Our study showed that the prevalence surveys and the drug sales statistics provided similar estimates for both the total use of antibiotics and the therapy pattern. Both methods have their limitations, but more precise knowledge on how antibiotics are used can be obtained by collating the data.
The prevalence of antibiotic use in the five Norwegian nursing homes exceeded 8 %. This was higher than the average for the participating nursing homes in other European countries, where it amounted to approximately 6 % (12, 13). However, the results from the nursing homes included are not necessarily representative for all nursing homes. For example, the nursing homes in our study were selected because of their interest in infection control and because they had active pharmacists. .
The prescription pattern in this study is within the area of what has been found in other Norwegian studies (4, 14) – (17). Both methods used in our study revealed differences in the use of antibiotics between the five nursing homes. Such differences between nursing homes are known also from previous studies undertaken in Norway as well as abroad (4, 12, 18, 19). The causes of these variations may include risk factors associated with the residents, such as the use of catheters, or linked to the institution, such as measures for infection control (20). Different assessments as to whether an indication for treatment is present may also account for some of the variation. Differences in the use of methenamine account for a large proportion of the variation between the nursing homes – the reason is perhaps that the effect of methenamine is controversial (21). The European study showed that methenamine was used only in Norway, Finland and Denmark (13).
The antibiotics used by the nursing homes were of a variety of types, but they were mainly in line with the national guidelines for the use of antibiotics in the primary health services (5).
Prevalence surveys are characterised by their rough methodology, which makes it difficult to control for random fluctuations. Repeated registrations may provide more precise estimates (22). We undertook only two measurements, and this may explain the poorer correspondence between findings from the prevalence surveys and the findings made on the basis of drug sales statistics in the smallest of the four nursing homes.
Drug sales statistics also have their limitations. For antibiotics that are used rarely, the drug sales statistics may falsely indicate a high rate of use, if the package sizes purchased are large and thus left in storage. A Norwegian study that compared the true amounts of antibiotics administered to drug sales statistics found that use of the sales data from pharmacies was reliable, provided that the study periods exceeded six months (23). Our study used data for an entire year.
To improve practice related to antibiotic prescribing in nursing homes, it will be essential that results from the studies are discussed and used locally. It has been shown that measures such as training courses and antibiotic stewardship have reduced and changed the use of antibiotics (24, 25). In this context, surveillance of the use of antibiotics is a key tool.
Continuous surveillance is assumed to be the optimal method for showing the use of antibiotics, but as long as medication overviews in electronic patient records remain unavailable, this method will be highly resource-intensive. The combination of prevalence surveys and drug sales statistics requires relatively few resources, but the extent to which these will provide results corresponding to those from continuous registration of the use of antibiotics is not known. Further research on this topic is recommended.
To sum up, our study shows that the methods provide similar estimates, and by combining prevalence surveys with drug sales statistics the nursing homes obtain information on the total amount of antibiotics purchased as well as an indication of whether their prescribing practice is in line with national guidelines. Pharmacist advisors could be a resource in the surveillance of antibiotic use.