Anthelmintics for dogs and cats

Comparative plasma exposure of albendazole after administration of rapidly disintegrating tablets in dogs

The main objectives of this study were (a) to evaluate the in vitro performance of the rapid disintegration tablets as a way to improve the solid dispersions and (b) to study the in vivo pharmacokinetics of the albendazole modified formulation in dogs. Rapid disintegration of tablets seems to be a key factor for efficiency of solid dispersions with regard to improvement of the albendazole bioavailability. The in vivo assays performed on dogs showed a marked increase in drug plasma exposure when albendazole was given in solid dispersions incorporated into rapid disintegration tablets compared with conventional solid dosage form.

In vitro effect of seven antiparasitics on Acolpenteron ureteroecetes (Dactylogyridae) from largemouth bass Micropterus salmoides (Centrarchidae)

Few drugs are approved by the United States Food and Drug Administration for treating parasite infections in minor species such as fish, due in part to the high cost of developing such drugs and to a relatively small market share for drug sponsors. Because in vivo effectiveness trials for antiparasitic drugs are costly, time consuming, and use many animals, a systematic in vitro screening approach to describe parasite motility could help find promising drug candidates. We evaluated the effects of 7 antiparasitics on the activity and survival of the endoparasitic monogenean Acolpenteron ureteroecetes (Dactylogyridae) collected from the posterior kidneys of juvenile largemouth bass Micropterus salmoides (Lacepede, 1802) (Centrarchidae) held in the laboratory. Tests were conducted in 12 well tissue culture plates; each well had 3 parasites, and we tested 3 concentrations and 1 control for each of the 7 antiparasitics. The parasites were observed immediately after adding the drug, at 1 to 3 h, and 17 to 26 h, and video recordings were made. Drug effects were recorded by documenting morbidity (reduced movement, tremors, contracted body, abnormal morphology) and mortality. A. ureteroecetes was strongly affected by the quinoline praziquantel, the imidazothiazide levamisole, and the organophosphates dichlorvos and trichlorfon. The parasites were moderately affected by the macrocyclic lactones ivermectin and emamectin, and generally unaffected by the benzimidazole mebendazole. Our study demonstrates the utility of characterizing in vitro responses with video microscopy to document responses of fish parasites for initial screens of drug effects on a fish monogenean.

Improved albendazole dissolution rate in pluronic 188 solid dispersions

Solids dispersions (SDs) have been proposed as an alternative to improve the dissolution rate of low solubility drugs. SDs containing albendazole (ABZ; 5, 10, 25, and 50% w/w) and Pluronic 188 (P 188) as hydrophilic carrier were formulated. The obtained SDs were assessed in comparison to physical mixtures (PMs). Drug-polymer interactions in solid state were investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. No chemical interaction was found between ABZ and poloxamer. The dissolution profiles indicated that ABZ incorporated in SDs and PMs was rapidly released, reaching rapidly the steady state. Increased dissolution rates are usually observed at the highest polymer proportions. However, an opposite effect for SDs as well as for PMs was observed in the assays described here. The systems with the lowest P 188 percentages (SD4, SD3; PM4, PM3) tended to be more effective in increasing the ABZ dissolution rate. Such a result can be attributed to the fact that concentrated aqueous solutions of Poloxamer may form thermo-reversible gels. The physical-mechanical properties indicated that SDs possess improved flow and compacting properties compared to PMs. Thus, ABZ SDs would be more convenient for solid dosage form design and manufacture.

Comparative pharmacokinetics of some injectable preparations containing ivermectin in dogs

Little is known about the kinetics of ivermectin formulations following subcutaneous administration in dogs. The vehicle components used in production may change the pharmacokinetics of the drug. The present study was aimed at the comparison of the pharmacokinetics of seven injectable ivermectin formulation of different brand names (A-G). The animals were allocated to seven groups, each comprising seven dogs. The dogs were administered ivermectin at a dose of 200 microg/kg bw by subcutaneous route and blood samples were collected from all groups up to 288h post-injection. Plasma ivermectin analyses were performed using a HPLC with a fluorescence detector. Compared to Group 1(A), it was determined that statistically significant differences existed in Groups 2(B), 3(C), 4(D), 5(E), and 7(G) for C(max) values; and in Groups 3(C), 4(D), 6(F), 7(G) for AUC(0-->288) and AUC(0-->infinity) values. These values were highest in Group 1(A) and lowest in Group 7(F). The results obtained in the present study demonstrated that, in cases which require subacute administration, optimal exposure is achieved with the preparation A. However, it must be noted that this evaluation was based on pharmacokinetic parameters and not antiparasitic efficacy.

