Comparison of ivermectin, oxibendazole, and pyrantel pamoate in suppressing fecal egg output in horses

Thirty resident horses at a boarding stable in Alberta were used to evaluate the relative efficacies of ivermectin, oxibendazole, and pyrantel pamoate in reducing fecal egg output in adult horses under routine management conditions during spring and early summer, and to more clearly define the duration of suppression of fecal egg production following anthelmintic treatment. Horses were blocked according to pretreatment egg counts and randomly assigned to one of three treatments: pyrantel pamoate at 6.6 mg/kg body weight; oxibendazole at 10 mg/kg body weight; or ivermectin at 200 μg/kg body weight. All treatments were administered orally as a paste on day 0.Fecal samples were collected for examination by the modified Wisconsin procedure before treatment, and then at 4-11 day intervals up to day 72.

Very few if any strongyle eggs were found in the feces of any horses up to day 35. On days 42, 50 and 57, the geometric mean egg count for the ivermectin group was significantly (p<0.05) lower than that for the oxibendazole or pyrantel pamoate groups. Based on a survival curve analysis of the data, the mean number of days for recurrence of eggs in the feces was significantly longer for the ivermectin group than for the oxibendazole and pyrantel pamoate groups.

Under conditions encountered in this study, the posttreatment interval to resumption of fecal egg out-put in horses treated with ivermectin was eight to nine weeks, compared with five to six weeks for horses treated with oxibendazole or pyrantel pamoate.

     

Determination of the efficacy of pyrantel pamoate at the therapeutic dose rate against the tapeworm Anoplocephala perfoliata in equids using a modification of the critical test method

A total of 59 equids (54 horses and five Shetland ponies) were treated with pyrantel pamoate once, at the dose rate of approximately 6.6 mg base kg-1, during the period November 1985-January 1988. The drug was administered as a paste formulation (51 equids) intraorally or as a suspension formulation by stomach tube (eight equids). The purpose of treatment was to evaluate the activity of pyrantel pamoate (at the therapeutic dose rate) for removal of the tapeworm, Anoplocephala perfoliata, by a modified (24-h) critical test. The presence or absence of tapeworms was not determined for the equids before treatment. Twenty-three (39%) of the 59 treated equids were found to be infected with A. perfoliata (from one to 180 specimens per infected equid) at necropsy. Removals varied from 67 to 100% (average 88%) for the 18 infected equids treated with the paste formulation. For the five infected equids treated with the suspension, removals were 58-100% (average 75%). The combined average removal of A. perfoliata for both formulations was 87%. Two abnormal (triradiate) specimens of A. perfoliata were recovered; one from each of two different equids.     

Target animal safety and tolerance study of pyrantel pamoate paste (19.13% w/w pyrantel base) administered orally to horses

Pyrantel pamoate paste (19.13% w/w pyrantel base) for the treatment of tapeworm, Anoplocephala spp was evaluated for target animal safety and tolerance in horses treated orally at 0, 1, 3, 5, and 10 times the clinical dose of 13.2 mg pyrantel base/kg body weight administered daily for six consecutive days. Parameters evaluated included clinical signs, food and water consumption, body weights, physical examinations, clinical pathology (hematology, coagulation, serum chemistry, urinalyses, and fecal examinations), complete necropsy, organ weights, and histopathology. No adverse events or test article-related effects were observed in any treatment group during daily clinical observations of the test animals. Statistically significant changes (P < .05) lacked a dose- and/or time-dependent trend and were considered incidental. Administration of pyrantel pamoate paste did not produce any macroscopic or microscopic tissue effects in any dose group of either sex. The no-observed-effect-level (NOEL) for pyrantel pamoate paste, when administered orally to horses once daily for 6 consecutive days, was determined to be 132 mg/kg/day. Pyrantel pamoate paste (19.13% w/w pyrantel base) can be safely administered orally to horses at 13.2 mg of pyrantel base/kg for the treatment of Anoplocephala infestations.     

