Clinical complexity and epidemiologic uncertainty in case-control research. Fenoterol and asthma management

The global decline in asthma death rates: can we relax now?

Whilst global asthma mortality seems to be decreasing, childhood asthma incidence is rising, and early warnings from Australia show an increase in asthma-related deaths in under-15s; this article considers whether we should view the future impact of asthma with trepidation. Age-adjusted mortality statistics for asthma have been reevaluated to provide an international standard. Comparisons across regions and time are complex, yet over the last two decades asthma mortality has clearly decreased, coinciding with a significant change in asthma management. The majority of remaining asthma deaths are preventable. Nonetheless, ongoing vigilance is required. Asthma remains under-diagnosed and under-treated. Childhood asthma has become more common; it is a matter of debate whether it is also more severe. Rather than being encouraged by the fall in numbers of asthma deaths, we should focus on the surging numbers of children suffering from the disease - and the worrying increase in asthma death rates in Australian children - and work to avert future issues.

A new index of prognostic severity for chronic asthma

OBJECTIVE

To develop a prognostic clinical index for adults with chronic stable asthma.

DESIGN

Analysis of data from a 48-week randomized, crossover trial of regular vs as-needed inhaled beta-agonist therapy.

PATIENTS

Eligible patients included 70 men and women between the ages of 15 and 64 years with asthma for > 1 year.

OUTCOME MEASURE

Asthma deterioration within 20 weeks, defined as either a marked decline in FEV1 (> or = 1.0 L or > or = 30% from baseline) or initiation of systemic corticosteroid therapy for asthma exacerbation.

RESULTS

Three baseline factors independently predicted asthma deterioration: frequent symptoms on waking in the 4 weeks before baseline, past hospitalization for asthma, and age 35 years or older. Based on cross-stratification and consolidation of these prognostic factors, an index was developed that stratified subjects into four risk groups with distinctive deterioration rates of 9%, 21%, 39%, and 67% (p<0.001).

CONCLUSION

For adults with chronic stable asthma, three simple clinical factors can be combined to stratify effectively for risk of subsequent asthma deterioration.

End of the New Zealand asthma mortality epidemic

In 1989, a case-control study reported that inhaled fenoterol was associated with the epidemic of asthma deaths that had affected New Zealand since 1976. The New Zealand Department of Health issued warnings about the safety of fenoterol and restricted its availability. The associated time trends are consistent with the hypothesis that fenoterol was the main factor in the New Zealand asthma mortality epidemic. The epidemic commenced when fenoterol was introduced in 1976, and the New Zealand death rate remained the highest in the world for more than a decade. After publication of the case-control study, the death rate fell by half and has now remained low for a further 3 years (1990-92). Time-trend data do not suggest a class effect of inhaled beta-agonists in the epidemic: there was no association between beta-agonist sales and the start of the epidemic, and total sales of inhaled beta-agonists actually increased slightly during 1989-90 when the epidemic came to an end. Time-trend data are also inconsistent with the hypothesis that the epidemic may have occurred because of underprescribing of inhaled corticosteroids. Similarly, time-trend data is incosistent with hypotheses postulating a major role of social factors such as unemployment. Data on time trends should be assessed with caution, because time trends in asthma deaths can be affected by many factors. Nevertheless, the New Zealand time trends are consistent with fenoterol being the main cause of the New Zealand asthma mortality epidemic and are inconsistent with a significant role for other suggested causes.

