabetes

USE WITH CAUTION in pets that: 

• Are pregnant  
• 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?

Several medications should be used with caution when given with chlorothiazide or hydrochlorothiazide, including:

• Amphotericin B
• Calcium salts
• Corticosteroids
• Insulin
• Myelosuppressive agents
• Neuromuscular blocking agents
• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Vitamin D

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

Chlorothiazide/hydrochlorothiazide can interact with many laboratory tests including:

• Amylase
• Cortisol
• Histamine
• Parathyroid-function tests
• Phentolamine tests
• Tyramine tests
• Urinary estrogen

Is any monitoring needed with this medication?

• Your veterinarian will likely monitor electrolytes, kidney values, blood sugar levels, hydration, blood pressure, and general blood cell counts.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store chlorothiazide/hydrochlorothiazide?

• Store chlorothiazide/hydrochlorothiazide at room temperature, protected from light.
• Protect the liquid suspension 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. Be prepared to provide information about the product and your pet's weight and symptoms.