Pharmacoepidemiology: Using randomised control trials and observational studies in clinical decision-making

Statin Use and Amyotrophic Lateral Sclerosis Survival: A Population-Based Cohort Study

BACKGROUND

Dyslipidemia is common in amyotrophic lateral sclerosis (ALS). Statin use has been associated with both favorable and poor prognoses. We assessed whether statin use affects ALS survival.

METHODS

We linked four Norwegian health surveys (1972-2003) with mandatory national registries to obtain information on premorbid health, ALS diagnosis, and death. Using the Norwegian Prescribed Drug Registry, we identified participants who had dispensed statins pre- and post-diagnosis. We first compared pre-diagnosis statin discontinuation rates between ALS patients and matched controls. Flexible parametric models were then fitted to estimate the relationship between statin use and survival time in ALS, using restricted mean survival time and hazard ratio (HR) as effect measures.

RESULTS

A total of 524 patients (43% female) with ALS were included. Mean time from ALS diagnosis to death or end of study was 2.0 (SD 2.1) years. A substantial proportion of statin users (21%) discontinued statins during the year leading up to diagnosis. This group was characterized by poorer ALS prognosis compared to those adhering to statins and were included as statin users in our analysis. After adjusting for sex, age, birth year, riluzole use and premorbid smoking status, body mass index, and total cholesterol levels, statin use was not associated with ALS survival. The estimated mean survival difference comparing statin users to non-users was 0.74 (95% CI -5.98 to 7.47) months, corresponding to a HR of 0.97 (95% CI 0.77-1.23).

CONCLUSION

Statin use was not associated with ALS survival, suggesting that statins should not routinely be discontinued in ALS.

Intraoperative transcutaneous electrical acupoint stimulation combined with anesthesia to prevent postoperative cognitive dysfunction: A systematic review and meta-analysis

BACKGROUND

Postoperative cognitive dysfunction (POCD) is associated with an increased risk of dementia and may lead to chronic neurodegeneration. The utilization of intraoperative Transcutaneous Electrical Acupoint Stimulation (TEAS) in conjunction with anesthesia is expected to become an effective preventive measure for POCD in clinical practice.

METHODS

We conducted a comprehensive literature review focusing on the use of TEAS in the prevention of POCD during surgical anesthesia. We searched various databases for relevant literature, including PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI), and Wanfang Data. The synthesis of data was performed using RevMan version 5.4.

RESULTS

Our meta-analysis incorporated data from 20 Randomized Controlled Trials (RCTs) involving 1549 patients. The findings revealed that intraoperative TEAS significantly reduced the incidence of POCD when compared to the control group [Odds Ratio (OR) 0.29, 95% Confidence Interval (CI) 0.22-0.39, p < 0.00001]. Moreover, patients receiving intraoperative TEAS exhibited a significant increase in MMSE scores (MD 1.21, 95% CI 0.53-1.89, p = 0.0005). Additionally, intraoperative TEAS demonstrated efficacy in reducing the contents of perioperative serum S100β protein (S100β), neuron-specific enolase (NSE), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in patients, and the improvement of these indexes may be the potential mechanism of TEAS in preventing POCD.

CONCLUSION

Our results suggest that intraoperative TEAS combined with anesthesia prevents cognitive dysfunction in the immediate postoperative period, however we need additional evidence of its utility in preventing long-term cognitive dysfunction. We advocate for the broader promotion and application of this approach in clinical surgical settings.

TRIAL REGISTRATION

PROSPERO (CRD42023457910).

Case studies of health economic analyses informing pharmaceutical health technology assessments for essential medicine selection and public-sector guidelines in South Africa

BACKGROUND

Constrained resources under universal health coverage (UHC) necessitate a balance between medication costs and essential health system requirements. Policymakers practice priority-setting, as either implicit or explicit rationing, embedded in evidence-informed decision-making processes to guide funding decisions. Health technology assessment (HTA) is a method that may assist explicit evidence-informed priority setting. South Africa developed an official HTA methods guide in 2022, however before this, commissioning and performing economic evaluations was not standardized.

METHODS

We conducted a descriptive collective case study to explore the impact of economic analyses on the selection of, and access to, essential medicines in South Africa. Four cases were purposefully selected, and both official information and secondary data, including media reports, were reviewed. Data elements were extracted and organized in a matrix. Cases were reported narratively with a positivist epistemological approach, presenting the authors' reflections.

