What kind of interaction is it?

Caution: an interaction that may reduce efficacy or raise side-effect risk and warrants monitoring.

Is this interaction backed by published research?

Yes. NutriStack lists 2 citation rows for the Ampicillin + Vitamin K2 pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·a caution·Emerging evidence

Ampicillin + Vitamin K2

Q: Can I take Ampicillin and Vitamin K2 together?

Possibly, but with caution. Ampicillin and Vitamin K2 have a documented caution-tier interaction. Broad-spectrum antibiotics such as ampicillin can suppress vitamin K-producing gut bacteria, occasionally lowering vitamin K status. This is most clinically relevant in patients on warfarin, where prolonged antibiotic courses plus poor dietary vitamin K intake can potentiate anticoagulant effect and raise bleeding risk. Vitamin K2 supplementation may stabilize vitamin K status.

Q: How does this affect a NutriStack Stack Score?

-5 to your Stack Score per scored caution row.

Caution Emerging evidence

Broad-spectrum antibiotics such as ampicillin can suppress vitamin K-producing gut bacteria, occasionally lowering vitamin K status. This is most clinically relevant in patients on warfarin, where prolonged antibiotic courses plus poor dietary vitamin K intake can potentiate anticoagulant effect and raise bleeding risk. Vitamin K2 supplementation may stabilize vitamin K status.

Supplement × Prescription

Open the interaction checker → Read the methodology

From the database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, and the recommendation.

Substances

Ampicillin and Vitamin K2

Pair type

Caution

Evidence

Emerging

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

CautionEmerging evidence

What is happening. Broad-spectrum antibiotics such as ampicillin can suppress vitamin K-producing gut bacteria, occasionally lowering vitamin K status. This is most clinically relevant in patients on warfarin, where prolonged antibiotic courses plus poor dietary vitamin K intake can potentiate anticoagulant effect and raise bleeding risk. Vitamin K2 supplementation may stabilize vitamin K status.

Mechanism. Ampicillin reduces gut flora that synthesize menaquinones (vitamin K2), potentially lowering vitamin K-dependent clotting factor activity, especially relevant to warfarin pharmacodynamics.

Recommendation. Routine vitamin K2 supplementation is not required for short ampicillin courses in well-nourished patients. In patients on warfarin or with poor nutritional intake, monitor for signs of vitamin K deficiency (easy bruising, bleeding) and keep vitamin K intake consistent; do not start or stop vitamin K abruptly while on warfarin. Discuss any vitamin K supplement with the prescriber managing anticoagulation.

Stack Score

How it moves the number.

Effect on the composite score

If both Ampicillin and Vitamin K2 are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).

The full algorithm, the clamping rules, and four worked stacks are at /methodology/stack-score.

Sources

Sources, by evidence tier.

Every claim on this page is cited. PMIDs link straight to PubMed.

Reference material

1Conly JM, Stein K. The production of menaquinones (vitamin K2) by intestinal bacteria and their role in maintaining coagulation homeostasis. Prog Food Nutr Sci. 1992.Needs sourceNo link
2Baillargeon J, Holmes HM, Lin YL, et al. Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults. Am J Med. 2012.Needs sourceNo link

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