How the dose is calculated
Neonatal vitamin K prophylaxis is a fixed dose by birth-weight band, not a per-kg calculation — infants under 1.5 kg receive a lower fixed dose than those at or above 1.5 kg.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Under 1.5 kg birth weight | 0.5 mg | single IM dose at birth | 0.5 mg |
| 1.5 kg or more birth weight | 1 mg | single IM dose at birth | 1 mg |
Clinical use
- A single IM dose of vitamin K at birth is standard practice worldwide to prevent vitamin K deficiency bleeding (VKDB), including the rare but serious late-onset form.
- Oral vitamin K regimens exist as an alternative in some settings but require multiple doses and are less reliably protective against late-onset VKDB than a single IM dose — confirm local policy.
- Very low birth weight or unwell infants may receive the dose IV instead of IM per neonatal unit protocol, and preterm infants may need additional considerations beyond this birth-weight threshold.
- Parental refusal of vitamin K should prompt clear counselling on the specific risk of VKDB, since this is a rare but potentially fatal and largely preventable condition.
Frequently asked questions
Why do all newborns get a vitamin K injection?
Newborns have low vitamin K stores and immature liver function, putting them at risk of vitamin K deficiency bleeding (VKDB), including serious bleeding into the brain — a single IM dose at birth reliably prevents this.
Why is the dose lower for very small babies?
Infants under 1.5 kg birth weight receive a lower fixed dose (0.5 mg instead of 1 mg) appropriate to their smaller size, while still providing adequate protection against vitamin K deficiency bleeding.
Is oral vitamin K as good as the injection?
Oral regimens exist but require multiple doses over weeks and are considered less reliably protective against late-onset vitamin K deficiency bleeding than a single IM dose — many national guidelines prefer the IM route for this reason.
Can vitamin K be given IV instead of IM?
Yes, particularly in very unwell or very preterm infants, per local neonatal unit protocol — the IV route is considered in specific clinical circumstances rather than routine practice.
References
- American Academy of Pediatrics. Committee on Fetus and Newborn — Vitamin K Prophylaxis in Newborns.
- World Health Organization. Recommendations on Newborn Health.
- British National Formulary for Children (BNFc) — Phytomenadione (Vitamin K).