Misoprostol

Prostaglandin E1 analog Gastroprotective agent; Abortifacient; Cervical ripening agent

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2-5 mcg/kg q8-12h Duration: As long as NSAID therapy continues; for ulcer treatment, 2-4 weeks
Notes: For ulcer prevention, administer with food. For abortion, higher doses (5-10 mcg/kg) may be used, but use with caution.
Cat PO 2-5 mcg/kg q8-12h Duration: As long as NSAID therapy continues; for ulcer treatment, 2-4 weeks
Notes: Use with caution; may cause vomiting. For abortion, doses up to 10 mcg/kg have been used.
Horse PO 2-4 mcg/kg q12h Duration: For ulcer treatment, 2-4 weeks
Notes: For induction of parturition, use 1-2 mg intravaginally (off-label).
Cattle PO 2-5 mcg/kg q12h Duration: For ulcer treatment, 2-4 weeks
Notes: For induction of parturition, use 1-2 mg intravaginally (off-label).
Small Ruminants (sheep/goats) PO 2-5 mcg/kg q12h Duration: For ulcer treatment, 2-4 weeks
Notes: For induction of parturition, use 1-2 mg intravaginally (off-label).
Rabbit PO 0.1-0.2 mg/kg q8-12h Duration: As long as NSAID therapy continues
Notes: Use with caution; may cause diarrhea.
Bird/Poultry Not applicable Not established Not applicable Duration: Not applicable
Notes: Not commonly used; no established dosage.
Exotic/Other (ferrets) PO 2-5 mcg/kg q8-12h Duration: As long as NSAID therapy continues
Notes: Use with caution; may cause gastrointestinal upset.

Clinical Indications & Species Uses

General Indications
  • Gastroprotective agent for NSAID therapy
  • Induction of abortion or labor
  • Cervical ripening
Dog (Canine)
  • Prevention and treatment of gastric ulcers induced by NSAIDs (e.g., carprofen, meloxicam)
  • Treatment of gastric ulceration and gastritis
  • Induction of abortion (in pregnant bitches)
  • Cervical ripening and induction of labor (off-label)
  • Treatment of retained placenta (off-label)
Cat (Feline)
  • Prevention of NSAID-induced gastric ulcers (off-label)
  • Treatment of gastric ulcers (off-label)
  • Induction of abortion (off-label)
Horse (Equine)
  • Treatment of gastric ulcers (off-label)
  • Induction of parturition (off-label)
  • Cervical ripening (off-label)
Cattle (Bovine)
  • Induction of parturition (off-label)
  • Treatment of retained placenta (off-label)
  • Cervical ripening (off-label)
Small Ruminants (Sheep / Goat)
  • Induction of parturition (off-label)
  • Cervical ripening (off-label)
Rabbit & Small Mammals
  • Prevention of NSAID-induced gastric ulcers (off-label)
  • Treatment of gastric ulcers (off-label)
Exotic & Other Species
  • Gastric ulcer prevention in ferrets (off-label)
  • Induction of abortion in exotic species (off-label)

Pharmacology & Mechanism of Action

Drug Class: Prostaglandin E1 analog | Pharmacological Group: Gastroprotective agent; Abortifacient; Cervical ripening agent

Mechanism of Action: Misoprostol is a synthetic analog of prostaglandin E1 (PGE1). It binds to prostaglandin EP receptors (EP2, EP3, EP4) on parietal cells, inhibiting the adenylate cyclase pathway, thereby reducing basal and stimulated gastric acid secretion. Additionally, it stimulates mucus and bicarbonate secretion, increases mucosal blood flow, and enhances mucosal cell integrity, providing cytoprotection. In reproductive tissues, it causes uterine contractions, cervical ripening, and myometrial stimulation, which can induce abortion or labor. It also has vasodilatory effects and may affect smooth muscle tone.

Pharmacodynamics: Misoprostol exhibits dose-dependent inhibition of gastric acid secretion, with effects lasting up to 3 hours after oral administration. It also increases gastric mucus and bicarbonate production, and promotes mucosal healing. In the uterus, it induces strong myometrial contractions, especially in pregnant animals, and causes cervical softening and dilation. It may also have bronchodilatory and vasodilatory effects. The drug's effects on gastric mucosa are more pronounced at lower doses, while higher doses are used for reproductive indications.

