Efficacy and safety of tribendimidine against Opisthorchis viverrini: two randomised, parallel-group, single-blind, dose-ranging, phase 2 trials

Efficacy and Safety of Ascending Dosages of Tribendimidine Against Hookworm Infections in Children: A Randomized Controlled Trial

BACKGROUND

The global strategy to control soil-transmitted helminthiasis is mainly focused on preventive chemotherapy with albendazole and mebendazole. We assessed the efficacy and safety of ascending tribendimidine doses against hookworm infections in African school-aged children, key information for the development of tribendimidine.

METHODS

We performed a single blind, randomized, controlled trial in Côte d'Ivoire between June and August 2017. Eligible participants were randomly assigned to placebo, 100, 200, or 400 mg tribendimidine. Cure rates (CRs, primary outcome) and egg reduction rates (ERRs) were determined 14-21 days after treatment. Clinical symptoms were assessed before treatment and adverse events monitored 3 and 24 hours posttreatment.

RESULTS

CRs calculated for 130 children dose-dependently increased. The observed CRs were 20.6% (7/34), 21.2% (7/33), 38.7% (12/31), and 53.1% (17/32) for placebo, 100, 200, and 400 mg of tribendimidine, respectively. The Emax model predicted a placebo corrected net effect of 34.3 percentage points (95% confidence interval [CI], 13.3-54.4) for the 400-mg tribendimidine dose. The ERRs (geometric mean) were 30.6% (95% CI, -24.7 to 64.1), 65.4% (95% CI, 24.5-85.9), 82.1% (95% CI, 58.4-92.5) and 92.2% (95% CI, 81.0-97.1) for placebo, 100, 200, and 400 mg tribendimidine, respectively. The Emax model predicted an ERR of 95% at 500 mg. Only mild adverse events and no abnormal biochemical parameters were observed.

CONCLUSION

A 400-mg dose of tribendimidine yielded the highest efficacy and was well tolerated. Because children were mostly lightly infected, further investigations with tribendimidine against moderate/heavy hookworm infection are needed.

CLINICAL TRIALS REGISTRATION

The trial is registered at www.isrctn.com number ISRCTN81391471.

One mean to rule them all? The arithmetic mean based egg reduction rate can be misleading when estimating anthelminthic drug efficacy in clinical trials

Animal and human helminth infections are highly prevalent around the world, with only few anthelminthic drugs available. The anthelminthic drug performance is expressed by the cure rate and the egg reduction rate. However, which kind of mean should be used to calculate the egg reduction rate remains a controversial issue. We visualized the distributions of egg counts of different helminth species in 7 randomized controlled trials and asked a panel of experts about their opinion on the egg burden and drug efficacy of two different treatments. Simultaneously, we calculated infection intensities and egg reduction rates using different types of means: arithmetic, geometric, trimmed, winsorized and Hölder means. Finally, we calculated the agreement between expert opinion and the different means. We generated 23 different trial arm pairs, which were judged by 49 experts. Among all investigated means, the arithmetic mean showed poorest performance with only 64% agreement with expert opinion (bootstrap confidence interval [CI]: 60−68). Highest agreement of 94% (CI: 86−96) was reached by the Hölder mean M_0.2, followed by the geometric mean (91%, CI: 85−94). Winsorized and trimmed means showed a rather poor performance (e.g. winsorization with 0.1 cut-off showed 85% agreement, CI: 78−87), but they performed reasonably well after excluding treatment arms with a small number of patients. In clinical trials with moderate sample size, the currently recommended arithmetic mean does not necessarily rank anthelminthic efficacies in the same order as might be obtained from expert evaluation of the same data. Estimates based on the arithmetic mean should always be reported together with an estimate, which is more robust to outliers, e.g. the geometric mean.

Besides cure rates, egg reduction rates represent an important indicator of anthelminthic drug efficacy in clinical trials. However, there is an ongoing controversy whether the arithmetic or the geometric mean should be used for its calculation. The arithmetic mean is problematic in skewed distributions mainly because the mean is sensitive to outliers, whereas the geometric mean does not correspond to our intuitive interpretation of average reduction. Several studies tried to compare the performance of different means but they relied on assumptions, which favored one approach over another. Despite the ongoing debate, the World Health Organization (WHO) recommends the arithmetic mean to calculate egg reduction rates. To overcome limitations from previous studies, we visualized data from several clinical trials and asked a panel of experts to compare drug efficacy of two different treatments. Afterwards, we estimated efficacy by using different means. Finally, we calculated the raw agreement between expert opinion and the different means. From all investigated methods to calculate efficacy, the arithmetic mean showed the poorest performance in terms of agreement with expert opinion. In anthelminthic human drug trials, which are characterized by small sample size and non-adherence, estimates more robust to outliers should be reported to assess drug efficacy performance.

Drug resistance in liver flukes

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.

