Treatment of late stage sleeping sickness caused by T . b . gambiense : a new approach to the use of an old drug

Current estimates indicate that some 300,000–500,000 people have human African trypanosomiasis (HAT) or sleeping sickness, and that about 60 million people live in areas where the disease is transmitted [1]. Thirty-six sub-Saharan countries of Africa are affected by the problem at different levels of endemicity (figure 1). The areas most affected are parts of the Democratic Republic of Congo (DRC), Angola, Southern Sudan, and Northern Uganda [2]. The epidemiological situation in some countries is totally unknown. Only a fraction of the population at risk is under appropriate surveillance and therefore the reported number of cases in 1999 (45,000) rather reflects poor reporting than the real situation [1]. Sleeping sickness is an ancient disease, which recently has regained epidemic dimensions. Large-scale control campaigns largely reduced the case number and in the mid sixties only sporadic cases occurred throughout the continent. Subsequently, following the attainment of independence from colonial rule, sleeping sickness control has not been given due attention by National Health Authorities because of political and civil unrest, deteriorating economies of the endemic countries, overpopulation, and competing health priorities [3]. Recent data on sleeping sickness surveillance indicate an important increase of the number of detected cases per year [4]. In some regions of the Democratic Republic of Congo trypanosomes were detected in 40–70% of the examined people of rural areas. The mortality caused by HAT and AIDS in this country is now of a comparable magnitude [5]. A prevalence survey conducted in 13 villages in Sudan showed a marked increase of the seroprevalence from 0.3% in 1988 to 20.4% in 1997 [6]. If the DALY figures (i.e. loss of healthy life years by premature mortality and disability) are considered the social and economic impact of trypanosomiasis ranks third of all parasitic diseases behind malaria and schistosomiasis in sub-Saharan Africa [7]. Melarsoprol is the standard treatment of late stage trypanosomiasis. The development of treatment schedules was previously purely empirical. Generally melarsoprol is given in 3 series of three to four consecutive injections, given every 24 hours, with an interval of about one week between the series. Based on pharmacokinetic analysis, computer simulations and extensive literature research covering all schedules previously used and tested, a new schedule, consisting of ten daily consecutive doses of 2.16 mg/kg of the drug was suggested. The pharmacokinetic model was validated in uninfected vervet monkeys. No unexpected drug accumulation and no systemic toxic effects were observed. In a pilot clinical trial in Congo RDC a small group of T. b. gambiense patients (n = 11) was treated successfully with the new schedule. In an open randomised clinical trial conducted in 500 patients in Angola the clinical efficacy and safety of this new concise treatment were compared to those of standard protocol treatment. Parasitological cure 24 hours after treatment was 100% in both groups. Statistical analysis yielded no significant differences for adverse events between the two treatment protocols. The new schedule reduces the amount and cost for the drug by about one third, and those for hospitalisation by about half.

Current estimates indicate that some 300,000-500,000 people have human African trypanosomiasis (HAT) or sleeping sickness, and that about 60 million people live in areas where the disease is transmitted [1].Thirty-six sub-Saharan countries of Africa are affected by the problem at different levels of endemicity (figure 1).The areas most affected are parts of the Democratic Republic of Congo (DRC), Angola, Southern Sudan, and Northern Uganda [2].The epidemiological situation in some countries is totally unknown.Only a fraction of the population at risk is under appropriate surveillance and therefore the reported number of cases in 1999 (45,000) rather reflects poor reporting than the real situation [1].
Sleeping sickness is an ancient disease, which recently has regained epidemic dimensions.Large-scale control campaigns largely reduced the case number and in the mid sixties only sporadic cases occurred throughout the continent.Subsequently, following the attainment of independence from colonial rule, sleeping sickness control has not been given due attention by National Health Authorities because of political and civil unrest, deteriorating economies of the endemic countries, overpopulation, and competing health priorities [3].Recent data on sleeping sickness surveillance indicate an important increase of the number of detected cases per year [4].
In some regions of the Democratic Republic of Congo trypanosomes were detected in 40-70% of the examined people of rural areas.The mortality caused by HAT and AIDS in this country is now of a comparable magnitude [5].A prevalence survey conducted in 13 villages in Sudan showed a marked increase of the seroprevalence from 0.3% in 1988 to 20.4% in 1997 [6].If the DALY figures (i.e.loss of healthy life years by premature mortality and disability) are considered the social and economic impact of trypanosomiasis ranks third of all parasitic diseases behind malaria and schistosomiasis in sub-Saharan Africa [7].
Melarsoprol is the standard treatment of late stage trypanosomiasis.The development of treatment schedules was previously purely empirical.Generally melarsoprol is given in 3 series of three to four consecutive injections, given every 24 hours, with an interval of about one week between the series.
Based on pharmacokinetic analysis, computer simulations and extensive literature research covering all schedules previously used and tested, a new schedule, consisting of ten daily consecutive doses of 2.16 mg/kg of the drug was suggested.The pharmacokinetic model was validated in uninfected vervet monkeys.No unexpected drug accumulation and no systemic toxic effects were observed.In a pilot clinical trial in Congo RDC a small group of T. b. gambiense patients (n = 11) was treated successfully with the new schedule.In an open randomised clinical trial conducted in 500 patients in Angola the clinical efficacy and safety of this new concise treatment were compared to those of standard protocol treatment.Parasitological cure 24 hours after treatment was 100% in both groups.Statistical analysis yielded no significant differences for adverse events between the two treatment protocols.The new schedule reduces the amount and cost for the drug by about one third, and those for hospitalisation by about half.

