Drug formulations transdermal patches

The solubilization of a drug substance in monophasic liquid crystalline vehicles gives semisolid formulations which are preferably used for topical application (see Surfactant Gels and Transdermal Patches above). 

Certain vestibular disorders respond to antimuscarinic drugs (and to antihistaminic agents with antimuscarinic effects). Scopolamine is one of the oldest remedies for seasickness and is as effective as any more recently introduced agent. It can be given by injection or by mouth or as a transdermal patch. The patch formulation produces significant blood levels over 48-72 hours. Useful doses by any route usually cause significant sedation and dry mouth. 

Apparatus. The nature of the dosage form will determine the type of dissolution apparatus that will be used for method development and validation. The following questions must be asked when selecting the dissolution apparatus. Is it a capsule Will a sinker be required How stable is the drug substance after dissolution in the medium Is the formulation an immediate release or an extended release formulation Is this a transdermal patch ... 

Formulation additives used in topical drug or pesticide formulations can alter the stratum comeum barrier. Surfactants are least likely to be absorbed, but they can alter the lipid pathway by fluidization and delipidization of lipids, and proteins within the keratinocytes can become denatured. This is mostly likely associated with formulations containing anionic surfactants than non-ionic surfactants. Similar effects can be observed with solvents. Solvents can partition into the intercellular lipids, thereby changing membrane lipophilicity and barrier properties in the following order ether/acetone > DMSO > ethanol > water. Higher alcohols and oils do not damage the skin, but they can act as a depot for lipophilic drugs on the skin surface. The presence of water in several of these formulations can hydrate the skin. Skin occlusion with fabric or transdermal patches, creams, and ointments can increase epidermal hydration, which can increase permeability. 

Formulation and/or development of advanced drug-delivery systems such as microencapsulated molecules, transdermal patches, or liposomes are frequently accomplished in the laboratory. However, large-scale production of these dosage forms may be problematic because the same conditions of manufacture may not be attainable or desirable in the plant setting. Consultation with process development personnel during the finalization of the prototype development phase is one way of minimizing scale-up difficulties. 

Kanikkannan N, Andega S, Burton S, et al. Formulation and in vitro evaluation of transdermal patches of melatonin. Drug Dev Ind Pharm 2004 30 205-212. 

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