Vitamin A
Vitamin A and its retinoid derivatives (isotretinoin, tretinoin) are fat-soluble vitamins and hormones essential for normal vision, growth, reproduction, and the maintenance of epithelial tissues. In veterinary medicine, they are primarily used to treat **hypovitaminosis A** and specific dermatological conditions such as **sebaceous adenitis** or primary seborrhoea. > **WARNING:** Retinoids are highly **teratogenic**. Extreme caution must be exercised by both the prescribing veterinarian and the pet owner to prevent accidental exposure, particularly to pregnant women.
Mecanismo: Acts as a nutritional fat-soluble hormone that regulates **gene expression**. Tretinoin (**all-trans retinoic acid**) is the acid form of vitamin A, and isotretinoin (**13-cis retinoic acid**) is an isomer of tretinoin. **Clinical Pearl:** They bind to intracellular **retinoic acid receptors (RARs)** and **retinoid X receptors (RXRs)** → modifying gene transcription → regulating epithelial cell growth, differentiation, and sebum production.
Dosificación por especie
- Antioxidant support, liver disease, or malabsorption (EPI) · 1.6-8.3 mg/kg or 100-400 IU/dog · PO · q24h · for the first 30 days, then as needed · Dose can be calculated by weight or given as a flat dose per dog.
- Antioxidant support or malabsorption · 1.6-8.3 mg/kg or 30 IU/cat · PO · q24h · for the first 30 days, then as needed · Frequency is implied as q24h based on dog dosing.
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Pregnant animals
- Breeding animals
- Patients at high risk for thrombosis
- Neonates
Efectos adversos
- Teratogenicity (fetal malformations)
- Keratoconjunctivitis sicca (KCS / dry eye)
- Hepatotoxicity
- Hyperlipidaemia
- Hypercalcaemia (due to bone calcium loss with prolonged use)
- Skin redness and pigmentation
- Haematological abnormalities
- Nervous system changes
- Bone changes
- Thrombosis
- Anaphylactoid reactions
Interacciones farmacológicas
- Ciclosporin · Oral vitamin A may alter ciclosporin levels; requires close monitoring. · moderate
- Other topical drugs · Do not use topical vitamin A preparations simultaneously with other topical drugs. · moderate
- Vitamin A · May enhance vitamin A absorption, utilization, and storage. · minor
Monitorización
- Signs of vitamin A toxicity
- Tear production (Schirmer Tear Test) for KCS
- Liver enzymes (ALT, AST, ALP)
- Serum calcium levels
- Serum triglycerides/lipids
- Ciclosporin levels (if used concurrently)
- Ciclosporin blood levels (if used concurrently)
- Coagulation parameters (in patients at risk for thrombosis)
- Liver enzymes (if treating hepatopathy)
Sobredosis
High doses or prolonged use can lead to severe **vitamin A toxicity**. Signs of toxicity include: - **Hepatotoxicity** - **Hyperlipidaemia** - **Hypercalcaemia** (due to promotion of calcium loss from bone) - Severe skin, haematological, and nervous system abnormalities. > **Treatment:** Discontinue the drug immediately and provide supportive care. Monitor liver enzymes and serum calcium.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.