”the physico chemical properties of a drug in a topical dosage form affect that drugs trans-dermal delivery (percutaneous absorption) and topical bio-availability. The molecules of the formulation , after penetrating through stratum corneum and thence into viable epidermis and
dermis , produces its characteristic pharmacological response through receptors even before blood or lymph circulations remove it, in which case it may set in a cascade of systemic effects. Though the horny layer is very impermeable to most chemicals contributing the
rate limiting step in trans dermal absorption because of its high diffusional resistance, providing a small fractional area of 0.1% only as permeable appendageal shunt route, it is not an efficient heat insulator – the penetration rate of material through human skin can change ten fold for a large temperature variation, as the diffusion coefficient varies according to temperature changes. Besides the appendageal shunt route , the drug molecule may penetrate through the hair follicles and sebaceous glands or through the hydration (water opens up the compact part of horny layer ),
pH etc., not forgetting the roles of drug concentration ,
molecular size and shape , diffusion coefficient , partition coefficient etc. The methods of enhancing bio availability of trans dermal drug applications recently followed , like ultrasound and electrical driving of charged molecules (iontophoresis) is replaced in
Ayurveda by the increased temperature that induces
sudation, hydration through enhanced sweating and by massage for effecting a manual type of iontophoresis. Even external use of sneha alone slightly increases body temperature, which in turn favours production of sweat by
sweat glands. Though this sweat is not excreated at the moment because of partial closure of sweat pores by the film of fat , subsequent application of heat releases the barricade of fat to effect full sneha used in conjunction with sveda in Ayurveda- it provides both hydration and temperature increase .
Thus Ayurveda has its own concept of a rich tradition of transdermal therapeutical system, it is convinient, effective, eliminates variables that influence gut absorption, it enters systemic circulation directly, by passing the
first-pass effect of enzymes in the gut and the liver; it provides a controlled , constant
drug administration, displaying a single pharmacological effect, it is patient compliant as it eliminates the effect taste or gastric irritations.Little wonder that when the world is still in experimental stages by introducing topically acting counterirritants, nsaids, steroids and transdermal clinical patches of oestradiol, clonidine, nitroglycerine, testosterone etc, Ayurveda has addressed transdermal use of medicenes in versatile conditions from neurological affections to rheumatological conditions and also for skin ailments in various modes and methods aroud 2500 years ago, snehana done externally through skin is only one example- (ARTICLE TAKEN FROM ASTANGA HRDAYA SUTRASTHANA COMMENTRY II BY DR.T.SREEKUMAR)”
Medical e-books
No comments:
Post a Comment