How many of you have taken Trimethopr... - Pernicious Anaemi...

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How many of you have taken Trimethoprim (the anti-biotic) ?


I am working my way through some more info on what might be affecting my B12 etc and came accross this info, that I had not heard before:

taking the antibiotic Trimethoprim stop production of DHFR enzyme which is needed to regulate methylation, and can reduce the regulation of DNA leading to issues with autoimmune diseases and cancer.

I do not remember the paperwork (Patient information leaflet) for this antibiotic advising me of this when the doc prescribed this for me a couple of years ago.

Has anyone else heard of this?

7 Replies

I'm a newbie here but am desperate for answers and advice. I took trimethoprim in July this year and have been I'll ever since with Many b12deficiency symptoms including tingling legs and face. After extensive blood tests GP has diagnosed fibromyalgia. Neurologist says it's anxiety! I've had the b12active test done privately with a result of 71 but wonder if I skewed these results as I 've taken high strength multi in previous 2 months.? I have read that trimethoprim can affect b12 by blocking folate but docs didn't confirm. Hope your issues now sorted

Poppet11 in reply to Myrtle13

I can't comment on that particular antibiotic but yes, it is very likely you have raised your b12 levels by taking a multivit.

Have your doctors actually provided treatment for any of your symptoms and have they offered you a serum b12 test?

I'm finding it affects folate but nothing on b12 absorption. Just out of interest has anyone checked your folate levels? Folate deficiency can cause the same symptoms as b12 deficiency but they are reversible.

Edit again to say I found this

Myrtle13 in reply to Poppet11

Thanks for replying. I saw doc day after finishing a/biotics as I felt so ill ,burning legs,twitching,fatigue etc. Blood tests that day (29 July) showed serum b12 at 532 & serum folate above range more than 20 (3.1 - 19.9). Just got a txt to say bloods ok but vit d a bit low 54 (60-150) pick up a diet sheet at surgery! Seen my usual GP several times since who's done loads more blood tests but could'nt but find anything wrong so suggested fibro which has a lot of similar symptoms and gave me a printout and script for amitryptiine for the pain. I tried half a tablet but felt worse. I'm due to see her again mid no after follow up appointment with neurologist at his NHS clinic. Suggested could be MS. Anyway I found this site with so many helpful people and did the active b12test last week in desperation only to realise the multivits might have skewed the reading. My serum folate (17/10) had dropped to 9.4 that is since taking the Trim but is it low enough to warrant symptoms? When Ihave been eating made sure it 's been green as we have an allotment . Also had thyroid test with blue horizon which was within range. Any idea what to do next? I feel I'm getting worse must do something but what? apologies for the diatribe but any advice welcome thanks


Yes, its usually on the B12 product info leaflet, and often on the antibiotic leaflet. See this topic for more drug interactions with B12:


Thanks for that Marre. I' m really tempted to just buy some B12&folate since I've probably already skewed the active b12 reading. Just feel so awful all the time & look like I've aged 10 years in the last 3 months. Do you think my the drop in my folate level is significant enough (more than 20 end of July) 9.4 on 17/10 my ferritin level in October was 136 ( range 13-150) thanks


Hi Myrtle,

Its hard to say, some people just feel a lot better with higher serum folate levels. I feel folic acid lifts me mentally, seems to affect my mood, whilst B12 lifts me physically say, but we all are so different. There is how ever some research that implies possible harm from to much folic acid (not the natural form in foods as in folate) as to much folic acid seems to stay in the body unmetabolised, it is currently not known if that does harm or not, research not conclusive say. This does not seem to count for vit B12, but again its what is currently known. Best bet is to try and feel what helps you best, trying to stay in "normal" ranges of lab though as it is important to keep all vits in balance. Taking to much of one buts that out of balance and many B vits need each other in metaboilising so if you give loads of one but not enough of the other thenj that one in over flow is just wasted say. Taking a good multi vitamin may help make sure all stays in blanse. Many MS people seem to do well on B12 treatment, but I think for that you may need a more unconventional GP than one from NHS to help you try injected B12,

Perhaps read up a bit see:


I hope this helps,


Myrtle13 in reply to Hidden

Sorry Marre think my lazy grammar may have suggested I've been diagnosed with MS which I haven't. My GP said that's what the neurologist would be checking for when I see him again next week. Thanks again for the advice

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