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]]> Definition and introduction
The basic definition of the defined daily dose (DDD) is:
The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults.
The DDD is a unit of measurement and does not necessarily reflect the recommended or Prescribed Daily Dose. Therapeutic doses for individual patients and patient groups will often differ from the DDD as they will be based on individual characteristics (such as age, weight, ethnic differences, type and severity of disease) and pharmacokinetic considerations.
Only one DDD is assigned per ATC code and route of administration (e.g. oral formulation). The DDD is nearly always a compromise based on a review of available information including doses used in various countries when this information is available. The DDD is sometimes a “dose” that is rarely if ever prescribed, because it might be an average of two or more commonly used doses.
Drug utilization data presented in DDDs only give a rough estimate of consumption and not an exact picture of actual use. DDDs provide a fixed unit of measurement independent of price, currencies, package size and strength enabling the researcher to assess trends in drug consumption and to perform comparisons between population groups.
General principles for DDD assignment
DDDs are only assigned to drugs with an ATC code and a DDD will normally not be assigned for a substance before a product is approved and marketed in at least one country.
The basic principle is to assign only one DDD per route of administration within an ATC code.
DDDs for single substances are normally based on monotherapy. Exceptions to this rule are given in the guidelines of the relevant ATC groups.
For substances indicated for rare disorders with highly individual dosing schedules, the Working Group could decide not to assign a DDD.
DDDs are not established for topical products, sera, vaccines, antineoplastic agents, allergen extracts, general and local anesthetics and contrast media.
When a new DDD is assigned, various sources are used to get the best overview of the actual or expected use of a substance. The assigned DDD is based on the following principles:
DDDs for combinations products
The DDDs assigned for combination products are based on the main principle of counting the combination as one daily dose, regardless of the number of active ingredients included in the combination. If a treatment schedule for a patient includes e.g. two single ingredient products, then the consumption will be measured by counting the DDDs of each single ingredient product separately. If, however, a treatment schedule includes a combination product containing two active ingredients, then the calculated consumption measured in DDDs will normally be lower since the DDD for the combination will be counted.
Example I:
Treatment with two products, each containing one active ingredient:
Product A:
Tablets containing 20 mg of substance X (DDD = 20 mg)
Product B:
Tablets containing 25 mg of substance Y (DDD = 25 mg)
The dosing schedule 1 tablet of A plus 1 tablet of B daily will be calculated as a consumption of 2 DDDs.
Example II:
Treatment with a combination product containing two active ingredients:
Product C:
Tablets containing 20 mg of substance X and 12.5 mg of substance Y. The DDD of the combination products is assigned as 1 UD = 1 tablet.
The dosing schedule 1 tablet of C daily will be calculated as 1 DDD (even though it will be equivalent to 1.5 DDD of the single active ingredients).
The following principles for assigning DDDs to combination products apply:
2.For combination products used for treatment of hypertension (i.e. ATC group C02, C03, C07, C08 and C09), DDDs are based on the average number of dosing intervals per day. This means that: 1 tablet is the DDD for combinations given once daily, whereas 2 tablets is the DDD for combinations given twice daily and 3 tablets is the DDD for combinations given three times daily etc. This principle means that the assigned DDDs may differ from the DDD assigned for the main active ingredient (according to ATC code).
For all combination products where the DDD assigned deviates from the principles given above, a list of DDDs are available on this website List of DDDs combined products.
MCQ on Pharmacovigilance given at the end of Lecture (see above lecture)
Pharmacovigilance Lectures Playlist
Disclaimer: The presented matter is compilation of various online materials available on the topic with modification and simplification. The content is presented here for student’s easy accessibility as online study material and not for commercial purpose. Plagiarism is not removed.
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