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Despite the attractiveness of topical dosage forms, only a handful of systemic medications are routinely delivered through the skin: clonidine, oestrogen, testosterone, scopolamine, nitroglycerin, nicotine and fentanyl. With few exceptions, most of these compounds are delivered via transdermal patches. However, through the use of proprietary absorption enhancers, several topical drug delivery companies are developing the first of a new series of transdermally delivered formulations containing compounds previously thought to be impractical due to poor skin penetration. These preparations typically combine an off-patent active with one of those proprietary enhancers. If successful, these pilot products may encourage more companies to consider absorption-enhanced topical delivery for their new and expiring-patent single chemical entities.
When compared to the wide range of controlled-release oral medication, transdermal patches and depot drug delivery systems, the use of gels, creams and sprays to deliver drugs systemically is a small segment of the billion drug delivery market and is often misperceived as 'low-tech'. Most pharmaceutical industry executives believe oral solid dosage forms to be the most convenient and predictable way to administer prescription drugs to most patients. Certainly, from development and manufacturing perspectives, solid dosage forms hold great appeal. Intestinal absorption is fairly predictable, and it is hard to dispute that for most people swallowing a tablet or capsule with a glass of water is an almost effortless administration method. However, anyone who has tried to administer a solid dosage form to a very young child or a very old adult can appreciate the potential advantage of a topical gel or cream that requires little or no co-operation from the patient. |
