A randomized comparison of chloroquine and chloroquine plus ketotifen in the treatment of acute, uncomplicated, Plasmodium falciparum malaria in children

Repurposing Drugs to Fight Hepatic Malaria Parasites

Malaria remains one of the most prevalent infectious diseases worldwide, primarily affecting some of the most vulnerable populations around the globe. Despite achievements in the treatment of this devastating disease, there is still an urgent need for the discovery of new drugs that tackle infection by Plasmodium parasites. However, de novo drug development is a costly and time-consuming process. An alternative strategy is to evaluate the anti-plasmodial activity of compounds that are already approved for other purposes, an approach known as drug repurposing. Here, we will review efforts to assess the anti-plasmodial activity of existing drugs, with an emphasis on the obligatory and clinically silent liver stage of infection. We will also review the current knowledge on the classes of compounds that might be therapeutically relevant against Plasmodium in the context of other communicable diseases that are prevalent in regions where malaria is endemic. Repositioning existing compounds may constitute a faster solution to the current gap of prophylactic and therapeutic drugs that act on Plasmodium parasites, overall contributing to the global effort of malaria eradication.

A class of tricyclic compounds blocking malaria parasite oocyst development and transmission

Malaria is a deadly infectious disease in many tropical and subtropical countries. Previous efforts to eradicate malaria have failed, largely due to the emergence of drug-resistant parasites, insecticide-resistant mosquitoes and, in particular, the lack of drugs or vaccines to block parasite transmission. ATP-binding cassette (ABC) transporters are known to play a role in drug transport, metabolism, and resistance in many organisms, including malaria parasites. To investigate whether a Plasmodium falciparum ABC transporter (Pf14_0244 or PfABCG2) modulates parasite susceptibility to chemical compounds or plays a role in drug resistance, we disrupted the gene encoding PfABCG2, screened the recombinant and the wild-type 3D7 parasites against a library containing 2,816 drugs approved for human or animal use, and identified an antihistamine (ketotifen) that became less active against the PfABCG2-disrupted parasite in culture. In addition to some activity against asexual stages and gametocytes, ketotifen was highly potent in blocking oocyst development of P. falciparum and the rodent parasite Plasmodium yoelii in mosquitoes. Tests of structurally related tricyclic compounds identified additional compounds with similar activities in inhibiting transmission. Additionally, ketotifen appeared to have some activity against relapse of Plasmodium cynomolgi infection in rhesus monkeys. Further clinical evaluation of ketotifen and related compounds, including synthetic new derivatives, in blocking malaria transmission may provide new weapons for the current effort of malaria eradication.

Small molecule anti-malarial patents: a review (January 2010-June 2011)

INTRODUCTION

Malaria causes a huge humanitarian and economic burden. Parasite resistance to established and recently launched anti-malarials is a major issue which, when combined with a malaria eradication agenda, means there is a considerable need for new small molecule anti-malarials. Catalyzed by a recent surge in funding for malaria drug discovery and development, there is an increasing number of compounds in the malaria pipeline.

AREAS COVERED

This review covers patents published in English between January 2010 and June 2011, which feature small molecules for the treatment of malaria. Approximately 50 series of compounds are described. Patents covering clinical applications, diagnosis kits or vaccines are not included, nor patents where the principle disease focus is not malaria.

EXPERT OPINION

There is considerable activity in the field of small molecules for malaria which is likely to continue. The ultimate goal is to identify novel drugs to support the malaria eradication agenda. This requires safe and efficacious compounds, from novel chemotypes, which rapidly kill parasites and which are readily synthesized from cheap starting materials. In addition, compounds which have activity in the liver stages or in transmission blocking may be prioritized for development over analogs related to established anti-malarial series targeting the asexual blood stages of the parasite.

Chemical genomic profiling for antimalarial therapies, response signatures, and molecular targets

Malaria remains a devastating disease largely because of widespread drug resistance. New drugs and a better understanding of the mechanisms of drug action and resistance are essential for fulfilling the promise of eradicating malaria. Using high-throughput chemical screening and genome-wide association analysis, we identified 32 highly active compounds and genetic loci associated with differential chemical phenotypes (DCPs), defined as greater than or equal to fivefold differences in half-maximum inhibitor concentration (IC(50)) between parasite lines. Chromosomal loci associated with 49 DCPs were confirmed by linkage analysis and tests of genetically modified parasites, including three genes that were linked to 96% of the DCPs. Drugs whose responses mapped to wild-type or mutant pfcrt alleles were tested in combination in vitro and in vivo, which yielded promising new leads for antimalarial treatments.

