Significant achievements Clinical Pharmacology

During 2018 the Africa Asia Programme ran around 70 clinical studies – observational, case-control, pharmacokinetics/pharmacodynamic (PK/PD) and randomised controlled trial (RCTs) – at any one time. Highlights include:

• A large multinational trial testing triple artemisinin combination therapies (TACTs) for the treatment of drug resistant falciparum malaria (TRAC II) was completed in 2018, demonstrating that TACTs are well tolerated and effective at treating multi-drug resistant malaria prevalent in much of the GMS;
• These studies have been complemented by detailed drug-drug interaction studies of the components of the triple therapies in healthy volunteers. The most important finding to date – which allowed the multinational clinical trials to proceed – was to show that mefloquine did not potentiate the effects of piperaquine on ventricular repolarisation;
• A large study of the safety of single low dose primaquine, using a novel age-based dosing regimen, in G6PD deficient African children with uncomplicated falciparum malaria is underway in Kinshasa (KIMORU) and Uganda (Imperial-KEMRI-Wellcome);
• The largest ever multicentre study on primaquine radical treatment of vivax malaria (IMPROV) was completed in 2018 and offers an efficacious and tolerated double dose primaquine regimen over 7 days; and
• An RCT in Bangladesh showed a reno-protective effect of paracetamol in adult severe malaria through an anti-oxidative mechanism.

Work by Clinical Pharmacology has led to a number of potentially new therapeutics interventions being uncovered, including:

• Use of triple artemisinin combination therapies to prevent the emergence and spread of drug resistant malaria. A large multicentre multi-country trial (TRAC II) finished recruiting in 2018, and preliminary results show that they are reasonably well tolerated and effective against multi-drug resistant malaria;
• The RTS,S malaria vaccine provides short term drug-independent protection against falciparum malaria, and may be a useful tool for malaria elimination campaigns. We have assessed for the first time the immunogenicity of RTS,S in Asian adults, and whether concomitant dihydroartemisinin-piperaquine affects it. These studies have now been completed and show good immunogenicity, no significant interactions, and they inform appropriate dosing;
• Dihydroartemisinin-piperaquine was evaluated as seasonal chemoprevention in young children in Burkina Faso. Our Clinical Pharmacology Department conducted the bioanalysis and described the PK/PD properties of piperaquine using modelling and simulation, showing that young children need a relatively higher dosage compared to adults. Increased piperaquine dosage and extended coverage during the high transmission season could have a substantial impact on the incidence of malaria;
• The renoprotective effects of paracetamol were evaluated in patients with severe and moderately severe falciparum malaria in a randomised, controlled, open-label trial. The pharmacokinetic-pharmacodynamic analysis showed that higher exposure to paracetamol increased the probability of creatinine improvement, and therefore, a renoprotective effect of paracetamol;
• A comprehensive pharmacokinetic-pharmacodynamic evaluation of the endectocide ivermectin has shown that mosquitocidal effects persist beyond the elimination of the predominant component of the parent compound. This opens up the possibility of either an unidentified active metabolite, or slower elimination of the more active minor component. In either case this has firmly put ivermectin in centre stage as a potential elimination tool. WHO has endorsed this and encouraged further research to identify the active principals - which is ongoing within the pharmacology department;
• Primaquine is widely recommended but often not used. We have calculated the proportions of patients unable to receive the new 8-aminoquinoline tafenoquine and thereby shown that primaquine will still be necessary if tafenoquine is introduced for the radical cure of vivax malaria. We have shown, using a new approach combining genotyping and time to event modelling, that if primaquine is used properly it can prevent nearly all relapses. This currently requires testing for G6PD deficiency and this is relatively expensive and generally unavailable. We have modelled an ascending dose regimen that should avoid dangerous haemolytic toxicity and could therefore be used without G6PD testing. This regimen is being tested in an adaptive trial design in known G6PD deficient healthy volunteers.

We have characterised the pharmacokinetic properties of primaquine in two separate projects. For the first time, the enantiospecific pharmacokinetic properties of primaquine and its main metabolite, carboxyprimaquine, were described using nonlinear mixed effects modelling (J Antimicrob Chemother. 2018; 73(11):3102-13). Potential drug-drug interactions with three commonly used blood stage antimalarial drugs (i.e. chloroquine, dihydroartemisinin/ piperaquine and pyronaridine/artesunate) were also assessed in these volunteers.

