Iontophoresis is a medical procedure to administer a liquid drug into the skin and deeper tissue without using a syringe. The drug is transported through the skin via an electrical current. The administration of procaine into joints is one of the common scenarios where iontophoresis is used.
Iontophoresis seems to be widely used to treat rheumatic, dental and joint pain and it is listed in many studies as a treatment administered to patients. But I couldn't find many studies examining the effectiveness of iontophoresis itself.
This study "Clinical Evaluation and Treatment Options for Herniated Lumbar Disc" states:
The use of either ultrasound (phonophoresis) or electricity (iontophoresis) over the injected area may provide additional relief, although the benefits of these methods have not been proved.
Whereas "Selected Medicines Used in Iontophoresis" states:
Iontophoresis allows delivery of about 10–2000 times more polar hydrophilic therapeutic molecules than typical application of a drug substance to the skin surface.
It was found that 2% lidocaine with epinephrine can be delivered up to 5 mm below the surface of the skin.
Dexamethasone/dexamethasone phosphate can be delivered to depths of up to 12 mm.
That basically means it's more effective than rubbing a cream on your skin. BUT 5 mm is not very deep and depending on the size of your dog it might not be deep enough to numb the pain caused by a spinal disk. (To be absolutely technically correct here let it be stated that lidocaine is a different substance than procaine and may react differently, but even 12 mm is not very deep if you want to reach the spinal cord.)
The fact that iontophoresis is commonly used in pain therapy suggests that it does indeed work. There is even a study examining how effective iontophoresis is for the Transport of Local Anesthetics, although I don't know what the result actually means for your specific case...
Our results suggest that of the properties studied, the best predictors of iontophoretic transport of local anesthetics are ionic mobility (or pKa) and molecular size.
There's no drug without side effects. Your dog could swallow a pain pill, but in contrast to a pill iontophoresis transports the drug to the place where it should work instead of spreading it through the whole body. You need less drugs to have the same effect.
All pain pills are rather agressive to the stomach and/or liver and can cause severe organic damage when taken over long periods of time. Coxib is known to be less aggressive on the stomach than most pills, but not significantly so. Iontophoresis has no negative effect on the stomach and is much better for the liver because the amount of administered drugs is much smaller.
And there are no needles involved. You could inject the drug into the painful area, but in this case there are very delicate and fragile structures like the spinal cord right next to it. If the dog moves during the injection, it could injure itself.
Iontophoresis is a method to administer a local anesthetic, but it won't cure the intervertebral disk disease.
I'm not sure how well the therapy works if the fur is not shaved where the electrodes are placed. If the electrodes are not wet enough to soak the fur down to the skin, it cannot work at all. If the therapist made a mess and there is a wet patch connecting both electrodes, the current runs over the surface of the skin instead of through it and the drug is not absorbed at all.
The one study that measured how deep an anesthetic similar to procaine can be delivered into the tissue found a maximum depth of 5 mm. This might not be deep enough to numb the pain caused by a spinal disk.
From what I understand, your dog gets 2 types of painkillers:
- Procaine as local anesthetic to numb the pain
- Coxib as anti-inflammatory and well tolerable pain killer
If the current condition is caused by an inflammation, it will hopefully be cured in a few weeks and you can stop the treatment. But if it is caused by a herniated disc, your dog will need painkillers over a long time.
- Stop the iontophoresis treatment and observe if your dog shows more signs of being in pain
- Ask your vet for a different long-term oral drug like drops of opiates
- Consider surgery