RESULTS

We found economic analyses that reflected methodologies described in the HTA guide: international reference pricing, cost-minimization, cost-effectiveness, cost-utility, and budget impact analyses. Economic analyses informing the 'resource-use' domain in the GRADE evidence-to-decision framework supported decision-making, influenced market-shaping with price reductions of interventions through benchmarking (fosfomycin, flucytosine), improved equitable access nationally (flucytosine), and prioritized a defined patient group in a justifiable and transparent manner (bortezomib).

CONCLUSION

A standardized HTA evaluation process guided by a nationally accepted framework is necessary for evidence-informed decision-making. Economic analyses (cost-effectiveness, affordability, and resource use) should be consistently included when making decisions on new interventions.

Adverse Drug Reactions in Children with Congenital Heart Disease: A Scoping Review

BACKGROUND

Congenital heart disease (CHD) is one of the leading causes of death. Safe and timely medical interventions, especially in children, can prolong their survival. The drugs prescribed for children with CHD are mainly based on the outcomes of drug therapy in adults with cardiovascular diseases, and their adverse drug reactions (ADRs) might be different. Therefore, the aim of this study was to investigate ADRs in children with CHD.

METHODS

This was a scoping review conducted in 2023. PubMed, Web of Science, Scopus, the Cochrane Library, Ovid, ProQuest, and Google Scholar databases were searched. All studies that reported ADRs for children with CHD and were published in English by 1 November 2023 were included in this study. Finally, the results were reported using a content analysis method.

RESULTS

A total of 87 articles were included in the study. The results showed that symptoms/signs/clinical findings, and cardiovascular disorders were the most common ADRs reported in children with CHD. The results also showed that most of the ADRs were reported for prostaglandin E1, amiodarone, prostaglandin E2, dexmedetomidine, and captopril, respectively.

CONCLUSION

The review underscores the wide array of ADRs in children with CHD, particularly in antiarrhythmics, diuretics, beta-blockers, anticoagulants, and vasodilators, which affected cardiovascular, respiratory, endocrine, metabolic, genitourinary, gastrointestinal, and musculoskeletal systems. Tailored treatment is imperative, considering individual patient characteristics, especially in the vulnerable groups. Further research is essential for optimizing dosing, pharmacogenetics, and alternative therapies to enhance patient outcomes in CHD management.

Physician and patient adherence in hypertension trials: a point of view on an important issue to resolve

INTRODUCTION

Randomized controlled trials (RCTs) are important sources of evidence that strongly influence guidelines for patient management, including for elevated blood pressure in adults.

AREAS COVERED

Critical questions regarding the interpretation of hypertension trial results have recently increased, especially for concerns over methodology. In particular, investigator adherence to the protocol and patient adherence to investigational drugs are often far from optimal. These issues may be ignored or underreported because physicians' behavior during trials is often not monitored and patients' medication adherence is neither measured adequately nor reported or analyzed in the final report or in the publication. This situation may lead to misinterpretations of study results and misevaluations of the safety and efficacy profile of new drugs. In this short review, the problem of measuring, reporting, and analyzing drug adherence in RCTs is discussed and illustrated with several examples in the field of hypertension.

EXPERT OPINION

The main conclusion is that drug adherence should always be measured in clinical trials, possibly with more than one method. In addition, prespecified analyses of adherence data should be included in the statistical plan of all trials to improve their overall quality.

Real-world effectiveness of intravitreal dexamethasone implants - Comparison between eyes eligible and ineligible for clinical trials and their associated outcomes

BACKGROUND

Concerns about the generalizability of pivotal randomized controlled trials (pRCTs) findings have been raised. We aimed to compare intravitreal dexamethasone implants' (IDIs) effectiveness for diabetic macular edema (DME) and central retinal vein occlusion (CRVO), between eyes eligible and ineligible for pRCTs.

METHODS

This retrospective cohort study analyzed Taiwan's Chang Gung Research Database, including DME or CRVO eyes initiating IDIs during 2015-2020. We classified all treated eyes as eligible or ineligible for pRCTs following major selection criteria of the MEAD and GENEVA trials, and evaluated three-, six-, and twelve-month changes in central retinal thickness (CRT) and visual acuity (VA) after initiating IDIs.