Prevalence and Treatment of Tapeworms in Horses

A study was initiated to determine the prevalence of tapeworms in horses in Southern Ontario and to investigate the efficacy of pyrantel pamoate, niclosamide and mebendazole. Fecal samples were taken from 580 horses of various breeds, ages and sexes in 24 locations and Anoplocephala perfoliata was found in 13.6%. This was regarded as a minimum, the true rate being probably significantly higher and the reasons for this are discussed. A brief review of the life cycle and effects of tapeworms in horses and a comparison of two flotation techniques for the diagnosis of A. perfoliata eggs in feces is given.Pyrantel pamoate, niclosamide and mebendazole were compared for efficacy in field and critical trials. In field trials, pyrantel base and niclosamide at 6.6 and 50 mg/kg respectively were found to be effective, but in critical trials their efficacy was poor, 15 and 5.6% respectively. These anthelmintics at these dose rates caused only an elimination of the terminal egg bearing segments and were without significant effect on the entire tapeworm. When pyrantel base was administered at 13.2 and 19.8 mg/kg (twice and three times the therapeutic dose rate for nematodes respectively) the efficacy was 97.8 and 100%. It would appear that pyrantel pamoate administered at 13.2 mg pyrantel base/kg is an effective therapeutic dose for tapeworms in horses. Further dose titration studies are needed for niclosamide. Mebendazole was without effect at up to four (35.2 mg/kg) times the therapeutic dose for nematodes.     

Effect of early season ivermectin and pyrantel treatments on strongylid infections in young Shetland ponies in The Netherlands

Two groups of three ponies were used to study the effect of three ivermectin or pyrantel treatments given at intervals of 5 weeks at the beginning of the grazing season. Although each pyrantel treatment resulted in a greater than 95% reduction in faecal egg counts during the first 3 weeks, high pasture larval counts were seen from the beginning of August onwards and substantial cyathostomine burdens were found at necropsy in December. The ivermectin treatments resulted in an even more pronounced reduction in faecal egg output, and the pasture larval counts and cyathostomine burdens at necropsy were considerably lower than in the pyrantel group. The proportion of inhibited early L3 of the cyathostomines was lower in the ivermectin than in the pyrantel group. Faecal egg output of the large strongyles was completely suppressed in the ivermectin group. Nevertheless, Strongylus vulgaris larvae were found in the arteries of all three ponies, possibly as a result of overwintering of infective larvae on pasture. In the pyrantel group, the egg output of Strongylus edentatus and, to a much lesser extent, Strongylus vulgaris, was not completely suppressed.     

A combination treatment strategy using pyrantel pamoate and oxibendazole demonstrates additive effects for controlling equine cyathostomins

Anthelmintics of the avermectin/milbemycin class continue to demonstrate the highest efficacy against cyathostomin nematodes; however, over‐reliance on these drugs is increasing the likelihood that recent emerging resistance to these drugs will worsen. Use of benzimidazole and pyrantel compounds given concurrently may provide sufficiently high efficacy to serve as a viable treatment alternative to the avermectin/milbemycin drugs, thus reducing the selective pressures for resistance development. The study was conducted to determine if oxibendazole (OBZ) and pyrantel pamoate (PYR) would have greater efficacy when used in combination vs. what either drug could achieve individually, and to determine if the combination protocol would consistently achieve faecal egg count reduction (FECR) rates >90%, the general threshold for acceptable efficacy. Horses of various ages and breeds on 11 horse farms were assigned randomly to treatment with OBZ (n = 34), PYR (n = 35), or a combination of both (n = 61). A faecal egg count was performed for each horse prior to treatment and 9–14 days post treatment. Mean FECR percentages were calculated for each treatment group on individual farms, and for each treatment group across all farms. Combination treatment achieved >90% mean FECR on all 11 farms, and >95% on 9 of the 11 farms. Overall arithmetic mean FECR rates were 90.03%, 81.10% and 96.35% for horses treated respectively with OBZ, PYR, and the 2 drugs in combination. Combination treatment with OBZ and PYR demonstrated an additive effect whereby horses given both anthelmintics concurrently had mean FECR percentages that were significantly greater than in horses given either drug alone. Combination treatment with OBZ and PYR can be an efficacious and viable treatment choice for controlling cyathostomins, thereby reducing the over‐reliance on avermectin/milbemycin drugs.     

Survey for drug-resistant gastrointestinal nematodes in 13 commercial sheep flocks.

