Antimicrobial drug utilisation in Dunedin Hospital, New Zealand, and its association with antimicrobial resistance

Antimicrobial resistance (AR) to a drug can be considered a natural response to the selection pressure of that drug, with over prescribing being one of the major causes. Few investigations have evaluated the relationships between antimicrobial drug use in a hospital and antimicrobial resistance.

Antimicrobial drug utilisation (AU) data were collated for Dunedin Hospital, New Zealand, and expressed as defined daily doses per 1000 patient days according to the World Health Organization's definition. The drug groups studied were glycopeptides, carbapenems, third and fourth generation cephalosporins and fluoroquinolones. Antibiograms were also analysed and possible associations between antimicrobial utilisation and resistance were investigated. The reduction of antimicrobial utilisation has also been explored by various means.

The utilisation of fluoroquinolones at Dunedin Hospital was high compared with hospitals in South Australia, increasing from 1999 to 2003 then decreasing in 2004 and 2005. The Spearman rank correlation coefficients for the associations between fluoroquinolone utilisation and resistance to ciprofloxacin were: rs = 0.79, p = 0.06 for Pseudomonas aeruginosa and rs = -0.37, p = 0.5 for Escherichia coli.

The findings of antimicrobial drug utilisation studies in hospital can serve to describe the pattern of drug use in the institution, to detect areas of concern, and to evaluate the impact of interventions taken to influence the use of drugs, especially when this use is associated with increasing antimicrobial drug resistance.