Anaphylactic shock to B12 injection - Pernicious Anaemi...

Pernicious Anaemia Society

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Anaphylactic shock to B12 injection



I was diagnosed with PA about a year ago. I had the initial loading dose of 6 injections of B12 in 2 weeks and then continued with regular injections. I found my level to require a B12 injection every 8ish weeks. I had to change doctor a couple of months ago due to moving house and had my first routine B12 injection with them 5 weeks ago. A few minutes after that injection, i suffered anaphylactic shock and so the doctor has said that i cannot receive the injection anymore for risk of another reaction. Unfortunately though, he hasn't been able to decide who to refer me to see in order to establish an effective course of treatment for the future. I am getting panicked now cos the weeks are ticking by and I am feeling worse and worse. I haven't felt well at all since the last B12 so not convinced it actually worked at all. Anybody know who I should see?!! Also, is there a possibility that the injections differ between surgeries and that there could have been something else in there that i am allergic to that wasn't in the other injections i received? Getting so frustrated - don't know where to turn!!

22 Replies

Thank you. Will pass that information on to my doctor.

fbirder in reply to raustinrb4

I've never seen benzyl alcohol in the excipients list of any of the hydroxocobalamin I've ever had (and I do look). I know it's common in methylcobalamin.

Are you in the UK?

raustinrb4 in reply to fbirder

yes in the UK.

fbirder in reply to raustinrb4

Probably not benzyl alcohol then. Annoyingly.

I suggest you get a selection of sublingual tablets from Amazon and try one a day.

Not sure it helps but, by coincidence, I came across this post this morning (I'm plucking up courage to do my first self injection!) :

raustinrb4 in reply to Polaris

Good luck :)

Polaris in reply to raustinrb4

Thank you raustinrb4. I hope you can get to the bottom of why this has happened to you !

Deuto in reply to Polaris

Hi Polaris

For you and everyone else, the discussion on that thread relates to hydoroxocobalamin B12 injections available in Australia and New Zealand.

I am a New Zealander in NZ, and Bethatthebeach is an Australian normally resident on mainland Australia but a frequent visitor to Norfolk Island, part of Australia but in the Tasman Sea between Australia and New Zealand. Just saying ...

The doctor's practice is investigating the difference between the two injections so will let them know this ingredient. Thank you

Good spot! Mono sodium phosphate is in Cobalin-H, one of the types of hydroxocobalamin used by the NHS. I'd forgotten about that.

I really hope that's the cause.

I think it really comes down to figuring out what the exact allergy is. Very few people are allergic to cobalamin itself, so it is most likely something else. And, assuming that is the case, there should be a different version of injectable B12 that you could safely be given. Perhaps an allergist could help you pinpoint the problem, but they would need to compare the two preparations and it sounds like your doctor's office is already trying to do that.


Hi raustinrb4. I'm sending a private message containing details of doctors who deal with desensitising those with allergies to vitamin B12 injections.

Your GP can contact them for advice or refer you to them.

Good luck 👍

Hi. I just saw this and have recently had this issue myself with having an allergic reaction to a hydroxocobalamin injection. Would it be possible for you to private message me with the list of doctors who deal with desensitisation as well please?

FoggymeAdministrator in reply to theverytiredperson

Hi theverytiredperson.

I previously obtained this information from the PAS website but it doesn’t appear to be there at the moment.

If you contact the Pernicious Anaemia Society they may be able to help with details (contact details are on their website - phone or email).

Good luck 👍

Oh OK. I already tried them and although they knew of 2 doctors who had experience of this they are both now apparently retired so they were unable to give me any info.

FoggymeAdministrator in reply to theverytiredperson

Oh dear...that must be why their names no longer appear on the website.

Allergic reactions are very rare...was it an a reaction of the anaphylactic type? If so, here’s a couple of suggestions for your GP to follow-up on...(because if you are deficient in B12, they have to find a way to get it into your body)...

1) they could try giving you cyanocobalamin or methylcobalamin (under medical supervision in the surgery). The reaction may have been due to excipients rather than to the B12 itself. If that doesn’t work...

2) in circumstances of severe reactions, B12 is given in hospital along with antihistamines (and access to full medical support) to try and control the reaction (your GP should be able to organise that) or...

3) Your GP can get advice from or refer you to an immunologist (specialist who deals with allergic reactions) - as an urgent referral if you are severely deficient or are having neurological symptoms.

Hope this helps and good luck. xx

If your GP is not willing to help you (because many of them are ill informed about the importance of vitamin B12 or the issues surrounding B12 deficiency)...get a new GP 😬.

P.s. put up a new post and let us know how you’re doing (this is a three year old post and no one else in the forum will see it) 😉

OK thanks for the info. My GP is going down route 3 but there is along wait to see the immunologist, regardless of the urgency. I have posted separately my situation already. This is a very useful forum!

forgot to say, no it wasnt anaphylaxis, but there was some swelling on my face as well as a weal near the injection site so GP was concerned about a worse reaction next time.

FoggymeAdministrator in reply to theverytiredperson

So...sounds like your GP is doing the right things...but NHS waiting times are a disgrace!

If you have neurological symptoms or you get worse, might be worth having a conversation with your GP...they may (should) be able to get the appointment brought forward.

He may not be fully aware of the neurological damage B12 deficiency can wreak on the body, so worth downloading some information from the PAS website to take and show them (particularly about subacute degeneration of the spinal cord). Not suggesting you have or will get this but it might focus their mind a little.

Here's something else that may help if you need it...


reatment of B12 / Folate Deficiencies) (UKNEQAS B12 Treatment Alert, Neurological Symptoms and Risk of Subacute Combined Degeneration of the Spinal Cord – Immediate Treatment with B12 Injections)

If your GP picks up the telephone and actually speaks to an immunologist, that may pay dividends. Or they could email to express their concerns and ask advice - that sometimes works too.

Good luck x

Thanks. Unfortunately my GP is convinced that I will have such high levels of B12 in my blood for months to come that I will be fine to wait for the appointment. I tried to get my neurologist to comment as to the urgency but his view is similar so I am trying out other options in the meantime like patches and possibly sublinguals

FoggymeAdministrator in reply to theverytiredperson

Crikey...that's shocking isn't it (but unfortunately not surprising given what we read here in the forum) 😬.

B12 level’s are meaningless following injections (even one)'s symptoms that count...and symptoms that should be treated. Irrespective of B 12 levels following an injection...or injections (but I bet you know that).

If you get into difficulties and become more unwell, might be worth collecting evidence (from the PAS website and from the pinned posts to the right of this page)...and see if you can educate your GP about B12 levels being irrelevant after injections (and unfortunately, neurologists, gastroenterologist and many other 'ologies' are no better informed) 😬.

Has your GP considered trying an injection of cyanocobalamin whilst you’re there in the surgery? May be worth a shot since some who can not tolerate Hydroxocobalamin can tolerate cyanocobalamin.

Good luck x

Thank you :)

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