Permeating the Skin
Iontophoresis relies on the use of an electric current to drive the uptake of an ionized pharmaceutical agent. The pharmaceutical agent, which acts as the current carrier, is contained in an electrode pad which is placed under one electrode (the active electrode). A second electrode (the return electrode) is used to complete the circuit, with the primary current path between the active and return electrodes being the patient’s skin. When power is applied, the active electrode repels the pharmaceutical agent, thereby forcing it into the skin. Since iontophoresis can be used to deliver either positively or negatively charged drugs, the drug formulation determines whether the cathode or the anode electrode is the active or the return electrode.
The NP101 Migraine SmartRelief
It is useful to elaborate on the critical elements of an iontophoretic patch, thereby providing a clearer understanding of the design challenges pharmaceutical companies face in expanding transdermal drug delivery therapies.
The formulation for the return electrode is less complex; it should include an ionic molecule of the opposite charge to that of the active ingredient. Buffering and minimization of skin irritation should also be considered.
The electrode must be of an electrically conductive material, and its geometry should facilitate spreading of the electrical current to enable uniform delivery over the patch area. If the electrode is chemically inert, then electrolysis of water can result in pH changes. The use of active electrodes, comprising an electrochemical cell, in conjunction with a formulation which contains a solution of the ions of the cell (i.e., a Ag-AgCl electrode with a solution containing Cl
The manufacturing method of the electrodes can also affect the performance of active electrodes. The most common methods for creating electrodes are screen printing or deposition on a substrate. Various process parameters can affect the surface finish, thickness, and uniformity of the electrode, which all in turn affect the electrochemical behavior of the electrodes.
The quantity of drug delivered by an iontophoretic patch, determined by the amount of current applied to the patient and the time period over which the current is applied, is typically measured in mA-minutes. The therapeutic effect of the drug delivery, often measured via pharmacokinetic studies of drug level in the blood, also depends on peak current and duration of treatment.
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