Preventing SARS-CoV-2 infection by modulating viral host receptors, such as angiotensin-converting enzyme 2 (ACE2)¹, could represent a new chemoprophylactic approach for COVID-19 that complements vaccination^2,3. However, the mechanisms that control the expression of ACE2 remain unclear. Here we show that the farnesoid X receptor (FXR) is a direct regulator of ACE2 transcription in several tissues affected by COVID-19, including the gastrointestinal and respiratory systems. We then use the over-the-counter compound z-guggulsterone and the off-patent drug ursodeoxycholic acid (UDCA) to reduce FXR signalling and downregulate ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. We show that the UDCA-mediated downregulation of ACE2 reduces susceptibility to SARS-CoV-2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. Furthermore, we reveal that UDCA reduces the expression of ACE2 in the nasal epithelium in humans. Finally, we identify a correlation between UDCA treatment and positive clinical outcomes after SARS-CoV-2 infection using retrospective registry data, and confirm these findings in an independent validation cohort of recipients of liver transplants. In conclusion, we show that FXR has a role in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, paving the way for future clinical trials.

There is a rapidly expanding literature on thein vitroantiviral activity of drugs that may be repurposed for therapy or chemoprophylaxis against severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2). However, this has not been accompanied by a comprehensive evaluation of the target plasma and lung concentrations of these drugs following approved dosing in humans. Accordingly, concentration 90% (EC₉₀) values recalculated fromin vitroanti‐SARS‐CoV‐2 activity data was expressed as a ratio to the achievable maximum plasma concentration (C_max) at an approved dose in humans (C_max/EC₉₀ratio). Only 14 of the 56 analyzed drugs achieved a C_max/EC₉₀ratio above 1. A more in‐depth assessment demonstrated that only nitazoxanide, nelfinavir, tipranavir (ritonavir‐boosted), and sulfadoxine achieved plasma concentrations above their reported anti‐SARS‐CoV‐2 activity across their entire approved dosing interval. An unbound lung to plasma tissue partition coefficient (K_pU_lung) was also simulated to derive a lung C_max/half‐maximal effective concentration (EC₅₀) as a better indicator of potential human efficacy. Hydroxychloroquine, chloroquine, mefloquine, atazanavir (ritonavir‐boosted), tipranavir (ritonavir‐boosted), ivermectin, azithromycin, and lopinavir (ritonavir‐boosted) were all predicted to achieve lung concentrations over 10‐fold higher than their reported EC₅₀. Nitazoxanide and sulfadoxine also exceeded their reported EC₅₀by 7.8‐fold and 1.5‐fold in lung, respectively. This analysis may be used to select potential candidates for further clinical testing, while deprioritizing compounds unlikely to attain target concentrations for antiviral activity. Future studies should focus on EC₉₀values and discuss findings in the context of achievable exposures in humans, especially within target compartments, such as the lungs, in order to maximize the potential for success of proposed human clinical trials.

Tenofovir disoproxil fumarate, the prodrug of nucleotide reverse transcriptase inhibitor tenofovir, shows high efficacy and relatively low toxicity in HIV patients. However, long-term kidney toxicity is now acknowledged as a modest but significant risk for tenofovir-containing regimens, and continuous use of tenofovir in HIV therapy is currently under question by practitioners and researchers. Co-morbidities (hepatitis C, diabetes), low body weight, older age, concomitant administration of potentially nephrotoxic drugs, low CD4 count, and duration of therapy are all risk factors associated with tenofovir-associated tubular dysfunction. Tenofovir is predominantly eliminated via the proximal tubules of the kidney, therefore drug transporters expressed in renal proximal tubule cells are believed to influence tenofovir plasma concentration and toxicity in the kidney. We review here the current evidence that the actions, pharmacogenetics and drug interactions of drug transporters are relevant factors for tenofovir-associated tubular dysfunction. The use of creatinine and novel biomarkers for kidney damage, and the role that drug transporters play in biomarker disposition, is discussed. The lessons learnt from investigating the role of transporters in tenofovir kidney elimination and toxicity can be utilised for future drug development and clinical management programs.

