Methodological comparison of marginal structural model, time-varying Cox regression, and propensity score methods: the example of antidepressant use and the risk of hip fracture.

BACKGROUND: Observational studies including time-varying treatments are prone to confounding. We compared time-varying Cox regression analysis, propensity score (PS) methods, and marginal structural models (MSMs) in a study of antidepressant [selective serotonin reuptake inhibitors (SSRIs)] use and the risk of hip fracture. METHODS: A cohort of patients with a first prescription for antidepressants (SSRI or tricyclic antidepressants) was extracted from the Dutch Mondriaan and Spanish Base de datos para la Investigación Farmacoepidemiológica en Atención Primaria (BIFAP) general practice databases for the period 2001-2009. The net (total) effect of SSRI versus no SSRI on the risk of hip fracture was estimated using time-varying Cox regression, stratification and covariate adjustment using the PS, and MSM. In MSM, censoring was accounted for by inverse probability of censoring weights. RESULTS: The crude hazard ratio (HR) of SSRI use versus no SSRI use on hip fracture was 1.75 (95%CI: 1.12, 2.72) in Mondriaan and 2.09 (1.89, 2.32) in BIFAP. After confounding adjustment using time-varying Cox regression, stratification, and covariate adjustment using the PS, HRs increased in Mondriaan [2.59 (1.63, 4.12), 2.64 (1.63, 4.25), and 2.82 (1.63, 4.25), respectively] and decreased in BIFAP [1.56 (1.40, 1.73), 1.54 (1.39, 1.71), and 1.61 (1.45, 1.78), respectively]. MSMs with stabilized weights yielded HR 2.15 (1.30, 3.55) in Mondriaan and 1.63 (1.28, 2.07) in BIFAP when accounting for censoring and 2.13 (1.32, 3.45) in Mondriaan and 1.66 (1.30, 2.12) in BIFAP without accounting for censoring. CONCLUSIONS: In this empirical study, differences between the different methods to control for time-dependent confounding were small. The observed differences in treatment effect estimates between the databases are likely attributable to different confounding information in the datasets, illustrating that adequate information on (time-varying) confounding is crucial to prevent bias.

The Effect of Eighteen-Month Metformin Treatment in Obese Adolescents: Comparison of Results Obtained in Daily Practice with Results from a Clinical Trial.

Background. In a recent randomized controlled trial (RCT) in obese adolescents, 18 month-treatment with metformin versus placebo was reported to lead to stabilisation of the BMI. This study aimed to compare the effect of metformin on BMI in obese adolescents in daily practice versus results obtained in an RCT. Methods. Obese adolescents treated off label with metformin in daily practice in an outpatient clinic with a follow-up of ≥18 months were identified. Anthropometric and biochemical data were collected at baseline and at 18 months. Patients treated with metformin for 18 months in an RCT were used for comparison. BMI was compared between the two groups. Results. Nineteen patients (median age 14.3 (interquartile range 11.7-15.7) years, BMI 31.3 (28.8-33.8) kg/m2) treated in daily practice were compared to 23 patients receiving metformin in the RCT (age 13.6 (12.6-15.3) years, BMI 29.8 (28.1-34.5) kg/m2). BMI change after 18 months was -0.36 (-2.10-1.58) versus +0.22 (-2.87-1.27) kg/m2 for the two groups, respectively. In the multivariable model, BMI change was not statistically significantly different between the two groups (p = 0.61). Conclusion. Treatment with metformin in obese adolescents in daily practice resulted in a comparable change in BMI as observed in an RCT. This trial is registered with ClinicalTrials.gov number: NCT01487993.

Regulatory scientific advice on non-inferiority drug trials.

The active-controlled trial with a non-inferiority design has gained popularity in recent years. However, non-inferiority trials present some methodological challenges, especially in determining the non-inferiority margin. Regulatory guidelines provide some general statements on how a non-inferiority trial should be conducted. Moreover, in a scientific advice procedure, regulators give companies the opportunity to discuss critical trial issues prior to the start of the trial. The aim of this study was to identify potential issues that may benefit from more explicit guidance by regulators. To achieve this, we collected and analyzed questions about non-inferiority trials posed by applicants for scientific advice in Europe in 2008 and 2009, as well as the responses given by the European Medicines Agency (EMA). In our analysis we included 156 final letters of advice from 2008 and 2009, addressed to 94 different applicants (manufacturers). Our analysis yielded two major findings: (1) applicants frequently asked questions 'whether' and 'how' to conduct a non-inferiority trial, 26% and 74%, respectively, and (2) the EMA regulators seem mainly concerned about the choice of the non-inferiority margin in non-inferiority trials (36% of total regulatory answers). In 40% of the answers, the EMA recommended using a stricter margin, and in 10% of the answers regarding non-inferiority margins, the EMA questioned the justification of the proposed non-inferiority margin. We conclude that there are still difficulties in selecting the appropriate methodology for non-inferiority trials. Straightforward and harmonized guidance regarding non-inferiority trials is required, for example on whether it is necessary to conduct such a trial and how the non-inferiority margin is determined. It is unlikely that regulatory guidelines can cover all therapeutic areas; therefore, in some cases regulatory scientific advice may be used as an opportunity for tailored advice.

Differences in interaction and subgroup-specific effects were observed between randomized and nonrandomized studies in three empirical examples.

