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.     

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.     

Confirmation of the efficacy of a combination tablet of spinosad and milbemycin oxime against naturally acquired infections of canine intestinal nematode parasites

Four separate controlled and blinded studies were conducted to confirm the dose of spinosad and milbemycin oxime (MO) administered orally in combination to dogs for the treatment and control of naturally acquired infections of adult whipworm (Trichuris vulpis), hookworm (Ancylostoma caninum) and ascarids (Toxocara canis, Toxascaris leonina). Dogs were allocated randomly based on pre-treatment quantitative nematode egg counts of each species of interest to one of two treatment groups of 10 or 11 animals each. In each study, spinosad and MO in combination, was given orally to dogs using the lower half (30-45 mg/kg spinosad; 0.5-0.75 mg/kg MO) of the US commercial dose band (30-60 mg/kg spinosad; 0.5-1.0mg/kg MO) of each active ingredient on Day 0 using a tablet formulation. A corresponding vehicle control group was treated similarly in each individual study. Dogs were necropsied post-treatment on Day 7/8. All nematodes in the intestinal tract collected at necropsy were identified and counted by species and stage. The spinosad and MO combination group demonstrated significantly different adult intestinal nematode efficacy in each individual study as compared to the vehicle control group. Efficacy values for whipworm, hookworm, T. canis and T. leonina were 100%, 99.8%, 100%, 93.3%, respectively. Minor non-serious adverse events were observed in a small number of control and treated dogs that were attributed primarily to the natural nematode infections. In summary, flavored spinosad and MO combination tablets administered orally to dogs were both safe and highly efficacious delivering >93% up to 100% adult intestinal nematode control in naturally infected dogs.     

Anthelmintic efficacy of febantel combined with praziquantel in dogs

Ninety-four dogs were randomly assigned to 1 of 6 groups (5 treated and 1 untreated control) for evaluation of anthelmintic efficacy. Three anthelmintic formulations were studied: a febantel paste, a praziquantel paste, and a combination paste containing both active ingredients. Treated dogs were dosed once daily for 3 days. The minimal effective dosages in combination were established as 10 mg of febantel and 1 mg of praziquantel/kg of body weight. At those dosages for the combination, 99.5% to 100% of the major nematodes and cestodes identified (ie, Ancylostoma caninum, Trichuris vulpis, Toxocara canis, Dipylidium caninum, and Taenia pisiformis) were eliminated. Febantel paste (10 mg/kg) alone was ineffective against cestodes (14.2% elimination of Dipylidium caninum) and praziquantel paste (1 mg/kg) alone was ineffective (0% to 2.4% elimination) against nematodes.     

Efficacy and safety of selamectin against gastrointestinal nematodes in cats presented as veterinary patients

A series of randomized, controlled, masked, field (veterinary patient) studies were conducted in the USA and Europe to evaluate the efficacy of selamectin, a novel macrocyclic lactone of the avermectin subclass, in the treatment of naturally acquired gastrointestinal nematode infections in cats. After confirmation of ascarid and/or hookworm infection, 298 cats of various ages and breeds were randomly assigned to treatment with selamectin (n=202) or an existing commercially approved positive-control product (n=96). Unit doses of selamectin (providing a minimum dosage of 6mgkg(-1)) were administered topically to the skin in a single spot at monthly intervals. Quantitative fecal examinations were performed on days 0 (before treatment), 30, and 60. In the selamectin-treated cats, fecal ascarid egg counts were reduced by 99.6 to 100% on day 30, and by 99.9 to 100% on day 60. Fecal hookworm egg counts were reduced by 98.3% on day 30, and by 100% on day 60 in the selamectin-treated cats. The positive-control products achieved reductions in egg counts of 96.5 to 100% (ascarids) and 98.9 to 99.9% (hookworms). These studies have shown that monthly topical administration of selamectin is safe and highly effective in the treatment of naturally acquired ascarid and hookworm infections in cats.     