Tenofovir alafenamide produces lower plasma tenofovir and higher intracellular tenofovir diphosphate (DP) concentrations than tenofovir disoproxil fumarate but it is likely a victim of interactions with rifampicin. We aimed to investigate the pharmacokinetics of tenofovir alafenamide/emtricitabine with rifampicin. Healthy volunteers received tenofovir alafenamide/emtricitabine at 25/200 mg once daily, followed by tenofovir alafenamide/emtricitabine + rifampicin daily followed by tenofovir disoproxil fumarate. Plasma tenofovir alafenamide, tenofovir, emtricitabine and intracellular tenofovir-DP and emtricitabine triphosphate pharmacokinetics and genetic polymorphisms were assessed. Tenofovir alafenamide exposure decreased when tenofovir alafenamide/emtricitabine + rifampicin was used compared with tenofovir alafenamide/emtricitabine [geometric mean ratio (GMR) (90% CI): 0.45 (0.33–0.60)]. Plasma tenofovir and intracellular tenofovir-DP concentrations decreased with rifampicin [GMR (90% CI): 0.46 (0.40–0.52) and 0.64 (0.54–0.75), respectively]. GMR (90% CI) of intracellular tenofovir-DP AUC_0–24 for tenofovir alafenamide/emtricitabine + rifampicin versus tenofovir disoproxil fumarate was 4.21 (2.98–5.95). Rifampicin did not affect emtricitabine pharmacokinetics. CYP3A4*22 rs35599367 was associated with higher plasma tenofovir alafenamide AUC_0–24 at day 56. Following tenofovir alafenamide/emtricitabine administration with rifampicin, intracellular tenofovir-DP concentrations were still 4.21-fold higher than those achieved by tenofovir disoproxil fumarate, supporting further study during HIV/TB co-infection.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has been declared a global pandemic and urgent treatment and prevention strategies are needed. Nitazoxanide, an anthelmintic drug, has been shown to exhibit in vitro activity against SARS‐CoV‐2. The present study used physiologically based pharmacokinetic (PBPK) modelling to inform optimal doses of nitazoxanide capable of maintaining plasma and lung tizoxanide exposures above the reported SARS‐CoV‐2 EC₉₀.Methods: A whole‐body PBPK model was validated against available pharmacokinetic data for healthy individuals receiving single and multiple doses between 500 and 4000 mg with and without food. The validated model was used to predict doses expected to maintain tizoxanide plasma and lung concentrations above the EC₉₀ in >90% of the simulated population. PopDes was used to estimate an optimal sparse sampling strategy for future clinical trials.Results: The PBPK model was successfully validated against the reported human pharmacokinetics. The model predicted optimal doses of 1200 mg QID, 1600 mg TID and 2900 mg BID in the fasted state and 700 mg QID, 900 mg TID and 1400 mg BID when given with food. For BID regimens an optimal sparse sampling strategy of 0.25, 1, 3 and 12 hours post dose was estimated.Conclusion: The PBPK model predicted tizoxanide concentrations within doses of nitazoxanide already given to humans previously. The reported dosing strategies provide a rational basis for design of clinical trials with nitazoxanide for the treatment or prevention of SARS‐CoV‐2 infection. A concordant higher dose of nitazoxanide is now planned for investigation in the seamless phase I/IIa AGILE trial.

A clinical trial showed that efavirenz 400 mg once daily (EFV400) is as effective as the standard adult dose. World Health Organization recommends EFV400 as an alternative first-line agent, but data are lacking in the third trimester of pregnancy (TT). We investigated the pharmacokinetics, efficacy, and CYP2B6 pharmacogenetics in HIV-infected women (WLWH) on EFV400 during TT and post-partum (PP). An open-label 2-center study (United Kingdom, Uganda) was conducted in WLWH receiving antiretroviral regimens containing efavirenz 600 mg, who had their efavirenz dose reduced to EFV400. Weekly therapeutic drug monitoring (TDM), steady-state pharmacokinetic profiles (TT and PP), safety, virological efficacy, and CYP2B6 polymorphisms at positions 516 (C > T) and 938 (T > C) were evaluated. Twenty-five WLWH of African origin were enrolled. All had viral loads <50 copies/mL at baseline, which were maintained throughout the study. No infant was HIV infected. No WLWH were withdrawn due to low EFV400 TDM results. Geometric mean ratios (TT/PP; 90% confidence interval) for EFV400 maximum observed plasma concentration, area under the curve, and plasma concentration measured 24 hours after the observed dose were 0.97 (.85–1.10), 0.87 (.76–.99), and 0.77 (.65–.91), respectively. Five of 25 WLWH were slow metabolizers. Although EFV400 pharmacokinetic parameters were slightly lower for TT compared with PP values, efavirenz concentrations exceeded cutoff levels established by the study and those measured in antiretroviral-naive patients receiving EFV400 in ENCORE1. All subjects maintained a viral load <50 copies/mL, suggesting that EFV400 can be used in pregnant WLWH.