Faecal Cyathostomin Egg Count distribution and efficacy of anthelmintics against cyathostomins in Italy: a matter of geography?

BACKGROUND

In the framework of a trial carried out in 2008 in Europe to evaluate the efficacy of major parasiticides against horse cyathostomins, pre- and/or post-treatment Faecal Egg Counts (FEC) were evaluated in a total of 84 yards and 2105 horses from nine different regions from the South, the Center, the North-Center and North-East of Italy. Specifically, on the basis of FECs of the horses present in each property, 60 out of the 84 yards were enrolled for a Faecal Egg Count Reduction Test (FECRT) using fenbendazole, pyrantel, ivermectin and moxidectin.

RESULTS

Of the 1646 horses bred in the 60 recruited yards, 416 animals had a FEC between 50 and 150 Eggs Per Gram (EPG) of faeces and 694 a FEC >150 EPG (i.e. with total of 1110 positive animals). Of the 1110 positive animals, those with the highest FECs (i.e. 988) were included in the FECRT. The FECRT for four anthelmintic compounds showed remarkable differences in terms of prevalence of reduced and equivocal efficacy against cyathostomins in the different areas of Italy. Administration of fenbendazole and pyrantel resulted in resistance present or suspected in about half of the yards examined while resistance to ivermectin was found in one yard from central Italy and suspected resistance was detected in three more yards, one in each the North, the Center and the South. Treatment with moxidectin was 100% effective in all yards examined.

CONCLUSION

Cyathostomin populations in the South and the Center of Italy were more susceptible to fenbendazole and pyrantel than the populations present in the Center-North and North-Eastern areas of Italy. Fenbendazole and/or pyrantel were ineffective in almost all properties from the North of Italy. The reasons for such a difference among the Italian regions in terms of FECs and efficacy of antiparasitic drugs are discussed, together with the role that veterinarians, and horse owners and managers should have for effective worm control programs in this country.

Effects of worm control practices examined by a combined faecal egg count and questionnaire survey on horse farms in Germany, Italy and the UK

Background

For the control of worm infections, the strategic use of anthelmintics, often accompanied by additional farm and/or pasture management procedures, is currently applied on most horse farms in industrialized countries. However, the particular effects of the specific worm control procedures are often unclear and have only been investigated to a limited extent. We examined faecal egg count (FEC), faecal egg count reduction (FECR) and questionnaire data on farm and pasture management procedures. The aim of this study was to determine whether specific worm control practices reported to be applied in European horse farms affect worm prevalence.

Results

This study involved 20 German, 26 Italian and 16 UK horse farms for each of which FEC were performed on a minimum of 16 horses. In total, 2029 horse faecal samples were quantitatively analysed for helminth eggs, resulting in 56.3% of the faecal samples being positive for strongylid eggs. The prevalence in the 742 German horse samples (48.1%) was significantly lower than that in the 737 Italian (61.1%) and the 550 UK (60.9%) samples. As expected, a significant effect of horse age on the infection prevalence was observed, with adult horses showing lower prevalences and lower mean FEC than foals and yearlings. The majority of the participating farms were stud farms (n = 29), followed by riding stables (n = 27) and racehorse stables (n = 6). The prevalence of strongyle infection by farm type differed between countries. While in Germany, horses on riding farms were significantly less often strongyle positive, in the UK horses on stud farms showed the lowest strongyle prevalences, whereas in Italy, no significant difference between farm types were seen. On all farms, horses received routine/preventive anthelmintic treatment. An effect of treatment frequency on strongyle prevalence was only encountered with adult horses. On farms performing more than one annual treatment, faecal samples were significantly less often positive. Furthermore, by comparing the FECR results of individual horses with their pre-treatment FEC, it was found that high pre-treatment FEC were associated with a significantly higher probability for a FECR below 90%.

