The prevention and management of Pyridoxine (vitamin B6) deficiency.

Treatment of sideroblastic anaemias, homocystinuria or primary hyperoxaluria.

Pyridoxine (Vitamin B6) dependency in infants.

Actions:

Pyridoxine (vitamin B6) is a water-soluble vitamin involved principally in amino acid metabolism, but is also involved in carbohydrate and fat metabolism. It is also required for the formation of hemoglobin. Pyridoxine deficiency is rare in humans because of its widespread distribuion in foods. Pyridoxine deficiency may be drug induced, and inadequate utilization of pyridoxine may result from certain inborn errors of

metabolism. Pyridoxine deficiency may lead to sideroblastic anaemia, dermatitis, cheilosis and neurological symptoms such as peripheral neuritis and convulsions.

Pharmacokinetics:

Pyridoxine is readily absorbed from the gastrointestinal tract after oral administration and converted to the active forms pyridoxal phosphate and pyridoxamine phosphate. They are stored mainly in the liver where there is metabolisation to 4-pyridoxic acid and other inactive metabolites which are excreted in the urine. As the dose increases proportionally greater amounts are excreted unchanged in the urine. Pyridoxine (Vitamin B6) crosses the placenta and also appears in breast milk.

Contraindications:

Hypersensitivity to pyridoxine hydrochloride.

Warnings and Precautions:

Pyridoxine (Vitamin B6) is relatively nontoxic at normal doses however long-term administration of high doses (2-6g daily) is associated with the development of severe peripheral neuropathies.

Pyriren is presumed to be safe or unlikely to produce an effect on the ability to drive or use machinery.

Use in Pregnancy and Lactation:

Daily dietary requirements may increase slightly during pregnancy. No adverse effects have been reported with the use of physiologic doses during pregnancy. However the use of high doses during pregnancy has been implicated in some cases of Pyridoxine (Vitamin B6) dependent syndrome in infants.

Pyridoxine (Vitamin B6) is exreted in breast milk however no adverse have been reported with the use of physiologic doses during lactation.

Adverse Effects:

Nausea, headache, paresthesia, somnolence and low serum folic acid concentrations have been reported.

Pyridoxine (Vitamin B6) is relatively nontoxic at normal doses however long-term administration of high doses (2-6g daily) is associated with the development of severe peripheral neuropathies.

Transient dependency symptoms may occur upon withdrawal of therapy at a dose of 200mg/day for over 1 month. The significance of this is not known however for patients on large doses for long period of time withdrawal of therapy should probably be gradual.

Interactions:

Pyridoxine increases the peripheral metabolisation of levodopa. When levodopa is combined with carbidopa this effect is prevented.

Isoniazid, cycloserine, pyrazinamide and penicillamine may antagonise the effects of pyridoxine and lead to a secondary deficiency.

It has been reported that pyridoxine decreases serum concentrations of phenobarbitone.

Patients taking oestrogens e.g. oral contraceptives have higher Pyridoxine (vitamin B6) requirements.

Over dosage:

Sensory neuropathy can occur following long term administraton of large doses. Withdrawal should be started but should be started but should probably be gradual to prevent the occurrence of transient dependency symptoms.

Storage:

Store below 30oC. Protect from heat, light and moisture.

Keep container tightly closed. Keep out of reach of children.

Composition

Each uncoated tablet contains pyridoxine hydrochloride BP 25mg.

Presentation

Pyriren is packed as 10 x 10’s blister packs and 1000’s bulk packs in plastic jars.