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Metformin and cefalexin

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becca19962014

Well-Known Member
Relationship to Diabetes
Type 2
I began cefalexin at the weekend. I've noticed my BG is going low, it's generally low anyway except with infections and the leaflet has a warning for metformin but not what it is and though it supposedly impossible I've had hypos on metformin.

I was wondering if it's possible for it to be going low because of the antibiotic. Last night I ended up needing to eat some of the jelly babies I keep by my bed in case of night time hypos and woke feeling dreadful!. This afternoon is remained fairly low not hypo low but lower than usual and refuses to budge.

GP practice said if I can resolve using juice/jelly babies then it's not emergency and wait until my appointment on Thursday, nhsdirect said they'd phone back in 6-12 hours(!) and our out of hours dr is now via nhsdirect - took over 12 hours Saturday to be seen despite being very unwell by the time I got called back and those 12 hours I had an increasing very high temperature and I've not got that now.

I'm not sure I should just be eating jelly babies to stop it bottoming out. I've considered stopping the metformin temporarily anyway as I've been struggling massively with diahorrea as well, i don't think it'll cause massive issues if I do so (it might I guess). I'm aware I'm due my period soon and that can also be a trigger for me for low BG (hence eating sweet things around that time before but not during) but nothing like this.

Any suggestions?

EDIT I rang NHS just before posting so unlikely to hear anything before 11pm.
 
There is a listed interaction between cefalexin and Metformin that can cause lowering of BG. You should never have been prescribed them together. Cefalexin blocks the excretion of Metformin from the kidneys. The Pharmacy who prescribed this should have had a flag on their system. You might mention it to your GP.

So yes, stop the Metformin, but you may as well finish the course of Cefalexin if it’s only two three days. There’ll be enough Metformin swimming around your system for the time being.
 
I wasn't given it by a pharmacy but directly by the on call GP.
He knew I was taking metformin so that's really concerning.

I'm on 500mg of metformin twice a day. I've four days left of antibiotic and am seeing GP on Thursday so can mention it then.
 
I should mention that it's hanging around the 5 mark for BG which for me is lower than usual (it's usually 6ish) and I feel ill around 5 and use it as an indicator it's going too low as it drops fast from 4.8.

There's nothing in the leaflet to say it shouldn't be prescribed it just says to speak to your doctor about having a lower dose (and I'm on the lowest!!) That's really bad if it shouldn't be prescribed.

I'm really glad I posted as i thought it was just me. I'll speak to NHSdirect when (or if) they call me back as well but I'll miss my next dose anyway.

EDIT It says nothing in the BNF either about it (just had a look online).
 
mikeyB said:
There is a listed interaction between cefalexin and Metformin that can cause lowering of BG. You should never have been prescribed them together. Cefalexin blocks the excretion of Metformin from the kidneys. The Pharmacy who prescribed this should have had a flag on their system. You might mention it to your GP.

So yes, stop the Metformin, but you may as well finish the course of Cefalexin if it’s only two three days. There’ll be enough Metformin swimming around your system for the time being.
Click to expand...
That’s worrying Mike, I have been prescribed Cefalexin a couple of times for UTIs and have taken Metformin, 3000grms, for 8 years!
 
It doesn’t happen to everyone, Eggy, dinnae fash. It just happens often enough for the interaction to be listed.
 
I didn't mean for what I posted earlier to sound like you were lying by the way Mike! I was just surprised that it's a recognised problem yet there's nothing in the bnf and nothing in the leaflet other than to mention you take it to dr/pharmacist in a massive list of other things and they'll decide, nothing about the issue being low BG.
 
Don’t worry, becca, I didn’t take it is an accusation of fibbing, I’m as surprised as you are that it’s not in the BNF. It may be because it doesn’t send the BG dangerously low, but it’s more like taking a big dose of Metformin, which is not an ideal situation.
 
Sometimes it's hard to be sure people haven't taken things the wrong way! What you've said definitely makes sense so I'm going to miss my dose this evening and see how things go. My GP had been speaking to me about lowering it to one metformin a day anyway so maybe I'll use this as a reason to give it ago. It maybe the dr didn't think it would matter because my dose is so low though my last hb1ca was in normal range, I'm on it because of PCOS, so it should have been a consideration for him at least.

I'm really particular about taking all my meds and hate missing a dose of any of them but it makes sense to do so in these circumstances.

I'm having difficulty sleeping anyway due to possible sleep aponea (due to growths of unknown origin in my throat and neck which are partially blocking it anyway but worse at night) which I've been told could be effecting my BG as well during the night, hence the sleeping with jelly babies!

I'd definitely rather miss a dose and see what happens than end up needing jelly babies which whilst they sort the hypos then cause hypers and, I end up feeling even more unwell.
 
I didn't take the evening dose and have been very unwell. Rang 111 who told me to speak to GP immediately on phone and was told I should not have been given them together if my diabetes is well controlled, however, apparently there was no reason for the GP who saw me to know this as on Saturday it was high (but I thought Drs knew that was an indicator of infection so not necessarily how well BG is controlled) so I'm to stop the metformin apparently it'll stay in my system for a few days anyway.

I am annoyed about it though because I could have just ignored the continued drop and problems and continued with both and ended up very unwell because of it and there should definitely be some sort of warning in the medication leaflet!
 
With regard to the PCOS, Metformin is often used as treatment, but that is off licence. Your GP or specialist might like to think about changing treatment, all things considered.
 
GP knew nothing of this interaction at all, told me when I've completed the course to begin it again, but only one a day and see how I go. The uti culture supposedly was fine but on asking it showed some issues just not enough for full blown infection so it was helpful to get them as I now know what issues I've been having with the metformin but also the interaction. I've been told to record it as an allergy so I'm not given cefalexin in the future.
 
It’s not an allergy it’s an interaction, and it’s for the GP to “yellow card” that to the relevant authorities. Fair enough to record it as an allergy I suppose to prevent this happening again.
 
Yes sorry I should have explained it was to go down as allergy to stop it being prescribed again, there's no option on my file for interactions so I run the risk of being given it again. I did do a yellow card myself and gave my GP details for that as well so they can contact them.
 
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