Evaluation of febantel used concurrently with piperazine citrate in horses

Fifty horses from a herd known to have benzimidazole-resistant small strongyles were treated with febantel (6 mg/kg), combinations of febantel (6 mg/kg) and piperazine citrate (25 or 55 mg base/kg), thiabendazole (44 mg/kg), or placebo (0.6 ml of water/kg). Pretreatment and 7-day posttreatment fecal examinations were done. Fecal cultures, strongyle egg per gram (epg) counts, sugar flotation fecal examinations, and in vitro testing for benzimidazole resistance were performed. Results of fecal examinations before treatment were similar in all horses, and results of testing were positive for benzimidazole resistance. Horses treated with febantel and piperazine at all dosages had significantly lower mean strongyle epg counts and greater percentage reduction in mean strongyle epg counts (99.7% to 99.9%) 7 days after treatment, compared with those determined for horses treated with febantel, thiabendazole, or placebo. Adverse reactions to treatment were not observed.     

Efficacy of milbemycin oxime against fourth-stage larvae and adults of Ancylostoma tubaeforme in experimentally infected cats

The efficacy of milbemycin oxime against fourth-stage (L4) larvae and adults of Ancylostoma tubaeforme was investigated in a trial involving 24 young domestic shorthair cats. The animals were inoculated with approximately 300 infective stage three (L3) larvae and divided into three groups. After 12 days, eight cats (group 1) were treated with medicated tablets containing 4 mg milbemycin and 10 mg praziquantel to test the efficacy against L4 larvae; eight cats in group 2 were treated with the same tablets after 33 days to test the efficacy against adult worms; and eight cats in group 3 were treated with a placebo tablet. Faecal egg counts were determined periodically in each cat and after 40 or 41 days the number of worms in each animal was determined postmortem. The egg count reduction was determined by comparing the geometric mean numbers of eggs per gram of faeces in the placebo and medicated groups, and the worm reduction by comparing the geometric mean numbers of worms. The egg count reduction was more than 99 per cent in both treated groups, while the number of worms in groups 1 and 2 were reduced by 94.7 per cent and 99.2 per cent, respectively.     

Efficacy of milbemycin oxime against experimentally induced Ancylostoma caninum and Uncinaria stenocephala infections in dogs.

Twenty-eight helminth-naive Beagles, 16 to 26 weeks old, were inoculated with 200 third-stage larvae each of Ancylostoma caninum and Uncinaria stenocephala 5 times at weekly intervals. Dogs were randomly allocated to 4 groups of 7 on the basis of fecal egg counts, and treatments were randomly assigned. Groups 1 and 3 were given milbemycin oxime at a dosage of 500 micrograms/kg of body weight, PO, on day 0 and on days 0 and 30, respectively; groups 2 and 4 were nontreated controls. Fecal egg counts were evaluated before and after treatments. Feces were collected daily for 7 days after the final treatment for recovery of worms passed, and all dogs were euthanatized 7 days after the final treatment for recovery of worms retained. A 65.7% reduction from the pretreatment value for geometric mean hookworm egg count was found 7 days after the first treatment, and a 97.1% reduction 7 days after the second treatment. Although milbemycin oxime had 96.5% and 99.5% controlled efficacy against A caninum after 1 or 2 treatments, respectively, it lacked efficacy against U stenocephala. The geometric mean number of U stenocephala and the total number of hookworms retained after 1 or 2 treatments were not significantly different from the numbers retained by the corresponding control groups.     

High-level pyrantel resistance in the hookworm Ancylostoma caninum

While anthelmintic resistance is now a widely recognized issue in the livestock industries, its existence within companion animal medicine has been rarely established conclusively. We undertook a placebo-controlled in vivo trial to measure the efficacy of pyrantel embonate against pooled isolates of the hookworm Ancylostoma caninum from Brisbane, Australia. A statistically significant fall in adult worm burden was observed among dogs in the pyrantel treatment group compared to the control dogs (178.0+/-24.5 versus 239.7+/-14.0; p=0.02), equating to an efficacy of just 25.7% (95% CI, 15.0-35.1%), as based upon reduction in mean worm burden. Analysis of faecal egg count trends through the course of the study revealed that egg counts rose in both control and pyrantel-treated dogs, with a greater rise observed in the latter group (11.6+/-8.3% versus 17.3+/-7.6%; p=0.04), despite the decrease in adult worm numbers in this group. Our results indicate that high-level anthelmintic resistance does occur in companion animal medicine, and highlight the need for greater vigilance and more judicious use of anthelmintics in small animal practice. They further indicate that the faecal egg count reduction test needs to be used with caution with this parasite.     

