Relative Bioavailability of Liquid and Tablet Formulations of the Antiparasitic Moxidectin

Safety and tolerability of moxidectin and ivermectin combination treatments for lymphatic filariasis in Côte d'Ivoire: A randomized controlled superiority study

BACKGROUND

Moxidectin is a macrocyclic lactone registered for the treatment of human onchocerciasis. The drug has a good safety profile, large volume of distribution and a long elimination half-life. This paper reports tolerability data from the first use of moxidectin in persons with Wuchereria bancrofti infection.

METHODS

In this randomized, open-label, masked-observer superiority trial, adults with Wuchereria bancrofti microfilaremia in Côte d'Ivoire were randomized to 1 of 4 treatment arms: ivermectin + albendazole (IA), moxidectin + albendazole (MoxA), ivermectin + diethylcarbamazine (DEC) + albendazole (IDA), or moxidectin + DEC + albendazole (MoxDA). As part of a larger efficacy trial, all participants were closely monitored for 7 days after treatment.

RESULTS

One hundred sixty-four individuals were treated, and monitored for treatment emergent adverse events (TEAE). Eighty-seven participants (53%) experienced one or more mild (grade 1) or moderate (grade 2) TEAE. Four participants had transient Grade 3 hematuria after treatment (3 after IDA and 1 after IA). There were no serious adverse events. There were no significant differences in frequency or types of TEAE between treatment groups (IA = 22/41 (53%), MoxA = 24/40 (60%), IDA = 18/41 (44%), MoxDA = 15/42 (36%), p = 0.530). Fifty-nine participants (36%) had multiple TEAE, and 8.5% had a one or more grade 2 (moderate) TEAE. Grade 2 TEAE were more frequent after triple drug treatments (IDA, 14.6%; MoxDA, 9.5%) than after two-drug treatments (IA, 7.3%; MoxA, 2.5%). There was no difference in TEAEs based on baseline Mf counts (OR 0.69 (0.33, 1.43), p-value 0.319).

CONCLUSION

All treatment regimens were well tolerated. We observed no difference in safety parameters between regimens that contained ivermectin or moxidectin.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT04410406.

Pharmacokinetic and pharmacodynamic considerations for treating sarcoptic mange with cross-relevance to Australian wildlife

Sarcoptes scabiei is the microscopic burrowing mite responsible for sarcoptic mange, which is reported in approximately 150 mammalian species. In Australia, sarcoptic mange affects a number of native and introduced wildlife species, is particularly severe in bare-nosed wombats (Vombatus ursinus) and an emerging issue in koala and quenda. There are a variety of acaricides available for the treatment of sarcoptic mange which are generally effective in eliminating mites from humans and animals in captivity. In wild populations, effective treatment is challenging, and concerns exist regarding safety, efficacy and the potential emergence of acaricide resistance. There are risks where acaricides are used intensively or inadequately, which could adversely affect treatment success rates as well as animal welfare. While reviews on epidemiology, treatment strategies, and pathogenesis of sarcoptic mange in wildlife are available, there is currently no review evaluating the use of specific acaricides in the context of their pharmacokinetic and pharmacodynamic properties, and subsequent likelihood of emerging drug resistance, particularly for Australian wildlife. This review critically evaluates acaricides that have been utilised to treat sarcoptic mange in wildlife, including dosage forms and routes, pharmacokinetics, mode of action and efficacy. We also highlight the reports of resistance of S. scabiei to acaricides, including clinical and in vitro observations.

Ivermectin and moxidectin against soil-transmitted helminth infections

Ivermectin and moxidectin, two macrocyclic lactones, are potent antiparasitic drugs currently registered and mainly used against filarial diseases; however, their potential value for improved soil-transmitted helminth (STH) control has been acknowledged. This review provides insights on recent studies evaluating the efficacy of ivermectin and moxidectin as single or coadministered therapy against human soil-transmitted helminthiases (including Strongyloides stercoralis infections) and on pharmacokinetic/pharmacodynamic parameters measured in treated populations. Furthermore, we discuss current gaps for research, highlight advantages - but also existing challenges - for uptake of ivermectin and/or moxidectin treatment schemes into routine STH control in endemic countries.

The pipeline for drugs for control and elimination of neglected tropical diseases: 1. Anti-infective drugs for regulatory registration

The World Health Organization 'Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021-2030' outlines the targets for control and elimination of neglected tropical diseases (NTDs). New drugs are needed to achieve some of them. We are providing an overview of the pipeline for new anti-infective drugs for regulatory registration and steps to effective use for NTD control and elimination. Considering drugs approved for an NTD by at least one stringent regulatory authority: fexinidazole, included in WHO guidelines for Trypanosoma brucei gambiense African trypanosomiasis, is in development for Chagas disease. Moxidectin, registered in 2018 for treatment of individuals ≥ 12 years old with onchocerciasis, is undergoing studies to extend the indication to 4-11-year-old children and obtain additional data to inform WHO and endemic countries' decisions on moxidectin inclusion in guidelines and policies. Moxidectin is also being evaluated for other NTDs. Considering drugs in at least Phase 2 clinical development, a submission is being prepared for registration of acoziborole as an oral treatment for first and second stage T.b. gambiense African trypanosomiasis. Bedaquiline, registered for tuberculosis, is being evaluated for multibacillary leprosy. Phase 2 studies of emodepside and flubentylosin in O. volvulus-infected individuals are ongoing; studies for Trichuris trichuria and hookworm are planned. A trial of fosravuconazole in Madurella mycetomatis-infected patients is ongoing. JNJ-64281802 is undergoing Phase 2 trials for reducing dengue viral load. Studies are ongoing or planned to evaluate oxantel pamoate for onchocerciasis and soil-transmitted helminths, including Trichuris, and oxfendazole for onchocerciasis, Fasciola hepatica, Taenia solium cysticercosis, Echinococcus granulosus and soil-transmitted helminths, including Trichuris. Additional steps from first registration to effective use for NTD control and elimination include country registrations, possibly additional studies to inform WHO guidelines and country policies, and implementation research to address barriers to effective use of new drugs. Relative to the number of people suffering from NTDs, the pipeline is small. Close collaboration and exchange of experience among all stakeholders developing drugs for NTDs may increase the probability that the current pipeline will translate into new drugs effectively implemented in affected countries.

