Irbesartan
Irbesartan is an **Angiotensin-II Receptor Blocker (ARB)** primarily used in human medicine to manage hypertension and diabetic nephropathy. In veterinary medicine, its use is currently very limited, but it serves as a potential alternative or adjunct to ACE inhibitors (like enalapril or benazepril) for treating **canine hypertension associated with renal insufficiency**. > **Clinical Pearl:** ARBs like irbesartan are often considered when patients experience "ACE escape" (where aldosterone levels rebound despite ACE inhibitor therapy) or when ACE inhibitors are poorly tolerated. Unlike losartan, which requires hepatic conversion to an active metabolite (a process dogs are inefficient at), irbesartan is active in its parent form, making it a more reliable choice for canine patients. **Key Highlights:** * May be useful for hypertension secondary to kidney disease. * Lacks extensive documentation for heart failure in dogs. * **Strictly contraindicated in pregnancy** due to teratogenic effects.
Mechanism: Irbesartan selectively and competitively blocks the **AT1 (Angiotensin II Type 1) receptor** in the Renin-Angiotensin-Aldosterone System (RAAS). * **Pathway:** Angiotensinogen → Angiotensin I → Angiotensin II. * Angiotensin II normally binds to AT1 receptors to cause potent vasoconstriction and stimulate aldosterone release. * By blocking the AT1 receptor, irbesartan prevents these effects, leading to **vasodilation**, **decreased aldosterone synthesis**, **reduced potassium excretion**, and **increased sodium and water excretion**. * **Pharmacologic Advantage:** It does not inhibit ACE (kininase II), so it does not interfere with bradykinin or substance P responses. Furthermore, it does not require hepatic conversion to an active metabolite, which is a significant pharmacokinetic advantage in dogs compared to losartan.
Dosing by species
- As an alternative to ACE inhibitors for treatment of hypertension associated with renal insufficiency · 5 mg/kg PO q12-24 hours. · PO · q12-24h
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Pregnancy (teratogenic)
- Nursing/lactating animals
- Hypotension
- Uncorrected volume depletion
- Uncorrected sodium depletion
- Hypersensitivity to irbesartan
Adverse effects
- Diarrhea
- Dyspepsia (indigestion)
- Fatigue or somnolence
- Orthostatic hypotension
- Dizziness
Drug interactions
- Other antihypertensive agents (e.g., amlodipine, ACE inhibitors) · Increased risk of additive hypotension. Use with caution and monitor blood pressure closely.
- Diuretics · May exacerbate volume depletion and increase the risk of severe hypotension.
Monitoring
- Systemic blood pressure
- Heart rate
- Serum electrolytes (especially potassium)
- BUN and Creatinine (renal function)
- Clinical signs of adverse effects (GI upset, lethargy, weakness)
Overdose
**Toxicity Profile:** Irbesartan has a wide margin of safety in acute overdose scenarios. Rats and mice have survived acute oral overdoses exceeding 2000 mg/kg. **Clinical Signs of Overdose:** * Severe hypotension * Tachycardia (reflex) or bradycardia **Treatment:** * Treatment is largely **supportive and symptomatic**. * Address hypotension with intravenous fluids and cardiovascular support as needed. * Contact an animal poison control center for specific guidance.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.