A retrospective analysis of the protective efficacy of tafenoquine and mefloquine as prophylactic anti-malarials in non-immune individuals during deployment to a malaria-endemic area

The human malaria-Aotus monkey model: a historical perspective in antimalarial chemotherapy research at the Gorgas Memorial Laboratory-Panama

The human malaria-Aotus monkey model has served the malaria research community since its inception in 1966 at the Gorgas Memorial Laboratory (GML) in Panama. Spanning over five decades, this model has been instrumental in evaluating the in vivo efficacy and pharmacokinetics of a wide array of candidate antimalarial drugs, whether used singly or in combination. The animal model could be infected with drug-resistant and susceptible Plasmodium falciparum and Plasmodium vivax strains that follow a characteristic and reproducible course of infection, remarkably like human untreated and treated infections. Over the years, the model has enabled the evaluation of several synthetic and semisynthetic endoperoxides, for instance, artelinic acid, artesunate, artemether, arteether, and artemisone. These compounds have been evaluated alone and in combination with long-acting partner drugs, commonly referred to as artemisinin-based combination therapies, which are recommended as first-line treatment against uncomplicated malaria. Further, the model has also supported the evaluation of the primaquine analog tafenoquine against blood stages of P. vivax, contributing to its progression to clinical trials and eventual approval. Besides, the P. falciparum/Aotus model at GML has also played a pivotal role in exploring the biology, immunology, and pathogenesis of malaria and in the characterization of drug-resistant P. falciparum and P. vivax strains. This minireview offers a historical overview of the most significant contributions made by the Panamanian owl monkey (Aotus lemurinus lemurinus) to malaria chemotherapy research.

Tafenoquine for Relapsing Babesiosis: A Case Series

BACKGROUND

Relapsing babesiosis often occurs in highly immunocompromised patients and has been attributed to the acquisition of resistance against drugs commonly used for treatment such as atovaquone, azithromycin, and clindamycin. Tafenoquine, which is approved for malaria prophylaxis and presumptive antirelapse treatment of Plasmodium vivax malaria, has shown activity against Babesia microti in several animal models of acute infection and in a single human case of relapsing babesiosis. Here, we report 5 cases of relapsing babesiosis treated with tafenoquine, including the previous case, and begin to define the conditions for optimal use of tafenoquine in relapsing babesiosis.

METHODS

A definitive diagnosis of babesiosis was made by microscopic examination of Giemsa-stained thin blood smears or a real-time polymerase chain reaction (PCR) that targets the parasite 18S rRNA gene. Clearance of B. microti infection was ascertained by use of blood smear and real-time PCR.

RESULTS

Tafenoquine was initiated with a loading dose of 600 mg. A weekly maintenance dose consisted of 200 mg or 300 mg; the lower dose was associated with a delayed clearance of B. microti. In 2 cases, all antimicrobial agents but tafenoquine were discontinued prior to clearance of infection. In 2 other cases, clearance was achieved while tafenoquine was administered along with other antimicrobial agents. In 3 of these 4 cases, tafenoquine was used in combination with atovaquone-proguanil. Other agents included atovaquone, azithromycin, and/or clindamycin. In 1 case, tafenoquine was administered alone and failed to prevent relapse.

CONCLUSIONS

Tafenoquine can be a useful adjunct for the treatment of highly immunocompromised patients experiencing relapsing babesiosis caused by B. microti.

Cytochrome P450 2D6 profiles and anti-relapse efficacy of tafenoquine against Plasmodium vivax in Australian Defence Force personnel

Plasmodium vivax infections and relapses remain a major health problem for malaria-endemic countries, deployed military personnel, and travelers. Presumptive anti-relapse therapy and radical cure using the 8-aminoquinoline drugs primaquine and tafenoquine are necessary to prevent relapses. Although it has been demonstrated that the efficacy of primaquine is associated with Cytochrome P450 2D6 (CYP2D6) activity, there is insufficient data on the role of CYP2D6 in the anti-relapse efficacy of tafenoquine. We investigated the relationship between CYP2D6 activity status and tafenoquine efficacy in preventing P. vivax relapses retrospectively using plasma samples collected from Australian Defence Force personnel deployed to Papua New Guinea and Timor-Leste who participated in clinical trials of tafenoquine during 1999-2001. The CYP2D6 gene was amplified from plasma samples and fully sequenced from 92 participant samples, comprised of relapse (n = 31) and non-relapse (n = 61) samples, revealing 14 different alleles. CYP2D6 phenotypes deduced from combinations of CYP2D6 alleles predicted that among 92 participants 67, 15, and 10 were normal, intermediate, and poor metabolizers, respectively. The deduced CYP2D6 phenotype did not correlate with the corresponding participant's plasma tafenoquine concentrations that were determined in the early 2000s by high-performance liquid chromatography or liquid chromatography-mass spectrometry. Furthermore, the deduced CYP2D6 phenotype did not associate with P. vivax relapse outcomes. Our results indicate that CYP2D6 does not affect plasma tafenoquine concentrations and the efficacy of tafenoquine in preventing P. vivax relapses in the assessed Australian Defence Force personnel.

Efficacy of a 3-day pretravel schedule of tafenoquine for malaria chemoprophylaxis: a network meta-analysis

BACKGROUND

Chemoprophylaxis with weekly doses of tafenoquine (200 mg/day for 3 days before departure [loading dose], 200 mg/week during travel and 1-week post-travel [maintenance doses]) is effective in preventing malaria. Effectiveness of malaria chemoprophylaxis drugs in travellers is often compromised by poor compliance. Shorter schedules that can be completed before travel, allowing 'drug-free holidays', could increase compliance and thus reduce travel-related malaria. In this meta-analysis, we examined if a loading dose of tafenoquine alone is effective in preventing malaria in short-term travellers.

