Tecovirimat concentrations and viral suppression in seminal fluid from patients with mpox

Efficacy and viral dynamics of tecovirimat in patients with MPOX: A multicenter open-label, double-arm trial in Japan

INTRODUCTION

Tecovirimat's application in treating mpox remains under-researched, leaving gaps in clinical and virological understanding.

METHODS

The Tecopox study in Japan evaluated the efficacy and safety of tecovirimat in patients with smallpox or mpox, who were divided into oral tecovirimat and control groups. Patients with mpox enrolled between June 28, 2022, and April 30, 2023, were included. Demographic and clinical details along with blood, urine, pharyngeal swab, and skin lesion samples were gathered for viral analysis. A multivariable Tobit regression model was employed to identify factors influencing prolonged viral detection.

RESULTS

Nineteen patients were allocated to the tecovirimat group, and no patients were allocated to the control group. The median age was 38.5 years, and all patients were males. Ten patients (52.6%) were infected with human immunodeficiency virus (HIV). Sixteen patients (84.2%) had severe disease. Nine of the 15 patients (60.0%) (four patients withdrew before day 14) had negative PCR results for skin lesion specimens 14 days after inclusion. The mortality rates were 0% on days 14 and 30. No severe adverse events were reported. HIV status and the number of days from symptom onset to tecovirimat administration were associated with lower Ct values (p = 0.027 and p < 0.001, respectively). The median number of days when PCR testing did not detect the mpox virus in each patient was 19.5 days.

CONCLUSION

Early tecovirimat administration might reduce viral shedding duration, thereby mitigating infection spread. Moreover, patients infected with HIV showed prolonged viral shedding, increasing the transmission risk compared to those without HIV.

Pharmacokinetics of tecovirimat in subjects with Mpox

OBJECTIVE

To investigate the pharmacokinetics (PK) of tecovirimat in subjects with Mpox.

METHODS

This monocentric, prospective, observational study enrolled subjects with Mpox who received standard treatment with oral tecovirimat. Plasma samples for PK assessment were collected at steady state (5-8 days after initiation of antiviral therapy), before and 3, 5, 7 and 12 h after tecovirimat administration. Drug concentrations were determined by validated liquid chromatography coupled with tandem mass spectrometry. PK parameters were calculated using Phoenix 8.1.

RESULTS

Overall, 14 male patients hospitalized for severe Mpox with ongoing tecovirimat treatment were enrolled in this study. Six of the 14 patients were living with human immunodeficiency virus (HIV), all of whom were on antiretroviral therapy (ART) and virologically suppressed at the time of hospitalization. Significant differences in tecovirimat PK were observed in subjects without HIV compared with subjects with HIV. In subjects with HIV, the maximum tecovirimat plasma concentration (39%, P≤0.0001), minimum tecovirimat plasma concentration (42%, P=0.0079) and area under the curve from zero to the last measured time-point (40%, P≤0.0001) were significantly lower compared with subjects without HIV, but all concentrations remained above the in-vitro calculated 90% inhibitory concentration. No significant associations were found between demographic/clinical data and tecovirimat PK. All patients recovered completely within 14 (range 6-36) days of treatment initiation.

CONCLUSIONS

This study found a significant decrease in plasma exposure of tecovirimat in Mpox patients with HIV on effective ART compared with those without HIV, with no evident impact on clinical outcomes. Although these results need to be confirmed in larger studies, they may provide useful information on the PK of tecovirimat.

Early administration of tecovirimat shortens the time to mpox clearance in a model of human infection

Despite use of tecovirimat since the beginning of the 2022 outbreak, few data have been published on its antiviral effect in humans. We here predict tecovirimat efficacy using a unique set of data in nonhuman primates (NHPs) and humans. We analyzed tecovirimat antiviral activity on viral kinetics in NHP to characterize its concentration-effect relationship in vivo. Next, we used a pharmacological model developed in healthy volunteers to project its antiviral efficacy in humans. Finally, a viral dynamic model was applied to characterize mpox kinetics in skin lesions from 54 untreated patients, and we used this modeling framework to predict the impact of tecovirimat on viral clearance in skin lesions. At human-recommended doses, tecovirimat could inhibit viral replication from infected cells by more than 90% after 3 to 5 days of drug administration and achieved over 97% efficacy at drug steady state. With an estimated mpox within-host basic reproduction number, R0, equal to 5.6, tecovirimat could therefore shorten the time to viral clearance if given before viral peak. We predicted that initiating treatment at symptom onset, which on average occurred 2 days before viral peak, could reduce the time to viral clearance by about 6 days. Immediate postexposure prophylaxis could not only reduce time to clearance but also lower peak viral load by more than 1.0 log10 copies/mL and shorten the duration of positive viral culture by about 7 to 10 days. These findings support the early administration of tecovirimat against mpox infection, ideally starting from the infection day as a postexposure prophylaxis.

Inequity in the global distribution of monkeypox vaccines

Monkeypox (mpox) has been a public health emergency of international concern that emerged in mid-2022 and has spread to 110 countries. The clinical findings of the disease vary according to the seriousness of the cases. Although its case fatality risk has not been high, a significant percentage of patients require hospitalization. In this context, local initiatives were taken to extend the limited supply of vaccines against the disease; however, such measures have not been sufficient to contain the spread of cases and ensure an equitable distribution of health resources. As a result, endemic regions of low-income countries continue to have insufficient access to mpox vaccination. Despite this and considering the global scope of the disease, there is still little discussion in the literature about the difficulties in achieving adequate vaccination coverage rates for the target population of interest. In this article, we briefly discussed general aspects of the disease, including its surveillance, the current global context of challenges for mpox vaccination, and issues on global allocation of health resources as well as proposed related recommendations.