Predictors of the failure of treatment with trimethoprim–sulfamethoxazole in children with uncomplicated, Plasmodium falciparum malaria

In many African countries, trimethoprim-sulfamethoxazole (TS) is recommended for the treatment of children with malaria and pneumonia - in accordance with the guidelines for the integrated management of childhood illness (IMCI) - and, in some settings, for the home management of febrile illnesses. There have been few studies, however, of the risk of failure of treatment with this drug combination in children with acute, Plasmodium falciparum malaria. The factors that identify children at risk of treatment failure after being given TS were therefore evaluated in 101 children with acute, symptomatic, uncomplicated, P. falciparum malaria, in a hyper-endemic area of south-western Nigeria. Overall, 11% of the children failed treatment by day 14. In a multivariate analysis, two factors were found to be independent predictors of the failure of treatment with TS: an age of <3 years (adjusted odds ratio=0.1; 95% confidence interval=0.02-0.53; P=0.007); and a body temperature of >or=38 degrees C 2 days after the commencement of treatment (adjusted odds ratio=4.9; 95% confidence interval=1.2-21.3; P=0.03). These findings may have implications for control efforts in some sub-Saharan African countries, where TS is recommended for the management of malaria in children, with or without pneumonia.

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.

Open randomized study of artesunate-amodiaquine vs. chloroquine-pyrimethamine-sulfadoxine for the treatment of uncomplicated Plasmodium falciparum malaria in Nigerian children

BACKGROUND

Artemisinin-based combination antimalarials are currently considered effective alternatives for the treatment of malaria in Africa, but there are few studies of such combinations in Nigerian children. We assessed the safety, treatment efficacy and effects on gametocyte carriage of the combination of artesunate plus amodiaquine and chloroquine plus pyrimethamine-sulfadoxine in children.

METHODS

We evaluated 153 children who were aged 12 years or younger who had uncomplicated Plasmodium falciparum malaria. Patients were randomly assigned a combination of artesunate (4 mg/kg of body weight daily for 3 days) plus amodiaquine (30 mg/kg over 3 days), or chloroquine (25 mg/kg over 3 days) plus pyrimethamine-sulfadoxine (25 mg/kg of the sulfadoxine component at presentation). The primary endpoints were the proportions of children with adequate clinical and parasitological response, late parasitological failure, late clinical failure and early treatment failure. The parasitological cure rates on days 14-28 were also used as the primary endpoints.

RESULTS

Both regimens were well tolerated; no child was withdrawn because of drug intolerance. All children treated with artesunate plus amodiaquine had adequate clinical and parasitological response (ACPR), while all but five children treated with chloroquine plus pyrimethamine-sulfadoxine had similar response. Fever clearance times were similar in the two treatment groups. However, the proportion of patients whose parasitaemia cleared by day 2 was significantly higher (100 vs. 50%, P = 0.00001) and parasite clearance was significantly faster (1.7 +/- 0.4 vs. 2.5 +/- 0.8 days, P = 0.0001) in children treated with artesunate plus amodiaquine. The cure rates on days 21 (100%vs. 94%, P = 0.03) and 28 (100%vs. 90%, P = 0.003) were also significantly higher in children treated with artesunate plus amodiaquine than in those treated with chloroquine plus pyrimethamine-sulfadoxine. Overall, a significantly higher proportion of children treated with chloroquine plus pyrimethamine-sulfadoxine carried gametocytes at least once during follow-up compared with those treated with artesunate plus amodiaquine [5 of 50 (10%) vs. 1 of 103 (0.97%), P = 0.01].

CONCLUSION

The combination of artesunate plus amodiaquine is therapeutically superior to a combination of chloroquine plus pyrimethamine-sulfadoxine, and significantly reduced gametocyte carriage following treatment.

Plasmodium falciparum malaria in Nigerian children during high and low transmission seasons: gametocyte carriage and response to oral chloroquine

Plasmodium falciparum malaria during high and low transmission seasons was evaluated in 1031 children treated with different antimalarial drug in a hyperendemic area of southwestern Nigeria. Seventy-three (10.5%) of 693 and forty (11.8%) of 338 children were gametocyte carriers in the high transmission seasons (HTS) and low transmission seasons (LTS), respectively. In a multiple regression model, two factors were found to be independent risk factors for the presence of gametocytemia at enrolment in the HTS: duration of illness >3 d, and asexual parasite densities less than 10,000/microl. Similarly male gender, duration of illness >4 d and parasite density less than 5000/mul were found independent risk factors for presence of gametocytemia during LTS. The presenting parasitemia, parasite clearance times, intensity of gametocytemia and proportion carrying gametocytes post treatment differ significantly in the 333 (32.3%) of these children that were treated with chloroquine in the two seasons. These findings may be important in our understanding of P. falciparum transmission sustenance, response to chloroquine therapy and contribution of chloroquine to gametocyte carriage as seasonal changes occur.

