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Defined Daily Dose (DDD)

DDD Calculation Example
Consider a patient who has received a course of oral amoxicillin, 500 milligrams 3 times per day for five days. How many defined daily doses has this patient contributed to total antibiotic use in their hospital? So the daily dose is three times 500 milligrams, giving a total of 1.5 grams per day. The DDD for oral amoxicillin is one gram. So each day this patient is receiving 1.5 divided by 1, which is 1.5 defined daily doses. The course is for five days, giving a total for that patient of 7.5 DDD, so this patient has contributed 7.5 defined daily doses to the overall hospital use of antibiotics.

Calculation example

In this video William Malcolm shows you a worked example of a DDD calculation, using the WHO DDDs, for an individual patient prescribed oral amoxycillin. Remember this is to calculate the standardised dose and is not a clinical dose.

It is worth noting that a question often asked is whether the same antibiotic, given in oral or injectable forms, has the same DDD. In many cases, it does. For example, amoxicillin has a DDD of 1 gram whether given by mouth or by injection. And similarly, flucloxacillin has a DDD of 2 grams, whether in oral or parenteral forms. But there some examples of commonly used antibiotics where there is a different DDD for the oral and the parenteral forms. In such cases, it is generally either because there is different bioavailability between the oral and the injectable forms, or where the oral or injectable forms are used for very different types of infection.

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Antimicrobial Stewardship: Managing Antibiotic Resistance

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