METHODS

Four databases were searched in November 2020 for randomized controlled trials (RCTs) that assessed efficacy and/or safety of tafenoquine for chemoprophylaxis. Network meta-analysis using the generalized pair-wise modelling framework was utilized to estimate the odds ratio (OR) of malaria infection in long-term (>28 days) and short-term (≤28 days) travellers, as well as adverse events (AEs) associated with receiving loading dose of tafenoquine alone, loading dose of tafenoquine followed by maintenance doses, loading dose of mefloquine followed by maintenance doses, or placebo.

RESULTS

Nine RCTs (1714 participants) were included. In long-term travellers, compared to mefloquine, tafenoquine with maintenance doses (OR = 1.05; 95% confidence interval [CI]: 0.44-2.46) was equally effective in preventing malaria, while there was an increased risk of infection with the loading dose of tafenoquine alone (OR = 2.89; 95% CI: 0.78-10.68) and placebo (OR = 62.91; 95% CI: 8.53-463.88). In short-term travellers, loading dose of tafenoquine alone (OR = 0.98; 95% CI: 0.04-22.42) and tafenoquine with maintenance doses (OR = 1.00; 95% CI: 0.06-16.10) were as effective as mefloquine. The risk of AEs with tafenoquine with maintenance doses (OR = 1.03; 95% CI: 0.67-1.60) was similar to mefloquine, while loading dose of tafenoquine alone (OR = 0.58; 95% CI: 0.20-1.66) was associated with lower risk of AEs, although the difference was not statistically significant.

CONCLUSIONS

For short-term travellers, loading dose of tafenoquine alone was equally effective, had possibly lower rate of AEs, and likely better compliance than standard tafenoquine or mefloquine chemoprophylaxis schedules with maintenance doses. Studies are needed to confirm if short-term travellers remain free of infection after long-term follow-up.

REGISTRATION

The meta-analysis was registered in PROSPERO (CRD42021223756).

HIGHLIGHT

Tafenoquine is the latest approved drug for malaria chemoprophylaxis. A loading dose of tafenoquine (200 mg/day for 3 days before departure) is as effective in preventing malaria in short-term (≤28 days) travellers as chemoprophylaxis schedules of tafenoquine or mefloquine with maintenance doses, allowing travellers to have a 'drug-free holiday'.

Efficacy and safety of tafenoquine for malaria chemoprophylaxis (1998-2020): A systematic review and meta-analysis

BACKGROUND

In 2018, tafenoquine was approved for malaria chemoprophylaxis. We evaluated all available data on the safety and efficacy of tafenoquine chemoprophylaxis.

METHODS

This systematic review followed the PRISMA guidelines and was registered on PROSPERO (CRD42019123839). We searched PubMed, Embase, Scopus, CINAHL and Cochrane databases. Two authors (JDM, PS) screened all papers.

RESULTS

We included 44 papers in the qualitative and 9 in the quantitative analyses. These 9 randomized, controlled trials included 2495 participants, aged 12-60 years with 27.3% women. Six studies were conducted in Plasmodium spp.-endemic regions; two were human infection studies. 200 mg weekly tafenoquine and higher dosages lead to a significant reduction of Plasmodium spp. infection compared to placebo and were comparable to 250 mg mefloquine weekly with a protective efficacy between 77.9 and 100% or a total risk ratio of 0.22 (95%-CI: 0.07-0.73; p = 0.013) in favour of tafenoquine. Adverse events (AE) were comparable in frequency and severity between tafenoquine and comparator arms. One study reported significantly more gastrointestinal events in tafenoquine users (p ≤ 0.001). Evidence of increased, reversible, asymptomatic vortex keratopathy in subjects with prolonged tafenoquine exposures was found. A single, serious event of decreased macular sensitivity occurred.

CONCLUSION

This systematic review and meta-analysis of trials of G6PD-normal adults show that weekly tafenoquine 200 mg is well tolerated and effective as malaria chemoprophylaxis focusing primarily on Plasmodium falciparum but also on Plasmodium vivax. Our safety analysis is limited by heterogenous methods of adverse events reporting. Further research is indicated on the use of tafenoquine in diverse traveller populations.

Tafenoquine for preventing relapse in people with Plasmodium vivax malaria

BACKGROUND

Plasmodium vivax malaria has a persistent liver stage that causes relapse of the disease and continued P vivax transmission. Primaquine (PQ) is used to clear the liver stage of the parasite, but treatment is required for 14 days. Primaquine also causes haemolysis in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Tafenoquine (TQ) is a new alternative to PQ with a longer half-life and can be used as a single-dose treatment.

OBJECTIVES

To assess the effects of tafenoquine 300 mg (single dose) on preventing P vivax relapse.

SEARCH METHODS

We searched the following up to 3 June 2020: the Cochrane Infectious Diseases Group Specialized Register; CENTRAL; MEDLINE; Embase; and three other databases. We also searched the WHO International Clinical Trial Registry Platform and the metaRegister of Controlled Trials for ongoing trials using "tafenoquine" and "malaria" as search terms up to 3 June 2020.

SELECTION CRITERIA

Randomized controlled trials (RCTs) that gave TQ to prevent relapse in people with P vivax malaria. We planned to include trials irrespective of whether participants had been screened for G6PD enzyme deficiency.