Exposure to primaquine, but not the metabolite, increased by up to 30% when co-administered with commonly used antimalarial drugs. In the second project, we evaluated the distribution of primaquine into breastmilk (Clin Infect Dis. 2018; 67(7):1000-7).

The concentrations of primaquine in breast milk were low and therefore very unlikely to cause adverse effects in the breastfeeding infant. The estimated primaquine dose received by infants, based on measured breast milk levels, was 0.6% of a hypothetical infant daily dose of 0.5 mg/kg. There was no evidence of drug related haemolysis in the infants and we recommend that primaquine should not be withheld from breastfeeding mothers.

Individual patient-level data meta-analyses increase the power to identify and characterise pharmacological issues (e.g. under-dosing) in sub-groups of patients that are under-represented in traditional clinical trials, such as young children and pregnant women.

Lumefantrine concentration time data from 4,122 patients from 26 studies were collated and pooled for an individual participant data pharmacokinetic-pharmacodynamic meta-analysis (PLoS Med. 2018; 15(6):e1002579). Small children and women during their second and third pregnancy trimester displayed lower lumefantrine exposures than non-pregnant adults when receiving the recommended 3-day dosing regimen.

The developed lumefantrine population pharmacokinetic model was used to evaluate and suggest optimised dosing regimens. Similar individual patient-level data meta-analyses were conducted for sulfadoxine-pyrimethamine and amodiaquine (Antimicrob Agent Chemother. 2018;62(5):01370- 17 & Antimicrob Agents Chemother. 2018; 62(10): e02193-17) and proposed similar increased dose regimens in vulnerable groups of patients.

A clinical trial was conducted in Myanmar investigating monotherapy of artesunate and we used nonlinear mixed-effects modelling to evaluate the pharmacokinetic-pharmacodynamic properties of artesunate and its metabolite dihydroartemisinin in patients with both artemisinin-sensitive and artemisinin-resistant malaria infections (Malar J. 2018; 17(1):126).

Overall, 56% of the studied population was predicted to have resistant malaria infections. The developed pharmacometric model was used to construct a simplified nomogram to identify patients with artemisinin-resistant malaria infections using only two blood film samples and demonstrated an overall sensitivity of 90% compared to 55% with the traditional day-3 positivity test.

Two additional analyses are ongoing, evaluating the pharmacokinetic and pharmacodynamic properties of artesunate in patients with sensitive and resistant infections. These studies are built on larger patient trials, which makes it possible to confirm/refine the concentration-effect relationship and performance of this proposed nomogram.

Evaluation of drug-drug interactions has focused on ivermectin and blood stage active antimalarial drugs, and on antimalarial triple combination therapies (i.e. dihydroartemisinin-piperaquine plus mefloquine). Two clinical trials were completed in healthy volunteers to evaluate these interactions. Co-administration of ivermectin plus dihydroartemisinin-piperaquine led to increased concentrations of ivermectin, which imparted a greater mosquito-lethal effect (Clin Pharmacol Ther. 2020 May; 107(5):1221-1230). For antimalarial triple combinations, results demonstrated a significantly decreased exposure to dihydroartemisinin, when dihydroartemisinin-piperaquine was co-administered with mefloquine (Antimicrob Agents Chemother. 2019 Jul 25; 63(8):e00060-19). All combinations were demonstrated to be safe to be implemented in larger patient populations. In addition to the study in healthy volunteers a non-compartmental analysis of data from the above mentioned TRACII study showed a lower exposure of artemether, its metabolite dihydroartemisinin, and lumefantrine than co-administered with amodiaquine (Lancet. 2020 Apr 25; 395(10233):1345-1360).

A systematic literature review demonstrated a very complex relationship between malaria and malnutrition, but chronic malnutrition was relatively consistently associated with severity of malaria such as high-density parasitaemia and anaemia (BMC Med. 2018;16(1):186). The particular impact of malnutrition on the pharmacokinetic properties of lumefantrine was evaluated in children with severe acute malnutrition in Niger.

