Transdermal drug delivery

The primary function of human skin is to act as a protective barrier and as such, it does impose physicochemical limitations to the type of permeate that can transverse it’s highly stratified structure. It is generally accepted that for a drug to be delivered passively via the skin it needs to have adequate lipophilicity and also a molecular weight < 500 Da.

The US Food and Drug Administration (FDA) approved the first transdermal ‘patch’ products in 1981. These delivery systems provided the controlled systemic absorption of scopolamine for the prevention of motion sickness (Transderm-Scop®, ALZA Corp.) and nitroglycerine for the prevention of angina pectoris associated with coronary artery disease (Transderm-Nitro®). Until the commercial success of these products, it was still perceived too difficult for an active molecule to overcome the barrier properties of human skin and penetrate into the blood system at adequate quantities to elicit a therapeutic effect. However, the obvious benefits of transdermal drug delivery compared to more conventional, oral or parenteral drug delivery soon became apparent. The avoidance of hepatic first-pass metabolism, improved patient compliance and ease of access to the absorbing membrane, i.e. the skin.. all helped to open the way for a wide range of effective transdermal products As such, over the last two decades more than 35 transdermal products have been approved generating a multibillion dollar market. This rapid increase in market value has lead to transdermal drug delivery becoming one of the fastest growing sectors within the pharmaceutical industry.

There are three traditional designs for transdermal patches as described below::

• Adhesive systems
– simplest, consist of a drug containing adhesive with a backing layer
– degree of control often small
– no rate controlling membrane,
– adhesive controls drug release

• Matrix or layered systems
– more complex, different polymer compositions to provide drug containing matrix and adhesive
– often no rate controlling membrane
– Matrix may control drug release

• Reservoir system
– comprises

(i) an enclosed reservoir of drug (solution or suspension),

(ii) a polymeric rate controlling membrane 
 

All present common surfaces and  hold an excessive payload of drug within a patch to ensure that the drug is absorbed systemically at a rate sufficient for a sustained pharmacological effect. This often means that over 95% of the drug payload is still remaining when the patch is removed.

MedPharm’s core expertise is in the design and development of adhesive ‘patch’ systems and has all the equipment, facilities and instrumentation required for this