Factors contributing to delay in parasite clearance in uncomplicated falciparum malaria in children

Background

Drug resistance in Plasmodium falciparum is common in many endemic and other settings but there is no clear recommendation on when to change therapy when there is delay in parasite clearance after initiation of therapy in African children.

Methods

The factors contributing to delay in parasite clearance, defined as a clearance time > 2 d, in falciparum malaria were characterized in 2,752 prospectively studied children treated with anti-malarial drugs between 1996 and 2008.

Results

1,237 of 2,752 children (45%) had delay in parasite clearance. Overall 211 children (17%) with delay in clearance subsequently failed therapy and they constituted 72% of those who had drug failure, i.e., 211 of 291 children. The following were independent risk factors for delay in parasite clearance at enrolment: age less than or equal to 2 years (Adjusted odds ratio [AOR] = 2.13, 95% confidence interval [CI]1.44-3.15, P < 0.0001), presence of fever (AOR = 1.33, 95% CI = 1.04-1.69, P = 0.019), parasitaemia >50,000/ul (AOR = 2.21, 95% CI = 1.77-2.75, P < 0.0001), and enrolment before year 2000 (AOR= 1.55, 95% CI = 1.22-1.96, P < 0.0001). Following treatment, a body temperature ≥ 38°C and parasitaemia > 20000/μl a day after treatment began, were independent risk factors for delay in clearance. Non-artemisinin monotherapies were associated with delay in clearance and treatment failures, and in those treated with chloroquine or amodiaquine, with pfmdr 1/pfcrt mutants. Delay in clearance significantly increased gametocyte carriage (P < 0.0001).

Conclusion

Delay in parasite clearance is multifactorial, is related to drug resistance and treatment failure in uncomplicated malaria and has implications for malaria control efforts in sub-Saharan Africa.

Factors contributing to anaemia after uncomplicated Plasmodiumfalciparum malaria in children

The factors contributing to anaemia in falciparum malaria were characterized in 1261 prospectively studied children in an endemic area of southwestern Nigeria. Of these, 487 (39%) presented with anaemia (haematocrit <30%). The following were found to be independent risk factors for anaemia at presentation: age <5 years, history of illness >3 days before presentation, presence of fever, a palpable liver, >parasitaemia 10,000/microl blood, and gametocytaemia. The mean maximum fractional fall in haematocrit (FFH) after treatment was 13.8% (95% confidence interval [CI] 13-14.6) of the baseline value. This occurred 3 days after treatment began and correlated positively with enrolment haematocrit. In children whose haematocrit was >30% at enrolment, the following were found to be independent risk factors associated with subsequent development of anaemia during follow-up: age <5 years and parasitaemia > or =100,000 parasites/microl. Haematological recovery was usually complete by 4-5 weeks, but was slower in children who were anaemic at enrolment and in those with recrudescence of their infections. Half of the children with recrudescence were still anaemic at 4 weeks. These findings have implications for the control of the burden of malarial anaemia in children in sub-Saharan African countries.

Predictors of the failure of treatment with pyrimethamine-sulfadoxine in children with uncomplicated falciparum malaria

The prevalence of pyrimethamine-sulfadoxine (PS)-resistant Plasmodium falciparum malaria has been increasing in sub-Saharan Africa or other parts of the world in the last one or two decades. The factors that identify children at risk of treatment failure after being given PS were evaluated in 291 children with acute, symptomatic, uncomplicated, P. falciparum malaria. The children took part in four antimalarial drug trials between July 1996 and July 2004 in a hyperendemic area of southwestern Nigeria. Following treatment, 64 (22%) of 291 children failed treatment by day 7 or 14. In a multivariate analysis, an age < or = 1.5 years (AOR=2.9, 95% CI 1.3-6.4, P = 0.009) and presence of fever (AOR = 3.3, 95% CI 1.28-7.14, P = 0.01) were independent predictors of the failure of treatment with PS at presentation. Following treatment, delay in parasite clearance >3 days (AOR = 2.56, CI 1.19-5.56, P = 0.016) was an independent predictor of the failure of treatment with PS. In addition, compared with the children who had no fever then, children with fever three or more days after starting treatment were more likely to be treatment failures. These findings may have implications for malaria control efforts in some sub-Saharan African countries where treatment of malaria disease depends almost entirely on PS monotherapy, and for programmes employing PS or PS-based combination therapy.