The beta 2-agonist controversy. Observations, explanations and relationship to asthma epidemiology

Links between frequent use of inhaled beta 2-agonists and morbidity and mortality from asthma appear probable. Two mortality epidemics followed the marketing of potent inhaled adrenergic agents. Case-control studies in New Zealand linked mortality with prescription of fenoterol, especially in severe asthma. A Saskatchewan case-control study confirmed an association of mortality with fenoterol, and also with frequent use of salbutamol (albuterol). Cardiac effects of beta 2-agonists do not cause mortality, but frequent use of these agents may increase the chronic severity of asthma, hence increasing the number of asthmatic patients at risk of death in an acute attack. Frequent use of beta 2-agonists may reduce lung function, increasing airway responsiveness, and impair control of asthma, despite use of inhaled corticosteroids. Mechanisms for this effect may include tachyphylaxis to nonbronchodilator effects, increased responsiveness to allergen, interaction with corticosteroid receptors, altered mucociliary function, differential effects of enantiomers, and masking of symptoms by beta 2-agonist use. The withdrawal of fenoterol from New Zealand in 1990 was associated with a substantial decline in morbidity and mortality. Overall, the evidence suggests that frequent use of inhaled beta 2-agonists has a deleterious effect on the control of asthma. Epidemics of mortality are explained by an increase in chronic severity of asthma following introduction of more potent beta 2-agonists. While beta 2-agonists remain essential for relief of breakthrough symptoms, long term use, particularly with high doses of potent agents, appears to be detrimental.

Confounding by severity does not explain the association between fenoterol and asthma death

Three recent case-control studies from New Zealand, and one from Saskatchewan, Canada, have found that fenoterol increases the risk of death in patients with severe asthma. It has been suggested that these findings may be due to confounding by severity, if fenoterol was selectively prescribed to more severe asthmatics. This 'confounding by severity' hypothesis has now been investigated in further analyses of data from the New Zealand case-control studies. This analysis found that among patients whose asthma was severe enough to require hospital admission (the population in whom the case-control studies were conducted), fenoterol was not preferentially prescribed to the more severe asthmatics. There was greater co-prescribing of other drugs with fenoterol (compared with salbutamol) during the later years of the epidemic, but these differences did not explain the excess risk associated with fenoterol, and there was little evidence of greater co-prescribing during the earlier years of the New Zealand epidemic of asthma deaths. There was no association between the prescription of fenoterol and markers of acute asthma severity or psychosocial problems. Patients were not selectively changed to fenoterol as a result of a severe attack resulting in a hospital admission. Most importantly, in the case-control studies of asthma deaths, the inhaled fenoterol relative risk increased when the analysis was restricted to sub-groups defined by markers of chronic asthma severity; whereas the relative risk would have decreased towards 1.0 in these sub-group analyses if the overall elevated risk for fenoterol was due to confounding by severity.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of beta-agonists and the risk of death and near death from asthma

BACKGROUND

Morbidity and mortality from asthma appear to be increasing, and it has been suggested that medications used to treat asthma are contributing to this trend. We investigated a possible association between death or near death from asthma and the regular use of beta 2-agonist bronchodilators.

METHODS

Using linked health insurance data bases from Saskatchewan, Canada, we conducted a matched case-control study of subjects drawn from a cohort of 12,301 patients for whom asthma medications had been prescribed between 1978 and 1987. We matched 129 case patients who had fatal or near-fatal asthma with 655 controls (who had received medications for asthma but had not had fatal or near-fatal events) with respect to region of residence, age, receipt of social assistance, and previous hospitalization for asthma.

RESULTS

The use of beta-agonists administered by a metered-dose inhaler was associated with an increased risk of death from asthma (odds ratio, 2.6 per canister per month; 95 percent confidence interval, 1.7 to 3.9) and of death or near death from asthma, considered together (odds ratio, 1.9; 95 percent confidence interval, 1.6 to 2.4). For death from asthma, use of the beta-agonist fenoterol was associated with an odds ratio of 5.4 per canister, as compared with 2.4 for the beta-agonist albuterol. On a microgram-equivalent basis, the odds ratio for this outcome with fenoterol was 2.3, as compared with 2.4 with albuterol.

CONCLUSIONS

An increased risk of death or near death from asthma was associated with the regular use of inhaled beta 2-agonist bronchodilators, especially fenoterol. Regardless of whether beta-agonists are directly responsible for these adverse effects or are simply a marker for more severe asthma, heavy use of these agents should alert clinicians that it is necessary to reevaluate the patient's condition.