Impact of parasite genomic dynamics on the sensitivity of Plasmodium falciparum isolates to piperaquine and other antimalarial drugs

BACKGROUND

Dihydroartemisinin-piperaquine (DHA-PPQ) is an alternative first-line antimalarial to artemether-lumefantrine in Kenya. However, recent reports on the emergence of PPQ resistance in Southeast Asia threaten its continued use in Kenya and Africa. In line with the policy on continued deployment of DHA-PPQ, it is imperative to monitor the susceptibility of Kenyan parasites to PPQ and other antimalarials.

METHODS

Parasite isolates collected between 2008 and 2021 from individuals with naturally acquired P. falciparum infections presenting with uncomplicated malaria were tested for in vitro susceptibility to piperaquine, dihydroartemisinin, lumefantrine, artemether, and chloroquine using the malaria SYBR Green I method. A subset of the 2019-2021 samples was further tested for ex vivo susceptibility to PPQ using piperaquine survival assay (PSA). Each isolate was also characterized for mutations associated with antimalarial resistance in Pfcrt, Pfmdr1, Pfpm2/3, Pfdhfr, and Pfdhps genes using real-time PCR and Agena MassARRAY platform. Associations between phenotype and genotype were also determined.

RESULTS

The PPQ median IC₅₀ interquartile range (IQR) remained stable during the study period, 32.70 nM (IQR 20.2-45.6) in 2008 and 27.30 nM (IQR 6.9-52.8) in 2021 (P=0.1615). The median ex vivo piperaquine survival rate (IQR) was 0% (0-5.27) at 95% CI. Five isolates had a PSA survival rate of ≥10%, consistent with the range of PPQ-resistant parasites, though they lacked polymorphisms in Pfmdr1 and Plasmepsin genes. Lumefantrine and artemether median IC₅₀s rose significantly to 62.40 nM (IQR 26.9-100.8) (P = 0.0201); 7.00 nM (IQR 2.4-13.4) (P = 0.0021) in 2021 from 26.30 nM (IQR 5.1-64.3); and 2.70 nM (IQR 1.3-10.4) in 2008, respectively. Conversely, chloroquine median IC₅₀s decreased significantly to 10.30 nM (IQR 7.2-20.9) in 2021 from 15.30 nM (IQR 7.6-30.4) in 2008, coinciding with a decline in the prevalence of Pfcrt 76T allele over time (P = 0.0357). The proportions of piperaquine-resistant markers including Pfpm2/3 and Pfmdr1 did not vary significantly. A significant association was observed between PPQ IC₅₀ and Pfcrt K76T allele (P=0.0026).

CONCLUSIONS

Circulating Kenyan parasites have remained sensitive to PPQ and other antimalarials, though the response to artemether (ART) and lumefantrine (LM) is declining. This study forms a baseline for continued surveillance of current antimalarials for timely detection of resistance.

Management of Seizures in Children with Falciparum Malaria

Falciparum malaria is the most common cause of convulsions in children admitted to hospital in malaria endemic areas. Detection of convulsions requires close monitoring and one should be on the look out for signs of subtle convulsions. About a third of acute seizures in children with cerebral malaria, do not manifest as convulsions, but as changes in eye deviation, salivation and/or eye deviation. It is important to terminate convulsions lasting more than 5 min, since prolonged convulsions are associated with neurological deficits in survivors of children with severe malaria. Initial management should include putting the child into the left lateral position, checking the blood glucose and administering oxygen if hypoxic. The benzodiazepines, particularly diazepam, are used as the initial anticonvulsants. Phénobarbital and Phenytoin are used as second-line treatments. Prompt and effective management of falciparum malaria associated convulsions may contribute to a better outcome in children with severe malaria.