⚑ Pharmacokinetics Summary

Absorption: Misoprostol is rapidly and extensively absorbed after oral administration. It undergoes rapid de-esterification to its active metabolite, misoprostol acid. Peak plasma concentrations of misoprostol acid occur within 30 minutes to 1 hour. Food may delay absorption but does not significantly reduce total bioavailability.
Distribution: Misoprostol acid is widely distributed in tissues. It crosses the placenta and is distributed into milk. Protein binding is approximately 80-90%, primarily to albumin. Volume of distribution is not well characterized in veterinary species.
Metabolism: Misoprostol is rapidly de-esterified to misoprostol acid (active form) in the liver and gastrointestinal tract. The acid is further metabolized by beta-oxidation and reduction to inactive metabolites. No significant cytochrome P450 involvement.
Excretion: Metabolites are primarily excreted in urine (about 80%) and feces (about 15%). The elimination half-life of misoprostol acid is short, approximately 20-40 minutes in humans, but may vary in animals. In dogs, the half-life is approximately 30 minutes.
Half-Life: Approximately 20-40 minutes (active metabolite) in humans; in dogs, about 30 minutes; in other species, not well documented.
Bioavailability: Oral bioavailability of misoprostol acid is about 80% (as measured by AUC) after oral administration, but food reduces peak concentrations.
Protein Binding: 80-90% (misoprostol acid) bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 100 mcg, 200 mcg (PO)
Vaginal Tablet (for reproductive use) 25 mcg, 100 mcg, 200 mcg (Intravaginal)
Oral Solution (compounded) Various (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Pregnancy (when used for gastroprotection, as it can cause abortion)
  • Hypersensitivity to misoprostol or other prostaglandins
  • Patients with cardiovascular disease (hypotension, arrhythmias)
  • Patients with inflammatory bowel disease (may exacerbate diarrhea)
  • Patients with a history of uterine rupture or previous cesarean section (for reproductive use)
Warnings & Clinical Precautions:
  • Use with caution in animals with renal or hepatic impairment.
  • May cause diarrhea, especially at higher doses; ensure adequate hydration.
  • In pregnant animals, use only for induction of abortion or parturition when intended.
  • Wear gloves when handling tablets, especially if pregnant (transdermal absorption can cause abortion).
  • Do not use in animals with a history of gastrointestinal bleeding.
  • Use with caution in animals with hypotension or cardiovascular instability.
  • For reproductive use, monitor uterine contractions and fetal viability.
  • In food animals, observe withdrawal times; extra-label use requires veterinary oversight.

Adverse Effects & Reactions

Common:

  • Diarrhea
  • Vomiting
  • Abdominal pain
  • Flatulence
  • Nausea (in humans; may be inferred in animals)

Serious / Severe:

  • Uterine rupture (when used for abortion/parturition)
  • Severe hypotension
  • Cardiac arrhythmias
  • Hyperthermia
  • Seizures (rare)

Rare:

  • Allergic reactions (urticaria, angioedema)
  • Bronchospasm
  • Hepatotoxicity
  • Renal failure

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
NSAIDs (e.g., carprofen, meloxicam, flunixin) Misoprostol reduces NSAID-induced gastric ulcers; no negative interaction, but may reduce NSAID absorption if given concurrently. Mild
Antacids (magnesium-containing) May worsen diarrhea; separate administration times. Mild
Oxytocin Additive uterine stimulatory effects; risk of uterine rupture. High
Corticosteroids May increase risk of gastrointestinal ulceration; misoprostol may be used to counteract, but monitor. Moderate
Prostaglandins (e.g., dinoprost) Additive effects on uterine contraction; risk of hyperstimulation. High

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe diarrhea
  • Vomiting
  • Abdominal cramps
  • Hypotension
  • Tachycardia
  • Hyperthermia
  • Uterine hyperstimulation (if pregnant)
  • Respiratory depression (in severe cases)

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide fluid therapy for dehydration and electrolyte imbalances. Monitor cardiovascular status and treat hypotension with IV fluids and vasopressors if needed. Control hyperthermia with cooling measures. For uterine hyperstimulation, administer tocolytics (e.g., terbutaline) if necessary. There is no specific antidote.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Misoprostol is not approved for food animals; extra-label use requires extended withdrawal times. Consult FARAD for specific recommendations. In general, a withdrawal time of at least 7 days for meat and 72 hours for milk is suggested, but must be based on regulatory guidance.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25Β°C, 68-77Β°F). Protect from moisture.

Handling & Special Conditions: Keep in original container, tightly closed. Do not handle tablets without gloves if pregnant.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use (Cytotec) for prevention of NSAID-induced gastric ulcers.

Extra-Label (Off-Label) Use: Misoprostol is not FDA-approved for veterinary use in most species. Use in animals is extra-label and requires a valid veterinarian-client-patient relationship (VCPR) under AMDUCA. For food animals, extra-label use is prohibited unless a withdrawal time is established and followed. Misoprostol is a prostaglandin analog and may be subject to state regulations.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Misoprostol is primarily used in veterinary medicine for the prevention and treatment of NSAID-induced gastric ulcers, especially in dogs. It is also used off-label for reproductive purposes such as induction of abortion, cervical ripening, and treatment of retained placenta. The drug is generally well-tolerated, but diarrhea is a common dose-limiting side effect. For gastroprotection, it is often administered concurrently with NSAIDs. For reproductive use, it should be used with extreme caution due to the risk of uterine rupture. In food animals, extra-label use is limited and requires careful withdrawal time management. Always wear gloves when handling the drug to prevent accidental absorption in pregnant personnel. Monitor animals for adverse effects, especially when using higher doses.

References & Literature

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