The prevalence of drug-resistant ovine parasites in the United States has not been widely reported. Thirteen flocks, typical of commercial sheep production units, were selected for survey. Four anthelmintics (fenbendazole, ivermectin, pyrantel pamoate, and levamisole) were tested for their ability to reduce herd mean pretreatment fecal egg count. If a properly dosed and administered drug failed to reduce herd mean pretreatment fecal egg count by 80%, it was considered ineffective in that flock, and the presence of parasites resistant to that drug was inferred. Fenbendazole administration changed pretreatment fecal egg counts by +9% to -100%. On the basis of the aforementioned definition, drug resistance existed in 6 of 13 flocks. Posttreatment larval culture indicated that Haemonchus contortus survived administration of fenbendazole. Levamisole, pyrantel pamoate, and ivermectin reduced pretreatment fecal egg count by -83% to -100%; resistance to these products was not evident in the flocks surveyed.     

Clinical field efficacy and safety of pyrantel pamoate paste (19.13% w/w pyrantel base) against Anoplocephala spp. in naturally infected horses

Clinical field trials were conducted at five geographical locations in the USA (Oklahoma, Wisconsin, Tennessee, Virginia and Idaho) to evaluate the efficacy and safety of pyrantel pamoate paste (19.13%, w/w, pyrantel base) administered at the recommended dosage of 13.2 mg pyrantel base/kg (6.0 mg pyrantel base/lb) body weight (b.w.) against tapeworm infections of Anoplocephala spp. in naturally infected horses. Horses at each study site were allocated by restricted randomization based on the cestode status (positive or negative) of pre-treatment fecal egg counts to complete sets of four animals each or incomplete sets of fewer than four animals. Within sets comprising of two to four horses, one animal was randomly allocated to receive placebo vehicle paste and the remaining horse(s) received pyrantel pamoate paste administered orally at a minimum dosage of 13.2 mg pyrantel base/kg b.w. on Test Day (TD) 0. Single animal sets received pyrantel pamoate paste. Fecal samples of horses were collected and examined for equine tapeworm (Anoplocephala spp.) eggs a minimum of four times (once or thrice between TD -28 and -14, twice between TD -14 and -7, and once on TD 0) prior to treatment on TD 0. Fecal samples of horses that were positive for cestode infection pre-treatment were examined for cestode eggs on TD 7, 8, 9, 14, 15 and 16. Cestode-negative pre-treatment horses were not sampled again after treatment. A total of 241 horses (141 mares, 16 stallions and 84 geldings; 6 months-30 yrs of age; 173-646 kg; 13 recognized breeds and various crossbreds) were evaluated. The prevalence of Anoplocephala spp. determined by pre-treatment fecal examination ranged from 38.3% in Idaho to 68.1% in Tennessee with an overall prevalence of 52.3%. Ninety cestode-positive and 88 cestode-negative horses were treated with pyrantel pamoate paste, 36 cestode-positive and 27 cestode-negative horses were treated with placebo vehicle paste. Overall, 178 horses were treated with pyrantel pamoate paste, and 63 horses were treated with placebo paste. Of the 178 horses treated with pyrantel pamoate paste, no drug related, adverse clinical or neurological health events were observed. No doses of pyrantel pamoate paste were refused or lost during dosing. At each post-treatment time sampling interval, significantly fewer cestode eggs (P < 0.0115) were passed by cestode-positive horses treated with pyrantel pamoate paste compared to cestode-positive horses that received placebo paste. Efficacy of the pyrantel pamoate paste treatment ranged from 92 to 96% from TD 7 to TD 16 with an overall efficacy of 95%. The results of these trials demonstrated that pyrantel pamoate paste (19.13%, w/w, pyrantel base) administered orally at a dosage of 13.2 mg pyrantel base/kg b.w. is highly efficacious (95%) against Anoplocephala spp. and safe for use in horses with no adverse clinical or neurological health events observed under field use conditions.     

