Cost effectiveness analysis of inhaled anticholinergics for acute childhood and adolescent asthma

A recent systematic review by the Cochrane Airways Group showed that adding multiple doses of anticholinergics to β₂ agonists is safe and effective in improving lung function and avoiding hospital admission for school aged children and adolescents attending casualty departments with severe acute asthma.¹ The estimated reduction in the risk of admission was 9.4% (0.4% to 18.4%). This intervention presumably improves bronchodilatation until systemic corticosteroids take effect. Evidence of cost effectiveness, however, is lacking. To clarify whether scarce health resources should be spent on this intervention we conducted an economic evaluation.

Methods and results

We used various assumptions to estimate the financial implications of treatment (see table on the BMJ's website). The costs of drug administration were not included, as anticholinergics are always given with β₂ agonists and involve little additional manipulation. The cost of nebulisers, other drugs, and the casualty attendance were also excluded. No consideration was given to possible changes in length of stay in casualty. The effect of changing the various assumptions was tested by simple, one way, sensitivity analysis, and by multivariate probabilistic sensitivity analysis.² The latter is a simulation approach that enables estimation of uncertainty ranges containing 95% of replicated results.³

We estimated that treatment would cost about £8 (uncertainty range £1 to £47) per admission avoided (table). This implies a net saving of £80 (£0 to £157) per severe case treated. Varying the risk reduction within 95% confidence limits varied the mean net saving from £3 to £157 per severe case treated. More precision is expected when the Cochrane review is updated. Varying the cost of hospital admissions within the interquartile range for English providers (£620 to £907) varied the mean savings from £58 to £85 per severe case treated. Changes to the dose and unit cost of ipratropium had very little effect on the results.

Further assumptions were used to extrapolate the findings to a national level. About 7200 children aged 5-15 years are admitted from casualty with a diagnosis of asthma each year (hospital episode statistics 1988 to 1996). About 40% of children in this age group attending casualty with asthma are admitted.⁴ We assumed that 50% of people with asthma attending casualty have severe asthma.⁵ The rate of uptake of the review recommendations was assumed to be 5% a year; therefore an additional 5% of eligible patients would be treated in the first year, 10% in the second year, and so on. If doctors treated patients with mild or moderate asthma, this would add to treatment costs with no evidence of clinical benefit. We assumed that for every five patients with severe asthma who were treated, one patient with mild or moderate asthma would be treated. Costs were discounted at an annual rate of 6%.

Net savings were estimated to be £437 800 (−£3700 to £1 078 100) over five years in England. An increase in the number of patients for whom treatment is indicated, or in the proportion of eligible patients who are treated, leads to a proportionate increase in savings. For example, if all eligible patients were to be treated, after five years the estimated savings would be quadrupled. A reduction in the annual discount rate from 6% to 3% leads to an increase of £47 600 in expected savings. Increasing the ratio of inappropriate to appropriate treatment from 20% to 100% leads to a small decrease (£2800) in expected savings.

Comment

The addition of multiple dose anticholinergics to inhaled β₂ agonists for children and adolescents attending casualty with severe acute asthma would result in savings in health service resources. This finding is robust to changes in modelling assumptions, although some uncertainties remain. The personal value of the health effects and avoided hospital admissions provide additional benefits that have not been quantified in this analysis.

Table.

Results of baseline analysis, with uncertainty ranges estimated by probabilistic sensitivity analysis

	Per severe case treated
	Best estimate	Uncertainty range*
Admissions avoided†	0.09	0-0.18
Cost of treatment‡	£0.75	£0.28-£1.40
Savings due to avoided admissions§	£81	£0-£158
Cost of treatment per admission avoided¶	£8	£1-£47
Net monetary saving to the health service**	£80	£0-£157

^*Interval containing 95% of 5000 simulation replications. ^†Risk difference estimated by meta-analysis.¹ 

^‡Cost of ipratropium bromide 25p per 0.25 mg (from British National Formulary March 1999), and total dose per patient 0.625 mg (median for multiple dose protocols included in the meta-analysis¹). Authors assumed that one mild to moderate case is treated for every five severe cases treated. 

^§Mean cost of non-elective inpatient admissions £860 (NHS Executive's reference costs 1998 (HRG D21 and D22)). ^¶Cost of treatment divided by the number of admissions avoided. 

^**Savings due to avoided admissions minus the cost of treatment.