Higher sensitive selective spectrofluorometric determination of ritonavir in the presence of nirmatrelvir: application to new FDA approved co-packaged COVID-19 pharmaceutical dosage and spiked human plasma

Stability indicating RP-HPLC technique for simultaneous estimation of nirmatrelvir and ritonavir in their new copackaged dosage form for COVID-19 treatment

RP-HPLC technique was developed and optimized for simultaneous identification and estimation of nirmatrelvir (NIR) and ritonavir (RIT) in their new copackaged tablet. Stability of nirmatrelvir (NIR) was studied after exposure to different five stress conditions; alkali, acid, heat, photo and oxidation degradation. The chromatographic separation was achieved using VDSpher PUR 100 ODS (4.6-mm x 15-mm), 3.5 μm column and mixture of 0.03 M potassium di-hydrogen phosphate buffer pH 4 and acetonitrile (45:55, v/v) as mobile phase. The column temperature was set at 40 °C, flow rate at 1mL/min and UV detection at 215 nm. The NIR and RIT retention times were 3.94 ± 0.08 min and 9.08 ± 0.1 min, respectively. Linear relationship was established in range of (1.5-105 µg/mL) for NIR and (1-70 µg/mL) for RIT with good reproducibility. The found mean percentage recoveries of nirmatrelvir (NIR) and ritonavir (RIT) were 100.03% and 99.85%, respectively. The developed method shows very good sensitivity as the LOQ and LOD were found to be 3.001 & 0.990 µg/mL, respectively for NIR and 2.765 & 0.912 µg/mL, respectively for RIT. The developed approach was validated concerning to ICH guidelines and applied successfully for the simultaneous estimation of NIR and RIT in their new copackaged dosage from. The results of assay using the proposed approach were compared statistically to the results found by applying the published one with good agreement.

Pharmacokinetic analysis of placental transfer of ritonavir as a component of paxlovid using microdialysis in pregnant rats

Background

Ritonavir is one of the most potent CYP3A4 inhibitor currently on the market, and is often used together with other antiviral drugs to increase their bioavailability and efficacy. Paxlovid, consisting of nirmatrelvir and ritonavir, was approved for the treatment of COVID-19. As previous studies regarding the use of ritonavir during pregnancy were limited to ex-vivo experiments and systemic safety data, to fully explore the detailed pharmacokinetics of ritonavir in pregnant rats' blood and conceptus, an analytical method consisted of multi-microdialysis coupled with UHPLC-MS/MS were developed to analyze the pharmacokinetics of ritonavir, both as a component of Paxlovid and by itself. 17 days pregnant female Sprague-Dawley rats were randomly split into three experimental group: normal dosage of ritonavir alone (7 mg kg-1), normal dosage of Paxlovid (ritonavir 7 mg kg-1 + nirmatrelvir 15 mg kg-1), and 3× dosage of ritonavir (21 mg kg-1).

Results

3× dosage of ritonavir produced a more than 3× increase in rats' blood and placenta. Transfer rate of ritonavir to the placenta, amniotic fluid, and fetus were determined to be 20.7%, 13.8%, and 4.7% respectively. Concentration of ritonavir in the placenta, amniotic fluid, and fetus did not significantly go down after 8 h.

Significance

Overall, ritonavir's metabolism was not influenced by the presence of nirmatrelvir in pregnant rats. A 3× increase in dosage produced a concentration of roughly 4×, most likely a result of ritonavir's auto-inhibition effect on cytochrome P450 proteins. Accumulation of ritonavir is possible in placenta, amniotic fluid, and fetus.