# N-Acetylcysteine (NAC): veterinary dose and monograph

> N-Acetylcysteine (NAC) is a veterinary drug. A glutathione precursor with two main veterinary roles: (1) the specific ANTIDOTE for paracetamol (acetaminophen) toxicosis — critical in cats — and for other oxidative injuries (e.g. Indications include paracetamol (acetaminophen) toxicosis — antidote (dogs and especially cats); oxidative haemolysis / methaemoglobinaemia support (e.g. acetaminophen, certain toxins); acute hepatic injury / hepatoprotection (adjunct). This monograph lists 5 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/n-acetylcysteine · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** NAC, Acetylcysteine, Mucomyst, Mucinac, Fluimucil
- **Species with doses:** Dogs, Cats and Horses
- **General dose range:** 70–140 mg/kg IV loading then q6h (antidote) — check the species tables for the indication
- **Routes:** IV, Inhaled, Rectal
- **Last reviewed:** 1 October 2026

## Indications

- Paracetamol (acetaminophen) toxicosis — antidote (dogs and especially cats)
- Oxidative haemolysis / methaemoglobinaemia support (e.g. acetaminophen, certain toxins)
- Acute hepatic injury / hepatoprotection (adjunct)
- Mucolytic for thick airway secretions (nebulised)
- Melting (collagenase) corneal ulcers — topical anticollagenase

## N-Acetylcysteine (NAC) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*N-Acetylcysteine (NAC) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Paracetamol toxicosis / hepatoprotection | 70–140 mg/kg | IV | load, then q4–6h | — |
| Mucolytic (nebulised) | No nebulisation dose in Papich 5e or Plumb’s 10e — follow a specialist protocol | Inhaled | — | — |

- Paracetamol toxicosis / hepatoprotection: Plumb’s p.31: 140 mg/kg PO or IV (diluted to 5%) then 70 mg/kg q6h for 7 treatments (Wismer; Grauer); xylitol hepatotoxicity 140–280 mg/kg load then 70 mg/kg four times daily (Talcott 2008); phenol toxicity 140 mg/kg then 50 mg/kg q4h for 3 days. Papich 5e: 140 mg/kg then 70 mg/kg q4h for five doses; contrast nephropathy prevention 17 mg/kg IV then q12h for 48 h.
- Mucolytic (nebulised): Plumb’s 10e p.12 notes acetylcysteine has been used as an inhaled mucolytic but its Dosages section gives no nebulisation dose, and nebulisation has caused hypersensitivity and bronchospasm. It can cause hypersensitivity and bronchospasm in the airway — pre-treat with a bronchodilator. Use non-reactive (plastic/glass) nebuliser parts.

### Cats

*N-Acetylcysteine (NAC) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Paracetamol toxicosis (antidote) | 140 mg/kg | IV | loading once, then 70 mg/kg q6h | — |
| Hepatic lipidosis (adjunct) | 70–140 mg/kg | IV | 140 mg/kg over 20 min, then 70 mg/kg q12h | — |

- Paracetamol toxicosis (antidote): Plumb’s p.31 (Wismer 2006): loading 140 mg/kg PO or slowly IV (diluted to 5%, over 15–20 min), then 70 mg/kg q6h for 7 treatments; 280 mg/kg load and 12–17 doses after massive ingestion. Papich 5e: 140 mg/kg then 70 mg/kg q4h IV or PO for five doses. Wait 2–3 h after activated charcoal before oral NAC. Add ascorbic acid/SAMe; treat methaemoglobinaemia.
- Hepatic lipidosis (adjunct): Plumb’s p.31 (Center 2006): dilute the 10% solution 1:4 with saline and give through a 0.25 µm filter; correct hypokalaemia and hypophosphataemia; watch for refeeding syndrome.

### Horses

*N-Acetylcysteine (NAC) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Meconium retention (foal retention enema) | 4% retention enema for meconium retention | Rectal | per protocol | — |

- Meconium retention (foal retention enema): Plumb’s p.31: with the foal in lateral recumbency, infuse 100–200 mL of 4% acetylcysteine by gravity through a 30 Fr Foley (30 mL bulb) and retain for 30–45 min (Pusterla 2003); or 8 g with 20 g sodium bicarbonate in 200 mL water as an enema to effect (Freeman 1999). Guttural pouch chondroids: instil 20% solution.

## Contraindications

Known hypersensitivity (rare anaphylactoid reactions, especially rapid IV). Caution nebulising in bronchospastic patients (can provoke bronchospasm — pre-treat with a bronchodilator). For IV use, dilute and infuse slowly. Active GI haemorrhage (oral, minor concern).

## Species-specific warnings

> **Caution:** Cats: Cats poisoned by paracetamol need NAC urgently — it is lifesaving. Combine with supportive care (oxygen, ascorbic acid/SAMe); avoid delays.