RESULTS

We included 177 IDI-treated eyes (DME: 72.3%; CRVO: 27.7%), of which 39.8% and 55.1% were ineligible for DME and CRVO pRCTs, respectively. LogMAR-VA and CRT changes at different times were comparable in DME eyes eligible (LogMAR-VA difference: 0.11 to 0.16; CRT difference: -32.7 to -96.9 μm) and ineligible (LogMAR-VA difference: -0.01 to 0.15; CRT difference: -54.5 to -109.3 μm) for the MEAD trial. By contrast, CRVO eyes ineligible for the GENEVA trial had greater LogMAR-VA changes (0.37 ~ 0.50) than those eligible (0.05 ~ 0.13), with comparable CRT reductions (eligible eyes: -72.3 to -106.4 μm; ineligible eyes: -61.8 to -110.7 μm) (all p-values <0.05 of the mean differences between eligible and ineligible CRVO eyes for all follow-ups).

CONCLUSIONS

IDIs had similar VA and CRT outcomes among DME eyes, regardless of pRCT-eligibility. However, among CRVO eyes, those ineligible for pRCTs showed greater deterioration in VA than those eligible.

Correlation of effectiveness and tolerability assessments from a pharmacy-based observational study investigating the fixed-dose combination of 400 mg ibuprofen plus 100 mg caffeine for the treatment of acute headache

Introduction

Observational studies are valuable for investigating correlations between patient-reported treatment outcomes. In this study, we report a secondary analysis of a published pharmacy-based observational (patient-centered "real-world" outcomes) study on experiences reported by patients who treated their headache with an over-the-counter analgesic.

Methods

A pharmacy-based exploratory survey was conducted in German community pharmacies. Patients buying a fixed-dose analgesic combination product (400 mg ibuprofen + 100 mg caffeine; IbuCaff) to treat their headache were offered a questionnaire that contained-among others-questions about time to onset of pain relief (OPR), assessment of time to onset of pain relief (AOPR), assessment of efficacy and tolerability, and pain intensity 2 h after intake. A correlation analysis of the data was performed. Moreover, perceived treatment effects compared to other acute headache medications used in the past were collected.

Results

The correlation between OPR and AOPR was high (Spearman rank correlation r = 0.594, p < 0.0001). Headache patients assessed the onset of analgesic action within 15 min as "very fast" and within 30 min as "fast". The other readouts were correlated as well [assessment of efficacy and % pain intensity difference (%PID) at 2 h: r = 0.487; OPR/AOPR and %PID at 2 h: r = 0.295/0.318; OPR/AOPR and assessment of tolerability: r = 0.206/0.397; OPR/AOPR and assessment of efficacy: r = 0.406/0.594; assessment of efficacy and assessment of tolerability: r = 0.608; p < 0.0001 for all correlations]. Compared to previous treatments, most patients (>89%) assessed the speed of analgesic action, efficacy, and tolerability of IbuCaff as equal to or better than for the previous treatment.

Discussion

Headache patients assessed the onset of analgesia within 15 min as "very fast" and within 30 min as "fast". Efficacy assessments for acute headache medication appear to be highly correlated.

Real-World Retrospective Study into the Effects of Oral Semaglutide (As a Switchover or Add-On Therapy) in Type 2 Diabetes

(1) Background: Oral semaglutide represents the first oral GLP-1 RA approved for the treatment of type 2 diabetes mellitus (T2DM). This real-world retrospective study aimed at evaluating its effectiveness and tolerability in the treatment of patients with T2DM when patients switched from a glucose-lowering agent to it and when it was added to the usual therapy. (2) Methods: Adult patients with T2DM taking oral semaglutide and followed in the ASUGI Diabetes Center were identified with the use of electronic medical records between October 2022 and May 2023. (3) Results: A total of 129 patients were recruited. The median follow-up was 6 months. Be it as a switchover or as an add-on therapy, oral semaglutide significantly reduced HbA1c and BMI. Switching from DPPIV inhibitors to oral semaglutide was associated with a significant reduction in HbA1c and BMI, switching from SGLT2 inhibitors was associated with a significant reduction in HbA1c, and switching from sulphonylureas was associated with a significant reduction in BMI. The median HbA1c change was associated with baseline HbA1c. SBP significantly decreased in the add-on group. Oral semaglutide was well tolerated. (4) Conclusions: This study shows that in the real-world setting, oral semaglutide is effective and safe as a switchover or as an add-on therapy for the treatment of T2DM.

