Morphine Sulfate: veterinary dose and monograph

At a glance

Drug class

Analgesic

Also known as

MS Contin, Morphine HCl

Species with doses

Dogs, Cats, Horses, Goats, Sheep, Pigs, Rabbits and Primates

General dose range

0.1–1 mg/kg IM q4–6h (variable) — check the species tables for the indication

Routes

IM, IV, Epidural, SC

Last reviewed

1 October 2026

Indications

• Severe acute pain (post-operative, trauma)
• Pre-anaesthetic medication (with sedative)
• Epidural analgesia (caesarean, hindlimb / pelvic surgery)
• Chronic cancer pain (oral SR formulation)
• Cardiogenic pulmonary oedema (mild analgesia + venodilation)
• Antitussive (low dose)

Morphine Sulfate 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

• Acute pain — IM / SC: Plumb's: 0.1–1 mg/kg IM or SC q4–6h. Start low; titrate.
• Acute pain — slow IV: Plumb's: 0.1–0.5 mg/kg IV slowly (dilute, give over 2 min) — rapid IV causes histamine release / hypotension.
• Epidural (preservative-free): Papich 5e: 0.1 mg/kg epidurally. Plumb’s p.862: 0.1 mg/kg preservative-free, duration 12–24 h (Thomas 2000); 0.1 mg/kg in 0.3 mL/kg (max 6 mL) (Matthews 2008). Preservative-free product preferred. Preservative-free morphine 0.1–0.2 mg/kg epidurally q8h; spinal 0.05 mg/kg (Hansen 2007).
• CRI for severe pain: Papich 5e: load 0.2 mg/kg IV then 0.1 mg/kg/h; for severe pain 0.3 mg/kg then 0.17 mg/kg/h. Plumb’s p.862: 0.05–0.2 mg/kg/h (Grubb; Hansen) — above 0.1 mg/kg/h for more than 12 h sedation and side effects increase, so the rate often has to be reduced.

Cats

• Acute pain — SC / IM: Papich 5e: 0.1–0.2 mg/kg IM, IV or SC q3–6h. Plumb’s p.862: 0.1–0.4 mg/kg IM or SC q3–6h with concomitant tranquilisation (Hendrix & Hansen 2000); 0.2–0.5 mg/kg IM/SC q3–4h (Hansen 2007). Give IV slowly (histamine release).
• CRI: Papich 5e: cats — loading dose 0.2 mg/kg IV, then 0.05–0.1 mg/kg/h IV.
• Epidural: Papich 5e: 0.1 mg/kg diluted in saline to 0.3 mL/kg. Plumb’s p.862 (Hansen 2007): preservative-free 0.1–0.2 mg/kg epidurally q8h.

Horses

• Analgesia — IM: Plumb’s p.862 (Abrahamsen 2007): 0.1 mg/kg IM q4h — limits the effect on GI motility; small doses of acepromazine (0.011–0.022 mg/kg IM) are usually included to cover excitement. Narcotics can mask signs of mild colic. ARCI Class 1.
• Moderate to severe pain (escalating): Papich 5e: start 0.1-0.2 mg/kg IV or IM q6h for mild pain, increasing gradually to 0.5-1 mg/kg for severe pain. Give IV slowly. Morphine can cause excitement in horses - sedate first with an alpha-2 agonist. Watch for reduced GI motility / ileus.
• Light chemical restraint (with a sedative): Papich 5e: 0.3-0.5 mg/kg IV in combination with other sedatives. Never as a sole agent - excitement is likely.
• Epidural analgesia: Plumb’s p.862: 0.1–0.2 mg/kg diluted with saline to 0.04 mL/kg (≈20 mL per 450 kg); onset 20–30 min, analgesia 8–24 h without motor loss. May be combined with detomidine 0.03–0.06 mg/kg (Sellon 2007). Foals: preservative-free 0.1 mg/kg.

Goats

• Analgesia (benefit debated): Papich 5e (ruminants): 0.05–0.1 mg/kg IV, up to 0.4 mg/kg IV, for pain and perioperatively — benefits are controversial. Plumb’s p.862 (Jenkins 1987): sheep and goats up to 10 mg TOTAL IM. Extra-label in a food animal.

Sheep

• Analgesia (benefit debated): Papich 5e (ruminants): 0.05–0.1 mg/kg IV, up to 0.4 mg/kg IV, for pain and perioperatively — benefits are controversial. Plumb’s p.862 (Jenkins 1987): sheep and goats up to 10 mg TOTAL IM. Extra-label in a food animal.

Pigs

• Pre-anaesthetic: Plumb’s p.862: pre-anaesthetic/analgesic 0.2–0.9 mg/kg IM — may cause undesirable stimulation (Booth 1988); analgesia 0.2 mg/kg IM up to 20 mg total (Jenkins 1987).

Rabbits

• Analgesia (rabbits): Plumb's: rabbits need much HIGHER doses than dogs/cats due to fast metabolism — 2–5 mg/kg SC q2–4h.

