Membrane-controlled patches

In ophthalmic delivery the area of contact is necessarily restricted to approximately 3 cm2 and thus the concentration gradient is the major determinant of absorption of a particular drag. By other routes, this can be achieved by adhering a reservoir of drag as a membrane-controlled patch or osmotic pump on the epithelium (see Chapters 4 and 8). However, the function of the eye as a visual apparatus limits the possibility of such an attachment of these dosage forms to the cornea. 

Fig. 45. Schematic of transdermal patch in which the rate of deUvery of dmg to the body is controlled by a polymer membrane. Such patches are used to...

There is a wide variety of transdermal systems on the market at present. These patches are diversely referred to as reservoir , monolithic , membrane-controlled , adhesive , matrix , and so on. Unfortunately, these terms are not always used consistently and, worse, they are sometimes used inaccurately. In all cases, however, the idea is that the system offers a means to hold a payload of the drag and a configuration (or platform ) to ensure presentation of the active agent to the skin surface at a rate sufficient to ensure a systemic pharmacological effect after the drag has crossed the skin s barrier. Most simplistically, one can divide the transdermal formulations presently available into three categories (Figure 8.3) ... 

Membrane-moderated patches have been utilized in many FDA-approved transdermal patches such as Duragesic, Transderm Scop, and Catapress TTS. This type of patch utilizes a rate-controlling membrane to precisely control the release of... 

In membrane diffusion systems the polymer membrane with a given pore size or pore size distribution controls the diffusion of the active substance from the drug reservoir. Dosage forms with membrane-controlled drug delivery can be coated tablets, coated granules or pellets, or so-called multiparticulate systems on which various coats are applied. One possibility for transdermal drug administration is the transdermal patch controlled with a membrane [4-7,34-39]. 

Mulch membranes Cardboard below, left) used as a mulch membrane around nonornamental plants synthetic landscape fabric (right) controlling weeds in a strawberry patch. 

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