Dermal and Transdermal Administration - Transdermal Patches
9. Dermal and Transdermal Administration:
Preparations for dermal (or cutaneous) administration include liquid preparations (lotions and shampoos), semi-solid preparations (ointments and creams) and solid preparations (powders). They are used to obtain local effects.
Unintended systemic absorption through the dermis is a potential risk with many APIs. The stratum corneum is deficient in preterm neonates. Children have a lower volume of distribution per unit area of skin.
Depending on the dosage form, various excipients are needed. The safety profile of each must be considered (see section 4.3) including the risk of sensitization of the skin. Preparations containing ethanol should be avoided in very young children because ethanol may dehydrate the skin and cause pain.
Liquid suspensions, semi-solid preparations and patches should be subject to dissolution testing (18).
9.1 Transdermal Patches:
Transdermal patches are used for systemic delivery of APIs which are capable of diffusion through the stratum corneum and are therapeutically active at the low plasma concentrations that can be achieved. The manufacture of transdermal patches of the “drug-in-adhesive” type is now well developed and less problematic than the earlier “drug-in-reservoir” type; the API is dispersed in a suitable polymeric adhesive to be fixed in a thin layer on a backing and covered by a removable liner.
The size and shape of a transdermal patch should be adapted to fit the child’s body. It should stick firmly to the skin and not be too difficult to remove. Application sites which cannot easily be reached by the child should be chosen to avoid removal of the patch by the child. The risk of deliberate removal and its consequences for therapy must be considered. The increased systemic absorption through the skin, for the reasons mentioned above, may increase the systemic delivery from transdermal patches, in particular in newborns and young infants.
When designed to be cut, information on the cutting technique should be provided in the patient leaflet and facilitated by the presence of cutting lines to ensure equal division. Reservoir systems should never be cut.
Adhesives should have a low allergenic potential to avoid irritation and infection. Local tolerance and acceptability should be tested.
Development of Paediatric Medicines: points to consider in formulation,
(Annex 5, WHO Technical Report Series 970, 2012)
