How to Calculate a Defined Daily Dose
- 1). Multiply the number of items issued by the amount of drug contained in each item. For example, a patient is given a prescription of 54 painkiller tablets, each containing 10 mg of ibuprofen. The prescription as a whole contains 540 mg of ibuprofen.
- 2). Search for the drug's DDD measurement on the WHO Collaborating Centre for Drug Statistics Methodology website (see Resources), by name or ATC code. Ibuprofen's DDD measurement, for example, is 30 mg.
- 3). Divide the total amount of the drug by the DDD measurement. In the ibuprofen example, this would give the equation (54 times 10 mg divided by 30 mg, yielding a final value of 18. This number is the drug usage, or number of defined daily doses, in the prescription: we have here a prescription containing 18 DDDs of ibuprofen.
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