Management of relapsing Plasmodium vivax malaria

Alternative Invasion Mechanisms and Host Immune Response to Plasmodium vivax Malaria: Trends and Future Directions

Plasmodium vivax malaria is a neglected tropical disease, despite being more geographically widespread than any other form of malaria. The documentation of P. vivax infections in different parts of Africa where Duffy-negative individuals are predominant suggested that there are alternative pathways for P. vivax to invade human erythrocytes. Duffy-negative individuals may be just as fit as Duffy-positive individuals and are no longer resistant to P.vivax malaria. In this review, we describe the complexity of P. vivax malaria, characterize pathogenesis and candidate invasion genes of P. vivax, and host immune responses to P. vivax infections. We provide a comprehensive review on parasite ligands in several Plasmodium species that further justify candidate genes in P. vivax. We also summarize previous genomic and transcriptomic studies related to the identification of ligand and receptor proteins in P. vivax erythrocyte invasion. Finally, we identify topics that remain unclear and propose future studies that will greatly contribute to our knowledge of P. vivax.

Primaquine alternative dosing schedules for preventing malaria relapse in people with Plasmodium vivax

BACKGROUND

Plasmodium vivax liver stages (hypnozoites) may cause relapses, prolonging morbidity, and impeding malaria control and elimination. The World Health Organization (WHO) recommends three schedules for primaquine: 0.25 mg/kg/day (standard), or 0.5 mg/kg/day (high standard) for 14 days, or 0.75 mg/kg once weekly for eight weeks, all of which can be difficult to complete. Since primaquine can cause haemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, clinicians may be reluctant to prescribe primaquine without G6PD testing, and recommendations when G6PD status is unknown must be based on an assessment of the risks and benefits of prescribing primaquine. Alternative safe and efficacious regimens are needed.

OBJECTIVES

To assess the efficacy and safety of alternative primaquine regimens for radical cure of P vivax malaria compared to the standard or high-standard 14-day courses.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE (PubMed); Embase (Ovid); LILACS (BIREME); WHO International Clinical Trials Registry Platform and ClinicalTrials.gov up to 2 September 2019, and checked the reference lists of all identified studies.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of adults and children with P vivax malaria using either chloroquine or artemisinin-based combination therapy plus primaquine at a total adult dose of at least 210 mg, compared with the WHO-recommended regimens of 0.25 or 0.5 mg/kg/day for 14 days.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and quality, and extracted data. We calculated risk ratios (RRs) with 95% confidence intervals (CIs) for dichotomous data. We grouped efficacy data according to length of follow-up, partner drug, and trial location. We analysed safety data where included.

