b12 is still low with injections How Can Vitamin Shots Help Me Feel Refreshed Sublingual B12 vs. B12 Injections:
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10.1007/978-981-32-9779-1 42.Kwatra S, Taneja G, Nasa N (2012) Alternative routes of drug administration- transdermal, pulmonary & parenteral

Common bleeding sites include the umbilical cord, skin, nose, circumcision site, intestine and brain

However, the SL route of administration has more advantages and fewer disadvantages than IM and oral routes

The best thing to do is to space out their timing
no other choice