My grandmother is taking Prilosec for heartburn. She has also been prescribed Dilantin and is now concerned about taking the two together. She has read these can be fatal if taken together. Is that true?

C.H.

Heartburn is a frequent, almost universal, symptom of gastroesophageal reflux disease (GERD). This disease is caused by abnormal reflux of stomach acid into the esophagus.

Commonly used medications for GERD include acid-blockers such as cimetidine (Tagamet) and ranitidine (Zantac), which are now available over-the-counter. The most effective acid-blockers known are prescription drugs called proton-pump inhibitors, such as omeprazole (Prilosec). The package insert for Prilosec states that it can interact with other medications that require a certain liver enzyme (known as P450) to break down the medication in the body. Phenytoin (Dilantin), a drug commonly used for the treatment of epilepsy, is one of these medications.

Thus, taking Prilosec and Dilantin together can interfere with the metabolism of Dilantin and lead to higher blood levels of Dilantin. Although this is stated as a possible interaction, it is not common. Personally, I have yet to encounter a patient who has had a complication as a result of taking these medications together.

However, I do suggest that you discuss your concerns with the doctors who prescribed these medications. There are several options in this case. The simplest would involve stopping Prilosec and starting one of the other acid-blocking drugs that will not interact with Dilantin. Another option might be to substitute another drug in place of Dilantin, or possibly to continue both drugs and measure Dilantin blood levels to ensure that they are not too high.

The key is talking to your doctors about the risks and benefits of any strategy, as well as continuing to see your doctors for close follow-up.