I was recently taking a self-administered B12 shot (methylcobalamin). The pharmacy gave me a vial filled with 10,000 mcg/vial in powder form, and a separate vial with 11 mL of bacteriostatic water (label says sterile water with 0.9% benzyl alcohol for preservative). Prescribed dosage is 1 mL (1,000 mcg) per shot, intramuscular into buttock with 1 inch needle.

The directions said to transfer 10 mL of the bacteriostatic water into the vial with B12 powder, and then shake well. I misread the label and only transferred 5 mL. I then gave myself a 1 mL shot in the upper left quadrant of the buttock, twice the recommended dosage. From reading several research articles online, I understand that the 2,000 mcg dose itself is harmless given B12 is water soluble.

However, I am worried that the liquid was cloudy, and may have contained precipitate (undissolved powder) in it. From reading about IM injections online, it appears that injecting a precipitate can cause pulmonary embolism. It seems that this occurs pretty rarely, do I have anything to worry about? I took this dose over 24 hours ago, has the window in which this could occur passed?