The effects of physician specialty and patient comorbidities on the use and discontinuation of coxibs

Reducing Bias Amplification in the Presence of Unmeasured Confounding Through Out-of-Sample Estimation Strategies for the Disease Risk Score

The prognostic score, or disease risk score (DRS), is a summary score that is used to control for confounding in non-experimental studies. While the DRS has been shown to effectively control for measured confounders, unmeasured confounding continues to be a fundamental obstacle in non-experimental research. Both theory and simulations have shown that in the presence of unmeasured confounding, controlling for variables that affect treatment (both instrumental variables and measured confounders) amplifies the bias caused by unmeasured confounders. In this paper, we use causal diagrams and path analysis to review and illustrate the process of bias amplification. We show that traditional estimation strategies for the DRS do not avoid bias amplification when controlling for predictors of treatment. We then discuss estimation strategies for the DRS that can potentially reduce bias amplification that is caused by controlling both instrumental variables and measured confounders. We show that under certain assumptions, estimating the DRS in populations outside the defined study cohort where treatment has not been introduced, or in outside populations with reduced treatment prevalence can control for the confounding effects of measured confounders while at the same time reduce bias amplification.

Selective prescribing of simvastatin and atorvastatin by patient characteristics at treatment initiation over a 7-year period in Finland

PURPOSE

The aim of the study was to investigate preferential initiation with the two most frequently used statins, simvastatin and atorvastatin, by patient characteristics over time.

METHODS

Statin initiators without a statin prescription during the 365 days preceding the initiation from 1 January 1998 through 31 December 2004 were captured from the nation-wide Prescription Register in Finland. Associations of demographic factors and morbidities with atorvastatin versus simvastatin at initiation of statin treatment were analysed by a logistic regression model adjusted for significant covariates separately for each year.

RESULTS

Of all new statin users in 1998, atorvastatin was chosen for 18% and simvastatin for 39%. In 2004, the corresponding figures were 32 and 38%. Atorvastatin was more likely than simvastatin to be initiated in younger age groups than in persons older than 74 years (reference group). Initiation with atorvastatin was less likely for people with than without coronary artery disease; adjusted odds ratios ranged from 0.62 to 0.73 over the years 1998-2003.

CONCLUSION

Channelling of atorvastatin over simvastatin toward the younger and healthier population was found during the first 4 years after its launch in Finland. Channelling may lead to confounding by indication, which must be taken into account when designing pharmacoepidemiology studies on statins.

Coxibs: evolution of prescription's behaviour in France

The aim of the present study was, first to characterize profiles of coxibs' prescribers [general practitioners (GPs) and rheumatologists] in 2002 in France and, secondly, to identify factors associated with modification of this profile 1 year later. All GPs and rheumatologists from Midi-Pyrenees, Aquitaine, Languedoc-Roussillon and Pays de Loire areas (South of France: 11 050 000 inhabitants) were included in the study. For each practitioner, we used data concerning all non-steroidal anti-inflammatory drugs (NSAIDs) including coxibs reimbursed during period 1 (P1; January-March 2002) and period 2 (P2; January-March 2003). The ratio between the number of coxibs' prescriptions and the total number of NSAIDs' prescriptions (including coxibs) was used to define the two profiles of prescribers, one with a low level of coxibs' prescriptions and another one with a high level of coxibs' prescriptions. Characteristics of practitioners and characteristics of their practices were compared according to this profile. In the second step, we investigated the characteristics (of practitioners and practices) associated with an increase in the level of coxibs' prescriptions in P2 for practitioners with a low level of coxibs' prescriptions in P1. Results are expressed as odds ratio with their 95% confidence intervals. A positive statistical link was found between a high level of coxibs' prescriptions, the speciality of rheumatologist or extra costs for consultation. In contrast, a negative association was observed with female gender or age below 44 years. No relationship was found with the status of referent. Concerning practices' characteristics of practitioners, there was a positive statistical link between a high ratio of coxibs' prescriptions and high co-prescriptions of gastroprotective agents and a negative association with a high number of acts, a high proportion of patients with chronic disabling diseases (CDD) or a high number of patients between 15 and 64 years. There was no statistical link with proportion of patients covered by Universal Medical Coverage (UMC) or aged more than 65 years. Among the factors involved in the increase in the ratio (between P1 and P2), no relationship was found with practitioners' characteristics. In contrast, some factors related to practices (level of gastroprotective co-prescriptions, number of acts, number of CDD patients) were related to a change in coxibs' prescriptions between P1 and P2. This study allowed to discuss some relationships between coxibs' prescription and practitioners' (age, gender, medical speciality or extra costs for consultation) or practices' (level of medical practice, patients' age, number of CDD patients or level of gastroprotective prescriptions) characteristics. In contrast, some other factors like the referent status or the number of patients with UMC are not related. Physicians, initially low prescribers of coxibs and increasing their coxibs' prescriptions during the period of our study, were those with a high level of gastroprotective prescriptions, a low number of acts or a small proportion of CDD patients.