In vivo anthelmintic activity of Phytolacca icosandra against Haemonchus contortus in goats

Two separate controlled and blinded studies were conducted to confirm the dose and non-interference of spinosad and milbemycin oxime (MO) administered orally in combination or alone to dogs for the treatment and control of experimentally induced flea infestations (Ctenocephalides felis) and adult hookworm infections (Ancylostoma caninum). For each study, dogs were allocated randomly based on pre-treatment adult flea and hookworm egg counts to one of four treatment groups of 10 animals each. In each study, spinosad and MO in combination, using the lower half (30-45 mg/kg spinosad; 0.5-0.75 mg/kg MO) of the US commercial dose band (30-60 mg/kg spinosad; 0.5-1.0mg/kg MO) of each active ingredient, or individually alone using the full dose range, were given orally to dogs on Day 0 using a tablet formulation. A placebo control was treated similarly. In one study, on Days -1, 5, 12, 19, 28 and 35 each dog was infested with approximately 100 unfed adult C. felis obtained from the investigator's established flea colony. All dogs were infested via the same method. Forty-eight hour post-infestation flea comb counts were conducted on Days 1, 7, 14, 21, 30 and 37 and were used to determine the knockdown and residual flea activity. In the second study, on Day -27 each of 48 dogs were experimentally inoculated with 100 third-stage infective larvae of the hookworm, A. caninum. Dogs were treated on Day 0 and necropsied on Day 7 or Day 8. All nematodes in the intestinal tract were collected on Day 7 or Day 8, identified and counted by species and stage. Post-treatment, the geometric mean live flea counts were significantly different (p-value<0.0001) between the spinosad/MO combination and the spinosad only treatment groups as compared to the vehicle control group. The flea counts in the MO only group and the control group were not statistically different. The spinosad and MO combination group and the spinosad only treatment group demonstrated significantly different knockdown (100%) and post-treatment residual flea efficacy at Day 30 was 100% for both groups as compared to the vehicle control. The presence of MO in combination with spinosad did not interfere with the flea efficacy of spinosad as compared to the spinosad only group. MO alone did not demonstrate any flea efficacy. Post-treatment, the geometric mean A. caninum worm counts were significantly different (p-value<0.0001) between the spinosad and MO combination group as compared to the vehicle control group. The worm counts in the MO only group and the combination group were not statistically different. The spinosad and MO combination group (99.8% reduction) and the MO only treatment group (99.5% reduction) both demonstrated significantly different hookworm efficacy as compared to the vehicle control group. The presence of spinosad in combination with MO did not interfere with the hookworm efficacy of MO as compared to the MO only group. Spinosad alone did not demonstrate any hookworm efficacy. In summary, flavored spinosad and MO combination tablets administered orally to dogs at the lower end (30-45 mg/kg spinosad; 0.5-0.75 mg/kg MO) of the US commercial tablet unit dose range (30-60 mg/kg spinosad; 0.5-1.0mg/kg MO) were both safe and highly efficacious delivering 100% knockdown and 30 days of residual adult flea control on experimentally infested dogs as well as >99% adult hookworm efficacy evaluated under laboratory conditions. Interference between either drugs was not demonstrated for both of these dose limiting parasites.     

