More Mix-ups between Propylthiouracil and Purinethol

The Institute for Safe Medication Practices (ISMP) is warning about mix-ups between the trade name of one drug and the generic name of another. Purinethol® (mercaptopurine), is the trade name of a potent antimetabolite used in oncology. Propylthiouracil is an anti-thyroid agent that only comes in generic form. The ISMP points out that although these drug names may appear to be quite distinct, there are several common characteristics that may cause confusion. Both names start with "P" and end with "L", both come in 50 mg. tablets, and the "your" sound in "purine" and "uracil" can increase the risk of error. Also, propylthiouracil is sometimes abbreviated "PTU," which can be mistaken to mean Purinethol®. ISMP describes several examples of mix-ups between Purinethol® and propylthiouracil. In one case, a child with acute lymphoblastic leukemia mistakenly received propylthiouracil instead of Purinethol® for 6 months, even after his parents asked why the tablet looked different. As a result, the patient missed 6 months of chemotherapy. The reverse type of error, when Purinethol® is given instead of propylthiouracil, can be even more serious. The dose of propylthiouracil is often several hundred milligrams a day, which could be many times more than the maximum dose for Purinethol®. If Purinethol® is given at these high doses, this can lead to significant harm, including bone marrow suppression, hepatotoxicity, immunosuppression, and teratogenicity. ISMP cites a tragic case where a pregnant patient with a longstanding history of hyperthyroidism was given a prescription for "PTU". The prescription was mistakenly filled and refilled with Purinethol®. The patient became increasingly fatigued and over time developed a fever, a painful anal fissure and vaginal bleeding. She was sent to the emergency department where she was diagnosed with sepsis and spontaneously aborted the fetus at 16 weeks gestation. She was then taken to the OR to deliver the placenta, where she coded multiple times and died. The patient's death remained a mystery until her family gave prescription records from her community pharmacy to a pathologist, who was then able to see the link with Purinethol toxicity. ISMP says that electronic prescribing and barcode-assisted dispensing can offer some protection, but they cannot entirely eliminate errors. Here are some of ISMPs additional suggestions: • First, install computer order entry system warnings for both drugs, with hard stops that require documentation before proceeding. • Do not store Purinethol and propylthiouracil near each other, and consider use of warning labels on product containers. • Encourage prescribers to avoid using abbreviations, list the brand and generic names on orders for Purinethol, and include the purpose when prescribing either drug. • When dispensing in community pharmacies, match the drug's NDC number to the one listed in the computer unless barcode scanning is used. • Finally, counsel patients before dispensing these two drugs, and fully investigate situations where patients report that their drugs look different than usual.