Impact of the Neck and/or Shoulder Pain on Self-reported Headache Treatment Responses – Results From a Pharmacy-Based Patient Survey

Neck and/or shoulder pain (NSP) frequently occurs together with headache. Therefore, we explored how patients with and without concomitant NSP differ in their baseline characteristics and in perceived treatment responses to an analgesic. An anonymous survey was performed among 895 patients with headache (735 self-reported tension-type headache [TTH]) who used an analgesic fixed-dose combination containing 400 mg ibuprofen and 100 mg caffeine as a non-prescription treatment. NSP was abundant among patients in our survey (60%) and was associated with >1 additional day of headache per month. Patients with NSP reported predominantly sedentary work more frequently than those without (40 vs. 29%); they also reported physical tension/poor posture as a perceived trigger factor more frequently (70 vs. 16%). The reported pain reduction was comparable in those with and without concomitant NSP regardless of whether assessed as mean pain rating (from about 6 to 1.5 on a 10-point rating scale), patients experiencing a ≥50% in pain reduction (89.6 vs. 88.8%) or becoming pain-free within 2 h (57 vs. 64%). However, recurrence of pain and use of another dose within the same day were more frequent with than without NSP. We conclude that concomitant NSP is frequent in patients with headache but does not substantially alter responses to a non-prescription medication.

Clinical epidemiology and pharmacoepidemiology studies with real-world databases

Hospital-based registry data, including patients' information collected by academic societies or government based research groups, were previously used for clinical research in Japan. Now, real-world data routinely obtained in healthcare settings are being used in clinical epidemiology and pharmacoepidemiology. Real-world data include a database of claims originating from health insurance associations for reimbursement of medical fees, diagnosis procedure combinations databases for acute inpatient care in hospitals, a drug prescription database, and electronic medical records, including patients' medical information obtained by doctors, derived from electronic records of hospitals. In the past ten years, much evidence of clinical epidemiology and pharmacoepidemiology studies using real-world data has been accumulated. The purpose of this review was to introduce clinical epidemiology and pharmacoepidemiology approaches and studies using real-world data in Japan.

Transcutaneous Electrical Acupoint Stimulation for the Prevention of Postoperative Cognitive Dysfunction: A Systematic Review and Meta-Analysis

Background: No specific treatment is available for postoperative cognitive dysfunction (POCD). Recently, interest in the prevention of POCD during the perioperative period has increased. Although some studies suggest that transcutaneous electrical acupoint stimulation (TEAS) may be beneficial, the relevant evidence remains uncertain. Objective: To evaluate the preventive effects of TEAS on POCD. Methods: Seven databases including PubMed, EMBASE, CENTRAL, China National Knowledge Infrastructure (CNKI), Chinese Scientific Journal Database (VIP), Wanfang Database, and Chinese Biomedical Literature Database (CBM) were electronically searched up to April 2021. Two reviewers independently selected the studies, collected data, and assessed the risks of bias and grading of recommendations, assessment, development, and evaluations certainty of the evidence. A meta-analysis of the incidence of POCD, cognitive function score, pain, adverse reactions, and length of hospital stay after surgery was also performed. Results: Twenty-nine randomized controlled trials with 1,994 participants were included. The results of the meta-analysis showed that the TEAS group has a significantly lower incidence of POCD compared with the control group on postoperative days 1 [OR = 0.33 (95%CI: 0.23, 0.47); p < 0.001, I ² = 0%, moderate certainty], 3 [OR = 0.38 (95%CI: 0.29, 0.50); p < 0.001, I ² = 0%, low certainty], and 7 [OR = 0.51 (95%CI: 0.32, 0.81); p = 0.005, I ² = 0%, low certainty] but not on day 5 (p > 0.05, low certainty). Moreover, TEAS improved the Mini-Mental State Examination scores on postoperative days 1, 3, and 7 [MD = 2.44 (95%CI: 1.61, 3.27); p < 0.001, I ² = 93%, low certainty]; [MD = 2.07 (95%CI: 1.53, 2.62); p < 0.001, I ² = 87%, low certainty]; and [MD = 0.49 (95%CI: 0.18, 0.79); p = 0.002, I ² = 21%, low certainty], respectively, but not on day 5 (p > 0.05, very low certainty). TEAS promoted a postoperative analgesic effect within 24 h after surgery. Furthermore, patients receiving TEAS showed a lower incidence of postoperative nausea and vomiting and a shorter hospital stay. Conclusions: Limited evidence suggests that the application of TEAS in the perioperative period is associated with a reduced POCD rate and a protected early postoperative cognitive function.