Primates

• Analgesia (monkeys, marmosets): Carpenter Exotic Animal Formulary 6th ed, Table 13-4 (p.697): monkeys/macaques/baboons 1–2 mg/kg IM/IV q4h; New World monkeys/marmosets/lemurs 1 mg/kg PO/SC/IM/IV q4h; marmosets 0.1–2 mg/kg SC/IM q3–6h. May cause profound respiratory depression — reverse with naloxone.

Contraindications

Severe respiratory depression. Head trauma / increased ICP. Severe hepatic / renal disease. CATS: histamine release with rapid IV — give SC or slow IV diluted. HORSES: causes excitement at high doses — combine with sedative (alpha-2 or acepromazine). Hypothyroidism, adrenocortical insufficiency, biliary tract disease.

Species-specific warnings

Cats: Lower doses than dogs (0.05–0.4 mg/kg). Avoid rapid IV — histamine release. Switch to buprenorphine for home discharge.

Horses: Always combine with alpha-2 sedative or acepromazine — pure morphine excites horses.

Rabbits: Rabbits metabolise morphine fast — need 2–5 mg/kg SC q2–4h. Below 2 mg/kg is ineffective.

Adverse effects

• Respiratory depression (dose-dependent)
• Sedation, dysphoria (cats — at higher doses)
• Bradycardia (vagally-mediated)
• Histamine release with rapid IV — hypotension, urticaria
• GI: nausea / vomiting / decreased motility, constipation
• Urine retention
• Hyperthermia in cats / horses (paradoxical)

Drug interactions

• Other CNS depressants (benzodiazepines, alpha-2 agonists, anaesthetics): additive sedation / respiratory depression — reduce doses 30–50 %
• MAO inhibitors (selegiline): risk of serotonin syndrome
• Tramadol: additive serotonergic risk
• Acepromazine: synergistic sedation — common pre-anaesthetic combo (neuroleptanalgesia)
• Naloxone: REVERSAL agent for respiratory depression

Pregnancy and lactation

Crosses placenta. Used in caesarean section but can depress neonatal respiration — have naloxone available. Excreted in milk. FDA Category C.

Monitoring

• Respiratory rate / SpO2 — most critical parameter
• Heart rate (bradycardia)
• Pain score (Glasgow, UMPS, Colorado) every 2–4 h
• Sedation depth — avoid over-sedation
• GI motility — risk of ileus with prolonged use
• Urine output — opioid-related retention

Toxicity and overdose

Respiratory depression is the chief life-threat. Pinpoint pupils (miosis in dogs; mydriasis in cats). Hypotension (rapid IV). Bradycardia. Coma. Cats: dose carefully — rapid IV causes excitation / dysphoria. Horses: high doses → excitement / locomotor activity; always combine with sedative.

Management: Naloxone 0.01–0.04 mg/kg IV titrated to respiratory effort (not full consciousness — to avoid acute pain crisis). Repeat naloxone q30–60 min as needed (shorter half-life than morphine). Intubation + assisted ventilation. IV fluids for hypotension. Atropine 0.04 mg/kg IV for bradycardia.

Clinical pearls

• Severe post-op pain (orthopaedic, abdominal): 0.5 mg/kg IM q4h or CRI 0.1–0.3 mg/kg/h
• Cesarean section epidural: 0.1 mg/kg preservative-free morphine epidural gives 18–24 h analgesia for both mother and bone-deep abdominal pain
• Cat at home post-op: switch from morphine to buprenorphine 0.02 mg/kg SC q6–8h — same analgesia, no schedule II paperwork
• Horse with severe colic: morphine 0.05–0.1 mg/kg slow IV with detomidine 10 µg/kg IV — synergistic analgesia without excitement
• Rabbits need 5–10× the dog dose — they metabolise morphine fast; doses below 2 mg/kg SC are ineffective
• Always document log entries for controlled-substance dispensing — DEA / state-board requirement

Mechanism of action

Pure mu-opioid receptor agonist with weaker kappa- and delta-receptor activity. Mu-agonism in the spinal cord dorsal horn and supraspinal sites (periaqueductal grey, rostral ventromedial medulla) inhibits ascending nociceptive transmission. Histamine release from mast cells with rapid IV is the source of the hypotension / urticaria. Hepatic glucuronidation (CYP-independent) — cats have slower clearance than dogs.

Formulations and products

• Morphine sulfate 10 mg/mL injection (parenteral)
• Morphine sulfate 15 mg/mL injection (high-strength)
• Morphine sulfate 5 mg tablet (oral)
• Morphine sulfate sustained-release 15 / 30 mg tablet

Storage

Schedule II controlled substance — store in locked cabinet with logbook. 15–25 °C protected from light.

Before you use this dose

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.

Other analgesics

• Gabapentin
• Hydromorphone
• Lidocaine HCl
• Methadone
• Nalbuphine
• Paracetamol (Acetaminophen)
• Pethidine (Meperidine)
• Pregabalin

Frequently asked questions