I had the pleasure of being lectured by a physician about a drug interaction. It was regarding Zithromax and Coumadin.
Basically it started out with the doctor calling in a prescription for a Zpak for a patient who is taking Coumadin. This comes up as a major interaction in our computer system and seeing that the patient had never taken the two of them together and the Zpak was from a different prescriber than the Coumadin, I wanted to call the office to make sure if the doctor calling in the antibiotic was aware.
I must have hit a nerve with this doctor because, amazingly, I ended up speaking to him directly. "Name one antibiotic that doesn't potentially raise the INR. Azithromycin is not like the other macrolides. It's not like Biaxin or Erythromycin. Those drugs I would absolutely avoid in a Coumadin patient as well as any patient taking statins such as Zocor. I've never had a single problem with Zithromax."
He wouldn't allow me to get in a word. All I could say was "Yes, I agree," and I repeated it over and over again.
You see... The doctor is correct. Zithromax (azithromycin) isn't like the other macrolides. It doesn't have the same cytochrome P450 interactions, and it generally is much safer to use in patients taking Coumadin than the other macrolides. However, there are a number of case reports where the INR was elevated following a course of azithromycin. The mechanism is unclear (azithromycin may inhibit p-glycoprotein), and a good pattern could not be established. These case reports do show that there is some risk. Moreover, I actually worked for a little bit in a Coumadin clinic, and I've seen a patient's INR increase after getting a ZPak. It may be the safer choice, and in general, I don't mind seeing azithromycin used in Coumadin patients as long as the patient's INR is checked shortly after, and the patient is advised to monitor for signs and symptoms of bleeding. However, if it's possible to treat someone just as effectively with a different antibiotic, I'd rather see that.
And that was the case in this situation. Before calling the doctor, I asked the patient what he was getting the antibiotic for, and he said he had a cold. What do we know about colds? The common cold is caused by a virus. In fact, well over 90% of all upper respiratory tract infections are viral. Therefore, an antibiotic really isn't appropriate, especially in this case where the chosen antibiotic has the potential to increase the patients risk for bleeding.
Unfortunately, I'm not assertive enough and the doctor was too pushy to allow me to explain my reasoning for calling him about the interaction. All I could say was that I understood and agreed with what he was saying, but their still was some risk. If he wanted to stay with the Zpak, I wouldn't have much of a protest. I just wanted to make sure that he was aware of the situation.
After he was done lecturing me, he changed the patient to Amoxicillin. He and I both knew that he was simply giving out an antibiotic to make the patient think he was doing something to treat his cold. It didn't really matter which antibiotic he chose because the patient was going to get better in a couple days anyway. A ZPak is just so easy to write for, and with its once daily dosing, it's easy for patients to take.
That could lead to another point about overusing antibiotics, especially broad spectrum ones like azithromycin, but I'll save that for perhaps another day.