Hydrochlorothiazide: veterinary dose and monograph

At a glance

Drug class

Diuretic

Also known as

HCTZ, Aquazide, Hydrazide

Species with doses

Dogs, Cats, Horses and Rabbits

General dose range

1–4 mg/kg PO q12h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Refractory CHF — sequential nephron blockade (added to furosemide)
• Nephrogenic diabetes insipidus (paradoxical reduction of urine output)
• Calcium-oxalate urolith prevention (reduces urinary calcium excretion)
• Mild systemic hypertension / oedema (adjunct)

Hydrochlorothiazide dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Refractory CHF (with furosemide) / hypertension: Papich 5e: 2–4 mg/kg q12h PO; antihypertensive 1 mg/kg q12h. Plumb’s p.613: refractory CHF with furosemide 2–4 mg/kg q12h (Kittleson) or furosemide halved + HCTZ 2 mg/kg q12h (Saunders); hypertension 1 mg/kg q12–24h with spironolactone (Brown & Henik). Sequential nephron blockade — monitor electrolytes and renal values closely.
• Nephrogenic diabetes insipidus: Plumb’s p.613: 2 mg/kg PO twice daily with a low-sodium diet (Takemura 1998); 2.5–5 mg/kg PO twice daily (Nichols 1989).
• Calcium oxalate urolith prevention (hypercalciuria): Plumb’s p.613: 2 mg/kg q12h (Polzin; Adams); 2.2 mg/kg q12h with urinalysis every 2–4 weeks and electrolytes after starting or changing dose (Lulich 2000); 2–4 mg/kg q12h (Bartges 2006).

Cats

• Refractory CHF (with furosemide): Papich 5e: congestive heart failure 1–2 mg/kg q12–24h PO; reduce urinary calcium 1 mg/kg q12h; alkalinise urine 2 mg/kg q12h. Plumb’s p.613: refractory CHF with furosemide 1–2 mg/kg q12h (Kittleson); hypertension 1 mg/kg q12–24h (second-choice; not effective alone and may be contraindicated in CKD).

Horses

• Hyperkalaemic periodic paralysis (HYPP): Plumb’s p.613 (Valberg 2008): 0.5–1 mg/kg PO q12h when diet adjustment does not control episodes. ARCI Class 4.

Rabbits

• Diuresis / CHF adjunct: Carpenter's 6th ed (Rabbit cardiovascular table): 1 mg/kg PO q12h (up to 1–4 mg/kg PO q12h).

Contraindications

Significant renal impairment (thiazides lose efficacy at low GFR), severe electrolyte disturbance (hypokalaemia, hyponatraemia), dehydration, and anuria. Diabetes (can worsen hyperglycaemia). Sulfonamide hypersensitivity. Aggressive combination with furosemide without monitoring. Known hypersensitivity.

Species-specific warnings

Cats: Cats dehydrate and become azotaemic easily — start low, especially when combined with furosemide, and monitor electrolytes/renal values.

Adverse effects

• Hypokalaemia, hyponatraemia, hypochloraemic alkalosis (often pronounced with furosemide)
• Dehydration, pre-renal azotaemia
• Hypercalcaemia, hyperglycaemia, hyperuricaemia
• Weakness, hypotension

Drug interactions

• Furosemide: synergistic diuresis (intended) but markedly additive electrolyte/volume depletion — monitor
• Digoxin: thiazide-induced hypokalaemia increases digoxin toxicity
• ACE inhibitors: additive hypotension/azotaemia
• Corticosteroids: additive potassium loss
• NSAIDs: reduced diuretic effect, increased nephrotoxicity

Pregnancy and lactation

Generally avoided in pregnancy (volume contraction, fetal electrolyte effects) unless clearly indicated.

Monitoring

• Electrolytes (K, Na, Cl) and renal values — frequently, especially with furosemide
• Hydration status and body weight
• Blood glucose and calcium on chronic use
• Efficacy (congestion control / urine output / stone recurrence)

Toxicity and overdose

Overdose/over-diuresis causes dehydration, hypokalaemia, hyponatraemia, hypochloraemic alkalosis, hypotension and azotaemia; metabolic effects include hyperglycaemia, hypercalcaemia and hyperuricaemia. The combination with furosemide is the usual setting for dangerous electrolyte/volume depletion.

Management: No specific antidote. Stop the drug; rehydrate with IV fluids and correct electrolytes (especially potassium and sodium). Support blood pressure and renal perfusion; monitor until stable. Anticipate that combination diuretic therapy can deplete a patient quickly.

Clinical pearls

• The classic add-on for furosemide-refractory CHF — "sequential nephron blockade" gives a big diuretic boost, but also a big electrolyte/volume hit, so monitor closely
• Paradoxically treats nephrogenic diabetes insipidus (reduces urine output)
• Reduces urinary calcium — useful for calcium-oxalate stone prevention
• Less effective when GFR is low; not a substitute for a loop diuretic in azotaemic patients
• Watch potassium (and digoxin toxicity) carefully when combining with other diuretics

Mechanism of action

Inhibits the Na-Cl co-transporter (NCC) in the distal convoluted tubule, blocking sodium and chloride reabsorption to produce a moderate natriuresis/diuresis. Added to a loop diuretic it blocks a second nephron segment ("sequential nephron blockade") for a powerful combined effect. It enhances distal calcium reabsorption (reducing urinary calcium — the basis of oxalate-stone prevention) and, in nephrogenic DI, reduces plasma volume to paradoxically lessen polyuria.

Formulations and products

• 12.5 mg tablet
• 25 mg tablet
• Aquazide — 12.5 / 25 mg tablet, Tablet (human-label)
• Hydrazide — 12.5 / 25 mg tablet, Tablet (human-label)

Storage

Tablets: 15–30 °C, dry, protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other diuretics

• Acetazolamide
• Furosemide
• Mannitol
• Spironolactone
• Torsemide (Torasemide)

Frequently asked questions