Chloramphenicol pharmacokinetics in African children with severe malaria

The objective of this study was to determine if the current dosage regimen for chloramphenicol CAP administered to children with severe malaria SM for presumptive treatment of concomitant bacterial meningitis achieves steady state plasma CAP concentrations within the reported therapeutic range of 10-25 mg/l. Fifteen children (11 male, 4 female) with a median age of 45 months (range: 10-108 months) and having SM, were administered multiple intravenous doses (25 mg/kg, 6 hourly for 72 h) of chloramphenicol sodium succinate CAPS for presumptive treatment of concomitant bacterial meningitis. Blood samples were collected over 72 h, and plasma CAPS, CAP and CSF CAP concentrations determined by high performance liquid chromatography. Average steady state CAP concentrations were approximately 17 mg/l, while mean fraction unbound (0.49) and CSF/plasma concentration ratio (0.65) were comparable to previously reported values in Caucasian children. Clearance was variable (mean = 4.3 l/h), and trough plasma concentrations during the first dosing interval were approximately 6 mg/l. Simulations indicated that an initial of loading dose of 40 mg/kg CAPS, followed by a maintenance dose of 25 mg/kg every 6 h would result in trough CAP concentrations of approximately 10 mg/l and peak concentrations <25 mg/l throughout the treatment period. The current dosage regimen for CAP needs to include a loading dose of 40 mg/kg CAPS to rapidly achieve plasma CAP concentrations within the reported therapeutic range.

The role of sequential administration of sulphadoxine/pyrimethamine following quinine in the treatment of severe falciparum malaria in children

Sulphadoxine/pyrimethamine (SP) is often administered with quinine in the treatment of severe falciparum malaria to shorten the course of quinine. The efficacy of SP alone in the treatment of non-severe malaria has been declining rapidly in East Africa, raising concerns of the usefulness of a shortened course of quinine followed SP. We audited the efficacy of quinine/SP in the treatment of severe malaria in Kenyan children. Children with severe falciparum malaria were treated with parenteral quinine followed by a single oral dose of SP. A clinical evaluation was performed 3 weeks later in which a blood sample was obtained for full haemogram, blood slide and analysis of the parasite dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) codons, mutations of which are associated with resistance to SP. A total of 452 children were enrolled, of whom 374 completed the study. Fifty-two (13.9%) children were parasitaemic by 3 weeks of whom 17 (4.5%) had fever as well. The treatment failure group had a significantly higher parasitaemia (129 061 vs. 43 339; P<0.001) and haemoglobin on admission, but only admission parasitaemia independently predicted treatment failure. Those with treatment failure had a significantly lower rise in haemoglobin at 3 weeks compared with treatment successes (9.0 vs. 10.0 g/dl). Of the 76 parasite isolates collected before treatment, 40 (53%) were triple mutant DHFR-double DHPS (Tp-Db), the genotype most associated with SP resistance. Three weeks after SP treatment, the proportion of Tp-Db increased to 72% (31/43). The high treatment failure rate and proportion of parasites with Tp-Db negate the use of SP to shorten the course of quinine treatment in East Africa.

Selective and sensitive liquid chromatographic assay of amodiaquine and desethylamodiaquine in whole blood spotted on filter paper

We have developed a sensitive, selective and reproducible reversed-phase HPLC method with ultraviolet detection (340 nm) for the simultaneous quantification of amodiaquine (AQ) and its major metabolite, desethylamodiaquine (AQm) in a small volume (200 microl) of whole blood spotted on filter paper. The method involves liquid-liquid extraction with diethyl ether followed by elution from a reversed-phase phenyl column with an acidic (pH 2.8) mobile phase (25 mM KH2PO4-methanol; 80:20% (v/v) +1% (v/v) triethylamine). Calibration curves in spiked whole blood were linear from 100-2500 ng/ml (r2 > or = 0.99) for AQ and 200-2500 ng/ml (r2 > or = 0.99) for AQm. The limit of detection was 5 ng for AQ and 10 ng for AQm. The relative recovery at 150 ng/ml of AQ (n = 6) was 84.0% and at 300 ng/ml of AQm the relative recovery was 74.3%. The intra-assay coefficients of variation at 150, 600 and 2250 ng/ml of AQ and 300, 600 and 2250 ng/ml of AQm were 7.7, 8.9 and 6.2% (AQ) and 10.1, 5.4 and 3.9% (AQm), respectively. The inter-assay coefficient of variation at 150, 600 and 2250 ng/ml of AQ and 300, 600 and 2250 ng/ml of AQm were 5.2, 8.1 and 6.9% (AQ) and 3.3, 2.3 and 4.6% (AQm). There was no interference from other commonly used antimalarial and antipyretic drugs (chloroquine, quinine, sulfadoxine, pyrimethamine, artesunate, acetaminophen and salicylate). The method is particularly suitable for pharmacokinetic studies in settings where facilities for storing blood/plasma samples are not available.