OBJECTIVE: To determine the comparability of subgroup-specific and interaction effects (differences between subgroups) between different study designs. STUDY DESIGN AND SETTING: We compared effects of interventions based on observational studies, randomized clinical trials (RCTs), and individual patient data meta-analyses (IPDMAs) of RCTs (reference) on three clinical topics: (1) mammography screening and breast cancer mortality, (2) coronary artery bypass surgery (CABG) and all-cause mortality, and (3) statins and incidence of major coronary events. Main, subgroup-specific, and interaction effects were compared. RESULTS: Main and subgroup-specific effects were comparable with respect to the direction of the effects. Differences in the magnitude of subgroup-specific effects in observational studies yielded different interactions compared with those in IPDMA. In the mammography example, the ratio of risk ratios (RRR) (i.e., interaction effect) among observational studies was 1.46 [95% confidence interval (CI): 1.09, 1.96] compared with an IPDMA effect of 1.10 (95% CI: 0.89, 1.37). For the CABG studies, the observational RRR was 1.03 (95% CI: 0.84, 1.26), whereas in the IPDMA, this was 1.40 (95% CI: 1.08, 1.1.81). Finally, in the statin example, the RRR was 1.35 (95% CI: 1.13, 1.61) and 0.90 (95% CI: 0.84, 0.97) for observational studies and IPDMA, respectively. CONCLUSION: Main and subgroup-specific effects based on observational data were similar to main and subgroup-specific effects in IPDMAs based on RCTs, yet interactions differed.

Drug costs associated with non-adherence to cholesterol management guidelines for primary prevention of cardiovascular disease in an elderly population: the Rotterdam study.

BACKGROUND: In The Netherlands, costs of HMG-CoA reductase inhibitor (statin) use have recently increased sharply compared with costs of other drugs. However, several studies have established both undertreatment and non-guidelines-indicated treatment with statins, suggesting a suboptimal use of resources. OBJECTIVE: To estimate the drug costs associated with non-guidelines-indicated treatment and undertreatment with statins in an elderly population. PATIENTS AND SETTING: Data were obtained from the Rotterdam Study, a population-based prospective cohort study which began in 1990 with 7983 participants aged > or =55 years. Subjects with a history of cardiovascular disease (CVD) were excluded. Pharmacy records were used to assess patterns of medication use in daily medical practice. MAIN OUTCOME MEASURE: Non-guidelines-indicated treatment and undertreatment with statins were established in relation to Dutch cholesterol management guidelines for all participants. We calculated the costs of statin therapy associated with non-guidelines-indicated treatment, and the costs of statins if all those undertreated were to receive statins. The results were projected on to the Dutch population to determine the economic implications of non-adherence to cholesterol management guidelines in the elderly. RESULTS: Of the participants who started treatment with statins for the primary prevention of CVD during follow-up, 69% received non-guidelines-indicated treatment. More men (7.5%) were undertreated than women (1.6%) and more women (6.2%) received non-guidelines-indicated treatment than men (1.5%). Among the participants without CVD who were still alive at 1 January 2002, 14% were eligible for statin therapy but were untreated. After projection of the prevalence of non-guidelines-indicated treatment and undertreatment to the Dutch population, the absolute costs for non-guidelines-indicated treatment with statins in 2005 were estimated to be approximately 23 million euro(uncertainty limits [UL]: 19-28 million euro), while the cost to eliminate undertreatment was also 23 million euro (UL: 19-28 million euro). CONCLUSION: Reallocation of resources used for statin therapy from those receiving non-guidelines-indicated treatment to those being undertreated could lead to a more efficient use of resources.

The trade-off between cardiovascular and gastrointestinal effects of rofecoxib.

BACKGROUND: The cyclooxygenase-2 (COX-2) inhibitor rofecoxib was registered in 1999. By 2000, the first reports were published indicating that the agent was possibly associated with an increased risk of myocardial infarction. Since then a surge of data supporting this association has become available. To interpret these data it is essential to ascertain the cardiovascular risk profile of users of rofecoxib relative to other non-steroidal anti-inflammatory drug (NSAID) recipients. OBJECTIVE: To assess differences in cardiovascular risk between starters of rofecoxib versus starters of any other NSAID. SETTING: Data sampled from a representative research network of Dutch general practitioners (GPs) in 2001. DESIGN: New users (starters) of rofecoxib were compared to starters of any other NSAID, unmatched and matched on age, gender, and indication nested in the cohort of the second Dutch National Survey of General Practice. RESULTS: A total of 40.4% of patients starting on rofecoxib had cardiovascular co-morbidity. Patients starting on rofecoxib were twice more likely to have a history of gastrointestinal (GI) morbidity, compared to patients starting on other NSAIDs (OR(adj) = 2.09; 95%CI = 1.65-2.66). These patients were also more likely to have cardiovascular co-morbidity (OR = 1.90; 95%CI = 1.60-2.24) compared to recipients of rofecoxib with no GI co-morbidity. Cardiovascular morbidity was present at the time of rofecoxib exposure in over 61% of carriers of a composite risk profile including age 60 years or older, GI co-morbidity and diagnosis of rheumatoid arthritis and osteoarthritis. CONCLUSIONS: In general, a typical recipient of an NSAID is aged and carrier of a serious cardiovascular risk profile. Selective prescribing of rofecoxib to provide claimed gastroprotection, indirectly and unintentionally resulted in prescribing rofecoxib in a population with high frequencies of cardiovascular morbidities.