Table 1.

Definitions of included numerators of inpatient quantity metrics for antibiotic use following the systematic review

Defined daily dose (DDD)	An agreed technical statistical unit developed by the WHO Collaborating Centre for Drug Statistics Methodology; it is the assumed average maintenance dose per day for a drug used for its main indication in adults.
Hospital-adjusted defined daily dose (haDDD)	Determined from recommendations in regional or national guidelines on antibiotic use in hospital.
Prescribed daily dose (PDD)	Derived from actually prescribed/administered dose to a patient. It is the average dose prescribed according to a representative sample of prescriptions. The PDD will give the average daily amount of a drug that is actually prescribed.
Recommended daily dose (RDD)	Similar to DDD but the daily dose is defined by local guidelines; usually varies according to the weight of the patient.
Doses/units	Expressed in mg/kg/day or g/patient/day or g or mg.
Packages	The number or vials, bottles, pills/tablets, infusion bags, packages.
Prescriptions	The number or percentage of prescriptions containing antibiotics.
Days of therapy (DOT)a	The number of days that a patient receives antibiotics regardless of the dose. When a patient receives more than one antibiotic, more than one DOT may be counted.Synonym: antibiotic days or antimicrobial days.
Agent days	The number of days that a patient received a particular agent; defined by subtracting the date of the first dose of the antibiotic course from the date of the last dose.
Length of therapy (LOT) or duration of treatment (DOT) or days of treatment (DOT)	The number of days that a patient receives systemic antimicrobial agents, irrespective of the number of different antibiotics. Therefore, LOT will be lower than or equal to days of therapy (DOT) because the DOT is calculated for each antibiotic.
Treatment courses	Period during which the same agent (regardless of dose or route) was administered to the same patient on consecutive days. One patient may be given more than one treatment course at a time.Synonym: treatment period.
Length of stay (LOS) or antibiotic-related length of stay (ALOS)	Defined as the length of an inpatient episode of care, calculated from the day of admission to the day of discharge, and based on the number of nights spent in hospital. Patients admitted and discharged on the same day have a length of stay of <1 day.
Patients	Defined as the number or percentage of patients receiving one or more antibiotics or patients exposed to antibiotics.
Drug utilization index (DU)	The number of drugs accounting for 75%/90%/100% of total drug use.
Antibiotic costs	Defined as the total amount or percentage of costs of antibiotic per total drug costs.
Drug cost index 90% (DC 90%)	The costs of drugs accounting for 90% of total drug costs.

^aIn the literature, the acronym DOT is also used for duration of treatment and days of treatment, which are used as synonyms of length of therapy.