Intramuscular AZD7442 (Tixagevimab-Cilgavimab) for Prevention of Covid-19.

BACKGROUND: The monoclonal-antibody combination AZD7442 is composed of tixagevimab and cilgavimab, two neutralizing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that have an extended half-life and have been shown to have prophylactic and therapeutic effects in animal models. Pharmacokinetic data in humans indicate that AZD7442 has an extended half-life of approximately 90 days. METHODS: In an ongoing phase 3 trial, we enrolled adults (≥18 years of age) who had an increased risk of an inadequate response to vaccination against coronavirus disease 2019 (Covid-19), an increased risk of exposure to SARS-CoV-2, or both. Participants were randomly assigned in a 2:1 ratio to receive a single dose (two consecutive intramuscular injections, one containing tixagevimab and the other containing cilgavimab) of either 300 mg of AZD7442 or saline placebo, and they were followed for up to 183 days in the primary analysis. The primary safety end point was the incidence of adverse events after a single dose of AZD7442. The primary efficacy end point was symptomatic Covid-19 (SARS-CoV-2 infection confirmed by means of reverse-transcriptase-polymerase-chain-reaction assay) occurring after administration of AZD7442 or placebo and on or before day 183. RESULTS: A total of 5197 participants underwent randomization and received one dose of AZD7442 or placebo (3460 in the AZD7442 group and 1737 in the placebo group). The primary analysis was conducted after 30% of the participants had become aware of their randomized assignment. In total, 1221 of 3461 participants (35.3%) in the AZD7442 group and 593 of 1736 participants (34.2%) in the placebo group reported having at least one adverse event, most of which were mild or moderate in severity. Symptomatic Covid-19 occurred in 8 of 3441 participants (0.2%) in the AZD7442 group and in 17 of 1731 participants (1.0%) in the placebo group (relative risk reduction, 76.7%; 95% confidence interval [CI], 46.0 to 90.0; P<0.001); extended follow-up at a median of 6 months showed a relative risk reduction of 82.8% (95% CI, 65.8 to 91.4). Five cases of severe or critical Covid-19 and two Covid-19-related deaths occurred, all in the placebo group. CONCLUSIONS: A single dose of AZD7442 had efficacy for the prevention of Covid-19, without evident safety concerns. (Funded by AstraZeneca and the U.S. government; PROVENT ClinicalTrials.gov number, NCT04625725.).

An analytical method for disentangling the roles of adhesion and crowding for random walk models on a crowded lattice.

Migration of cells and molecules in vivo is affected by interactions with obstacles. These interactions can include crowding effects, as well as adhesion/repulsion between the motile cell/molecule and the obstacles. Here we present an analytical framework that can be used to separately quantify the roles of crowding and adhesion/repulsion using a lattice-based random walk model. Our method leads to an exact calculation of the long time Fickian diffusivity, and avoids the need for computationally expensive stochastic simulations.

Communication: Distinguishing between short-time non-Fickian diffusion and long-time Fickian diffusion for a random walk on a crowded lattice.

The motion of cells and molecules through biological environments is often hindered by the presence of other cells and molecules. A common approach to modeling this kind of hindered transport is to examine the mean squared displacement (MSD) of a motile tracer particle in a lattice-based stochastic random walk in which some lattice sites are occupied by obstacles. Unfortunately, stochastic models can be computationally expensive to analyze because we must average over a large ensemble of identically prepared realizations to obtain meaningful results. To overcome this limitation we describe an exact method for analyzing a lattice-based model of the motion of an agent moving through a crowded environment. Using our approach we calculate the exact MSD of the motile agent. Our analysis confirms the existence of a transition period where, at first, the MSD does not follow a power law with time. However, after a sufficiently long period of time, the MSD increases in proportion to time. This latter phase corresponds to Fickian diffusion with a reduced diffusivity owing to the presence of the obstacles. Our main result is to provide a mathematically motivated, reproducible, and objective estimate of the amount of time required for the transport to become Fickian. Our new method to calculate this crossover time does not rely on stochastic simulations.

Calculating the Fickian diffusivity for a lattice-based random walk with agents and obstacles of different shapes and sizes.