Predictors of the failure of treatment with chloroquine in children with acute, uncomplicated, Plasmodium falciparum malaria, in an area with high and increasing incidences of chloroquine resistance

Resistance to chloroquine (CQ) in Plasmodium falciparum has reached unacceptably high levels in many endemic countries. The pre-treatment factors that identify the children who are at risk of treatment failure after being given CQ were evaluated in 385 children with acute, uncomplicated, Plasmodium falciparum malaria. These children each took part in one of six antimalarial drug trials conducted, between July 1996 and July 2004, in a hyper-endemic area of south-western Nigeria. Following treatment with CQ, 149 (39%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =7 years [giving an adjusted odds ratio (AOR) of 2.17, with a 95% confidence interval (CI) of 1.19-3.85; P = 0.01], an asexual parasitaemia of > or =100,000/microl (AOR = 2.17; CI = 1.08-4.35; P = 0.03), the presence of gametocytaemia (AOR = 2.08; CI = 1.14-3.85; P = 0.02) and enrolment >4 years after commencement of the study (i.e. after 2000; AOR = 2.13; CI = 1.3-4.0; P = 0.003) were found to be independent predictors at presentation of the subsequent failure of treatment with CQ. Compared with the other children, those who failed to clear their parasitaemias within 3 days and those who still had fever 1-2 days after commencing treatment were more likely to be treatment failures. Together, these findings may have implications for malaria-control efforts in all areas of sub-Saharan Africa where treatment of malaria depends almost entirely on antimalarial monotherapy.

Predictors of the failure of treatment with chloroquine plus chlorpheniramine, in children with acute, uncomplicated, Plasmodium falciparum malaria

Resistance to chloroquine in Plasmodium falciparum can be reversed, both in vitro and in vivo, by chlorpheniramine, a histamine H(1) receptor antagonist. This reversal raises the possibility of using chlorpheniramine to prolong the clinical usefulness of chloroquine in resource-poor communities. The factors that identify children at risk of treatment failure after being given chloroquine plus chlorpheniramine have now been evaluated in 281 children with uncomplicated, P. falciparum malaria. The children, who had taken part in six trials of antimalarial drugs between February 1996 and September 1999, in a hyper-endemic area of south-western Nigeria, were enrolled prospectively for the present study. Following treatment with chloroquine plus chlorpheniramine, 13 (5%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =3 years (adjusted odds ratio = 11.1; 95% confidence interval = 2.2-55.3; P = 0.003) and a parasitaemia that took >3 days to clear (adjusted odds ratio=7.9; 95% confidence interval = 1.3-49.4; P = 0.027) were found to be independent predictors of treatment failure. In addition, compared with the children who had a lower axillary temperature then, the children who had an axillary temperature of > or =38 degrees C 2 days after commencing treatment were significantly more likely to be treatment failures. In resource-poor communities using chloroquine plus chlorpheniramine, the easily identifiable predictors of treatment failure might be used to identify children requiring alternative antimalarial drugs.

Risk factors for gametocyte carriage in uncomplicated falciparum malaria in children

The risk factors associated with gametocytaemia at presentation and after treatment with different antimalarial drug regimens were evaluated in 767 children enrolled prospectively in 5 antimalarial drug trials between July 1996 and December 2002 in a hyperendemic area of southwestern Nigeria. The children were assigned to one of 6 treatment groups: chloroquine (CQ) only; pyrimethamine-sulfadoxine (PS) only; amodiaquine (AQ) only; CQ combined with chlorpheniramine (CQCP); or PS combined with CQ (CQPS) or AQ (AQPS). At enrolment, 115 (15%) of 767 children were gametocyte carriers. During follow-up, 15·6% of all patients (i.e. 120 patients) developed patent gametocytaemia, which in 85% (102 patients) had developed by day 7 following treatment. In a multiple regression model, 4 factors were found to be independent risk factors for the presence of gametocytaemia at enrolment: male gender (adjusted odds ratio [AOR]=0·55, 95% confidence interval [CI] 0·36–0·83,P=0·005), absence of fever (AOR=1·61, 95% CI 1·05–2·5,P=0·03), duration of illness >3 days (AOR=1·57, 95% CI 1·0–2·4,P=0·047), and asexual parasite densities less than 5000/μl (AOR=0·42, 95% CI 0·24–0·73,P=0·002). The presence of patent gametocytaemia at enrolment (AOR=0·04, 95% CI 0·02–0·07,P<0·001) and recrudescence of asexual parasites within 14 days were associated with the presence of gametocytaemia 7 or 14 days after enrolment (AOR=0·5, 95% CI 0·3–0·8,P=0·007). Delay in the time taken to clear the initial parasitaemia (>2 days) was associated with increased risk of subsequent gametocyte carriage. These findings may have implications for malaria control efforts in sub-Saharan Africa where control of the disease depends almost entirely on chemotherapy.