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.

Polymorphisms in Plasmodium falciparum dhfr and dhps genes and age related in vivo sulfadoxine-pyrimethamine resistance in malaria-infected patients from Nigeria

Mutations in Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes have been used as means to predict treatment failure to sulfadoxine-pyrimethamine (SP) and for monitoring/surveillance of resistance to the drug in many areas where malaria is endemic. However, patients responses to treatment are significantly dependent on factors like host immunity profile of treated patients. In order to investigate the relationship between molecular markers of SP resistance, host immunity and clinical outcome, the association between pre-treatment dhfr and dhps genotypes, age and treatment outcomes was evaluated in 109 children treated with SP for acute uncomplicated malaria in Ibadan, Nigeria. Seventy-three percent of the children were cured with the drug, while 27% failed treatment after 28 days of follow-up. All children infected with parasites harboring less than two dhfr/dhps mutations were cured with SP. The dhfr triple (Asn-108/Ile-51/Arg-59) mutants or the dhps double mutants (Gly-437/Glu-540) were independently associated with SP treatment failure in children aged less than 5 years, but not in older children. The dhfr and dhps quintuple mutant (dhfr triple mutant+dhps double mutant) was the genotype most strongly associated with SP treatment failure (OR=24.72, 95%CI=8.24-74.15) in both younger and older children.

Effects of antifolates--co-trimoxazole and pyrimethamine-sulfadoxine--on gametocytes in children with acute, symptomatic, uncomplicated, Plasmodium falciparum malaria

Antimalarial drugs including the antifolate, pyrimethamine-sulfadoxine (PS), can modulate the prevalence and intensities of gametocytaemia following treatment of acute malaria infections. They may also directly influence the transmission and spread of drug insensitivity. Little is known of the effects of co-trimoxazole (Co-T), another antifolate antimalarial, on gametocytes in children with acute malaria infections. We compared the effects of Co-T and PS on the prevalence and intensities of gametocytaemia and gametocyte sex ratios in 102 children aged 0.5-12 years presenting with acute and uncomplicated falciparum malaria. Compared to pre-treatment, both drugs significantly increased gametocyte carriage post-initiation of treatment. However, gametocyte carriage was significantly lower on day 14 in those treated with Co-T than PS. Significant increase in gametocytaemia with time occurred in PS--but not Co-T-treated children. Kaplan-Meier survival curve of the cumulative probability of remaining gametocyte-free in children who were agametocytaemic at enrollment showed that by day 7 of follow up, children treated with PS had a significantly higher propensity to have developed gametocytes than in Co-T-treated children (Log-rank statistic 5.35, df = 1, P = 0.02). Gametocyte sex ratio changes were similar following treatment with both drugs. PS and Co-T treatment of acute malaria infections in children from this endemic area is associated with significant increases in prevalence and intensities of gametocytaemia but these effects are more marked in those treated with PS than Co-T.

Efficacy of chloroquine plus chlorpheniramine in chloroquine-resistant falciparum malaria during pregnancy in Nigerian women: a preliminary study

The efficacy of chloroquine plus chlorpheniramine, a histamine H receptor antagonist, which reverses chloroquine 1 insensitivity in Plasmodium falciparum in vitro and in vivo , was evaluated in 30 pregnant women with recrudescent chloroquine-resistant Plasmodium falciparum malaria. All patients had at least one or more treatment failures with one or more courses of chloroquine or pyrimethamine-sulphadoxine. There was a prompt response to treatment with parasitaemia and fever clearing in all patients within 48 and 96 hours respectively of commencement of therapy with the combination. The cure rate on day 14 was 77%. Parasitaemia recurred in seven patients after day 14 and was successfully treated with oral mefloquine. The combination was well tolerated; pruritus and drowsiness were the only noticeable adverse effects. The progress of pregnancy and its outcome were not adversely affected by treatment with the combination. When fully developed, the combination of chloroquine plus chlorpheniramine may be an alternative in the treatment of chloroquine-resistant malaria during pregnancy in Nigerian women.