Conclusion

Overall, age-dependent strongyle infection patterns and general worm control approaches were found to be similar on horse farms in the three countries. Also, a negative association of pre-treatment FEC and treatment efficacy was consistently found in all countries. However, mean strongyle prevalences and frequencies of anthelmintic treatments were considerably different. In addition to the age-dependent prevalence patterns, the finding of a possible negative association between high FEC and reduced FECR might argue for a focus on horses showing high pre-treatment FEC when monitoring anthelmintic treatment efficacy in the field.

Moxidectin: a review of chemistry, pharmacokinetics and use in horses

This article reviews the current knowledge of the use of moxidectin (MOX) in horses, including its mode of action, pharmacokinetic and pharmacodynamic properties, efficacy, safety and resistance profile.Moxidectin is a second generation macrocyclic lactone (ML) with potent endectocide activity. It is used for parasite control in horses in an oral gel formulation. The principal mode of action of MOX and of other MLs is binding to gamma-aminobutyric (GABA) and glutamate-gated chloride channels. Moxidectin is different from other MLs in that it is a poor substrate for P-glycoproteins (P-gps) and therefore less susceptible to elimination from parasite cells through this mechanism. Due to its unique physicochemical and pharmacokinetic characteristics, MOX provides broad distribution into tissues, long half-life, significant residual antiparasitic activity, and high efficacy against encysted cyathostomin larvae. These characteristics allow for high efficacy and longer treatment interval against all important nematodes, when compared to other equine anthelmintics. A combination of MOX with praziquantel provides expanded spectrum of activity by adding activity against cestodes. Appropriate use of MOX allows for the development of strategic anthelmintic programmes that are different from those with conventional anthelmintics. Fewer treatments are required over a period of time, and therefore impose less frequent selection pressure for resistance.

Anthelmintic resistance in cyathostomin populations from horse yards in Italy, United Kingdom and Germany

BACKGROUND

A large survey was carried out in 2008 in Europe to evaluate the efficacy of fenbendazole (FBZ), pyrantel (PYR), ivermectin (IVM) and moxidectin (MOX), i.e. the major anthelmintic molecules used in current practice against cyathostomins affecting horses. A total of 102 yards and 1704 horses was studied in three countries: 60 yards and 988 horses from Italy, 22 and 396 from the UK, 20 and 320 from Germany. The survey consisted of Faecal Egg Count Reduction Tests (FECRTs) with a faecal egg count reduction (FECR) categorization of (I) resistance present if FECR <90% and the lower 95% confidence limit (LCL) <90%, (II) resistance suspected if FECR >/= 90% and/or LCL <90% and (III) no resistance if FECR >/= 90% and LCL >90%. The calculation of FECR data was performed employing bootstrap analysis of group arithmetic means.

RESULTS

The testing of FBZ on a total of 80 yards resulted in resistance present on more than 80% of the UK and German yards and on significantly fewer in Italy, i.e. in 38% (p < 0.01). PYR, IVM and MOX were tested on a total of 102 yards. For PYR resistance present was found in 25% of the yards with no significant differences between countries. For IVM resistance present was encountered in one Italian and two UK yards (3%), resistance present to MOX was not found in any yard in any country.

CONCLUSION

The results indicate that single and/or multiple drug resistance in equine cyathostomins is present in the three countries, is widespread particularly for FBZ and/or PYR and in one UK yard multiple resistance present was detected to FBZ, PYR and IVM. Macrocylic lactones proved to be the most effective drugs, with some evidence of resistance to IVM and highest activity of MOX, despite a single case of reduced efficacy in Germany. These data call for the development and implementation, among practitioners, owners and managers, of further plans to reduce the expansion of the anthelmintic resistant populations and to use those anthelmintics that remain effective in a manner that preserves their efficacy as long as possible.

Comparison of pharmacodynamic and pharmacokinetic indices of efficacy for 5 fluoroquinolones toward pathogens of dogs and cats

BACKGROUND

Fluoroquinolones are often used interchangeably in dogs and cats.

