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Risk for Death Associated with Medications for Recently Diagnosed COPD
Submit responseTo the Editor:
In their pharmacoepidemiology study, Lee and colleagues (1) report the possible association between ipratropium and elevated risk for all-cause and cardiovascular mortality in patients with newly diagnosed chronic obstructive pulmonary disease (COPD). During an Evidence Based Medicine presentation for a group of internal medicine residents we studied this paper with keen interest in research methodologies. The paper refers to a cohort of 145 020 veterans with a new diagnosis of COPD, which excludes those not receiving any respiratory treatment. But all-cause mortality analysis in their study included 320 501 control participants, some of whom obviously would not belong to their cohort. This makes one wonder the source of controls, who are supposed to be patients with COPD who were alive at the end of the study period. If the control group had included patients without COPD, the sensitivity analysis for unmeasured confounders (severity of COPD in this case) would be inaccurate. Also, in table 3, patients not on any respiratory medications or those only on short acting beta-agonists were considered as the reference standard. But as per the study protocol, patients who were not on any respiratory medications were excluded from the study.
We understand that much of medical research is observational and the reporting of observational studies is often of insufficient quality. Thus, we study such research in light of The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies (2). However, this type of fundamental law in the study design would not have been appreciated without an in depth review of the paper.
References
1. Lee TA, Pickard S, Au DH, Bartle B, Weiss KB. Risk for death associated with medications for recently diagnosed chronic obstructive pulmonary disease. Ann Intern Med. 2008; 149: 380-390.
2. Von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE Initiative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: Guidelines for Reporting Observational Studies. Ann Intern Med. 2007; 147: 573-577.
Conflict of Interest:
None declared
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Authors' Reply
Submit responseWe thank the correspondents for their thoughtful comments. Drs. Suissa and Ernst raise three concerns about our paper. First, to alleviate concerns that the observed risk for ipratropium and cardiovascular mortality was a result of an increased risk of exacerbations in the cases, we conducted an analysis restricted to those without an exacerbation in the 180 days preceding their event date and found a level of risk (OR 1.45, 95% CI 1.14-1.85) similar to the results reported in the article. Second, unmeasured confounding and bias is one possible explanation for discordant results between the TORCH study and our study. Among the other explanations, the difference in outcomes may be related to the patient populations. The population included in our analysis was older, had higher overall and cause-specific mortality rates, was nearly all male, had more co-existing conditions and had differential respiratory medication use prior to entering the study. Third, we were able to measure medications used within the VA healthcare system during inpatient stays and thus the analysis was not subject to concerns about immeasurable time bias.
Dr. Gross raises concerns about observational studies and our ability to adjust for disease severity and smoking status. The inability to measure smoking status was acknowledged in the paper, and the proportion of current smokers in the ipratropium group needed to be nearly 2.5 times higher than in the comparator group to negate the observed association with ipratropium and cardiovascular mortality. COPD exacerbations and hospitalizations were used to characterize disease severity. The observed association with respiratory mortality and theophylline may have been related to residual confounding by severity, given its place in treatment guidelines. However, this is unlikely to be the case with ipratropium as it is used as a first-line medication in the treatment of COPD. The specific hypotheses tested in this study were based on prior research, including a large prospective study of ipratropium that showed an increased risk of cardiovascular hospitalizations and deaths(1). In addition our findings are consistent with a recent meta-analysis that reported similar risks with anticholinergics and cardiovascular outcomes(2).
Finally, the doctor's notes that socioeconomic status may confound the association between medication use and mortality. An advantage of conducting this analysis among US veterans who received care from Veterans Health Administration is the strong emphasis that VA places on equal access to health care that likely minimizes the effects of socioeconomic status compared to other populations.(3,4)
References
(1) Anthonisen NR, Connett JE, Enright PL, Manfreda J. Hospitalizations and mortality in the Lung Health Study. Am J Respir Crit Care Med. 2002;166:333-39.
(2) Singh S, Loke YK, Furberg CD. Inhaled anticholinergics and risk of major adverse cardiovascular events in patients with chronic obstructive pulmonary disease: a systematic review and meta-analysis. JAMA. 2008;300:1439-50.
(3) Jha AK, Shlipak MG, Hosmer W, Frances CD, Browner WS. Racial differences in mortality among men hospitalized in the Veterans Affairs health care system. JAMA. 2001;285:297-303.
