US Pharm. 2009;34(4):43. 

Because of the strong magnetic field created by the equipment during an MRI, ferromagnetic metal objects can be pulled by the magnet at high speed toward the patient on the scanner table. Prior to an MRI, patients are told to remove all metal objects they may be wearing and are asked about the presence of any metal implants (e.g., pacemaker, prosthetic hip, implanted IV port). Even retained bullets and shrapnel, tattoos, and permanent eyeliner may create problems. However, few people are aware that transdermal patches—such as Androderm (testosterone); Transderm-Nitro and Deponit (nitroglycerin); Habitrol, Nicoderm, and Nicotrol (nicotine); Transderm-Scop (scopolamine); and Catapres-TTS (clonidine)—should also be removed prior to scanning. 

These patches are not ferromagnetic and, therefore, will not be drawn to the magnet. However, transdermal delivery systems with a metallic component are conductive. Some patches are formulated with an aluminized backing that could potentially cause injury to the patient if worn during an MRI procedure. MRI systems require the use of radiofrequency (RF) pulses to create the magnetic resonance signal. When conducting materials (i.e., aluminized backing) are placed within the RF field, the result may be a concentration of electrical currents sufficient to cause excessive heating and tissue damage. 

The FDA is aware of two adverse events in which patients who were wearing a nicotine transdermal patch during an MRI experienced burns. In the first report, a patient entered an MRI scanner wearing a Habitrol 21-mg patch. He started thrashing upon initiation of the third scanning cycle, and the test was stopped immediately. When the patient was removed from the MRI, he stated that his arm was burning. Upon examination, his upper left arm was mildly erythematous, and there was a small, denuded blister where the patch had been placed. In the second report, a patient underwent a short (<40 seconds) MRI of the lumbar spine while wearing a nicotine patch. Later, the patient complained of burn lines on his upper arms. In addition, www.MRIsafety.com contains reports of a patient who underwent an MRI while wearing a Deponit patch and received second-degree burns. For a list of objects that cannot be worn during an MRI, visit www.newmri.com/html/mr_safety.asp. 

In light of these recent incidents, patients should be questioned about their use of any transdermal patch before an MRI. Unless it is certain that the patch does not contain metal, patients should be counseled to remove it temporarily to avoid unnecessary burns. 

Sun Exposure: Another problem that can occur involves topical patches and sun tanning. ISMP received a report about a patient who experienced hot flashes after several days of tanning while wearing Climara (once-a-week estradiol transdermal system). She also noticed dark spots where her patch had been applied. It is unknown whether an early release of estrogen from a heated patch occurred, leading to an abrupt drop in continuous drug delivery, decreased estrogen blood levels, and the subsequent symptoms. However, the report suggested there might be such a tie, and that people are often unaware of problems associated with exposing transdermal systems to excessive heat. The report also mentioned that, until more is known, patients who are currently using the Ortho Evra (norelgestromin/ethinyl estradiol) contraceptive patch should be advised to avoid prolonged sun exposure in the area of the patch. 

The total amount of drug absorbed and the resulting plasma drug concentrations from transdermal systems can increase during heat exposure. Duragesic (fentanyl transdermal) labeling, for example, advises patients to avoid exposing the application site to direct external heat sources, such as heating pads, electric blankets, heat lamps, saunas, and hot tubs. Keep in mind that heat can increase skin permeability, vasodilation, and blood flow to the skin and may influence the delivery of other drugs from transdermal systems. Educate patients about this possibility, as increased drug absorption has compromised efficacy or led to drug toxicity.1 

REFERENCES

1. Carter KA. Heat-associated increase in transdermal fentanyl absorption. Am J Health Syst Pharm. 2003;60:191-192.

This column was prepared by the Institute for Safe Medication Practices (ISMP). ISMP is an independent nonprofit agency that analyzes medication errors, near misses, and potentially hazardous conditions as reported by pharmacists and other practitioners. ISMP then makes appropriate contacts with companies and regulators, gathers expert opinion about prevention measures, and publishes its recommendations. To read about the risk reduction strategies that you can put into practice today, subscribe to ISMP Medication Safety Alert!® Community/Ambulatory Edition by visiting www.ismp.org. ISMP is a Federally Certified Patient Safety Organization, providing legal protection and confidentiality for submitted patient safety data and error reports. ISMP is also a Food and Drug Administration (FDA) MedWatch partner. Call 1-800-FAIL-SAF(E) to report medication errors to the ISMP Medication Errors Reporting Program (MERP) or report online at www.ismp.org. ISMP address: 200 Lakeside Dr, Suite 200, Horsham, PA 19044. Phone: 215/947-7797. E-mail: ismpinfo@ismp.org.

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