Vitamin B12 injections are introduced into a muscle or underneath the skin. Your doctor will recommend the dosage depending upon the age, dietary habits and other aspects including pregnancy or breastfeeding. If you are suffering from pernicious anemia, your doctor will prescribe you to take these injections throughout your life.
Although folic acid is useful in the maintenance of RBCs in this disease, yet vitamin B12 deficiency will not be treated folic acid alone. So, it is needed to follow the recommendations of your doctor. And if you took overdose in greed of getting better and quick results, it may cause poison in your body.
For injection, use the syringe and needle only one time and dispose them off after use. Prevent the medications from heat and direct sunlight and keep them at dry surface.