Channelling of patients taking NSAIDs or cyclooxygenase-2-specific inhibitors and its effect on interpretation of outcomes

Core concepts in pharmacoepidemiology: Key biases arising in pharmacoepidemiologic studies

Pharmacoepidemiology has an increasingly important role in informing and improving clinical practice, drug regulation, and health policy. Therefore, unrecognized biases in pharmacoepidemiologic studies can have major implications when study findings are translated to the real world. We propose a simple taxonomy for researchers to use as a starting point when thinking through some of the most pervasive biases in pharmacoepidemiology. We organize this discussion according to biases best assessed with respect to the study population (including confounding by indication, channeling bias, healthy user bias, and protopathic bias), the study design (including prevalent user bias and immortal time bias), and the data source (including misclassification bias and missing data/loss to follow up). This tutorial defines, provides a curated list of recommended references, and illustrates through relevant case examples these key biases to consider when planning, conducting, or evaluating pharmacoepidemiologic studies.

Major bleeding risk associated with warfarin and co-medications in the elderly population

PURPOSE

Warfarin management in the elderly population is complex as medicines prescribed for concomitant diseases may further increase the risk of major bleeding associated with warfarin use. We aimed to quantify the excess risk of bleeding-related hospitalisation when warfarin was co-dispensed with potentially interacting medicines.

METHODS

A retrospective cohort study was undertaken over a 4-year period from July 2002 to June 2006 to examine bleeding risk associated with medications co-administered in patients taking warfarin using an administrative claims database from the Australian Department of Veterans' Affairs. All veterans aged 65 years and over who were new users of warfarin were followed until death or study end. Risk of bleeding was assessed using a Poisson GEE model adjusting for age, gender, socioeconomic status, co-morbidity index, previous bleeding related hospitalisations and indicators of health service use.

RESULTS

Overall, 17661 veterans who used warfarin at any time during the study period were included. The overall incidence rate of bleeding-related hospitalisations was 4.1 (95% CI 3.7-4.6) per 100 person-years in veterans who were not receiving potentially interacting medicines. Bleeding-related hospitalisation rates were significantly increased when warfarin was co-prescribed with low-dose aspirin (Adjusted rate ratio (AdjRR) 1.44, 95% CI 1.00-2.07), clopidogrel (AdjRR 2.23, 95% CI 1.48–3.36), clopidogrel with aspirin (AdjRR 3.44, 95% CI 1.28-9.23), amiodarone (AdjRR 3.33, 95% CI 1.38–8.00) and antibiotics (AdjRR 2.34, 95% CI 1.55-3.54).

CONCLUSIONS

Models assessing bleeding risk with warfarin should take account of the range of potentially harmful medicine combinations used in elderly people with comorbid conditions.

Sensory and vascular changes in a rat monoarthritis model: prophylactic and therapeutic effects of meloxicam

OBJECTIVE AND DESIGN

The objective of this study was to determine the ability of meloxicam prophylaxis and therapy to blunt the effect of complete Freund's adjuvant (CFA) induced monoarthritis.

MATERIALS AND METHODS

First the validity of this animal model was established by examining joint changes at multiple levels after injecting CFA into the tibio-tarsal joint. Next, meloxicam (5 mg/kg) or vehicle was administered on days 0-7 (prophylactic) and on days 7-16 (therapeutic) in separate groups of animals.

RESULTS

The CFA-injected joint demonstrated hallmark histological and structural changes such as pannus formation, bone remodeling, cartilage erosion and immune cell infiltration. Both prophylactic and therapeutic treatment with meloxicam effectively reduced swelling (ankle circumference), oedema and extravasation of Evans blue dye in the affected joint. Moreover, meloxicam reduced loss in range of motion and also reduced mechanical stimulus evoked pain scores. Notably, these effects persisted after discontinuing drug treatment.

CONCLUSION

The present study provides a unique comparison of prophylactic versus therapeutic effects of meloxicam in the CFA-induced model of monoarthritis.

Discrepancy among observational studies: example of naproxen-associated adverse events

Background:

Observational studies assessing the cardiovascular adverse effect of naproxen have had conflicting results. It is not clear whether variation in population characteristics between studies may explain some of this discrepancy.

Objective:

To determine whether changes in patient characteristics of naproxen users occurred between 1999 and 2004 in Québec, Canada and to examine whether these temporal changes were accompanied by changes in estimates of naproxen-related hospitalizations for gastrointestinal (GI) ulcers and myocardial infarction, using provincial health services administrative databases.