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.

Comparison of chlorproguanil-dapsone with sulfadoxine-pyrimethamine for the treatment of uncomplicated falciparum malaria in young African children: double-blind randomised controlled trial

BACKGROUND

Increasing resistance to sulfadoxine-pyrimethamine is leading to a decline in its effectiveness. We aimed to assess the safety profile of chlorproguanil-dapsone (CD), and to compare the safety and efficacy of this drug with that of sulfadoxine-pyrimethamine (SP) as treatment for uncomplicated falciparum malaria.

METHODS

We undertook a double-blind, randomised trial in 1850 consecutively recruited children with uncomplicated falciparum malaria, pooling data from five African countries. Analyses were based on all randomised patients with available data.

FINDINGS

CD was significantly more efficacious than SP (odds ratio 3.1 [95% CI 2.0-4.8]); 1313 patients (96%) given CD and 306 (89%) given SP achieved acceptable clinical and parasitological response by day 14. Adverse events were reported in 46% and 50% of patients randomised to CD and SP, respectively (treatment difference -4.4%, [95% CI -10.1 to 1.3]). Haemoglobin in the CD group was significantly lower than in the SP group at day 7, a difference of -4 g/L (95% CI -6 to -2). Mean day 14 haemoglobin (measured only for the small number of patients whose day 7 data caused concern) was 94 g/L (92-96) and 97 g/L (92-102) after CD and SP, respectively. Glucose-6-phosphate dehydrogenase deficient patients on CD had greater odds than those on SP of having a fall of 20 g/dL or more in haemoglobin when baseline temperature was high. Methaemoglobinaemia was seen in the CD group (n=320, mean 0.4% [95% CI 0.4-0.4]) before treatment, 4.2% (95% CI 3.8-4.6) (n=301) at day 3, and 0.6% (0.6-0.7) (n=300) at day 7).

INTERPRETATION

CD had greater efficacy than SP in Africa and was well tolerated. Haematological adverse effects were more common with CD than with SP and were reversible. CD is a useful alternative where SP is failing due to resistance.

Efficacy of herbal remedies used by herbalists in Oyo State Nigeria for treatment of Plasmodium falciparum infections--a survey and an observation

In the course of evaluating the contribution of phytomedicine to possible drug discovery of antimalarial drugs, an ethnomedical survey of specialized children traditional clinics was done. In the observational multi center study, efficacy of eight different herbal remedies, each consisting of 3-8 ingredients and administered by herbalists were investigated in clients enrolled in the six traditional clinics in Oyo (urban center) and Otu (rural center) of Oyo State, Nigeria. The clients, aged between six months and fifteen years with clinical symptoms of malaria were enrolled in the clinics of the herbalists, as their usual practice. Oral informed consents were obtained from their parents or guardians. Microscopic diagnosis of malaria infection was used to evaluate parasitaemia and validate efficacy of herbal remedies. Results of the analysis showed that, of the 163 clients of the herbalists, only 62 (30 from Oyo, 32 from Otu) had microscopically confirmed P. falciparum infection. Only results from 54 clients (29/30 (Oyo) and 25/32 (Otu) with P. falciparum infection could be evaluated. Plasmodium falciparum infection in 88% (23/29) of clients from Oyo responded to treatment with the herbal remedies while cure rate in clients from Otu was 42% (13/25). Parasite densities ranged from 171 to 53,613 parasites/microl blood and 87 to 36,209 parasites/microl blood in patients from Oyo and Otu respectively. The herbalists administered the remedies and Gossypium arboreum, Anarcadium occidentalis, Citrus medica, Phyllanthus amarus and Lippia multiflora were the main ingredients in the efficacious remedies. The herbalists gave detailed descriptions of each of the 8 herbal remedies proffered. The results confirm the efficacy of two of the eight herbal remedies, thereby validating the role of ethnomedicine as a possible source for the discovery of new chemotherapeutic agents in the treatment of P. falciparum malaria.

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.

