Dexamethasone treatment interferes with the pharmacokinetics of ivermectin in young cattle

Topical Dexamethasone Counters Intravitreal Ivermectin-Induced Ocular Toxicity in a Rabbit Model

PURPOSE

Systemic use of Ivermectin has been reported to incite blindness in humans and veterinary patients. This study was designed to investigate the systemic and intravitreal effect of Ivermectin on ocular and retinal health and its attenuation with topical Dexamethasone.

METHODS

Systemic injection of Ivermectin@ 1.6 mg/kg S/C was administered, thrice a week for three weeks to New Zealand White rabbits (N = 4) with and without topical drops of Verapamil (N = 4). Pre and post-treatment ocular examination was conducted. At the end of three weeks the eyes were collected for histopathology.0.2 ml of Ivermectin solution (1.6 mg/ml) was injected intravitreally in one eye of the rabbit (N = 8), Half the rabbits received 0.1% dexamethasone drops thrice daily for 7 days, while the controls received PBS. Pre and post-treatment, detailed examination was conducted, which included the Schirmer Tear test, Fluorescein staining, Intraocular pressure, slit lamp biomicroscopy and fundus photography. The retina was harvested for histopathological and tunnel assay.

RESULTS

Systemic therapy with Ivermectin, with and without Verapamil did not incite any adverse response in the eye. Intravitreal Ivermectin evoked severe uveitis 4/4, cataract 3/4, corneal erosion 3/4 eyes and severe inflammatory response. Eyes that received dexamethasone were rescued from the adverse changes as demonstrated clinically, by histopathology and prevention of apoptosis.

CONCLUSIONS

Intravitreal Ivermectin incites severe inflammatory response. Topical dexamethasone counters the ocular toxicity incited by Ivermectin.

Drug-Drug Interactions Involving Dexamethasone in Clinical Practice: Myth or Reality?

Concomitant administration of multiple drugs frequently causes severe pharmacokinetic or pharmacodynamic drug-drug interactions (DDIs) resulting in the possibility of enhanced toxicity and/or treatment failure. The activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp), a drug efflux pump sharing localization and substrate affinities with CYP3A4, is a critical determinant of drug clearance, interindividual variability in drug disposition and clinical efficacy, and appears to be involved in the mechanism of numerous clinically relevant DDIs, including those involving dexamethasone. The recent increase in the use of high doses of dexamethasone during the COVID-19 pandemic have emphasized the need for better knowledge of the clinical significance of drug-drug interactions involving dexamethasone in the clinical setting. We therefore aimed to review the already published evidence for various DDIs involving dexamethasone in vitro in cell culture systems and in vivo in animal models and humans.

Efficacy of ivermectin against gastrointestinal nematodes of cattle in Denmark evaluated by different methods for analysis of faecal egg count reduction

The efficacy of ivermectin (IVM) against gastrointestinal nematodes in Danish cattle was assessed by faecal egg count reduction test (FECRT). Six cattle farms with history of clinical parasitism and avermectin use were included. On the day of treatment (Day 0), 20 naturally infected calves per farm (total n = 120) were stratified by initial faecal egg counts (FEC) and randomly allocated to a treatment group dosed with 0.2 mg IVM kg-1 body weight s.c. (IVM; n = 10) or an untreated control group (CTL; n = 10). Individual FEC were obtained at Day 0 and Day 14 post-treatment and pooled faeces by group were cultured to isolate L3 for detection of Ostertagia ostertagi and Cooperia oncophora by qPCR. Treatment efficacies were analysed using the recommended WAAVP method and two open-source statistical procedures based on Bayesian modelling: 'eggCounts' and 'Bayescount'. A simulation study evaluated the performance of the different procedures to correctly identify FEC reduction percentages of simulated bovine FEC data representing the observed real data. In the FECRT, reduced IVM efficacy was detected in three farms by all procedures using data from treated animals only, and in one farm according to the procedures including data from treated and untreated cattle. Post-treatment, O. ostertagi and C. oncophora L3 were detected by qPCR in faeces of treated animals from one and three herds with declared reduced IVM efficacy, respectively. Based on the simulation study, all methods showed a reduced performance when FEC aggregation increased post-treatment and suggested that a treatment group of 10 animals is insufficient for the FECRT in cattle. This is the first report of reduced anthelmintic efficacy in Danish cattle and warrants the implementation of larger surveys. Advantages and caveats regarding the use of Bayesian modelling and the relevance of including untreated cattle in the FECRT are discussed.

Preclinical Study of Single-Dose Moxidectin, a New Oral Treatment for Scabies: Efficacy, Safety, and Pharmacokinetics Compared to Two-Dose Ivermectin in a Porcine Model

Background

Scabies is one of the commonest dermatological conditions globally; however it is a largely underexplored and truly neglected infectious disease. Foremost, improvement in the management of this public health burden is imperative. Current treatments with topical agents and/or oral ivermectin (IVM) are insufficient and drug resistance is emerging. Moxidectin (MOX), with more advantageous pharmacological profiles may be a promising alternative.

