Pyridoxine (Vitamin B6)

Pyridoxine is a precursor of vitamin B6 coenzymes required for amino-acid metabolism and neurotransmitter synthesis. Its most important veterinary antidotal application is isoniazid poisoning. Other uses include correction of deficiency and selected toxicologic or chemotherapy-support protocols. These applications differ in both their biological rationale and supporting clinical evidence.

Group

Water-soluble vitamin; antidote

Mechanism of Action

Pyridoxine is converted to pyridoxal phosphate, a cofactor for enzymes including glutamate decarboxylase, which produces the inhibitory neurotransmitter GABA. Isoniazid disrupts availability of this cofactor; replacement restores GABA synthesis and helps control the resulting seizures. Vitamin B6 coenzymes also support amino-acid reactions, heme synthesis and other metabolic pathways in deficient patients.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Isoniazid poisoning - unknown amount	71 mg/kg	IV	Once	Infuse as a 5-10% solution over 30-60 minutes; source also describes bolus use. Known exposures require mg-for-mg pyridoxine/isoniazid matching instead.
Crimidine poisoning	20 mg/kg	IV	Once
Liposomal doxorubicin skin toxicity prevention	50 mg/animal	PO	Every 8 h	Investigated during the pegylated-liposomal doxorubicin protocol; not a general nutritional dose.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Crimidine poisoning	20 mg/kg	IV	Once

Indications

Antidotal treatment of isoniazid poisoning in dogs and other veterinary patients.
Treatment of selected crimidine poisoning or other documented vitamin-B6-antagonist intoxication.
Correction of vitamin B6 deficiency.
Selected adjunctive reduction of skin toxicity associated with pegylated liposomal doxorubicin in dogs, supported by limited regimen-specific evidence.

Contraindications

Hypersensitivity; avoid prolonged excessive dosing.

Interactions

Can reduce levodopa efficacy unless carbidopa is present.
High doses may reduce phenobarbital or phenytoin concentrations.
Isoniazid and several other drugs increase functional B6 requirements.

Adverse effects

High or prolonged doses may cause sensory neuropathy and ataxia.

Toxicity

Discontinue excess exposure; neurologic recovery may be slow. Massive acute exposure can cause seizures.

Preparations

Preparation	Form	Strength	Route
Pyridoxine hydrochloride injection 100 mg/mL	Injection	100 mg / mL	IV
Pyridoxine hydrochloride 50 mg tablet	Tablet	50 mg / tablet	PO
Pyridoxine hydrochloride 100 mg tablet	Tablet	100 mg / tablet	PO

Monitoring and Administration

For known isoniazid ingestion, match pyridoxine dose in mg to the ingested isoniazid mg; this is an exposure-based calculation, not a standard mg/kg regimen.

Use a single-ingredient antidotal preparation rather than injectable B-complex vitamins. Protect injection from light and freezing.

Assess seizure control and neurologic recovery; do not mix with alkaline/oxidising solutions or iron salts.