A single subcutaneous administration of a sustained-release ivermectin suspension eliminates Psoroptes cuniculi infection in a rabbit farm

Abstract

Background: Psoroptes cuniculi mites are the most common ear parasites infesting breeding female rabbits. The suffering rabbits show cutaneous signs of the infestation in the ears and are prone to secondary infections.

Objectives: This trial was conducted to eliminate P. cuniculi in farm rabbits with a sustained-release ivermectin-loaded solid dispersion suspension (IVM-SD) suspension, and studied the stability of the formulation.

Animals: There were 986 breeding female Hyplus rabbits naturally infected with P. cuniculi.

Methods: All rabbits infected with P. cuniculi were subcutaneously administered with a single dose of IVM-SD suspension at 2?mg/kg body weight. Twenty-seven rabbits with severe infections were observed daily and examined on days 0 and 14 to score the lesions and count mites in crusts.

Results: Fourteen days after the treatment no live mites were detected, demonstrating 100% therapeutic efficacy. The mean lesion scores decreased from 4.33 to 0.11 in the left ears and from 4.22 to 0.22 in the right ears. No reinfection occurred within 60?days of treatment.

Conclusions: A single subcutaneous administration of the IVM-SD suspension at 2?mg/kg was effective in eliminating P. cuniculi infection in the rabbit farm.     

杀虫抗生素的发展概况与展望

杀虫抗生素是生物源杀虫剂,具有高效、低毒、选择性强、对环境无公害等特点,在害虫综合治理中有重要地位,是无公害作物中首选农药之一。作者就杀虫抗生素的品种开发情况进行了阐述,对杀虫素的杀虫机理、抗性机制及进一步加大研究开发力度等问题进行了讨论。     

伊维菌素缓释微球注射液制备工艺研究

以乳化溶剂挥发法制备伊维菌素(IVM)聚乳酸(PLA)微球,用该微球制备注射液并进行质量控制研究。采用Central Composite试验设计,对微球制备中的搅拌速度、投料比IVM:PLA、聚乙烯醇浓度3个因素进行响应面优化;采用L16(34)正交实验对助悬体系进行优化;制备IVM缓释微球注射液并进行质量评价。研究结果表明：优化后的搅拌速度为651 r/min,投料比为7:16,PVA浓度为1.47%,此条件下微球载药率为29.4%;优化后的助悬体系为微球粒径80μm,微球、吐温20与羟甲基纤维素钠含量分别为2.5%、1.5%、1%,在此条件下注射液沉降体积比为91.5%;经测定注射液的平均pH为7.2,体外20d内可以平稳释放,达到缓释效果,稳定性良好,这一研究过程为IVM缓释微球注射液的工业制备及在临床上安全应用奠定了一定基础。     

Injectable PLA-based in situ forming implants for controlled release of Ivermectin a BCS Class II drug: solvent selection based on physico-chemical characterization

In situ forming implants (ISI) prepared from biodegradable polymers such as poly(d,l-lactide) (PLA) and biocompatible solvents can be used to obtain sustained drug release after parenteral administration. The aim of this work was to study the effect of several biocompatible solvents with different physico-chemical properties on the release of ivermectin (IVM), an antiparasitic BCS II drug, from in situ forming PLA-based implants. The solvents evaluated were N-methyl-2-pyrrolidone (NMP), 2-pyrrolidone (2P), triacetine (TA) and benzyl benzoate (BB). Hansen’s solubility parameters of solvents were used to explain polymer/solvent interactions leading to different rheological behaviours. The stability of the polymer and drug in the solvents were also evaluated by size exclusion and high performance liquid chromatography, respectively. The two major factors determining the rate of IVM release from ISI were miscibility of the solvent with water and the viscosity of the polymer solutions. In general, the release rate increased with increasing water miscibility of the solvent and decreasing viscosity in the following order NMP>2P>TA>BB. Scanning electron microscopy revealed a relationship between the rate of IVM release and the surface porosity of the implants, release being higher as implant porosity increased. Finally, drug and polymer stability in the solvents followed the same trends, increasing when polymer-solvent affinities and water content in solvents decreased. IVM degradation was accelerated by the acid environment generated by the degradation of the polymer but the drug did not affect PLA stability.     

