Defined Daily Doses

Defined daily doses (DDDs) are a WHO statistical measure of drug consumption. DDDs are used to standardise the comparative usage of various drugs between themselves or between different healthcare environments.

The problem is that different medication can be of different strengths and different potencies. Simply comparing 1g of one, with 1mg of another can be confusing, particularly if different countries use different doses.

DDDs aims to solve this by relating all drug use to a standardised unit which is analogous to one day's worth

The formula for calculating DDDs is as follows.

$$Drug\ Usage(DDDs) = \left( \frac{Items\ issued \times Amount\ of\ Drug\ per\ item}{WHO\ DDD\ Measure } \right)$$

For example, paracetamol has a DDD of 3g. This is equivalent to six standard (500mg) tablets. If a patient consumes twenty four (500mg) tablets (i.e. 12g of paracetamol in total)over the space of six days, he can have said to have consumed four DDDs of this drug.

$$(12g(total amount of drug)/3g(amount of drug in a DDD)=Number of DDDs$$

See also:
 * ADQ (Pharmacy)(Average Daily Quantity) for a British alternative
 * World Health Organisation Collaborative Centre for more on this.