Objective To ascertain the current burden of adverse drug reactions (ADRs) through a prospective analysis of all admissions to hospital. Design Prospective observational study. Setting Two large general hospitals in Merseyside, England. Participants 18 820 patients aged > 16 years admitted over six months and assessed for cause of admission.

Drug regulatory agencies should ensure that the benefits of drugs outweigh their risks, but licensed medicines sometimes do not perform as expected in everyday clinical practice. Failure may relate to lower than anticipated efficacy or a higher than anticipated incidence or severity of adverse effects. Here we show that the problem of benefit-risk is to a considerable degree a problem of variability in drug response. We describe biological and behavioural sources of variability and how these contribute to the long-known efficacy-effectiveness gap. In this context, efficacy describes how a drug performs under conditions of clinical trials, whereas effectiveness describes how it performs under conditions of everyday clinical practice. We argue that a broad range of pre- and post-licensing technologies will need to be harnessed to bridge the efficacy-effectiveness gap. Successful approaches will not be limited to the current notion of pharmacogenomics-based personalized medicines, but will also entail the wider use of electronic health-care tools to improve drug prescribing and patient adherence.

Bill & Melinda Gates Foundation.

The rate of elimination, apparent volume of distribution, plasma clearance, and relative anticoagulant potency of the enantiomers of warfarin have been determined in man. In 9 subjects the plasma half‐life (T½) of R warfarin after a single oral dose of 0.5 mg/kg ranged from 19.9 to 69.S hours, and was significantly longer than that of S warfarin, which ranged from 18.0 to 34.1 hours. There was no significant difference in the apparent volume of distribution of the enantiomers, and thus the plasma clearance of R warfarin was significantly less than that of S warfarin. After multiple dosing to steady state, the plasma T% of R warfarin in 8 subjects ranged from 37.4 to 88.6 hours and was significantly longer than that of S warfarin, which ranged from 21.2 to 42.6 hours. The apparent volume of distribution of the enantiomers was the same, and thus the plasma clearance of R was again significantly less than that of S warfarin. The plasma T½ of R but not of S was significantly longer after multiple dosing than after a single dose. The ratio of the steady‐state plasma concentration of R to S warfarin was 3.80 : 1 in 4 patients with the same degree of anticoagulant control. The relative dose requirements of R to S warfarin were 1.5.9 : 1 in these sub;ects. S warfarin is a more potent anticoagulant than R warfarin in man.

Drug repurposing has been proposed as a strategy to develop new therapies that has fewer risks, lower costs and shorter timelines than developing completely new drugs. However, the potential of this strategy has not been as widely realized as hoped, in part owing to legal and regulatory barriers. Here, we highlight these barriers and consider how they could be overcome.