Development of an Assay for the COVID-19 Drug Remdesivir- Toward Proper Remdesivir Use in Patients with Pre-Existing Conditions

Significance of the topic

The antiviral agent remdesivir was granted special approval for COVID-19 treatment in Japan in May 2020. Despite global use, pharmacokinetic data remain scarce, particularly in patients with renal impairment or comorbidities. Monitoring drug and metabolite blood levels can guide safer dosing, reduce adverse events, and optimize therapeutic outcomes under conditions of limited clinical trial data.

Objectives and study overview

This study aimed to develop and validate a liquid chromatography–tandem mass spectrometry assay for GS-441524, the predominant remdesivir metabolite in plasma, and to apply it to clinical samples. Blood concentrations were measured in COVID-19 patients with varying renal function. Population pharmacokinetic (popPK) modeling was performed to link GS-441524 clearance to renal function (eGFR) and support individualized dosing.

Methodology and instrumentation

Sample preparation involved protein precipitation of EDTA plasma with isopropanol and acetonitrile, spiked with stable isotope–labeled internal standards ([13C6]-remdesivir and [13C5]-GS-441524). After centrifugation, supernatants were analyzed by LC–MS/MS.

• Liquid chromatography: Shimadzu Nexera X2 system, Shim-pack Scepter C18-120 column (50 × 2.1 mm, 1.9 µm), 40 °C, gradient elution with 0.05 % formic acid in water (A) and acetonitrile (B), flow 0.4 mL/min.
• Mass spectrometry: Shimadzu LCMS-8060, ESI positive mode, multiple reaction monitoring transitions optimized for remdesivir, GS-441524, and labeled standards.

Main results and discussion

Calibration curves for remdesivir (100–5000 ng/mL) and GS-441524 (5–500 ng/mL) exhibited excellent linearity (R2 > 0.999). In 37 COVID-19 patients, trough GS-441524 levels rose significantly in those with reduced eGFR. PopPK analysis identified non-indexed eGFR as a significant covariate for clearance. The final model:

• CL (L/h) = 11.8 × (eGFRnon-indexed/74.7)^1.09
• Vd (L) = 382 × (1 – 0.429 × AGE ≥ 75 year indicator)

Simulations suggest dose adjustments based on eGFR to prevent accumulation and limit toxicity in patients with renal dysfunction.

Benefits and practical applications

Therapeutic drug monitoring of GS-441524 enables:

• Individualized dosing for patients with impaired renal function
• Enhanced safety by avoiding excessive metabolite accumulation
• Evidence-based guidance where clinical data are limited

Future trends and opportunities

Broader implementation of high-throughput MS assays in clinical settings is anticipated. Future work may expand to additional remdesivir metabolites and excipients, integrate real-time popPK feedback, and apply similar approaches to other antiviral or critical care drugs, particularly for populations with comorbidities.

Conclusion

The validated LC–MS/MS method for GS-441524 and the derived popPK model provide a framework for renal-function–based dosing of remdesivir in COVID-19 patients. This approach addresses gaps in standard clinical trial data and supports safer, individualized antiviral therapy.

References

1) Sukeishi A, Itohara K, Yonezawa A, Sato Y, Matsumura K, Katada Y, Nakagawa T, Hamada S, Tanabe N, Imoto E, Kai S, Hirai T, Yanagita M, Ohtsuru S, Terada T, Ito I. Population pharmacokinetic modeling of GS-441524, the active metabolite of remdesivir, in Japanese COVID-19 patients with renal dysfunction. CPT Pharmacometrics Syst Pharmacol. 2022;11(1):94–103. doi:10.1002/psp4.12736.