DATA COLLECTION AND ANALYSIS

All review authors independently extracted data and assessed risk of bias. As true relapse and reinfection are difficult to differentiate in people living in endemic areas, studies report "recurrences" of infection as a proxy for relapse. We carried out meta-analysis where appropriate, and gave estimates as risk ratios (RR) with 95% confidence intervals (CI). We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

Three individually randomized RCTs met our inclusion criteria, all in endemic areas, and thus reporting recurrence. Trials compared TQ with PQ or placebo, and all participants received chloroquine (CQ) to treat the asexual infection). In all trials, pregnant and G6PD-deficient people were excluded. Tafenoquine 300 mg single dose versus no treatment for relapse prevention Two trials assessed this comparison. TQ 300 mg single dose reduces P vivax recurrences compared to no antihypnozoite treatment during a six-month follow-up, but there is moderate uncertainty around effect size (RR 0.32, 95% CI 0.12 to 0.88; 2 trials, 504 participants; moderate-certainty evidence). In people with normal G6PD status, there is probably little or no difference in any type of adverse events (2 trials, 504 participants; moderate-certainty evidence). However, we are uncertain if TQ causes more serious adverse events (2 trials, 504 participants; very low-certainty evidence). Both RCTs reported a total of 23 serious adverse events in TQ groups (One RCT reported 21 events) and a majority (15 events) were a drop in haemoglobin level by > 3g/dl (or >30% reduction from baseline). Tafenoquine 300 mg single dose versus primaquine 15 mg/day for 14 days for relapse prevention Three trials assessed this comparison. There is probably little or no difference between TQ and PQ in preventing recurrences (proxy measure for relapse) up to six months of follow-up (RR 1.04, 95% CI 0.8 to 1.34; 3 trials, 747 participants; moderate-certainty evidence). In people with normal G6PD status, there is probably little or no difference in any type of adverse events (3 trials, 747 participants; moderate-certainty evidence). We are uncertain if TQ can cause more serious adverse events compared to PQ (3 trials, 747 participants; very low-certainty evidence). Two trials had higher point estimates against TQ while the other showed the reverse. Most commonly reported serious adverse event in TQ group was a decline in haemoglobin level (19 out of 29 events). Some other serious adverse events, though observed in the TQ group, are unlikely to be caused by it (Hepatitis E infection, limb abscess, pneumonia, menorrhagia).

AUTHORS' CONCLUSIONS

TQ 300 mg single dose prevents relapses after clinically parasitologically confirmed P vivax malaria compared to no antihypnozoite treatment, and with no difference detected in studies comparing it to PQ to date. However, the inability to differentiate a true relapse from a recurrence in the available studies may affect these estimates. The drug is untested in children and in people with G6PD deficiency. Single-dose treatment is an important practical advantage compared to using PQ for the same purpose without an overall increase in adverse events in non-pregnant, non-G6PD-deficient adults.

Approval of Tafenoquine for Malaria Chemoprophylaxis

Malaria chemoprophylaxis has become increasingly prominent now that it is used for vulnerable populations in endemic regions in addition to nonimmune travelers to those regions. The objective would be a drug with > 95% efficacy and that is easily tolerated, including in children and pregnant women. For individuals who prefer weekly rather than daily drug administration, a further objective is a product that is administered weekly. The deficiencies of present agents are parasite resistance to chloroquine, neuropsychiatric liability of mefloquine, the need for daily dosing for atovaquone-proguanil, and daily dosing plus adverse reactions for doxycycline. A primaquine analogue, tafenoquine, has a 17-day half-life and was approved for weekly prophylaxis in the United States and in Australia in 2018. Weekly tafenoquine was equal to mefloquine in efficacy in nonimmunes. The tafenoquine label contains a contraindication for preexisting psychosis, but not for the broad number of other neuropsychiatric disorders which are listed as contraindications in the mefloquine label. As an 8-aminoquinoline, tafenoquine is contraindicated for glucose-6-phosphate dehydrogenase (G6PD)-deficient persons or in pregnancy if the fetus might be G6PD deficient. Other possible significant adverse reactions for tafenoquine are declines in hemoglobin levels reported in some G6PD-normal patients, asymptomatic elevations in methemoglobin, and minor psychiatric events. The lack of broad neuropsychiatric adverse reactions suggests that tafenoquine may have a role as the weekly prophylactic of choice for G6PD-normal persons.

Guidance for Using Tafenoquine for Prevention and Antirelapse Therapy for Malaria - United States, 2019

An estimated 219 million cases of malaria occurred worldwide in 2017, causing approximately 435,000 deaths (1). Malaria is caused by intraerythrocytic protozoa of the genus Plasmodium transmitted to humans through the bite of an infective Anopheles mosquito. Five Plasmodium species that regularly cause illness in humans are P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi (2). The parasite first develops in the liver before infecting red blood cells. Travelers to areas with endemic malaria can prevent malaria by taking chemoprophylaxis. However, most antimalarials do not kill the liver stages of the parasite, including hypnozoites that cause relapses of disease caused by P. vivax or P. ovale. Therefore, patients with these relapsing species must be treated with two medications: one for the acute infection, and another to treat the hypnozoites (antirelapse therapy). Until recently, primaquine was the only drug available worldwide to kill hypnozoites. Tafenoquine, a long-acting 8-aminoquinoline drug related to primaquine, was approved by the Food and Drug Administration (FDA) on July 20, 2018, for antirelapse therapy (Krintafel) and August 8, 2018, for chemoprophylaxis (Arakoda) (3,4). This report reviews evidence for the efficacy and safety of tafenoquine and provides CDC guidance for clinicians who prescribe chemoprophylaxis for travelers to areas with endemic malaria and treat malaria.

2018 in review: five hot topics in tropical medicine

The year 2018 heralded many new developments in the field of tropical medicine, including licensure of novel drugs for novel indications, licensure of existing drugs for existing indications but in novel settings, and globalized outbreaks of both vector-borne and zoonotic diseases. We herein describe five top stories in tropical medicine that occurred during 2018, and illuminate the practice-changing development within each story.