Methodology/Principal Findings

Using a porcine scabies model, 12 pigs were randomly assigned to receive orally either MOX (0.3 mg/kg once), IVM (0.2 mg/kg twice) or no treatment. We evaluated treatment efficacies by assessing mite count, clinical lesions, pruritus and ELISA-determined anti-S. scabiei IgG antibodies reductions. Plasma and skin pharmacokinetic profiles were determined. At day 14 post-treatment, all four MOX-treated but only two IVM-treated pigs were mite-free. MOX efficacy was 100% and remained unchanged until study-end (D47), compared to 62% (range 26–100%) for IVM, with one IVM-treated pig remaining infected until D47. Clinical scabies lesions, pruritus and anti-S. scabiei IgG antibodies had completely disappeared in all MOX-treated but only 75% of IVM-treated pigs. MOX persisted ~9 times longer than IVM in plasma and skin, thereby covering the mite’s entire life cycle and enabling long-lasting efficacy.

Conclusions/Significance

Our data demonstrate that oral single-dose MOX was more effective than two consecutive IVM-doses, supporting MOX as potential therapeutic approach for scabies.

Scabies caused by the Sarcoptes scabiei mite affects many people worldwide and has been recently recognized by the WHO as a truly neglected tropical disease. Currently available treatments are insufficient to overcome this insidious disease and its co-morbidities for example impetigo, rheumatic heart disease and post-streptococcal glomerulonephritis. Treatment management is a major issue, as problems with compliance as well as mite resistance to current drugs are reported. Data have accumulated indicating that moxidectin could be a genuine new candidate drug for sustainable scabies control. To provide proof of concept, we utilized an experimental scabies pig model that closely resembles the human route of scabies infection. We demonstrated that a single moxidectin dose, when compared with the currently recommended two-doses ivermectin treatment routine, achieved a better and faster acaricidal efficacy. Importantly, the skin half-life of moxidectin is longer, potentially covering the entire mite life cycle. Our baseline data demonstrate in principle the potential and feasibility of moxidectin treatment for scabies, thereby enabling the move into larger high-powered efficacy and dose ranging studies in human populations. Moxidectin could indeed play a game-changing role in scabies control and has the potential to accelerate the steps towards elimination of this insidious disease.

Ivermectin exposure leads to up-regulation of detoxification genes in vitro and in vivo in mice

The biodisposition of the antiparasitic drug ivermectin in host and parasite is decisive for its efficacy and strongly depends on the efflux by ATP-Binding Cassette (ABC) transporters and on its biotransformation by cytochromes P450. The purpose of this study was to evaluate, in vitro and in vivo, the ivermectin ability in modulating the expression of the most important genes involved in drug detoxification. Gene expression of ABC transporters and cytochromes was evaluated by RT-qPCR in murine hepatic and intestinal cell lines exposed to increasing ivermectin doses, and in liver and intestine of mice orally administered with single or repeated therapeutic doses of ivermectin (0.2 mg/kg). Plasma, brain, liver and intestinal concentrations of ivermectin and its main metabolite were measured by HPLC in ivermectin-treated mice. In hepatocyte cell line, ivermectin up-regulated expression of Abcb1a, Abcb1b, Abcc2, Cyp1a1, Cyp1a2, Cyp2b10; while Abcb1a, Abcb1b, Abcg2, Cyp1a1, Cyp1a2, Cyp2b10 and Cyp3a11 levels were induced in intestinal cell line. In mice, repeated administration of ivermectin induced the expression of Abcb1a, Abcc2, Cyp1a1 and Cyp2b10 in intestine while only Cyp3a11 was induced in liver. Compared with single administration, repeated ivermectin administration lowered plasma, liver and intestine drug concentration, while increasing main metabolite content in plasma and intestine. These findings can be regarded as a warning that repeated ivermectin exposure is able to induce detoxification systems in mammals that may lead to subtherapeutic drug concentration. This may also be an important consideration in the assessment of drug-drug interaction and toxicity for other ABC transporters and CYP450s substrates.

A controlled study on gastrointestinal nematodes from two Swedish cattle farms showing field evidence of ivermectin resistance

BACKGROUND

Anthelmintic resistance (AR) is an increasing problem for the ruminant livestock sector worldwide. However, the extent of the problem is still relatively unknown, especially for parasitic nematodes of cattle. The effect of ivermectin (IVM) (Ivomec inj.®, Merial) was investigated in Swedish isolates of gastrointestinal nematode (GIN) populations showing signs of AR in the field to further characterise the AR status by a range of in vivo and in vitro methods.