Malaria diagnosis: false negative parasight-F tests in falciparum malaria patients in Nigeria

This study was designed to assess the relative reliability of microscopy, the dipstick technique based on the detection of Plasmodium falciparum-specific histidine rich protein II (HRPII) (Parasight-F) and PCR assays in diagnosing falciparum malaria infections in Nigerian children. The prevalence of P. falciparum infections in enrolled patients was 100% by microscopy. Parasite density ranged from 329 to 81,194 parasites/microL of blood, with a geometric mean parasite density of 5168 parasites/microL of blood. The sensitivity of the HRPII based dipstick, PCR and microscopy were 80%, 92% and 100% respectively. A false negative rate of 20% was observed with Parasight-F as compared with microscopy. The parasitemia in patients with false negative Parasight-F tests ranged from 319 to 54,680 parasites/microL of blood. Detailed PCR analysis of Isolates obtained from five out of the eight patients who exhibited a negative Parasight-F test, showed that the average numbers of P. falciparum clones in these five isolates were: 1.7 +/- 1.02 with MSPI, 3.2 +/- 1.3 with MSP2 and 1.4 +/- 1.72 with GLURP. Comparison of microscopy and HRPII results showed a significant (p=0.009) difference as opposed to microscopy and PCR (p=0.239). This study showed that caution should be exercised when excluding P. falciparum infections on the basis of HRPII based dipstick results alone. Microscopy or PCR diagnosis where possible, should be carried out in order to confirm negative P. falciparum HRPII-based dipstick tests.

Plasmodium berghei: efficacy and safety of combinations of chloroquine and promethazine in chloroquine resistant infections in gravid mice

Efficacy and safety of combinations ofChloroquine (CQ) and doses of Promethazine (PR) against CQ resistant Plasmodium berghei infections in gravid mice was evaluated. Parasites were cleared faster in mice treated with CQ combined with doses of PR ranging from 20mg/kg to 50mg/kg (3.4 +/- 0.5 to 2.7 +/- 0.7) compared with CQ alone (4.7 +/- 0.8) (P<0.5). Parturition resulting in live pups in animals treated with CQ and 20mg/ kg and 30mg/kg of PR (81%) was significantly higher than in animals treated with CQ alone (44%) or saline (13%). Mean birth weight of pups delivered by infected gravid animals treated with CQ and 30mg/kg or 40mg/kg of PR (1.51 +/- 0.16 or 1.56 +/- 0.16) was significantly higher than animals treated with CQ alone (1.33 +/- 0.13) (P=0.00004, 0.0014 respectively). No gross malformations were observed in pups delivered by infected or non-infected animals treated with the combinations of chloroquine and Promethazine.

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.

Molecular analysis of Plasmodium falciparum recrudescent malaria infections in children treated with chloroquine in Nigeria

Parasite genotyping by a polymerase chain reaction was used to distinguish recrudescent from newly acquired Plasmodium falciparum infections in 50 of 160 Nigerian children taking part in a chloroquine efficacy study in Ibadan, Nigeria. A finger prick blood sample was taken from each child before and after treatment to identify recrudescent parasites. By investigating allelic variation in three polymorphic antigen loci, merozoite surface protein-1 (MSP-1), MSP-2, and glutamate-rich protein (GLURP), we determined parasite diversity in the population and in the infected host. DNA from pretreatment and post-treatment samples from 47 of the 50 patients who failed therapy was successfully amplified by the PCR. The MSP-1, MSP-2, and GLURP genotypes in all samples showed extensive diversity, indicating polyclonal infections. The average number of clones per infection in pre-treatment sample was 2.5 with MSP-1, 4.9 with MSP-2, and 2 with GLURP. The extent of multiplicity decreased significantly (P = 0.016) in posttreatment samples. Multiplicity of infection and initial parasite density were not age dependent. Comparison of the variant alleles in pretreatment and post-treatment samples of each patient indicates that 26 of the 47 children had genuinely recrudescent disease. Conversely, post-treatment samples from five children showed completely new genotypes, indicating either a previously sequestered population of parasites or a newly acquired infection. Overall, this study has shown the diversity and complexity of P. falciparum population in Ibadan, Nigeria. The study has also shown the dynamics of P. falciparum infections in this population before and after chloroquine treatment in an area of high malaria transmission.

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.

