pyridoxine
vitamin B6· Brands: Pydox, Hexa-Betalin, PyridoxIMIVPOSC
Mechanism of action
Pyridoxine is a water-soluble vitamin that acts as a coenzyme in the form of pyridoxal 5'-phosphate. It is involved in amino acid metabolism, neurotransmitter synthesis, and heme synthesis. It also plays a role in carbohydrate and lipid metabolism. Deficiency leads to various neurological and dermatological symptoms.
Pharmacokinetics
Pyridoxine is well absorbed from the gastrointestinal tract. It is converted in the liver to its active coenzyme forms, pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. It is widely distributed throughout the body, crosses the placenta, and is excreted in breast milk. The half-life is approximately 15 to 20 days. The majority of the dose is metabolized to 4-pyridoxic acid and excreted renally.
Indications & dosing
Prevention and treatment of vitamin B6 deficiency
For treatment, higher doses may be needed; for prevention, a dietary supplement is often used.
- adult · PO: 10–20 mg once daily · For treatment, higher doses may be needed; for prevention, a dietary supplement is often used.
Prophylaxis of isoniazid-induced peripheral neuropathy
Given concurrently with isoniazid.
- adult · PO: 10 mg once daily · Given concurrently with isoniazid.
Treatment of isoniazid-induced peripheral neuropathy
Dose may be adjusted based on response.
- adult · PO: 50–100 mg once daily · Dose may be adjusted based on response.
Pyridoxine-dependent seizures (initial treatment)
May be repeated after 30 minutes. For maintenance, oral pyridoxine 5-10 mg/kg/day.
- neonatal · IV: 50–100 mg single dose · May be repeated after 30 minutes. For maintenance, oral pyridoxine 5-10 mg/kg/day.
Nausea and vomiting in pregnancy
Often combined with other antiemetics.
- adult · PO: 10–25 mg three times daily · Often combined with other antiemetics.
Contraindications & precautions
- Hypersensitivity to pyridoxine or any component of the formulation · Rare, but may cause allergic reactions.
- Parkinson's disease (concurrent use of levodopa) · Pyridoxine may reduce the therapeutic effect of levodopa.
- Avoid high doses (e.g., >200 mg/day) for prolonged periods due to risk of peripheral neuropathy.
- Use caution in patients with Parkinson's disease taking levodopa, as pyridoxine may reduce its effectiveness.
- Monitor for signs of neuropathy in patients on long-term high-dose therapy.
- Patients with known sensitivity to vitamin B6 should use pyridoxine with caution.
- Doses should not exceed recommended amounts in pregnancy and breastfeeding unless prescribed by a clinician.
Adverse effects
- Peripheral neuropathy (dose-related)serious
- Nausea
- Headache
- Somnolence
- Skin rash
Monitoring, pregnancy & toxicity
- Clinical response (resolution of deficiency symptoms) · Assess at baseline and periodically during therapy
- Neurological examination for peripheral neuropathy · Periodically in patients on high-dose therapy (>200 mg/day)
- Pregnancy: Pyridoxine is considered safe in pregnancy, and it is used in the management of nausea and vomiting of pregnancy. No dose adjustment is required, but avoid excessive doses.
- Toxicity: Peripheral sensory neuropathy, ataxia, and paraesthesia, particularly with chronic high-dose therapy. · Stop pyridoxine; symptoms usually resolve on withdrawal, but may be irreversible if severe.
Clinical notes
Pyridoxine is used to treat and prevent vitamin B6 deficiency, as well as for conditions such as sideroblastic anaemia, pyridoxine-dependent epilepsy, and isoniazid-induced peripheral neuropathy. It is also used for the management of morning sickness, though evidence is not strong. Doses vary by indication. High doses over prolonged periods can cause peripheral neuropathy. Always consult local guidelines and the prescribing information.
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BNF; local formulary