(4) Selim AJ, Fincke G, Berlowitz DR, Cong Z, Miller DR, Ren XS et al. No racial differences in mortality found among Veterans Health Administration out-patients. J Clin Epidemiol. 2004;57:539-42.
Conflict of Interest:
Honoraria: T.A. Lee (Astra-Zeneca, Novartis), D.H. Au (GlaxoSmithKline). Stock ownership or options (other than mutual funds): D.H. Au (Pfizer). Grants received: T.A. Lee (Altana, Aventis, AstraZeneca, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Merck & Co., Novartis, Pfizer, Schering-Plough, Sepracor, University of Kentucky). Other: D.H. Au (Assessing the Impact of Recent Updates for Advair and Serevent Special Issues Board).
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Biases in the study of COPD medications on mortality
Submit responseLee et al report, using an observational study design, that the use of ipratropium is associated with a 34 % increase in the risk of cardiovascular death and the use of inhaled corticosteroids (ICS) is associated with a 20% reduction in all-cause mortality in COPD patients.(1) Some methodological considerations should be addressed in judging the validity of these findings.
The excess risk of cardiovascular death seen with ipratropium (odds ratio 1.34; 95% CI 1.22-1.47) is possibly due to the marked imbalance in the occurrence of COPD exacerbations during the prior 6 months between cases (64%) and controls (22%).(2) While the data analysis adjusted the odds ratio from 1.75 (crude) to 1.34, the statistical approach did not consider the timing of the exacerbation and was thus unable to distinguish whether the cardiac outcomes occur through the increased likelihood of an exacerbation or whether they require the occurrence of an exacerbation. It is possible that a more refined analysis that can take the timing of exacerbations into account could further reduce the adjusted risk.
The protective effect of inhaled corticosteroids (ICS) on all-cause mortality (odds ratio 0.80; 95% CI 0.78-0.83) contradicts the TORCH randomized controlled trial that found a 6% increase in the death rate (rate ratio 1.06; 95% CI 0.89-1.27) with the ICS fluticasone compared with placebo.(3) Unlike observational studies, the randomized controlled trial design avoids the problem of confounding factors, measured and unmeasured, resulting from imbalances between ICS users and non-users.
The study may also have been subject to immeasurable time bias.(4) In a case-control study of mortality involving a chronic illness such as COPD, hospitalizations just prior to death will be common, so that outpatient prescriptions identified from computerized databases cannot be measured during this hospitalized time period. Thus, hospitalizations before death will lead to an apparently lower use of drugs, while being likely associated with an increased risk of death. This phenomenon will thus create the illusion that the drug is effective at preventing mortality. An illustration of this phenomenon using a cohort of COPD patients showed that fatal cases spent more time in hospital prior to death than controls, so that the odds ratio of death associated with ICS use was 0.60, while a data analysis that accounted for the varying out of hospital measurable times changed this odds ratio to 0.98.(4)
While observational studies are essential to evaluate drug safety, their methods can introduce bias.
References
(1) Lee TA, Pickard AS, Au DH, Bartle B, Weiss KB. Risk for death associated with medications for recently diagnosed chronic obstructive pulmonary disease. Ann Intern Med. 2008;149:380-390.
(2) Soler-Cataluna JJ, Martinez-Garcia MA, Roman SP, Salcedo E, Navarro M, Ochando R. Severe acute exacerbations and mortality in patients with chronic obstructive pulmonary disease. Thorax. 2005;60:925-31.
(3) Calverley PM, Anderson JA, Celli B, Ferguson GT, Jenkins C, Jones PW et al. Salmeterol and fluticasone propionate and survival in chronic obstructive pulmonary disease. N Engl J Med. 2007;356:775-89.
(4) Suissa S. Immeasurable time bias in observational studies of drug effects on mortality. Am J Epidemiol. 2008;168:329-35.
Conflict of Interest:
SS and PE have received grants or served on advisory boards for Astra-Zeneca, Boehringer-Ingelheim, GlaxoSmithKline and Sepracor.
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Risk of Death Associated with COPD Medications
Submit responseDespite its very large data base, the study has problems that are inherent in observational data analyses where potential confounding factors cannot be reliably controlled for. Of particular concern in the present study are the absence of data about disease severity and smoking status, as the authors acknowledge. Attempts to adjust for these confounders by reference to a small pilot study of questionable relevance (1) or by internal “measures of disease severity” that are not described in any detail are unreassuring. When the effect size of a treatment of interest, ipratropium versus no ipratropium, is quite small, as here, the inability to adjust with confidence for 2 very weighty confounders throws considerable doubt on the conclusion. Furthermore, after adjustment for covariates the authors calculate the odds ratio for mortality with ipratropium use is reduced to 1.11, which is below the 1.15 threshold of 80% power on which their sample size was calculated.