Asymptomatic, recrudescent, chloroquine-resistant Plasmodium falciparum infections in Nigerian children: clinical and parasitological characteristics and implications for the transmission of drug-resistant parasites

The clinical features of their primary Plasmodium falciparum infections and of the recrudescent infections that emerged after chloroquine (CQ) treatment were evaluated in 48 children. Compared with the primary infections, the recrudescent infections were accompanied by significantly fewer symptoms and lower densities of parasitaemia but a much higher gametocytaemia:parasitaemia ratio (0.051 v. 0.00097; P = 0.0000000). There was a negative correlation between the recrudescent parasitaemia and the time elapsing between its detection and the subsequent onset of symptoms (r = -0.44; P = 0.006). The recrudescent parasitaemia was significantly lower [with geometric means and (ranges) of 117 (40-9756) v. 1112 (30-25,592) asexual forms/microl; P = 0.009] and the recrudescent gametocytaemia:parasitaemia ratio significantly higher (0.59 v. 0.024; P = 0.0000002) in those who were asymptomatic for at least 5 days after detection of the recrudescent parasitaemia than in those who were symptomatic at recrudescence. The disposition kinetics of the gametocytaemias in 18 primary infections--from nine children who failed CQ treatment and nine other children, matched for age and gender with the failures, who were CQ-treatment successes--were analysed. The results showed that the maximum gametocytaemia, time taken to reach the maximum gametocytaemia, the half-life of the gametocytaemia and the area inscribed by the plot of gametocytaemia against time were significantly higher, and the clearance of gametocytaemia significantly slower, in the children with primary infections that recrudesced. It therefore appears that continuing the use of CQ in areas where some parasites are resistant to the drug may confer survival and propagation advantages on the resistant parasites.

Point mutations in the pfcrt and pfmdr-1 genes of Plasmodium falciparum and clinical response to chloroquine, among malaria patients from Nigeria

Chloroquine (CQ) resistance in Plasmodium falciparum has been associated with specific point mutations in the pfcrt and pfmdr-1 genes. In the present study, 30 children aged 1-12 years, who were all suffering from acute, uncomplicated, P. falciparum malaria in Ibadan, Nigeria, were evaluated to assess the association between these mutations and clinical outcome following treatment with CQ. The parasites, in blood samples collected pre-treatment and, in those who failed treatment, on the day symptoms re-occurred post-treatment, were genotyped using the polymorphic MSP1, MSP2 and GLURP loci and PCR-RFLP. The results showed that, pre-treatment, all 30 patients had polyclonal infections, the mean numbers of P. falciparum clones detected per infection being 2.6 with MSP1, 4.2 with MSP2 and 2.8 with GLURP. The T76 allele of pfcrt and the Y86 allele of pfmdr-1 were found in 53% and 40%, respectively, of the pre-treatment samples from the 15 patients who failed CQ treatment, but the Y1246 mutation in pfmdr-1 was never detected. Although the parasites from the two patients with high-grade (RIII) resistance to CQ had both of these point mutations, the presence of the T76 allele of pfcrt or the Y86 allele of pfmdr-1 (considered individually) could not be used to predict treatment outcome. However, a high frequency of clonal multiplicity may confound attempts to associate the point mutations in pfcrt or pfmdr-1 with clinical response to CQ. It remains unclear whether the present results represent the characteristics of the predominant parasite populations in the study area. Further studies are needed before the strength of the association between the point mutations identified as markers of drug resistance and clinical outcome can be accurately evaluated, in this and other regions of intense transmission.

Plasmodium falciparum gametocytaemia in Nigerian children: Peripheral immature gametocytaemia as an indicator of a poor response to chloroquine treatment, and its relationship to molecular determinants of chloroquine resistance