Clinical utility of tafenoquine in the prevention of relapse of Plasmodium vivax malaria: a review on the mode of action and emerging trial data

Tafenoquine is an 8-aminoquinoline with activity against all human life cycle stages of Plasmodium vivax, including dormant liver stages – so called hypnozoites. Its long half-life of ~15 days is allowing for a single exposure regimen. It has been under development since 1980 and received approval by the US Food and Drug Administration in summer 2018 as an anti-relapse drug for P. vivax malaria in patients aged 16 years and older and for prophylaxis of malaria caused by any Plasmodium species in adults. Prior to tafenoquine administration, glucose-6-phosphate dehydrogenase (G6PD) deficiency needs to be excluded by testing. Individuals with a deficient G6PD activity are at risk of tafenoquine-induced hemolysis – as is the case for primaquine, the mainstay drug for P. vivax radical cure. A wealth of clinical studies have been conducted and are still ongoing to assess the safety, tolerability, and efficacy of tafenoquine. This review focuses on data emerging from the latest clinical trials on P. vivax radical cure with tafenoquine, the key studies for regulatory approval of tafenoquine, and elucidates the latest hypothesis on the mode of action.

Blood Schizonticidal Activity and Safety of Tafenoquine When Administered as Chemoprophylaxis to Healthy, Nonimmune Participants Followed by Blood Stage Plasmodium falciparum Challenge: A Randomized, Double-blind, Placebo-controlled Phase 1b Study

Background

Tafenoquine was recently approved for chemoprophylaxis of malaria. Its specific activity against liver and blood stages of Plasmodium species has been separately characterized in animals but not in humans.

Methods

In this randomized, double-blind, placebo-controlled study, 16 malaria-naive, glucose-6-phosphate dehydrogenase–normal participants aged 20–42 years received tafenoquine chemoprophylaxis prior to challenge with blood stage Plasmodium falciparum. Participants were randomly assigned to either tafenoquine (n = 12) or placebo (n = 4) and took blinded study medication (single 200-mg dose) on days 1, 2, 3, and 10, followed by intravenous inoculation with approximately 2800 P. falciparum parasitized erythrocytes on day 13. The primary endpoint was the number of participants requiring rescue treatment with artemether/lumefantrine due to the onset of parasitemia as determined by quantitative polymerase chain reaction.

Results

None of the 12 participants who received tafenoquine developed parasitemia, whereas all placebo participants developed parasitemia (P = .0005). Two cases of mild hemoglobin decrease and a single case of mild hyperbilirubinemia occurred in the tafenoquine group.

Conclusions

Tafenoquine chemoprophylaxis is safe and effective in preventing malaria in healthy nonimmune participants challenged with blood stage P. falciparum.

Clinical Trials Registration

Australian and New Zealand Clinical Trials Registry (ANZCTR): ACTRN12617000102370.

Tafenoquine for travelers' malaria: evidence, rationale and recommendations

Background

Endemic malaria occurring across much of the globe threatens millions of exposed travelers. While unknown numbers of them suffer acute attacks while traveling, each year thousands return from travel and become stricken in the weeks and months following exposure. This represents perhaps the most serious, prevalent and complex problem faced by providers of travel medicine services. Since before World War II, travel medicine practice has relied on synthetic suppressive blood schizontocidal drugs to prevent malaria during exposure, and has applied primaquine for presumptive anti-relapse therapy (post-travel or post-diagnosis of Plasmodium vivax) since 1952. In 2018, the US Food and Drug Administration approved the uses of a new hepatic schizontocidal and hypnozoitocidal 8-aminoquinoline called tafenoquine for the respective prevention of all malarias and for the treatment of those that relapse (P. vivax and Plasmodium ovale).

Methods

The evidence and rationale for tafenoquine for the prevention and treatment of malaria was gathered by means of a standard search of the medical literature along with the package inserts for the tafenoquine products Arakoda™ and Krintafel™ for the prevention of all malarias and the treatment of relapsing malarias, respectively.

Results

The development of tafenoquine-an endeavor of 40 years-at last brings two powerful advantages to travel medicine practice against the malaria threat: (i) a weekly regimen of causal prophylaxis; and (ii) a single-dose radical cure for patients infected by vivax or ovale malarias.

Conclusions

Although broad clinical experience remains to be gathered, tafenoquine appears to promise more practical and effective prevention and treatment of malaria. Tafenoquine thus applied includes important biological and clinical complexities explained in this review, with particular regard to the problem of hemolytic toxicity in G6PD-deficient patients.

Mefloquine for preventing malaria during travel to endemic areas

BACKGROUND

Mefloquine is one of four antimalarial agents commonly recommended for preventing malaria in travellers to malaria-endemic areas. Despite its high efficacy, there is controversy about its psychological side effects.

OBJECTIVES

To summarize the efficacy and safety of mefloquine used as prophylaxis for malaria in travellers.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published on the Cochrane Library; MEDLINE; Embase (OVID); TOXLINE (https://toxnet.nlm.nih.gov/newtoxnet/toxline.htm); and LILACS. We also searched the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP; http://www.who.int/ictrp/en/) and ClinicalTrials.gov (https://clinicaltrials.gov/ct2/home) for trials in progress, using 'mefloquine', 'Lariam', and 'malaria' as search terms. The search date was 22 June 2017.

