Morphine

Dogs: 0.05–0.4 mg/kg, IV, q 1–4 h; 0.2–1 mg/kg, IM or SC, q 2–6 h; 0.1 mg/kg diluted with 0.9% saline administered epidurally at 0.23 mL/kg, q 8–24 h

Cats: 0.1–0.25 mg/kg, IV, IM, or SC, q 2–4 h

Incremental IV bolus technique: dogs—increments of 0.1 mg/kg until analgesia appears adequate; cats—increments of 0.02 mg/kg. In dogs, this can be followed by CRI at 0.1 mg/kg/h that can be increased incrementally if needed. Rapid IV injections may cause histamine release.

Oxymorphone/hydromorphone

Dogs: 0.02–0.1 mg/kg, IV, q 2–4 h; 0.05–0.2 mg/kg, IM or SC, q 2–6 h

Minimal cardiovascular effects; may cause panting or emesis

Cats: 0.02–0.05 mg/kg, IV, q 2–4 h; 0.05–0.1 mg/kg, IM or SC, q 2–6 h

Can be given as a CRI with the dose divided over 4 hours

Fentanyl

Dogs: 2–10 mcg/kg, IV, q 30–60 min; 2–20 mcg/kg/h, IV as a CRI

With short half-life, fentanyl is best administered as a CRI.

Fentanyl transdermal patch

12.5 mcg/h for animals < 2.5 kg body wt; 25 mcg/h for animals 2.5–10 kg body wt; 50 mcg/h for animals 10–20 kg body wt; 75 mcg/h for animals 20–30 kg body wt; 100 mcg/h for animals >30 kg body wt

The patches cannot be cut. More than one patch may be used in larger animals. Injectable repository fentanyl solutions may be an alternative if available.

Butorphanol

Dogs: 0.2–0.5 mg/kg, IM, IV, or SC, q 1–3 h

Has a ceiling effect; short duration of effect (1–2 h) in most dogs

Cats: 0.1–0.4 mg/kg, IM, IV, or SC, q 1–6 h

Can be given as a CRI with the dose divided over 4 hours

Buprenorphine

Dogs: 0.005–0.02 mg/kg, IM or IV, q 1–6 h

May be more difficult to reverse

Cats: 0.005–0.01 mg/kg, IM, IV, or sublingual, q 4–8 h

Sublingual absorption reported to be excellent in cats

Methadone

0.1–0.5 mg/kg, IV, IM, or SC, q 4–6 h

Less vomiting than morphine, less panting than hydromorphone