From the July 2006 issue

In September, a new form of inhaled insulin, EXUBERA (insulin human [rDNA origin]) will become available. The drug has an onset of action similar to rapid-acting insulin analogs and must be inhaled about 10 minutes before a meal. It also has a duration of glucose-lowering activity comparable to subcutaneously administered regular human insulin. The drug will be available in 1 mg and 3 mg blisters of insulin powder, which are administered using the Exubera Inhaler. We have already received a report from a pharmacist who alerted us to the risk of serious medication errors with this high-alert drug. Exubera is dosed in mg (as during clinical trials), with a weight-based dosing chart for initial mg doses, and a conversion chart for equivalent doses in units (see table 1), the long-standing, usual way insulin is prescribed.

Table 1: Approximate Equivalent IU Dose of Regular Human Subcutaneous Insulin for EXUBERA Inhaled Insulin Doses Ranging from 1 mg to 6 mg (from: www.pfizer.com/pfizer/download/uspi_exubera.pdf)

Confusion between mg and units seems inevitable, especially given the following: The 1 mg blister is equivalent to 3 units of insulin, thus the risk of confusion between the 3 mg blister and 3 units is heightened. Another potential source of error is that the equivalency of mg to units is not exactly incremental. For example, although 1 mg of the drug is equal to 3 units of insulin, a 3 mg dose is equal to 8 units, not 9 units, as may be expected. Likewise, consecutive inhalation of three 1 mg blisters results in significantly greater insulin exposure than inhalation of one 3 mg blister, due to differences in retention of blister contents. Thus, three 1 mg doses should NOT be substituted for one 3 mg dose. While this less-intrusive route of administration for insulin is welcomed, for safety reasons, current dosing instructions and labeling should not have been approved. We have alerted FDA and Pfizer to these problems. Please warn practitioners about this serious problem as soon as possible. By the way, the Exubera package insert includes the abbreviation “U” for units, and the dosing table refers to “unit” equivalents as “international units,” expressed as “IU.” Both are abbreviations included in ISMP’s and FDA’s lists of error-prone abbreviations.