Effect of a single dose of 8 mg moxidectin or 150 μg/kg ivermectin on O. volvulus skin microfilariae in a randomized trial: Differences between areas in the Democratic Republic of the Congo, Liberia and Ghana and impact of intensity of infection

Background

Our study in CDTI-naïve areas in Nord Kivu and Ituri (Democratic Republic of the Congo, DRC), Lofa County (Liberia) and Nkwanta district (Ghana) showed that a single 8 mg moxidectin dose reduced skin microfilariae density (microfilariae/mg skin, SmfD) better and for longer than a single 150μg/kg ivermectin dose. We now analysed efficacy by study area and pre-treatment SmfD (intensity of infection, IoI).

Methodology/Principal findings

Four and three IoI categories were defined for across-study and by-study area analyses, respectively. We used a general linear model to analyse SmfD 1, 6, 12 and 18 months post-treatment, a logistic model to determine the odds of undetectable SmfD from month 1 to month 6 (UD1-6), month 12 (UD1-12) and month 18 (UD1-18), and descriptive statistics to quantitate inter-interindividual response differences. Twelve months post-treatment, treatment differences (difference in adjusted geometric mean SmfD after moxidectin and ivermectin in percentage of the adjusted geometric mean SmfD after ivermectin treatment) were 92.9%, 90.1%, 86.8% and 84.5% in Nord Kivu, Ituri, Lofa and Nkwanta, and 74.1%, 84.2%, 90.0% and 95.4% for participants with SmfD 10–20, ≥20-<50, ≥50-<80, ≥80, respectively. Ivermectin’s efficacy was lower in Ituri and Nkwanta than Nord Kivu and Lofa (p≤0.002) and moxidectin’s efficacy lower in Nkwanta than Nord Kivu, Ituri and Lofa (p<0.006). Odds ratios for UD1-6, UD1-12 or UD1-18 after moxidectin versus ivermectin treatment exceeded 7.0. Suboptimal response (SmfD 12 months post-treatment >40% of pre-treatment SmfD) occurred in 0%, 0.3%, 1.6% and 3.9% of moxidectin and 12.1%, 23.7%, 10.8% and 28.0% of ivermectin treated participants in Nord Kivu, Ituri, Lofa and Nkwanta, respectively.

Conclusions/Significance

The benefit of moxidectin vs ivermectin treatment increased with pre-treatment IoI. The possibility that parasite populations in different areas have different drug susceptibility without prior ivermectin selection pressure needs to be considered and further investigated.

Clinical Trial Registration

Registered on 14 November 2008 in Clinicaltrials.gov (ID: NCT00790998).

Onchocerciasis or river blindness is a parasitic disease primarily in sub-Saharan Africa and Yemen. It can cause debilitating morbidity including severe itching, skin changes, visual impairment and even blindness. Many years of control efforts, today primarily based on mass administration of ivermectin (MDA) in endemic communities, have reduced morbidity and the percentage of infected individuals so that elimination of parasite transmission is now planned. WHO estimated that in 2020 more than 239 million people required MDA. Ivermectin may not be sufficiently efficacious to achieve elimination everywhere. Our study in areas in Liberia, Ghana and the Democratic Republic of the Congo where MDA had not been implemented yet showed that one treatment with 8 mg moxidectin reduced parasite levels in the skin better and for longer than one treatment with 150 μg/kg ivermectin, the dose used during MDA. Here we show that people with higher numbers of parasites in the skin benefited more from moxidectin treatment than those with lower numbers and that the efficacy of ivermectin and moxidectin differed between study areas. Provided WHO and countries include moxidectin in guidelines and policies, this information could help decisions on when and where to use moxidectin.

Pharmacokinetics of oral moxidectin in individuals with Onchocerca volvulus infection

Background

Onchocerciasis (“river blindness”), is a neglected tropical disease caused by the filarial nematode Onchocerca volvulus and transmitted to humans through repeated bites by infective blackflies of the genus Simulium. Moxidectin was approved by the United States Food and Drug Administration in 2018 for the treatment of onchocerciasis in people at least 12 years of age. The pharmacokinetics of orally administered moxidectin in 18- to 60-year-old men and women infected with Onchocerca volvulus were investigated in a single-center, ivermectin-controlled, double-blind, randomized, single-ascending-dose, ascending severity of infection study in Ghana.