Open randomized study of pyrimethamine-sulphadoxine vs. pyrimethamine-sulphadoxine plus probenecid for the treatment of uncomplicated Plasmodium falciparum malaria in children

BACKGROUND

Increasing drug resistance in Plasmodium falciparum has necessitated renewed search for cheap, effective alternatives to commonly available antimalarials, chloroquine and pyrimethamine-sulphadoxine, for the treatment of malaria in Africa. Probenecid, an inhibitor of organic anion transporters and multiresistance-associated proteins, can chemosensitize P. falciparum to pyrimethamine and sulphadoxine in vitro, but the clinical significance is unclear. We assessed the safety, treatment efficacy, and effects on gametocyte carriage of adding probenecid to pyrimethamine-sulphadoxine.

METHODS

We evaluated 151 children aged 12 years or younger who had uncomplicated P. falciparum malaria. Patients were randomly assigned pyrimethamine-sulphadoxine (25 mg/kg of the sulphadoxine component) or pyrimethamine-sulphadoxine as above plus probenecid 20-25 mg/kg of bodyweight in two divided doses daily for 3 days. The primary endpoints were parasitological cure rates on days 14 and 28.

RESULTS

Both regimens were well tolerated; no child was withdrawn because of drug intolerance. Fever (1.9 +/- 1.1 vs. 2.4 +/- 1.2 days, P = 0.02) and parasite clearance (2.3 +/- 0.9 vs. 2.7 +/- 1.1 days, P = 0.04) were significantly shorter, and the parasitological cure rate on day 14 (96.2%vs. 83.5%, P = 0.02) but not day 28 (79.4%vs. 72.6%, P = 0.4), was significantly higher in children treated with pyrimethamine-sulphadoxine-probenecid than in those treated with pyrimethamine-sulphadoxine. Gametocyte carriage was similar with both treatment regimens.

CONCLUSIONS

The combination of pyrimethamine-sulphadoxine, and probenecid, at a relatively moderate dose, improved treatment efficacy but had no effect on gametocyte carriage. The pyrimethamine-sulphadoxine-probenecid combination merits further evaluation as a potential treatment for use in Nigeria.

Gametocyte sex ratios in children with asymptomatic, recrudescent, pyrimethamine-sulfadoxine-resistant, Plasmodium falciparum malaria

The clinical features of the primary Plasmodium falciparum infections in 25 children, and of the recrudescent infections that emerged after pyrimethamine-sulfadoxine (PS) treatment of the children had failed, were evaluated. In addition, the gametocyte sex ratios in these children and in age- and gender-matched controls who had PS-sensitive (PS-S) infections were also examined. Compared with the primary infections, the recrudescent infections were accompanied by significantly fewer symptoms and lower levels of parasitaemia but significantly higher gametocytaemia:parasitaemia ratios. Although the mean gametocyte sex ratio was female-biased pre-treatment, in both the PS-resistant (PS-R) and PS-S infections it became male-biased on days 7 and 14 post-treatment. The times taken to attain a sex ratio of 1 were similar in both groups. The predominance of macrogametocytes seen 'early' post-treatment (on day 3) was later replaced by a predominance of microgametocytes (on days 7 and 14). Analysis of the disposition of gametocytaemia, from the time to attain a sex ratio of 1, showed that the area under the curve of the plot of the level of microgametocytaemia upsilon. time and the mean half-life of the microgametocytaemia were significantly greater and microgametocytaemia clearance was significantly slower than the corresponding values for macrogametocytaemia. Although sex ratios in Plasmodium may naturally become more male-biased as the infection progresses, it is possible that PS treatment may have contributed to the male-biased sex ratios observed post-treatment.