Evidence of Ivermectin Resistance by Parascaris equorum on a Texas Horse Farm

By collecting fecal samples every 2 weeks beginning at 2 months of age, 32 foals from a single Texas farm were monitored. The foals were administered ivermectin paste at the time of the first collection and again monthly. When foals had Parascaris egg counts higher 2 weeks after ivermectin treatment than at treatment, they were administered pyrantel pamoate at the manufacturer's recommended dose (6.6 mg/kg) or at twice the recommended dose (13.2 mg/ kg) when tapeworm eggs were also detected. An elevation or only minimal reduction (less than 75%) in Parascaris egg counts was seen 2 weeks after ivermectin treatment until the foals were 8 months of age, at which time there was an 85% reduction in fecal egg count after treatment. When pyrantel was administered at the manufacturer's recommended dose, a 42% to 84% reduction in egg counts occurred, but at 13.2 mg/kg there was a 98% to 100% reduction in fecal egg counts 2 weeks posttreatment. However, pyrantel failed to control strongylate egg counts even at the elevated dose, whereas ivermectin reduced strongylate fecal egg counts by greater than 99%, determined 2 weeks posttreatment. Pyrantel, but not ivermectin, lowered Parascaris egg counts. Ivermectin, but not pyrantel, lowered strongyle egg counts 2 weeks post administration. A single drug for all ages of horses approach to parasite control requires rethinking. Combinations of drugs or more careful evaluation of anthelmintics in foals may be necessary for continued parasite control.     

Development of a novel in vitro equine anthelmintic assay

An in vitro assay involving the use of a horse strongyle (Strongylus edentatus) and the micromotility meter has been developed to test for equine anthelmintic activity. Three commercially available equine anthelmintics (dichlorvos, ivermectin, and pyrantel pamoate) and an investigational drug (p-toluoyl chloride phenylhydrazone) were evaluated in this assay at four concentrations. After a 24-h incubation, greater than or equal to 10 micrograms/ml of all four drug treatments significantly (P less than or equal to 0.05) reduced the motility of ensheathed L-3 S. edentatus larvae, thereby indicating anthelmintic activity. Pyrantel pamoate also reduced motility at 1 microgram/ml, while the hydrazone significantly increased movement at this level. At 0.1 microgram/ml, none of the treatments significantly reduced motility; one treatment (dichlorvos) significantly increased larval motility. Incubation for 48 h resulted in significant activity (reduction in motility) at greater than or equal to 1 microgram/ml with two drugs (ivermectin, pyrantel pamoate); dichlorvos and the hydrazone reduced motility at greater than or equal to 10 micrograms/ml. None of the treatments significantly reduced motility at the lowest concentration (0.1 microgram/ml); however, at 48 h, two treatments (dichlorvos, hydrazone) significantly increased motility at the lowest concentration (0.1 microgram/ml). The in vitro S. edentatus motility assay proved to be sensitive, accurate and rapid. This assay system should be a valuable addition to tests used to identify potential equine anthelmintics, monitor helminth resistance to drugs, and perhaps define the kinetics and mode of action for drugs.     

Suppression of the pathogenic effects of Strongylus edentatus larvae with thiabendazole.

Four pony foals were inoculated with Strongylus edentatus infective larvae and on days 3 and 4 postinfection two of the ponies were treated with thiabendazole, each at the rate of 440 mg/kg of body weight. Total circulating eosinophil counts in untreated ponies increased to over 1700 per cu mm after the second week postinfection. In the treated ponies as well as in an uninfected untreated pony eosinophil counts did not increase beyond 100 per cu mm. At necropsy on day 35 postinfection the cecum, colon and omentum of treated ponies were normal and few tracks were present on the surface of the liver. In untreated ponies nodules were observed on the serosal surface of the cecum and right ventral colon and white foci and tracks were numerous on the surface of the liver. A total of 53 fourth stage larvac was recovered from the livers of the thiabendazole treated ponies and 1194 from the untreated ones.     

