Elena asked
I'm pregnant and have tinzaparin injections daily and I've got tonsilitis. My doctor as prescribed erythromycin 250mg. I've taken the first one tonight and then afterwards read the leaflet. It basically says dont take if you are on blood thinners so I had a look online and found it says to find a different antibiotic as these two mixed together can be potentially life threatening. Can you please tell me if this is true? Thank you
Answer
Erythromycin (brand name Erythrocin) is an antibiotic that is classified as a "macrolide". It is used for a variety of indications including skin infections, respiratory tract infections and pneumonia. Although a relatively safe and effective antibiotic, it is associated with various drug interactions due to it's effects on the CYP3A4 liver enzyme. In most cases, it inhibits CYP3A4, which can potentially lead to increased concentrations of other drugs that are metabolized by that enzyme.
Erythromycin Blood Thinner Interactions
In terms of blood thinner interactions, erythromycin is known to interact with one of the most commonly used drugs, Coumadin (warfarin).
Erythromycin may increase blood concentrations of Coumadin (warfarin). As mentioned above, erythromycin inhibits the metabolizing enzyme CYP3A4. Inhibition of this enzyme decreases the clearance of warfarin, and thus, increase levels of the drug in the body. This could potentially lead to side effects such as bleeding and bruising. When using erythromycin with warfarin, INR should be monitored carefully.
Erythromycin is known to interact with other oral blood thinners that are metabolized via CYP3A4 including:
- Eliquis (Apixaban)
- Xarelto (Rivaroxaban)
- Brilinta (Ticagrelor)
- Vontivity (Vorapaxar)
Erythromycin however, does not interact with most injectable blood thinners, as they are not metabolized via CYP3A4. There are no reported interactions between erythromycin and:
- Heparin
- Lovenox (Enoxaprin)
- Innohep (Tinzaparin)
With Innohep specifically, there is no reported or listed interaction between it and erythromycin.
Summary
Erythromycin interacts with many oral blood thinners as it can inhibit the metabolism of them via inhibition of the CYP3A4 liver enzyme. Erythromycin does not however, interact with most injectable blood thinners.