Methodology/Principal findings

Participants were randomized to either a single dose of 2, 4 or 8 mg moxidectin or ivermectin. Pharmacokinetic samples were collected prior to dosing and at intervals up to 12 months post-dose from 33 and 34 individuals treated with 2 and 4 mg moxidectin, respectively and up to 18 months post-dose from 31 individuals treated with 8 mg moxidectin. Moxidectin plasma concentrations were determined using high-performance liquid chromatography with fluorescence detection. Moxidectin plasma AUC_0-∞ (2 mg: 26.7–31.7 days*ng/mL, 4 mg: 39.1–60.0 days*ng/mL, 8 mg: 99.5–129.0 days*ng/mL) and C_max (2mg, 16.2 to17.3 ng/mL, 4 mg: 33.4 to 35.0 ng/mL, 8 mg: 55.7 to 74.4 ng/mL) were dose-proportional and independent of severity of infection. Maximum plasma concentrations were achieved 4 hours after drug administration. The mean terminal half-lives of moxidectin were 20.6, 17.7, and 23.3 days at the 2, 4 and 8 mg dose levels, respectively.

Conclusion/Significance

We found no relationship between severity of infection (mild, moderate or severe) and exposure parameters (AUC_0-∞ and C_max), T_1/2 and T_max for moxidectin. T_max, volume of distribution (V/F) and oral clearance (CL/F) are similar to those in healthy volunteers from Europe. From a pharmacokinetic perspective, moxidectin is an attractive long-acting therapeutic option for the treatment of human onchocerciasis.

The 2017 Global Burden of Disease Study estimated 20.9 million individuals with onchocerciasis, primarily in Africa. Onchocercal vision impairment/blindness and skin disease (e.g., skin pigment loss, debilitating itching) impact the social and economic life of infected individuals and their communities. This motivates onchocerciasis elimination efforts, today primarily through annual or biannual ivermectin treatment of affected communities. Despite progress towards elimination in many areas, others are not progressing well towards elimination and may require alternative treatment strategies. Moxidectin, approved by the United States Food and Drug Administration in 2018 for treatment of onchocerciasis in people at least 12 years old, could be an alternative. How the amount of a drug in the body changes over time is important for choosing a dose and treatment regimen and for regulatory approval. We measured moxidectin blood levels in 18 to 60 year old men and women with onchocerciasis. We found that moxidectin blood levels peaked around three-four hours after ingestion, that moxidectin stayed in the body for a long time (i.e., its elimination half-life was around 20 days) and that moxidectin blood levels depended on the dose, but not the infection severity as measured by the number of onchocerciasis parasites in the skin.

Low Selectivity Indices of Ivermectin and Macrocyclic Lactones on SARS-CoV-2 Replication In Vitro

Ivermectin was first approved for human use as an endectocide in the 1980s. It remains one of the most important global health medicines in history and has recently been shown to exert in vitro activity against SARS-CoV-2. However, the macrocyclic lactone family of compounds has not previously been evaluated for activity against SARS-CoV-2. The present study aims at comparing their anti-viral activity in relevant human pulmonary cell lines in vitro. Here, in vitro antiviral activity of the avermectins (ivermectin and selamectin) and milbemycins (moxidectin and milbemycin oxime) were assessed against a clinical isolate from a CHU Montpellier patient infected with SARS-CoV-2 in 2020. Ivermectin, like the other macrocyclic lactones moxidectin, milbemycin oxime and selamectin, reduced SARS-CoV-2 replication in vitro (EC50 of 2–5 μM). Immunofluorescence assays with ivermectin and moxidectin showed a reduction in the number of infected and polynuclear cells, suggesting a drug action on viral cell fusion. However, cellular toxicity of the avermectins and milbemycins during infection showed a very low selectivity index of <10. Thus, none of these agents appears suitable for human use for its anti-SARS-CoV-2 activity per se, due to low selectivity index.

Onchocerciasis drug development: from preclinical models to humans

Twenty diseases are recognized as neglected tropical diseases (NTDs) by World Health Assembly resolutions, including human filarial diseases. The end of NTDs is embedded within the Sustainable Development Goals for 2030, under target 3.3. Onchocerciasis afflicts approximately 20.9 million people worldwide with > 90% of those infected residing in Africa. Control programs have made tremendous efforts in the management of onchocerciasis by mass drug administration and aerial larviciding; however, disease elimination is not yet achieved. In the new WHO roadmap, it is recognized that new drugs or drug regimens that kill or permanently sterilize adult filarial worms would significantly improve elimination timelines and accelerate the achievement of the program goal of disease elimination. Drug development is, however, handicapped by high attrition rates, and many promising molecules fail in preclinical development or in subsequent toxicological, safety and efficacy testing; thus, research and development (R&D) costs are, in aggregate, very high. Drug discovery and development for NTDs is largely driven by unmet medical needs put forward by the global health community; the area is underfunded and since no high return on investment is possible, there is no dedicated drug development pipeline for human filariasis. Repurposing existing drugs is one approach to filling the drug development pipeline for human filariasis. The high cost and slow pace of discovery and development of new drugs has led to the repurposing of “old” drugs, as this is more cost-effective and allows development timelines to be shortened. However, even if a drug is marketed for a human or veterinary indication, the safety margin and dosing regimen will need to be re-evaluated to determine the risk in humans. Drug repurposing is a promising approach to enlarging the pool of active molecules in the drug development pipeline. Another consideration when providing new treatment options is the use of combinations, which is not addressed in this review. We here summarize recent advances in the late preclinical or early clinical stage in the search for a potent macrofilaricide, including drugs against the nematode and against its endosymbiont, Wolbachia pipientis.

Characterization of the Population Pharmacokinetics of Moxidectin in Adults Infected with Strongyloides Stercoralis: Support for a Fixed-Dose Treatment Regimen

Background

Moxidectin has recently attracted attention as a novel candidate for the treatment of helminth infections, including Strongyloides stercoralis. This study aims to characterize the population pharmacokinetics (PPK) of moxidectin in S. stercoralis-infected adults using a pharmacometric approach, and to perform model-based simulations to explore different drug dosing strategies.

