Grapiprant

Nonsteroidal anti-inflammatory drug (NSAID) Piprant (EP4 receptor antagonist)

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2 mg/kg Once daily (q24h) Duration: Chronic use as needed; typically for osteoarthritis management
Notes: Administer with or without food. Tablets are scored for dose adjustment. Safety and efficacy have been demonstrated for up to 9 months in dogs.

Clinical Indications & Species Uses

General Indications
  • Management of pain and inflammation associated with osteoarthritis in dogs.
Dog (Canine)
  • Management of pain and inflammation associated with osteoarthritis

Pharmacology & Mechanism of Action

Drug Class: Nonsteroidal anti-inflammatory drug (NSAID) | Pharmacological Group: Piprant (EP4 receptor antagonist)

Mechanism of Action: Grapiprant is a selective antagonist of the prostaglandin E2 (PGE2) receptor subtype EP4. By blocking the binding of PGE2 to EP4 receptors, it inhibits downstream signaling pathways that mediate pain, inflammation, and fever. Unlike traditional NSAIDs that inhibit cyclooxygenase (COX) enzymes, grapiprant does not directly inhibit COX-1 or COX-2, thereby sparing the production of cytoprotective prostaglandins in the gastrointestinal tract and those involved in renal homeostasis. This selectivity is believed to reduce the risk of gastrointestinal ulceration and renal adverse effects commonly associated with non-selective NSAIDs.

Pharmacodynamics: Grapiprant exhibits anti-inflammatory, analgesic, and antipyretic effects by selectively antagonizing EP4 receptors. It has a high affinity for the EP4 receptor with minimal binding to other prostanoid receptors. In animal models of osteoarthritis, grapiprant reduces lameness and joint inflammation. Its effect on pain is comparable to that of traditional NSAIDs but with a potentially improved safety profile. The drug does not affect platelet aggregation or renal blood flow to the same extent as COX inhibitors, as these functions are largely mediated by COX-1-derived prostaglandins.

⚡ Pharmacokinetics Summary

Absorption: Grapiprant is rapidly absorbed after oral administration. In dogs, peak plasma concentrations are achieved within 1-2 hours. The oral bioavailability is approximately 70-80% in dogs. Food may slightly delay absorption but does not significantly affect overall exposure.
Distribution: Grapiprant is widely distributed in tissues. The volume of distribution is moderate, and it is highly bound to plasma proteins (approximately 99%). It crosses the blood-brain barrier to a limited extent. Distribution into inflamed joints has been demonstrated, with concentrations in synovial fluid correlating with plasma levels.
Metabolism: Grapiprant is extensively metabolized in the liver, primarily via oxidation and glucuronidation. The major metabolic pathways involve cytochrome P450 enzymes (CYP3A4 and CYP2D6) and UDP-glucuronosyltransferases. Several metabolites have been identified, but they are not pharmacologically active.
Excretion: Grapiprant is eliminated primarily via the biliary route into feces, with a smaller fraction excreted in urine. In dogs, approximately 70% of the dose is recovered in feces and 20% in urine. The elimination half-life in dogs is approximately 8-10 hours.
Half-Life: Dogs: ~8-10 hours; Cats: ~4-6 hours (extrapolated); Horses: ~2-4 hours (extrapolated)
Bioavailability: Oral bioavailability in dogs is approximately 70-80%.
Protein Binding: Approximately 99% bound to plasma proteins, primarily albumin.

Available Formulations & Strengths

Oral Tablet 20 mg, 60 mg, 100 mg (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to grapiprant or any excipients
  • Dogs with known gastrointestinal ulceration or bleeding
  • Dogs with significant renal or hepatic impairment
  • Concurrent use with other NSAIDs or corticosteroids (due to increased risk of adverse effects)
  • Use in breeding, pregnant, or lactating dogs (safety not established)
Warnings & Clinical Precautions:
  • Use with caution in dogs with pre-existing renal, hepatic, or cardiovascular disease.
  • Monitor for signs of gastrointestinal intolerance (vomiting, diarrhea, decreased appetite) during therapy.
  • Not for use in cats, as safety and efficacy have not been established.
  • Do not exceed the recommended dose or duration of therapy.
  • Use with caution in dogs that are dehydrated, hypovolemic, or hypotensive, as renal perfusion may be compromised.
  • Safety in puppies younger than 9 months of age has not been evaluated.
  • May cause a delay in parturition if used in pregnant dogs; avoid use during pregnancy.

Adverse Effects & Reactions

Common:

  • Vomiting
  • Diarrhea
  • Decreased appetite
  • Lethargy

Serious / Severe:

  • Gastrointestinal ulceration or perforation (rare but possible)
  • Renal toxicity (especially in dehydrated or renally impaired dogs)
  • Hepatic toxicity (rare)

Rare:

  • Hypersensitivity reactions (skin rash, facial swelling)
  • Blood dyscrasias (thrombocytopenia, leukopenia)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Other NSAIDs (e.g., carprofen, meloxicam) Additive risk of gastrointestinal ulceration and renal toxicity. High
Corticosteroids (e.g., prednisone) Increased risk of gastrointestinal ulceration and perforation. High
Diuretics (e.g., furosemide) May increase risk of renal toxicity due to volume depletion. Moderate
ACE inhibitors (e.g., enalapril) May reduce renal blood flow and increase risk of renal impairment. Moderate
Anticoagulants (e.g., warfarin) Potential for increased bleeding risk, although grapiprant has minimal effect on platelet function. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea
  • Lethargy
  • Loss of appetite
  • Gastrointestinal bleeding
  • Acute renal failure (in severe cases)

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if ingestion is recent (within 2 hours) and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain hydration and renal perfusion. Monitor renal and hepatic function. Gastrointestinal protectants (e.g., sucralfate, H2 antagonists) may be considered. There is no specific antidote for grapiprant overdose.

Food Animal Withdrawal Times

Not approved for use in food-producing animals. Withdrawal times are not established.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20°C to 25°C (68°F to 77°F); excursions permitted between 15°C and 30°C (59°F and 86°F).

Handling & Special Conditions: Keep in a dry place. Protect from moisture.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved by the FDA for use in dogs for the control of pain and inflammation associated with osteoarthritis (brand name Galliprant).

Extra-Label (Off-Label) Use: In the US, grapiprant is approved for use in dogs only. Extra-label use in other species is permitted under AMDUCA only with a valid veterinarian-client-patient relationship and if no approved animal drug is available. However, safety and efficacy in other species are not established, and use in food animals is prohibited due to lack of withdrawal times.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Grapiprant is a novel NSAID that offers a targeted approach to managing osteoarthritis pain in dogs by selectively blocking the EP4 receptor. It is particularly beneficial for dogs that may be sensitive to traditional NSAIDs due to gastrointestinal or renal concerns. Clinical studies have shown that grapiprant is effective in reducing pain and improving mobility in dogs with osteoarthritis, with a safety profile that appears to be more favorable than that of non-selective NSAIDs. However, it is not a substitute for comprehensive osteoarthritis management, which may include weight management, physical therapy, and other modalities. As with any NSAID, the lowest effective dose should be used for the shortest duration necessary, and dogs should be monitored regularly for adverse effects. Grapiprant should not be used in cats or other species due to lack of safety data. Always follow label instructions and consult with a veterinarian before use.

References & Literature

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