By Jonathan S. Katz, M.D.
Many patients with Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) are treated with intravenous immune globulin (IVIG). But, the dose of IVIG that each patient is prescribed for CIDP can vary greatly. I have seen patients need anywhere from between a quarter of their weight in grams all the way up to more than their weight in grams, with infusion intervals ranging from every few weeks to more than once per month. Ultimately, the dose a patient will need depends mainly on how active his or her disease is.
The immune globulin Intravenous CIDP Efficacy (ICE) trial, which was a large clinical study of IVIG against a placebo in CIDP, proved IVIG treatment is better than a placebo. It also provided a large amount of information about the natural history of CIDP and the responses to treatment over roughly the first year of therapy. Since that study was finished, many doctors choose to use the same starting dose as the trial: about 2 grams per kilogram, usually given over a few days, followed by three follow-up therapies of 1 gram per kilogram, at three-week intervals. This dosing regimen is continued for approximately three months.
While the ICE trial proved IVIG is an effective treatment for CIDP, it also revealed that IVIG is not a perfect therapy. Only about half of patients will respond to IVIG therapy. A poor response to IVIG therapy may either mean the diagnosis was incorrect, or that the diagnosis is correct, but there is simply no response to treatment. We have seen CIDP mistaken for B12 deficiency, diabetes and other types of neuropathy. Therefore, a non-response could be a good time to re-review records and to consider an alternative diagnosis or therapy.
For patients who do respond to therapy, the next step is to determine what dose to continue with and for how long. After the initial three-month period described above, if the initial response is incomplete or the response wears off too quickly, many doctors will attempt to adjust the dose upward or shorten the infusion intervals. In contrast, if the response is more than adequate, the doctor may try to adjust the IVIG dose downward with the goal of searching for the lowest dose that keeps the disease in check. This often leads to either using less than a 1-gram dose every three weeks or keeping the same dose but with a longer interval of perhaps four or five weeks. At some point, many insurance companies actually require this adjustment after a patient has initially responded to therapy. This usually occurs before the end of one year of treatment, or when the doctor tries to renew the prescription. A dose adjustment is actually good advice, especially when the same dose of IVIG is being given month after month and there is still no sign of relapse to suggest the disease is still active.
In our next blog, we will continue the discussion of IVIG therapy for CIDP.