Dinoprost Tromethamine

Prostaglandin F2α analogue Luteolytic agent / Oxytocic

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog SC 0.1-0.25 mg/kg (for luteolysis) Once daily Duration: 2-5 days (for pyometra) or single dose for abortion
Notes: For pyometra, combine with antibiotics. Monitor for side effects.
Cat SC 0.1-0.25 mg/kg Once daily Duration: 2-5 days
Notes: Use with caution in cats; may cause vomiting and diarrhea.
Horse IM 5-10 mg per horse (total dose) Single dose Duration: Single administration
Notes: For estrus synchronization, administer during diestrus. For induction of parturition, use 10 mg IM.
Cattle IM 25 mg (5 mL of 5 mg/mL solution) per cow Single dose Duration: Single administration
Notes: For estrus synchronization, administer during luteal phase. For induction of parturition, use 25 mg IM after 270 days of gestation.
Sheep/Goat IM 5-10 mg per animal Single dose Duration: Single administration
Notes: For estrus synchronization, administer during luteal phase.

Clinical Indications & Species Uses

General Indications
  • Luteolysis in domestic animals
  • Induction of abortion
  • Uterine evacuation
Dog (Canine)
  • Estrus induction (to terminate pregnancy)
  • Treatment of pyometra (in combination with antibiotics)
  • Treatment of open pyometra
  • Induction of abortion (mismating)
Cat (Feline)
  • Estrus induction (to terminate pregnancy)
  • Treatment of pyometra (in combination with antibiotics)
  • Induction of abortion (mismating)
Horse (Equine)
  • Luteolysis for estrus synchronization
  • Induction of parturition (in mares)
  • Treatment of persistent corpus luteum
  • Treatment of endometritis (to promote uterine evacuation)
  • Evacuation of uterine fluid (pyometra, mucometra)
Cattle (Bovine)
  • Estrus synchronization (for timed AI)
  • Treatment of luteal cysts
  • Induction of parturition (in cows)
  • Treatment of pyometra and chronic endometritis
  • Termination of pregnancy (up to 150 days gestation)
  • Expulsion of mummified fetus
Small Ruminants (Sheep / Goat)
  • Estrus synchronization (in sheep and goats)
  • Termination of pregnancy
  • Treatment of pyometra (in goats)

Pharmacology & Mechanism of Action

Drug Class: Prostaglandin F2α analogue | Pharmacological Group: Luteolytic agent / Oxytocic

Mechanism of Action: Dinoprost tromethamine is a naturally occurring prostaglandin F2α (PGF2α) that binds to specific G-protein-coupled receptors on luteal cells, activating phospholipase C and increasing intracellular calcium. This leads to luteolysis (regression of the corpus luteum) in cycling animals, causing a rapid decline in progesterone levels. In the uterus, it stimulates myometrial contractions, facilitating expulsion of uterine contents. It also causes contraction of smooth muscle in other tissues, including the bronchial tree and gastrointestinal tract.

Pharmacodynamics: The primary pharmacodynamic effect is luteolysis, which is essential for synchronizing estrus and terminating pregnancy. In cattle, a single dose induces luteolysis within 24-48 hours, with estrus occurring 2-5 days later. It also increases uterine tone and motility, which is useful in treating pyometra and retained fetal membranes. In mares, it causes luteolysis and uterine evacuation, and can induce parturition. The drug also has a direct stimulatory effect on the myometrium, which is dose-dependent.

⚡ Pharmacokinetics Summary

Absorption: After intramuscular or subcutaneous injection, dinoprost is rapidly absorbed, with peak plasma concentrations occurring within 30-60 minutes. Oral absorption is poor and erratic; therefore, parenteral routes are used.
Distribution: The drug is widely distributed in body tissues, with highest concentrations in the liver, kidneys, and reproductive organs. It crosses the placenta to a limited extent. Protein binding is low (approximately 40-50%).
Metabolism: Dinoprost is rapidly metabolized in the lungs, liver, and kidneys via oxidation and reduction pathways. The primary metabolite is 15-keto-13,14-dihydro-PGF2α, which is biologically inactive.
Excretion: Metabolites are excreted primarily in the urine (about 70-90%) and feces (10-30%). In lactating animals, small amounts may be excreted in milk.
Half-Life: The plasma half-life is very short, approximately 1-3 minutes in most species, due to rapid metabolism. However, the luteolytic effect persists for several days.
Bioavailability: Intramuscular and subcutaneous routes have high bioavailability (near 100%). Oral bioavailability is negligible.
Protein Binding: Approximately 40-50% bound to plasma proteins.

