Download Determining Your Dose

Immune Globulin Dosing: An Overview
Determining the proper dosage of immune globulin (IG) varies from patient to patient,
across diagnoses and many other influencing factors. IG is not a one-size-fits-all drug.
The clinical assessment is the most important step in determining dosage but other nonclinical factors also play a role. Understanding the intersection of all of these pieces will
ensure patients are given the most therapeutic amount of drug possible.
When prescribing IG, the first clinical consideration is the patient’s disease. Initially
prescribed to treat primary immune deficiency diseases (PIDD) and immune
thrombocytopenic purpura (ITP), time has shown IG to also be effective in treating
numerous inflammatory and immune-mediated diseases affecting the neuromuscular
system. Currently, the FDA approves IG for a few diagnoses and each IG product’s
dosing recommendations are included in its package insert (PI). In addition, physicians
also can prescribe IG for off-label indications, but by law, these dosing guidelines
cannot be included on the PI. Instead, physicians must use peer-reviewed literature,
clinical observations and their best judgement when deciding on the proper dose. An
interesting note, once a drug is FDA-approved, physicians can legally prescribe
medications for any other purpose. And insurance companies often will cover certain
off-label indications as long as it is the standard of care for that particular disease.
Establishing the correct dose of IG, which is typically given intravenously (IVIG), is
driven by the diagnosis of the patient, the weight of the patient and also the individual
response to therapy. Since clinical effects of IG dosing can have significant
consequences, clinical trials and scientific studies are employed to help establish
maximum and minimum IG dosing standards. Although it is not well-known how much
IG is too much there seems to be no medical benefit above a certain level. Using more
IG than is medically necessary simply increases costs for all including risk of side
effects, fluid volume overload and the need for an already limited natural resource
needed to make IG. Too little IG results in ineffective treatment and a poor clinical
response and may be more common than realized. This predicament may cause both
patient and physician to think the treatment is not working and cause a myriad of
negative symptoms causing more testing and treatments, potential disability and
decreased productivity and decreased quality of life.
There are many factors that can lead to undertreating patients such as: insurance
policies attempting to standardize treatments; prescribers not staying current on latest
research; limited research funding; product shortages causing rationing of supplies;
patient tolerance of treatment; patient compliance. In some cases, insurance policies
will carry a reauthorization clause that requires patients, once stabilized on IG, to try a
lower dose to see if maintenance can be attained at a lower cost. Another factor that
can affect dosing of IG are vial sizes of each product. Each manufacturer has a limited
number of vial size options for each product. Doses are determined partly by the
patient’s weight and if that requirement adds up to an odd-sized dose that doesn’t
evenly match the vial size, the dose is generally rounded up to the nearest available
size.
Overall, this expensive, lifesaving treatment is certainly unique and complicated to dose
correctly and many variables must be considered when trying to ensure patients get the
full benefit. More research is definitely needed but in the meantime, following dosing
recommendations and staying educated are the best ways to maximize patient
outcomes.
For more information on this topic see the February/March 2011 issue of IGLiving
Magazine online at http://www.igliving.com under Feature Articles.
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