Acitretin — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.5-1 mg/kg	q24h	Duration: 4-8 weeks for initial response; maintenance may be continued as needed Notes: Start at low end and titrate based on response and tolerability. Administer with food to enhance absorption.
Cat	PO	0.5-1 mg/kg	q24h	Duration: 4-8 weeks for initial response; maintenance may be continued as needed Notes: Use cautiously in cats; monitor for signs of toxicity. Administer with food.
Horse	PO	0.5-1 mg/kg	q24h	Duration: Variable; monitor response Notes: Limited data; use with caution.

Clinical Indications & Species Uses

General Indications

Treatment of keratinization disorders, seborrhea, and certain dermatoses

Dog (Canine)

Idiopathic seborrhea
Ichthyosis
Primary keratinization disorders
Cutaneous lymphoma (adjunctive)
Epidermal dysplasia

Cat (Feline)

Feline acne (severe)
Idiopathic seborrhea
Ichthyosis
Eosinophilic granuloma complex (some cases)

Horse (Equine)

Equine hyperkeratosis
Chronic proliferative dermatitis (rarely used)

Pharmacology & Mechanism of Action

Drug Class: Retinoid | Pharmacological Group: Systemic retinoid

Mechanism of Action: Acitretin is a synthetic retinoid that binds to nuclear retinoic acid receptors (RARs), particularly RAR-β and RAR-γ, modulating gene transcription. It normalizes epidermal cell proliferation, differentiation, and keratinization. It reduces sebum production, decreases stratum corneum thickness, and has anti-inflammatory and immunomodulatory effects.

Pharmacodynamics: Acitretin inhibits keratinocyte proliferation and promotes normal differentiation. It reduces the activity of sebaceous glands and has anti-comedogenic effects. It also modulates the immune response by inhibiting neutrophil chemotaxis and reducing the production of pro-inflammatory cytokines. Clinical effects are typically seen after 4-8 weeks of therapy.

⚡ Pharmacokinetics Summary

Absorption: Acitretin is well absorbed orally, with peak plasma concentrations occurring 1-4 hours after administration. Absorption is enhanced when taken with food, especially fatty meals.

Distribution: Acitretin is highly lipophilic and extensively distributed in tissues. It is highly protein-bound (>99%) in plasma, primarily to albumin. It accumulates in adipose tissue and skin.

Metabolism: Acitretin undergoes hepatic metabolism, including isomerization to its cis-isomer (13-cis-acitretin) and glucuronidation. It does not metabolize to etretinate in most species, but in some animals, it may be converted to etretinate, which has a long half-life.

Excretion: Acitretin is excreted primarily in bile and feces, with a small amount excreted in urine. Enterohepatic recirculation may occur. The elimination half-life is approximately 50 hours in humans, but in dogs it is around 5-10 days.

Half-Life: Dogs: ~5-10 days; Cats: ~2-4 days; Humans: ~50 hours (for reference)

Bioavailability: Oral bioavailability is approximately 60-70% in humans; in dogs, it is estimated to be around 40-60%.

Protein Binding: >99% (primarily albumin)

Available Formulations & Strengths

Oral Capsule 10 mg, 25 mg (PO)

Contraindications & Clinical Warnings

Contraindications:

Pregnancy or breeding animals (teratogenic)
Hypersensitivity to acitretin or other retinoids
Severe hepatic or renal impairment
Hyperlipidemia (uncontrolled)
Concurrent use of methotrexate (increased risk of hepatotoxicity)

Warnings & Clinical Precautions:

Teratogenic: extreme caution in females of reproductive age; use contraception if necessary.
May cause pseudotumor cerebri (benign intracranial hypertension), especially when used with tetracyclines.
Monitor liver enzymes and lipid profile periodically during therapy.
May cause mucocutaneous dryness; provide supportive care.
Use with caution in animals with diabetes mellitus, as retinoids may affect glucose metabolism.
Avoid in animals with a history of pancreatitis.
May cause photosensitivity; limit sun exposure.

Adverse Effects & Reactions

Common:

Dry skin and mucous membranes
Cheilitis
Pruritus
Alopecia
Lethargy
Anorexia
Vomiting
Diarrhea

Serious / Severe:

Hepatotoxicity
Hyperlipidemia
Pseudotumor cerebri
Bone abnormalities (with long-term use)
Teratogenicity

Rare:

Pancreatitis
Thrombocytopenia
Nephrotoxicity
Ocular effects (e.g., corneal opacities)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Methotrexate	Increased risk of hepatotoxicity	High
Tetracyclines (e.g., doxycycline)	Increased risk of pseudotumor cerebri	High
Vitamin A or other retinoids	Additive toxicity (hypervitaminosis A)	High
Corticosteroids	Potential for increased immunosuppression and skin thinning	Moderate
Progestins (e.g., megestrol acetate)	Potential for reduced efficacy of progestins	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Severe mucocutaneous dryness
Vomiting
Diarrhea
Lethargy
Ataxia
Hepatotoxicity
Hyperlipidemia
Seizures (in severe cases)

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce vomiting if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide fluid therapy, monitor liver enzymes and lipid levels, and manage signs as needed. In severe cases, consider gastric lavage.

Food Animal Withdrawal Times

Not approved for food animals; withdrawal times not established. Do not use in food-producing animals.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C, 68-77°F)

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep in original container.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use (Soriatane).

Extra-Label (Off-Label) Use: In the US, acitretin is not FDA-approved for veterinary use; use in animals is extra-label. Must follow AMDUCA regulations, including a valid VCPR and appropriate withdrawal times for food animals (though not recommended).

Clinical Pearls & Practice Notes

💡 Clinical Insights: Acitretin is a potent systemic retinoid used primarily in dogs and cats for keratinization disorders. It requires a thorough baseline evaluation including liver function tests, lipid profile, and pregnancy screening in intact females. Therapy should be initiated at the lowest effective dose and titrated based on response and adverse effects. Clinical improvement may take several weeks. Regular monitoring (e.g., liver enzymes, lipids) is essential. Due to its teratogenic potential, strict precautions must be taken in breeding animals. Acitretin should be used only when other therapies have failed, and owners should be fully informed of potential side effects.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)