Primaquine in glucose-6-phosphate dehydrogenase deficiency: an adaptive pharmacometric assessment of ascending dose regimens in healthy volunteers

Background: Primaquine is an 8-aminoquinoline antimalarial. It is the only widely available treatment to prevent relapses of Plasmodium vivax malaria. The 8-aminoquinolines cause dose-dependent haemolysis in glucose-6-phosphate dehydrogenase deficiency (G6PDd). G6PDd is common in malaria endemic areas but testing is often not available. As a consequence primaquine is underused. Methods: We conducted an adaptive pharmacometric study to characterise the relationship between primaquine dose and haemolysis in G6PDd. The aim was to explore shorter and safer primaquine radical cure regimens compared to the currently recommended 8-weekly regimen (0.75 mg/kg once weekly), potentially obviating the need for G6PD testing. Hemizygous G6PDd healthy adult Thai and Burmese male volunteers were admitted to the Hospital for Tropical Diseases in Bangkok. In Part 1, volunteers were given ascending dose primaquine regimens whereby daily doses were increased from 7.5 mg up to 45 mg over 15–20 days. In Part 2 conducted at least 6 months later, a single primaquine 45 mg dose was given. Results: 24 volunteers were enrolled in Part 1, and 16 in Part 2 (13 participated in both studies). In three volunteers, the ascending dose regimen was stopped because of haemolysis (n=1) and asymptomatic increases in transaminases (n=2; one was hepatitis E positive). Otherwise the ascending regimens were well tolerated with no drug-related serious adverse events. In Part 1, the median haemoglobin concentration decline was 3.7 g/dL (range: 2.1–5.9; relative decline of 26% [range: 15–40%]). Primaquine doses up to 0.87 mg/kg/day were tolerated subsequently without clinically significant further falls in haemoglobin. In Part 2, the median haemoglobin concentration decline was 1.7 g/dL (range 0.9–4.1; relative fall of 12% [range: 7–30% decrease]). The ascending dose primaquine regimens gave seven times more drug but resulted in only double the haemoglobin decline. Conclusions: In patients with Southeast Asian G6PDd variants, full radical cure treatment can be given in under 3 weeks compared with the current 8-week regimen. Funding: Medical Research Council of the United Kingdom (MR/R015252/1) and Wellcome (093956/Z/10/C, 223253/Z/21/Z)

Weekly primaquine for radical cure of patients with Plasmodium vivax malaria and glucose-6-phosphate dehydrogenase deficiency

Background The World Health Organization recommends that primaquine should be given once weekly for 8-weeks to patients with Plasmodium vivax malaria and glucose-6-phosphate dehydrogenase (G6PD) deficiency, but data on its antirelapse efficacy and safety are limited. Methods Within the context of a multicentre, randomised clinical trial of two primaquine regimens in P. vivax malaria, patients with G6PD deficiency were excluded and enrolled into a separate 12-month observational study. They were treated with a weekly dose of 0.75 mg/kg primaquine for 8 weeks (PQ8W) plus dihydroartemisinin piperaquine (Indonesia) or chloroquine (Afghanistan, Ethiopia, Vietnam). G6PD status was diagnosed using the fluorescent spot test and confirmed by genotyping for locally prevalent G6PD variants. The risk of P. vivax recurrence following PQ8W and the consequent haematological recovery were characterized in all patients and in patients with genotypically confirmed G6PD variants, and compared with the patients enrolled in the main randomised control trial. Results Between July 2014 and November 2017, 42 male and 8 female patients were enrolled in Afghanistan (6), Ethiopia (5), Indonesia (19), and Vietnam (20). G6PD deficiency was confirmed by genotyping in 31 patients: Viangchan (14), Mediterranean (4), 357A-G (3), Canton (2), Kaiping (2), and one each for A-, Chatham, Gaohe, Ludhiana, Orissa, and Vanua Lava. Two patients had recurrent P. vivax parasitaemia (days 68 and 207). The overall 12-month cumulative risk of recurrent P. vivax malaria was 5.1% (95% CI: 1.3–18.9) and the incidence rate of recurrence was 46.8 per 1000 person-years (95% CI: 11.7–187.1). The risk of P. vivax recurrence was lower in G6PD deficient patients treated with PQ8W compared to G6PD normal patients in all treatment arms of the randomised controlled trial. Two of the 26 confirmed hemizygous males had a significant fall in haemoglobin (>5g/dl) after the first dose but were able to complete their 8 week regimen. Conclusions PQ8W was highly effective in preventing P. vivax recurrences. Whilst PQ8W was well tolerated in most patients across a range of different G6PD variants, significant falls in haemoglobin may occur after the first dose and require clinical monitoring. Trial registration This trial is registered at ClinicalTrials.gov (NCT01814683)

Assessment of therapeutic responses to gametocytocidal drugs in Plasmodium falciparum malaria.