SELECTION CRITERIA

We included randomized controlled trials (for efficacy and safety) and non-randomized cohort studies (for safety). We compared prophylactic mefloquine with placebo, no treatment, or an alternative recommended antimalarial agent. Our study populations included all adults and children, including pregnant women.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility and risk of bias of trials, extracted and analysed data. We compared dichotomous outcomes using risk ratios (RR) with 95% confidence intervals (CI). Prespecified adverse outcomes are included in 'Summary of findings' tables, with the best available estimate of the absolute frequency of each outcome in short-term international travellers. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 20 RCTs (11,470 participants); 35 cohort studies (198,493 participants); and four large retrospective analyses of health records (800,652 participants). Nine RCTs explicitly excluded participants with a psychiatric history, and 25 cohort studies stated that the choice of antimalarial agent was based on medical history and personal preference. Most RCTs and cohort studies collected data on self-reported or clinician-assessed symptoms, rather than formal medical diagnoses. Mefloquine efficacyOf 12 trials comparing mefloquine and placebo, none were performed in short-term international travellers, and most populations had a degree of immunity to malaria. The percentage of people developing a malaria episode in the control arm varied from 1% to 82% (median 22%) and 0% to 13% in the mefloquine group (median 1%).In four RCTs that directly compared mefloquine, atovaquone-proguanil and doxycycline in non-immune, short-term international travellers, only one clinical case of malaria occurred (4 trials, 1822 participants). Mefloquine safety versus atovaquone-proguanil Participants receiving mefloquine were more likely to discontinue their medication due to adverse effects than atovaquone-proguanil users (RR 2.86, 95% CI 1.53 to 5.31; 3 RCTs, 1438 participants; high-certainty evidence). There were few serious adverse effects reported with mefloquine (15/2651 travellers) and none with atovaquone-proguanil (940 travellers).One RCT and six cohort studies reported on our prespecified adverse effects. In the RCT with short-term travellers, mefloquine users were more likely to report abnormal dreams (RR 2.04, 95% CI 1.37 to 3.04, moderate-certainty evidence), insomnia (RR 4.42, 95% CI 2.56 to 7.64, moderate-certainty evidence), anxiety (RR 6.12, 95% CI 1.82 to 20.66, moderate-certainty evidence), and depressed mood during travel (RR 5.78, 95% CI 1.71 to 19.61, moderate-certainty evidence). The cohort studies in longer-term travellers were consistent with this finding but most had larger effect sizes. Mefloquine users were also more likely to report nausea (high-certainty evidence) and dizziness (high-certainty evidence).Based on the available evidence, our best estimates of absolute effect sizes for mefloquine versus atovaquone-proguanil are 6% versus 2% for discontinuation of the drug, 13% versus 3% for insomnia, 14% versus 7% for abnormal dreams, 6% versus 1% for anxiety, and 6% versus 1% for depressed mood. Mefloquine safety versus doxycyclineNo difference was found in numbers of serious adverse effects with mefloquine and doxycycline (low-certainty evidence) or numbers of discontinuations due to adverse effects (RR 1.08, 95% CI 0.41 to 2.87; 4 RCTs, 763 participants; low-certainty evidence).Six cohort studies in longer-term occupational travellers reported our prespecified adverse effects; one RCT in military personnel and one cohort study in short-term travellers reported adverse events. Mefloquine users were more likely to report abnormal dreams (RR 10.49, 95% CI 3.79 to 29.10; 4 cohort studies, 2588 participants, very low-certainty evidence), insomnia (RR 4.14, 95% CI 1.19 to 14.44; 4 cohort studies, 3212 participants, very low-certainty evidence), anxiety (RR 18.04, 95% CI 9.32 to 34.93; 3 cohort studies, 2559 participants, very low-certainty evidence), and depressed mood (RR 11.43, 95% CI 5.21 to 25.07; 2 cohort studies, 2445 participants, very low-certainty evidence). The findings of the single cohort study reporting adverse events in short-term international travellers were consistent with this finding but the single RCT in military personnel did not demonstrate a difference between groups in frequencies of abnormal dreams or insomnia.Mefloquine users were less likely to report dyspepsia (RR 0.26, 95% CI 0.09 to 0.74; 5 cohort studies, 5104 participants, low certainty-evidence), photosensitivity (RR 0.08, 95% CI 0.05 to 0.11; 2 cohort studies, 1875 participants, very low-certainty evidence), vomiting (RR 0.18, 95% CI 0.12 to 0.27; 4 cohort studies, 5071 participants, very low-certainty evidence), and vaginal thrush (RR 0.10, 95% CI 0.06 to 0.16; 1 cohort study, 1761 participants, very low-certainty evidence).Based on the available evidence, our best estimates of absolute effect for mefloquine versus doxycyline were: 2% versus 2% for discontinuation, 12% versus 3% for insomnia, 31% versus 3% for abnormal dreams, 18% versus 1% for anxiety, 11% versus 1% for depressed mood, 4% versus 14% for dyspepsia, 2% versus 19% for photosensitivity, 1% versus 5% for vomiting, and 2% versus 16% for vaginal thrush.Additional analyses, including comparisons of mefloquine with chloroquine, added no new information. Subgroup analysis by study design, duration of travel, and military versus non-military participants, provided no conclusive findings.

AUTHORS' CONCLUSIONS

The absolute risk of malaria during short-term travel appears low with all three established antimalarial agents (mefloquine, doxycycline, and atovaquone-proguanil).The choice of antimalarial agent depends on how individual travellers assess the importance of specific adverse effects, pill burden, and cost. Some travellers will prefer mefloquine for its once-weekly regimen, but this should be balanced against the increased frequency of abnormal dreams, anxiety, insomnia, and depressed mood.

