Penicllin interactions with estrogen / testosterone / or blood tests?

[Tills]

Hi folks,

Does anyone know if penicillin has any effect on estrogen / testosterone / blood test results? I can't see any mention of it interacting with the E and T but I wondered if penicillin can alter blood readings in our area of testing?

Background: I have an ingrowing toenail infection and have been put on a 14-day course of flucloxacillin 500mg x 4 daily. My next blood tests are in 10 days time.

I'm ideally after any informed responses please rather than well-meaning second guesses And ideally I don't want to move the blood test.

xx

p.s. the background to the toenail feels like a SoB slap. I was having a feminine pedicure at a Vietnamese run place and before I could stop the lass she had cut right down the side of my toenail. Years of carefully managing the toe were undone and, sure enough, it's now become infected.

[Lori Dee ✅]

The only warnings I find are:

"Flucloxacillin may interact with other medications, including oral contraceptives (birth control pills). It can reduce the effectiveness of hormonal contraceptives and increase the risk of unintended pregnancy. Alternative or additional contraceptive methods should be considered while taking flucloxacillin and after discontinuing the medication. Discussing potential interactions with other medications with a healthcare professional is important."

Although not stated explicitly, this could indicate that it interferes with progestins (synthetic progesterone) and possibly with estrogen. It is not clear if it reduces the bioavailability (which might affect lab work) or if it merely interferes with the hormone receptors to make birth control meds less effective.

I would do the lab tests anyway, then maybe advise the ordering GP that you were on antibiotics at that time. It may not matter, but if your lab results are off, they may want to rerun the tests after the 14-day treatment to confirm.

[Tills]

The only warnings I find are:

"Flucloxacillin may interact with other medications, including oral contraceptives (birth control pills). It can reduce the effectiveness of hormonal contraceptives and increase the risk of unintended pregnancy. Alternative or additional contraceptive methods should be considered while taking flucloxacillin and after discontinuing the medication. Discussing potential interactions with other medications with a healthcare professional is important."

Although not stated explicitly, this could indicate that it interferes with progestins (synthetic progesterone) and possibly with estrogen. It is not clear if it reduces the bioavailability (which might affect lab work) or if it merely interferes with the hormone receptors to make birth control meds less effective.

I would do the lab tests anyway, then maybe advise the ordering GP that you were on antibiotics at that time. It may not matter, but if your lab results are off, they may want to rerun the tests after the 14-day treatment to confirm.

Thanks so much Lori Dee. That's really helpful.

I've been reading around the medicine itself for this kind of infection and it's normally prescribed for 5-7 days. The fact that I was supplied a 14-day box might not be intended.

So if the toe improves I may stop the course in 5 to 7 days as per NHS guidelines, which would leave a few days before my blood test. Not perfect, but still.

[Lori Dee ✅]

I've been reading around the medicine itself for this kind of infection and it's normally prescribed for 5-7 days. The fact that I was supplied a 14-day box might not be intended.

Usually, with antibiotics, they intend for you to run the full course of treatment. They will sometimes include the instructions to take it all as directed. That is to make sure all the bugs are dead and don't return when you stop taking it. Is there a number you can call or an email to get clarification?

[Paulie]

I asked AI " Does penicillin has any effect on estrogen / testosterone / blood test results?" and got this:

Penicillin usually does not directly change testosterone or estrogen levels, and it does not commonly distort routine blood tests by itself. The main exception people worry about is birth control: some older reports and biologic theory suggest penicillin-class antibiotics could reduce estrogen recycling in the gut, but more recent evidence does not show a meaningful drop in hormonal contraceptive effect for most people.[pmc.ncbi.nlm.nih]

Hormones
Penicillin is not known to directly lower testosterone or estrogen in a predictable way. If hormone levels change while you're taking it, that is more likely due to the underlying illness, stress, changes in eating, or another medication rather than the penicillin itself.[pmc.ncbi.nlm.nih]

Blood tests
Penicillin generally does not interfere with standard blood tests the way some drugs do, such as biotin with hormone assays. Some antibiotics can affect certain lab markers or specific infection tests, but penicillin is not a common cause of false testosterone or estrogen results.[bluehorizonbloodtests +3]

Practical note
If you're getting a hormone panel, it's still worth telling the clinician or lab exactly what you're taking, because interpretation can depend on timing, dose, and the reason for the test. If your question is about fertility, menstrual changes, or a specific blood test, I can help interpret that more precisely.[mdlinx +1]