Assessment of coxib utilization by rheumatologists for nonsteroidal antiinflammatory drug gastroprotection prior to the coxib market withdrawals

OBJECTIVE

To examine cyclooxygenase 2 inhibitor (coxib) utilization by rheumatologists for patients receiving nonsteroidal antiinflammatory drugs (NSAIDs) prior to the coxib market withdrawals.

METHODS

A prospective study of patients with rheumatoid arthritis enrolled in the Consortium of Rheumatology Researchers of North America registry was performed.

RESULTS

Of 1,833 patients receiving prescription NSAIDs, 1,380 (75.3%) received gastroprotection, defined as either coxib monotherapy and/or gastroprotective agent (GPA) cotherapy, and 1,207 (65.8%) received coxibs. The distribution of gastroprotective strategies included 860 (46.9%) patients who were prescribed coxib monotherapy, 347 (18.9%) prescribed dual coxib plus GPA cotherapy, 173 (9.4%) prescribed a nonselective NSAID (NS-NSAID) plus GPA cotherapy, and 453 (24.7%) prescribed an NS-NSAID without GPA cotherapy. For patients with 0, 1, and > or =2 identifiable gastrointestinal (GI) risk factors, coxib prescribing rates as a proportion of NSAID agents were 64.1%, 66.4%, and 68.6%, respectively; among dual aspirin/NSAID users, coxib prescribing rates were 66.2%, 78.3%, and 68.5% of NSAID prescriptions, respectively.

CONCLUSION

The majority of NSAID users were prescribed a gastroprotective strategy, primarily attributable to coxib utilization. Coxib utilization rates were consistently high across all levels of GI risk, including patients without identifiable risk factors. These data indicate that rheumatologists broadly adopted the coxib class of NSAIDs in a nonselective manner with respect to underlying GI risk and concomitant aspirin use. As novel therapeutic classes are introduced, early evaluation of prescribing patterns using arthritis registries can determine the appropriateness of prescribing patterns and may improve patient outcomes.

Evaluating short-term drug effects using a physician-specific prescribing preference as an instrumental variable

BACKGROUND

Postmarketing observational studies of the safety and effectiveness of prescription medications are critically important but fraught with methodological problems. The data sources available for such research often lack information on indications and other important confounders for the drug exposure under study. Instrumental variable methods have been proposed as a potential approach to control confounding by indication in nonexperimental studies of treatment effects; however, good instruments are hard to find.

METHODS

We propose an instrument for use in pharmacoepidemiology that is based on a time-varying estimate of the prescribing physician's preference for one drug relative to a competing therapy. The use of this instrument is illustrated in a study comparing the effect of exposure to COX-2 inhibitors with nonselective, nonsteroidal antiinflammatory medications on gastrointestinal complications.

RESULTS

Using conventional multivariable regression adjusting for 17 potential confounders, we found no protective effect due to COX-2 use within 120 days from the initial exposure (risk difference = -0.06 per 100 patients; 95% confidence interval = -0.26 to 0.14). However, the proposed instrumental variable method attributed a protective effect to COX-2 exposure (-1.31 per 100 patients; -2.42 to -0.20) compatible with randomized trial results (-0.65 per 100 patients; -1.08 to -0.22).

