Reduced Exposure to Piperaquine, Compared to Adults, in Young Children Receiving Dihydroartemisinin-Piperaquine as Malaria Chemoprevention

The effect of malaria-induced alteration of metabolism on piperaquine disposition in Plasmodium yoelii infected mice and predicted in malaria patients

OBJECTIVES

Malaria-induced alteration of physiological parameters and pharmacokinetic properties of antimalarial drugs may be clinically relevant. Whether and how malaria alters the disposition of piperaquine (PQ) was investigated in this study.

METHODS

The effect of malaria on drug metabolism-related enzymes and PQ pharmacokinetic profiles was studied in Plasmodium yoelii-infected mice in vitro/in vivo. Whether the malaria effect was clinically relevant for PQ was evaluated using a validated physiologically-based pharmacokinetic model with malaria-specific scalars obtained in mice.

RESULTS

The infection led to a higher blood-to-plasma partitioning (Rbp) for PQ, which was concentration-dependent and correlated to parasitemia. No significant change in plasma protein binding was found for PQ. Drug metabolism-related genes (CYPs/UDP-glucuronosyltransferase/nuclear receptor, except for CYP2a5) were downregulated in infected mice, especially at the acute phase. The plasma oral clearances (CL/F) of three probe substrates for CYP enzymes were significantly decreased (by ≥35.9%) in mice even with moderate infection. The validated physiologically-based pharmacokinetic model indicated that the hepatic clearance (CLH) of PQ was the determinant of its simulated CL/F, which was predicted to slightly decrease (by ≤23.6%) in severely infected mice but not in malaria patients. The result fitted well with the plasma pharmacokinetics of PQ in infected mice and literature data on malaria patients. The blood clearance of PQ was much lower than its plasma clearance due to its high Rbp.

CONCLUSIONS

The malaria-induced alteration of drug metabolism was substrate-dependent, and its impact on the disposition of PQ and maybe other long-acting aminoquinoline antimalarials was not expected to be clinically relevant.

Determination of unbound piperaquine in human plasma by ultra-high performance liquid chromatography tandem mass spectrometry

Piperaquine (PQ) is an antimalarial drug that is highly protein-bound. Variation in plasma protein contents may affect the pharmacokinetic (PK) exposure of unbound drug, leading to alteration of clinical outcomes. All published methods for determination of PQ in human plasma measure the total PQ including both bound and unbound PQ to plasma proteins. There is no published method for unbound PQ determination. Here we report an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for determination of PQ in human plasma filtrate prepared by filtering human plasma through Millipore Microcon® centrifugal filters (10k NMWL). The filter cup had to be treated with 5% benzalkonium chloride to reduce non-specific binding to the filter devices before filtration of plasma samples. Multiple reactions monitoring (MRM) of the ion pairs m/z 535/288 for PQ and m/z 541/294 for the internal standard (IS) was selected for quantification. When electrospray ionization (ESI⁺) was used, paradoxical matrix effect was observed despite the structure similarity of the deuterated IS: Ion suppression for PQ versus ion enhancement for the PQ-d₆, even though they were closely eluted: 0.62 min versus 0.61 min. Separation was achieved on Evo C₁₈ column (50 × 2.1 mm, 1.7 μm, Phenomenex Inc.) eluted with 10 mM NH₄OH and MeCN. When atmospheric pressure chemical ionization in positive mode (APCI⁺) was used for ion source, matrix effect diminished. Separation was achieved on a PFP column (30 × 2.1 mm, 1.7 μm, Waters, Corp.) eluted with aqueous 20 mM ammonium formate 0.14% trifluoroacetic acid (A) and methanol-acetonitrile (4:1, v/v) containing 0.1% trifluoroacetic acid (B) at 0.8 mL/min flow rate in a gradient mode: 30–30–80–80–30–30%B (0–0.1–1.0–1.40–1.41–1.50 min). The retention time was 0.67 min for both PQ and the IS. The method was validated with a linear calibration range from 20 to 5,000 pg/mL and applied to clinical samples.

Identifying an optimal dihydroartemisinin-piperaquine dosing regimen for malaria prevention in young Ugandan children

Intermittent preventive treatment (IPT) with dihydroartemisinin-piperaquine (DP) is highly protective against malaria in children, but is not standard in malaria-endemic countries. Optimal DP dosing regimens will maximize efficacy and reduce toxicity and resistance selection. We analyze piperaquine (PPQ) concentrations (n = 4573), malaria incidence data (n = 326), and P. falciparum drug resistance markers from a trial of children randomized to IPT with DP every 12 weeks (n = 184) or every 4 weeks (n = 96) from 2 to 24 months of age (NCT02163447). We use nonlinear mixed effects modeling to establish malaria protective PPQ levels and risk factors for suboptimal protection. Compared to DP every 12 weeks, DP every 4 weeks is associated with 95% protective efficacy (95% CI: 84-99%). A PPQ level of 15.4 ng/mL reduces the malaria hazard by 95%. Malnutrition reduces PPQ exposure. In simulations, we show that DP every 4 weeks is optimal across a range of transmission intensities, and age-based dosing improves malaria protection in young or malnourished children.

Determination of piperaquine concentration in human plasma and the correlation of capillary versus venous plasma concentrations

Background

A considerable challenge in quantification of the antimalarial piperaquine in plasma is carryover of analyte signal between assays. Current intensive pharmacokinetic studies often rely on the merging of venous and capillary sampling. Drug levels in capillary plasma may be different from those in venous plasma, Thus, correlation between capillary and venous drug levels needs to be established.

Methods

Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to develop the method. Piperaquine was measured in 205 pairs of capillary and venous plasma samples collected simultaneously at ≥24hr post dose in children, pregnant women and non-pregnant women receiving dihydroartemisinin-piperaquine as malaria chemoprevention. Standard three-dose regimen over three days applied to all participants with three 40mg dihydroartemisinin/320mg PQ tablets per dose for adults and weight-based dose for children. Correlation analysis was performed using the program Stata® SE12.1. Linear regression models were built using concentrations or logarithm transformed concentrations and the final models were selected based on maximal coefficient of determination (R²) and visual check.

Results

An LC-MS/MS method was developed and validated, utilizing methanol as a protein precipitation agent, a Gemini C₁₈ column (50x2.0mm, 5μm) eluted with basic mobile phase solvents (ammonium hydroxide as the additive), and ESI⁺ as the ion source. This method had a calibration range of 10–1000 ng/mL and carryover was negligible. Correlation analysis revealed a linear relationship: C_cap = 1.04×C_ven+4.20 (R² = 0.832) without transformation of data, and lnC_cap = 1.01×lnC_ven+0.0125, (R² = 0.945) with natural logarithm transformation. The mean ratio (±SD) of C_cap/C_ven was 1.13±0.42, and median (IQR) was 1.08 (0.917, 1.33).

Conclusions

Capillary and venous plasma PQ measures are nearly identical overall, but not readily exchangeable due to large variation. Further correlation study accounting for disposition phases may be necessary.