Sodium-Glucose Co-Transporter 2 Inhibitors (SGLT2i) Exposure and Outcomes in Type 2 Diabetes: A Systematic Review of Population-Based Observational Studies

INTRODUCTION

Sodium-glucose co-transporter 2 inhibitors (SGLT2is) are licensed for the treatment of type 2 diabetes (T2D) and more recently for heart failure with or without diabetes. They have been shown to be safe (from the cardiovascular (CV) perspective) and effective (in terms of glycaemia, and in some cases, in reducing CV events) in extensive randomised controlled trials (RCTs). However, there remain concerns regarding the generalisability of these findings (to those ineligible for RCT participation) and about non-CV safety. For effectiveness, population-based pharmacoepidemiology studies can confirm and extend the findings of RCTs to broader populations and explore safety, for which RCTs are not usually powered, in more detail.

METHODS

A pre-planned and registered ((International PROSPEctive Register Of Systematic Reviews) PROSPERO registration CRD42019160792) systematic review of population-based studies investigating SGLT2i effectiveness and safety, following Meta-analyses Of Observational Studies in Epidemiology (MOOSE) guidelines was conducted.

RESULTS

A total of 37 studies were identified (total n = 1,300,184 adults; total follow-up 910,577 person-years; exposures: SGLT2i class, canagliflozin, dapagliflozin and empagliflozin) exploring CV disease (CVD) outcomes, acute kidney injury (AKI), lower limb amputation (LLA), diabetic ketoacidosis (DKA), bone fracture, urinary tract infection (UTI), genital mycotic infection (GMI), hypoglycaemia, pancreatitis and venous thromboembolism. For CV and mortality outcomes, studies confirmed the associated safety of these drugs and correlated closely with the findings from RCTs, which may extend to primary CVD prevention (major adverse cardiovascular events point estimate range (PER) hazard ratio (HR) 0.78-0.94; hospitalised heart failure PER HR 0.48-0.79). For safety outcomes, SGLT2i exposure was not associated with an increased risk of AKI (PER HR 0.40-0.96), fractures (PER HR 0.87-1.11), hypoglycaemia (PER HR 0.76-2.49) or UTI (PER HR 0.72-0.98). There was a signal for increased association for GMIs (PER HR 2.08-3.15), and possibly for LLA (PER HR 0.74-2.79) and DKA (PER HR 0.96-2.14), but with considerable uncertainty.

CONCLUSION

In T2D, SGLT2is appear safe from the CV perspective and may have associated benefit in primary as well as secondary CVD prevention. For safety, they may be associated with an increased risk of GMI, LLA and DKA, although longer follow-up studies are needed.

Association between antihypertensive treatment and adverse events: systematic review and meta-analysis

OBJECTIVE

To examine the association between antihypertensive treatment and specific adverse events.

DESIGN

Systematic review and meta-analysis.

ELIGIBILITY CRITERIA

Randomised controlled trials of adults receiving antihypertensives compared with placebo or no treatment, more antihypertensive drugs compared with fewer antihypertensive drugs, or higher blood pressure targets compared with lower targets. To avoid small early phase trials, studies were required to have at least 650 patient years of follow-up.

INFORMATION SOURCES

Searches were conducted in Embase, Medline, CENTRAL, and the Science Citation Index databases from inception until 14 April 2020.

MAIN OUTCOME MEASURES

The primary outcome was falls during trial follow-up. Secondary outcomes were acute kidney injury, fractures, gout, hyperkalaemia, hypokalaemia, hypotension, and syncope. Additional outcomes related to death and major cardiovascular events were extracted. Risk of bias was assessed using the Cochrane risk of bias tool, and random effects meta-analysis was used to pool rate ratios, odds ratios, and hazard ratios across studies, allowing for between study heterogeneity (τ2).

