Drug Classification & Information

Hydrochlorothiazide (HCTZ) is a thiazide diuretic (‘water pill’) used for the adjunctive treatment of congestive heart failure (CHF).  It causes water loss from the body by causing loss of electrolytes into the urine such as sodium and chloride (salt). Ensure animals are eating and drinking normally while taking this medication.

Indications for Use

CHF in animals.  Occasionally used to prevent recurrence of calcium oxalate stones in dogs.

Potential Drug Interactions

May increase risk for digoxin toxicity by causing loss of potassium.  NSAIDs may reduce diuretic effects of HCTZ and may increase risk for renal dysfunction.  May increase insulin requirements in Diabetic patients.    

Drug Side Effects

HCTZ can lead to significant dehydration and electrolyte loss and may lead to renal dysfunction (azotemia).  Regular access to fresh drinking water is essential when receiving HCTZ (do not limit water intake).  HCTZ will increase both thirst and urination.  Skin reactions are rarely reported.  It should be used with caution in patients with pre-existing renal disease.

Therapeutic Monitoring

Renal values (BUN, creatinine) and electrolytes should be monitored regularly when receiving this medication (1-2 weeks after any dose adjustment, then every 4-6 months). 

Dosage Forms

Human: 12.5, 25 & 50 mg tablets

Combination with spironolactone (Aldactazide – spironolactone/HCTZ):  25/25 mg & 50/50 mg tablets