Plasmodium falciparum gametocytaemia in Nigerian children: before, during and after treatment with antimalarial drugs

We evaluated gametocyte carriage and intensities of gametocytaemia in 710 children presenting with acute, symptomatic, uncomplicated Plasmodium falciparum malaria who were treated with various antimalarial drug regimens: chloroquine (CQ); chloroquine plus chlorpheniramine, a histamine H1 receptor antagonist that reverses CQ resistance in P. falciparum in vitro and in vivo (CQCP); chloroquine plus ketotifen, a histamine H1 receptor antagonist that reverses CQ resistance in P. falciparum in vitro but not in vivo in the present study (CQK); chloroquine plus pyrimethamine-sulphadoxine (CQPS); amodiaquine (AQ); amodiaquine plus pyrimethamine-sulphadoxine (AQPS); and pyrimethamine-sulphadoxine (PS). On presentation, gametocyte carriage was significantly higher in CQ-resistant (CQ-R) than in CQ-sensitive (CQ-S) infections. Following CQ treatment, gametocyte carriage was significantly higher at all times after treatment and gametocyte density significantly higher on day 7 of follow-up in children with CQ-R than CQ-S infections. CQ treatment of CQ-R infections resulted in significantly higher density of gametocytaemia on day 7 compared with pre-treatment (day 0), but similar treatment of CQ-S infections resulted in significantly lower density of gametocytaemia on day 14 compared with day 0. Among children with CQ-R infections, those with mild (RI) resistance carried gametocytes significantly more often than those with moderate (RII) resistance on days 5 and 7 of follow-up (P = 0.04 and 0.01, respectively). Disposition kinetics of gametocytaemia using a non-compartmental method showed that the half life of gametocytaemia was longer and the clearance slower in children with CQ-R than in those with CQ-S infections. PS treatment was associated with significantly higher gametocyte carriage at all times between days 1 and 14, and significantly higher gametocytaemias on days 7 and 14 than in the other treatment regimens. Combination of AQ with PS significantly decreased gametocyte carriage at all times between days 1 and 14 of follow-up. Continuing use of CQ in CQ-R infections may encourage transmission of CQ-R infections; SP monotherapy is associated with significant gametocyte carriage and gametocytaemia and may encourage transmission of SP resistant infections as resistance to the drug increases.

Chloroquine or amodiaquine combined with sulfadoxine-pyrimethamine for treating uncomplicated malaria

BACKGROUND

Amodiaquine and chloroquine give fast relief from malaria symptoms, particularly fever. When used alone in areas where there is some parasite resistance they do not completely clear parasites from the blood in all cases, and so not all patients are cured of infection. The major disadvantage of using sulfadoxine-pyrimethamine alone is that it takes a relatively long time to relieve fever.

OBJECTIVES

To assess the effectiveness of chloroquine or amodiaquine given with sulfadoxine-pyrimethamine to treat uncomplicated falciparum malaria.

SEARCH STRATEGY

The Cochrane Infectious Diseases Group trials register, the Cochrane Controlled Trials Register, MEDLINE, EMBASE, Science Citation Index, African Index Medicus and LILACS were searched. Experts in the field and drug companies were contacted.

SELECTION CRITERIA

Randomised and quasi-randomised trials of chloroquine or amodiaquine given with sulfadoxine-pyrimethamine compared with either drug alone in adults or children with confirmed uncomplicated falciparum malaria.

DATA COLLECTION AND ANALYSIS

Two people independently applied the inclusion criteria. Data were extracted by the reviewer and checked independently by another person.

MAIN RESULTS

Five trials were included. Fever clearance time was reduced by combination therapy compared with sulfadoxine-pyrimethamine alone. Parasite clearance at day seven follow-up was not significantly different for chloroquine or amodiaquine treatment with or without sulfadoxine-pyrimethamine. Parasite clearance at day 28 was better with combination therapy compared with chloroquine or amodiaquine alone (odds ratio 14.28, 95% confidence interval 6.76 to 30.19), but not significantly better than sulfadoxine-pyrimethamine alone (odds ratio 3.17, 95% confidence interval 0.96 to 10.43). There was no evidence from the included trials of serious side effects with combination treatment.

REVIEWER'S CONCLUSIONS

In areas where chloroquine or amodiaquine are still effective, despite some degree of resistance, using these drugs in combination with sulfadoxine-pyrimethamine, rather than sulfadoxine-pyrimethamine alone, may make people feel better faster and improve sustained parasites clearance.