Random walk models are often used to interpret experimental observations of the motion of biological cells and molecules. A key aim in applying a random walk model to mimic an in vitro experiment is to estimate the Fickian diffusivity (or Fickian diffusion coefficient), D. However, many in vivo experiments are complicated by the fact that the motion of cells and molecules is hindered by the presence of obstacles. Crowded transport processes have been modeled using repeated stochastic simulations in which a motile agent undergoes a random walk on a lattice that is populated by immobile obstacles. Early studies considered the most straightforward case in which the motile agent and the obstacles are the same size. More recent studies considered stochastic random walk simulations describing the motion of an agent through an environment populated by obstacles of different shapes and sizes. Here, we build on previous simulation studies by analyzing a general class of lattice-based random walk models with agents and obstacles of various shapes and sizes. Our analysis provides exact calculations of the Fickian diffusivity, allowing us to draw conclusions about the role of the size, shape and density of the obstacles, as well as examining the role of the size and shape of the motile agent. Since our analysis is exact, we calculate D directly without the need for random walk simulations. In summary, we find that the shape, size and density of obstacles has a major influence on the exact Fickian diffusivity. Furthermore, our results indicate that the difference in diffusivity for symmetric and asymmetric obstacles is significant.

Characterizing transport through a crowded environment with different obstacle sizes.

Transport through crowded environments is often classified as anomalous, rather than classical, Fickian diffusion. Several studies have sought to describe such transport processes using either a continuous time random walk or fractional order differential equation. For both these models the transport is characterized by a parameter α, where α = 1 is associated with Fickian diffusion and α < 1 is associated with anomalous subdiffusion. Here, we simulate a single agent migrating through a crowded environment populated by impenetrable, immobile obstacles and estimate α from mean squared displacement data. We also simulate the transport of a population of such agents through a similar crowded environment and match averaged agent density profiles to the solution of a related fractional order differential equation to obtain an alternative estimate of α. We examine the relationship between our estimate of α and the properties of the obstacle field for both a single agent and a population of agents; we show that in both cases, α decreases as the obstacle density increases, and that the rate of decrease is greater for smaller obstacles. Our work suggests that it may be inappropriate to model transport through a crowded environment using widely reported approaches including power laws to describe the mean squared displacement and fractional order differential equations to represent the averaged agent density profiles.

Non-interventional study of the safety and effectiveness of fluticasone propionate/formoterol fumarate in real-world asthma management.

INTRODUCTION: In recognition of the value of long-term real-world data, a postauthorization safety study of the inhaled corticosteroid (ICS) fluticasone propionate and long-acting ß2-agonist (LABA) formoterol fumarate (fluticasone/formoterol; Flutiform®) was conducted. METHODS: This was a 12-month observational study of outpatients with asthma aged ⩾ 12 years in eight European countries. Patients were prescribed fluticasone/formoterol according to the licensed indication, and independently of their subsequent enrolment in the study. They were then treated according to local standard practice. The study objectives were to evaluate the safety and effectiveness of fluticasone/formoterol under real-world conditions. RESULTS: The safety population for this study comprised 2539 patients (mean age 47.7 years; 94.3% aged ⩾ 18 years; 63.4% female). Most patients (1538/2539, 60.6%) had switched to fluticasone/formoterol from another ICS/LABA, primarily due to lack of efficacy (1150/2539, 45.3%). Three quarters (77.4%) of patients were treated for 12 months, and 80.6% continued fluticasone/formoterol treatment after the study. Adverse events (AEs) occurred in 60.0% patients, and 10.2% had AEs considered possibly related to fluticasone/formoterol [most commonly asthma exacerbation (2.0% patients), dysphonia (1.8%) and cough (1.1%)]. Thirty-six severe AEs, but no serious AEs, were considered possibly related to fluticasone/formoterol. The proportion of patients with controlled asthma (based on Asthma Control Test score ⩾ 20) increased from 29.4% at baseline to 67.4% at study end (last observation carried forward). The proportion of patients experiencing at least one severe exacerbation decreased from 35.8% in the year prior to enrolment to 9.8% during the study. Improvements from baseline to study end were also observed in Asthma Quality of Life scores and physician/patient reports of satisfaction with treatment. CONCLUSION: In this real-world postauthorization safety study, fluticasone/formoterol demonstrated a safety profile consistent with that seen in controlled clinical trials, with effectiveness in improving asthma control.

Efficacy and Safety of 5-Fluorouracil 0.5%/Salicylic Acid 10% in the Field-Directed Treatment of Actinic Keratosis: A Phase III, Randomized, Double-Blind, Vehicle-Controlled Trial.