Key words: human African trypanosomiasis; sleeping sickness; treatment; melarsoprol
The disease is caused by the protozoan parasites Trypanosoma brucei gambiense (West African form) and Trypanosoma brucei rhodesiense (East African form), and is solely transmitted by the Tsetse fly, Glossina sp [7].
The West African form of sleeping sickness is characterised by a chronic progressive course, which may last from months up to several years before death.The East African form is usually acute and death occurs within weeks or months.In this article we focus on the West African form of sleeping sickness.

Early or hemolymphatic stage
In rare instances a chancre may become visible at the site of inoculation of the trypanosomes.Intermittent fever attacks, persistent headache, joint pains, weight loss, and pruritus are common symptoms of the early hemolymphatic stage.Weeks or months after the infection a general lymphadenopathy develops and typically the posterior cervical lymph nodes are often visibly enlarged ("Winterbottoms sign").Generalised endocrine disorders like reduced libido, amenorrhea, abnormal thirst or appetite, and prominent anaemia are frequent [8].The liver and the spleen may be slightly enlarged and a localised oedema may be observed.

Late stage
The onset of the clinically different late stage is defined by the invasion of the CNS by trypanosomes [8].
Early signs are changes of the personality and the behaviour, and may be very subtle.Speech may become indistinct and slow, and frequently extrapyramidal signs occur with tremors of the tongue and the fingers.The most impressive sign is daytime somnolence, often alternating with insomnia at night.Epileptiform seizures, euphoria and manical changes are observed and the patient becomes indifferent to his environment.The final phase is characterised by progressive mental deterioration and general wasting.Death results from the disease itself, concurrent infections like pneumonia, or malnutrition.The symptoms and signs of 500 patients treated for late stage sleeping sickness in Dondo, Angola, are listed in table 1.

Clinical aspects
The distinction of the stages influences the choice of drugs for treatment and is based on the analysis of the cerebrospinal fluid (CSF).If trypanosomes can be found in the CSF, or if the WBC count is more than 5 WBC/mm 2 , or if there is a protein content above 25 mg/100 ml (method of Siccard & Cantaloube) the patient is attributed to the late stage and treated with melarsoprol [2].
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Treatment
Pentamidine is currently used for treatment of early stage T. b. gambiense sleeping sickness.The organo-arsenical compound melarsoprol (Arsobal ® ) is the drug mainly used in the late stage.The recently introduced α-difluoromethylornithine (DFMO; eflornithine) [9] is effective in Gambian sleeping sickness in over 95%.However, the use of eflornithine is limited due to its application in four infusions per day for fourteen days.In addition the drug is very expensive due to its very complex synthesis, and had no longer been produced for several years.In the year 2001 an agreement between WHO and Aventis was reached guaranteeing the free availability of the drug over the next five years [10].This will only allow the use of the drug in selected situations, like the treatment of relapse patients, interventions financed by non-governmental organizations, and treatment of patients in industrialised countries.The complicated and costly application will prevent the re-placement of melarsoprol as the first line drug.Therefore WHO TDR has recently initiated a program to investigate the application by oral route.
Despite ample basic research on trypanosomes and screening activities to identify new active molecules, no new compounds are currently under development for treatment of second stage sleeping sickness.Therefore melarsoprol is likely to remain the first-line drug for the next decade.For this reason WHO has advocated optimisation of the use of the present drugs [2].

