Response to comment on 'The clinical pharmacology of tafenoquine in the radical cure of Plasmodium vivax malaria: An individual patient data meta-analysis'

In our recent paper on the clinical pharmacology of tafenoquine (Watson et al., 2022), we used all available individual patient pharmacometric data from the tafenoquine pre-registration clinical efficacy trials to characterise the determinants of anti-relapse efficacy in tropical vivax malaria. We concluded that the currently recommended dose of tafenoquine (300 mg in adults, average dose of 5 mg/kg) is insufficient for cure in all adults, and a 50% increase to 450 mg (7.5 mg/kg) would halve the risk of vivax recurrence by four months. We recommended that clinical trials of higher doses should be carried out to assess their safety and tolerability. Sharma and colleagues at the pharmaceutical company GSK defend the currently recommended adult dose of 300 mg as the optimum balance between radical curative efficacy and haemolytic toxicity (Sharma et al., 2024). We contend that the relative haemolytic risks of the 300 mg and 450 mg doses have not been sufficiently well characterised to justify this opinion. In contrast, we provided evidence that the currently recommended 300 mg dose results in sub-maximal efficacy, and that prospective clinical trials of higher doses are warranted to assess their risks and benefits.

The clinical pharmacology of tafenoquine in the radical cure of Plasmodium vivax malaria: An individual patient data meta-analysis

Tafenoquine is a newly licensed antimalarial drug for the radical cure of Plasmodium vivax malaria. The mechanism of action and optimal dosing are uncertain. We pooled individual data from 1102 patients and 72 healthy volunteers studied in the pre-registration trials. We show that tafenoquine dose is the primary determinant of efficacy. Under an Emax model, we estimate the currently recommended 300 mg dose in a 60 kg adult (5 mg/kg) results in 70% of the maximal obtainable hypnozoiticidal effect. Increasing the dose to 7.5 mg/kg (i.e. 450 mg) would result in 90% reduction in the risk of P. vivax recurrence. After adjustment for dose, the tafenoquine terminal elimination half-life, and day 7 methaemoglobin concentration, but not the parent compound exposure, were also associated with recurrence. These results suggest that the production of oxidative metabolites is central to tafenoquine's hypnozoiticidal efficacy. Clinical trials of higher tafenoquine doses are needed to characterise their efficacy, safety and tolerability.

375. High Laboratory-confirmed SARS-CoV-2 Attack Rate in Lima Health Care Personnel During August 2020-March 2021 Suggests Role for Improved Infection Control

Background

Peru has one of the highest per capita SARS-CoV-2 death rates in Latin America. Healthcare workers (HCW) are a critical workforce during the COVID-19 pandemic but are themselves often at increased risk of infection. We evaluated SARS-CoV-2 attack rate and risk factors among frontline HCWs.

Methods

We performed a prospective cohort study of HCW serving two acute care hospitals in Lima, Peru from Aug 2020 to Mar 2021. Participants had baseline SARS-CoV-2 serology using the CDC ELISA, active symptom monitoring, and weekly respiratory specimen collection with COVID-19 exposure/risk assessment for 16-weeks regardless of symptoms. Respiratory specimens were tested by real-time reverse transcriptase PCR (rRT-PCR).

Results

Of 783 eligible, 667 (85%) HCW were enrolled (33% nurse assistants, 29% non-clinical staff, 26% nurses, 7% physicians, and 6% other). At baseline and prior to COVID-19 vaccine introduction, 214 (32.1%; 214/667) were reactive for SARS-CoV-2 antibodies. In total, 72 (10.8%; 72/667) HCWs were found to be rRT-PCR positive during weekly follow-up. Of the rRT-PCR positive HCWs, 37.5% (27/72) did not report symptoms within 1-week of specimen collection. During follow up, HCW without detectable SARS-CoV-2 antibodies at baseline were significantly more likely to be rRT-PCR positive (65/453, 14.3%) compared to those with SARS-CoV-2 antibodies at baseline (4/214, 1.9%) (p-value: < 0.001). Three HCW were both serologically reactive and rRT-PCR positive at baseline. Looking only at HCW without SARS-CoV-2 antibodies, nurse assistants (rRT-PCR positive: 18.6%; 27/141) and non-clinical healthcare workers (16.5%; 21/127) were at greater risk of infection compared to nurses (8.5%; 10/118), physicians (7.9%; 3/38), and other staff (10.3%; 4/29) (RR 1.95;95%CI 1.2,3.3; p-value: 0.01).