Pyrantel in small animal medicine: 30 years on

Pyrantel, a tetrahydropyrimidine nicotinic agonist anthelmintic, has been used in companion animal medicine since the 1970s to control two important nematode groups, the hookworms and the roundworms. Given the zoonotic potential of these parasites, pyrantel has served a dual role in helping to protect the health of both companion animals and the public for more than 30 years. This review describes the history and mechanism of action of this drug, and collates evidence that resistance to pyrantel has developed in at least one canine nematode, the hookworm Ancylostoma caninum. The role of in vitro diagnosis tests in managing anthelmintic resistance in companion animal parasites is discussed, as are management practices that may reduce the rate at which resistance develops.

Comparative plasma disposition of fenbendazole, oxfendazole and albendazole in dogs

The plasma disposition of fenbendazole (FBZ), oxfendazole (OFZ) and albendazole (ABZ); and the enantiospecific disposition of OFZ, and ABZSO produced were investigated following an oral administration (50 mg/kg) in dogs. Blood samples were collected from 1 to 120 h post-administration. The plasma samples were analysed by high performance liquid chromatography (HPLC). The plasma concentration of FBZ, OFZ, ABZ and their metabolites were significantly different from each other and depended on the drug administered. The sulphone metabolite (FBZSO2) of FBZ was not detected in any plasma samples and the parent molecule ABZ did not reach quantifiable concentrations following FBZ and ABZ administration, respectively. OFZ and its sulphone metabolite attained a significantly higher plasma concentration and remained much longer in plasma compared with FBZ and ABZ and their respective metabolites. The maximum plasma concentrations (Cmax), area under the concentration time curve (AUC) and mean residence time (MRT) of parent OFZ were more than 30, 68 and 2 times those of FBZ, respectively. The same parameters for ABZSO were also significantly greater than those of FBZSO. The ratio for total AUCs of both the parent drug and the metabolites were 1:42:7 for following FBZ, OFZ and ABZ administration, respectively. The enantiomers were never in racemic proportions and (+) enantiomers of both OFZ and ABZSO were predominant in plasma. The AUC of (+) enantiomers of OFZ and ABZSO was, respectively more than three and seven times larger than that of (-) enantiomers of both molecules. It is concluded that the plasma concentration of OFZ was substantially greater compared with FBZ and ABZ. The data on the pharmacokinetic profile of OFZ presented here may contribute to evaluate its potential as an anthelmintic drug for parasite control in dogs.

Pharmacological approaches towards rationalizing the use of endoparasitic drugs in small animals

Parasitic diseases are an important health concern to small animal veterinarians worldwide, and their zoonotic potential is also of relevance to human medicine. The treatment and control of such conditions relies heavily on pharmaceutical intervention using a range of antiparasitic drugs and/or their biologically active metabolites. Broad spectrum agents have been produced, although narrow and even monospecific drugs are used in some situations. Their efficacy may depend on dosage, the target pathogen(s), the host species and/or the site of infection. Optimal use of antiparasitics requires a detailed consideration of the pharmacokinetic and pharmacodynamic properties of the drugs in specific clinical contexts. This review summarizes the present status of knowledge on the metabolism, and physicochemical and pharmacological properties of the major antiparasitic drugs currently used in small animal veterinary practice. In addition, data relevant to therapeutic dosage, efficacy and clinical indication/contraindication, particularly in relation to combination drug therapy, are included.

