Injecting prescribed vitamin B12

Key points

• 01Why injection is used at all. B12 from food and tablets is absorbed in the small intestine with the help of intrinsic factor. When that pathway is broken, by pernicious anaemia, by gastric or ileal surgery, or by some conditions and medications, the injectable route bypasses it entirely.
• 02Oral versus injection has been studied properly. A pragmatic randomised trial published in BMJ Open in 2020 compared oral and intramuscular B12 in primary care, and a 2022 review in American Family Physician summarised the comparison. This is a real clinical decision with evidence behind it, and it belongs to your prescriber.
• 03The route is on your label. Cyanocobalamin injection is labelled for intramuscular or deep subcutaneous administration. Which of those applies to you is a prescribing decision, and it changes the needle length, the site and whether you pinch a fold of skin.
• 04Intramuscular usually means the arm for small volumes. The deltoid is the standard site for a small intramuscular volume, and our deltoid injection site guide covers the acromion landmark. Larger volumes go to the hip, which is covered in our ventrogluteal injection site guide.
• 05Deep subcutaneous is a different technique. If your prescription specifies subcutaneous, you are lifting a fold of skin and putting the medication into fat, not muscle. Our subcutaneous injection post covers the sites and our pinch guide covers the grip. The two routes are not interchangeable.
• 06The solution is meant to be pink. Cyanocobalamin is coloured, so a clear pink to red liquid is expected rather than a warning sign. What matters is that it is clear rather than cloudy, with no particles, and that the label and expiry date are readable.
• 07Multi-dose vials have an in-use clock. Once a multi-dose vial is punctured, it has a limited in-use period even though it looks unchanged. Write the date of first puncture on the label. Our post on multi-dose vial storage after first use covers the rule and why the preservative exists.
• 08One needle, one syringe, one puncture. Never reuse a needle or a syringe, including on yourself. Each entry into the vial uses a fresh sterile needle. This is the single most important habit with any vial-based medication and it is the one most often relaxed at home.
• 09Unlike a prefilled syringe, the air does come out here. You filled this syringe, so the bubbles are yours and they are removed before injecting. Prefilled anticoagulant syringes are the opposite case, where the manufactured bubble stays in. Our air bubbles post explains why the two rules differ.
• 10Rotate sites and record them. If you are on a regular schedule, alternate arms or sides and write down which one you used. Repeated injection into the same patch is associated with hardened tissue and unpredictable absorption. Our injection record guide has a layout with a side column.
• 11Do not self-diagnose the deficiency. Fatigue, tingling and low mood have many causes. B12 injection given without a diagnosis can also complicate the picture, because treating with B12 can mask a folate deficiency while nerve damage progresses. The blood work comes first.
• 12There is a specific early-treatment warning. The prescribing information notes that potassium can fall during the early treatment of severe megaloblastic anaemia. That is a monitoring matter for the clinician who starts you, and it is one more reason this treatment is supervised rather than self-started.

Pre-injection checklist

• ✓B12 injection is a prescription treatment for a diagnosed deficiency, not a wellness top-up. If nobody has tested you and written a prescription, the first step is a clinician appointment, not a syringe.
• ✓Read your label for the route. Cyanocobalamin injection is labelled for intramuscular or deep subcutaneous use, and which one applies to you is on your prescription. The two routes need different needles and different sites.
• ✓Check whether your vial is single-dose or multi-dose. A multi-dose vial contains a preservative and has an in-use period after the first puncture. Our posts on single-use and multi-dose vial concentration cover the difference.
• ✓Buy from a pharmacy against a prescription. This site does not link suppliers, and unlabelled vials from online sellers are a well-documented source of harm.
• ✓This is a technique reference, not medical advice. Your dose, your route, your site and your schedule are set by your prescriber.