Methods

A PPK study embedded in a dose-escalation phase IIa trial was conducted in NamBak, Laos. Eight micro blood samples were collected from each of 96 S. stercoralis-infected adults following a moxidectin dose-ranging study, from 2 to 12 mg. A PPK model was developed using nonlinear mixed-effects modeling, and dosing strategies were explored using simulations in S. stercoralis-infected subjects with varying age and body weight (n = 5000 per dosing strategy).

Results

A two-compartment model including delayed absorption with lag-time best described the available PK data. Allometric scaling was applied to account for the influence of body weight. High clearance was found in the infected adults (4.47 L/h [95% confidence interval 3.63–5.39] for a 70 kg individual) compared with that previously reported for healthy adults. Model-based simulations indicated similar variability in mean ± standard deviation area under the curve from time zero to infinity of 1907 ± 1552 and 2175 ± 1670 ng × h/mL in the 60–70 kg weight group, after 8 mg fixed- or weight-based dosing, respectively.

Conclusion

We describe the first PPK model for moxidectin in adults with S. stercoralis infection. Equivalent exposures after fixed-dose and weight-dependent dosing strategies support the use of a simple fixed-dose approach, particularly in large-scale treatment programs.

Trial Registration

Registered at ClinicalTrials.gov (NCT04056325).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01048-4.

Development and validation of an LC-MS/MS method for the quantification of the anthelmintic drug moxidectin in a volumetric absorptive microsample, blood, and plasma: Application to a pharmacokinetic study of adults infected with Strongyloides stercoralis in Laos

Moxidectin is a promising candidate for addition to the lean repertoire of drugs against neglected tropical diseases (NTD) including strongyloidiasis. Pharmacokinetic (PK) and -dynamic studies are required to support its clinical development. Microsampling approaches enable PK studies in the challenging environments where NTDs are most prevalent, due to simplified collection and processing. We developed a liquid chromatography tandem mass spectrometry method for the sensitive quantification of moxidectin in human blood obtained by capillary sampling with the microsampling device Mitra® compared to blood and plasma obtained by venous sampling. Sample preparation consisted of protein precipitation, evaporation and reconstitution and also included phospholipid filtration for blood and plasma. Moxidectin was detected by multiple reaction monitoring (640.4 → 528.5 m/z) using a Luna C8(2) (30 × 2.0 mm, 3 µm particle size, 100 Å) analytical column with a gradient program of 6 min duration. Validation was performed with respect to accuracy, precision, sensitivity, selectivity, linearity, stability, recovery, and haematocrit influence with a limit of quantification of 0.5 and 2.5 ng/mL, for venous and capillary blood respectively. Moxidectin was stable up to 2 months at storage condition (blood and plasma: -20 °C, microsamples: room temperature), 3 cycles of temperature shift, for at least 4 h on the bench-top and 24 h in the autosampler (4 °C). Deviations of inter- and intra-assay accuracy and precision were smaller than 12.6% and recoveries were in the range of 80.7-111.2%. The method was applied to samples obtained from nine Strongyloides stercoralis-infected adults from northern Laos. A good agreement in the time-concentration profiles of moxidectin and a high consistency in PK parameters was found between the different matrixes and sampling strategies: e.g. identical time to reach maximal concentration of 4.0 h and a similar maximal concentration of 83.9-88.5 ng/mL of moxidectin. The simple and practical capillary procedure using Mitra® microsampling has been demonstrated to be suitable for PK studies of moxidectin and will pave the way for future PK studies.

Moxidectin: an oral treatment for human onchocerciasis

INTRODUCTION

Moxidectin is a milbemycin endectocide recently approved for the treatment of human onchocerciasis. Onchocerciasis, earmarked for elimination of transmission, is a filarial infection endemic in Africa, Yemen, and the Amazonian focus straddling Venezuela and Brazil. Concerns over whether the predominant treatment strategy (yearly mass drug administration (MDA) of ivermectin) is sufficient to achieve elimination in all endemic foci have refocussed attention upon alternative treatments. Moxidectin's stronger and longer microfilarial suppression compared to ivermectin in both phase II and III clinical trials indicates its potential as a novel powerful drug for onchocerciasis elimination.

AREAS COVERED

This work summarizes the chemistry and pharmacology of moxidectin, reviews the phase II and III clinical trials evidence on tolerability, safety, and efficacy of moxidectin versus ivermectin, and discusses the implications of moxidectin's current regulatory status.

EXPERT OPINION

Moxidectin's superior clinical performance has the potential to substantially reduce times to elimination compared to ivermectin. If donated, moxidectin could mitigate the additional programmatic costs of biannual ivermectin distribution because, unlike other alternatives, it can use the existing community-directed treatment infrastructure. A pediatric indication (for children <12 years) and determination of its usefulness in onchocerciasis-loiasis co-endemic areas will greatly help fulfill the potential of moxidectin for the treatment and elimination of onchocerciasis.

Scabies: A comprehensive review and current perspectives

Human scabies is a contagious skin infestation caused by the parasitic mite Sarcoptes scabiei var. hominis. It is a common skin disease worldwide that occurs not only in the underprivileged sections of society but also in developed countries. In 2009, World Health Organization (WHO) recognized scabies as "neglected tropical disease (NTD)" or NTD thus emphasizing the need for community awareness and proper treatment strategies. This review attempts to summarize the varied clinical presentation of the disease and describes the advances in diagnosis and management including the ongoing search for novel agents to overcome the problems associated with conventional treatments. The literature research includes peer-reviewed articles (clinical trials or scientific reviews). Studies were identified by searching electronic databases (MEDLINE and PubMed) till February 2020 and reference lists of respective articles. Only articles published in English language were included.

