Discrepancy in plasma melarsoprol concentrations between HPLC and bioassay methods in patients with T. gambiense sleeping sickness indicates that melarsoprol is metabolized

Lack of Clinical Pharmacokinetic Studies to Optimize the Treatment of Neglected Tropical Diseases: A Systematic Review

INTRODUCTION

Neglected tropical diseases (NTDs) affect more than one billion people, mainly living in developing countries. For most of these NTDs, treatment is suboptimal. To optimize treatment regimens, clinical pharmacokinetic studies are required where they have not been previously conducted to enable the use of pharmacometric modeling and simulation techniques in their application, which can provide substantial advantages.

OBJECTIVES

Our aim was to provide a systematic overview and summary of all clinical pharmacokinetic studies in NTDs and to assess the use of pharmacometrics in these studies, as well as to identify which of the NTDs or which treatments have not been sufficiently studied.

METHODS

PubMed was systematically searched for all clinical trials and case reports until the end of 2015 that described the pharmacokinetics of a drug in the context of treating any of the NTDs in patients or healthy volunteers.

RESULTS

Eighty-two pharmacokinetic studies were identified. Most studies included small patient numbers (only five studies included >50 subjects) and only nine (11 %) studies included pediatric patients. A large part of the studies was not very recent; 56 % of studies were published before 2000. Most studies applied non-compartmental analysis methods for pharmacokinetic analysis (62 %). Twelve studies used population-based compartmental analysis (15 %) and eight (10 %) additionally performed simulations or extrapolation. For ten out of the 17 NTDs, none or only very few pharmacokinetic studies could be identified.

CONCLUSIONS

For most NTDs, adequate pharmacokinetic studies are lacking and population-based modeling and simulation techniques have not generally been applied. Pharmacokinetic clinical trials that enable population pharmacokinetic modeling are needed to make better use of the available data. Simulation-based studies should be employed to enable the design of improved dosing regimens and more optimally use the limited resources to effectively provide therapy in this neglected area.

Drug-drug interactions between antiretrovirals and drugs used in the management of neglected tropical diseases: important considerations in the WHO 2020 Roadmap and London Declaration on Neglected Tropical Diseases

The group of infections known as the neglected tropical diseases (NTDs) collectively affect one billion people worldwide, equivalent to one-sixth of the world's population. The NTDs cause severe physical and emotional morbidity, and have a profound effect on cycles of poverty; it is estimated that NTDs account for 534 000 deaths per year. NTDs such as soil-transmitted helminth infections and the vector-borne protozoal infections leishmaniasis and trypanosomiasis occur predominantly in the most economically disadvantaged and marginalized communities. It is estimated that all low-income countries harbour at least five of the NTDs simultaneously. NTDs are neglected because they do not individually rank highly in terms of mortality data, and because they affect populations with little political voice. There is considerable geographic overlap between areas with high prevalence of NTDs and HIV, raising the possibility of complex polypharmacy and drug-drug interactions. Antiretrovirals pose a particularly high risk for potential drug-drug interactions, which may be pharmacokinetic or pharmacodynamic in nature and can result in raising or lowering plasma or tissue concentrations of co-prescribed drugs. Elevated drug concentrations may be associated with drug toxicity and lower drug concentrations may be associated with therapeutic failure. The aim of this paper is to review the currently available data on interactions between antiretrovirals and drugs used in the management of NTDs. It is intended to serve as a resource for policy makers and clinicians caring for these patients, and to support the recent WHO 2020 Roadmap and the 2012 London Declaration on NTDs.

Human African trypanosomiasis: pharmacological re-engagement with a neglected disease

This review discusses the challenges of chemotherapy for human African trypanosomiasis (HAT). The few drugs registered for use against the disease are unsatisfactory for a number of reasons. HAT has two stages. In stage 1 the parasites proliferate in the haemolymphatic system. In stage 2 they invade the central nervous system and brain provoking progressive neurological dysfunction leading to symptoms that include the disrupted sleep wake patterns that give HAT its more common name of sleeping sickness. Targeting drugs to the central nervous system offers many challenges. However, it is the cost of drug development for diseases like HAT, that afflict exclusively people of the world's poorest populations, that has been the principal barrier to new drug development and has led to them becoming neglected. Here we review drugs currently registered for HAT, and also discuss the few compounds progressing through clinical trials. Finally we report on new initiatives that might allow progress to be made in developing new and satisfactory drugs for this terrible disease.