Melarsoprol treatment
Melarsoprol was introduced in 1949 [11] but its basic pharmaco-chemical and pharmacological properties were only investigated recently.The terminal elimination half life (t 1/2) is 35 hours, as determined by a biological assay [12].The corresponding parameter determined by HPLC was 1 Schedule used in Uganda [2] (adapted) hour, indicating the existence of active metabolites [13], which currently are under investigation.The total protein binding of melarsoprol is 79% as determined by ultrafiltration [14].The exact mode of action of melarsoprol remains unclear, but the drug was shown to unspecifically bind to disulphide moieties of proteins [15].Early studies performed in urine indicated that melarsoprol was only eliminated from the body to a very limited extent.To avoid accumulation of arsenic in the body, treatment interruptions after each 3 rd or 4 th injection of melarsoprol were introduced [16,17].Later studies revealing that melarsoprol is mainly eliminated in the faeces didn't get proper attention and hence treatment schedules have remained unchanged since 50 years.No unusual drug accumulation was found in elimination studies in rats [18], and kinetic investigations in monkeys [19] and humans [12,18].
The development of treatment schedules is purely empirical and there is no standardised treatment regimen [20].Generally, melarsoprol treatment consists of several series of three or four consecutive injections, given every 24 hours, with an interval of about one week between each series.In most of the schedules the doses increase progressively either during the course of treatment or within a single series (see fig. 2) [2].
Melarsoprol treatment is frequently accompanied by adverse effects, which may be severe.Common problems with melarsoprol are motor and sensitivity polyneuropathies, skin reactions, fever, diarrhoea, pruritus, and pain in the chest.A local reaction that can be attributed to the propyleneglycol solvent is thrombophlebitis at the site where the drug has been injected.
However, the most feared complications of melarsoprol treatment are encephalopathies.They occur at varying frequencies in 5-10% of all treated cases.The reaction is fatal for about 10-70% of the patients afflicted [2,21].
Its clinical manifestations are either a fulminant convulsive status, a progressive coma, or psychotic reactions.The fulminant convulsive status seems to be often preceded by minor prodromes such as dizziness or nausea and it is associated with acute cerebral oedema as shown by papilloedema and elevated CSF pressure.The progressive coma develops within hours without signs of cerebral oedema.The pressure of the CSF is normal and the protein levels are just moderately elevated.The psychotic reactions are characterised by aggression, restlessness, and emotional disorders lasting for a few days without other neurological signs [22,23].
A post mortem study showed no association between the encephalopathy and the severity of the trypanosome-induced meningoencephalitis.The principal abnormalities in patients dying from encephalopathy are hypoxic brain damage, brain swelling, and the features of acute haemorrhagic leukoencephalopathy.The hypoxic brain damage was clinically associated with convulsions or heart failure, the acute haemorrhagic leukoencephalopathy with progressive coma [23,24].
The cause of the reaction and the influence of the treatment schedule on its frequency, have been extensively discussed during the last decade.Generally an immune reaction is thought to underlie the syndrome [2,21,23], but the mechanism remains unknown.In a large-scale study [25] the concomitant application of prednisolone was shown to have a protective effect against encephalopathies.There were also reports of reactive encephalopathy after the application of other trypanocidal drugs like eflornithine and nifurtimox [26]; underlining the idea that this severe adverse event may not be attributed to the inherent toxicity of melarsoprol.
Relapses are another major problem of sleeping sickness treatment with melarsoprol.For many decades the frequency reported remained stable at levels between 1% to 10% [21].However, significantly higher rates of patients refractory to melarsoprol were recently reported from Northern Uganda (26.9%) [27], Northern Angola (25%) [28], and Southern Sudan.An overview on the epidemiology and research on underlying factors has been done by Brun et al. [29].No recommendation for the treatment of cases refractory to therapy exists so far.Where feasible eflornithine is used either alone or in combination with melarsoprol.Clinical trials for the evaluation of combination of eflornithine, melarsoprol, and/or nifurtimox are currently ongoing and preliminary results were encouraging.Nifurtimox is the first line drug for treatment of T. cruzi (Chagas disease) in South America, but it is not registered for use against human African trypanosomiasis [2].
Finally a severe drawback of melarsoprol therapy is the long period of hospitalisation required due to the complicated treatment schedules (see fig. 2).This is a major social and economic burden for the families affected because all patients must be taken care of at the hospital by family members.