The blood schizonticidal activity of tafenoquine makes an essential contribution to its prophylactic efficacy in nonimmune subjects at the intended dose (200 mg)

Tafenoquine (TQ) is an 8-aminoquinoline anti-malarial being developed for malaria prophylaxis. It has been generally assumed that TQ, administered prophylactically, acts primarily on the developing exoerythrocytic stages of malaria parasites (causal prophylaxis), and that polymorphisms in metabolic enzymes thought to impact the activity of other 8-aminoquinolines also inhibit this property of TQ. Furthermore, it has been suggested that a diagnostic test for CYP2D6 metabolizer status might be required. In field studies in which metabolic status was not an exclusion criteria, TQ has been shown to exhibit similar prophylactic efficacy as blood schizonticidal drugs (mefloquine). Also, its blood schizonticidal and anti-relapse efficacy is independent of 2D6 metabolizer status. The most reasonable explanation for the field study results, supported by other clinical and non-clinical data, is that TQ is not completely causal and exhibits substantial blood schizonticidal activity at the intended dose. Pharmacokinetic simulations demonstrate that trough concentrations of TQ exceed the proposed MIC of 80 ng/ml in >95% of individuals. Based on these data a companion diagnostic for CP450 enzyme status is not required.

Tafenoquine for malaria prophylaxis in adults: An integrated safety analysis

BACKGROUND

Tafenoquine is a new prophylactic antimalarial drug. The current analysis presents an integrated safety assessment of the Tafenoquine Anticipated Clinical Regimen (Tafenoquine ACR) from 5 clinical trials, including 1 conducted in deployed military personnel and 4 in non-deployed residents, which also incorporated placebo and mefloquine comparator groups.

METHODS

Adverse events (AEs) were coded according to the Medical Dictionary for Regulatory Activities (MedDRA^®, Version 15.0) and summarized. Among all subjects who had received the Tafenoquine ACR, safety findings were compared for subjects who were deployed military personnel from the Australian Defence Force (Deployed ADF) versus non-deployed residents (Resident Non-ADF).

RESULTS

The incidence of at least one AE was 80.6%, 64.1%, 67.6% and 94.9% in the mefloquine, placebo, tafenoquine Resident Non-ADF and tafenoquine Deployed ADF groups, respectively. The latter group had a higher incidence of AEs related to military deployment. AEs that occurred at ≥ 1% incidence in both tafenoquine sub-groups and at a higher frequency than placebo included diarrhea, nausea, vomiting, gastroenteritis, nasopharyngeal tract infections, and back/neck pain.

CONCLUSIONS

Weekly administration of tafenoquine for up to six months increased the incidence of gastrointestinal AEs, certain infections, and back/neck pain, but not the overall incidence of AEs versus placebo. CLINICAL TRIAL REGISTRATION NUMBERS/CLINICALTRIALS.

GOV IDENTIFIERS

NCT02491606; NCT02488980; NCT02488902.

Cytochrome P450 2D-mediated metabolism is not necessary for tafenoquine and primaquine to eradicate the erythrocytic stages of Plasmodium berghei

BACKGROUND

Due to the ability of the 8-aminoquinolines (8AQs) to kill different stages of the malaria parasite, primaquine (PQ) and tafenoquine (TQ) are vital for causal prophylaxis and the eradication of erythrocytic Plasmodium sp. parasites. Recognizing the potential role of cytochrome (CYP) 450 2D6 in the metabolism and subsequent hepatic efficacy of 8-aminoquinolines, studies were designed to explore whether CYP2D-mediated metabolism was related to the ability of single-dose PQ and TQ to eliminate the asexual and sexual erythrocytic stages of Plasmodium berghei.

METHODS

An IV P. berghei sporozoite murine challenge model was utilized to directly compare causal prophylactic and erythrocytic activity (asexual and sexual parasite stages) dose-response relationships in C57BL/6 wild-type (WT) mice and subsequently compare the erythrocytic activity of PQ and TQ in WT and CYP2D knock-out (KO) mice.

RESULTS

Single-dose administration of either 25 mg/kg TQ or 40 mg/kg PQ eradicated the erythrocytic stages (asexual and sexual) of P. berghei in C57BL WT and CYP2D KO mice. In WT animals, the apparent elimination of hepatic infections occurs at lower doses of PQ than are required to eliminate erythrocytic infections. In contrast, the minimally effective dose of TQ needed to achieve causal prophylaxis and to eradicate erythrocytic parasites was analogous.

CONCLUSION

The genetic deletion of the CYP2D cluster does not affect the ability of PQ or TQ to eradicate the blood stages (asexual and sexual) of P. berghei after single-dose administration.

Antibody profiles to plasmodium merozoite surface protein-1 in Cambodian adults during an active surveillance cohort with nested treatment study

BACKGROUND

In addition to evidence for a protective role of antibodies to the malaria blood stage antigen merozoite surface protein 1 (MSP1), MSP1 antibodies are also considered as a marker of past malaria exposure in sero-epidemiological studies.

METHODS

In order to better assess the potential use of MSP1 serology in malaria chemoprophylaxis trials in endemic areas, an analysis for the prevalence of antibodies to both Plasmodium falciparum and Plasmodium vivax MSP142 in healthy Cambodian adults was conducted at two sites as part of an active, observational cohort evaluating the efficacy of dihydroartemisinin-piperaquine (DP) for uncomplicated malaria (ClinicalTrials.gov identifier NCT01280162).

RESULTS

Rates of baseline sero-positivity were high (59 and 73% for PfMSP142 and PvMSP142, respectively), and titers higher in those who lived in a higher transmission area, although there was little correlation in titers between the two species. Those volunteers who subsequently went on to develop malaria had higher baseline MSP142 titers than those who did not for both species. Titers to both antigens remained largely stable over the course of the 4-6 month study, except in those infected with P. falciparum who had multiple recurrences.

CONCLUSION

These findings illuminate the difficulties in using MSP142 serology as either a screening criterion and/or biomarker of exposure in chemoprophylaxis studies. Further work remains to identify useful markers of malarial infection and/or immunity.