Efficacy of selamectin against experimentally induced and naturally acquired infections of Toxocara cati and Ancylostoma tubaeforme in cats

The efficacy of selamectin against experimentally induced and naturally acquired infections of adult ascarids (Toxocara cati) and adult hookworms (Ancylostoma tubaeforme) was evaluated in five controlled studies in cats. Two studies evaluated the efficacy of selamectin against both ascarid (natural or induced) and hookworm (induced) infections; two studies evaluated the efficacy of selamectin against single natural infections of T. cati or A. tubaeforme; and the fifth study evaluated the efficacy of selamectin against induced infections of A. tubaeforme. Cats received selamectin topically in unit doses designed to deliver a minimum of 6mgkg(-1). Treatments were applied to the skin on each animal's back at the base of the neck in front of the scapulae. For experimentally induced infections, cats were inoculated orally with approximately 500 embryonated eggs of T. cati 56 days prior to treatment and/or approximately 150-250 larvae (L(3)) of A. tubaeforme 30 or 42 days prior to treatment. For both induced and naturally acquired infections, cats were allocated randomly to treatments (6-12 cats per treatment) on the basis of fecal egg counts to receive either selamectin or a vehicle containing the inert formulation ingredients. In all studies, adult worm counts were performed at necropsy 14 days after the last treatment administration. Against T. cati, a single application of selamectin provided a 100% reduction in the geometric mean number of adult worms for both experimentally induced and naturally acquired infections. Against A. tubaeforme, a single administration of selamectin provided a 99.4% reduction in the geometric mean number of adult worms in cats with natural infections, and an 84.7-99.7% reduction in adult worms in cats with induced infections.Two doses of selamectin administered at monthly intervals provided a 91.9% reduction in the geometric mean number of adult A. tubaeforme worms in cats with experimentally induced infections. The geometric mean numbers of adult worms (T. cati and A. tubaeforme) from selamectin-treated cats were significantly (P< or =0.0018) lower than for vehicle-treated cats in all studies. Thus, a single topical unit dosage providing a minimum dosage of 6mgkg(-1) selamectin was highly effective in the treatment of naturally acquired and experimentally induced infections of T. cati and A. tubaeforme in cats.     

Controlled dosage titration of febantel paste in naturally parasitized cattle

A controlled anthelmintic trial was conducted to determine the efficacy of febantel paste (45.5%) at dosages of 2.5, 5.0, 7.5, and 10.0 mg/kg in calves harboring natural gastrointestinal nematode infections. Dosages of 5.0, 7.5 and 10.0 mg of febantel/kg of body weight were greater than 96% effective in removing adults of Haemonchus contortus, Ostertagia spp, Cooperia spp, and Oesophagostomum radiatum. The 2.5 mg/kg dosage was considered suboptimal because of low efficacy against Ostertagia and Cooperia spp. Efficacies against Trichostronglylus axei, Trichuris spp, Bunostomum phlebotomum, and Stronglyloides papillosus were difficult to determine because fewer numbers of these nematodes were recovered. Efficacies of febantel paste against immature bovine parasites ranged from 83.62% to 97.72%.     

Pharmacokinetics and anthelmintic efficacy of febantel in the racing pigeon (Columba livia)

This paper reports on the pharmacokinetics and the efficacy of febantel against Capillaria obsignata and Ascaridia columbae in the racing pigeon. Febantel was rapidly cleared from the circulation and highly metabolized. The efficacy of febantel against Capillaria and Ascaridia was studied on lightly and heavily infected pigeons. The efficacy against Ascaridia was 100% for the faecal egg count reduction (FECR) as well as for the worm reduction in all treated pigeons. After two treatments with febantel against Capillaria in heavily infected pigeons the FECR amounted to 96.7% and worm reduction was 95%. In order to effectively remove both parasites from the host, repeated treatments with febantel at a short interval could be the treatment of choice.     

Efficacy of a chewable formulation of ivermectin against a mixed infection of Ancylostoma braziliense and Ancylostoma tubaeforme in cats.