MAIN RESULTS

0.5 mg/kg/day for seven days versus standard 0.25 mg/kg/day for 14 days There may be little or no difference in P vivax recurrences at six to seven months when using the same total dose (210 mg adult dose) over seven days compared to 14 days (RR 0.96, 95% CI 0.66 to 1.39; 4 RCTs, 1211 participants; low-certainty evidence). No serious adverse events were reported. We do not know if there is any difference in the number of adverse events resulting in discontinuation of primaquine (RR 1.04, 95% CI 0.15 to 7.38; 5 RCTs, 1427 participants) or in the frequency of anaemia (RR 3.00, 95% CI 0.12 to 72.91, 1 RCT, 240 participants) between the shorter and longer regimens (very low-certainty evidence). Three trials excluded people with G6PD deficiency; two did not provide this information. Pregnant and lactating women were either excluded or no details were provided. High-standard 0.5 mg/kg/day for 14 days versus standard 0.25 mg/kg/day for 14 days There may be little or no difference in P vivax recurrences at six months with 0.5 mg/kg/day primaquine for 14 days compared to 0.25 mg/kg/day for 14 days (RR 0.84 (95% CI 0.49 to 1.43; 2 RCTs, 677 participants, low-certainty evidence). No serious adverse events were reported. We do not know whether there is a difference in adverse events resulting in discontinuation of treatment with the high-standard dosage (RR 4.19, 95% CI 0.90 to 19.60; 1 RCT, 778 participants, very low-certainty evidence). People with G6PD deficiency and pregnant or lactating women were excluded. 0.75 mg/kg/week for eight weeks versus high-standard 0.5 mg/kg/day for 14 days We do not know whether weekly primaquine increases or decreases recurrences of P vivax compared to high-standard 0.5 mg/kg/day for 14 days, at 11 months' follow-up (RR 3.18, 95% CI 0.37 to 27.60; 1 RCT, 122 participants; very low-certainty evidence). No serious adverse events and no episodes of anaemia were reported. G6PD-deficient patients were not randomized but included in the weekly primaquine group (only one patient detected). 1 mg/kg/day for seven days versus high standard 0.5 mg/kg/day for 14 days There is probably little or no difference in P vivax recurrences at 12 months between 1.0 mg/kg/day primaquine for seven days and the high-standard 0.5 mg/kg/day for 14 days (RR 1.03, 95% CI 0.82 to 1.30; 2 RCTs, 2526 participants; moderate-certainty evidence). There may be moderate to large increase in serious adverse events in the 1.0 mg/kg/day primaquine for seven days compared with the high-standard 0.5 mg/kg/day for 14 days, during 42 days follow-up (RR 12.03, 95% CI 1.57 to 92.30; 1 RCT, 1872 participants, low-certainty evidence). We do not know if there is a difference between 1.0 mg/kg/day primaquine for seven days and high-standard 0.5 mg/kg/day for 14 days in adverse events that resulted in discontinuation of treatment (RR 2.50, 95% CI 0.49 to 12.87; 1 RCT, 2526 participants, very low-certainty evidence), nor if there is difference in frequency of anaemia by 42 days (RR 0.93, 95% CI 0.62 to 1.41; 2 RCTs, 2440 participants, very low-certainty evidence). People with G6PD deficiency were excluded. Other regimens Two RCTs evaluated other rarely-used doses of primaquine, one of which had very high loss to follow-up. Adverse events were not reported. People with G6PD deficiency and pregnant or lactating women were excluded.

AUTHORS' CONCLUSIONS

Trials available to date do not detect a difference in recurrence between the following regimens: 1) 0.5 mg/kg/day for seven days versus standard 0.25 mg/kg/day for 14 days; 2) high-standard 0.5 mg/kg/day for 14 days versus standard 0.25 mg/kg/day for 14 days; 3) 0.75 mg/kg/week for eight weeks versus high-standard 0.5 mg/kg/day for 14 days; 4) 1 mg/kg/day for seven days versus high-standard 0.5 mg/kg/day for 14 days. There were no differences detected in adverse events for Comparisons 1, 2 or 3, but there may be more serious adverse events with the high seven-day course in Comparison 4. The shorter regimen of 0.5 mg/kg/day for seven days versus standard 0.25 mg/kg/day for 14 days may suit G6PD-normal patients. Further research will help increase the certainty of the findings and applicability in different settings.

Primaquine at alternative dosing schedules for preventing relapse in people with Plasmodium vivax malaria

BACKGROUND

Malaria caused by Plasmodium vivax requires treatment of the blood-stage infection and treatment of the hypnozoites that develop in the liver. This is a challenge to effective case management of P vivax malaria, as well as being a more general substantial impediment to malaria control. The World Health Organization (WHO) recommends a 14-day drug course with primaquine, an 8-aminoquinoline, at 0.25 mg/kg/day in most of the world (standard course), or 0.5 mg/kg/day in East Asia and Oceania (high-standard course). This long treatment course can be difficult to complete, and primaquine can cause dangerous haemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, meaning that physicians may be reluctant to prescribe in areas where G6PD testing is not available. This Cochrane Review evaluated whether more patient-friendly alternative regimens are as efficacious as the standard regimen for radical cure ofP vivax malaria.

