Pharmacokinetics of molnupiravir and favipiravir in plasma separation cards from patients with COVID-19: Agile CST-2 and CST-6

Abstract

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Pharmacokinetics of molnupiravir and favipiravir in plasma separation cards from patients with COVID-19: Agile CST-2 and CST-6

Beth Thompson¹, Laura Else¹, Elizabeth Challenger¹, Richard Fitzgerald^1,2, Helen Reynolds^1,2, Laura Dickinson¹, Colin Hale², Tom Fletcher^2,3, Tim Rowland^2,3 and Saye Khoo^1,2

¹University of Liverpool; ²Royal Liverpool University Hospital; ³Liverpool School of Tropical Medicine

Background: Molnupiravir (MPV) and favipiravir (FVP) are broadly active antiviral ribonucleoside analogues. Both have demonstrated efficacy in treatment of COVID-19 and have been investigated for use against other high-consequence infections. Collection of liquid plasma (L-PL) in remote settings, where diseases like haemorrhagic fevers are endemic, can be challenging. HemaSep dried blood spots (HS-DBS) offer a useful alternative to L-PL, separating plasma upon contact as a distinct outer ring (HS-PL) and shipped at ambient temperatures. HS-DBS were collected alongside L-PL in the AGILE CST-2/CST-6 clinical trials to evaluate the pharmacokinetics of single and repeat doses of these agents in patients with confirmed COVID-19 disease.

Materials and methods: AGILE-CST-2 and CST-6 were open-label 2:1 randomized controlled phase I trials comparing MPV and FVP, respectively, with standard of care, designed to determine the optimal dose for treatment of symptomatic COVID-19 patients (CST-2; n = 12, CST-6; n = 16). MPV was orally delivered twice daily (BD) for 10 doses, with dose escalations (300/600/800 mg BD) across three cohorts, whereas FVP was intravenously administered BD for 14 doses, with dose escalations across four cohorts (600/1200/1800/2400 mg). Paired L-PL and HS-DBS were collected over 0–4 h post-dose (CST-2) and 0–12 h post-dose (CST-6) following administration of single (day 1) and multiple doses (day 5–CST-2; day 3–CST-6). HS-PL were excised and extracted with 50:50 acetonitrile:1 mM ammonium acetate (CST-2) and acetonitrile (CST-6). Concentrations of MPV active metabolite ß-d-N4-hydroxycytidine (NHC) and FVP were quantified using LC-MS (NHC-HS-PL: 2.5–250 ng/sample, L-PL: 2.5-5000 ng/mL; FVP-HS-PL: 50-5000 ng/sample, L-PL: 1000-100 000 ng/mL). HS-PL values were normalized to ng/mL and pharmacokinetic parameters (C_max, AUC_last) derived using non-compartmental analysis. Linear regression and Bland–Altman plots were used to compare methods.

Results: NHC L-PL geometric mean Cmax increased with each dosing cohort (n = 4/cohort) 300/600/800 mg [day 1: 1197/2440/3447 ng/mL; day 5: 1065/1865/3546 ng/mL]. The mean difference between all HS-PL and L-PL NHC was 27% (−69%–143%). HS-PL C_max were: day 1, 1749/2441/4986 ng/mL; day 5, 1559/1992/4618 ng/mL. Intersubject variability within each dosing cohort was <61% (L-PL) and <90% (HS-PL). L-PL and HS-PL concentrations (r = .967; p = <.001; n = 81) and AUC_last (r = .958; p = <.001; n = 23) were highly correlated with a mean difference of 1.32 ng/mL between the two methods.

FVP L-PL geometric mean C_max increased between days and with increasing doses 600/1200/1800/2400 mg [day 1: 16 481/28 006/52 044/88 486 ng/mL; day 3: 11 713/61 907/85362.4/195066.5 ng/mL]. The mean difference between all HS-PL and L-PL FVP was −6% (−115%–72%). HS-PL concentrations were [day 1: 14 307/38 107/57 448/90 607 ng/mL; day 3: 15 216/62 019/78 527/145 964 ng/mL]. Intersubject variability within each dosing cohort was <60% (L-PL) and <48% (HS-PL). FVP L-PL and HS-PL concentrations were highly correlated (r = .965; p = <.001; n = 124) (AUC_last; r = .942; p = <.001; n = 32). The mean difference between the two methods was 1.08 ng/mL.

Conclusion: HemaSep DBS are a useful alternative to L-PL for collection and transport of clinical samples for studies of high-risk infections in field settings, as NHC and FVP concentrations were correlated with respective L-PL values, with a minimal mean difference between methods. HS-PL concentrations were generally higher than respective L-PL, likely due to variable plasma ring volumes.