METHODS

Three groups, each of 11 calves, were infected with an equal mixture of third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi. Group A was inoculated with an IVM-susceptible laboratory isolate and groups B and C with isolates originating from 'resistant' cattle farms. Faecal egg counts (FEC) were monitored from 0 to 45 days post infection (d.p.i.), and L3 were harvested continuously for larval migration inhibition testing (LMIT) and species-specific PCR (ITS2). At 31 d.p.i., one calf from each group was necropsied and adult worms were recovered pre-treatment. At 35 d.p.i., calves from all groups were injected with IVM at the recommended dose (0.2 mg/kg bodyweight). At 45 d.p.i., another two animals from each group were sacrificed and established gastrointestinal worms were collected and counted.

RESULTS

A few animals in all three groups were still excreting eggs (50-150 per g faeces) 10 days post IVM injection. However, there was no significant difference in the FEC reductions in groups A (95%; 95% CI 81-99), B (98%; 92-100) and C (99%; 97-100) between 35 and 44 d.p.i. Furthermore, LMIT showed no significant difference between the three groups. Approximately 100 adult O. ostertagi were found in the abomasum of one calf (group B), whereas low to moderate numbers (400-12 200) of C. oncophora remained in the small intestine of the calves in all three groups at 45 d.p.i. PCR on L3 harvested from faecal samples up to 10 days post treatment showed a ratio of 100% C. oncophora in the calves inoculated with isolates A and B, whereas C also had 8% O. ostertagi.

CONCLUSIONS

Overall, this experiment showed that the animals were successfully treated according to the Faecal egg count reduction test (FECRT) standard (≥ 95% reduction). However, several adult worms of the dose-limiting species C. oncophora demonstrably survived the IVM treatment.

Limited efficacy of pour-on anthelmintic treatment of cattle under Swedish field conditions

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The use of topical formulations of macrocyclic lactones has increased in Sweden.

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Anthelmintic efficacy of topical ML under Swedish field conditions is insufficient.

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Cooperia oncophora was the predominant species surviving deworming.

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Herds that require treatment can be identified by faecal samples, 4–6 weeks after turnout.

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Swedish beef herds should be considered for GIN control to a greater extent than is done today.

A study on the effect of topical macrocyclic lactones (ML) against gastrointestinal nematodes (GIN) in Swedish first season grazing cattle (FSG) was performed during the grazing seasons of 2009 and 2010. Herds were recruited through farming press and both dairy and beef cattle farms were invited. A questionnaire revealed that 64% of participating farmers dewormed their animals in previous years, and of these 76% used topical formulations with ML. Four to six weeks after turnout, 107 (2009) and 64 (2010) farmers sent in individual faecal samples from 6–10 FSG. Faecal egg counts (FEC) were determined by the FECPAK®-method in 2009 and the McMaster-method in 2010, when also larvae were cultured. Average FEC of ⩾100 eggs per gram faeces (EPG) was seen in 39% of the herds in 2009 and 42% in 2010 and with arithmetic means of 258 ± 110 and 252 ± 350 EPG, respectively. Interestingly, FSG in dairy and beef herds had similar mean FEC. In herds with mean FEC of ⩾100 EPG, farmers dewormed all FSG in the tested grazing group with ivermectin (IVM) or doramectin (DOR) pour-on. In 2009, 33 (31%), and in 2010, 26 (40%) of the herds were retested 7–16 days post treatment. Mean reduction was 89% and 88%, respectively, and in only 12 (36%) and 10 (38%) herds it was ⩾95%. Beef herds had mean reductions similar to those of the dairy herds. No significant difference (P = 0.66) in reduction was seen between the groups treated with three different pour-on formulations, nor was there any correlation between the previous year’s usage of anthelmintics and the efficacy. Larvae from post-treatment cultures analysed in 2010 with a species-specific ITS2 qPCR showed that Cooperia oncophora was the predominant species after deworming. Four (15%) groups also harboured surviving Ostertagia ostertagi post treatment.

The Binding Interactions of the Macrolide Endectocide Ivermectin with the Antibiotics Ampicillin, Chloramphenicol and Tetracycline HCL

Ivermectin, chloramphenicol, ampicillin and tetracycline HCl are common drugs in human and veterinary practice. The purpose of this study is to investigate the possible binding interactions between ivermectin and the antibiotics chloramphenicol, ampicillin and tetracycline HCl. Isothermal titration calorimetry was used to determine the binding interactions between ivermectin and these antibiotics. Results indicated that, about three molecules of ampicillin can bind to one molecule of ivermectin and about one molecule of chloramphenicol with one molecule of ivermectin. However, no binding stoichiometry can be detected with tetracycline HCl-ivermectin titration. Furthermore, the binding interactions were accompanied by various biophysical and biochemical mechanisms. This is the first report of such interactions of ivermectin with chloramphenicol, ampicillin and tetracycline HCl. There are possible binding interactions of ivermectin with chloramphenicol and ampicillin. Further studies are required for detecting the impact of this binding on biological aspects of drug actions.