Pharmacology. Nicotinamide (niacinamide, vitamin B3), one of the B vitamins, is required for the functioning of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD and NADP are responsible for energy transfer reactions. Niacin deficiency, which results in pellagra, can be corrected with nicotinamide.
Indications. Nicotinamide is used to prevent the neurologic and endocrinologic toxicity associated with the ingestion of Vacor (PNU), a rodenticide that is believed to act by antagonizing nicotinamide. The best results are achieved when nicotinamide therapy is instituted within 3 hours of ingestion. It may also be effective for treatment of poisoning with Vacor analogs, such as alloxan and streptozocin.
Contraindications. No known contraindications.
Headache and dizziness.
Hepatotoxicity (reported after chronic use with daily dose ≥3 g).
Use in pregnancy. No assigned FDA category. This does not preclude its acute, short-term use in a seriously symptomatic patient (See Introduction in Section III).
Drug or laboratory interactions. No known interactions.
Dosage and method of administration (adults and children). Note: The parenteral preparation is no longer available in the United States. The oral form may be substituted but is of unknown efficacy.
Give 500 mg IV initially, followed by 100–200 mg IV every 4 hours for 48 hours. Then give 100 mg orally 3–5 times daily for 2 weeks. If clinical deterioration from the Vacor progresses during initial therapy with nicotinamide, change the dosing interval to every 2 hours. The maximum suggested daily dose is 3 g.
Note: Nicotinic acid (niacin) is not a substitute for nicotinamide in the treatment of Vacor ingestions.
Parenteral. Niacinamide, 100 mg/mL (not available in the United States).
Oral. Niacinamide, 100- and 500-mg tablets, is available without a prescription. Suggested minimum stocking levels to treat a 100-kg adult for the first 8 hours and 24 hours: niacinamide, first 8 hours: 1 g; first 24 hours: 3 g.