## Adverse effects

- Anaphylactoid reaction (flushing, urticaria, bronchospasm) — especially rapid IV
- Nausea/vomiting (oral, unpleasant sulphur taste/smell)
- Bronchospasm on nebulisation
- Local irritation

## Drug interactions

- Activated charcoal: can adsorb oral NAC — separate dosing or prefer IV NAC after charcoal
- Oxidising drugs/agents: NAC counteracts oxidative effects (the basis of its antidotal use)
- Nitroglycerin: potentiated vasodilation/hypotension (theoretical)

## Pregnancy and lactation

Considered acceptable when needed as an antidote/hepatoprotectant; benefits in serious toxicosis outweigh limited risk data.

## Monitoring

- In paracetamol toxicosis: mucous-membrane colour/methaemoglobin, PCV (Heinz-body anaemia), liver enzymes
- Infusion reactions during IV administration (slow the rate)
- Respiratory status if nebulising (bronchospasm)
- Response of the underlying condition (hepatic values, secretions, corneal ulcer)

## Toxicity and overdose

Very wide safety margin. The main adverse events are anaphylactoid reactions with rapid IV infusion (dose-rate dependent — slow the infusion) and GI upset/vomiting from the oral sulphur taste. True overdose toxicity is uncommon.

Management: Slow or stop the infusion for anaphylactoid reactions and treat with antihistamine ± corticosteroid (and epinephrine if severe); they are usually rate-related and resolve on slowing. Otherwise supportive care; no specific antidote needed.

## Clinical pearls

- Keep NAC stocked: it is THE antidote for paracetamol poisoning — and feline paracetamol toxicosis is a true emergency where minutes matter
- Give the loading dose then q6h; the earlier it starts, the more liver/red-cell injury it prevents
- Dilute and infuse IV slowly to avoid anaphylactoid reactions
- As a mucolytic, always pre-treat with a bronchodilator before nebulising — NAC itself can trigger bronchospasm
- A handy adjunct hepatoprotectant in acute liver injury and an anticollagenase for melting corneal ulcers

## Mechanism of action

Supplies cysteine to replenish hepatic glutathione, the cofactor needed to detoxify the reactive paracetamol metabolite NAPQI — neutralising the toxin and protecting liver and red cells from oxidative injury; it also acts as a direct antioxidant/free-radical scavenger. As a mucolytic, its free sulphydryl group cleaves the disulphide bonds that cross-link mucus glycoproteins, thinning secretions; topically it inhibits matrix metalloproteinases (collagenase) in melting corneal ulcers.

## Formulations and products

- Injection 200 mg/mL (20 %)
- Effervescent/oral sachet 200 / 600 mg
- Nebuliser/respiratory solution 100–200 mg/mL
- Mucinac — 200 / 600 mg effervescent; 200 mg/mL injection, Effervescent / injection (human-label)
- Fluimucil — 200 mg/mL injection; sachets, Injection / sachet (human-label)

## Storage

Vials/ampoules: 15–30 °C; once opened, refrigerate and use within ~24–96 h per product (may discolour slightly — usually still usable). Sachets: dry, 15–30 °C.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of N-Acetylcysteine (NAC) for dogs?

Reference doses for N-Acetylcysteine (NAC) in dogs: 70–140 mg/kg IV load, then q4–6h (Paracetamol toxicosis / hepatoprotection); No nebulisation dose in Papich 5e or Plumb’s 10e — follow a specialist protocol Inhaled — (Mucolytic (nebulised)). Confirm against the label and the patient before use.

### What is the dose of N-Acetylcysteine (NAC) for cats?

Reference doses for N-Acetylcysteine (NAC) in cats: 140 mg/kg IV loading once, then 70 mg/kg q6h (Paracetamol toxicosis (antidote)); 70–140 mg/kg IV 140 mg/kg over 20 min, then 70 mg/kg q12h (Hepatic lipidosis (adjunct)). Confirm against the label and the patient before use.

### What is the dose of N-Acetylcysteine (NAC) for horses?

Reference doses for N-Acetylcysteine (NAC) in horses: 4% retention enema for meconium retention Rectal per protocol (Meconium retention (foal retention enema)). Confirm against the label and the patient before use.

### When should N-Acetylcysteine (NAC) not be used?

Known hypersensitivity (rare anaphylactoid reactions, especially rapid IV). Caution nebulising in bronchospastic patients (can provoke bronchospasm — pre-treat with a bronchodilator). For IV use, dilute and infuse slowly. Active GI haemorrhage (oral, minor concern).

### What are the side effects of N-Acetylcysteine (NAC) in animals?

Anaphylactoid reaction (flushing, urticaria, bronchospasm) — especially rapid IV; Nausea/vomiting (oral, unpleasant sulphur taste/smell); Bronchospasm on nebulisation; Local irritation.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.