INTRODUCTION: Due to the high prevalence of actinic keratosis (AK) and potential for lesions to become cancerous, clinical guidelines recommend that all are treated. The objective of this study was to evaluate the efficacy and safety of 5-fluorouracil (5-FU) 0.5%/salicylic acid 10% as field-directed treatment of AK lesions. METHODS: This multicenter, double-blind, vehicle-controlled study (NCT02289768) randomized adults, with a 25 cm2 area of skin on their face, bald scalp, or forehead covering 4-10 clinically confirmed AK lesions (grade I/II), 2:1 to treatment or vehicle applied topically once daily for 12 weeks. The primary endpoint was the proportion of patients with complete clinical clearance (CCC) of lesions in the treatment field 8 weeks after the end of treatment. Secondary endpoints included partial clearance (PC; ≥75% reduction) of lesions. Safety outcomes were assessed. RESULTS: Of 166 patients randomized, 111 received 5-FU 0.5%/salicylic acid 10% and 55 received vehicle. At 8 weeks after the end of treatment, CCC was significantly higher with 5-FU 0.5%/salicylic acid 10% than with vehicle [49.5% vs. 18.2%, respectively; odds ratio (OR) 3.9 (95% CI) 1.7, 8.7; P = 0.0006]. Significantly more patients achieved PC of lesions with treatment than with vehicle [69.5% vs. 34.6%, respectively; OR 4.9 (95% CI 2.3, 10.5); P < 0.0001]. Treatment-emergent adverse events, predominantly related to application- and administration-site reactions, were more common with 5-FU 0.5%/salicylic acid 10% than with vehicle (99.1% vs. 83.6%). CONCLUSIONS: Compared with vehicle, field-directed treatment of AK lesions with 5-FU 0.5%/salicylic acid 10% was effective in terms of CCC. Safety outcomes were consistent with the known and predictable safety profile. TRIAL REGISTRATION: NCT02289768. FUNDING: Almirall S.A.

Simplified approach for calculating moments of action for linear reaction-diffusion equations.

The mean action time is the mean of a probability density function that can be interpreted as a critical time, which is a finite estimate of the time taken for the transient solution of a reaction-diffusion equation to effectively reach steady state. For high-variance distributions, the mean action time underapproximates the critical time since it neglects to account for the spread about the mean. We can improve our estimate of the critical time by calculating the higher moments of the probability density function, called the moments of action, which provide additional information regarding the spread about the mean. Existing methods for calculating the nth moment of action require the solution of n nonhomogeneous boundary value problems which can be difficult and tedious to solve exactly. Here we present a simplified approach using Laplace transforms which allows us to calculate the nth moment of action without solving this family of boundary value problems and also without solving for the transient solution of the underlying reaction-diffusion problem. We demonstrate the generality of our method by calculating exact expressions for the moments of action for three problems from the biophysics literature. While the first problem we consider can be solved using existing methods, the second problem, which is readily solved using our approach, is intractable using previous techniques. The third problem illustrates how the Laplace transform approach can be used to study coupled linear reaction-diffusion equations.

Critical time scales for advection-diffusion-reaction processes.

The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J. 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. E 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math. 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.

Moments of action provide insight into critical times for advection-diffusion-reaction processes.

Berezhkovskii and co-workers introduced the concept of local accumulation time as a finite measure of the time required for the transient solution of a reaction-diffusion equation to effectively reach steady state [Biophys J. 99, L59 (2010); Phys. Rev. E 83, 051906 (2011)]. Berezhkovskii's approach is a particular application of the concept of mean action time (MAT) that was introduced previously by McNabb [IMA J. Appl. Math. 47, 193 (1991)]. Here, we generalize these previous results by presenting a framework to calculate the MAT, as well as the higher moments, which we call the moments of action. The second moment is the variance of action time, the third moment is related to the skew of action time, and so on. We consider a general transition from some initial condition to an associated steady state for a one-dimensional linear advection-diffusion-reaction partial differential equation (PDE). Our results indicate that it is possible to solve for the moments of action exactly without requiring the transient solution of the PDE. We present specific examples that highlight potential weaknesses of previous studies that have considered the MAT alone without considering higher moments. Finally, we also provide a meaningful interpretation of the moments of action by presenting simulation results from a discrete random-walk model together with some analysis of the particle lifetime distribution. This work shows that the moments of action are identical to the moments of the particle lifetime distribution for certain transitions.