Modelling and simulations demonstrated that anthropometric indicators of malnutrition were significantly associated with decreased absorption of lumefantrine, and that malnourished children were at risk of under-exposure to lumefantrine and an increased risk of malaria reinfection compared to well-nourished children (Clin Pharmacol Ther. 2019 Dec; 106(6): 1299–1309). An optimised dosing regimen was suggested for this group of patients. This work has been submitted and is under review for publication.

Dihydroartemisinin-piperaquine was evaluated as seasonal chemoprevention in young children in Burkina Faso. Pharmacokinetic and pharmacodynamic properties of piperaquine were described using modelling and simulation and showed that young children need a relatively higher dosage compared to adults (Nat Commun. 2019 Jan 29; 10(1):480).

Results demonstrated that an increased piperaquine dosage and extended coverage during the high transmission season could have a substantial impact on the incidence of malaria. The clinical data was also used to estimate an in vivo minimal inhibitory concentration for piperaquine, correlated to successful prevention of malaria. This work has been submitted and is under review for publication.

The pharmacokinetic properties of isoniazid and rifampicin were evaluated when used in children with pulmonary tuberculosis in India. Modelling and simulation showed inadequate rifampicin drug levels in children with the currently available dosing regimens, and the developed population pharmacokinetic model was used to suggest an optimised dosing regimen in these children (Br J Clin Pharmacol. 2019 Mar; 85(3): 644–654). Pharmacokinetic and pharmacodynamic analysis of a large study in Vietnamese children with tuberculosis meningitis found that exposure to the drug isoniazid was associated with survival (Clin Pharmacol Ther. 2020 Apr; 107(4): 1023–1033). A third pharmacokinetic-pharmacodynamic analysis of another study in Vietnamese children with tuberculosis meningitis showed that the dose of rifampicin might need to be increase. This study also showed that rifampicin exposure in surviving children was associated with treatment outcome. This work has been submitted.

Using a metabolomics approach, we identified several organic acids associated with severe malaria. The relationship between plasma acids, urine acids and renal function was investigated in adult patients with severe malaria, patients with uncomplicated malaria, patients with non-malaria sepsis, and healthy volunteers (Malar J. 2018;17(1):128). Both plasma and urine concentrations of p-hydroxyphenyllactic acid were closely correlated with acute kidney injury in patients with severe falciparum malaria.

In a separate study, the renoprotective effects of acetaminophen were evaluated in patients with severe and moderately severe falciparum malaria in a randomised, controlled, open-label trial (Future Sci OA. 2018;4(8):FSO331 & Clin Infect Dis. 2018;67(7):991-9. The pharmacokinetic-pharmacodynamic analysis showed that higher exposure to acetaminophen increased the probability of creatinine improvement, and therefore, a renoprotective effect of acetaminophen.

Bioanalysis in the department has traditionally focused on anti-malaria drugs, with more than 20 bioanalytical methods in use currently. We have broadened the scope of applications to include a variety of antibiotics, antiviral and anti-parasitic drugs. Besides anti-tuberculosis drugs, we have validated and implemented methods for ivermectin and ceftriaxone into routine bioanalysis. Particular focus has been directed towards developing assays for field-adapted pharmacokinetic sampling methodologies (i.e. capillary blood spot assays).

We use high-resolution mass spectrometry-based metabolomics and proteomics approaches to identify cellular markers of infectious diseases and pathways involved in the metabolism of the drugs used for their treatment. The anti-helminth drug, ivermectin, was shown to exhibit substantial sporontocidal effects against Plasmodium vivax in the South American vectors An. aquasalis and An. darlingi (PLoS Negl Trop Dis. 2018;12(2):e0006221).

We used a metabolomics approach to evaluate in-vitro samples and clinical patient samples to identify several metabolites of ivermectin, with potentially higher mosquito lethal activities than the parent compound. We plan to synthesise these metabolites in order to confirm their activity and pharmacokinetic properties. Furthermore, using a lipidomic approach, we were able to identify Orientia-specific Cardiolipins that could be potential novel drug targets.