Unit of measurement: (defined daily dose, DDD)
The World Health Organization Collaborating Center of Drug Statistics Methodology defined the DDD as the assumed average maintenance dose per day for a drug used in ist main indication in adults . It is a theoretical dose, a compromise between the dosage recommendations of various indications, fixed and regularly updated by the WHO. The DDD system measures the quantity of used drugs, independently of the dosage and the package size, which facilitates the comparisons of consumption between hospitals or countries .
The quantities in grams of antibiotics were converted in DDD and then expressed in DDD per 100 bed-days (density of use). They are recommended by the WHO as the unit of measurement for drug utilization studies in the hospital care setting [3, 4]. According to the Federal Statistical Office, the beddays correspond to the number of days during which a person is hospitalized. In addition, we measurend the density of use in DDD per 100 admissions.
Data collection and results
Pharmacists were mainly recruited among members of the Swiss Society of Public Health Administration and Hospital Pharmacists (GSASA) because of their easy access to the data concerning the quantities of antibiotics delivered to the hospital units, setting up a sentinel network of acute care hospitals.
Data were provided for 62 hospitals in 2007 and 67 in 2017. The density of use expressed in DDD per 100 bed-days and in DDD per 100 admissions is shown in the Figure 1.
Figure 1 : Global density of antibiotic use from 2007 to 2017, expressed in DDD per 100 bed-days (bars) and in DDD per 100 admissions (black line) in whole hospitals (light grey) and in intensive care units (dark grey).
The most commonly used class of antibiotics was the penicillins (ATC group J01C), followed by the other beta-lactam antibacterials, including cephalosporins (ATC group J01D) and quinolones (ATC group J01M).
The implementation of a sentinel network allowed to compare the use of the Swiss hospitals with the European countries. The present study showed that the global antibiotic use in the Swiss hospitals was close to the European median .
 World Health Organization Collaboration Center for Drug Statistics Methodology. ATC index with DDDs. Oslo : World Health Organization, 2005.
 Natsch S, Hekster YA, de Jong R, Heerdink ER, Herings RM, van der Meer JW. Application of the ATC/DDD methodology to monitor antibiotic drug use. Eur J Clin Microbiol Infect Dis 1998 ; 17(1) :20-4.
 Dukes MN. Drug utilization studies. Methods and uses. WHO Reg Publ Eur Ser 1993 ; 45 :1-4.
 de With K, Maier L, Steib-Bauert M, Kern P, Kern WV. Trends in antibiotic use at a university hospital: defined or prescribed daily dose ? Patient days or admissions as denominator ? Infection. 2006; 34(2): 91-4.
 Plüss-Suard C, Pannatier A, Kronenberg A, Mühlemann K, Zanetti G. Hospital antibiotic consumption in Switzerland: comparison of a multicultural country with Europe. J Hosp Infect. 2011; 79(2): 166-71.