Conclusion

Baseline SARS-CoV-2 prevalence and 16-week cumulative incidence were substantial in this pre-vaccination Peruvian HCW cohort. Almost 40% of new infections occurred in HCW without complaint of symptoms illustrating a limitation of symptom-based HCW screening for COVID-19 prevention. Nurse assistants and non-clinical healthcare workers were at greater risk of infection indicating a role for focused infection prevention and risk reduction strategies for some groups of HCW.

Disclosures

Fernanda C. Lessa, MD, MPH, Nothing to disclose

Traditional nets interfere with the uptake of long-lasting insecticidal nets in the Peruvian Amazon: the relevance of net preference for achieving high coverage and use

Background

While coverage of long-lasting insecticide-treated nets (LLIN) has steadily increased, a growing number of studies report gaps between net ownership and use. We conducted a mixed-methods social science study assessing the importance of net preference and use after Olyset® LLINs were distributed through a mass campaign in rural communities surrounding Iquitos, the capital city of the Amazonian region of Peru.

Methods

The study was conducted in the catchment area of the Paujil and Cahuide Health Centres (San Juan district) between July 2007 and November 2008. During a first qualitative phase, participant observation and in-depth interviews collected information on key determinants for net preference and use. In a second quantitative phase, a survey among recently confirmed malaria patients evaluated the acceptability and use of both LLINs and traditional nets, and a case control study assessed the association between net preference/use and housing structure (open vs. closed houses).

Results

A total of 10 communities were selected for the anthropological fieldwork and 228 households participated in the quantitative studies. In the study area, bed nets are considered part of the housing structure and are therefore required to fulfil specific architectural and social functions, such as providing privacy and shelter, which the newly distributed Olyset® LLINs ultimately did not. The LLINs' failure to meet these criteria could mainly be attributed to their large mesh size, transparency and perceived ineffectiveness to protect against mosquitoes and other insects, resulting in 63.3% of households not using any of the distributed LLINs. Notably, LLIN usage was significantly lower in houses with no interior or exterior walls (35.2%) than in those with walls (73.8%) (OR = 5.2, 95CI [2.2; 12.3], p<0.001).

Conclusion

Net preference can interfere with optimal LLIN use. In order to improve the number of effective days of LLIN protection per dollar spent, appropriate quantitative and qualitative methods for collecting information on net preference should be developed before any LLIN procurement decision is made.

Adherence to 7-day primaquine treatment for the radical cure of P. vivax in the Peruvian Amazon

Despite being free of charge, treatment adherence to 7-day primaquine for the radical cure of Plasmodium vivax was estimated at 62.2% among patients along the Iquitos-Nauta road in the Peruvian Amazon. The principal reason for non-adherence was the perceived adverse effects related to local humoral illness conceptions that hold that malaria produces a hot state of body, which is further aggravated by the characteristically hot medical treatment. Notably, patients were willing to adhere to the first 3 days of treatment during which symptoms are most apparent and include the characteristic chills. Nevertheless, as symptoms abate, the perceived aggravating characteristics of the medication outweigh the perceived advantages of treatment adherence. Improving community awareness about the role of primaquine to prevent further malaria transmission and fostering a realistic system of direct observed treatment intake, organized at community level, can be expected to improve adherence to the radical cure of P. vivax in this area.

Biochemical characterization of Leishmania (Viannia) braziliensis and Leishmania (Viannia) peruviana by isoenzyme electrophoresis

Leishmanial organisms isolated from 24 patients with Andean cutaneous leishmaniasis (uta) and from 7 with sylvatic leishmaniasis in both cutaneous and mucosal forms were characterized on the basis of their isoenzyme profiles for 13 enzymes using both cellulose acetate (CA) and thin-layer starch gel (TLS) electrophoretic techniques. Malate dehydrogenase (MDH) after electrophoresis on CA or TLS and mannose phosphate isomerase (MPI) on TLS were the only enzymes of 13 examined which discriminated between the organisms from patients with uta (L. (V.) peruviana) and those with sylvatic leishmaniasis (L. (V.) braziliensis). Mannose phosphate isomerase gave more clear-cut and reproducible discrimination than did MDH on either TLS or CA, and it is suggested that MPI is a reliable enzyme marker that can be used in routine TLS electrophoresis to distinguish between L. (V.) peruviana and L. (V). braziliensis.