Praziquantel

Anthelmintic Isoquinoline-pyrazine derivative

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 5 mg/kg Single dose Duration: One day
Notes: For tapeworms; repeat in 2-4 weeks for Echinococcus. For Paragonimus: 25 mg/kg q8h for 2 days.
Cat PO 5 mg/kg Single dose Duration: One day
Notes: For tapeworms; for Paragonimus: 25 mg/kg q8h for 2 days.
Horse PO 2.5-5 mg/kg Single dose Duration: One day
Notes: For Anoplocephala perfoliata, use 2.5 mg/kg; for other tapeworms, 5 mg/kg.
Cattle PO 10-20 mg/kg Single dose Duration: One day
Notes: For Moniezia; for Fasciola hepatica (immature), 20 mg/kg.
Sheep/Goat PO 10-20 mg/kg Single dose Duration: One day
Notes: For Moniezia and Dicrocoelium.
Rabbit PO 5-10 mg/kg Single dose Duration: One day
Notes: For tapeworms.
Birds PO 10-20 mg/kg Single dose Duration: One day
Notes: For tapeworms; may repeat in 2 weeks.
Reptiles PO or IM 5-10 mg/kg Single dose Duration: One day
Notes: For tapeworms; may repeat in 2 weeks.

Clinical Indications & Species Uses

General Indications
  • Treatment of cestode and trematode infections in various species
Dog (Canine)
  • Treatment of tapeworm infections (Dipylidium caninum, Taenia spp., Echinococcus spp.)
  • Treatment of fluke infections (Paragonimus kellicotti)
Cat (Feline)
  • Treatment of tapeworm infections (Dipylidium caninum, Taenia taeniaeformis, Echinococcus multilocularis)
  • Treatment of fluke infections (Paragonimus kellicotti)
Horse (Equine)
  • Treatment of tapeworm infections (Anoplocephala perfoliata, Anoplocephala magna, Paranoplocephala mamillana)
Cattle (Bovine)
  • Treatment of tapeworm infections (Moniezia spp.)
  • Treatment of fluke infections (Fasciola hepatica - immature stages)
Small Ruminants (Sheep / Goat)
  • Treatment of tapeworm infections (Moniezia spp.)
  • Treatment of fluke infections (Dicrocoelium dendriticum)
Rabbit & Small Mammals
  • Treatment of tapeworm infections (e.g., Taenia pisiformis)
Avian & Poultry
  • Treatment of tapeworm infections (e.g., Raillietina spp., Davainea proglottina)
Exotic & Other Species
  • Treatment of tapeworm infections in reptiles, amphibians, and small mammals

Pharmacology & Mechanism of Action

Drug Class: Anthelmintic | Pharmacological Group: Isoquinoline-pyrazine derivative

Mechanism of Action: Praziquantel is rapidly absorbed and causes severe spasms and paralysis of the worm's musculature by increasing the permeability of the cell membrane to calcium ions. This leads to tetanic contraction, vacuolization, and disruption of the tegument, exposing the parasite to the host's immune system. The drug is effective against adult and immature stages of susceptible cestodes and trematodes.

Pharmacodynamics: Praziquantel exhibits rapid onset of action, with visible effects on parasites within minutes. It is highly effective against a wide range of cestodes (tapeworms) and trematodes (flukes). The drug's activity is dependent on calcium influx, which is enhanced by the presence of host antibodies. It has minimal effects on mammalian cells due to differences in calcium channel sensitivity.

⚡ Pharmacokinetics Summary

Absorption: Praziquantel is rapidly and almost completely absorbed from the gastrointestinal tract after oral administration. Peak plasma concentrations are reached within 1-2 hours in most species. In ruminants, absorption may be slower due to rumen degradation, but the drug is still effective.
Distribution: Praziquantel is widely distributed throughout the body, including the liver, kidneys, and central nervous system. It crosses the blood-brain barrier and is found in cerebrospinal fluid. It is also excreted in milk and crosses the placenta.
Metabolism: Praziquantel undergoes extensive first-pass metabolism in the liver, primarily by cytochrome P450 enzymes, to form inactive metabolites. The major metabolite is 4-hydroxypraziquantel, which retains some activity but is less potent.
Excretion: Metabolites are excreted primarily in the urine (up to 80%) and the remainder in bile and feces. Biliary excretion leads to enterohepatic circulation, which may prolong the drug's presence in the body.
Half-Life: Dog: 2-3 hours; Cat: 2-3 hours; Horse: 2-4 hours; Cattle: 2-3 hours; Sheep: 2-3 hours; Rabbit: 2-3 hours; Birds: 1-2 hours.
Bioavailability: Oral bioavailability is high in monogastric animals (80-100%) but lower in ruminants (30-50%) due to ruminal degradation. Injectable formulations provide complete bioavailability.
Protein Binding: Approximately 80-85% bound to plasma proteins in most species.