HYPOTHESIS

Predicted therapeutic efficacy differs among fluoroquinolones.

ANIMALS

Bacterial pathogens isolated from dogs and cats.

METHODS

Using microtube-dilution procedures, percent resistance and 2 pharmacodynamic/pharmacokinetic indices (maximum concentration/minimum inhibitory concentration [Cmax/MIC] [target 0.10] and area under curve/minimum inhibitory concentration [AUC/MIC] [target 0.125]) were compared prospectively at low and high doses (mg/kg) for ciprofloxacin (5 and 20), difloxacin (5 and 10), enrofloxacin (including enrofloxacin+ciprofloxacin) (5 and 20), marbofloxacin (2.5 and 5), and orbifloxacin (2.5 and 7.5). Indices were calculated for organisms represented by < or = 15 isolates.

RESULTS

Percent resistance for all Gram-negative (n = 180; 20+/-3%; 39+/-5% for Escherichia coli) and Gram-positive isolates (n = 66; 18+/-3%) did not differ among drugs or organisms. The pattern of Cmax/MIC was generally enrofloxacin+ciprofloxacin > or = enrofloxacin or ciprofloxacin > or = marbofloxacin > or = orbifloxacin > or = difloxacin; and for AUIC/ MIC, enrofloxacin+ciprofloxacin > or = marbofloxacin > or = ciprofloxacin > or = enrofloxacin > difloxacin > orbifloxacin. Among susceptible Gram-negative isolates studied (n = 117), targeted Cmax/MIC or AUC/MIC were achieved in 88% of E. coli, 53% of Proteus mirabilis, and 35% of Pseudomonas aeruginosa; and for susceptible Gram-positive isolates studied (n = 49), 53% of Streptotoccus spp. and Staphylococcus intermedius and 27% of Staphylococcus spp. At the high dose, the proportion of isolates for which a target was reached was: ciprofloxacin, enrofloxacin+ciprofloaxin, and marbofloxacin (77%), enrofloxacin (73%), orbifloxacin (51%), and difloxacin (40%); and at the low dose, enrofloxacin+ciprofloxacin and enrofloxacin (43%), ciprofloxacin (40%), marbofloxacin (39%), orbifloxacin (29%), and difloxacin (28%).

CONCLUSIONS

E. coli resistance to fluoroquinolones approximated 40%. For susceptible isolates, enrofloxacin, marbofloxacin, and ciprofloxacin more consistently reached indices associated with predicted efficacy, but only at the high dose.

Evaluation of the concentration of marbofloxacin in alveolar macrophages and pulmonary epithelial lining fluid after administration in dogs

OBJECTIVE

To determine concentrations of marbofloxacin in alveolar macrophages (AMs) and epithelial lining fluid (ELF) and compare those concentrations with plasma concentrations in healthy dogs.

ANIMALS

12 adult mixed-breed and purebred hounds.

PROCEDURE

10 dogs received orally administered marbofloxacin at a dosage of 2.75 mg/kg every 24 hours for 5 days. Two dogs served as nontreated controls. Fiberoptic bronchoscopy and bronchoalveolar lavage procedures were performed while dogs were anesthetized with propofol, approximately 6 hours after the fifth dose. The concentrations of marbofloxacin in plasma and bronchoalveolar fluid (cell and supernatant fractions) were determined by use of high-performance liquid chromatography with detection of fluorescence.

RESULTS

Mean +/- SD plasma marbofloxacin concentrations 2 and 6 hours after the fifth dose were 2.36 +/- 0.52 microg/mL and 1.81 +/- 0.21 microg/mL, respectively. Mean +/- SD marbofloxacin concentration 6 hours after the fifth dose in AMs (37.43 +/- 24.61 microg/mL) was significantly greater than that in plasma (1.81 +/- 0.21 microg/mL) and ELF (0.82 +/- 0.34 microg/mL), resulting in a mean AM concentration-to-plasma concentration ratio of 20.4, a mean AM:ELF ratio of 60.8, and a mean ELF-to-plasma ratio of 0.46. Marbofloxacin was not detected in any samples from control dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Marbofloxacin concentrations in AMs were greater than the mean inhibitory concentrations of major bacterial pathogens in dogs. Results indicated that marbofloxacin accumulates in AMs at concentrations exceeding those reached in plasma and ELF The accumulation of marbofloxacin in AMs may facilitate treatment for susceptible intracellular pathogens or infections associated with pulmonary macrophage infiltration.