Summary of anti-malarial prophylactic efficacy of tafenoquine from three placebo-controlled studies of residents of malaria-endemic countries

Background

Tafenoquine is a long half-life primaquine analog being developed for malaria prophylaxis. The US Army recently performed a unified analysis of efficacy in preparation for a regulatory submission, utilizing legacy data from three placebo-controlled studies conducted in the late 1990s and early 2000s. The subjects were residents of Africa who were naturally exposed to Plasmodium falciparum for 12–26 weeks.

Methods

The prophylactic efficacy of tafenoquine and mefloquine (included in some studies as a comparator) was calculated using incidence density among subjects who had completed the three-day loading doses of study drug, had at least one maintenance dose and had at least one blood smear assessed during the prophylactic period. The three placebo-controlled studies were analysed separately and then in two pooled analyses: one for tafenoquine versus placebo (three studies) and one for tafenoquine and mefloquine versus placebo (two studies).

Results

The pooled protective efficacy (PE) of a tafenoquine regimen with three daily loading doses plus weekly maintenance at 200-mg for 10 weeks or longer (referred to as 200-mg weekly hereafter) relative to placebo in three placebo-controlled studies was 93.1 % [95 % confidence interval (CI) 89.1–95.6 %; total N = 492]. The pooled PEs of regimens of tafenoquine 200-mg weekly and mefloquine 250-mg weekly relative to placebo in two placebo-controlled studies (total N = 519) were 93.5 % (95 % CI 88.6–96.2 %) and 94.5 % (95 % CI 88.7–97.3 %), respectively. Three daily loading plus weekly maintenance doses of 50- and 100-mg, but not 25-mg, exhibited similar PEs. The PEs of tafenoquine regimens of a three-day loading dose at 400-mg with and without follow-up weekly maintenance doses at 400-mg were 93.7 % (95 % CI 85.4–97.3 %) and 81.0 % (95 % CI 66.8–89.1 %), respectively.

Conclusions

Tafenoquine provided the same level of prophylactic efficacy as mefloquine in residents of Africa. These data support the prophylactic efficacy of tafenoquine and mefloquine that has already been demonstrated in the intended malaria naive population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0991-x) contains supplementary material, which is available to authorized users.

Safety, Tolerability, and Compliance with Long-Term Antimalarial Chemoprophylaxis in American Soldiers in Afghanistan

Long-term antimalarial chemoprophylaxis is currently used by deployed U.S. military personnel. Previous small, short-term efficacy studies have shown variable rates of side effects among patients taking various forms of chemoprophylaxis, though reliable safety and tolerability data on long-term use are limited. We conducted a survey of troops returning to Fort Drum, NY following a 12-month deployment to Operation Enduring Freedom, Afghanistan from 2006 to 2007. Of the 2,351 respondents, 95% reported taking at least one form of prophylaxis during their deployment, and 90% were deployed for > 10 months. Compliance with daily doxycycline was poor (60%) compared with 80% with weekly mefloquine (MQ). Adverse events (AEs) were reported by approximately 30% with both MQ and doxycycline, with 10% discontinuing doxycycline compared with 4% of MQ users. Only 6% and 31% of soldiers reported use of bed nets and skin repellents, respectively. Compliance with long-term malaria prophylaxis was poor, and there were substantial tolerability issues based on these anonymous survey results, though fewer with MQ than doxycycline. Given few long-term antimalarial chemoprophylaxis options, there is an unmet medical need for new antimalarials safe for long-term use.

Tafenoquine for preventing relapse in people with Plasmodium vivax malaria

BACKGROUND

Plasmodium vivax malaria is widespread, and the persistent liver stage causes relapse of the disease which contributes to continued P. vivax transmission. Primaquine is currently the only drug that cures the parasite liver stage, but requires 14 days to be effective and can cause haemolysis in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency. In addition, there is some evidence of parasite resistance to the drug. Tafenoquine is a new alternative with a longer half-life.

OBJECTIVES

To assess the effects of tafenoquine in people with P. vivax infection.

SEARCH METHODS

We searched the following databases up to 13 April 2015: the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in The Cochrane Library; MEDLINE; EMBASE; CINAHL; SCOPUS; and LILACS. We also searched the World Health Organization (WHO) International Clinical Trial Registry Platform and the metaRegister of Controlled Trials (mRCT) for ongoing trials using "tafenoquine" and "malaria" as search terms up to 13 April 2015.

SELECTION CRITERIA

Randomized controlled trials (RCTs) in people with P. vivax malaria. Adverse effects of tafenoquine are assessed in populations where people with G6PD deficiency have been excluded, and in populations without screening for G6PD deficiency.

DATA COLLECTION AND ANALYSIS

All review authors independently extracted data and assessed trial quality. Meta-analysis was carried out where appropriate, and estimates given as relative risk with 95% confidence intervals. We assessed the quality of the evidence using the GRADE approach.

MAIN RESULTS

Three RCTs met our inclusion criteria, with the asexual infection in both the tafenoquine and comparator arm treated with chloroquine, and in all trials G6PD deficiency patients were excluded. Tafenoquine dose comparisonsThree of the included trials compared eight different dosing regimens. Tafenoquine doses of 300 mg and above resulted in fewer relapses than no hypnozoite treatment over six months follow-up in adults (300 mg single dose: RR 0.19, 95% CI 0.08 to 0.41, one trial, 110 participants, moderate quality evidence; 500 to 600 mg single dose: RR 0.14, 95%CI 0.06 to 0.34, two trials, 122 participants, moderate quality evidence; 1800 mg to 3000 mg in divided doses: RR 0.05, 95% CI 0.01 to 0.23, two trials, 63 participants, low quality evidence).In people with normal G6PD status, there may be little or no difference in serious adverse events (three trials, 358 participants, low quality evidence); or any adverse event (one trial, 272 participants, low quality evidence). Tafenoquine versus primaquine Two of the included trials compared four different dosing regimens of tafenoquine against the standard primaquine regimen of 15 mg/day for 14 days. A single tafenoquine dose of 600 mg may be more effective than primaquine in relation to relapses at six months follow-up (RR 0.29, 95% CI 0.10 to 0.84, two trials, 98 participants, low quality evidence)In people with normal G6PD status, there may be little or no difference for serious adverse events (two trials, 323 participants, low quality evidence) or any adverse event (two trials, 323 participants, low quality evidence) between tafenoquine and primaquine.