Current and Novel Therapies Against Helminthic Infections: The Potential of Antioxidants Combined with Drugs

Infections caused by Schistosoma haematobium and Opisthorchisviverrini are classified as Group 1 biological carcinogen and it has been postulated that parasites produce oxysterol and estrogen-like metabolites that might be considered as initiators of infection-associated carcinogenesis. Chemotherapy for these helminthic infections relies on a single drug, praziquantel, (PZQ) that mainly targets the parasite. Additionally, PZQ has some major drawbacks as inefficacy against juvenile form and alone it is not capable to counteract pathologies associated to infections or prevent carcinogenesis. There is an urgent need to develop novel therapeutic approaches that not only target the parasite but also improve the pathologies associated to infection, and ultimately, counteract or/and prevent the carcinogenesis processes. Repurposing the drug in combination of compounds with different modes of action is a promising strategy to find novel therapeutics approaches against these helminthic infections and its pathologies. Here, we emphasized that using antioxidants either alone or combined with anthelmintic drugs could ameliorate tissue damage, infection-associated complications, moreover, could prevent the development of cancer associated to infections. Hence, antioxidants represent a potential adjuvant approach during treatment to reduce morbidity and mortality. Despite the success of some strategies, there is a long way to go to implement novel therapies for schistosomiasis.

Development and application of anthelminthic drugs in China

China was once a country plagued by parasitic diseases. At the beginning of the founding of the People's Republic of China, nearly 80% of the population suffered from parasitic diseases because of poverty and poor sanitary conditions. After nearly 70 years of development, China has made remarkable achievements in the prevention and control of parasitic diseases, and the prevalence of parasitic diseases has been greatly reduced. In addition to organizational leadership from the government and various preventive measures, drug treatment and drug research & development are important and irreplaceable links in prevention and control work. Since the 1950s, China has begun to introduce, produce and imitate antiparasitic drugs from abroad, such as santonin, benzimidazole, and praziquantel. Chinese scientists have also contributed to the optimization of production techniques, improvements in drug formulation, the application in the clinic and the mechanisms of actions of generic drugs. At the same time, China has independently developed tribendimidine (TrBD, a broad spectrum anthelminthic), and its anthelminthic spectrum has been comprehensively studied. It is active against almost 20 parasites, is especially superior to benzimidazoles against Necator americanus, and surpasses the effectiveness of praziquantel against Clonorchis sinensis. In the treatment of tapeworm disease, the traditional Chinese medicines pumpkin seeds and betel nuts have good curative effects for taeniasis. Chinese scientists have explored the action modes and clinical administration methods of pumpkin seeds and betel nuts, which is still the main clinical regimen for the disease. This paper reviews the history and progress of the study of anthelmintics in intestinal helminth infections since the founding of the People's Republic of China and aiming to support clinicians and drug researchers in China and other countries.

Pooled Population Pharmacokinetic Analysis of Tribendimidine for the Treatment of Opisthorchis viverrini Infections

Opisthorchiasis, caused by the foodborne trematode Opisthorchis viverrini, affects more than 8 million people in Southeast Asia. In the framework of a phase 2b clinical trial conducted in Lao People’s Democratic Republic, pharmacokinetic samples were obtained from 125 adult and adolescent O. viverrini-infected patients treated with 400 mg tribendimidine following the design of a sparse sampling scheme at 20 min and 2, 7.75, 8, and 30 h after treatment using dried blood spot sampling.

Opisthorchiasis, caused by the foodborne trematode Opisthorchis viverrini, affects more than 8 million people in Southeast Asia. In the framework of a phase 2b clinical trial conducted in Lao People’s Democratic Republic, pharmacokinetic samples were obtained from 125 adult and adolescent O. viverrini-infected patients treated with 400 mg tribendimidine following the design of a sparse sampling scheme at 20 min and 2, 7.75, 8, and 30 h after treatment using dried blood spot sampling. Pharmacokinetic data for the metabolites deacetylated amidantel (dADT) and acetylated dADT (adADT) were pooled with data from two previous ascending-dose trials and evaluated using nonlinear mixed-effects modeling. The observed pharmacokinetic data were described using a flexible transit absorption model for the active metabolite dADT, followed by one-compartment disposition models for both metabolites. Significant covariates were age, body weight, formulation, and breaking of the enteric coating on the tablets. There were significant associations between O. viverrini cure and both the dADT maximum concentration and the area under the concentration-time curve (P < 0.001), with younger age being associated with a higher probability of cure. Modeling and simulation of exposures in patients with different weight and age combinations showed that an oral single dose of 400 mg tribendimidine attained therapeutic success in over 90% of adult patients. Our data confirmed that tribendimidine could be a valuable novel alternative to the standard treatment, praziquantel, for the treatment of O. viverrini infections.

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.