A group of 161 children who presented with acute, symptomatic, uncomplicated, Plasmodium falciparum malaria in an endemic area of Nigeria was investigated. The aims of the study were to determine the clinical characteristics and responses to oral chloroquine (CQ) therapy of children who were gametocytaemic on presentation and those who were not [including those who were found to have developed peripheral immature gametocytaemias (PIG) when checked 72 h after commencing treatment], and to follow the development of PIG 72-336 h after the start of treatment. The 40 consecutive children who did have peripheral gametocytaemia on presentation and the 40 who did not were similar in their clinical characteristics and responses to oral CQ therapy. Nine of the 40 children who did not initially have gametocytaemias but who subsequently developed PIG (stages I-III) 72-336 h after commencing CQ treatment failed the treatment. In order to evaluate the presence of PIG as an indicator of response to CQ, the smears of blood from 81 children--66 classified as resistant to CQ (60, five and one considered RI, RII, RIII, respectively) and 15 who, though considered to have sensitive responses to CQ, cleared their peripheral parasitaemias > or =72 h after commencing CQ therapy--were examined for PIG. Most (42) of the 66 children with CQ-resistant (CQ-R) infections but none of the 15 with sensitive responses had PIG. Among the 66 children with CQ-R infections, the clinical features of those with PIG were generally similar to those without PIG, although those with PIG were more likely to have hepato-splenomegaly and less likely to have hepatomegaly alone. In the children with CQ-R infections, plasma concentrations of CQ on days 7 and 14 were generally above the level necessary to clear sensitive infections in the study area. The results of molecular analyses of isolates from children with both CQ-R infections and PIG revealed that all 14 checked for mutations in pfcrt had the T76 mutation associated with CQ resistance, and that four of the five also checked for mutations in pfmdr1 had the Y86 mutation associated with CQ resistance. The detection of PIG 72 h after the commencement of CQ treatment may be used as a microscopical indicator of a poor response to CQ in children from this endemic area.

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

The increasing resistance of Plasmodium falciparum to chloroquine (CQ) has created urgent needs for the evaluation of alternative antimalarial drugs that are effective, safe, readily available and affordable. Ketotifen, a histamine H(1)-receptor antagonist that reverses CQ resistance in P. falciparum in vitro, may potentially enhance the effects of CQ in vivo. The effects of oral treatment with CQ alone (30 mg/kg base given over 3 days) were compared with those of this CQ regimen combined with ketotifen fumarate (0.25 mg at presentation followed by 0.125 mg/kg every 8 h for 5 days). The subjects were 145 children aged 1-10 years who were suffering from acute, symptomatic, uncomplicated, P. falciparum malaria: 74 given CQ alone and 71 given CQ plus ketotifen (CQK). Although the mean fever-clearance time was significantly shorter following treatment with CQK than after treatment with CQ alone, all other therapeutic responses were similar in the two treatment groups. Among siblings in whom there was clustering of infections, the likelihood of cure was also similar in the two treatment groups. Retreatment of 17 CQ-treatment failures with CQK produced a cure in six children, and retreatment of 22 CQK-treatment failures with CQK produced a cure in eight children. Retreatment of all drug failures with a combination of amodiaquine plus pyrimethamine-sulfadoxine resulted in complete clearance of parasitaemia and symptoms within 2-3 days and a cure 'rate' of 100% on day 28. The prevalences and intensities of gametocytaemias on day 3 or days 3, 7 and/or 14 combined were similar in the two groups. Adverse drug reactions were always tolerable, and limited to pruritus, gastro-intestinal disturbances, drowsiness and weight gain; the latter two adverse effects were significantly more frequent in those treated with CQK than in those given CQ alone. Haematological and biochemical parameters were not adversely affected by either treatment regimen. The findings indicate that - at least at the dosing regimen used in the present study and among children with acute, uncomplicated, P. falciparum malaria from Ibadan - the addition of ketotifen to CQ produced little or no significant enhancement of the antimalarial effect of CQ.

Exposure to cyanide following a meal of cassava food

Exposure to cyanide from gari, a popular cassava food in West Africa, is implicated in the causation of ataxic polyneuropathy and amblyopia, but this has been questioned because cyanide was not detected in gari in a study. This study was carried out to determine if gari is a source of exposure to cyanide. Gari (150 g) containing cyanohydrin, from which 128 micromol of cyanide ions could be released, was dissolved in 500 ml of cold water for each of the 12 healthy subjects to drink. Concentrations of cyanide in plasma and erythrocytes were determined at baseline and following the meal at 30 min, 1 h, hourly for 4 h and two hourly for 12 h. The mean concentrations of cyanide in the plasma were 6 micromol/l (95% CI 2-10) at baseline, 12 micromol/l (95% CI 6-17) at peak and 6 micromol/l (95% CI 2-10) on return to baseline. The mean amount of cyanide absorbed into the plasma was 13 micromol (S.D. 12), while the transit time of absorbed cyanide was 7.3 h (S.D. 2.1). This study shows that exposure to cyanide follows consumption of gari, but the amount of cyanide absorbed into the plasma from a single meal is small and unlikely to cause acute intoxication. The long transit time of absorbed cyanide in the plasma suggests that frequent intake of gari could cause cyanide to accumulate in the plasma.

