What is the clinical evidence from this study?

Study design: Other. Population: Healthy adults (n=14). Intervention: Nirmatrelvir/ritonavir vs. Non-Chinese participants (historical data). Primary outcome: Steady-state nirmatrelvir area under the concentration-time curve over the dosing interval (AUC tau) in µg·h/mL.

What question did this study set out to answer?

This study aimed to assess the pharmacokinetic profiles of nirmatrelvir/ritonavir in healthy Chinese adults and compare them with non-Chinese participants.

May 8, 2026Open Access

Pharmacokinetics of Nirmatrelvir/Ritonavir after Multiple Administration in a Phase 1, Open-Label Study in Healthy Chinese Adults and Compared with Non-Chinese Participants

Key Result

Nirmatrelvir 300 mg plus ritonavir 100 mg twice daily demonstrated comparable pharmacokinetic profiles in healthy Chinese adults (steady-state AUC 32.01 µg·h/mL) compared to non-Chinese participants.

Key Points

This study aimed to assess the pharmacokinetic profiles of nirmatrelvir/ritonavir in healthy Chinese adults and compare them with non-Chinese participants.
Phase 1, open-label, single-site study
14 healthy Chinese participants administered nirmatrelvir 300 mg + ritonavir 100 mg twice daily for 10 days
Pharmacokinetic parameters assessed using liquid chromatography-tandem mass spectrometry.
Initial plasma concentrations were 3.08 μg/mL, reaching 4.50 μg/mL at steady state on day 5
42.9% reported adverse events, with 28.6% related to treatment (mild dysgeusia)
No serious adverse events or discontinuations observed; PK characteristics were comparable with non-Chinese participants.

Structured PICO

Does nirmatrelvir/ritonavir have comparable pharmacokinetic profiles and safety in healthy Chinese adults compared to non-Chinese adults?

Population

14 healthy Chinese adults, age range 24 to 43 years

Intervention

Nirmatrelvir 300 mg plus ritonavir 100 mg administered twice daily for 10 days

Comparator

Healthy non-Chinese adult participants who received the same nirmatrelvir/ritonavir dose in other Phase 1 studies

Outcome

Pharmacokinetic (PK) profiles and safety/tolerabilitysurrogate

Nirmatrelvir/ritonavir has a comparable pharmacokinetic and safety profile in healthy Chinese adults as in non-Chinese populations, supporting its use in this demographic.

Main Result

Absolute Event Rate: 32.01% vs 33.35%

Limitations

Relatively small sample size of Chinese/Asian participants may limit detection of subtle ethnic differences.
Differences in treatment duration complicate direct comparisons across ethnic groups.
Use of distinct drug formulations (suspensions vs tablets) in Chinese and non-Chinese Phase 1 studies introduces potential variability in bioavailability.
Extrapolation of efficacy findings to Chinese/Asian populations carries inherent uncertainty due to limited clinical efficacy data from these groups in the EPIC-HR trial.

Abstract

BACKGROUND AND OBJECTIVES: Nirmatrelvir (PF-07321332) has demonstrated antiviral activity and an acceptable safety profile in clinical studies. This study aimed to demonstrate the pharmacokinetic (PK) profiles of Chinese participants after administration of nirmatrelvir/ritonavir, and to further evaluate the ethnic differences between different races. METHODS: This Phase 1, open-label, single-site study assessed the PK, safety, and tolerability of nirmatrelvir 300 mg plus ritonavir 100 mg administered twice daily for 10 days in healthy Chinese adults. In total, 14 Chinese participants were enrolled with an age range of 24 to 43 years. Samples were collected after first-dose administration on day 1 (0, 0.5, 1, 1.5, 2, 4, 6, 8, 12 h after drug administration) and last-dose administration on day 10 (0, 0.5, 1, 1.5, 2, 4, 6, 8, 12, 24, and 48 h after drug administration) to assess PK parameters after a single dose and multiple doses; pre-dose samples were collected on days 5, 8, and 10 to confirm that steady-state was achieved. All PK samples were assayed with a liquid chromatography-tandem mass spectrometry method to quantify plasma concentration of nirmatrelvir and ritonavir. Study participants were monitored for safety for 28-35 days after the last-dose administration. Adverse events (AEs), clinical safety laboratory tests, vital signs, and 12-lead electrocardiograms were all monitored during study. Results for Chinese participants were compared with results in healthy non-Chinese adult participants who received the same nirmatrelvir/ritonavir dose in other Phase 1 studies. RESULTS: and AUC were 3.08 μg/mL and 19.66 μg·h/mL after the first dose and increased to 4.50 μg/mL and 32.01 μg·h/mL at steady state, with less than 2-fold accumulation and a mean terminal half-life of 6.84 h. Steady-state concentrations were achieved before day 5. Nirmatrelvir/ritonavir was well tolerated; 6 participants (42.9%) reported AEs, 4 of which (28.6%) were treatment-related mild dysgeusia. No serious AEs or discontinuations were reported. The results showed that the PK characteristics of nirmatrelvir/ritonavir in healthy Chinese adults were comparable with results from previous studies in non-Chinese healthy adults, with no apparent clinically significant differences observed between Chinese and non-Chinese participants. CONCLUSIONS: In healthy Chinese participants, the PK profile of nirmatrelvir 300 mg plus ritonavir 100 mg twice daily was comparable with that observed in non-Chinese participants, with an overall favorable safety profile, supporting the use of this dosing regimen for the Chinese population. GOV ID: NCT05339334.

Bookmark

View Full Paper