The efficacy of a beef-based, chewable formulation of ivermectin against a mixed infection of Ancylostoma braziliense and A tubaeforme was determined in cats. Ivermectin administered orally at approximately 24 micrograms/kg of body weight was 92.8% effective against adult A braziliense and 90.7% effective against adult A tubaeforme. The number of eggs per gram of feces had decreased 98.1% by 7 days after treatment. Clinical signs of hookworm disease also decreased after treatment. Location of adult parasites within the small intestine, percentage of infecting larvae that developed to the adult stage, and egg size in cats with infections of A braziliense and A tubaeforme were similar to those reported for cats with separate infections of either species.     

Detection of antibodies to Hypoderma lineatum in cattle by Western blotting with recombinant hypodermin C antigen

A study was conducted to evaluate the therapeutic efficacy of doramectin administered intramuscularly at a dose rate of 200 microg/kg to sheep harbouring naturally acquired infections of gastrointestinal nematodes and Oestrus ovis in the southwestern region of France. On day 0, 24 sheep were selected on the basis of positive faecal egg counts (>100 EPG) and positive assessment of O. ovis infection (including positive O. ovis antibody level and positive clinical score). The sheep were randomly allocated to a non-medicated control group (T1) or a doramectin-treated group (T2) of 12 animals each. On day 0, sheep in group T2 received a single intramuscular injection of doramectin (200 microg/kg), whereas those in group T1 received an intramuscular injection of saline solution (sodium chloride, 0.02ml/kg). Individual faecal egg counts were performed on days 0, 1, 2, 3, 4, 5, 6, 7, and 14. Between days 14 and 16, all sheep were slaughtered, and worm and O. ovis burdens were determined. In doramectin-treated sheep, faecal egg counts had decreased to zero by day 4 for all recovered types of nematode eggs: strongyles, Nematodirus sp., Trichuris sp., and Rhabditidae sp. For strongyles, Nematodirus sp., and Rhabditidae, the percentage reductions in faecal egg counts (geometric means) of doramectin-treated sheep, compared to the non-medicated control sheep were 100% from days 4-7. For Trichuris sp., they were 100, 99.7, 99.9, and 100% on days 4, 5, 6, and 7, respectively. On day 14, percentage reductions were 100% for Nematodirus sp. and Rhabditidae, and 99.8 and 99.1% for strongyles and Trichuris sp., respectively. At necropsy, only adult nematodes and mainly first-stage O. ovis larvae were recovered. Doramectin was highly efficacious against the adult stages of Teladorsagia circumcincta (100%), Nematodirus battus (100%), Nematodirus filicollis (99.9%), Oesophagostomum venulosum (99.8%), and Trichuris sp. (99.3%). It was also 100% efficacious against first-stage larvae of O. ovis. No abnormal clinical signs or adverse reactions in any of the sheep treated with doramectin were observed.     

The efficacy of a pour-on formulation of moxidectin in young red and wapiti-hybrid deer

AIMS: To measure the efficacy of a pour-on formulation of moxidectin against lungworm and abomasal parasites in weaner wapiti x red deer and to compare this with its efficacy in weaner red deer. METHODS: Six red and six wapiti hybrid deer, naturally infected with lungworm and gastro-intestinal parasites, were treated with pour-on moxidectin at 500 microg/kg body weight and slaughtered 14 or 16 days later, along with six red and six wapiti hybrid untreated control deer. Total worm counts were performed on the lungs, abomasum and abomasal digest of each deer. RESULTS: The efficacy of moxidectin pour-on was 100% against adult and immature lungworms (Dictyocaulus viviparus) in red deer, and 100% and 99.7% effective against adult and immature lungworm in wapiti hybrid deer. The efficacy of moxidectin pour-on was 100, 100, 99.9 and 99.9% respectively against adult, fifth stage, late fourth stage and early fourth stage larvae of Ostertagia-type nematodes (assumed to be Ostertagia, Spiculopteragia, Skrjabinagia and Apteragia spp.) in both red and wapiti hybrid deer. CONCLUSIONS: The pour-on formulation of moxidectin, at 500 microg/kg body weight, is highly effective against mature and immature lungworms and abomasal nematodes in wapiti hybrid deer and equally effective in red deer.     