Identification and characterization of the Onchocerca volvulus Excretory Secretory Product Ov28CRP, a putative GM2 activator protein

Onchocerca volvulus is the nematode pathogen responsible for human onchocerciasis also known as "River blindness", a neglected tropical disease that affects up to 18 million people worldwide. Helminths Excretory Secretory Products (ESPs) constitute a rich repertoire of molecules that can be exploited for host-parasite relationship, diagnosis and vaccine studies. Here, we report, using a range of molecular techniques including PCR, western blot, recombinant DNA technology, ELISA, high performance thin-layer chromatography and mass spectrometry that the 28 KDa cysteine-rich protein (Ov28CRP) is a reliable component of the O. volvulus ESPs to address the biology of this parasite. We showed that (1) Ov28CRP is a putative ganglioside GM2 Activator Protein (GM2AP) conserved in nematode; (2) OvGM2AP gene is transcriptionally activated in all investigated stages of the parasitic life cycle, including larval and adult stages; (3) The full-length OvGM2AP was detected in in-vitro O. volvulus ESPs of adult and larval stages; (4) the mass expressed and purified recombinant OvGM2AP purified from insect cell culture medium was found to be glycosylated at asparagine 173 and lacked N-terminal signal peptide sequence; (5) the recombinant OvGM2AP discriminated serum samples of infected and uninfected individuals; (6) OvGM2AP competitively inhibits MUG degradation by recombinant β-hexosaminidase A but not MUGS, and could not hydrolyze the GM2 to GM3; (7) humoral immune responses to the recombinant OvGM2AP revealed a negative correlation with ivermectin treatment. Altogether, our findings suggest for the first time that OvGM2AP is an antigenic molecule whose biochemical and immunological features are important to gain more insight into our understanding of host-parasite relationship, as well as its function in parasite development at large.

Drug Combinations Against Soil-Transmitted Helminth Infections

The soil-transmitted helminths (STHs), Ascaris lumbricoides, hookworm and Trichuris trichiura are common in areas with warm and moist climates with little access to adequate water, sanitation, and hygiene affecting the poorest populations. The current control strategy of the World Health Organization is preventive chemotherapy (PC), i.e., the administration of the two benzimidazoles (albendazole and mebendazole) using single, oral doses to at risk populations without prior diagnosis. The recent success of PC is threatened by anthelmintic drug resistance and the low efficacy of the drugs against hookworm (mebendazole) and T. trichiura (albendazole and mebendazole). Only a handful of alternative drugs with anthelmintic properties are available, however, none of the drugs show high efficacy against all three STHs. The combination of two drugs with different activity profiles presents an attractive alternative, which could prevent the development of drug resistance and increase the efficacy compared to monotherapy. In this review, we summarize the efficacy of current and alternative anthelmintics, coadministrations and triple drug therapies assessed by means of network meta-analysis including only randomized controlled trials. Our results highlight that coadministrations have improved efficacy over monotherapy and the necessity of adapting current STH control strategies for the successful continuation of PC programs.

A Review of Scabies: An Infestation More than Skin Deep

Human scabies, a common infestation, has a worldwide distribution with a variable impact and presentation depending on the clinical situation. In developed, high-income settings, health institution and residential home outbreaks challenge health and social care services. In resource-poor settings, it is the downstream sequelae of staphylococcal and streptococcal bacteraemia, induced by scratching, which have a significant impact on the long-term health of communities. Over the past decade scabies has been recognised as a “neglected tropical disease” (NTD) by the World Health Organisation, has an accepted practical system of global diagnostic criteria and is being adopted into integrated programmes of mass drug administration for NTDs in field settings. This review seeks to summarise the recent advances in the understanding of scabies and highlight the advocacy and research headlines with their implication for diagnosis and management of outbreaks and individuals. In addition, it will indicate the priorities and questions that remain.

Single dose moxidectin versus ivermectin for Onchocerca volvulus infection in Ghana, Liberia, and the Democratic Republic of the Congo: a randomised, controlled, double-blind phase 3 trial

BACKGROUND

The morbidity and socioeconomic effects of onchocerciasis, a parasitic disease that is primarily endemic in sub-Saharan Africa, have motivated large morbidity and transmission control programmes. Annual community-directed ivermectin treatment has substantially reduced prevalence. Elimination requires intensified efforts, including more efficacious treatments. We compared parasitological efficacy and safety of moxidectin and ivermectin.

METHODS

This double-blind, parallel group, superiority trial was done in four sites in Ghana, Liberia, and the Democratic Republic of the Congo. We enrolled participants (aged ≥12 years) with at least 10 Onchocerca volvulus microfilariae per mg skin who were not co-infected with Loa loa or lymphatic filariasis microfilaraemic. Participants were randomly allocated, stratified by sex and level of infection, to receive a single oral dose of 8 mg moxidectin or 150 μg/kg ivermectin as overencapsulated oral tablets. The primary efficacy outcome was skin microfilariae density 12 months post treatment. We used a mixed-effects model to test the hypothesis that the primary efficacy outcome in the moxidectin group was 50% or less than that in the ivermectin group. The primary efficacy analysis population were all participants who received the study drug and completed 12-month follow-up (modified intention to treat). This study is registered with ClinicalTrials.gov, number NCT00790998.

