Short answer: Menadione (vitamin K3, usually labeled menadione sodium bisulfite complex or MSBC) is a synthetic vitamin K source used by the pet food industry to meet AAFCO vitamin K nutrient requirements. The FDA's regulatory approval for MSBC explicitly covers poultry feed only; an AAFCO 2021 expert panel recommended extending approval to all-species pet food but no FDA rulemaking followed. The substance is banned in over-the-counter human multivitamins because of historical hemolytic-anemia case reports.

What menadione is and why it is added

Vitamin K is a fat-soluble cofactor required for blood clotting (it activates several clotting factors via gamma-carboxylation) and bone metabolism. Three forms exist: K1 (phylloquinone, the form in leafy greens), K2 (menaquinone, the form in fermented foods and animal liver), and K3 (menadione, a synthetic naphthoquinone). Dogs can synthesize functional K2 from K3 via gut bacterial metabolism and hepatic conversion, which is why the synthetic form is nutritionally adequate at AAFCO-required doses.

Per the National Research Council Nutrient Requirements of Dogs and Cats (NRC, 2006), the recommended adult dog vitamin K intake is approximately 22 micrograms per kilogram of body weight per day, doubling for growing puppies. AAFCO Dog Food Nutrient Profiles do not list a separate vitamin K minimum because dogs can synthesize K2 endogenously and a clinical deficiency is rare absent antibiotic-induced gut sterilization or coumarin (rodenticide) exposure. When K is added to pet food, it is added as MSBC at typical levels of 1 mg/kg dry matter.

The poultry-only approval and the AAFCO 2021 panel

This is the regulatory peculiarity that sets menadione apart from most pet food ingredients. Per US 21 CFR 573, FDA-approved feed additives are tied to specific intended uses. Menadione sodium bisulfite complex is approved by FDA only for poultry feed. The pet food industry's use of MSBC in dog and cat food does not have a corresponding FDA approval; it operates under AAFCO's ingredient definition framework, which states feed control officials may treat the ingredient as suitable based on long-standing industry use.

In 2021, AAFCO convened an expert panel to address this disconnect. The panel reviewed the scientific literature and concluded that MSBC may be used as a safe and suitable source of vitamin K activity in food for all animal species. Per the AAFCO Official Publication and follow-up communications, the recommendation was forwarded to FDA. As of 2024, no formal FDA regulation has codified the all-species expansion. The result: most US pet food using MSBC is technically using an ingredient outside the FDA's explicit-use approval scope, but inside the AAFCO industry consensus.

Why menadione is banned in human OTC multivitamins

The FDA prohibits menadione in over-the-counter human multivitamin products. The basis is a series of case reports from the 1950s-60s documenting hemolytic anemia, hyperbilirubinemia, and kernicterus in newborns who received high-dose menadione injections. The doses involved (typically 5-10 mg parenteral) were one to two orders of magnitude above modern dietary recommendations. Subsequent reformulation work led to the development of the bisulfite complex (which is more water-soluble and lower-toxicity than free menadione) and replacement of menadione in human pediatric and adult vitamin K supplements with phylloquinone (K1).

The pet food regulatory framework treats the case-report toxicity as a high-dose phenomenon, not a low-dose one, and per NRC 2006 finds tolerance margins exceeding 1,000-fold over expected dietary intake. The human OTC ban does not legally bind pet food formulation; it does color the consumer-perception question.

How menadione appears on dog food labels

Per AAFCO ingredient declaration rules, menadione is declared by its full chemical name. The most-common label entries are:

  • menadione sodium bisulfite complex — the dominant form; bisulfite improves stability and reduces free-menadione exposure
  • menadione dimethylpyrimidinol bisulfite — an alternative complex sometimes used in higher-end formulations
  • menadione nicotinamide bisulfite — a less-common third complex
  • vitamin K3 or simply “source of vitamin K activity” in marketing copy (the technical declaration on the actual ingredient line will be one of the above)

If the bag does not declare any of these and the ingredient list includes liver, kidney, or generous portions of dark leafy material (alfalfa, kale, spinach, parsley), the food is meeting vitamin K requirements through natural K1 and K2 background. This is rare in dry kibble where micronutrient density per gram is low; common in fresh and freeze-dried diets.

What KibbleIQ does with this

The KibbleIQ Dry Kibble Rubric v15 does not deduct for menadione. Our rationale: the ingredient is industry-standard, AAFCO-supported via the 2021 expert panel, and at typical doses far below adverse-event thresholds. We do not credit foods that omit menadione either — those foods either rely on natural K1/K2 background (which is fine) or are subclinically marginal on vitamin K (which is also fine because dogs synthesize K2 from K3 endogenously). The menadione question is most usefully understood as an indicator question: brands that highlight “menadione-free” on their marketing typically also avoid synthetic preservatives, artificial dyes, and other ingredients we do penalize. The correlation matters more than menadione itself.

Want to check your current bag for menadione and the related synthetic preservatives? Paste the ingredient list into the KibbleIQ analyzer. For more on the synthetic-additive landscape in pet food, see our explainers on BHA and BHT and ethoxyquin, plus our best dog food overall guide.