The presence of a sufficient quantity of a drug in the epidermis is a
necessary prerequisite for influencing epidermal proliferation and dif
ferentiation processes. With the aim of obtaining a high concentration
of a potential active agent (biotin) at the target area after topical
application, the influence of the vehicle on biotin release and penet
ration was investigated. Liberation studies (multi-layer membrane mode
l) showed that over 50% of the biotin in an oil-in-water (O/W) emulsio
n (64.8 +/- 1.9%) and a micro-emulsion (ME, 54.5 +/- 2.4%) is released
within 300 min, whereas the degree of release from a water-in-oil emu
lsion does not exceed 16%. For this latter vehicle, the influence of a
controlled drug release on the penetration processes in human skin (F
ranz cell) results in the penetration of only small quantities of the
drug into the skin layers (into the horny layer 7.9 +/- 2.6%, living e
pidermis 0.11 +/- 0.06%, dermis 0.38 +/- 0.31% within 300 min). The ap
plication of an O/W emulsion or an ME appears to be more favourable. B
oth vehicles lead to not only a large reservoir in the horny layer (O/
W 26.5 +/- 3.5%, ME 26.0 +/- 0.8% within 300 min) of the skin but also
important epidermal and dermal concentrations (living epidermis: O/W
2.0 +/- 0.9%, ME 0.3 +/- 0.2%; dermis: O/W 3.4 +/- 1.3%, ME 1.6 +/- 0.
8% within 300 min). The time-dependent concentration profiles in the s
kin layers suggest that the use of an ME produces an immediate effect,
whereas the application of an O/W emulsion results in a delayed and/o
r long-term effect.