Comparative efficacy of chloroquine and cotrimoxazole in the treatment of acute uncomplicated falciparum malaria in Nigerian children

OBJECTIVES

To evaluate the efficacy of two dosing regimens of cotrimoxazole in the treatment of falciparum malaria and compare the efficacy with that of chloroquine, the first-line antimalaria drug in the area of study.

DESIGN

A prospective cross sectional study.

SETTINGS

Department of Clinical Pharmacology, University College Hospital, Ibadan, Nigeria.

SUBJECTS

Ninety eight children with acute symptomatic uncomplicated falciparum malaria.

MAIN OUTCOME MEASURES

Fever and other symptoms clearance times, parasite clearance times and the cure rates for chloroquine, three day and five day cotrimoxazole.

RESULTS

Ninety eight children with acute symptomatic uncomplicated falciparum malaria were randomised to receive three doses of oral chloroquine and two regimens of cotrimoxazole. Pre-treatment clinical and parasitological parameters were similar in the three treatment groups. The fever and other symptoms clearance times were comparable in all the treatment groups: 1.83 +/- 1.3, 1.9 +/- 1.0 and 2.4 +/- 1.3 days for chloroquine, three day cotrimoxazole and five day cotrimoxazole, respectively p = 0.24. Parasite clearance times for the three treatment groups were also similar; 3.0 +/- 1.0, 3.1 +/- 0.7, and 3.0 +/- 1.0 days respectively for chloroquine, three day- and five day- cotrimoxazole; p = 0.96. The cure rates for chloroquine, three day and five day cotrimoxazole were 74.2%, 88.2% and 84.8%, respectively (x2 = 2.40, p = 0.30). The three treatment regimens were well tolerated.

CONCLUSION

These results indicate that cotrimoxazole is as effective as chloroquine in treatment of acute symptomatic uncomplicated falciparum malaria in children resident in an endemic area of southwest Nigeria. It is an added advantage when malaria coexists with respiratory tract infections for which cotrimoxazole is the recommended drug.

The effects of chloroquine, amodiaquine and chloroquine plus chlorpheniramine on the disposition kinetics of the hepatomegaly associated with acute, uncomplicated, Plasmodium falciparum malaria in children

The effects of chloroquine (CQ), amodiaquine (AQ) and CQ plus chlorpheniramine (a histamine H(1) antagonist that reverses CQ resistance in vitro and in vivo) on the disposition of the enlarged liver associated with acute, symptomatic, uncomplicated, Plasmodium falciparum malaria were evaluated. The subjects, 131 children aged 0.6-12 years who lived in an endemic area of Nigeria, were randomly allotted to the three treatment groups. The cumulative proportions of the children with complete resolution of their enlarged livers at 48, 96, 168 or 336 and 504 h after commencement of treatment were significantly higher in those treated with CQ plus chlorpheniramine (CQCP) than in the other two treatment groups (with P-values of 0.02, 0.001, 0.00000 and 0.00002, respectively). Among those with complete resolution, however, the times to resolution of 50% (HR50) or 90% (HR90) of the liver enlargement were similar in all the treatment groups. Complete resolution of the enlarged liver within 168 h was associated with a sensitive response to each treatment. Overall, in children with complete or partial resolution of their enlarged livers, the area produced by plotting liver size against time (i.e. the area under the curve of hepatomegaly v. time, or AUC(hp)) and the half-life of the hepatomegaly (t(1/2hp)) were significantly lower in the CQCP group than in the other two groups. The volume of blood completely cleared of the 'hepatic pathological processes' which led to the hepatomegaly (CL(Bhp)) and the fractional reduction of AUC(hp) at 48 and 96 h (i.e. AUC(hpFr148) and AUC(hpFr96)) were significantly higher in the CQCP group than in the other treatment groups. When the children with complete resolution of their liver enlargement were considered separately, t(1/2hp) (P=0.0008) but not AUC(hp) was found to be significantly lower, and AUC(hpFr196) (P=0.01) and CL(Bhl) (P=0.002) were found to be significantly higher in the CQCP group than in the other groups. Among the children with only partial resolution of their enlarged livers, the indices of resolution and the kinetic parameters of disposition were similar in all three groups. The data indicate that the addition of chlorpheniramine to chloroquine had a beneficial effect on both the early and late stages of the resolution of the liver enlargement associated with acute, symptomatic, uncomplicated, P. falciparum malaria.