Pyridoxine (Vitamin B-6)
**Pyridoxine (Vitamin B6)** is a water-soluble vitamin essential for numerous metabolic processes. In veterinary medicine, its primary specific indications are as an **antidote** for isoniazid (INH) or crimidine toxicity, and to delay cutaneous toxicity (palmar-plantar erythrodysesthesia) associated with liposomal doxorubicin (**Doxil®**). *Clinical Pearl*: While dietary deficiency is extremely rare in dogs and cats consuming balanced commercial diets, cats with severe gastrointestinal disease may have increased requirements for pyridoxine. Additionally, in vitro studies have demonstrated that pyridoxine can suppress the growth of feline mammary tumors.
Mechanism: Pyridoxine is converted in erythrocytes to **pyridoxal phosphate** and, to a lesser extent, **pyridoxamine**, which act as vital coenzymes for protein, lipid, and carbohydrate utilization. * **Neurotransmitter Synthesis**: Required for the synthesis of **GABA** (gamma-aminobutyric acid) in the CNS, and the conversion of tryptophan → **serotonin** or niacin. * **Metabolic Pathways**: Essential for glycogen breakdown, heme synthesis, and the conversion of oxalate → glycine. * **Toxicity Antidote**: Acts as an antidote by directly enhancing the renal excretion of cycloserine and isoniazid.
Dosing by species
- To replace pyridoxine antagonized by crimidine ingestion · 20 mg/kg · IV · Once
- Isoniazid (INH) toxicity · If quantity of INH ingested is known, give pyridoxine on a mg for mg (1:1) basis. If it is not known, give pyridoxine initially at 71 mg/kg as a 5-10% IV infusion over 30-60 minutes · IV · Once · Some sources say it can be given as an IV bolus. Do not use injectable B-complex vitamins.
- To replace pyridoxine antagonized by crimidine ingestion · 20 mg/kg · IV · Once
- To delay the development of cutaneous toxicity (PPES) associated with doxorubicin containing pegylated liposomes (Doxil®) · 50 mg · PO · q8h (three times daily) · During chemotherapy protocol period
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Documented hypersensitivity or sensitivity to pyridoxine
Adverse effects
- Paresthesias (reported in humans)
- Somnolence (reported in humans)
- Reduced serum folic acid levels
- Peripheral neuropathy (associated with massive overdoses)
Drug interactions
- Chloramphenicol · May cause increased pyridoxine requirements
- Estrogens · May cause increased pyridoxine requirements
- Hydralazine · May cause increased pyridoxine requirements
- Immunosuppressants (e.g., azathioprine, chlorambucil, cyclophosphamide, corticosteroids) · May cause increased pyridoxine requirements
- Isoniazid · May cause increased pyridoxine requirements
- Penicillamine · May cause increased pyridoxine requirements
- Levodopa · Pyridoxine may reduce levodopa efficacy (no interaction when levodopa is used with carbidopa)
- Phenobarbital · High dose pyridoxine may decrease phenobarbital serum levels
- Phenytoin · High dose pyridoxine may decrease phenytoin serum concentration
Monitoring
- Efficacy for intended use
- Neurologic signs (gait, coordination) if on high doses
Overdose
> **Warning**: While single overdoses are generally not problematic unless massive, chronic high doses can cause severe neurologic toxicity. * **Massive Acute Overdose**: Laboratory animals given 3-4 grams/kg developed seizures and died. * **Chronic Overdose**: Dogs (Beagles) repeatedly given 3 gram oral daily doses developed uncoordinated gait and neurologic signs. Neuronal lesions were noted in sensory, dorsal root ganglia, and trigeminal ganglia. Signs generally resolved over a 2-month drug-free period.
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.