Tadalafil
Also known as: Cialis · Adcirca · GF-196960 · IC-351 · tadalafiili · tadalafilo · tadalafilum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pulmonary arterial hypertension | 1 mg/kg PO q48h (every other day) | PO | q48h | — | 🌎 NA |
| Pulmonary arterial hypertension | 1 mg/kg PO once daily | PO | q24h | — | 🌎 NA |
- Pulmonary arterial hypertension: Added to background treatment (furosemide, spironolactone, benazepril, dexamethasone, oxygen).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Tadalafil is a long-acting phosphodiesterase type 5 (PDE5) inhibitor primarily used in veterinary medicine for the management of pulmonary arterial hypertension (PAH) in dogs.
- Clinical Pearl: Compared to sildenafil (Viagra®), tadalafil has a significantly longer half-life, allowing for once-daily or every-other-day dosing, which greatly improves owner compliance.
- It is often used as an adjunctive therapy alongside conventional heart failure medications (e.g., pimobendan, diuretics, ACE inhibitors) when right-sided heart pressures remain elevated.
- Note: Clinical data and published literature in veterinary species are currently very limited, and the medication can be cost-prohibitive.
Mechanism of action
Tadalafil selectively inhibits cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5).
Mechanism Pathway: Endothelial stimulation → Nitric Oxide (NO) release → Activation of guanylate cyclase → Increased cGMP production.
Normally, PDE5 (found in pulmonary vascular smooth muscle, corpus cavernosum, and platelets) degrades cGMP. By inhibiting PDE5, tadalafil prevents this degradation.
Increased intracellular cGMP → Decreased intracellular calcium in smooth muscle cells → Relaxation of pulmonary vascular smooth muscle → Vasodilation and significant reduction of pulmonary arterial pressure (PAP).
Safety & warnings
Contraindications
- Concurrent use of any form of organic nitrates (regularly or intermittently)
- Serious hypersensitivity to tadalafil
Adverse effects
- Cutaneous flushing of the inguinal region
- Gastrointestinal upset (dyspepsia, nausea)
- Decreased neutrophils and platelets (observed at 4X-18X human equivalent doses; reversible)
- Hypotension (especially if combined with other vasodilators)
- Myalgia or back pain (reported in humans)
- Headache or nasal congestion (reported in humans)
Precautions
Dosage reductions may be required in patients with severe hepatic or renal impairment. Use with extreme caution in patients on concurrent antihypertensive therapies. The safety profile in dogs is not fully established; monitor closely for adverse effects.
Drug interactions
May increase hypotensive effects
Potential to increase hypotensive effects
Potentially could increase hypotensive effects
May reduce tadalafil metabolism and increase AUC
May reduce tadalafil metabolism and increase AUC
May reduce tadalafil metabolism and increase AUC
Significant potentiation of vasodilatory effects; life-threatening hypotension possible
Significant potentiation of vasodilatory effects; life-threatening hypotension possible
May decrease tadalafil concentrations
May decrease tadalafil concentrations
Monitoring
- Clinical efficacy (improved syncope, cough, respiratory effort)
- Pulmonary artery pressure (via echocardiography)
- Systemic blood pressure
- Adverse effects (GI upset, flushing)
Pharmacokinetics
Half-life
Absorption
Human data: Maximum plasma concentrations occur at around 4 hours. Food does not alter the rate or extent of absorption.
Distribution
Human data: 94% bound to plasma proteins.
Metabolism
Human data: Metabolized by CYP3A4 to a catechol metabolite that undergoes methylation and glucuronidation (inactive metabolites).
Elimination
Human data: Excretion is primarily via fecal routes (61%) with the remainder in the urine (approximately 36%).
Overdose
Little information is available for veterinary species. In humans, single doses up to 500 mg and multiple daily doses up to 100 mg produced adverse reactions similar to those seen at lower doses. Overdoses in animals are expected to mirror the drug's adverse effect profile (e.g., severe hypotension, tachycardia, flushing). Treat supportively and contact an animal poison control center for guidance.
Available products
Formulations
- Oral tablets
Human-labeled
- Tadalafil Oral Tablets: 2.5 mg, 5 mg, 10 mg, 20 mg (Cialis®, Adcirca®)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets at room temperature between 59°-86°F (15° and 30°C).
Client information
What is this medication? Tadalafil is used to treat high blood pressure in the lungs (pulmonary hypertension), helping your dog breathe easier, improving exercise tolerance, and reducing fainting spells.
How to give: Can be given with or without food.
Important Warnings:
Never give this medication if your pet is taking any nitrate medications (like nitroglycerin), as it can cause a fatal drop in blood pressure.
Side Effects: Watch for stomach upset, redness/flushing of the skin (especially on the hairless belly area), or lethargy. Report any unusual signs to your veterinarian.
Cost & Off-label use: This is a human medication used "off-label" in pets. Because it is a newer, long-acting medication, it can be quite expensive. Discuss any financial concerns with your veterinarian.
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.