Iontophoresis Flashcards
(35 cards)
What is Iontophoresis
Use of low voltage direct current to move charged ions across a dermal barrier.
Biophysical Mechanism
- Primary route for ion transport through sweat glands, the pores of the skin or hair follicles.
- Assumption that the current “drove ions through the skin” is probably not correct.
- Current thought: Better to think of as facilitating absorption
Facilitating Absorption
- Electroporation- increase in number of pathways in skin for drug delivery.
- Epidermal cells’ lipid dipole layer has a negative charge.
- When current applied, cells rearrange to open pathways.
- This takes 3-4 minutes of current application.
Drugs can be delivered by iontophoresis if:
- Can be ionized
- Are stable in solution
- Not altered by electrical current
- Molecules are small in size
What would you place under (+)?
(+)
Same with negative
An electrode containing drug is called…
“treatment”, “active” or “delivery”
Opposite electrode is called…
“return” or “dispersive”
Depth of Delivery of Drug
- Reports vary by study ranging from a depth of 1 to 3 mm.
- Over 12-24 hours the drug diffuses more deeply (up to 17 m or 2/3 inch)
- There is also some evidence that shows distribution of drug up to 2 cm (3/4 inch) laterally in intact skin from the electrode.
- Used for acute, local, superficial tissues
Ion Transport
- For DC to be effective pushing drug molecules across the skin, current would need to overcome electrical impedance of the skin
- Difficult for DC = lack of ion transport to opposite electrode
To keep the drug in the area we need to…
keep blood flow low
Can iontophoresis be applied with other agents?
No it should not be applied in conjunction with any agent that may change skin permeability or blood flow.
Ex: Heat, Cold, US
Why use DC?
Need polarity for electroporation and to repel charged ions
AC and pulsed current are ineffective for transferring ions across skin.
Consequences of using DC
Polar Effects
- Skin normally acidic (pH ~ 4.7)
- Salt and water present on skin
- Electric charge creates formation of HCl at Anode and NaOH at Cathode
- AAA – Anode Attracts Acid
- CAB – Cathode Attracts Base
More concerned about NaOH due to skin naturally being more acidic can be more sensitive
Polar Effects - H2O and NaCl
Causes a split. NaCl split then H2O splits. Electrical reaction then chemical reaction results in HCl and NaOH. Skin irritation more likely at NaOH (cathode)
What are good ways to prevent chemical reactions?
- Buffered electrodes decrease likelihood of irritating or burning at the cathode.
- Decreasing current density at that electrode.
– Increasing size of the electrode
– Decrease current levels
– Increase distance between electrodes
Why deliver drug by iontophoresis rather than oral administration?
- Absorption and distribution may be unpredictable and problematic with oral administration.
- Greater likelihood of adverse side effects with systemic distribution vs local administration
Iontophroesis vs Injections
Iontophoresis less:
Invasive (lower risk of infection)
Painful
Expensive
Medications typically delivered by iontophoresis
- Anti-inflammatory meds (e.g., dexamethasone)
– 99% of the time
– Small molecule corticosteroid, negative charge
– Delivered under the negative electrode (cathode)
– 0.4 - 4.0% solution (% doesn’t change effects)
– Must have a prescription from the physician for this - Local anesthetics (e.g., lidocaine)
Indications for Dexamethasone
- Inflammatory disorders affecting tissues
- Superficial and localized
Lidocaine Hydrochloride
Local anesthetic, (+) charge, in the past was delivered with dexamethasone.
Was included to reduce discomfort, provide some buffering.
Newer electrodes are buffered so dexamethasone is usually delivered alone.
Indications for Lidocaine
Analgesia in acute inflammatory conditions (Acute pain relief)
Ex: Sports injury (inject and send back in)
Post-herpetic neuralgia (Pain that lasts at least three months after the shingles rash has healed)
- Lidocaine/prednisolone
Quantifying Iontophoresis
Quantification based upon Milliamp Minutes (mA-min)
mA-min=Current Amp x Time
Nothing to do with dosage.
Current and how long is what matters!
Ex: 2mA current for 10 minutes = 20mA-min.
Research has shown effective drug delivery with treatments in a range of 40 to 80 mA-min. (Most treatments tend to be 80mA but anything in range is fine)
Iontophoresis units: DC Generators
- Portable, battery-powered
- Used only for iontophoresis
- 1 or 2 channels
- Some provide automatic current ramp-up
- Dosage
- Set dosage in mA-min
Delivering Dosage
- Adjust the dosage, set the current at a level of patient comfort ,and then time usually automatically calculated
- Most units do not allow settings above 4 mA.
- Max out current based on patient comfort as it is able to pass the medication faster but patient comfort is most important.