Liver Fluke-Associated Biliary Tract Cancer

Cholangiocarcinoma (CCA) is an aggressive cancer arising from epithelial cells of the bile duct. Most patients with CCA have an unresectable tumor at the time of diagnosis. In Western countries, the risk of CCA increases in patients with primary sclerosing cholangitis, whereas liver fluke infection appears to be the major risk factor for CCA in Asian countries. A diagnosis of liver fluke infection often relies on stool samples, including microscopic examination, polymerase chain reaction-based assays, and fluke antigen detection. Tests of serum, saliva and urine samples are also potentially diagnostic. The presence of liver fluke along with exogenous carcinogens magnifies the risk of CCA in people living in endemic areas. The “liver fluke-cholangiocarcinoma” carcinogenesis pathways consist of mechanical damage to the bile duct epithelium, immunopathologic and cellular reactions to the liver fluke’s antigens and excretory/secretory products, liver fluke-induced changes in the biliary tract microbiome and the effects of repeated treatment for liver fluke. A vaccine and novel biomarkers are needed for the primary and secondary prevention of CCA in endemic areas. Importantly, climate change exerts an effect on vector-borne parasitic diseases, and awareness of liver fluke should be enhanced in potentially migrated habitat areas.

Human liver flukes

Liver fluke infections occur in people worldwide. In some low-income regions, a combination of ecological, agricultural, and culinary factors leads to a very high prevalence of infection but, in higher-income regions, infections are uncommon. Infection is associated with substantial morbidity and several liver fluke species are recognised as biological carcinogens. Here, we review the epidemiology, clinical significance, and diagnostic and treatment strategies of human infection with these pathogens.

Recent Advances in the Diagnosis and Detection of Opisthorchis viverrini Sensu Lato in Human and Intermediate Hosts for Use in Control and Elimination Programs

Opisthorchiasis is a neglected tropical disease, caused by infection with the fish-borne trematode Opisthorchis viverrini sensu lato that afflicts more than 10million people in Southeast Asia, including Thailand, Lao PDR, Vietnam and Cambodia. The disease is characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. This chronic inflammation eventually leads to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in approximately 1% of O. viverrini-infected individuals. In Thailand alone, CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce O. viverrini-associated morbidity and CCA, the primary intervention measures focus on opisthorchiasis control and elimination. Accurate diagnoses of O. viverrini infection, in both mammalian, snail and fish intermediate hosts, are important for achieving these goals. Despite extensive efforts over several decades to find sensitive and specific diagnostics for opisthorchiasis, a simple and robust diagnostic method is still required. Here we review earlier and current developments in the search for new diagnostics for opisthorchiasis, with practical applications in the research laboratory, the clinic and the field. Of the methods currently available, the urine antigen assay shows considerable potential for the diagnosis and screening of opisthorchiasis. Nevertheless, these new assays require validation, determination of their cost-effectiveness when applied for mass screening in an endemic setting in support of policy decisions for national public health programs aimed at the control and elimination of opisthorchiasis.

Efficacy and safety of tribendimidine versus praziquantel against Opisthorchis viverrini in Laos: an open-label, randomised, non-inferiority, phase 2 trial

BACKGROUND

Praziquantel is the only option for treatment of the liver fluke infection Opisthorchis viverrini. Tribendimidine could be an alternative drug. We aimed to assess the efficacy and safety of a single, oral dose of tribendimidine, compared with praziquantel administered in two doses, in participants with O viverrini infection.

METHOD

We did an open-label, randomised, non-inferiority, phase 2 trial in children (8-14 years) and adolescents and adults (≥15 years) in Champasack province, southern Laos. Participants infected with O viverrini were randomly assigned (1:1), via a computer-generated block-randomisation procedure (block sizes of two, four, and six), to receive a single, oral dose of tribendimidine (200 mg for children, 400 mg for adolescents and adults) or two oral doses of praziquantel (50 mg/kg bodyweight and 25 mg/kg bodyweight, 6 h apart). Physicians assessing adverse events and laboratory personnel were masked to treatment allocation, but the investigators administering treatment and the participants could have recognised the treatment group based on differences in the number, appearance, and odour of the tablets. The primary outcomes were cure rate, defined as no parasite eggs in stool at 3 weeks' follow-up, and egg reduction rate. We did available-case analysis of all participants with primary endpoint data. The non-inferiority margin for the difference in cure rates between the groups was pre-specified as -3 percentage points. Adverse events were monitored at 3 h and 24 h after treatment. This trial is registered, number ISRCTN96948551.

