A Model-Based Bayesian Estimation of the Rate of Evolution of VNTR Loci in Mycobacterium tuberculosis

Variable numbers of tandem repeats (VNTR) typing is widely used for studying the bacterial cause of tuberculosis. Knowledge of the rate of mutation of VNTR loci facilitates the study of the evolution and epidemiology of Mycobacterium tuberculosis. Previous studies have applied population genetic models to estimate the mutation rate, leading to estimates varying widely from around to per locus per year. Resolving this issue using more detailed models and statistical methods would lead to improved inference in the molecular epidemiology of tuberculosis. Here, we use a model-based approach that incorporates two alternative forms of a stepwise mutation process for VNTR evolution within an epidemiological model of disease transmission. Using this model in a Bayesian framework we estimate the mutation rate of VNTR in M. tuberculosis from four published data sets of VNTR profiles from Albania, Iran, Morocco and Venezuela. In the first variant, the mutation rate increases linearly with respect to repeat numbers (linear model); in the second, the mutation rate is constant across repeat numbers (constant model). We find that under the constant model, the mean mutation rate per locus is (95% CI: ,)and under the linear model, the mean mutation rate per locus per repeat unit is (95% CI: ,). These new estimates represent a high rate of mutation at VNTR loci compared to previous estimates. To compare the two models we use posterior predictive checks to ascertain which of the two models is better able to reproduce the observed data. From this procedure we find that the linear model performs better than the constant model. The general framework we use allows the possibility of extending the analysis to more complex models in the future

Addressing varenicline adherence through repackaging in a dose administration aid

Aaron D Drovandi, Sherryl G Robertson, Bunmi S Malau-Aduli, Peta Ann Teague, Beverley D Glass College of Medicine and Dentistry, James Cook University, Townsville, QLD, Australia Background: Ensuring adherence to prescribed smoking cessation medications, such as Champix® (varenicline), is essential during a quit attempt as non-adherence can significantly reduce the likelihood of achieving prolonged smoking abstinence. The use of dose administration aids may improve adherence, though medication stability on repackaging is not guaranteed, due to a lack of available data from manufacturers supporting this practice. Objective: To determine the suitability for repackaging varenicline tartrate tablets into a dose administration aid, by assessing its physical and chemical stability after being repackaged and stored at ambient conditions for 6 weeks. Methods: Varenicline tartrate (1.0 mg) tablets were repackaged into commercially available Webster-pak® blister compartments and stored for 42 days at ambient conditions characteristic of a Zone IVB climate (30 ± 2°C and 75 ± 5% relative humidity) according to the World Health Organization (WHO) guidelines on pharmaceutical stability testing. Physical and chemical tests were performed on the repackaged and control tablets, including an assessment of: tablet thickness, hardness, weight uniformity, friability, dissolution, disintegration, and content uniformity after exposure to ambient conditions and light according to International Council on Harmonisation of Technical Requirements of Pharmaceuticals for Human Use guideline Q1B. Results: Weight, friability, and thickness of the tablets complied with compendial standards. A validated high performance liquid chromatography method was used to confirm that after exposure to light, and repackaging at 30°C/75% relative humidity, the tablets remained within the required 95%–105% of the stated drug content. However, tablet hardness and disintegration decreased over time, with tablets becoming softer and undergoing more rapid disintegration in water. Conclusion: Repackaging 1.0 mg varenicline tartrate tablets into a dose administration aid can be undertaken to improve adherence rates and therefore smoking abstinence rates. This can be performed without compromising either the physical or chemical stability of the tablets. Keywords: stability, compliance, degradatio