CONCLUSIONS

The instrumental variable method that we have proposed appears to have substantially reduced the bias due to unobserved confounding. However, more work needs to be done to understand the sensitivity of this approach to possible violations of the instrumental variable assumptions.

Effect of cardiovascular comorbidities and concomitant aspirin use on selection of cyclooxygenase inhibitor among rheumatologists

OBJECTIVE

To evaluate the effects of cardiovascular comorbidities and aspirin coprescription on cyclooxygenase (COX)-2 inhibitor (coxib) prescribing patterns among rheumatologists.

METHODS

A prospective cohort study was carried out with rheumatoid arthritis and osteoarthritis patients in the Consortium of Rheumatology Researchers of North America registry. Medication and comorbidity data were obtained prospectively from physician and patient questionnaires between March 2002 and September 2003. Multivariate adjusted associations between coxib use and specific cardiovascular variables, including aspirin use, were examined.

RESULTS

A total of 3,522 arthritis patients were included. COX inhibitors, including coxibs, nonselective nonsteroidal antiinflammatory drugs (NSAIDs), and meloxicam, were prescribed to a larger proportion of osteoarthritis patients (68.4%) than rheumatoid arthritis patients (47.1%) in our study (P < 0.001). COX inhibitors were prescribed to the majority of aspirin users (51.5%) and a similar proportion of nonusers (49.8%). In multivariate analyses, independent predictors of coxib use versus nonselective NSAID use included diagnoses of osteoarthritis (odds ratio [OR] 2.52, 95% confidence interval [95% CI] 1.81-3.52) and diabetes (OR 1.63, 95% CI 1.06-2.51). Conversely, aspirin use independently predicted selection of a nonselective NSAID rather than a coxib (OR 0.73, 95% CI 0.55-0.98). Neither a history of myocardial infarction nor stroke predicted utilization of a coxib. Similarly, cardiovascular variables did not predict the use of rofecoxib versus celecoxib.

CONCLUSION

Our data indicate that COX inhibitor coprescription among aspirin users is frequent. Despite cardiovascular concerns regarding the coxibs, our data suggest that aspirin use, but not cardiovascular comorbidities, predicted the selection of nonselective NSAIDs over coxibs.

Pain management in osteoarthritis: A focus on onset of efficacy—a comparison of rofecoxib, celecoxib, acetaminophen, and nabumetone across four clinical trials

We compared onset of efficacy (during days 1 to 6) of 2 coxibs (rofecoxib, celecoxib) with acetaminophen and nabumetone by using a prespecified approach to data from 4 similarly designed 6-week randomized osteoarthritis trials. In 2 trials, rofecoxib (12.5 mg and 25 mg once daily) was compared with celecoxib (200 mg once daily) and acetaminophen (4000 mg daily). In the other 2 trials, rofecoxib (12.5 mg) was compared with nabumetone (1000 mg once daily) and placebo. Efficacy end points included Patient Global Response to Therapy and Western Ontario and McMaster Osteoarthritis Index scores. Rofecoxib (12.5- and 25-mg doses) consistently demonstrated a faster onset of osteoarthritis (OA) efficacy than the comparator drugs during the first 6 days of therapy of OA patients experiencing "flare." Acetaminophen resulted in the slowest onset of efficacy. There was a strong correlation (0.7) between efficacy response during days 1 to 6 and that averaged over 6 weeks. Rates of discontinuation as a result of lack of efficacy were significantly lower (P < .02) for each of the coxib-treated groups compared with acetaminophen and for rofecoxib 12.5 mg (P = .01) compared with nabumetone. Rofecoxib treatment, with its faster onset of OA efficacy and lower rates of related discontinuations, might provide efficacy advantages in the treatment of OA pain.

PERSPECTIVE

The efficacy of rofecoxib, celecoxib, nabumetone, and acetaminophen is established for the majority of OA patients within the first 6 days of therapy, and this predicts efficacy during the longer term. Rofecoxib provides significantly faster time to onset of efficacy and better improvement on multiple measures versus the comparators.