Measuring the quality and quantity of antibiotic use

So measurement of antibiotic use is a cornerstone of any antimicrobial stewardship programme and measurement can help to improve the quality of prescribing. The two main types of measurement are quantitative and qualitative approaches. Let’s look briefly at these.

Quantity

Let’s consider firstly the quantity of antibiotic use. This approach uses data from hospital pharmacy stock management systems showing information about antibiotics sent to wards and departments, which in the absence of electronic prescribing systems can be used as a proxy for antibiotics administered to patients.

The standard international surveillance measure is the World Health Organisation (WHO) Defined Daily Dose (DDD).

The basic definition for a defined daily dose is the assumed average maintenance dose per day for a drug used in its main indication in adults. So in simple terms, the DDD is the amount of drug that a typical adult patient will receive each day for treatment of an infection. It must be emphasised that the DDD is a technical measurement – a standardised dose used to evaluate drug use. DDDs are not clinical doses. As a measure of antibiotic use DDD are not perfect but are generally used within stewardship programmes.

The DDD data on total antibiotic use in a particular period must then be converted into a rate by division with a measure of hospital activity to enable the measurement of use over time and between hospitals to become meaningful. Normalising antibiotic use and presenting it as a rate will help account for fluctuations in hospital activity such as the number of patients in hospital and their length of stay.

One of the most commonly used denominators in hospital stewardship programmes is the number of patient days or occupied bed days.

Monitoring of trends in antibiotic use expressed for example as DDD per 1,000 occupied bed days over months or years is essential to understand changes in practice over time, to identify wards with high or increasing antibiotic use or highlight the use of antibiotics not recommended in local prescribing guidelines.

This activity can help identify areas where targeted stewardship interventions are required and can also be used to measure improvement after implementation of interventions.

Measuring the quantity of antibiotic use is therefore a fundamental component of stewardship programmes.

Quality

The key disadvantage of the quantitative approach is whether it really reflects the quality of antibiotic prescribing. A quantitative approach will tell you how many and where in the hospital antibiotics are being used, but does this really reflect the quality of antibiotic prescribing?

A qualitative approach is required to provide information on which patients are being given which antibiotics, their indication, which antibiotics are being used for treatment of particular infections and whether the antibiotics prescribed are in accordance with local prescribing guidelines.

This type of qualitative information can be collected in a structured way using Point Prevalence Surveys (PPS), which can then be fed back to prescribers to define areas for improvement.

In the next steps we will explain in more detail what a PPS is and the key principles for conducting a PPS in your hospital.

• In your hospital, do you tend to use qualitative or quantitative measurements for antibiotic use?
• Why do you think this is?
• Which do you think is more beneficial?

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