Drugs given once a week may be prone to deadly dosage errors

There are a few pills that you can take only once or twice a week, which is quite a convenience compared to most medicines. But harmful mistakes may happen because your doctor and your pharmacist are mostly used to medicines that are taken daily, not weekly. They've occasionally been known to accidentally write or type "daily" instead of "weekly." If you take weekly pills every day by accident, you could be harmed. Sadly, some people have even died.

In the future, we're likely to see more medicines that can be taken by mouth once weekly. But right now there are just a few. Methotrexate is one, if it's used to treat conditions other than cancer. Methotrexate is a cancer medicine. But in recent years doctors have used it successfully to treat other conditions such as rheumatoid arthritis and psoriasis.

Methotrexate works well for these other conditions if you take the medicine just once or at most twice a week in smaller doses, along with your blood count being monitored. Serious harm, even death, could occur if you take methotrexate daily for conditions other than cancer. Among other things, it causes abnormally low blood counts, mouth sores and bleeding, and can lead to serious infections. In one case a physician prescribed methotrexate 15 mg daily rather than weekly for a 79-year-old patient. The patient received nine doses before the error was discovered. The patient later died.

Some drugs for osteoporosis (bone loss, making you prone to spontaneous fractures) are available in a once weekly dosage form. Actonel (risedronate) is one. Another is Fosamax (alendronate). These drugs are already pretty hard on the stomach, often causing trouble swallowing and heartburn. But you could develop an ulcer if you take these pills daily instead of weekly.

In several instances we've learned about through the error reporting program on our consumer website, a patient took one of these drugs daily instead of weekly because they misread the directions on the prescription bottle. In one case, a man with arthritis mistakenly took one tablet of methotrexate each morning, but the directions said to take one tablet each Monday. He read Monday as morning. In another case, the prescription label said to take the medicine every 12 hours for just three doses. But a woman took the medicine every 12 hours for 6 days. Another woman took extra doses to help relieve her arthritis pain - something that should never be done.

Here are some things you can do if you are taking once a week medicines. With all medicines, but especially with methotrexate, be sure to ask your doctor to print the reason for it on the prescription, along with the directions. You might take a medicine like methotrexate daily if you have cancer, but weekly if you have arthritis. If the pharmacist knows your condition, he'll be in a better position to make sure the directions for taking your medicine are correct. If the purpose of the medication is not made apparent, pharmacists should speak directly with the prescriber to determine the reason to verify the proper dosing schedule and assure appropriate monitoring of the patient.

Never leave the doctor's office or the pharmacy unless you clearly understand how to take your medicine.

Ask your doctor if the medicine comes in a special package designed for weekly use. For example, Rheumatrex, one brand of methotrexate, comes in a special package called a dose pack that dispenses only one dose per week.

When dropping off a prescription, pick the day(s) of the week that you'll be taking your medicine, and ask your pharmacist to include that in the instructions. Avoid Monday since it could be misread as "morning." Ask for big print on the prescription label if you have poor eyesight.

When picking up your prescription, make sure the pharmacist goes over the label and directions for taking the medicine. If an error somehow crept into the process, this can become a stop gap measure. Be sure that what you hear agrees with what the doctor told you. It's a good idea to repeat back the instructions so the pharmacist can assure you know how to take it. When taking your medicine, never take any extra doses.

For more on ISMP's consumer website, go www.consumermedsafety.org.