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Morphine Sulfate

Opioid Analgesic (Full Agonist)
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
3 available
Interactions
7 documented
Formulations
4

Mechanism of action

Prototype full mu-opioid receptor agonist providing potent analgesia, sedation, and euphoria. Metabolized to active morphine-6-glucuronide (analgesic) and morphine-3-glucuronide (neuroexcitatory, poorly analgesic). Variable histamine release on IV bolus.

At a glance

Class
Opioid Analgesic (Full Agonist)
Schedule
Controlled Substance
Storage
Store at room temperature, protect from light; controlled substance secure storage required

Dosing

🐕

Dog

Standard full opioid for moderate-severe pain
Dose
0.1–0.5 mg/kg
Route
IV (slowly), IM, SQ, Epidural
Frequency
q2–4h (intermittent); continuous (CRI)
🐈

Cat

Effective in cats
Dose
0.1–0.2 mg/kg
Route
IM, SQ, Epidural, IV (with caution)
Frequency
q3–4h (intermittent); continuous (CRI)

Formulations

💊

Other — 4

Strength
—
Strength
—
Strength
—
Strength
—

Storage

Store at room temperature, protect from light; controlled substance secure storage required

Safety

Monitoring parameters

Respiratory rateSpO2Pain scoresBlood pressureLevel of sedationGI motility

Interactions

Major — 2

Buprenorphine
major
Buprenorphine is a partial mu-agonist with very high receptor binding affinity. It occupies mu-receptors and prevents full agonists from achieving full analgesic potential.
Management: Do not combine. Allow 4-6h for buprenorphine dissociation before giving full mu-agonist. If rescue needed on buprenorphine, use non-opioid (NSAID, ketamine CRI).
Naltrexone
major
Naltrexone is a long-acting competitive opioid antagonist (10-13h oral). Completely blocks morphine's analgesic, sedative, and respiratory effects.
Management: Stop naltrexone minimum 72h before anticipated opioid analgesia is needed (e.g., surgery). If emergency opioid needed while on naltrexone, much higher doses required and response is unpredictable.

Moderate — 5

Maropitant
moderate
Maropitant inhibits CYP enzymes that metabolize some opioids, potentially increasing opioid plasma levels. Also synergistic antiemetic effect (desired).
Management: Antiemetic co-administration is standard practice. Monitor for increased sedation. Clinical significance of PK interaction is modest.
Dexmedetomidine
moderate
Synergistic sedation and analgesia. Dexmedetomidine reduces opioid MAC-sparing by additional 40-60%. Additive bradycardia.
Management: Intended combination — reduce opioid dose by 30-50%. Monitor heart rate. Profound bradycardia may require glycopyrrolate.
Metoclopramide
moderate
Opioids slow GI motility (anti-prokinetic). Metoclopramide stimulates GI motility (prokinetic). Pharmacologically opposing effects.
Management: Metoclopramide antiemetic effect (D2 blockade) is preserved, but prokinetic effect is reduced by concurrent opioids. For prokinetic benefit, may need higher metoclopramide dose.
Diazepam
moderate
Additive CNS and respiratory depression via different mechanisms (mu-opioid vs GABA-A).
Management: Monitor respiratory rate and SpO2. Reduce opioid dose when adding benzodiazepine.
Medetomidine
moderate
Synergistic sedation and analgesia. Additive bradycardia. Standard premedication combination at reduced doses.
Management: Intended combination. Reduce individual doses by 30-50%. Monitor heart rate. Reverse medetomidine with atipamezole when appropriate.

Brands

Other markets

Morphine Sulfate
MS Contin
AVINZA

FAQs

Frequently asked questions

›What is Morphine Sulfate?
Morphine Sulfate is a opioid analgesic (full agonist) used in pets. Prototype full mu-opioid receptor agonist providing potent analgesia, sedation, and euphoria. Metabolized to active morphine-6-glucuronide (analgesic) and morphine-3-glucuronide (neuroexcitatory, poorly analgesic). Variable histamine release on IV bolus.
›What is Morphine Sulfate used for in pets?
Morphine Sulfate is used in veterinary medicine for: Standard full opioid for moderate-severe pain; Effective in cats.
›What is the Morphine Sulfate dose for dogs?
For dogs, Morphine Sulfate is typically dosed as follows — Standard full opioid for moderate-severe pain: 0.1–0.5 mg/kg IV (slowly)/IM/SQ/Epidural q2–4h (intermittent); continuous (CRI). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Morphine Sulfate dose for cats?
For cats, Morphine Sulfate is typically dosed as follows — Effective in cats: 0.1–0.2 mg/kg IM/SQ/Epidural/IV (with caution) q3–4h (intermittent); continuous (CRI). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Morphine Sulfate need a prescription?
Morphine Sulfate is available over the counter. Even so, you should consult your veterinarian before giving any medication to your pet.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Related medicines

Other medicines in the same class (Opioid Analgesic).

Meperidine (Pethidine)
Synthetic mu-opioid receptor agonist approximately 1/10th the potency of morphine. Also has local anesthetic properties (sodium channel blockade) and anticholinergic effects. No histamine release (unlike morphine). Short duration (1–2h).
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