Hydrochlorothiazide
Hydrochlorothiazide promotes distal tubular diuresis and decreases urinary calcium excretion.
Group
Thiazide diuretic
Mechanism of Action
Inhibits distal tubular sodium-chloride reabsorption, increasing sodium, potassium and water loss.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Diuresis | 2–4 mg/kg | PO | Every 12 h | |
| Hypertension | 1 mg/kg | PO | Every 12 h | |
| Nephrogenic diabetes insipidus | 2 mg/kg | PO | Every 12 h | Low-sodium diet; evidence includes a case report. |
| Nephrogenic diabetes insipidus | 2.5–5 mg/kg | PO | Every 12 h | |
| Hypertension | 1 mg/kg | PO | Every 12–24 h | Second-choice adjunct rather than reliable feline monotherapy. |
| Reduction of urinary calcium | 2 mg/kg | PO | Every 12 h | |
| Reduction of urinary calcium | 2.2 mg/kg | PO | Every 12 h | |
| Reduction of urinary calcium | 2–4 mg/kg | PO | Every 12 h | |
| Refractory congestive heart failure | 2 mg/kg | PO | Every 12 h | When adding to high-dose furosemide, one protocol reduces furosemide by 50%; monitor renal function and electrolytes. |
| Right-sided-heart-failure ascites | Reference only | PO | 2 mg/kg initially every other day with furosemide, spironolactone, ACE inhibition and dietary sodium restriction; adjust electrolytes and renal function. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Diuresis | 2–4 mg/kg | PO | Every 12 h | |
| Hypertension | 1 mg/kg | PO | Every 12 h | |
| Reduction of urinary calcium | 1 mg/kg | PO | Every 12 h | |
| Urine alkalinisation | 2 mg/kg | PO | Every 12 h | |
| Congestive heart failure | 1–2 mg/kg | PO | Every 12–24 h | |
| Hypertension | 1 mg/kg | PO | Every 12–24 h | Second-choice adjunct rather than reliable feline monotherapy. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Postparturient udder oedema | 125–250 mg/animal | IV, IM | Every 12–24 h |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hyperkalaemic periodic paralysis adjunct | 0.5–1 mg/kg | PO | Every 12 h | When dietary adjustment does not control episodes. |
Indications
- Diuresis and hypertension
- Calcium oxalate urolith prevention
- Postparturient udder oedema
Contraindications
- Hypercalcaemia
- Anuria or sulfonamide/thiazide hypersensitivity; intestinal absorptive hypercalciuria can worsen hypercalcaemia.
Interactions
- Other diuretics and antihypertensives have additive effects.
- Corticosteroids or amphotericin B increase hypokalaemia. Electrolyte depletion increases digoxin toxicity; lithium concentrations and insulin requirements may rise. Calcium or vitamin D increases hypercalcaemia risk.
Adverse effects
- Hypokalaemia and other electrolyte disturbances
- Dehydration
Toxicity
Overuse may cause hypovolaemia and electrolyte depletion; reassess renal function and electrolytes.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Hydrochlorothiazide 25 mg tablet | Tablet | 25 mg / tablet | PO |
| Hydrochlorothiazide 50 mg tablet | Tablet | 50 mg / tablet | PO |
| Hydrochlorothiazide 100 mg tablet | Tablet | 100 mg / tablet | PO |
| Hydrochlorothiazide 10 mg/mL oral solution | Oral Liquid | 10 mg / mL | PO |
| Hydrochlorothiazide 100 mg/mL oral solution | Oral Liquid | 100 mg / mL | PO |
| Hydrochlorothiazide 25 mg/mL injection Cattle injection. | Injection | 25 mg / mL | IV, IM |
Monitoring and Administration
Monitor hydration, electrolytes, calcium and renal function.
The oral maintenance drug mentioned for cattle after injectable treatment is chlorothiazide, a different medicine. Do not substitute its bolus dose here.
Check urine 2-4 weeks after starting calcium-oxalate prevention and electrolytes within several weeks of initiation or within 2 weeks of changing dose. Aldactazide ascites regimens are based on the spironolactone component, not hydrochlorothiazide mass.