Resumo de Electrically Assisted Transdermal And Topical Drug Delivery

In the recent years there is increasing demand on the
Pharmaceutical Scientist to develop dosage forms that would
be able the deliver biotechnologically produced mega-
molecules to the body. Gut being full of digestive enzymes
that destroy the protein drugs, injection is only practical
option left to the industries to formulate such drugs. But
injections are not popular mode for routine administration
of medicines and any noninvasive delivery route is thought
to be superior to them. Electrically assisted drug delivery
is an option being considered currently by the industries.
Ajay Banga?s Electrically Assisted Topical and
Transdermal Drug Delivery is a book that compiles all the
research done in this field till its publication time 1998.

By analyzing the available data the author, who is a worker
in the field concludes ?electrically assisted transdermal
delivery can become a major route of drug administration in
near future ? as it has the promise of both
noninvasiveness, (no piercing of the body), rate controlled
delivery (the quantity of the drug reaching the blood can
be monitored by adjusting the current density) that
increases the safety level of treatment.

The actual processes that take place when current is
applied on body can be divided into several categories
mainly Iontophoresis, Electro-osmosis and Electroporation .

Skin ?the covering of body is a composite organ having many
overlapping layers. The uppermost layer ,which is only 10
to 15 micrometer thick is the most impermeable and
expresses highest Electrical impedence. Only lipophilic and
unionized small molecules of size below 500 dalton can
cross this barrier successfully to pass through the inner
layers and reach blood circulation. Ions and high
molecular weight unionized species are clearly not
encouraged by skin to enter the body and stopped at the
periphery by the rate-controller membrane stratum scornium ?
the dead layer which forms the interface of the body with
environment., Transdermal iontophoresis aims to deliver
ionic and therapeutically active megamolecules by
propelling them into the skin using the electrical force.

Usually the drug is placed in ionic form on skin.
Electrical charge similar to that of drug moiety was
applied on it though some electrical device that provide
constant current at physiologically acceptable level. There
is repulsion between like charges and drug is pushed deep
within the skin. Another phenomenon, electro-osmosis which
is bulk fluid flow in the direction as that of the movement
of counter ions take place during the iontophoresis .Since
at normal condition skin has a negative charge,
iontophoretic devices supply negative charge at the drug
reservoir to propel the negatively charged drug ions and
counter ions are positive. Electro-osmotic flow take place
from anode to cathode and usually enhance the flux of
positively charged drug ions. Iontophoresis and electro-
osmosis take place together and drug flux is sum total of
both contributions.
In electroporation high voltage pulse is applied for a very
short time, which create pores in skin, leading to a
increase skin permeability. Porous skin then accommodates
the heavy molecules and relays them to the deeper layers.
The pores are resealed after a certain time depending on
rate and extent of the exposure to the current.

Data obtained from early iontophoretic experiments showed
good promise of permeation but the system needing an
electrical device did not find favour with the
industries. However the recent advances in micro-
electronics with miniaturized circuitry and button cells
had made it a practical possibility .One drug lidocaine is
already marketed as iontophoretic system and many are
likely to follow in near future.

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