The Defined Daily Dose (DDD)
Prices change with time, prices differ between alternative preparations and between countries. Statistics based on currency is hence of little professional value. Other quantities, independent of price changes and changing exchange rates, may offer a better basis for professional evaluations. But, when using quantities such as number of tablets, number of packages etc., comparisons between different drugs used alternatively on the same indications, will often not be possible.
The use of DDDs as units of measurement offers better possibilities for comparisons between alternative medicaments, independent of price differences. The evaluation of drug consumption over time, nationally and internationally, is simplified and improved by the use of DDDs. A DDD is defined as the assumed average maintenance dose per day for a drug used on its main indication in adults.
The DDDs are determined on the basis of evaluation of international use of the substance in question, bearing in mind that national therapy traditions (indications, dosages) often differ greatly. Each DDD should therefore be regarded as a technical measuring unit.
Drugs used for more than one indication are a challenge. For antipsychotics the doses used in psychoses and not the lower doses used in the treatment of neuroses, are chosen as the basis for assignment of the DDDs. With the exception of some specific pediatric products, adult dosages are used. The DDD for a substance will often be one and the same, irrespective of the route of adm-inistration. Drugs with different bioavailabilities for different routes of administrations may, however, have more than one DDD, each of them linked to a specific dosage form. For products where a booster dose is followed by a smaller maintenance dosage, the maintenance dose will form the basis for the DDD. Whenever possible, the DDD is indicated as the quantity of active substance. When this is impossible, as is the case with combination products and some liquid products, the DDD is given as the number of unit doses (no of tablets, millilitres etc.).
The DDDs are not necessarily the most frequently prescribed or used doses. This must be considered when evaluating the data. Accordingly it will often be difficult to estimate the number of users by using the DDD as the measuring unit.
The sales figures are given as the number of DDDs/1000 inhabitants/day, calculated as follows:
Total consumption measured in DDDs x 1000
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365 x number of inhabitants
This figure offers an estimation of what proportion of the population that may receive a certain drug treatment. An estimated drug consumption of
10 DDDs/1000 inhabitants/day corresponds to a daily use of this drug by 1% of the population. This estimate is, however, only valid if there is good correlation between the DDD and the actual consumed dose.
For some drug groups mainly used during shorter periods, a presentation of the sales data as the number of DDDs/inhabitant/year may be more convenient. An estimated sale of 5 DDDs/inhabitant/year will indicate that each inhabitant may undergo a treatment of 5 days duration. If the standard treatment lasts 7 days, one may alternatively estimate the number of 7-day courses by dividing the total number of sold DDDs by the course duration. The DDDs used in this book are for most drugs indicated in adjacent brackets.
See DDDs for combination products in Norway. The principles of the ATC/DDD system are more thoroughly described in the publication Guidelines for ATC classification and DDD assignment 2011, Oslo 2010.
The ATC index with DDDs includes all assigned DDDs for plain products. Both the Guidelines and the ATC/DDD Index can be ordered from the WHO Centre. Access to the Guidelines and ATC/DDD index is also available from the website of the Centre.
Costs in Norwegian currency
Estimates of the expenditure in NOK for the period 2006-2010 are specified in separate tables for each ATC 3rd level. These tables are included in connection with each ATC main group and the costs are expressed in pharmacy retail price (AUP). The calculation of the pharmacy retail price is from 2002 based on the invoiced pharmacy purchase price added the pharmacy margin including fees and VAT. This implies that the actual pharmacy retail price can be higher than the estimated AUP values.
From January 1995, there has been no price regulation of non-prescription medicines in Norway and it is therefore difficult to estimate the OTC sales in terms of pharmacy retail prices. The Norwegian Institute of Public Health has not an overview of actual retail prices for OTC medicines. The turnover in retail prices is calculated by using the purchase prices multiplied with a factor of 2.1.
It should be emphasized that the estimated cost given in pharmacy retail prices in this report probably underestimates the actual cost.
Figures retrieved from the Norwegian Prescription Database (NorPD) will give the actual cost in pharmacy retail prices of prescription medicines.