Epidemiology: Prevalence of intestinal parasites in dogs in some urban and rural areas of Hungary

A total of 490 canine faecal specimens collected in the eastern and northern regions of Hungary were examined for helminth eggs. From the results it appears that more than 50% of the dogs were infected with at least one parasite species. The prevalence of eggs (%) in the two regions was as follows: Toxocara canis (24.3-30.1); Trichuris vulpis (20.4-23.3); Ancylostomatidae (8.1-13.1); Capillaria spp. (0-7.3); Toxascaris leonina (2.1-0); Taenia-type (2.8-2.4); Dipylidium caninum (0.4-1); coccidia (3.5-3.4). Of the positive dogs, 8.5-18.1% harboured two or more species of parasites. The prevalence of parasitic infection was also evaluated according to the maintenance, feeding, and age of the animals. The significance of zoonotic diseases (echinococcosis, toxocarosis, ancylostomatidosis) caused by intestinal helminths makes it necessary to know the infection status of domestic dogs and to take measures for control.

Anthelmintic efficacy of oxibendazole against some important nematodes in dogs and cats

The anthelmintic efficacy and safety of the oxibendazole component in a combination oxibendazole-niclosamide paste were investigated in dogs and cats and in litters of pups with naturally acquired nematode infections. A single dose of 15 mg oxibendazole/kg body weight given to 70 dogs and to 29 cats reduced faecal worm egg counts (EPG) by 97.6% for Toxocara canis, 95.7% for Trichuris vulpis, 94.6% for Ancylostoma caninum, and 100% for Toxascaris leonina. In cats, 96.7% efficacy was demonstrated against Toxocara cati. In a second trial, 119 pups in 22 litters were treated with the same dosage at 2, 4, and 6 weeks of age. After treatment on two consecutive days, 95% of the pups did not shed T. canis eggs, compared with 85% after only a single treatment. Side effects were rare and only recorded in young animals. A 2-day treatment schedule is recommended for unweaned pups.

Aspects of Toxocara epidemiology: toxocarosis in dogs and cats

Toxocara canis and Toxocara cati are common roundworms of dogs and cats. In this review the life cycles of these parasites are described, including the various routes of transmission, such as transplacental, transmammary infection, and infection through paratenic hosts. The somatic and tracheal migration in the body of the hosts after infection with Toxocara eggs or larvae is discussed, with special reference to age resistance and differences between dog and cat. The clinical symptoms and pathology in adult and young dogs and cats are given. Diagnosis of patent infections can be obtained by fecal examination, and treatment consists of the use of anthelmintics. Control of the infection and disease is achieved by prevention of contamination of the environment, anthelmintic treatment strategy, and education. Special attention is given to the efficacy of anthelmintics against adult worms and against somatic larvae. It is concluded that education on the life cycles of the parasites, hygiene, and anthelmintic treatment schedules is required because of the zoonotic risks of Toxocara spp. Deworming of pregnant dogs and cats is not recommended.

Pharmacokinetics of fenbendazole in dogs

Fenbendazole was administered to dogs at a dose rate of 20 mg/kg body weight on a single occasion in gelatin capsules, on 5 consecutive days in feed, and on a single occasion as an alginate suspension. It was also administered at a dose rate of 100 mg/kg body weight on a single occasion in feed. Following single administration of 20 mg/kg fenbendazole mean maximum concentrations (Cmax) of the parent drug and its known active sulphoxide metabolite were 0.42 +/- 0.05 and 0.31 +/- 0.05 microgram/ml, respectively. Mean times until maximum concentrations were achieved (tmax) were 12.67 +/- 4.18 and 15.33 +/- 2.81 h, respectively, and areas under the plasma concentration-time curves (AUC) were 5.83 +/- 0.65 and 4.60 +/- 0.57 microgram.h/ml, respectively. Administration in feed increased the apparent bioavailability and administration for 5 consecutive days provided sustained plasma concentrations, generally greater than 0.2 microgram/ml. Administration as an alginate did not increase bioavailability or extend the persistence in plasma. It did increase the tmax to 16.80 +/- 2.93 and 20.00 +/- 2.53 h for fenbendazole and its sulphoxide metabolite, respectively. Increasing the dose from 20 mg/kg to 100 mg/kg did not substantially increase the Cmax or AUC.

Benzimidazoles: Veterinary uses

Benzimidazoles are valued for use against helminth infections in domestic animals. Here, Bill Campbell discusses efficacy, dosages, methods of administration and the species of parasite against which they are applied.