Efficacy of fipronil in the treatment of feline cheyletiellosis

The purpose of the present study was to confirm the efficacy of 10% (w/v) fipronil spot-on (Frontline spot-on for cats) in the treatment of feline cheyletiellosis under field conditions. A total of 16 cats of different breeds, sexes, 4 months to 14 years of age and weighing 0.5-6 kg were treated with a single topical application of 10% (w/v) fipronil spot-on according to label directions. The animals were naturally infested with Cheyletiella mites and housed in their normal environment throughout the study. Animals were selected based on clinical signs and infestation was confirmed by demonstration of mites. Mite counts and a clinical assessment of mite infestations (i.e. skin lesions and/or scales) were performed on days 0 and approximately days 14 and 28. Individual counts on day 0 ranged from 1 to 40 mites on individual animals. No mites were detected on cats treated with 10% (w/v) fipronil spot-on (Frontline spot-on for cats) at both post-treatment evaluations. Typical skin lesions and/or scales were present in all animals pre-treatment. In 56% of the cats, the lesions resolved within 14 days after treatment. At the final assessment, 75% cats were free of lesions. Two cats that still had clinical signs on day 28 were suspected of having allergic reactions to food or environmental allergens. The lesions on the remaining two cats could not be related to a specific cause. The efficacy of fipronil in elimination of mites was 100% on each occasion when compared to the pre-treatment count. The results of this study demonstrated that fipronil in a topical formulation is highly effective (100%) for the elimination of an existing Cheyletiella mite infestation under field conditions following a single topical application in cats.

Efficacy of fipronil/(S)-methoprene combination spot-on for dogs against shed eggs, emerging and existing adult cat fleas (Ctenocephalides felis, Bouché)

The inhibitory activities of fipronil (10% (w/v) solution), (S)-methoprene (9% (w/v) solution), and fipronil/(S)-methoprene (10 and 9% (w/v) solution, respectively) combination against eggs and emerging adult cat fleas (Ctenocephalides felis) and adulticidal activity were tested on experimentally infested dogs. Thirty-two Beagle dogs were selected for this study and eight replicates of four animals were formed based on body weight within sex. One dog in each replicate was randomly allocated to treatment with: (1) untreated control; (2) fipronil 10% (w/v) solution, (3) (S)-methoprene 9% (w/v) solution, and (4) fipronil 10% (w/v) and (S)-methoprene 9% (w/v) combination solution. Treatments were applied once topically on Day 0 at the rate of 0.067 ml/kg. On Days -12, -1, 21, and weekly to Day 84 each dog was infested with approximately 200 fleas and comb counted approximately 24h later, or 2 days (our 48 h) after in the case of Day -1 infestation. On Days -11, 1, 22, and weekly to Day 85 each dog was again infested with approximately 200 fleas. Flea eggs were collected over approximately 24 h beginning 3 days after infestation. Fleas were combed off of the dogs and counted at the end of the egg collection period (approximately 96 h count). One aliquot of up to about 100 eggs, if available, from each animal at each infestation time was incubated for approximately 72 h to determine larval hatch and the other for 35 days to determine the number of adults that developed. The 10% (w/v) fipronil spot-on provided excellent control (>95%) of adult fleas on dogs for 5 weeks. Similarly, the combination spot-on of 10% (w/v) fipronil and 9% (w/v) (S)-methoprene provided excellent control of adult fleas, i.e., >95% for 5 weeks. From week 6 post-treatment onward, the relatively low inhibition of adult flea emergence substantiated the lack of significant ovicidal/larvicidal activity in the fipronil (10%, w/v) treatment group. However, the combination product provided excellent (>90%) ovicidal activity for 8 weeks and high (91.4%) inhibition of adult flea emergence for 12 weeks. In addition, a synergistic effect of the two compounds in combination was demonstrated with fipronil enhancing the ovicidal and inhibition of adult flea emergence activity of (S)-methoprene against cat flea eggs. When all stages of the life cycle of the cat flea are considered, the combination spot-on product provided a high level of total flea control yielding a curative effect against adult fleas and inhibition of flea development stages with little to no potential reinfestation pressure on the animal or in the environment for 12 weeks.

Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin in dogs following single oral administration of enrofloxacin at 7.5, 10, or 20 mg/kg

Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin were monitored following oral administration of enrofloxacin at 7.5, 10, and 20 mg/kg to six healthy female bloodhounds using a randomized crossover design. Plasma samples were collected at various times over 24 hours following drug administration. Both the parent drug and its metabolite were detected by high-performance liquid chromatography, and plasma drug concentration-versus-time curves were subjected to noncompartmental pharmacokinetic analysis. Descriptive statistics were determined for each dosage, and comparisons were made among dosage groups for selected pharmacokinetic parameters. Increasing dosages of enrofloxacin resulted in increased plasma concentrations of both enrofloxacin and ciprofloxacin. Maximum concentration (Cmax) was 2.12 +/- 0.59, 2.1 +/- 0.34, and 4.74 +/- 1.05 mcg/ml for enrofloxacin and 1.30 +/- 0.31, 1.30 +/- 0.32, and 1.86 +/- 0.35 mcg/ml for ciprofloxacin when enrofloxacin was given at dosages of 7.5, 10, and 20 mg/kg, respectively. Cmax and area under the curve (AUC) for both enrofloxacin and ciprofloxacin were significantly greater at 20 mg/kg than at 7.5 and 10 mg/kg. Disappearance half-life was similar for all dosages, ranging from 4.6 to 5.2 hours for enrofloxacin and 8.8 to 10.7 hours for ciprofloxacin. Ciprofloxacin contributed up to 42% of the Cmax and up to 55% of the AUC of the total (enrofloxacin plus ciprofloxacin). For organisms with a minimum inhibitory concentration (MIC) of 0.5 mcg enrofloxacin/ml, an inhibitory quotient (IQ; Cmax:MIC) of 8 or more was achieved in plasma only at 20 mg/kg.

Dosing regimen and hematologic effects of pentoxifylline and its active metabolites in normal dogs

The disposition of pentoxifylline and two of its active metabolites (metabolite 1 [M1] and metabolite 5 [M5]) were studied following i.v. (8 mg/kg) and p.o. (30 mg/kg) administration to eight normal dogs using a randomized crossover design. Blood samples were collected at fixed time intervals after drug administration for determination of drug concentrations, platelet aggregation, and plasma fibrinogen. Complete blood counts, serum chemistry profiles, fibrinogen, and urinalysis were monitored at the beginning and end of each phase of the study (p.o. versus i.v. administration). Pentoxifylline was readily metabolized and bioavailable (50% +/- 26%). Both M1 and M5 were present throughout the study, with M5 predominating. Human drug therapeutic concentrations (1,000 ng/ml) were present for 170 +/- 24 minutes following i.v. administration and 510 +/- 85 minutes after p.o. dosing. These findings suggest that a 12-hour dosing regimen is appropriate. None of the dogs experienced any adverse effects after pentoxifylline administration. The lack of hematologic effects suggests that the immunologic effects of pentoxifylline may be of more importance in dogs.