AUTHORS' CONCLUSIONS

Tafenoquine prevents relapses after clinically and parasitologically confirmed P. vivax malaria. The drug is untested in pregnancy, children and in G6PD-deficient people. The shorter treatment course is an important practical advantage in people who do not have G6PD deficiency, but the longer half-life may have more substantive consequences if given inadvertently to people with G6PD deficiency.

Differential cytochrome P450 2D metabolism alters tafenoquine pharmacokinetics

Cytochrome P450 (CYP) 2D metabolism is required for the liver-stage antimalarial efficacy of the 8-aminoquinoline molecule tafenoquine in mice. This could be problematic for Plasmodium vivax radical cure, as the human CYP 2D ortholog (2D6) is highly polymorphic. Diminished CYP 2D6 enzyme activity, as in the poor-metabolizer phenotype, could compromise radical curative efficacy in humans. Despite the importance of CYP 2D metabolism for tafenoquine liver-stage efficacy, the exact role that CYP 2D metabolism plays in the metabolism and pharmacokinetics of tafenoquine and other 8-aminoquinoline molecules has not been extensively studied. In this study, a series of tafenoquine pharmacokinetic experiments were conducted in mice with different CYP 2D metabolism statuses, including wild-type (WT) (reflecting extensive metabolizers for CYP 2D6 substrates) and CYPmouse 2D knockout (KO) (reflecting poor metabolizers for CYP 2D6 substrates) mice. Plasma and liver pharmacokinetic profiles from a single 20-mg/kg of body weight dose of tafenoquine differed between the strains; however, the differences were less striking than previous results obtained for primaquine in the same model. Additionally, the presence of a 5,6-ortho-quinone tafenoquine metabolite was examined in both mouse strains. The 5,6-ortho-quinone species of tafenoquine was observed, and concentrations of the metabolite were highest in the WT extensive-metabolizer phenotype. Altogether, this study indicates that CYP 2D metabolism in mice affects tafenoquine pharmacokinetics and could have implications for human tafenoquine pharmacokinetics in polymorphic CYP 2D6 human populations.

A small-fish model for behavioral-toxicological screening of new antimalarial drugs: a comparison between erythro- and threo-mefloquine

Background

New antimalarial drugs need to be developed because over time resistance against the existing drugs develops. Furthermore, some of the drugs have severe side effects. Here we describe a behavioral small-fish model for early detection of neurotoxic effects of new drugs. As case example we compare the effects of two mefloquine diastereomers on the behavior of goldfish using an automated 3D tracking system.

Findings

In a preliminary experiment, the overall toxic effects in terms of motor and respiratory impairments were determined during a 3-hour exposure to the drugs at relatively high doses (21.5 and 43 mgL). In the second experiment, behavioral testing was performed 24 h after a 3.5-h drug exposure to a low dose (14.25 mgL) of either drug. For the two high doses, erythro-mefloquine resulted in severe motor problems and respiratory problems occurred. In goldfish treated with threo-mefloquine, at 43 mgL the motor/respiratory impairments were less severe and at 21.5 mgL no such problems were observed. For the lower dose (14.25 mgL), erythro-mefloquine reduced locomotion. There was also a tendency for increased freezing, and the preference for quadrant two of the observation container was increased. No behavioral effects of threo-mefloquine were found.

Conclusions

The results demonstrate that in goldfish exposed to the drugs dissolved in the water, threo-mefloquine has less severe toxic effects as compared to erythro-mefloquine. These findings are consistent with other studies and support the usefulness of the small-fish model for predicting adverse effects of new antimalarial drugs during the initial phases of drug development.

Antirelapse Efficacy of Various Primaquine Regimens for Plasmodium vivax

Background. Efficacy of standard dose of primaquine (PQ) as antirelapse for P. vivax has decreased. We aimed to assess efficacy of different PQ regimens. Methods. It was an open label, randomized, controlled, parallel group, assessor blind study comparing antirelapse efficacy of 3 PQ regimens (B = 15 mg/day × 14 days, C = 30 mg/day × 7 days, and D = 30 mg/day × 14 days) with no PQ group (A) in P. vivax patients. Paired primary and recurrence samples were subjected to 3 methods: (i) month of recurrence and genotyping, (ii) by PCR-RFLP, and (iii) PCR sequencing, to differentiate relapse and reinfection. The rates of recurrence relapse and reinfection were compared. Methods were compared for concordance between them. Results. The recurrence rate was 16.39%, 8.07%, 10.07%, and 6.62% in groups A, B, C, and D, respectively (P = 0.004). The relapse rate was 6.89%, 1.55%, 4%, and 3.85% as per the month of recurrence; 8.2%, 2%, 4.58%, and 3.68% (P = 0.007) as per PCR-RFLP; and 2.73%, 1.47%, 1.55%, and 1.53% as per PCR sequencing for groups A, B, C, and D, respectively. The concordance between methods was low, 45%. Conclusion. The higher recurrence rate in no PQ as compared to PQ groups documents PQ antirelapse activity. Regimens tested were safe. However, probable resistance to PQ warrants continuous monitoring and low concordance and limitations in the methods warrant caution in interpreting.