FINDINGS

Between April 22, 2009, and Jan 23, 2011, we enrolled and allocated 998 participants to moxidectin and 501 participants to ivermectin. 978 received moxidectin and 494 ivermectin, of which 947 and 480 were included in primary efficacy outcome analyses. At 12 months, skin microfilarial density (microfilariae per mg of skin) was lower in the moxidectin group (adjusted geometric mean 0·6 [95% CI 0·3-1·0]) than in the ivermectin group (4·5 [3·5-5·9]; difference 3·9 [3·2-4·9], p<0·0001; treatment difference 86%). Mazzotti (ie, efficacy-related) reactions occurred in 967 (99%) of 978 moxidectin-treated participants and in 478 (97%) of 494 ivermectin-treated participants, including ocular reactions (moxidectin 113 [12%] participants and ivermectin 47 [10%] participants), laboratory reactions (788 [81%] and 415 [84%]), and clinical reactions (944 [97%] and 446 [90%]). No serious adverse events were considered to be related to treatment.

INTERPRETATION

Skin microfilarial loads (ie, parasite transmission reservoir) are lower after moxidectin treatment than after ivermectin treatment. Moxidectin would therefore be expected to reduce parasite transmission between treatment rounds more than ivermectin could, thus accelerating progress towards elimination.

FUNDING

UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases.

Evaluation of the Cardiac Safety of Long-Acting Endectocide Moxidectin in a Randomized Concentration-QT Study

Potential effects on cardiac repolarization of single doses of moxidectin, a potent long‐acting macrocyclic lactone endectocide, were assessed in a concentration‐QT (c‐QT; exposure‐response) study. This double‐blind, placebo‐controlled, parallel‐group study in healthy male volunteers (n = 60) randomized subjects to a single oral dose of moxidectin (4 mg, 8 mg, 16 mg, 24 mg, or 36 mg) or matching placebo. Serial plasma samples for pharmacokinetic (PK) analysis and concurrent triplicate electrocardiogram measurements were taken at baseline and 14 prespecified time points over 72 hours, yielding 900 QT interval‐plasma concentration time‐matched pairs. Moxidectin had no statistically significant or clinically relevant impact on QT interval at any dose level. The primary mixed effects model analysis revealed no treatment‐related impact on the Fridericia‐corrected QT interval‐plasma concentration gradient (−0.0077, 90% confidence interval (CI) −0.0255 to +0.0101).

The Skin-A Common Pathway for Integrating Diagnosis and Management of NTDs

Many of the neglected tropical diseases (NTDs) have major skin manifestations. These skin-related NTDs or ‘skin NTDs’ cause significant morbidity and economic hardship in some of the poorest communities worldwide. We draw attention to the collective burden of skin disease and suggest that the skin be used as a platform for the integration of control activities for NTDs. The opportunities for integration are numerous, ranging from diagnosis and disease mapping to mass drug administration and morbidity management. The dermatology community has an important role to play, and will be expected to support research and control activities globally.

Preclinical evaluation of avermectins as novel therapeutic agents for alcohol use disorders

The deleterious effects of alcohol use disorders (AUDs) on human health have been documented worldwide. The enormous socioeconomic burden coupled with lack of efficacious pharmacotherapies underlies the need for improved treatment strategies. At present, there is a growing body of preclinical evidence that demonstrates the potential of avermectins [ivermectin (IVM), selamectin (SEL), abamectin (ABM), and moxidectin (MOX)] in treatment of AUDs. Avermectins are derived by fermentation of soil micro-organism, Streptomyces avermitilis, and have been extensively used for treatment of parasitic infections. From the mechanistic standpoint, avermectins are positive modulators of purinergic P2X4 receptors (P2X4Rs). P2X4Rs belong to P2X superfamily of cation-permeable ion channels gated by adenosine 5'-triphosphate (ATP). Building evidence has implicated a role for P2X4Rs in regulation of ethanol intake and that ethanol can inhibit ATP-gated currents in P2X4Rs. Investigations using recombinant cell models and animal models of alcohol drinking have reported that IVM, ABM, and MOX, but not SEL, were able to antagonize the inhibitory effects of ethanol on P2X4Rs in vitro and reduce ethanol intake in vivo. Furthermore, IVM was shown to reduce ethanol consumption via P2X4R potentiation in vivo, supporting the involvement of P2X4Rs in IVM's anti-alcohol effects and that P2X4Rs can be used as a platform for developing novel anti-alcohol compounds. Taken together, these findings support the utility of avermectins as a novel class of drug candidates for treatment of AUDs.

In Vitro Efficacy of Moxidectin versus Ivermectin against Sarcoptes scabiei

Moxidectin is under consideration for development as a treatment for human scabies. As some arthropods show decreased sensitivity to moxidectin relative to ivermectin, it was important to assess this for Sarcoptes scabieiIn vitro assays showed that the concentration of moxidectin required to kill 50% of mites was lower than that of ivermectin (0.5 μM versus 1.8 μM at 24 h; P < 0.0001). This finding provides further support for moxidectin as a candidate for the treatment of human scabies.