Hyperactivity and alopecia associated with ingestion of valproic acid in a cat

A 1-year-old castrated male cat was evaluated because of alopecia of approximately 4 to 5 months' duration as well as hyperactive behavior. It was later determined that the cat was ingesting valproic acid by eating food to which it had been added for daily administration to a child in the household who had cerebral palsy. The clinical signs slowly resolved after the source of valproic acid was removed. This emphasizes the sensitivity of cats to drugs that are commonly used in humans. It was not determined whether the clinical signs that developed in this cat were caused by an adverse reaction or from toxicosis as a result of prolonged hepatic elimination of valproic acid, which requires glucuronide metabolism for disposition. However, the cat recovered completely following removal of the drug and prevention of further exposure. This report emphasizes the importance of obtaining a careful and complete history from the owner regarding an animal and its environment. In the cat of this report, the owner had not considered the impact of the presence of the drug in the child's food.

Time course of enrofloxacin and its active metabolite in peripheral leukocytes of dogs

The accumulation of fluoroquinolones in peripheral leukocytes is well established for several members of this family of drugs. This study documented accumulation of enrofloxacin and its active metabolite, ciprofloxacin, in canine peripheral leukocytes after oral administration at 7.5, 10, or 20 mg/kg, doses that are within the currently approved label of Baytril (Bayer Corporation Animal Health, Shawnee Mission, KS) in the United States. Accumulation index, as defined by C(max) in white blood cells (WBCs) divided by C(max) in plasma at the same time points, ranged from 47-fold to 63-fold for enrofloxacin and 28- to 35-fold for ciprofloxacin. Time course of both enrofloxacin and ciprofloxacin in WBCs paralleled the time course in plasma. Disappearance half-life of ciprofloxacin from WBCs was significantly (P = .001) longer than was enrofloxacin (P= .015) for all doses studied. The accumulation of enrofloxacin in peripheral leukocytes may contribute to the antimicrobial efficacy of this compound.

Pharmacokinetics of the bovine formulation of enrofloxacin (Baytril 100) in horses

Following approval of a concentrated injectable formulation of enrofloxacin for cattle (Baytril 100 Injectable, Bayer Corp. Agricultural Division, Shawnee Mission, KS), equine practitioners have started administering this preparation both parenterally and orally to horses, despite the lack of pharmacokinetic data in this species. Six healthy horses received enrofloxacin at 7.5 mg/kg both orally and intravenously, with the sequence being randomly assigned and at least 1 week of washout allowed between administrations. Blood samples were collected from each horse at various intervals after drug administration to study the pharmacokinetic profile of this product. As concentration-dependent antimicrobials, fluorinated quinolones such as enrofloxacin are most efficacious when the inhibitory quotient is at least 8. In this study, based on inhibitory quotients between 8 and 10, the bovine injectable formulation of enrofloxacin administered to horses intravenously or orally once daily at 7.5 mg/kg may be effective against susceptible organisms whose minimum inhibitory concentration for 90% of the isolates is lower than 0.5 microg/ml.

Tissue concentrations of enrofloxacin and ciprofloxacin in anesthetized dogs following single intravenous administration

Concentrations of enrofloxacin and its active metabolite, ciprofloxacin, were detected in tissues following single intravenous administration of 20 mg/kg to four anesthetized dogs. Two hours after treatment, serum samples were collected, animals were euthanized, and tissues were collected from each dog. Solid tissues were homogenized, and both enrofloxacin and ciprofloxacin were detected using high-performance liquid chromatography. Enrofloxacin was detected in all tissues examined; the highest concentrations were found in the gall bladder, urine, bile, stomach, and liver. Concentrations in the cerebral cortex, cerebrospinal fluid, skin, and prostate were 5.7, 5.3, 9.2, and 23.5 microg/ml, respectively. Tissues for which the concentration of enrofloxacin was 4 microg/ml or lower included the trachea, articular cartilage, aqueous humor, fat, and tendon. An inhibitory quotient of 8 or more was achieved for enrofloxacin in the majority of tissues studied. Ciprofloxacin was detected in 29 of 40 tissues examined.