Biomedical Engineering Reference
In-Depth Information
they are easily formed through spontaneous self-assembly of supramolecules and
being organic in nature, are resistant to microbial contamination [2, 36]. Hence
it accrues to desirable features of easy handling and longer product shelf-life for
pharmaceutical formulations.
3.3.1
Dermal and Transdermal Formulation
Dermal and transdermal drug delivery is well accepted by patients as it is
non-invasive and usually easily self-administered. From the pharmacological per-
spective, its effect is localized and hence has less systemic side effects. It is also an
alternative route to oral administration for sustained and controlled of drugs which
are readily metabolized by the liver to bypass the first-pass effect. Lecithin-based
organogel as a vehicle for topical drug delivery have been well-studied [23-25].
Willimann and co-workers have illustrated that the lecithin organogel matrix is
biocompatible, has low skin irritancy potential, can increase the solubility of drugs,
and improve the transdermal transport rate of scopolamine across human skin
in
vitro
[25]. In addition, an open vial of lecithin organogel is stable for at least one
month at room temperature. Unfortunately, the skin is an effective natural barrier
and hence development of transdermal drug delivery has been hindered. Chemical
penetration enhancers have been deployed to modify the skin structure so as to
increase its permeability. Many of these chemical penetration enhancers were
found to be organogelators. The dual properties of these molecules unquestionably
pave way for further development of organogels in dermal and transdermal drug
delivery.
Our research group had previously investigated the application of small-
molecular organogel in transdermal drug delivery of haloperidol, using an amino
acid-type small-molecular-weight gelator, dibutyllauroylglutamide (GP1) in two sol-
vents, isostearyl alcohol (ISA) and propylene glycol (PG) [37]. It was found that GP1
did not influence the drug permeation rate, but it increased permeation lag time.
The
in vitro
human skin permeation study showed that drug permeation reached
pseudo steady state faster in ISA-based gels than PG-based gels. In a separate
study, we illustrated that the use of penetration enhancers improved transdermal
drug delivery, through which we discovered that the incorporation of limonene into
GP1/PG organogel was able to increase skin permeability, shorten lag time, facili-
tate delivery of drug
in vitro
, and enhance gel stability [38]. Further examinations of
the physiochemical effects of terpenes on organogel for transdermal drug delivery
illustrated that the oxygen-containing terpenes linalool and cineole decreased gel
moduli and brittleness, and the reverse was observed for the hydrocarbon terpene,
limonene [39]. It was proposed that linalool and cineole interfered with hydrogen
bonding between GP1 molecules. On the other hand, limonene may have initiated
a phase separation-mediated gelation, resulting in a change of the gel morphology.
Although the terpenes altered the rheology, they did not significantly affect the
chemical stability of the gels. Therefore, based on choice of terpenes, desired
viscosity of small-molecular organogel with enhanced skin penetrating properties
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