Indirect clinical measures assessing anti-malarial drug transmission-blocking activity in falciparum malaria include measurement of the duration of gametocytaemia, the rate of gametocyte clearance or the area under the gametocytaemia-time curve (AUC). These may provide useful comparative information, but they underestimate dose-response relationships for transmission-blocking activity. Following 8-aminoquinoline administration P. falciparum gametocytes are sterilized within hours, whereas clearance from blood takes days. Gametocytaemia AUC and clearance times are determined predominantly by the more numerous female gametocytes, which are generally less drug sensitive than the minority male gametocytes, whereas transmission-blocking activity and thus infectivity is determined by the more sensitive male forms. In choosing doses of transmission-blocking drugs there is no substitute yet for mosquito-feeding studies

Primaquine dose and the risk of haemolysis in patients with uncomplicated Plasmodium vivax malaria: a systematic review and individual patient data meta-analysis

Background: Primaquine radical cure is used to treat dormant liver-stage parasites and prevent relapsing Plasmodium vivax malaria but is limited by concerns of haemolysis. We undertook a systematic review and individual patient data meta-analysis to investigate the haematological safety of different primaquine regimens for P vivax radical cure. Methods: For this systematic review and individual patient data meta-analysis, we searched MEDLINE, Web of Science, Embase, and Cochrane Central for prospective clinical studies of uncomplicated P vivax from endemic countries published between Jan 1, 2000, and June 8, 2023. We included studies if they had active follow-up of at least 28 days, if they included a treatment group with daily primaquine given over multiple days where primaquine was commenced within 3 days of schizontocidal treatment and was given alone or coadministered with chloroquine or one of four artemisinin-based combination therapies (ie, artemether–lumefantrine, artesunate–mefloquine, artesunate–amodiaquine, or dihydroartemisinin–piperaquine), and if they recorded haemoglobin or haematocrit concentrations on day 0. We excluded studies if they were on prevention, prophylaxis, or patients with severe malaria, or if data were extracted retrospectively from medical records outside of a planned trial. For the meta-analysis, we contacted the investigators of eligible trials to request individual patient data and we then pooled data that were made available by Aug 23, 2021. The main outcome was haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL by day 14. Haemoglobin concentration changes between day 0 and days 2–3 and between day 0 and days 5–7 were assessed by mixed-effects linear regression for patients with glucose-6-phosphate dehydrogenase (G6PD) activity of (1) 30% or higher and (2) between 30% and less than 70%. The study was registered with PROSPERO, CRD42019154470 and CRD42022303680. Findings: Of 226 identified studies, 18 studies with patient-level data from 5462 patients from 15 countries were included in the analysis. A haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL occurred in one (0·1%) of 1208 patients treated without primaquine, none of 893 patients treated with a low daily dose of primaquine (<0·375 mg/kg per day), five (0·3%) of 1464 patients treated with an intermediate daily dose (0·375 mg/kg per day to <0·75 mg/kg per day), and six (0·5%) of 1269 patients treated with a high daily dose (≥0·75 mg/kg per day). The covariate-adjusted mean estimated haemoglobin changes at days 2–3 were –0·6 g/dL (95% CI –0·7 to –0·5), –0·7 g/dL (–0·8 to –0·5), –0·6 g/dL (–0·7 to –0·4), and –0·5 g/dL (–0·7 to –0·4), respectively. In 51 patients with G6PD activity between 30% and less than 70%, the adjusted mean haemoglobin concentration on days 2–3 decreased as G6PD activity decreased; two patients in this group who were treated with a high daily dose of primaquine had a reduction of more than 25% to a concentration of less than 7 g/dL. 17 of 18 included studies had a low or unclear risk of bias. Interpretation: Treatment of patients with G6PD activity of 30% or higher with 0·25–0·5 mg/kg per day primaquine regimens and patients with G6PD activity of 70% or higher with 0·25–1 mg/kg per day regimens were associated with similar risks of haemolysis to those in patients treated without primaquine, supporting the safe use of primaquine radical cure at these doses. Funding: Australian National Health and Medical Research Council, Bill & Melinda Gates Foundation, and Medicines for Malaria Venture

