Menadione (Vitamin K3) is a synthetic, water-soluble form of vitamin K. It functions as a pro-vitamin, requiring conversion in the body to its active hydroquinone form (menadiol) to exert its essential role in the synthesis of functional clotting factors II, VII, IX, and X in the liver. The 5.2mg strength is a specific formulation used for therapeutic intervention in deficiency states. Its use is now largely restricted due to the availability of safer, naturally-derived vitamin K analogues (K1, MK-4).
Adult: Oral: 5 to 10 mg once daily. The 5.2mg tablet approximates this range. Parenteral: 5 to 15 mg IM/SC, frequency as directed by physician based on PT/INR.
Note: Oral tablets should be taken with food to enhance bile-dependent absorption. For malabsorption conditions, the parenteral route is essential. Do not crush or chew unless specified. Administer at the same time each day.
Menadione acts as a precursor to menadiol, which serves as a cofactor for the hepatic microsomal enzyme gamma-glutamyl carboxylase. This enzyme catalyzes the post-translational carboxylation of specific glutamic acid residues on the precursor proteins of clotting factors II, VII, IX, X, and proteins C, S, and Z. This carboxylation is essential for these factors to bind calcium and become functionally active in the coagulation cascade. Menadione participates in the vitamin K cycle, where it is reduced to the hydroquinone form (active), gets oxidized to vitamin K epoxide during the carboxylation reaction, and is then recycled back by the enzyme vitamin K epoxide reductase (VKOR).
Pregnancy: Category C (US FDA). Safety not established. Crosses the placenta. Use only if potential benefit justifies potential risk to the fetus, especially near term due to neonatal toxicity risk. Phytonadione is preferred.
Driving: Unlikely to affect ability to drive or operate machinery. However, dizziness is a rare side effect.
| Warfarin and other Vitamin K Antagonists | Menadione antagonizes the anticoagulant effect, reducing INR and increasing risk of thrombosis. | Major |
| Broad-spectrum Antibiotics (e.g., Cephalosporins like Cefoperazone) | May potentiate hypoprothrombinemia; menadione may be used to correct it. | Moderate |
| Orlistat, Bile Acid Sequestrants (Cholestyramine) | Reduce absorption of fat-soluble vitamins including menadione. | Moderate |
| Salicylates (High Dose) | May potentiate hypoprothrombinemia. | Moderate |
| Mineral Oil (long-term use) | Impairs fat-soluble vitamin absorption. | Moderate |
Same composition (Menadione (5.2mg)), different brands: