Tablet dissolution & dissolution testing

What is Tablet Dissolution?

The administration of drugs via oral dosage forms is one of the most common and effective means of delivering treatments to patients. When a dosage form is swallowed, the rate at which it releases the active ingredient is critical to ensure that the drug is delivered properly. The rate at which the drug is released is called the dissolution rate. In fact, all drug forms have a dissolution rate. Creams, skin patches and implants and others, all release their drugs so they can be taken up by the body.

One of the problems facing pharmaceutical manufacturers is to how optimise the amount of drug available to the body, i.e. its bioavailability. Inadequacies in bioavailability can mean that the treatment is ineffective and at worst potentially dangerous (toxic overdose). All kinds of factors affect this from the formulation of the dosage form, size, shape, excipients, bindings and other physical characteristics, to the pH, temperature and so on.

The actual drug release in the human body can be measured in-vivo by measuring the plasma or urine concentrations in the patient. However, there are certain obvious impracticalities involved in employing such techniques on a routine basis. These difficulties have led to the introduction of official in-vitro tests which are now rigorously and comprehensively defined in the respective Pharmacopoeia and recent harmonisation between the various Pharmacopoeia (notably the USP, BP, EP and JP) has lead to global standardisation in the measurement of drug release rates.

Tablet Dissolution Testing

When it comes to measuring the release rates of drugs in a manufacturing environment then the technique of Tablet Dissolution testing is employed.

Tablet Dissolution is a standardised method for measuring the rate of drug release from a dosage form and the key word here is "standardisation" because for any results to be meaningful, it is essential that all the apparatus used for the testing, produces the same sets of results given all other parameters are equal.

There are many discussions about how good dissolution testing may or may not be compared with the actual in-vivo effects, but without a standardised test it is impossible to gain comparative data

The principle function of the dissolution test may be summarised as follows:

• Optimisation of therapeutic effectiveness during product development and stability assessment.
• Routine assessment of production quality to ensure uniformity between production lots.
• Assessment of "bioequivalence", that is to say, production of the same biological availability from discrete batches of products from one or different manufacturers.
• Prediction of in-vivo availability, i.e. bioavailability (where applicable).

Dissolution testing was initially developed for oral dosage forms, but the role of the test has now been extended to drug release studies on various other forms such as topical and trans-dermal systems and suppositories.