OBJECTIVES

To assess the efficacy and safety of alternative primaquine regimens for radical cure of P vivax malaria compared to the standard or high-standard 14 days of primaquine (0.25 or 0.5 mg/kg/day), as well as comparison of these two WHO-recommended regimens.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group (CIDG) Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE (PubMed); Embase (Ovid); and LILACS (BIREME) up to 17 December 2018. We also searched the WHO International Clinical Trials Registry Platform (ICTRP) and ClinicalTrials.gov, and checked the reference lists of all studies identified by the above methods.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of adults and children with P vivax malaria using any regimen of either chloroquine or an artemisinin-based combination therapy (ACT) plus primaquine with either higher daily doses for 14 days, shorter regimens with the same total dose, or using weekly dosing regimens; compared with the usual standard regimens recommended by the WHO (0.25 or 0.5 mg/kg/day for 14 days), or a comparison of these two WHO-recommended regimens.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and quality, and extracted data. We calculated risk ratios (RRs) with 95% confidence intervals (CIs) for dichotomous data. We grouped efficacy data according to length of follow-up. We analysed safety data where this information was included.

MAIN RESULTS

High-standard 14-day course versus standard 14-day courseTwo RCTs compared the high-standard 14-day regimen with the standard 14-day regimen. People with G6PD deficiency and pregnant or lactating women were excluded. We do not know if there is any difference in P vivax recurrences at 6 months with 0.5 mg/kg/day primaquine therapy for 14 days compared to 0.25 mg/kg/day primaquine therapy for 14 days (with chloroquine: RR 0.82, 95% CI 0.47 to 1.43, 639 participants, very low-certainty evidence; with chloroquine or an ACT: RR 1.11, 95% CI 0.17 to 7.09, 38 participants, very low-certainty evidence). No serious adverse events were reported. We do not know whether there is a difference in adverse events with the higher dosage (very low-certainty evidence).0.5 mg/kg/day primaquine for 7 days versus standard 14-day courseFive RCTs compared 0.5 mg/kg/day primaquine for 7 days with the standard 14-day course. There may be little or no difference in P vivax recurrences at 6 to 7 months when using the same total dose (0.5 mg/kg/day to 210 mg) over 7 days as compared to 14 days (RR 0.96, 95% CI 0.66 to 1.39; 1211 participants; low-certainty evidence). No serious adverse events were reported. There may be little or no difference in the number of adverse events known to occur with primaquine between the primaquine shorter regimen as compared to the longer regimen (RR 1.06, 95% CI 0.64 to 1.76; 1154 participants; low-certainty evidence). We do not know whether there is any difference in the frequency of anaemia or discontinuation of treatment between groups (very low-certainty evidence). Three trials excluded people with G6PD deficiency, and two did not provide this information. Pregnant and lactating women were either excluded or no details were provided regarding their inclusion or exclusion.0.75 mg/kg primaquine/week for 8 weeks versus high-standard course One RCT compared weekly primaquine with the high-standard 14-day course. G6PD-deficient patients were not randomized but were included in the weekly primaquine group. Only one G6PD-deficient participant was detected during the trial. We do not know whether weekly primaquine increases or decreases recurrences of P vivax compared to the 14-day regimen at 11 months' follow-up (RR 3.18, 95% CI 0.37 to 27.6; 122 participants; very low-certainty evidence). No serious adverse events and no episodes of anaemia were reported.Three other RCTs evaluated different alternative regimens and doses of primaquine, but one of these RCTs did not have results available, and two used regimens that have not been widely used and the evidence was of very low certainty.

AUTHORS' CONCLUSIONS

Although limited data were available, the analysis did not detect a difference in recurrence between the 7-day regimen and the standard 14-day regimen of 0.5 mg/kg/day primaquine, and no serious adverse events were reported in G6PD-normal participants taking 0.5 mg/kg/day of primaquine. This shorter regimen may be useful in G6PD-normal patients if there are treatment adherence concerns. Further large high-quality RCTs are needed, such as the IMPROV trial, with more standardised comparison regimens and longer follow-up to help resolve uncertainties.