 [ Symptoms ] would it be ok for someone that gets b12 injections once a month to take b12 supplements occasionally  my father gets b12 injections once a month due to b12 deficiency usually by week 3 his symptoms of fatigue memory loss and irritability are prevalent would it hurt for him to possibly take a b12 supplement in that last week before his scheduled injection [ Disease ] many people not all who are allergic to penicillin may also be allergic to cephalosporins like keflex so it would be wise to be skin tested by an allergist with a dilute amount to see if you have an allergic reaction keflex is not made from any mold it is synthetic