Haemolysis in G6PD Heterozygous Females Treated with Primaquine for <i>Plasmodium vivax</i> Malaria: A Nested Cohort in a Trial of Radical Curative Regimens

<div><p>Background</p><p>Radical cure of <i>Plasmodium vivax</i> malaria with 8-aminoquinolines (primaquine or tafenoquine) is complicated by haemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD heterozygous females, because of individual variation in the pattern of X-chromosome inactivation (Lyonisation) in erythroid cells, may have low G6PD activity in the majority of their erythrocytes, yet are usually reported as G6PD “normal” by current phenotypic screening tests. Their haemolytic risk when treated with 8-aminoquinolines has not been well characterized.</p><p>Methods and Findings</p><p>In a cohort study nested within a randomised clinical trial that compared different treatment regimens for <i>P</i>. <i>vivax</i> malaria, patients with a normal standard NADPH fluorescent spot test result (≳30%–40% of normal G6PD activity) were randomised to receive 3 d of chloroquine or dihydroartemisinin-piperaquine in combination with primaquine, either the standard high dose of 0.5 mg base/kg/day for 14 d or a higher dose of 1 mg base/kg/d for 7 d. Patterns of haemolysis were compared between G6PD wild-type and G6PD heterozygous female participants. Between 21 February 2012 and 04 July 2014, 241 female participants were enrolled, of whom 34 were heterozygous for the G6PD Mahidol variant. Haemolysis was substantially greater and a larger proportion of participants reached the threshold of clinically significant haemolysis (fractional haematocrit reduction >25%) in G6PD heterozygotes taking the higher (7 d) primaquine dose (9/17 [53%]) compared with G6PD heterozygotes taking the standard high (14 d) dose (2/16 [13%]; <i>p</i> = 0.022). In heterozygotes, the mean fractional haematocrit reductions were correspondingly greater with the higher primaquine dose (7-d regimen): −20.4% (95% CI −26.0% to −14.8%) (nadir on day 5) compared with the standard high (14 d) dose: −13.1% (95% CI −17.6% to −8.6%) (nadir day 6). Two heterozygotes taking the higher (7 d) primaquine dose required blood transfusion. In wild-type participants, mean haematocrit reductions were clinically insignificant and similar with both doses: −5.8 (95% CI −7.2% to −4.4%) (nadir day 3) compared with −5.5% (95% CI −7.4% to −3.7%) (nadir day 4), respectively. Limitations to this nested cohort study are that the primary objective of the trial was designed to measure efficacy and not haemolysis in relation to G6PD genotype and that the heterozygote groups were small.</p><p>Conclusion</p><p>Higher daily doses of primaquine have the potential to cause clinically significant haemolysis in G6PD heterozygous females who are reported as phenotypically normal with current point of care tests.</p><p>Trial Registration</p><p><a href="https://clinicaltrials.gov/" target="_blank">ClinicalTrials.gov</a><a href="https://clinicaltrials.gov/ct2/show/NCT01640574" target="_blank">NCT01640574</a>.</p></div

Characteristics of two G6PD heterozygous participants who required transfusion.

<p>Characteristics of two G6PD heterozygous participants who required transfusion.</p

Comparison of the mean maximum individual fractional haematocrit reductions between G6PD heterozygous and wild-type females taking PMQ-1 or PMQ-0.5 adjusted for initial parasitaemia.

<p>Comparison of the mean maximum individual fractional haematocrit reductions between G6PD heterozygous and wild-type females taking PMQ-1 or PMQ-0.5 adjusted for initial parasitaemia.</p

Correlation between maximum individual fractional haematocrit reduction and mean G6PD activity (IU/RBC)*.

<p>*Three G6PD heterozygous females with missing data. The difference between the regression lines for heterozygote PMQ-1 and heterozygote PMQ-0.5 was not statistically significant (<i>p</i> = 0.433). The haemoglobin type was normal unless otherwise indicated. Circled shapes represent participants who received a blood transfusion.</p

Comparison of the mean maximum individual fractional haematocrit reductions between G6PD heterozygous and wild-type females taking PMQ-1 or PMQ-0.5 not adjusted for initial parasitaemia.

<p>Comparison of the mean maximum individual fractional haematocrit reductions between G6PD heterozygous and wild-type females taking PMQ-1 or PMQ-0.5 not adjusted for initial parasitaemia.</p