Acetylcysteine (N-acetylcysteine, NAC)

What is this medication for?

• Acetaminophen toxicity (the antidote); xylitol and phenol liver damage; any glutathione-depleted oxidative liver injury
• Nebulized mucolytic (bronchial secretions); topical ophthalmic (melting corneal ulcers — see appendix); investigational chronic URI anti-inflammatory in cats

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Bronchospasm/hypersensitivity when nebulized (Pulmonary-route risk)
• into a vein rate-related reactions (Infuse slowly)

Worth a phone call to your veterinarian

• Nausea/vomiting (oral), rare hives (Main effects)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: None for antidotal use; hypersensitivity only for pulmonary use
• has or has had: Bronchospastic disease with nebulization; space 2–3 h from activated charcoal (charcoal adsorbs NAC)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Activated charcoal
  • Oxidizing agents

Storage and handling

10%/20% solutions; dilute to 5% in D5W/sterile water for into a vein. Rotten-egg taste — mask with cola/juice or dose via gastric/duodenal tube on empty stomach.

Good to know

• 140 then 70×7 — the NAC protocol number pair to memorize (identical to human medicine); earlier treatment = better outcome, but benefit persists hours post-ingestion.
• Cats are the sentinel species: acetaminophen (even 1 tablet) → NAPQI + methemoglobinemia (limited glucuronidation + saturated sulfation) — NAC + ascorbic acid is the core rescue.
• Charcoal-first sequencing: adsorb the toxin, WAIT 2–3 hours, then NAC (or use into a vein NAC to bypass the interaction).
• Same glutathione logic reuses for xylitol, phenol, and any oxidative hepatic insult — plus nebulized mucolytic and topical ophthalmic lives of the same molecule.