Cyathostomes in horses in Canada resistant to pyrantel salts and effectively removed by moxidectin

Clinical trials using fecal egg count reduction tests and coproculture were conducted with yearlings and mares on a farm in 1997. Fecal samples were taken from each horse to estimate the number of strongyle eggs/g feces with Cornell-Wisconsin centrifugal flotation and Cornell-McMaster dilution techniques. Eleven of 15 yearlings, which had been on a daily feeding of grain with pyrantel tartrate for 66 d were found with strongyle eggs in feces. This was the first time the in-feed medication had been used on the farm. Nine yearlings were randomised into three groups; continuation of daily pyrantel tartrate or one treatment with pyrantel pamoate or moxidectin. Two of three yearlings given pyrantel tartrate or pamoate had no reduction in the eggs/g feces. These six yearlings were then given moxidectin and in all yearlings the eggs/g feces was reduced to zero. The 66 d of pyrantel tartrate use was an inadequate time for development of resistant cyathostomes and a hypothesis was the resistance was due to extensive use on the farm over many years of pyrantel pamoate at twice the label dose for control of tapeworms. That hypothesis was tested with 12 mares with strongyle eggs in the feces randomised into two treatment groups: pyrantel pamoate at label dose or moxidectin. Five of six mares given pyrantel had <80% reduction in egg/g feces. These mares were then given moxidectin and in all mares the eggs/g feces was reduced to zero. Only cyathostomes were found on culture and apparently there was side resistance among the pyrantel salts.     

Evaluation of the efficacy and safety of two formulations of pyrantel pamoate in cats

The efficacy of paste and granule formulations of pyrantel pamoate against concurrent infections of Toxocara cati and Ancylostoma tubaeforme in cats was examined in a controlled trial. Three groups of 8 cats received either no medication (controls) or pyrantel pamoate in paste or granule formulations at a dosage of 20 mg/kg of body weight. After administration of the paste formulation, fecal egg counts of A tubaeforme and T cati were decreased by 98.6 and 96.4%, respectively, and 100% of hookworms and 93.5% of ascarids were removed from the intestine. After administration of the granule formulation, fecal egg counts of A tubaeforme and T cati were decreased by 99.4 and 78.2%, respectively, and 100% of adult hookworms and 88.9% of ascarids were removed. All reductions of egg counts and worm numbers were significant (P less than 0.01). The clinical safety of pyrantel pamoate was evaluated in 4- to 6-week-old kittens. Three groups of 10 kittens received either no medication (controls) or pyrantel pamoate in paste or granule formulations at the rate of 100 mg/kg for 3 consecutive days. Adverse effects were not observed in young kittens following administration of the high dose of pyrantel pamoate.     

Early Development of and Pathology Associated with Strongylus edentatus

Pony foals inoculated with infective Strongylus edentatus larvae were monitored for clinical signs and selected blood changes and were examined at necropsy from two to 56 days postinfection. Larvae penetrated the intestine and reached the liver intravenously before 40 hours postinfection. Occasional thrombi and larval tracks associated with the intima of cecal and colic veins suggested aberrant paths. Larvae in the liver doubled in width between seven and 15 days postinfection and a sudden increment in circulating eosinophils occurred between 11 and 15 days. These changes were probably associated with the third molt. At 30 days fourth stage larvae were migrating in the liver; at 42 days they were present in the hepatorenal ligament.

White foci were observed in the liver from two to 56 days. They contained mononuclear cells and eosinophils and later necrotic cores of eosinophils. By one month foci were overshadowed by tortuous tracks of migrating larvae. Aberrant larvae in the lungs were confined in granulomas. Massive granulomas in the wall of the cecum and colon contained small larvae which were probably inhibited by antibody associated with the third molt. Severe disruption of omental architecture and adhesions involving the intestine occurred several weeks after infection.

     

A modified critical test for the efficacy of pyrantel pamoate for Anoplocephala perfoliata in equids

