Acitretin
**Acitretin** is a second-generation systemic retinoid and the active metabolite of etretinate. * Primarily used in veterinary dermatology to manage severe keratinization disorders, sebaceous gland abnormalities, and certain cutaneous neoplasms. * It replaced etretinate on the human market due to a significantly shorter half-life, reducing the duration of tissue accumulation and associated long-term toxicity. * **Clinical Pearl**: While highly effective for conditions like canine lamellar ichthyosis, sebaceous adenitis, and precancerous solar lesions, its use in veterinary medicine is often limited by high cost, teratogenic risks, and the need for compounding to achieve accurate dosing in smaller patients.
Mechanism: Acitretin works by interacting with intracellular receptors to modulate cellular differentiation and proliferation. * Binds to nuclear **Retinoic Acid Receptors (RARs)** and **Retinoid X Receptors (RXRs)**. * Receptor-ligand complexes bind to specific DNA sequences → **alters gene transcription**. * **Pharmacodynamic Effects**: Normalizes keratinocyte differentiation, reduces epidermal hyperproliferation, decreases sebum production, and exerts anti-inflammatory and antineoplastic effects (particularly against squamous cell carcinomas).
Dosing by species
- Actinic keratosis/solar-induced squamous cell carcinoma; or Bowen's Disease · 10 mg per cat · PO · once daily · Note: This dose is for etretinate, but as the smallest capsule is 10 mg, this dose may need to suffice as well for cats.
- Bowen's Disease · 3 mg/kg/day · PO · once daily
- Dermatologic conditions where retinoids may be useful · 0.5-1 mg/kg · PO · once daily
- Dermatologic conditions where retinoids may be useful · 0.5-2 mg/kg · PO · once daily
- Sebaceous adenitis · 0.5-1 mg/kg · PO · once daily
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Pregnancy (absolute contraindication)
- Cardiovascular disease
- Hypertriglyceridemia
- Known sensitivity to acitretin or other retinoids
Adverse effects
- Anorexia
- Vomiting
- Diarrhea
- Cracking of foot pads
- Pruritus
- Ventral abdominal erythema
- Polydipsia
- Lassitude
- Joint pain/stiffness
- Eyelid abnormalities
- Keratoconjunctivitis sicca (KCS)
- Swollen tongue
- Behavioral changes
- Weight loss (especially in cats)
Drug interactions
- Alcohol · Acitretin can form etretinate in the presence of alcohol; etretinate is a teratogen with an extremely long terminal half-life that can persist in adipose tissue for years.
- Hepatotoxic drugs (e.g., methotrexate, ketoconazole, sulfonamides, fluconazole, macrolides) · May increase the potential for hepatotoxicity.
- Other retinoids (isotretinoin, tretinoin, vitamin A) · May cause additive toxic effects.
- Tetracyclines · May increase the potential for the occurrence of pseudotumor cerebri (cerebral edema and increased CSF pressure).
Monitoring
- Clinical efficacy
- Liver function tests (baseline and if clinical signs appear)
- Schirmer tear tests (monthly, especially in older dogs)
- Serum triglycerides and cholesterol (recommended based on human data)
Overdose
Information on overdoses with this agent remains limited. One oral overdose (525 mg) in a human patient resulted only in vomiting. The oral LD50 in rats and mice is >4 grams/kg.
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.