Efficacy of a drug combination of praziquantel, pyrantel embonate, and febantel against helminth infections in dogs.

Tablets containing praziquantel, pyrantel embonate, and febantel were tested for efficacy against helminths in dogs. A single treatment with this drug combination gave 100% reductions in Toxocara canis and Taenia hydatigena in experimentally induced infections in dogs. In dogs with naturally acquired infections, treatment gave > 97 to 98% reductions in fecal egg counts attributable to Toxascaris leonina, T canis, and Uncinaria stenocephala. Efficacy against Trichuris vulpis was > 92%.     

Anthelmintic efficacy of febantel combined with praziquantel against Ancylostoma tubaeforme, Toxocara cati, and Taenia taeniaeformis in cats

Forty cats, each harboring 2 or 3 parasitic infections (Ancylostoma tubaeforme, Toxocara cati, and/or Taenia taeniaeformis), were used to titrate the anthelmintic efficacy of a paste containing 3.4% febantel and 0.34% praziquantel. The cats were allotted into 4 groups (10 cats/group). For 3 consecutive days, the cats were given febantel/praziquantel at 5/0.5 mg/kg/day, 10/1 mg/kg/day, 15/1.5 mg/kg/day, or a blank paste vehicle (control) at 0.29 g/kg of body weight. The recommended dosage of 10 mg of febantel and 1 mg of praziquantel/kg cleared greater than or equal to 98% of the 3 helminth species.     

Effects of milbemycin oxime on adult hookworms in dogs with naturally acquired infections

Previous work indicated that adult Ancylostoma caninum can be removed from experimentally infected dogs, using a formulation of milbemycin oxime at dosage of 0.5 mg/kg of body weight. To determine the efficacy of this treatment in dogs naturally infected with adult hookworms, 24 mixed-breed dogs with patent hookworm infections were purchased from an out-of-state vendor, and 6 male and 6 female dogs were assigned to either a control group or a group that would be treated. Dogs were treated 10 days after their arrival and were euthanatized 1 week after treatment. Beginning 3 days before treatment, fecal samples were collected daily from all dogs, and the number of Ancylostoma eggs per gram of dry weight of feces was determined from each sample. By 1 week after treatment, the mean number of eggs being passed by the treated dogs had dropped from 12,700 to 10 eggs/g of dried feces; there was no apparent change in fecal egg counts for dogs of the control group. At necropsy, the mean number of adult A caninum in dogs of the treated and control groups was 1.3 and 56, respectively; in these naturally infected dogs, efficacy of treatment was calculated to be 97.8%. The mean number of adult Trichuris vulpis recovered in dogs of the control and treated groups at necropsy was 24 and 0, respectively, which yielded treatment efficacy of 100%. Although Uncinaria stenocephala and Toxocara canis appeared also to be removed by use of this dosage, too few dogs were in the study to calculate meaningful efficacies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Overberg Research Projects. XI. First stage larval reduction test to assess anthelmintic efficacy ante mortem in sheep.

Two field trials, one with suckling Merino ewe lambs and the other with yearling Dohne Merino rams, are described. In these the anthelmintic efficacy of febantel (a benzimidazole), ivermectin, levamisole and morantel are compared, using the 1st stage larval reduction test. The mean natural log (+1 for zero values) of the post treatment larval counts of the treated groups was compared with that of the untreated controls and the percentage reduction used to assess anthelmintic efficacy. Febantel was only 87.4% effective against Teladorsagia in suckling lambs but the other anthelmintics were more than 99% effective against this genus. Efficacy against Haemonchus and Trichostrongylus ranged from 93.2%-100% for all 4 compounds. In the rams all compounds were 100% effective against Trichostrongylus, with the exception of morantel which was only 87.5% effective. None of the compounds were effective against Teladorsagia, particularly morantel, animals treated with which having more larvae than the controls. The interpretation of anthelmintic efficacy; the advantages of the first stage larval reduction test, compared with the faecal egg count reduction test; and the importance of incubating cultures at 30 degrees C for 24 h, in order to harvest first stage larvae, are discussed.