Available Formulations & Strengths

Oral Tablet 34 mg, 50 mg, 100 mg, 200 mg, 300 mg, 600 mg (PO)
Oral Solution/Suspension 100 mg/mL (PO)
Injectable Solution 56.8 mg/mL (for cattle/sheep) (IM or SC)
Topical Spot-On Combination products (e.g., with pyrantel, fenbendazole) (Topical)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to praziquantel or any component of the formulation
  • Do not use in puppies or kittens less than 4 weeks of age (safety not established)
  • Do not use in animals with severe hepatic impairment
  • Do not use in lactating animals if milk is intended for human consumption (unless withdrawal times are observed)
Warnings & Clinical Precautions:
  • Use with caution in debilitated or severely parasitized animals; may cause severe inflammatory reactions due to rapid parasite death
  • In dogs with heavy tapeworm infections, vomiting may occur after treatment; ensure adequate hydration
  • For Echinococcus infections, strict hygiene measures should be taken to prevent human infection
  • In food animals, observe withdrawal times
  • Do not administer intravenously (rapid injection may cause adverse effects)
  • In horses, use with caution in foals under 4 months of age
  • In reptiles, ensure proper temperature and hydration before treatment

Adverse Effects & Reactions

Common:

  • Vomiting
  • Diarrhea
  • Anorexia
  • Drooling
  • Lethargy

Serious / Severe:

  • Allergic reactions (urticaria, anaphylaxis)
  • Hepatotoxicity (rare)
  • Neurological signs (ataxia, seizures) in overdose or sensitive animals

Rare:

  • Bone marrow suppression
  • Hemolytic anemia (in G6PD-deficient animals)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Cimetidine May increase praziquantel plasma concentrations by inhibiting its metabolism Moderate
Dexamethasone May reduce praziquantel concentrations in plasma and CSF, potentially reducing efficacy Moderate
Phenytoin May decrease praziquantel concentrations due to enzyme induction Mild
Rifampin May significantly reduce praziquantel concentrations, leading to treatment failure High
Ivermectin No significant interaction; often used in combination Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Salivation
  • Ataxia
  • Tremors
  • Seizures
  • Respiratory depression
  • Coma

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent oral ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids, anticonvulsants (e.g., diazepam) for seizures, and respiratory support if needed. Monitor hepatic and renal function.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 3 days

Withdrawal times vary by country and formulation. For cattle and sheep, meat withdrawal is typically 7 days and milk 3 days. For poultry, not approved for egg production in some countries; consult local regulations.

Storage, Handling & Regulatory Information

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

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Do not freeze oral solutions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for veterinary use in dogs, cats, horses, cattle, sheep, and goats. Combination products are also approved.

Extra-Label (Off-Label) Use: In the US, praziquantel is approved for use in dogs, cats, horses, cattle, sheep, and goats. Extra-label use in other species is permitted under AMDUCA with a valid veterinary-client-patient relationship. For food animals, observe withdrawal times and ensure no violative residues.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Praziquantel is a highly effective and safe anthelmintic for the treatment of tapeworm and fluke infections in a wide range of species. It is generally well-tolerated, with mild and transient adverse effects. For optimal efficacy, accurate dosing based on body weight is essential. In cases of Echinococcus infections, strict hygiene measures are necessary to prevent zoonotic transmission. In food animals, adherence to withdrawal times is critical. Praziquantel is often combined with other anthelmintics (e.g., pyrantel, fenbendazole) to broaden the spectrum of activity. It is important to consider the life cycle of the parasite and implement environmental control measures to prevent reinfection.

References & Literature

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