Praziquantel
Praziquantel is a highly effective, broad-spectrum **anticestodal (tapeworm)** and **antitrematodal (fluke)** anthelmintic widely used in veterinary medicine. Key clinical features include: * **Broad Spectrum:** Highly effective against major tapeworm species including *Dipylidium caninum*, *Taenia* spp., and *Echinococcus* spp. in dogs and cats. * **Trematode Efficacy:** Also utilized off-label for various fluke infections (e.g., *Paragonimus kellicotti*, liver flukes). * **High Safety Margin:** Generally very safe, though injectable formulations may cause transient local pain or mild systemic signs. * **Combination Therapy:** Frequently combined with other parasiticides (like pyrantel, febantel, ivermectin, or moxidectin) to provide comprehensive internal parasite control. *Clinical Pearl:* Because praziquantel damages the parasite's tegument, the worms are typically digested by the host. Therefore, intact tapeworms are rarely observed in the feces following successful treatment.
Mechanism: Praziquantel's exact mechanism is not fully elucidated, but it rapidly penetrates the parasite and alters the permeability of the cell membranes. * **Ion Flux Alteration:** Interacts with **phospholipids** in the parasite's integument โ induces rapid intracellular influx of **calcium ions (Ca2+)**, as well as sodium and potassium fluxes. * **Spastic Paralysis:** The sudden calcium influx causes severe, sustained contraction and spastic paralysis of the worm's musculature, impairing sucker function and dislodging the parasite. * **Tegumental Destruction:** At higher concentrations, it causes irreversible focal vacuolization โ subsequent disintegration of the cestodal integument. This exposes the parasite's internal antigens to the host's immune system and renders it susceptible to digestion by host enzymes. * **Trematodes:** Directly kills the parasite via similar calcium-mediated focal vacuolization and subsequent phagocytosis.
Dosing by species
- For susceptible cestodes (IM or SC) ยท <5 lbs: 11.4 mg (0.2 mL); 5-10 lbs: 22.7 mg (0.4 mL); >10 lbs: 34.1 mg (0.6 mL maximum) ยท IM/SC ยท Once ยท Using the 56.8 mg/mL injectable product
- For susceptible cestodes (Oral) ยท <4 lbs: 11.5 mg (ยฝ tab); 5-11 lbs: 23 mg (1 tab); >11 lbs: 34.5 mg (1.5 tabs) ยท PO ยท Once ยท Using the 23 mg feline tab
- For susceptible parasites using combination product with pyrantel pamoate (Drontal) ยท Administer a minimum dose of 2.27 mg praziquantel and 9.2 mg pyrantel pamoate per pound of body weight according to the dosing tables on labeling. ยท PO ยท Once ยท May be given directly by mouth or in a small amount of food. Do not withhold food.
- For treatment of Paragonimiasis (Paragonimus kellicotti) ยท 23-25 mg/kg ยท PO ยท q8h ยท 3 days
- For treatment of Giardia infections ยท Give two small dog tablets of Drontal Plus (febantel 113.4 mg; pyrantel 22.7 mg; praziquantel 22.7 mg) ยท PO ยท Once daily ยท 5 days
- For Alaria spp. ยท 20 mg/kg ยท PO ยท Once
- For Spirometra mansonoides ยท 30-35 mg/kg ยท PO ยท Once
- For Taenia, Echinococcus, Dipylidium caninum, Mesocestoides (adult) ยท 5 mg/kg ยท PO/SC ยท Once
- For Diphyllobothrium (adult) ยท 35 mg/kg ยท PO ยท Once
- For Sparganum proliferum (adult) ยท 7.5 mg/kg or 25 mg/kg ยท PO/SC ยท Daily ยท 2 days
Routes of administration
Contraindications
- Puppies less than 4 weeks old (for solo product)
- Kittens less than 6 weeks old (for solo product)
- Known hypersensitivity to praziquantel
- Unweaned puppies or kittens (unlikely to be affected by tapeworms at this age)
- Animals weighing < 1 kg (specifically for spot-on preparations)
Adverse effects
- Oral (uncommon, <5%): Anorexia, vomiting, lethargy, diarrhea, salivation (cats)
- Injectable (dogs): Pain at injection site, vomiting, drowsiness, staggering gait
- Injectable (cats): Diarrhea, weakness, vomiting, salivation, sleepiness, transient anorexia, pain at injection site
- Anorexia
- Vomiting
- Lethargy
- Diarrhoea
- Transient hypersalivation (if spot-on application site is licked)
- Localized tissue sensitivity and pain at injection site (particularly in cats)
Drug interactions
- Oxamniquine ยท Reportedly synergistic activity occurs in humans in the treatment of schistosomiasis; clinical implications in veterinary patients are unclear.
- Grapefruit juice ยท Can increase the area under the curve (AUC) of orally administered praziquantel by 150-200% in dogs.
- Dexamethasone ยท Concurrent administration may significantly decrease serum praziquantel concentrations. ยท moderate
- Cimetidine ยท May decrease the metabolic clearance of praziquantel, increasing its serum levels. ยท minor
Monitoring
- Clinical efficacy (resolution of parasite infection)
- Fecal examination for tapeworm proglottids or eggs to confirm efficacy of treatment
- Monitoring for resolution of clinical signs (e.g., scooting, visible segments in feces)
Overdose
Praziquantel has a **wide margin of safety**. * **Rodents:** Oral LD50 is at least 2 g/kg in rats and mice. * **Dogs:** An oral LD50 could not be determined because doses >200 mg/kg induce vomiting. In ASPCA APCC reports, dogs exposed to overdoses showed no clinical signs. * **Cats:** Parenteral doses of 50-100 mg/kg caused transient ataxia and depression. Injected doses at 200 mg/kg were lethal. In ASPCA APCC reports, a minority of exposed cats showed clinical signs. *Treatment:* Overdoses are generally self-limiting (especially oral, due to vomiting). Provide supportive care if severe neurological or gastrointestinal signs occur.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.