A Simple and Rapid LC-MS/MS Method for the Quantification of Nirmatrelvir/Ritonavir in Plasma of Patients with COVID-19

Table 6

Results of benchtop stability, three frozen-thaw cycles stability, and long-term stability of analytes (n = 3).

Analytes	Nominal concentration (ng/mL)	Room temperature 4 h			Three frozen-thaw cycles			Long-term stability
		Mean (%) ± SD	RSD (%)	RE (%)	Mean (%) ± SD	RSD (%)	RE (%)	Mean (%) ± SD	RSD (%)	RE (%)
Nirmatrelvir	5	4.6 ± 0.3	6.9	−7.5	4.9 ± 0.6	11.2	−1.2	5.4 ± 0.3	4.8	7.2
	1000	908.4 ± 65.5	7.2	−9.2	983.1 ± 67.3	6.8	−1.7	973.4 ± 26.2	2.7	−2.7
	2000	1851 ± 26.0	1.4	−7.5	2053 ± 110.3	5.4	2.7	2055 ± 31.9	1.6	2.8
Ritonavir	5	4.5 ± 0.2	3.4	−9.8	4.8 ± 0.6	12.4	−5.0	4.5 ± 0.2	3.7	−9.1
	1000	1076 ± 32.0	3.0	7.6	1076 ± 76.6	7.1	7.6	951.7 ± 53.8	5.7	−4.8
	2000	1873 ± 95.5	5.1	−6.4	2101 ± 106.2	5.1	5.0	1806 ± 39.1	3.8	−9.7