Preclinical development of moxidectin as a novel therapeutic for alcohol use disorder

Current pharmacotherapies for alcohol used disorder (AUD) are few and relatively ineffective illustrating the need for the development of new, effective medications. Using a translational approach, our laboratory reported that ivermectin, an FDA-approved, human and animal anti-parasitic agent, can significantly reduce ethanol intake in male and female mice across different drinking paradigms. Extending this line of investigation, the current paper investigated the utility of moxidectin (MOX), an analogue of ivermectin, to reduce ethanol intake. Notably, MOX is widely held to have lower neurotoxicity potential and improved margin of safety compared to ivermectin. Using a 24-h-two-bottle choice paradigm, MOX significantly reduced ethanol intake in a dose dependent manner in both male and female C57BL/6J mice, respectively (1.25-7.5 mg/kg) and (1.25-10 mg/kg). Further, multi-day administration of MOX (2.5 mg/kg; intraperitoneal injection) for 5 consecutive days significantly reduced ethanol intake in both the 24-h-two-bottle choice and Drinking-in-the-Dark paradigms in female mice. No overt signs of behavioral toxicity were observed. Notably in both male and female mice, MOX significantly reduced ethanol intake starting approximately 4 h post-injection. Using a Xenopus oocyte expression system, we found that MOX significantly potentiated P2X4 receptor (P2X4R) function and antagonized the inhibitory effects of ethanol on ATP-gated currents in P2X4Rs. This latter finding represents the first report of MOX having activity on P2X4Rs. In addition, MOX potentiated GABA_A receptors, but to a lesser degree as compared to ivermectin supporting the hypothesis that MOX would be advantageous (compared to ivermectin) with respect to reducing contraindications. Overall, the results illustrate the potential for development of MOX as a novel pharmacotherapy for the treatment of AUD.

Research for new drugs for elimination of onchocerciasis in Africa

Onchocerciasis is a parasitic, vector borne disease caused by the filarial nematode Onchocerca volvulus. More than 99% of the population at risk of infection live in Africa. Onchocerciasis control was initiated in West Africa in 1974 with vector control, later complemented by ivermectin mass drug administration and in the other African endemic countries in 1995 with annual community directed treatment with ivermectin (CDTI.) This has significantly reduced infection prevalence. Together with proof-of-concept for onchocerciasis elimination with annual CDTI from foci in Senegal and Mali, this has resulted in targeting onchocerciasis elimination in selected African countries by 2020 and in 80% of African countries by 2025. The challenges for meeting these targets include the number of endemic countries where conflict has delayed or interrupted control programmes, cross-border foci, potential emergence of parasite strains with low susceptibility to ivermectin and co-endemicity of loiasis, another parasitic vector borne disease, which slows down or prohibits CDTI implementation. Some of these challenges could be addressed with new drugs or drug combinations with a higher effect on Onchocerca volvulus than ivermectin. This paper reviews the path from discovery of new compounds to their qualification for large scale use and the support regulatory authorities provide for development of drugs for neglected tropical diseases. The status of research for new drugs or treatment regimens for onchocerciasis along the path to regulatory approval and qualification for large scale use is reviewed. This research includes new regimens and combinations of ivermectin and albendazole, antibiotics targeting the O. volvulus endosymbiont Wolbachia, flubendazole, moxidectin and emodepside and discovery of new compounds.

A randomized, single-ascending-dose, ivermectin-controlled, double-blind study of moxidectin in Onchocerca volvulus infection

BACKGROUND

Control of onchocerciasis as a public health problem in Africa relies on annual mass ivermectin distribution. New tools are needed to achieve elimination of infection. This study determined in a small number of Onchocerca volvulus infected individuals whether moxidectin, a veterinary anthelminthic, is safe enough to administer it in a future large study to further characterize moxidectin's safety and efficacy. Effects on the parasite were also assessed.

METHODOLOGY/PRINCIPAL FINDINGS

Men and women from a forest area in South-eastern Ghana without ivermectin mass distribution received a single oral dose of 2 mg (N = 44), 4 mg (N = 45) or 8 mg (N = 38) moxidectin or 150 µg/kg ivermectin (N = 45) with 18 months follow up. All ivermectin and 97%-100% of moxidectin treated participants had Mazzotti reactions. Statistically significantly higher percentages of participants treated with 8 mg moxidectin than participants treated with ivermectin experienced pruritus (87% vs. 56%), rash (63% vs. 42%), increased pulse rate (61% vs. 36%) and decreased mean arterial pressure upon 2 minutes standing still after ≥5 minutes supine relative to pre-treatment (61% vs. 27%). These reactions resolved without treatment. In the 8 mg moxidectin and ivermectin arms, the mean±SD number of microfilariae/mg skin were 22.9±21.1 and 21.2±16.4 pre-treatment and 0.0±0.0 and 1.1±4.2 at nadir reached 1 and 3 months after treatment, respectively. At 6 months, values were 0.0±0.0 and 1.6±4.5, at 12 months 0.4±0.9 and 3.4±4.4 and at 18 months 1.8±3.3 and 4.0±4.8, respectively, in the 8 mg moxidectin and ivermectin arm. The reduction from pre-treatment values was significantly higher after 8 mg moxidectin than after ivermectin treatment throughout follow up (p<0.01).

CONCLUSIONS/SIGNIFICANCE

The 8 mg dose of moxidectin was safe enough to initiate the large study. Provided its results confirm those from this study, availability of moxidectin to control programmes could help them achieve onchocerciasis elimination objectives.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00300768.

Effect of moxidectin on CYP3A4 activity as evaluated by oral midazolam pharmacokinetics in healthy subjects

In order to evaluate the potential for CYP3A4 induction by moxidectin, midazolam pharmacokinetic (PK) parameters were compared before and after moxidectin administration. Healthy subjects received a single 8 mg dose of moxidectin and 3 single 7.5 mg doses of midazolam 3 days before, and 7 and 89 days after the moxidectin. Blood samples were taken for 24 hours to measure midazolam and metabolites in plasma, and for 89 days to measure moxidectin in plasma after dose administration. Noncompartmental PK analyses were performed for each analyte. Analysis of variance was performed on log-transformed midazolam parameters with treatment day as a fixed effect. Adverse events were recorded and laboratory tests, physical examinations, pulse oximetry monitoring, vital sign measurement, and electrocardiograms performed. Thirty-nine subjects were enrolled in the study; PK data were available for 37 subjects. Moxidectin PK parameters were similar to previous studies. There were no significant changes in PK for midazolam or its metabolites 7 or 89 days after moxidectin administration. Adverse events were generally mild and there were no relevant changes in safety assessments. Thus, 8 mg moxidectin does not induce CYP3A4 activity and other CYP3A4 substrates are unlikely to be affected by moxidectin co-administration.

