It's important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with penicillin. Similarly, it's best to check with your doctor or pharmacist before taking any new medicines while taking penicillin, to make sure that the combination is safe. Some key points are:
Penicillin doesn't affect hormonal contraceptives such as the pill. However, if you experience vomiting or diarrhoea while taking this antibiotic, this can potentially make your pill less effective at preventing pregnancy. If this happens to you, follow the instructions for vomiting and diarrhoea described in the leaflet provided with your pills.
If you need to take the oral typhoid vaccine (Vivotif) you should wait until at least three days after you've finished your course of penicillin, because the antibiotic could make this vaccine less effective.
Penicillin may decrease the removal of the medicine methotrexate from the body, which could increase the risk of its side effects. If you're taking methotrexate your doctor may want you to have extra check-ups and blood tests while you're taking a course of this antibiotic.
Penicillin may rarely alter the anti-blood-clotting effects of coumarin anticoagulant medicines such as warfarin. Your doctor may wish to monitor your blood clotting time (INR) more frequently if you're taking this antibiotic with warfarin.
More information about penicillin
- What is penicillin used for and what should I know?
- Who shouldn't take penicillin?
- How do you take penicillin?
- What are the side effects of penicillin?
Last updated: 13.03.2019
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