Available Formulations & Strengths

Injectable Solution 5 mg/mL (as tromethamine salt) (IM, SC)

Contraindications & Clinical Warnings

Contraindications:
  • Do not use in pregnant animals unless termination of pregnancy is intended.
  • Do not use in animals with acute or chronic respiratory disease (may cause bronchoconstriction).
  • Do not use in animals with cardiovascular disease (may cause hypotension).
  • Do not use in animals with gastrointestinal ulceration or inflammatory bowel disease.
  • Do not use in animals with hypersensitivity to prostaglandins.
  • Do not use in animals with uterine rupture or obstruction.
Warnings & Clinical Precautions:
  • Use with caution in animals with asthma or other respiratory conditions.
  • Use with caution in animals with hepatic or renal impairment.
  • Use with caution in animals with hypertension or cardiovascular disease.
  • In food animals, observe withdrawal times.
  • Avoid accidental self-injection; may cause bronchospasm in humans.
  • Pregnant women and asthmatics should handle with care.
  • Do not administer intravenously.
  • May cause transient hyperthermia and increased heart rate.

Adverse Effects & Reactions

Common:

  • Salivation
  • Vomiting
  • Diarrhea
  • Abdominal cramping
  • Mild pyrexia
  • Tachycardia
  • Restlessness
  • Sweating (in horses)

Serious / Severe:

  • Bronchospasm
  • Hypotension
  • Uterine rupture
  • Anaphylaxis
  • Cardiovascular collapse

Rare:

  • Local injection site reactions
  • Seizures
  • Pulmonary edema

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Oxytocin Additive uterine contraction; may increase risk of uterine rupture. High
Nonsteroidal anti-inflammatory drugs (NSAIDs) May reduce the luteolytic effect of dinoprost by inhibiting prostaglandin synthesis. Moderate
Corticosteroids May have additive effects on induction of parturition. Moderate
Anticholinergics May reduce gastrointestinal side effects but may also affect uterine motility. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe vomiting
  • Diarrhea
  • Abdominal pain
  • Tachycardia
  • Hypotension
  • Bronchospasm
  • Respiratory distress
  • Hyperthermia

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Administer oxygen, fluids, and bronchodilators if respiratory distress occurs. Monitor cardiovascular status. In severe cases, atropine may be used to manage bradycardia if present, but tachycardia is more common.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days

Dinoprost is not approved for use in animals producing milk for human consumption in some countries; however, when used extra-label, withdrawal times may be extended. Consult local regulations. In the US, no withdrawal period is required for cattle when used according to label, but extra-label use may require extended withdrawal.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 15°C-30°C (59°F-86°F).

Handling & Special Conditions: Protect from freezing. Keep container tightly closed.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in cattle and horses in the US (e.g., Lutalyse).

Extra-Label (Off-Label) Use: In the US, extra-label use is permitted under AMDUCA for food animals, but requires a valid veterinarian-client-patient relationship and extended withdrawal times. In the EU, use in food animals is restricted; check local regulations.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Dinoprost tromethamine is a potent luteolytic agent widely used in veterinary reproductive management. It is essential for estrus synchronization programs in cattle and horses, and for treating pyometra in small animals. The drug should be administered with caution in animals with respiratory or cardiovascular disease. Adverse effects are common but usually transient. In food animals, adherence to withdrawal times is critical. Always confirm pregnancy status before administration to avoid unintended abortion. For pyometra treatment, combine with appropriate antibiotic therapy and monitor for uterine rupture. In horses, it can induce parturition; ensure proper facilities for foaling.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)