FINDINGS

Between Feb 1, and April 30, 2014, we assigned 607 participants with confirmed O viverrini infection to receive tribendimidine (n=300) or praziquantel (n=307). 11 participants (five in the tribendimidine group and six in the praziquantel group) did not provide stool samples at 3 weeks' follow-up and were excluded from the available-case analysis. 276 (93·6%) of 295 participants in the tribendimidine group were cured compared with 293 (97·3%) of 301 participants in the praziquantel group. The difference in cure rates between the two groups was -3·8 percentage points (95% CI -7·1 to -0·4), thus the lower limit of the confidence interval exceeded the non-inferiority margin. In both treatment groups, egg reduction rates were 99·9%. Adverse events were of mild and moderate intensity and were more frequent in the praziquantel group than in the tribendimidine group (odds ratio 4·5, 95% CI 3·2-6·3; p<0·0001). The most frequent adverse events were headache, vertigo, nausea, and fatigue.

INTERPRETATION

Tribendimidine has a slightly lower cure rate than praziquantel and non-inferiority was not shown. However, tribendimidine has a similar egg reduction rate to praziquantel and leads to fewer adverse events and thus might complement praziquantel in O viverrini control programmes, particularly in settings co-endemic for hookworm.

FUNDING

Joint Global Health Trials scheme from the Wellcome Trust, Department for International Development, and Medical Research Council.

Single-Ascending-Dose Pharmacokinetic Study of Tribendimidine in Opisthorchis viverrini-Infected Patients

Praziquantel is the only drug available for the treatment of Opisthorchis viverrini infections. Tribendimidine has emerged as a potential treatment alternative; however, its pharmacokinetic (PK) properties have not been sufficiently studied to date. Via two phase IIa dose-finding studies, 68 O. viverrini patients were treated with 25- to 600-mg doses of tribendimidine using 50- and 200-mg tablet formulations. Plasma, blood, and dried blood spots (DBS) were sampled at selected time points. The two main metabolites of tribendimidine, active deacetylated amidantel (dADT) and acetylated dADT (adADT), were analyzed in plasma, blood, and DBS. PK parameters were estimated by noncompartmental analysis. An acceptable agreement among plasma and DBS concentrations was observed, with a mean bias of ≤10%, and 60% dADT and 74% adADT concentrations being within ±20% margins. We found that 200-mg tribendimidine tablets possess immediate floating characteristics, which led to variable time to maximal concentration of drug (Tmax) values (2 to 24 h) between individuals. Dose proportionality was observed for dADT from 25 to 200 mg using 50-mg tablets, but at higher dosages (200 to 600 mg), saturation occurred. The median ratio of the area under the plasma concentration-time curve from 0 to 24 h (AUC0-24) of dADT to the AUC0- 24 of adADT ranged from 0.8 to 26.4, suggesting substantial differences in acetylation rates. Cure rates ranged from 11% (25-mg dose) to 100% (400-mg dose). Cured patients showed significantly higher dADT maximal serum concentrations (Cmax) and AUC0-24 values than uncured patients. Tribendimidine is a promising drug for the treatment of opisthorchiasis. However, the tablet formulation should be optimized to achieve consistent absorption among patients. Further studies are warranted to assess the large differences between individuals in the rate of metabolic turnover of dADT to adADT. (This study has been registered with the ISRCTN Registry under no. ISRCTN96948551.).

Population Pharmacokinetic Modeling of Tribendimidine Metabolites in Opisthorchis viverrini-Infected Adults

There is a pressing need for alternative treatments against the liver fluke Opisthorchis viverrini. Oral tribendimidine is a promising candidate, but its population pharmacokinetic properties are unknown. Two phase IIa trials were conducted in Laos in O. viverrini-infected adults receiving single oral doses of 25 to 600 mg tribendimidine administered as different formulations in each study (study 1 used 200-mg tablets, and study 2 used 50-mg tablets). Venous whole blood, plasma, and capillary dried blood spots were sampled frequently from 68 adults, and concentrations of the tribendimidine metabolites dADT (deacetylated amidantel) and adADT (acetylated dADT) were measured. Population pharmacokinetics were assessed by using nonlinear mixed-effects modeling. The relationship between drug exposure and cure (assessed at 21 days posttreatment) was evaluated by using univariable logistic regression. A six-transit compartment absorption model with a one-disposition compartment for each metabolite described the data well. Compared to the 50-mg formulation (study 2), the 200-mg formulation (study 1) had a 40.1% higher mean transit absorption time, a 113% higher dADT volume of distribution, and a 364% higher adADT volume of distribution. Each 10-year increase in age was associated with a 12.7% lower dADT clearance and a 21.2% lower adADT clearance. The highest cure rates (≥55%) were observed with doses of ≥100 mg. Higher dADT, but not adADT, peak concentrations and exposures were associated with cure (P = 0.004 and 0.003, respectively). For the first time, population pharmacokinetics of tribendimidine have been described. Known differences in the 200-mg versus 50-mg formulations were captured by covariate modeling. Further studies are needed to validate the structural model and confirm covariate relationships. (This study has been registered with the ISRCTN Registry under no. ISRCTN96948551.)