Pharmacology: Topical Drugs & Drug Diffusion Across Skin Flashcards
give some examples of conditions topical drug administration is used for
superficial skin disorders, skin infections, itching(pruritus), dry skin, warts
what are the different types of vehicle for topical drug administration, in order from most to least water content
gels, lotions, creams, ointments, pastes, powders
what is choice of vehicle indicated by when administrating topical drugs
physiochemical properties of the drug and what clinical condition it is
what law does rate of absorption of topical drugs follow
Fick’s Law of diffusion
what factors influence rate of absorption(J) of a drug, ie what is the equation
J = KpCv (Kp = permeability coefficient, Cv = conc. of drug in vehicle)
what factors are embodied in the permeability coefficient(Kp) in determining rate of absorption
partition coefficient(Km), diffusion coefficient(D), and the length of diffusion pathway(L) Kp = ((Km x D) / L)
how does the type of vehicle affect the rate of administration
profoundly affects the rate and extent of absorption of topically applied drug
in terms of drug conc. what drives the skin penetration of the drug for topical drugs
the fraction within the vehicle solubilised(Cv) is the driving force, NOT that undissolved
what affects can inclusion of excipients within the vehicle have on drug administration
can enhance drug solubility and enhance absorption
what affect can excess non-dissolved drug in transdermal patches in the vehicle have on drug administration
can increase duration of effectiveness and provide constant rate of delivery
give 2 examples of a physical or chemical factor that can improve partitioning of drug
hydration of the skin by occlusion, ie prevention of water loss by evaporation
(may be achieved by vehicle(ie ointment) or cling film)
or inclusion of excipients that also increase solubility of hydrophobic drugs
what does increased partitioning result from
reduction in the barrier function of the stratum corneum
what factors of the skin influence the absorption of topically applied drugs
site of application(ie nail, palm, scalp etc.), hydration of skin, integrity of epidermis(ie trauma, inflammation)
what factors of the drug itself influence the absorption of topically applied drugs
drug conc. and properties, the drug salt, the vehicle used