Trypanosomiasis relapse after melarsoprol therapy, Democratic Republic of Congo, 1982-2001

Recently, a high proportion of patients with late-stage Trypanosoma brucei gambiense trypanosomiasis, who had been treated with melarsoprol in some disease-endemic areas, subsequently relapsed. To determine whether the frequency of postmelarsoprol relapses increased over time, we reviewed data from 2,221 trypanosomiasis patients treated with melarsoprol during this period in Nioki, Democratic Republic of Congo, from 1982 to 2001. The frequency of relapses was 5.6%(31/553), 6.8%(35/512), 4.5%(18/398), 11.4%(34/299), and 5.0%(17/343) for those treated from 1982 to 1985, 1986 to 1989, 1990 to 1993, 1994 to 1997, and 1998 to 2001, respectively. The higher frequency of relapses in 1994 to 1997 was associated with an incremental dosage regimen of melarsoprol. In multivariate analysis, after adjustment for treatment regimen, sex, residence, and trypanosomes in cerebrospinal fluid, postmelarsoprol relapses did not increase in Nioki, perhaps because 1) little drug pressure exists; 2) subtherapeutic doses have rarely been administered; 3) little potential exists for the preferential transmission of melarsoprol-resistant strains.

Increased trypanolytic activity in sera of sleeping sickness patients after chemotherapy

We tested sera from patients previously treated for human African trypanosomiasis, from patients infected with trypanosomes, and from individuals never diagnosed with African trypanosomiasis living in the Trypanosoma brucei gambiense sleeping sickness focus of Mbini in Equatorial Guinea for their trypanolytic activity against bloodstream forms of T. b. rhodesiense expressing a metacyclic and bloodstream variant surface glycoprotein (VSG). Nearly 80% of the sera from treated patients showed high trypanolytic activity against trypanosomes expressing a metacyclic VSG. The trypanolytic activity of part of these sera was mediated by IgM while that of the other part was antibody-independent. On the other hand, only 40% of the sera exhibited high trypanolytic activity against trypanosomes expressing a bloodstream VSG which also was almost completely abolished by heat-inactivation. In contrast, most sera from infected and negative individuals displayed only low to moderate trypanolytic activity against either trypanosomes expressing a metacyclic or a bloodstream VSG. These results suggest that trypanolytic activity of sera increases after African sleeping sickness and is directed against trypanosomes expressing metacyclic VSG.

The phenomenon of treatment failures in Human African Trypanosomiasis

Treatment of Human African Trypanosomiasis (HAT or sleeping sickness) relies on a few drugs which are old, toxic and expensive. The most important drug for the treatment of second stage infection is melarsoprol. During the last 50 years treatment failures with melarsoprol were not a major problem in Trypanosoma brucei gambiense patients. Commonly a relapse rate of 5-8% was reported, but in recent years it has increased dramatically in some important foci of T. b. gambiense sleeping sickness. Treatment failures for T. b. rhodesiense are much less of a problem apart from some reports between 1960 and 1985 of refractoriness in T. b. rhodesiense patients in East Africa. Analysis of those isolates revealed that their in vitro sensitivity to melarsoprol was one-tenth that of sensitive isolates, and complete failure to cure the infection in the acute mouse model with melarsoprol levels comparable with those in human patients. There was very little indication of resistance in T. b. gambiense isolates from Côte d'Ivoire and NW Uganda. The in vitro melarsoprol sensitivities for populations from relapsing and from curable patients were in the same range. Melarsoprol concentrations in the plasma and cerebrospinal fluid of patients 24 h after treatment did not show any difference between patients who relapsed and those who could be cured. The reason for relapses in the recent T. b. gambiense epidemics are not known. Other parasite-related factors might be involved, e.g. affinity to extravascular sites other than the CNS which are less accessible to the drug. In conclusion, a combination of factors rather than a single one may be responsible for the phenomenon of melarsoprol treatment failures in T. b. gambiense patients.