Pharmacokinetics and anticonvulsant effects of diazepam in children with severe falciparum malaria and convulsions

AIMS

Convulsions are a common complication of severe malaria in children and are associated with poor outcome. Diazepam is used to terminate convulsions but its pharmacokinetics and pharmacodynamics have not been studied in this group. Accordingly, we carried out a comparative study of the pharmacokinetics of intravenous (i.v.) and rectal (p.r.) diazepam.

METHODS

Twenty-five children with severe malaria and a convulsion lasting >5 min were studied. Sixteen children received diazepam intravenously (i.v.; 0.3 mg kg(-1)) and nine rectally (p.r.; 0.5 mg kg(-1)). Plasma diazepam concentrations were measured by reversed phase high-performance liquid chromatography. The duration of convulsions, depth of coma, respiratory and cardiovascular parameters were monitored.

RESULTS

Median maximum plasma diazepam concentrations of 634 (range 402-1507) ng ml(-1) and 423 (range 112-1953) ng ml(-1) were achieved at 5 and 25 min following i.v. and p.r. administration, respectively. All patients except three (one i.v. and two p.r.) achieved plasma diazepam concentration >200 ng ml(-1) within 5 min. Following p.r. administration, plasma diazepam concentrations were more variable than i.v. administration. A single dose of i.v. diazepam terminated convulsions in all children but in only 6/9 after p.r. administration. However, nine children treated with i.v. and all those treated with p.r. diazepam had a recurrence of convulsions occurring at median plasma diazepam concentrations of 157 (range: 67-169) and 172 (range: 74-393) ng ml(-1) , respectively. All the children in the i.v. and four in the PR diazepam group who had recurrence of convulsions required treatment. None of the children developed respiratory depression or hypotension.

CONCLUSIONS

Administration of diazepam i.v. or p.r. resulted in achievement of therapeutic concentrations of diazepam rapidly, without significant cardio-respiratory adverse effects. However, following p.r. administration, diazepam did not terminate all convulsions and plasma drug concentrations were more variable.

High-performance liquid chromatographic determination of diazepam in plasma of children with severe malaria

A sensitive, selective and reproducible reversed-phase HPLC method with ultraviolet detection was developed for the quantification of diazepam in small plasma samples from children with severe malaria. The method involves plasma deproteinization with acetonitrile, followed by liquid-liquid extraction with ethyl acetate-n-hexane. Diazepam was eluted at ambient temperatures from a reversed-phase C18 column with an acidic (pH 3.5) aqueous mobile phase (10 mM KH2PO4-acetonitrile, 69:31, v/v). Calibration curves in spiked plasma were linear from 10 to 200 ng (r2 > or = 0.99). The limit of detection was 5.0 ng/ml, and relative recoveries at 25 and 180 ng were >87%. Intra- and inter-assay relative standard deviations were <15%. There was no interference from drugs commonly administered to children with severe malaria (phenobarbitone, phenytoin, chloroquine, quinine, sulfadoxine, pyrimethamine, halofantrine, cycloguanil, chlorcycloguanil, acetaminophen and salicylate). This method has been used for monitoring plasma diazepam concentrations in children with seizures associated with severe malaria.