The inherent methodological problems are probably responsible for a number of other apparent anomalies. I will mention just two. In Table I, the comorbidities hypertension and osteoarthritis appear to be substantially less common in respiratory deaths than case controls; conversely, the use of loop diuretics and digoxin are substantially more common in respiratory deaths. If the odds ratio for each were calculated one might conclude that hypertension and osteoarthritis were protective against, while loop diuretics and digoxin were risk factors for, respiratory death in COPD. Would anyone accept those conclusions?
Secondly in Figure 2, one notes the highest odds ratios for mortality are associated with theophylline usage. But, paradoxically, the risk is seen only in association with respiratory deaths, and not at all with cardiovascular deaths. Theophylline does not have major respiratory side effects. It does, of-course, have serious, sometimes fatal, cardiovascular side effects. How does one make sense of this apparent contradiction?
One is also struck that numerous prospective studies (2) except one very small one (3), have exonerated ipratropium of any associated increase in mortality in COPD, the reverse in fact. The present results could be well explained by disease severity, -a major confounding factor that was not or could not be precisely controlled for. We are left with the uncertainty whether sicker patients received more treatment, or whether the treatment itself contributed to patients’ mortality. I suspect the former.
References
1. Joo MJ, Lee TA, Bartle B, Van de Graaff W, Weiss KB. Patterns of healthcare utilization by COPD severity: a pilot study. Lung 2008;186:307-12
2. Salpeter SR, Buckley NS. Systematic review of clinical outcomes in chronic obstructive pulmonary disease: beta-agonist use compared with anticholinergics and inhaled corticosteroids. Clin Rev Allergy Immunol 2006;31:219-30.
3. Ringbaek T, Viskum K. Is there any association between inhaled ipratropium and mortality in patients with COPD and asthma? Respir Med 2003;97:264-72.
Conflict of Interest:
NJG has received payments for consulting with Boehringer-Ingelheim, GlaxoSmithKline, Altana, Almirall, Forest, Dey, and Astra-Zeneca. NJG has received speaking fees from Astra-Zeneca, Boehringer-Ingelheim, Dey, and Pfizer. I have no investments in any Pharmaceutical Company.
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A potential bias
Submit responseIt is interesting to note that patients taking inhaled corticosteroid (ICS) have reduced mortality in comparison with those taking other types of medication in patients with chronic obstructive pulmonary disease. However, before we start discussion about the direct association of the pharmacological effect of ICS with the reduced mortality, potentially confounding factors to the observation must be considered. Particularly, potential bias in patients deserves attention, as the authors stated. Although the authors proposed a bias in the severity of the disease and smoking status as potential confounders, a potential bias in the sociodemographic distribution among the patients seems to be more relevant to the reduced mortality in patients taking ICS. Although observations in patients with asthma, several studies have suggested that patients with disadvantaged sociodemographic background are less likely to use ICS, either through lower adherence to the treatment (1), or maybe through lower rates of prescription (2). On the other hand, socioeconomic status has been documented to have inverse association with mortality from cardiovascular diseases (3) and other diseases (4). Thus, it is prudent to take these potential confounders into account to adequately appreciate the observed differences in the mortality.
References
1. Apter AJ, Boston RC, George M, et al. Modifiable barriers to adherence to inhaled steroids among adults with asthma: it's not just black and white. J Allergy Clin Immunol 2003;111(6):1219-26.
2. Kozyrskyj AL, Mustard CA, Simons FE. Socioeconomic status, drug insurance benefits, and new prescriptions for inhaled corticosteroids in schoolchildren with asthma. Arch Pediatr Adolesc Med 2001;155(11):1219 -24.
3. Mackenbach JP, Bos V, Andersen O, et al. Widening socioeconomic inequalities in mortality in six Western European countries. Int J Epidemiol 2003;32(5):830-7.
4. Kunst AE, Groenhof F, Mackenbach JP, Health EW. Occupational class and cause specific mortality in middle aged men in 11 European countries: comparison of population based studies. EU Working Group on Socioeconomic Inequalities in Health. Bmj 1998;316(7145):1636-42.
Conflict of Interest:
None declared