Patient compliance with drug storage recommendations

Adequate drug storage is essential to guarantee the drug’s quality, safety and efficacy until the expiry date. In contrast with the tight regulations for drug storage and transport between drug companies, wholesalers and pharmacies, drug storage by patients at home is usually not monitored. There is little knowledge about the conditions at which drugs are stored in patients’ homes. Adequate drug storage includes several aspects, such as compliance with recommended storage temperature conditions, disposal of drugs that have passed the expiry date and having access to important drug usage instructions, e.g. through availability of drug information leaflets. This thesis first describes how patients store different drug products at home with regards to two domains; quality (criteria considering storage conditions, expiry date, package integrity) and information (criteria considering identifiability and drug information availability). It was found that half of the patients did not comply with at least one of these criteria and that the majority of patients having drugs requiring refrigeration (e.g. biologic drugs) did not comply with recommended storage conditions. Furthermore, it was found that older patients storing more than five different drugs at home are more often non-compliant with storage recommendations. Underlying reasons why patients are sometimes unable to store drugs at home adequately are largely unknown. We showed that personality traits seem to be unrelated to adequate drug storage conditions and practices at home. The majority of patients mentioned daily routines and visual reminders as their main reason considering drug storage locations. For drugs requiring refrigeration (i.e. biologic drugs) and kept in the refrigerator door were stored at higher mean temperatures (9.2°C) and were more often stored outside 2-8°C. The final part of this thesis described investigations on possible consequences of inadequate storage conditions. Consequences of inadequate storage temperature conditions for several biologic drugs were assessed by measuring the level of aggregation. All biologic drug products tested in this study were relatively resistant to freezing stress conditions, although in almost half of the tested product samples a small number of larger particles was detected. There is no evidence that these particles can result in the development of antidrug antibodies or other clinical consequences for patients. Several methodological considerations should be made when investigating the relationship between drug storage and possible consequences. Different categorizations for storage conditions greatly influences the number of inadequate storage periods and applying different time relationships seems to have a minimal effect on risk estimates. This study showed the methodological complexity when investigating the relationship between storage condition and clinical outcomes.

In conclusion, drug storage conditions and practices after dispensing are often inadequate. Patients are often non-compliant with drug storage recommendations on temperature and moisture, they store drugs that have passed the expiry date or do not have accompanying drug information. In theory, inadequate storage may reduce drug quality and thus could affect drug safety and effectiveness of the drug. In practice, current knowledge gaps limit reliable risk estimation when it comes to linking inadequate home storage of drugs with clinical outcomes. Gathering more knowledge on the consequences of inadequate storage by patients and improving compliance with drug storage recommendations should be a shared engagement between patients, pharmacists, healthcare authorities and drug companies.