Дәрілік заттарды қолдануды статистикалық өлшеу: Күнделікті доза (DDD)

Statistical measure of drug consumption
The defined daily dose (DDD) is a statistical measure of drug consumption, defined by the World Health Organization (WHO) Collaborating Centre for Drug Statistics Methodology. It is defined in combination with the ATC Code drug classification system for grouping related drugs. The DDD enables comparison of drug usage between different drugs in the same group or between different health care environments, or to look at trends in drug utilisation over time. The DDD is not to be confused with the therapeutic dose or prescribed daily dose (PDD), or recorded daily dose (RDD), and will often be different to the dose actually prescribed by a physician for an individual person. The WHO's definition is: "The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults."

Before a DDD is assigned by the WHO Collaborating Centre for Drug Statistics Methodology, it must have an ATC Code and be approved for sale in at least one country. The DDD is calculated for a 70kg adult, except if this drug is only ever used in children. The dose is based on recommendations for treatment rather than prevention, except if prevention is the main indication. Generally there is only one DDD for all formulations of a drug, however exceptions are made if some formulations are typically used in significantly different strengths (e. g., antibiotic injection in a hospital vs tablets in the community). The DDD of combination tablets (containing more than one drug) is more complex, most taking into account a "unit dose", though combination tablets used for high blood pressure take the number of doses per day into account.

The DDD is generally the same for all formulations of a drug, even if some (e. g., flavoured syrup) are designed with children in mind. Some types of drug are not assigned a DDD, for example: medicines applied to the skin, anaesthetics and vaccines. Because the DDD is a calculated value, it is sometimes a "dose" not actually ever prescribed (e. g., a midpoint of two prescribed tablet strengths may not be equal to or be a multiple of any available tablet). Because the primary purpose of the ATC/DDD system is drug consumption measurement, the WHO recommend caution when considering its use for cost analysis: "DDDs, if used with caution can be used to compare, for example, the costs of two formulations of the same drug." The Board recommend that provided the agreement between DDD and RDD is known and minimal, then a cost per DDD "can provide a rough idea of the treatment cost" but "caution should still be used, as misinterpretation of the results based on the DDD methodology may still occur". If the agreement between DDD and RDD is unknown or a significant disagreement is known, then the DDD methodology "should not be used in cost analyses". In all cases, the Board state "The DDD methodology should not be used in guiding policy decisions regarding reimbursement, therapeutic substitution and other pricing decisions".

If the DDD for a certain drug is given, the number of DDDs used by an individual patient or (more commonly) by a collective of patients is as follows. For example, the analgesic (pain reliever) paracetamol has a DDD of 3 g, which means that an average patient who takes paracetamol for its main indication, which is pain relief, uses 3 grams per day. This is equivalent to six standard tablets of 500 mg each. If a patient consumes 24 such tablets (12 g of paracetamol in total) over a certain span of time, this equals a consumption of four DDDs.