RESULTS

Of 15 023 articles screened for inclusion, 58 randomised controlled trials were identified, including 280 638 participants followed up for a median of 3 (interquartile range 2-4) years. Most of the trials (n=40, 69%) had a low risk of bias. Among seven trials reporting data for falls, no evidence was found of an association with antihypertensive treatment (summary risk ratio 1.05, 95% confidence interval 0.89 to 1.24, τ2=0.009). Antihypertensives were associated with an increased risk of acute kidney injury (1.18, 95% confidence interval 1.01 to 1.39, τ2=0.037, n=15), hyperkalaemia (1.89, 1.56 to 2.30, τ2=0.122, n=26), hypotension (1.97, 1.67 to 2.32, τ2=0.132, n=35), and syncope (1.28, 1.03 to 1.59, τ2=0.050, n=16). The heterogeneity between studies assessing acute kidney injury and hyperkalaemia events was reduced when focusing on drugs that affect the renin angiotensin-aldosterone system. Results were robust to sensitivity analyses focusing on adverse events leading to withdrawal from each trial. Antihypertensive treatment was associated with a reduced risk of all cause mortality, cardiovascular death, and stroke, but not of myocardial infarction.

CONCLUSIONS

This meta-analysis found no evidence to suggest that antihypertensive treatment is associated with falls but found evidence of an association with mild (hyperkalaemia, hypotension) and severe adverse events (acute kidney injury, syncope). These data could be used to inform shared decision making between doctors and patients about initiation and continuation of antihypertensive treatment, especially in patients at high risk of harm because of previous adverse events or poor renal function.

REGISTRATION

PROSPERO CRD42018116860.

Medications for attention-deficit/hyperactivity disorder in individuals with or without coexisting autism spectrum disorder: analysis of data from the Swedish prescribed drug register

BACKGROUND

Clinical studies found that medication for attention-deficit/hyperactivity disorder (ADHD) is effective in coexisting autism spectrum disorder (ASD), but current research is based on small clinical studies mainly performed on children or adolescents. We here use register data to examine if individuals with ADHD and coexisting ASD present differences in the prescribing patterns of ADHD medication when compared to individuals with pure ADHD.

METHODS

Data with information on filled prescriptions and diagnoses was retrieved from the Swedish Prescribed Drug Register and the National Patient Register. We identified 34,374 individuals with pure ADHD and 5012 individuals with ADHD and coexisting ASD, aged between 3 and 80 years. The first treatment episode with ADHD medications (≥ 2 filled prescriptions within 90 days) and daily doses of methylphenidate during a 3-year period was measured. Odds ratios (ORs) were calculated for the likelihood of being prescribed ADHD medication in individuals with and without ASD and Wilcoxon rank-sum test was used to compare group differences in dose per day.

RESULTS

Individuals with ADHD and coexisting ASD were less likely to start continuous treatment with ADHD medication (ADHD 80.5%; ADHD with ASD 76.2%; OR, 0.80; 95% confidence interval, 0.75-0.86), were less likely to be prescribed methylphenidate, and were more commonly prescribed second line treatments such as dexamphetamine, amphetamine, or modafinil. No group difference was observed for atomoxetine. In adults with ADHD and coexisting ASD, methylphenidate was prescribed in lower daily doses over three years as compared to individuals with pure ADHD.

CONCLUSIONS

The findings indicate that there are differences in the medical treatment of individuals with or without ASD. If these differences are due to different medication responses in ASD or due to other factors such as clinicians' perceptions of medication effects in patients with ASD, needs to be further studied.

Pharmacoepidemiology: Using randomised control trials and observational studies in clinical decision-making

Weighing up sources of evidence is a key skill for clinical decision-makers. Randomised controlled trials (RCTs) and observational studies each have advantages and disadvantages, and in both cases perceived weaknesses can be improved through modifications of design and analysis. In the field of pharmacoepidemiology, RCTs are the best way to determine whether an intervention modifies an outcome being studied, largely because randomisation reduces bias and confounding. Observational studies are useful to investigate whether benefits/harms of a treatment are seen in day-to-day clinical practice in a wider group of patients. Although observational studies, even in a small cohort, can provide very useful clinical evidence, they may also be misleading (as shown by subsequent RCTs), in part because of allocation bias. There is an unmet need for clinicians to become well versed in appraising the study design and statistical analysis of observational pharmacoepidemiology (OP) studies, rather like the medical training already offered for RCT evaluation. This is because OP studies are likely to become more common with the computerisation of healthcare records and increasingly contribute to the evidence base available for clinical decision-making. However, when the results of an RCT conflict with the results of an OP study, the findings of the RCT should be preferred, especially if its findings have been repeated elsewhere. Conversely, OP studies that align with the findings of RCTs can provide rich and useful information to complement that generated by RCTs.