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PetDosageChart

Lasix (Furosemide) Dosage for Cats

Loop diuretic ⏱ Onset: 30-60 minutes (oral), 5 minutes (injectable) ⏳ Duration: 6-8 hours

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

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Lasix Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 1.5mg 3mg 5.5mg every 8-24 hours (based on severity)
4 lbs (1.8 kg) 2mg 3.5mg 7mg every 8-24 hours (based on severity)
5 lbs (2.3 kg) 2.5mg 4.5mg 9mg every 8-24 hours (based on severity)
6 lbs (2.7 kg) 2.5mg 5.5mg 11mg (12.5mg tablet) every 8-24 hours (based on severity)
7 lbs (3.2 kg) 3mg 6.5mg 13mg (12.5mg tablet) every 8-24 hours (based on severity)
8 lbs (3.6 kg) 3.5mg 7mg 14.5mg (12.5mg tablet) every 8-24 hours (based on severity)
9 lbs (4.1 kg) 4mg 8mg 16.5mg every 8-24 hours (based on severity)
10 lbs (4.5 kg) 4.5mg 9mg 18mg every 8-24 hours (based on severity)
12 lbs (5.4 kg) 5.5mg 11mg (12.5mg tablet) 21.5mg every 8-24 hours (based on severity)
14 lbs (6.3 kg) 6.5mg 12.5mg (12.5mg tablet) 25mg (2 × 12.5mg) every 8-24 hours (based on severity)
16 lbs (7.3 kg) 7.5mg 14.5mg (12.5mg tablet) 29mg every 8-24 hours (based on severity)
18 lbs (8.2 kg) 8mg 16.5mg 33mg every 8-24 hours (based on severity)
20 lbs (9.1 kg) 9mg 18mg 36.5mg (3 × 12.5mg) every 8-24 hours (based on severity)
25 lbs (11.3 kg) 11.5mg (12.5mg tablet) 22.5mg (2 × 12.5mg) 45mg every 8-24 hours (based on severity)

What is Lasix (Furosemide) used for in cats?

congestive heart failure pleural effusion pulmonary edema fluid retention ascites

How to give Lasix to your cat

Give furosemide with food to reduce stomach upset. Ensure fresh water is always available, as this drug causes significant fluid loss through urination. Your cat will urinate much more frequently — this is expected and means the drug is working. Monitor litter box usage closely. Keep the litter box extra clean, as the increased volume can be unpleasant for cats. Your vet will need to check kidney values and electrolytes regularly.

Available Forms

tablet, injectable, liquid

Give with Food?

Yes — give with food

Side effects of Lasix in cats

Common side effects

increased urination
increased thirst
dehydration
electrolyte imbalances (low potassium)

Serious side effects

  • severe dehydration
  • kidney failure (prerenal azotemia)
  • dangerous electrolyte depletion
  • hearing loss (ototoxicity, especially with aminoglycosides)

When to call the vet

Call your vet immediately if your cat shows any of these signs:

  • Rapid or open-mouth breathing (worsening heart failure)
  • Extreme lethargy or collapse
  • No urine production despite medication
  • Severe loss of appetite or vomiting
  • Muscle weakness or twitching (electrolyte imbalance)

Related Medications for Cats

Anticonvulsant / Analgesic

Neurontin

Gabapentin

For pain management

View dosage chart
Antihistamine

Benadryl

Diphenhydramine

For allergies

View dosage chart
NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart
H2 receptor antagonist

Pepcid

Famotidine

For stomach acid reduction

View dosage chart

Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Furosemide.

Frequently Asked Questions

How does furosemide help cats with heart failure?
Furosemide removes excess fluid from the body by causing the kidneys to excrete more sodium and water. In cats with congestive heart failure, fluid accumulates in the lungs (pulmonary edema) or chest cavity (pleural effusion), making it difficult to breathe. Furosemide is the cornerstone emergency treatment to relieve this fluid buildup and improve breathing.
Will my cat pee a lot on furosemide?
Yes, significantly increased urination is the expected and desired effect. Your cat may need to use the litter box much more frequently. Keep the litter box accessible and clean, and always provide unlimited fresh water to prevent dehydration. This is a sign the medication is working correctly.
Can furosemide damage my cat's kidneys?
Yes, furosemide can worsen kidney function, especially in cats with pre-existing chronic kidney disease (common in senior cats). It causes fluid loss that reduces blood flow to the kidneys. Your vet will balance the need for fluid removal (to help the heart) against the impact on the kidneys through careful dose adjustments and regular blood work.
How long can a cat live on furosemide?
Many cats with heart failure live months to years on furosemide combined with other cardiac medications. Survival depends on the underlying heart condition, response to treatment, and any concurrent diseases like kidney disease. Regular veterinary monitoring every 1-3 months is essential for long-term management.
What happens if I give too much furosemide to my cat?
Overdose can cause severe dehydration, electrolyte depletion (especially dangerously low potassium), kidney failure, and collapse. Signs include extreme lethargy, weakness, loss of appetite, and reduced or no urination. This is a medical emergency — contact your vet immediately if you suspect an overdose.

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