Pharmacokinetic investigations in patients from northern Angola refractory to melarsoprol treatment

Melarsoprol, an organo-arsenical drug, has been the drug of choice for late-stage trypanosomiasis for 50 years. Because of the lack of alternatives any abatement of this medication will have a dramatic negative impact on the perspectives for patients. As a large number of patients refractory to melarsoprol treatment was recently reported from northern Uganda and northern Angola, we investigated in northern Angola whether interpatient pharmacokinetic differences influence the outcome of melarsoprol treatment. Drug levels were determined by a biological assay in serum and cerebrospinal fluid (CSF) of 22 patients. Nine patients could be successfully treated, eight were refractory and the outcome was unclear or no adequate follow-up information was available for five patients. No differences in the pharmacokinetic parameters (maximum serum concentration Cmax, half-life t1/2 beta, total clearance CL and the volume of distribution Vss) could be detected between the groups. Serum and CSF concentrations for all patients were in the expected range. This result indicates that other underlying factors are responsible for treatment failures.

Efficacy of new, concise schedule for melarsoprol in treatment of sleeping sickness caused by Trypanosoma brucei gambiense: a randomised trial

BACKGROUND

African trypanosomiasis is a fatal disease caused by protozoan parasites of the species Trypanosoma brucei. The disease has reached epidemic dimensions in various countries of central Africa. Treatment of the second stage is long and complicated, and is hampered by severe adverse reactions to the first-line drug, melarsoprol. Despite these problems, melarsoprol is likely to remain the drug of choice for the next decade. We therefore did a randomised trial comparing the standard treatment schedule with a new, concise regimen.

METHODS

The safety and efficacy of the new schedule were assessed in patients presenting to a hospital in Kwanza Norte, Angola with sleeping sickness. The control group followed the 26-day standard Angolan schedule of three series of four daily injections of melarsoprol at doses increasing from 1.2 to 3.6 mg/kg within each series, with a 7-day interval between series. The new treatment schedule comprised 10 daily injections of 2.2 mg/kg. Primary outcomes assessed were elimination of parasites, deaths attributed to treatment, and rate of encephalopathy. Analysis was by intention to treat.

FINDINGS

Of 767 patients with second-stage disease, 500 were enrolled: 250 were assigned the standard schedule, and 250 the new schedule. 40 patients on the standard schedule and 47 on the new schedule had adverse events which resulted in treatment disruption or withdrawal. 50 patients on the standard regimen deviated or withdrew from treatment, compared with two on the new regimen. Parasitological cure 24 h after treatment was 100% in both groups; there were six deaths (all due to encephalopathy) 30 days after treatment in each group. The number of patients with encephalopathic syndromes was also the same in each group (14). Skin reactions were more common with the new treatment, but all could be resolved by additional medication or withdrawal of treatment.

INTERPRETATION

Considering the economic and practical advantages of the new 10-day schedule over the standard 26-day treatment schedule, and the similarity of treatment outcome, the new schedule is a useful alternative to the present standard, especially in epidemic situations and in locations with limited resources.

An automated biological assay to determine levels of the trypanocidal drug melarsoprol in biological fluids

For the investigation of the pharmacokinetic properties of a drug, methods for sensitive and precise quantification are a prerequisite. Only few functional methods exist for the determination of the trypanocidal drug melarsoprol in biological fluids: A bioassay which requires microscopical evaluation and two HPLC methods, which require sample extraction and are difficult to automatize due to the drug's properties. We report the development of an automated biological assay, based on the fluorescent dye Alamar blue. To validate the assay for melarsoprol, 108 serum and 37 cerebrospinal fluid (CSF) samples were spiked with melarsoprol at concentrations of 17-92 ng/ml for CSF and 17 ng/ml-2.2 microg/ml for serum. The precision (repeatability) expressed as the interday average coefficient of variation was 9.9% for serum and 18.8% for CSF samples over the respective concentration range. The accuracy (measurement for the systematic error) of the test was 99.4% for serum and 96.4% for CSF. The assay's limit of quantitation with the use of the trypanosome stock STI 704 BABA was 4 ng/ml for both serum and CSF samples.