Treatment and control of scabies

PURPOSE OF REVIEW

The treatment of individual patients with scabies and its control in institutional and community settings remains challenging, with relatively few treatment choices available. In this review, evidence of the efficacy of available treatments will be discussed, and possible emerging drug resistance and new therapeutic directions outlined.

RECENT FINDINGS

Although there has been attention on the use of ivermectin for the treatment of ordinary scabies and for mass drug administration, evidence supporting its superiority for both indications over alternative treatment is inconclusive. This is particularly true in light of several case reports of drug resistance in human and veterinary settings when the drug has been intensively used. When used correctly, topical agents such as permethrin and benzyl benzoate are effective. Little research on the development of new and more effective acaricides suitable for human use is underway. While the in-vitro acaricidal properties of several natural products have been documented, these are yet to be evaluated in animal studies or clinical trials.

SUMMARY

When properly administered, chemotherapy for scabies remains effective in most situations. However, with reports of drug resistance increasing and with the need for therapies suitable for use in interventions to control community outbreaks, there is a need to develop new therapies.

Relative neurotoxicity of ivermectin and moxidectin in Mdr1ab (-/-) mice and effects on mammalian GABA(A) channel activity

The anthelmintics ivermectin (IVM) and moxidectin (MOX) display differences in toxicity in several host species. Entrance into the brain is restricted by the P-glycoprotein (P-gp) efflux transporter, while toxicity is mediated through the brain GABA(A) receptors. This study compared the toxicity of IVM and MOX in vivo and their interaction with GABA(A) receptors in vitro. Drug toxicity was assessed in Mdr1ab(−/−) mice P-gp-deficient after subcutaneous administration of increasing doses (0.11–2.0 and 0.23–12.9 µmol/kg for IVM and MOX in P-gp-deficient mice and half lethal doses (LD₅₀) in wild-type mice). Survival was evaluated over 14-days. In Mdr1ab(−/−) mice, LD₅₀ was 0.46 and 2.3 µmol/kg for IVM and MOX, respectively, demonstrating that MOX was less toxic than IVM. In P-gp-deficient mice, MOX had a lower brain-to-plasma concentration ratio and entered into the brain more slowly than IVM. The brain sublethal drug concentrations determined after administration of doses close to LD₅₀ were, in Mdr1ab(−/−) and wild-type mice, respectively, 270 and 210 pmol/g for IVM and 830 and 740–1380 pmol/g for MOX, indicating that higher brain concentrations are required for MOX toxicity than IVM. In rat α1β2γ2 GABA channels expressed in Xenopus oocytes, IVM and MOX were both allosteric activators of the GABA-induced response. The Hill coefficient was 1.52±0.45 for IVM and 0.34±0.56 for MOX (p<0.001), while the maximum potentiation caused by IVM and MOX relative to GABA alone was 413.7±66.1 and 257.4±40.6%, respectively (p<0.05), showing that IVM causes a greater potentiation of GABA action on this receptor. Differences in the accumulation of IVM and MOX in the brain and in the interaction of IVM and MOX with GABA(A) receptors account for differences in neurotoxicity seen in intact and Mdr1-deficient animals. These differences in neurotoxicity of IVM and MOX are important in considering their use in humans.

Ivermectin (IVM) is used for onchocerciasis mass drug administration and is important for control of lymphatic filariasis, strongyloidiases and Scarcoptes mange in humans. It is widely used for parasite control in livestock. Moxidectin (MOX) is being evaluated against Onchocerca volvulus in humans and is also widely used in veterinary medicine. Both anthelmintics are macrocyclic lactones (MLs) that act on ligand-gated chloride channels and share similar spectra of activity. Nevertheless, there are marked differences in their pharmacokinetics, pharmacodynamics and toxicity. Usually, both MLs are remarkably safe drugs. However, there are reports of severe adverse events to IVM, in some humans with high Loa loa burdens, and IVM can be neurotoxic in animals with defects in P-glycoproteins (P-gp) in the blood-brain barrier. We have compared the in vivo neurotoxicity of IVM and MOX in P-gp-deficient mice and their accumulation in brain. We also investigated their effects on mammalian GABA receptors. We show that MOX has a wider margin of safety than IVM, even when the blood-brain barrier function is impaired, and that the neurotoxicity in vivo is related to different effects of the drugs on GABA-gated channels. These observations contribute to understanding ML toxicity and open new perspectives for possible MOX use in humans.

Scratching the itch: new tools to advance understanding of scabies

Scabies remains a significant public health problem worldwide. Research into aspects of Sarcoptes scabiei biology and host-parasite interactions has been impeded by an inability to maintain mites in vitro and by limited access to parasite material and infected subjects. The generation of comprehensive expressed sequence tag libraries has enabled the initial characterisation of molecules of interest to diagnostics, vaccines, and drug resistance. The recent development and utilisation of animal models, combined with next-generation technologies, is anticipated to lead to new strategies to prevent, diagnose, and treat scabies, ultimately improving skin health in both human and veterinary settings. This article will summarise recent molecular and immunologic advances on scabies, and will address priorities for the exciting 'next chapter' of scabies research.