Other Routes of Protein and Peptide Delivery: Transdermal, Topical, Uterine, and Rectal - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 625

The movement of charges due to electromigration is illustrated in Fig. 12.3 . In
this diagram, the positively charged drug (D) and its counter ion (B-) are formu-
lated from the anodic donor reservoir for drug delivery. The cathodic counter reser-
voir contains biologically acceptable cations (C) and anions (B-). When an electric
field is applied, drug ions transfer into the skin, and endogenous anions, mostly chlo-
ride, transfer from the body into the donor reservoir. Simultaneously, at the cathodic
counter electrode, anions transfer from the counter reservoir into the skin, whereas
endogenous cations, mostly potassium and sodium, migrate from the body into the
counter reservoir. The movement of ions maintains a neutral environment for the skin
throughout the process [34,35] .
The increased flux during iontophoresis includes flux due to the electrochemical
potential gradient across the skin and change in the skin permeability due to the elec-
tric field applied by electroosmotic water flow and the resultant solvent drag. Hence,
Eq. (12.1):

ionto electric passive convective

J  J  J  J (12.1)

where:
J electric  flux due to electric current application
J passive  flux due to passive delivery through the skin
J convective  flux due to convective transport due to electroosmosis

Iontophoretic delivery is advantageous in many ways. It considerably reduces
the inter- and intraindividual variability because in iontophoretic delivery the rate
of drug delivery is more dependent on applied current than on characteristics of the
SC. It can deliver drugs both in ionized and unionized form. It enables continuous
or pulsatile delivery of the drug, depending on the applied current. Iontophoresis
offers enhanced control on the amount of drug delivered, as this depends on the area

Source of current

+ -

Donor
electrode

Receptor
electrode Anode Cathode

B-

D+
Drug repulsion

Movement to
cathod via anode

C+ B-

Skin

Blood vessel

Blood vessel

Figure 12.3 Schematic diagram of an iontophoresis system showing flow of ions when
voltage is applied.