Occurrence of ivermectin in bovine milk from the Brazilian retail market

High-performance liquid chromatography (HPLC) with fluorescence detection was used for the quantification of ivermectin residues in bovine milk intended for human consumption. After liquid-liquid extraction of ivermectin and purification of the extract, the compound was derivatized with 1-methylimidazol in N,N-dimethyl formamide to form a fluorescent derivative, which was separated by HPLC, using reversed-phase C₁₈, with methanol : water (96 : 4 v/v) mobile phase at a flow rate 0.7 ml min^-1. The excitation and emission wavelengths of the fluorescence detector were adjusted at 360 and 470 nm, respectively. The linearity of the method was in the range 10-100 ng ivermectin ml^-1. Based on a sample of 5.0 ml, the limit of detection and the limit of quantification for ivermectin in milk were 0.6 and 2 ng ml^-1, respectively. The recovery rate varied from 76.4 to 87.2%, with an average of 77.9 ± 3.2%, at four fortification levels. The inter-day precision of the method was 13% (n = 5). Of 168 samples analysed, 17.8% contained ivermectin above the limit of quantification. Nevertheless, none of the samples contained ivermectin above the maximum residue limit (10 ng ml^-1) established by the Brazilian Ministry of Agriculture.     

Results of an international ring test with the dung fly Musca autumnalis in support of a new OECD test guideline

A standardized bioassay using the face fly, Musca autumnalis L. (Diptera: Muscidae), was developed to test the lethal and sublethal toxicity of parasiticide residues in livestock dung. The repeatability of this test was assessed for the parasiticide ivermectin in seven tests performed in four laboratories in Germany and France. Additional results of limit tests were provided by two laboratories from the UK. Test results had an acceptable range of heterogeneity. The calculated effect concentration at which 50% emergence was observed (EC50) averaged 4.65 ± 2.17 (Standard Deviation (SD) µg ivermectin/kg fresh dung (range: 1.20-7.7)). Effects on emergence were, with one exception, not observed below the No Observed Effect Concentration (NOEC) ranging between 1.11 and 3.33 µg ivermectin/kg. No effect on development time was observed. We conclude that the face fly is suitably sensitive, and the methods sufficiently repeatable, to support use of this standardized bioassay by the international community in the registration of new veterinary pharmaceuticals. Following these considerations, this species was accepted as a possible test organism in a recently published OECD Guideline (No. 228).     

Determination of ivermectin and moxidecin residues in bovine milk and examination of the effects of these residues on acid fermentation of milk

Ivermectin (IVM) and moxidectin (MXD) are broad-spectrum antiparasitic drugs not approved for use in dairy animals, although their use in dairy sheep, goats and cattle nevertheless occurs in many parts of the world. The work reported here describes (1) the application of an HPLC method (including milk samples clean-up and chemical extraction) to quantify IVM and MXD residues in bovine milk, and (2) an assessment of the effect of different IVM and MXD concentrations on bovine milk acid fermentation. The latter was carried out using the 'yoghurt test' to determine the minimum IVM and MXD concentrations affecting milk acid fermentation. The sample clean-up, chemical extraction and the validated HPLC method allowed the quantification of IVM and MXD up to 0.1 ng ml^-1 in milk with acceptable validation coefficients. Drug recoveries from fortified milk samples ranged between 72% (CV = 9.1%) and 75% (CV = 13.3%) for MXD and IVM, respectively. Neither IVM nor MXD affected the acid fermentation of bovine milk. In fact, there was no drug-induced changes on milk acidity even at IVM and MXD concentrations as high as 1000 ng ml^-1. These results indicate that the yoghurt biological test is not suitable to evaluate the presence of milk residues for these antiparasitic compounds. Thus, a highly sensitive HPLC technique is the only reliable method for determining the presence of residual concentrations of IVM and MXD in milk and dairy products to assure consumer safety.