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Plasma level curves according to various formulations
Plasma level after extravascular administration of various formulations
1 rapid release
2 delayed release
3 slowed release, retarded
4 transdermal system

Retard ( Latin : slow-acting; English sustained release (SR), extended release (ER, XR), controlled / continuous release (CR) ) refers to a drug form in which the drug is released more slowly. Unlike depot dosage forms is meant by sustained-release pharmaceutical in the narrow sense orally administered dosage forms. Both terms are often used synonymously with one another. Drugs that are absorbed with a delay due to their pharmacokinetic properties or, in the case of prodrugs, are only converted into their actual active form by the organism, are not, however, sustained-release drug forms.


The pharmaceutical technology offers a number of ways, sustained-release preparations to manufacture, this is called Retardgalenik / sustained-release pharmaceutical technology. The simplest form is a tablet with a special coating, such as that used in gastro-resistant drugs. The sustained- release capsule , which contains small active substance-containing sustained- release pellets , which are released after the capsule shell has dissolved, is widespread . Tablets in which pellets are compressed into tablets ( Multiple Unit Pellet System (MUPS) ) are also increasingly being used . More complex forms store the drug in a slowly eroding matrix. Another possibility of retardation is the oral osmotic system .

Time course of the release

Defined temporal courses of the drug release can be achieved by means of retarding drug forms. Common examples are:

  • sustained release - release at a constant rate
  • prolonged release or slow release - release at a decreasing rate
  • delayed release

Sometimes retarded forms are combined with a fast-acting initial dose ( bolus ) in a tablet or capsule .


Areas of application are, for example, blood pressure regulating drugs or hormones . Retardation is used to prevent dangerous short-term high concentrations of drugs in the blood (plasma peaks) and / or to achieve the longest possible effect of a drug from a single drug form. By avoiding plasma peaks, side effects occur less frequently, and the long-term effect means that a patient has to take the drug less often, for example only once a day, which increases compliance .

Extended-release tablets must not be taken in a mortar , as this will cancel out the delayed release of the active ingredient, which can lead to undesired overdosing.

Other mechanisms of retardation

The term sustained- release preparation in the narrower sense usually refers to special dosage forms to be taken orally . The same effect can also be achieved with long-term preparations in which the drug itself has been chemically modified in order to achieve a slower effect. Depot preparations for parenteral use also have a delayed effect due to a slow release, for example from muscle tissue, into the bloodstream.


  • Kurt H. Bauer, Karl-Heinz Frömming, Claus Führer, Bernhardt C. Lippold: Textbook of Pharmaceutical Technology. 8th, revised and updated edition. Wissenschaftliche Verlagsgesellschaft, Stuttgart 2006, ISBN 3-8047-2222-9 .
  • Rudolf Voigt, Alfred Fahr : Pharmaceutical Technology. For studies and work. 9th, completely revised edition. Deutscher Apotheker-Verlag, Stuttgart 2000, ISBN 3-7692-2649-6 .
  • Hadgraft, Roberts, Rathbone, Stefan Fet: Modified-Release Drug Delivery Technology (Drugs and the Pharmaceutical Sciences) . Informa Healthcare (November 2002), ISBN 0-8247-0869-5

Individual evidence

  1. Constanze Schäfer (Ed.): Probe application of drugs. Wissenschaftliche Verlagsgesellschaft, Stuttgart 2010, p. 21. ISBN 978-3-8047-2374-0