Methods:

Demographic, pharmaceutical and physician billing records of patients 65 years and older, who received naproxen or acetaminophen prescriptions between 1999 and 2004 were used. Two identical cohort studies, labeled Study 1 and Study 2 were conducted and their results were compared. One study was confined to the time period 1999-2001 and the other to 2002-2004. Patient characteristics at index date (the date of the first naproxen or acetaminophen prescription during the corresponding period) were compared between the study cohorts in naproxen and acetaminophen users, respectively, and within each study cohort between naproxen and acetaminophen users, using logistic regression models. Cox regression models with time dependent exposure were used to assess the association between naproxen vs acetaminophen and hospitalizations for GI events or AMI, respectively within each study. Results were then compared between the two studies.

Results:

Study 1 (1999-2001) cohort included 240,568 patients (205,238 acetaminophen and 35,330 naproxen) and Study 2 (2002-2004) cohort included 213,802 patients (193,918 acetaminophen and 19,884 naproxen). Patient characteristics of naproxen and acetaminophen users differed between the two studies. Naproxen users in Study 2 vs Study 1 were slightly younger, less likely to be females, less likely to have concomitant GI disease, less likely to have osteoarthritis and other co-morbidities and more likely to have used proton pump inhibitors, antihypertensive agents, anticoagulants, clopidogrel and aspirin. In general, similar changes in patient characteristics were observed in acetaminophen users between the two study cohorts. Compared to acetaminophen (without aspirin), the estimates of the GI risks with naproxen whether, used with or without aspirin, were significantly higher in Study 2 vs Study 1 [Hazard Ratio (HR) (95% CI): 4.94 (3.48, 7.02)] vs [2.22 (1.62, 3.06)], naproxen with aspirin [4.94 (2.93, 8.33) vs 2.47 (1.48, 4.12)], and acetaminophen and aspirin: [2.31 (1.89, 2.82) vs 1.46 (1.20, 1.77)]. The estimate of the AMI risk with naproxen also seemed to be higher in Study 2 vs Study 1, however the increase was not statistically significant [HR (95% CI) in the naproxen group: 1.18 (0.83, 1.67) in Study 1 vs 0.94 (0.70, 1.25) in Study 2], naproxen with aspirin. [1.44 (0.95, 2.18) vs 1.05 (0.68, 1.61)]; and acetaminophen and aspirin. 1.15 (1.01, 1.30) vs 1.10 (0.97, 1.26).

Conclusion:

Variation in patient characteristics in naproxen users was observed between 1999 and 2004. This variation was likely to be accompanied by a variation in patient pre-disposition to GI events that may explain the increase in estimates of naproxen-related GI adverse events observed during this period.

Postdischarge thromboprophylaxis and mortality risk after hip-or knee-replacement surgery

BACKGROUND

Patients undergoing hip or knee replacement are at high risk of developing a postoperative venous thromboembolism even after discharge from hospital. We sought to identify hospital and patient characteristics associated with receiving thromboprophylaxis after discharge and to compare the risk of short-term mortality among those who did or did not receive thromboprophylaxis.

METHODS

We conducted a retrospective cohort study using system-wide hospital discharge summary records, physician billing information, medication reimbursement claims and demographic records. We included patients aged 65 years and older who received a hip or knee replacement and who were discharged home after surgery.

RESULTS

In total we included 10 744 patients. Of these, 7058 patients who received a hip replacement and 3686 who received a knee replacement. The mean age was 75.4 (standard deviation [SD] 6.8) years and 38% of patients were men. In total, 2059 (19%) patients received thomboprophylaxis at discharge. Patients discharged from university teaching hospitals were less likely than those discharged from community hospitals to received thromboprophylaxis after discharge (odds ratio [OR] 0.89, 95% confidence interval [CI] 0.80-1.00). Patients were less likely to receive thromboprophylaxis after discharge if they had a longer hospital stay (15-30 days v. 1-7 days, OR 0.69, 95% CI 0.59-0.81). Patients were more likely to receive thromboprophylaxis if they had hip (v. knee) replacement, osteoarthritis, heart failure, atrial fibrillation or hypertension, higher (v. lower) income or if they were treated at medium-volume hospitals (69-116 hip and knee replacements per year). In total, 223 patients (2%) died in the 3-month period after discharge. The risk of short-term mortality was lower among those who received thromboprophylaxis after discharge (hazard ratio [HR] 0.34, 95% CI 0.20-0.57).

INTERPRETATION

Fewer than 1 in 5 elderly patients discharged home after a hip-or knee-replacement surgery received postdischarge thromboprophylaxis. Those prescribed these medications had a lower risk of short-term mortality. The benefits of and barriers to thromboprophylaxis therapy after discharge in this population requires further study.