Intestinal parasitism remains a major concern in domestic cats throughout the world. Infestations with roundworms, hookworms, tapeworms, and others result in significant morbidity to cats and may pose a risk to humans living with them. The use of dewormers in domestic species is common and routine in most veterinary clinics; however, the pharmacokinetic profiles of many common dewormers have not been well described in cats. A thorough understanding of the kinetics of commonly used anthelminthic (deworming) drugs may help to tailor dosing regimes in cats.

Pyrantel is a commonly used dewormer usually administered as a pamoate salt (though pyrantel tartrate is also available). This drug is generally considered very safe even in young animals due to poor intestinal absorption – most of the effect occurs within the GI tract. Pyrantel is effective against roundworms, hookworms, and threadworms. Praziquantel is an anticestodal (tapeworm dewormer) that is effective against Taenia, Dipylidium, and other tapeworm species. It is used in combination with other dewormers in many products.

The purpose of this study was to determine the pharmacokinetic profiles of praziquantel and pyrantel after oral administration to domestic cats.

22 healthy cats were enrolled into the study. Cats were aged 18 to 3.6 years and weighed 2 to 3.2 kg. Cats were free of any clinical disease and were fasted prior to administration of medications. The cats were given 100mg/kg pyrantel and 8.5 mg/kg praziquantel orally. Blood samples were collected pre-treatment and at 0.5, 1, 1.5, 2, 4, 8, 12, 24, 36, and 48 hours post-dosing. Blood levels of both praziquantel and pyrantel were measured using a liquid chromatography–mass spectrometry unit. Statistical analysis was used to calculate mean and standard deviation plasma levels over the course of the study.

No clinical side effects were seen from the administration of these medications. Praziquantel reached higher blood levels than pyrantel, and no drug was detected after 12 hours post-dosing. Praziquantel’s half-life was determined to be 1.07 hours, and pyrantel’s 1.36 hours.

The bioavailability of both of these drugs was determined to be low. Praziquantel had a higher bioavailability than pyrantel, but a shorter half-life in cats than in other species. This drug is known to rapidly distribute from the blood into the organs and tissues, has poor water solubility, and is metabolized extensively by the liver (“first pass effect”); all factors contributing to its low plasma levels. Praziquantal’s efficacy is due to its systemic effects, and as such enough must be given to reach high plasma levels. The lethal dose of praziquantel has been reported as approaching 200mg/kg, and so the levels attained by oral dosing would be considered safe.

Pyrantel pamoate had very low bioavailability, with low plasma levels attained. It is known to be poorly soluble and is excreted largely unchanged in the feces, and the availability in cats is lower than what has been reported in other species. This is not concerning, as the efficacy of this drug is due to its actions in the GI tract itself.

This study confirms that in feline patients, oral administration of pyrantel/praziquantel combination products show pharmacokinetic profiles indicating good safety and efficacy. Further work into their efficacy in clinical situations and possibility of resistance induction should be considered. (MRK)