Physical therapists use a variety of modalities to help with pain and inflammation. Iontophoresis is one modality that pushes a steroid drug through the skin to the inflamed area. The idea is to deliver the steroid antiinflammatory to the local area. This way the patient can avoid the side effects of an oral drug.
It’s not clear how well or how fast iontophoresis works. Numerous animal studies have been done using monkeys, horses, rabbits, pigs, and rats. But animal skin and human skin are very different and can’t be compared directly. Human studies are difficult to conduct because it isn’t easy to examine the tissue once the treatment is done.
In this study, the authors asked two questions. Does the thickness of the patient’s skin make a difference? What is the effect of time on the absorption of the drug? For example, does the drug go through the skin right away? Or does it take awhile to cross as much as it’s going to?
This study was very unique. Patients were treated with iontophoresis right before having anterior cruciate ligament (ACL) reconstructive surgery. The steroid used was Dexamethasone sodium phosphate (DEX-P). DEX-P was infused through the skin right before the ACL operation.
The semitendinosus hamstrings tendon was treated. Then during the ACL operation, the tendon was removed (a routine part of ACL reconstruction). The tissue samples were sent to the lab and analyzed. The amount of DEX-P absorbed by the tendon was measured.
For half of the samples, there was no measurement of DEX-P found at all. The reason for this is unknown. It’s possible (though not likely) that the target tissue (tendon) was missed. In other samples, the amount of DEX-P increased as time went by.
The authors suggest that if iontophoresis works by electropulsion, then this should not happen. The electric charge drives the steroid through the skin. There shouldn’t be a delayed response with this mechanism. This finding suggests there may be a different way the drug is getting across the skin. Perhaps it passes through by diffusion or by the blood flow.
Further studies are needed to find out why some patients absorbed the DEX-P and others didn’t. The two groups of patients were very similar in most ways. The position used during the iontophoresis was the same. The temperature in the preoperative suite where they received the iontophoresis was the same. They all had the same surgery to remove the tendon. It’s possible that activity level before the procedure was different and that made the difference.
The skin thickness did not seem linked to absorption. Some patients with thick skin had the highest levels of DEX-P in the tendon. And some patients with the thinnest layer of skin had the lowest levels.
The authors conclude that iontophoresis can help transmit DEX-P through the skin. But it doesn’t do so for everyone. Why it works for some patients but not for others remains unknown.
At the present time, it’s not clear if the amount (dosage) that crossed over was enough to create an antiinflammatory response. More studies are needed to better understand how iontophoresis works and who can benefit from it.