Iontophoresis in Physiotherapy - Beyond Ultrasound

Note: The ultrasound equivalent is called phonophoresis (uses sound waves to drive drugs through skin). Iontophoresis uses electricity instead.

How It Works

• Charged drug ions are placed under an electrode of the same polarity - like charges repel, pushing the ions into the tissue
• Penetration depth: 0.2 to 1.5 cm, depending on drug and tissue type
• Electrical dose is measured in milliampere-minutes (mA-min) = current intensity x duration
• Treatment sessions: 10-20 minutes, repeated 3-8 times depending on response
• (Pfenninger and Fowler's Procedures for Primary Care, 3rd ed.)

Methods / Delivery Approaches Used in Physiotherapy

Common Drugs Delivered via Iontophoresis in Physiotherapy

Clinical Indications (Used in physiotherapy settings)

• Tendinitis (Achilles, rotator cuff, patellar, lateral epicondyle)
• Bursitis
• Plantar fasciitis
• Carpal tunnel syndrome
• de Quervain's tenosynovitis
• Trigger points
• Scar tissue remodeling
• Hyperhidrosis (palmar/plantar)
• Post-traumatic edema
• Wound healing
• Neuritis / local analgesia

Iontophoresis vs. Phonophoresis vs. Ultrasound

Contraindications

• Skin hypersensitivity to the drug being used
• Open wounds or broken skin at the electrode site
• Metal implants directly under the electrode
• Cardiac pacemakers
• Known drug allergy

Can Iontophoresis Be Used with IFT, TENS, or MS?

The Core Rule: Iontophoresis Requires DC (Direct Current) ONLY

Current-by-Current Breakdown

Why IFT, TENS, MS Cannot Deliver Drugs

• IFT uses two medium-frequency AC currents (e.g., 4000 Hz and 4100 Hz) that interfere inside the tissue to produce a 100 Hz beat frequency. Being AC, the electrode polarity flips thousands of times per second - ions are pushed in and then immediately pulled back out. Net delivery = zero.
• TENS pulses are biphasic (symmetrical or asymmetrical) - again, no consistent polarity to drive ions in one direction.
• MS/Russian stimulation uses 2500 Hz sinusoidal AC in bursts - also fully alternating, no net DC component.

What IFT, TENS, and MS ARE Used For (in physiotherapy)

Summary

Iontophoresis = DC current ONLY. IFT, TENS, and MS all use alternating or pulsed AC current, which cannot produce net ion flow through skin. Trying to use these for drug delivery would be ineffective. Each current type has its own separate, well-established physiotherapy applications.

When Is Iontophoresis Used in Electrotherapy?

The Simple Answer

The Electrotherapy Classification Tree

ELECTROTHERAPY
│
├── NERVE/MUSCLE STIMULATION (no drug)
│   ├── TENS → pain gate control, chronic/acute pain
│   ├── IFT  → deep pain, muscle spasm, oedema
│   ├── NMES/MS → muscle strengthening, re-education
│   └── FES  → functional movement in neuro patients
│
└── DRUG DELIVERY (with drug)
    ├── IONTOPHORESIS → DC current + ionic drug
    └── PHONOPHORESIS → Ultrasound + topical drug

Specific Situations When Iontophoresis is Chosen

When NOT to Choose Iontophoresis (use other electrotherapy instead)

The Practical Decision Rule

1. Is the target superficial? (within 1.5 cm of skin) - If yes, proceed
2. Is a drug needed at the site? - If yes, iontophoresis is the right electrotherapy choice

In Summary

Iontophoresis occupies a unique niche in electrotherapy - it is the only current-based modality that acts as a drug delivery system. It is used when localized, superficial, drug-dependent treatment is required and when avoiding needles is preferred. It is always delivered with DC current and is selected specifically because IFT, TENS, and MS cannot perform this function.

DC Current Types Used in Iontophoresis

1. Continuous DC (Galvanic Current) - THE GOLD STANDARD

• This is the primary and most widely used DC for iontophoresis
• Produces the strongest, most consistent ion flow
• Downside: can cause galvanic skin burns if intensity is too high or skin prep is poor

2. Pulsed DC (Modified Direct Current)

• Used when patient has sensitive skin or cannot tolerate continuous DC
• Pulses allow skin to briefly "recover" between pulses
• Drug delivery is slightly less efficient than continuous DC but still clinically effective

3. High Voltage Pulsed Current (HVPC)

• The very short pulse duration means average current is actually low and safe
• Can be used for iontophoresis because it is monophasic (net DC)
• Also used for wound healing and oedema reduction independently
• Less commonly used for iontophoresis compared to standard galvanic DC

Key DC Parameters You Must Set for Iontophoresis

The Polarity Rule (Most Important Concept)

Drug ion is POSITIVE (+) → Place under ANODE (+) electrode
Drug ion is NEGATIVE (-) → Place under CATHODE (-) electrode

Like charges REPEL → drug is pushed INTO the tissue

• Dexamethasone (negative ion) → Cathode (negative electrode)
• Lidocaine (positive ion) → Anode (positive electrode)
• Acetic acid (negative ion) → Cathode

Why AC Currents (IFT, TENS, MS) FAIL for Iontophoresis

AC current:  + → - → + → - → (polarity reverses constantly)
             Ion pushed IN, then pulled BACK OUT
             Net drug delivery = ZERO

DC current:  + → + → + → + → (stays same direction)
             Ion pushed IN consistently
             Net drug delivery = EFFECTIVE

Summary Table

Bottom line: Any current that maintains a net unidirectional (DC) flow can be used for iontophoresis. Continuous galvanic DC is the standard choice. Pulsed DC and HVPC are alternatives. All AC-based currents (IFT, TENS, MS) are completely unsuitable.

DC Devices Used in Physiotherapy

Category 1 - Dedicated Iontophoresis Devices

Category 2 - Galvanic (DC) Units

Category 3 - HVPC (High Voltage Pulsed Current) Devices

How a Typical Clinical DC/Iontophoresis Machine Looks

CONTROLS ON THE DEVICE:
┌─────────────────────────────────┐
│  Polarity switch: + / -         │  ← Set to match drug charge
│  Current intensity (mA): 0-4    │  ← Usually 1-4 mA
│  Timer (minutes): 0-20          │  ← 10-20 min per session
│  Dose display (mA-min)          │  ← Target: 40-80 mA-min
│  Output terminals: Red(+) Black(-)│ ← Connect electrodes
└─────────────────────────────────┘

Other DC Applications These Devices Are Also Used For

Key Point - Denervated Muscle

Only DC (galvanic) can stimulate a completely denervated muscle. TENS, IFT, and MS all require an intact nerve to work. If a nerve is completely cut/damaged (LMN lesion), the therapist must use a DC galvanic stimulator.

Summary

The DC device is the only electrotherapy machine capable of iontophoresis. TENS, IFT, and MS machines cannot be substituted - they do not have a DC output channel for drug delivery.