The new concise treatment schedule
Based on pharmacokinetic analysis, computer simulations, and extensive literature research covering all schedules previously used and tested, a new schedule consisting of ten daily consecutive doses of 2.16 mg/kg of the drug was suggested [12] (see fig. 2).The pharmacokinetic model was validated in uninfected vervet monkeys following the new and the standard treatment schedules [19].No unexpected drug accumulation and no systemic toxic effects were observed in the monkeys used for the trial.In a pilot clinical trial in Congo RDC a small group of T. b. gambiense patients (n = 11) was treated successfully with the new schedule.All patients could leave the hospital in good health after 10 days of melarsoprol treatment or with a distinct improvement of their condition.A non-significant increase of minor adverse reactions (diarrhoea, fever, cutaneous reactions) was observed.No case of reactive encephalopathy occurred and no relapse was reported in this group after 12 months [30].
The clinical efficacy and safety of this new concise treatment were compared to those of standard protocol treatment in an open randomised clinical equivalence trial conducted in 500 patients in Angola.Application of melarsoprol was either following the standard National Angolan protocol (S) of 3 series of 4 injections (1.2; 2.4; 3.6; 3.6 mg/kg bw /day) interrupted by rest periods of 7 days, total duration 26 days, or according to the new treatment protocol of 10 consecutive injections (2.2 mg/kg bw /day) of melarsoprol (N) (see fig. 2).The primary outcomes defined were mortality related to treatment, encephalopathy rate, and elimination of parasites at the end of treatment.Parasitological cure 24 hours after treatment was 100% in both groups.Statistical analysis yielded no significant difference for adverse events between the two treatment protocols.A total of 28 patients (S: 14, N: 14; 5.6%) suffered from an encephalopathic syndrome during the treatment, of whom 12 died (S: 6; N: 6; 2.4%).Severe motor (S: 1, N: 2) and sensitivity polyneuropathy (S: 1; N: 0) were extremely rare in both groups.An increase of skin reactions was observed with the new treatment: Severe bullous dermatitis leading to treatment interruption occurred in 4 cases (S: 1; N: 3; 1.2%), severe maculopapular rash in 18 cases (S: 6, 2.4%; N: 8, 3.2%), and severe pruritus in 14 cases (S: 6, 2.4%; N: 8, 3.2%).All reactions could be controlled by treatment interruption and application of corticosteroids, and remitted completely.All moderate adverse effects like fever, diarrhoea, headache were observed at comparable rates in both groups.One year after the end of enrolment (individual observation time 15-32 months) 16 patients had relapsed (S: 7, N: 9) [31].
Currently a large-scale, multinational clinical trial is ongoing to further assess the frequency of adverse events like encephalopathic and skin reactions, and the efficacy of the new treatment schedule in different populations and settings.
We underline that all investigations described here were done in T. b. gambiense patients and can not be extrapolated to T. b. rhodesiense sleeping sickness due to the differing clinical pattern of the disease and the markedly higher parasitemia.Until credible data are available we recommend the use of the new melarsoprol schedule in such patients, only in defined trial settings and with exceptional caution.
The new schedule reduces the amount and cost for the drug by about one third, and those for hospitalisation by about half.The socio-economic value is even increased by the fact that all patients have to be taken care of by relatives at the hospital.Therefore the duration of treatment has a direct impact on the economic situation of the affected family, and in case of an endemic situation on entire villages.In addition, the capacity of the medical facilities can be more than doubled by the use of the new treatment schedule.This may crucially improve the situation for patients in areas of high endemicity, where the demand largely surpasses the capacities of the centres.These circumstances particularly prevail in war affected countries like Sudan, Angola, and the Democratic Republic of Congo.
Given the economical and practicallity of the concise treatment protocol, it might be a useful alternative to the common lengthy treatment, especially in endemic situations.

Figure 2
Figure 2 Examples of different schedules for treatment of late stage T. b. gambiense sleeping sickness.
Med Wochenschr (1871-2000) Swiss Med Wkly (continues Schweiz Med Wochenschr from 2001) Editores Medicorum Helveticorum We thank Dr. C. Hatz for his critical analysis of the manuscript.International Advisory CommitteeProf.K. E. Juhani Airaksinen, Turku, Finland Prof. Anthony Bayes de Luna, Barcelona, Spain Prof. Hubert E. Blum, Freiburg, Germany Prof. Walter E. Haefeli, Heidelberg, Germany Prof. Nino Kuenzli, Los Angeles, USA Prof. René Lutter, Amsterdam, The Netherlands Prof. Claude Martin, Marseille, France Prof. Josef Patsch, Innsbruck, Austria Prof. Luigi Tavazzi, Pavia, Italy We evaluate manuscripts of broad clinical interest from all specialities, including experimental medicine and clinical investigation.We look forward to receiving your paper!Guidelines for authors: http://www.smw.ch/set_authors.htmlAll manuscripts should be sent in electronic form, to: Official journal of the Swiss Society of Infectious disease the Swiss Society of Internal Medicine the Swiss Respiratory Society