Transdermal medication patches and devices

The ease with which some dmgs can pass through the skin harrier into the circulating hlood means that the transdermal route of medication is a possible alternative to the oral route. Theoretically there are several advantages  

Rgure 9.27 The four main types of transdermal patch matrix, reservoir, multilaminate and drug-in-adhesive designs. The matrix/reservoir systems are cut away to show the drug. Illustration courtesy of 3M. 

Maximum flux from a saturated aqueous system of several dmgs was estimated to be 300 fig cm h and from a mineral oil system 250, ag cm h T Using a patch with a rate-limiting polymeric membrane (see section 8.6.4), delivery is controlled to 40-50/ g cm h that is, it is presented to the skin at that rate. A 10 cm device will therefore deliver 0.4-0.5 mg h h Control of release can be exercised by altering the membrane s properties and by changing the pH of the reservoir solution for a dmg such as hyoscine (Fig. 9.28). 

Iontophoresis is the process by which the migration of ionic dmgs into tissues such as skin is enhanced by the use of an electric current, a technique which has found application favour in facilitating the delivery of peptides and proteins. A typical iontophoretic device is shown in Fig. 9.29. 

Current can be applied in a continuous manner using either direct current (e.g. 0.1 mA cm ) or pulsed (0.1 mA cm 2000 Hz) to either solutions or gels of a dmg. Enhancement of migration results from several possible sources. 

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