Step-by-step guide

1. 1

   Wash your hands and set out the supplies

   Wash with soap and water for at least 20 seconds and dry on a clean towel. Lay the vial, syringe, needles, alcohol pads and gauze on a clean surface, and open the sharps container before you start so used sharps have somewhere to go immediately.

   Pro tip

   Always check the fluid is clear and colourless before injection.
2. 2

   Check the vial

   Read the label for the medication name, the strength and the expiry date, and look at the liquid. Cyanocobalamin solution is a clear pink to red colour. Do not use a vial that is cloudy, has particles, or whose label you cannot read.

   Pro tip

   Always check the fluid is clear and colourless before injection.
3. 3

   Clean the stopper

   Flip off the plastic cap if it is a new vial, then wipe the rubber stopper with an alcohol pad and let it air-dry for at least ten to fifteen seconds. The cap is a dust cover, not a sterile seal, so the stopper is wiped every single time.

   Pro tip

   Always check the fluid is clear and colourless before injection.
4. 4

   Draw air into the syringe

   Pull the plunger back to the volume you are going to withdraw. Injecting that air into the vial first replaces the volume you are taking out, which stops a vacuum forming and makes the liquid come easily instead of fighting you.

   Pro tip

   Always check the fluid is clear and colourless before injection.
5. 5

   Inject the air and draw the dose

   Push the needle through the centre of the stopper, push the air in, then invert the vial and pull back slowly to your prescribed volume. Our guide to drawing up medication from a vial covers the whole sequence in detail.

   Pro tip

   Always check the fluid is clear and colourless before injection.
6. 6

   Clear the air bubbles

   With the needle still in the inverted vial, tap the barrel so bubbles rise to the hub, then push them back into the vial and re-draw to your mark. This is a vial you draw yourself, so unlike a prefilled anticoagulant syringe the air does come out.

   Pro tip

   Always check the fluid is clear and colourless before injection.
7. 7

   Change the needle if instructed

   If your instructions say to inject with a fresh needle, swap it now. A needle that has been through a rubber stopper is duller, and medication on the outside of the shaft can be deposited along the needle track and sting.

   Pro tip

   Always check the fluid is clear and colourless before injection.
8. 8

   Choose the site your prescription specifies

   For an intramuscular dose in the arm, our deltoid injection site guide covers the landmark. For a deep subcutaneous dose, the sites and the pinch are covered in our subcutaneous injection guide. Do not switch between them on your own.

   Pro tip

   Always check the fluid is clear and colourless before injection.
9. 9

   Clean the skin and inject

   Wipe the site and let it air-dry for at least ten to fifteen seconds. Insert as you were taught for your route, follow any local instruction on aspiration for an intramuscular dose, and push the plunger slowly and steadily.

   Pro tip

   Always check the fluid is clear and colourless before injection.
10. 10

    Withdraw, press and dispose

    Pull the needle straight out along the line it went in, press a gauze square on the spot without rubbing, and put the whole syringe with the needle attached into the sharps container. Write down the date, the dose, the route and the side.

    Pro tip

    Always check the fluid is clear and colourless before injection.

After the injection

• Press a gauze square on the site for a few seconds without rubbing.
• Record the date, the dose, the route and which side you used.
• Write the date of first puncture on a multi-dose vial and store it as the label directs.
• Put the syringe in the sharps container with the needle attached and never recap it.

Common mistakes

Frequently asked questions

Sources

1. MedlinePlus. Cyanocobalamin Injection: patient drug information.
2. Oral versus intramuscular administration of vitamin B12 for vitamin B12 deficiency in primary care: a pragmatic, randomised, non-inferiority clinical trial. BMJ Open, 2020.
3. Oral vs. Intramuscular Vitamin B12 for Treating Vitamin B12 Deficiency. American Family Physician, 2022.
4. Ogston-Tuck S. 2014. Intramuscular injection technique: an evidence-based approach. Nursing Standard 29(4):52-59.
5. MedlinePlus. Giving a subcutaneous injection (patient instructions).