For medication in tablet form it is relatively straightforward to calculate the number of days supply based on a prescription. Some medications are less straightforward though because a prescription of a given number of doses may have a variable number of days supply because the number of doses to be taken per-day varies, for example with preventative corticosteroid inhalers prescribed for asthma where the number of inhalations to be taken daily may vary between individuals based on the severity of the disease. [ citation needed ]
Zhe Hui Hoo, 1,2 Rachael Curley, 1,2 Michael J Campbell, 1 Stephen J Walters, 1 Daniel Hind, 3 Martin J Wildman 1,2
1 School of Health and Related Research (ScHARR), University of Sheffield, 2 Sheffield Adult Cystic Fibrosis Centre, Northern General Hospital, 3 Sheffield Clinical Trials Research Unit, University of Sheffield, Sheffield, UK
Background: Preventative inhaled treatments in cystic fibrosis will only be effective in maintaining lung health if used appropriately. An accurate adherence index should therefore reflect treatment effectiveness, but the standard method of reporting adherence, that is, as a percentage of the agreed regimen between clinicians and people with cystic fibrosis, does not account for the appropriateness of the treatment regimen. We describe two different indices of inhaled therapy adherence for adults with cystic fibrosis which take into account effectiveness, that is, “simple” and “sophisticated” normative adherence.
Methods to calculate normative adherence: Denominator adjustment involves fixing a minimum appropriate value based on the recommended therapy given a person’s characteristics. For simple normative adherence, the denominator is determined by the person’s Pseudomonas status. For sophisticated normative adherence, the denominator is determined by the person’s Pseudomonas status and history of pulmonary exacerbations over the previous year. Numerator adjustment involves capping the daily maximum inhaled therapy use at 100% so that medication overuse does not artificially inflate the adherence level.
Three illustrative cases: Case A is an example of inhaled therapy under prescription based on Pseudomonas status resulting in lower simple normative adherence compared to unadjusted adherence. Case B is an example of inhaled therapy under-prescription based on previous exacerbation history resulting in lower sophisticated normative adherence compared to unadjusted adherence and simple normative adherence. Case C is an example of nebulizer overuse exaggerating the magnitude of unadjusted adherence.
Conclusion: Different methods of reporting adherence can result in different magnitudes of adherence. We have proposed two methods of standardizing the calculation of adherence which should better reflect treatment effectiveness. The value of these indices can be tested empirically in clinical trials in which there is careful definition of treatment regimens related to key patient characteristics, alongside accurate measurement of health outcomes.
Keywords: cystic fibrosis, medication adherence, nebulizers and vaporizers, epidemiologic methods
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