Aims of this study with 13 equids naturally infected with Anoplocephala perfoliata were to document (i) a critical test with a period of 48 h from treatment to necropsy to assess the efficacy of an anthelmintic against the tapeworm, (ii) the efficacy of pyrantel pamoate oral paste at 13.2 mg pyrantel base/kg body weight, and (iii) the time after treatment when fecal egg counts would best estimate the tapeworm's prevalence in a herd. Feces passed in successive 12-h periods after treatment were examined for tapeworms. At necropsy, tapeworms in equids were identified as attached to the mucosa or unattached and, with a stereoscope, as normal or abnormal. At the time of treatment and at 6-h intervals thereafter, fecal samples were taken for egg counts. The efficacy of pyrantel pamoate was 96.6%; in 1 equid the efficacy was 75.3%, and in 8 it was 100%. "Major fragments" (worms without a scolex) accounted for 10% of the tapeworms recovered; they were not included in the efficacy analysis but should be. In 3 untreated equids necropsied, tapeworms were in the cecum, and 21.3% were detached. This protocol, when compared with a 24-h one without examination of feces, was more efficient in the treatment of trial animals and reduced underestimation and overestimation of an anthelmintic's efficacy. However, a protocol similar to this 48-h critical test but with a 24- or 36-h post-treatment period should be investigated. The mean egg count peaked 18 to 24 h after treatment and the samples taken at that time would provide the best estimate of prevelance of tapeworms in a herd. The Cornell-Wisconsin centrifugal flotation technique had a sensitivity and specificity of 100% at 18 h and 92% and 100%, respectively, at 24 h.     

The Response of Ponies to Myxovirus influenzae A-equi 2 I. Serum and Antibody Titres Following Exposure

The antibody response in serum and nasal secretions of groups of ponies vaccinated or infected with Myxovirus influenzae A-equi 2 was examined. Following infection by aerosol with live virus, a weak antibody response was recorded in both serum and secretions. Antibody levels were undetectable in secretions at 31 days after infection.

After primary intramuscular vaccination with killed virus, using sodium alginate as an adjuvant, antibody was detected only in the serum. However, following revaccination, a pronounced antibody response was demonstrated in both serum and secretions. Antibody was still detectable in all four ponies when tested 135 days later.

Only a serum antibody response was detected in ponies after primary intramuscular vaccination with a commercial vaccine. Upon revaccination nasal antibody occurred in all ponies but this only persisted for about 30 days.

Neither serum nor nasal antibody response occurred following intranasal vaccination and revaccination with a killed virus vaccine.

     

A Field Study on the Effect of Some Anthelmintics on Cyathostomins of Horses in Sweden

The objective of the study was to investigate different aspects on the efficacy of three anthelmintics on cyathostomin nematodes of Swedish horses. A faecal egg count reduction (FECR) test was performed on 26 farms. Horses were treated orally with recommended doses of ivermectin, pyrantel pamoate or fenbendazole. Faecal samples were collected on the day of deworming and 7, 14 and 21 days later. No resistance was shown against ivermectin; the FECR was constantly >99%. The effect of pyrantel was assessed as equivocal in 6 farms 14 days after treatment; the mean FECR was 99%. As many as 72% of the fenbendazole-treated groups met the criteria for resistance; the mean FECR was 86%, ranging from 56% to 100%. A re-investigation of two farms where pyrantel resistance had been suspected clearly revealed unsatisfactory efficacy of pyrantel on one of these farms; the FECR varied from 72% to 89%. Twenty-six of the horses previously dosed with pyrantel or fenbendazole, and which still excreted ≥150 eggs per gram of faeces 14 days after treatment, were dewormed with ivermectin and fenbendazole or pyrantel in order to eliminate the remaining cyathostomins. A total of 13 cyathostomin species were identified from horses that initially received fenbendazole and seven species were identified from pyrantel-treated individuals. The egg reappearance period (ERP) following treatment with ivermectin and pyrantel was investigated on two farms. The shortest ERP after ivermectin treatment was 8 weeks and after pyrantel was 5 weeks. We conclude that no substantial reversion to benzimidazole susceptibility had taken place, although these drugs have scarcely been used (<5%) in horses for the last 10 years. Pyrantel-resistant populations of cyathostomins are present on Swedish horse farms, but the overall efficacy of pyrantel is still acceptable.     

