Neural tube defects

Question 1

Vitamins

Common indications

Answer 1

• Thiamine (B1) is used for the treatment and prevention of Wernicke’s encephalopathy and korsakoff psychosis, which are manifestations of severe thiamine deficiency
• Folic acid (this synthesis of folate or B9) is used for megaloblastic anaemia due to folate deficiency, and the first trimester of pregnancy to reduce the risk of neural tube defects.
• Hydroxocobalamin (B12) is used for megaloblastic anaemia and subacute combined degeneration of the cord due to B12 deficiency
• Phytomenadione (Vit K) is recommended for all newborns to prevent Vit K bleeding and reverse warfarin. (prothrombin complex should also be given in this case)

Question 2

Vitamins MOA

Answer 2

• Vitamins are organic substances required in small amounts for normal metabolic processes.
• Vitamin deficiencies and their associated clinical manifestations may be treated with a pharmaceutical form of the relevant vitamin
• In pregnancy and the preconception period, giving folic acid reduces the risk of congenital neural tube defects. As it is required for normal cell division, it may work by facilitating cell proliferation involved in neural tube closure, but this is not completely understood.
• Phytomenadione reverses warfarin by providing a fresh supply of vitamin K for the synthesis of vitamin K-dependent clotting factors by the liver.

Question 3

Vitmains

important side effects

Answer 3

• When given IV, phytomenadione and high-dose thiamine may rarely cause anaphylaxis

Question 4

Vitamins

Warnings

Answer 4

• In patients with co-existing B12 and folate deficiency, you should replace both vitamins simultaneously. This is because replacing folic acid alone may be associated with (and perhaps hasten) progression of the neurological manifestations of B12 deficiency.
• The major concern is the risk of provoking subacute combined degeneration of the cord.
• Phytomenadione is less effective in reversing warfarin in patients with severe liver disease, as clotting factors are synthesised in the liver.

Question 5

Vitamins

important interactions

Answer 5

• As noted above, vitamin K and warfarin have an antagonistic interaction which, initially, is desirable.
• However, when attempting to restart warfarin after vitamin K has been given, it may result in erratic dosing requirements.

Question 6

Vitamins

Dosage

Answer 6

• Thamine deficiency. Pabrinex prophylaxis= 1 pair BD for 3 days. Treatment= 2 pair BD for 3-5 days
• Prevention of neural tube defects. 400mcg pre-conception + pregnancy, if the patient is at high risk of NTD then 5mg
• Folate deficiency anaemia- 5mg OD
• Vit K deficiency bleeding- phytomenadione 1mg IM as a single dose
• Warfarin therapy- mild bleeding 1mg IV/PO or if major 10mg

Question 7

Vitamins

Communication and monitoring

Answer 7

• It is always worth raising folic acid supplementation with women of child-bearing age, due to the benefits of starting pre-conception
• Thiamine, folate and B12 and monitored clinically with FBC/levels
• Effect of phytomenadione on INR becomes evident in 12-24hrs post administration