The disposition of pyrantel in the gastrointestinal tract and effect of digesta flow rate on the kinetic behaviour of pyrantel in the pig

Pigs consuming a diet with slow digesta transit time were orally administered with molar equivalent doses of pyrantel as the citrate and pamoate salt. At appropriate intervals pigs were killed and the quantitative-time distribution of pyrantel throughout the gut contents was determined. Compared with the citrate, there appeared to be greater quantities of the less soluble pamoate salt in the small and large intestine. An additional group of pigs fed on diets with "slow" or "fast" digesta transit time were orally treated with molar equivalent amounts of pyrantel as the citrate and pamoate salt and the respective kinetic disposition of pyrantel in peripheral plasma and quantitative excretion in faeces was determined. The diet type had little effect on pyrantel availability after administration of the less soluble pamoate salt. However, the maximum concentration of pyrantel in plasma was lower and there appeared to be greater quantities of pyrantel retained in the gut and excreted in faeces when the citrate salt was orally administered to pigs fed the "fast" compared to the "slow" diet. Since it is the quantity of pyrantel contained in the gut lumen which is believed to affect efficacy against gastrointestinal parasites, greater efficacy with this anthelmintic should be obtained when pigs are consuming a high fibre diet.     

Dose-confirmation studies of the cestocidal activity of pyrantel pamoate paste in horses

Dose confirmation studies of the cestocidal activity of pyrantel pamoate paste were conducted at two sites in North America during 2001. Horses with naturally-acquired cestode infections were identified by detection of typical Anoplocephala spp. eggs in feces collected between 7 and 92 days prior to treatment. Twenty and 22 horses were enrolled at Site 1 (Urbana, IL) and Site 2 (Knoxville, TN), respectively. Candidate horses were acclimated to study conditions for 14 days, ranked by length of interval since coprologic confirmation, and allocated randomly to one of two treatment groups: (T1) pyrantel pamoate paste 13.2mg pyrantel base per kilogram body weight administered orally, and (T2) untreated controls. Individual doses of pyrantel pamoate paste were prepared on the basis of contemporaneous body weights and administered to Group T1 horses on Day 0. Trained personnel monitored the animals at regular intervals after treatment to detect potential adverse reactions. Horses were euthanatized and necropsied 10-12 days after treatment. The contents of the large and small intestines were collected, and the walls of each organ were rinsed with water and inspected. Attached cestodes were recovered and preserved in 10% formalin. The intestinal contents and rinsed ingesta were washed over a #10-mesh (2mm aperture) sieve and tapeworms were extracted and preserved. Recovered cestodes were counted and examined at 1-4x magnification for identification to genus and species. At Site 1, specimens of Anoplocephala perfoliata were recovered from seven of 10 control horses, and from one of 10 horses treated with pyrantel pamoate. Mean cestode numbers were 4.52 in the control group and 0.07 for treated horses. At Site 2, cestodes were found in 10 of 11 controls (mean 26.2) and in five of 11 horses (mean 1.2) treated with pyrantel pamoate. In both studies, Group T1 means were significantly lower than the control group (P<0.005). The calculated efficacies were 98.4 and 95.5% at Sites 1 and 2, respectively. In two dose-confirmation studies, a single, oral treatment of pyrantel pamoate paste (19.13% w/w pyrantel base) at 13.2mg/kg was >or=95.5% effective against A. perfoliata in naturally-infected horses.     

The efficacy of pyrantel pamoate against ascarids and hookworms in cats

The purposes of this study were to evaluate pyrantel pamoate administered orally at 20 mg/kg body weight for the removal of induced or natural infections of Ancylostoma tubaeformae and Toxocara cati in cats and to compare the efficacy of paste (40 mg base/g) and granule (80 mg base/g) formulations. Thirty cats of mixed breeding and various ages with natural and/or induced infections of A. tubaeformae and T. cati were assigned to one of three treatment groups: (1) non-medicated controls; (2) paste formulation at 20 mg base/kg; or (3) granule formulation at 20 mg base/kg. Infections were induced by feeding the cats on carcasses of infected mice. The study was conducted in replicates of at least one animal per treatment per replicate. The study parameters included clinical observations, physical examinations, faecal egg counts and the numbers, species and stages of worms recovered at necropsy. The paste formulation was 99.3% and 99.7% effective in reducing egg counts of Ancylostoma sp. and Toxocara sp. respectively. The granule formulation was 97.7% and 99.9% effective in reducing faecal egg counts of Ancylostoma sp. and Toxocara sp. respectively. When administered in paste form, pyrantel pamoate was 99.5% effective in removing adult Ancylostoma and 100.0% effective against adult Toxocara. The granule formulation was 97.9% effective against Ancylostoma and 100% effective against Toxocara. No toxic effects of either formulation of the drug were noted.