[johnep]

If you mean dosage codes, these go back to when all scripts were written in Latin to keep the pt in the dark about what they might be getting.
Eg pil panis = Bread pills ie a placebo.
Therefore:
od = each day, bd (bis die)= twice a day, tds or tid(ter in die sumendum)=
three times a day, qd(quatre die)=four times a day, prn (pro re nata) = when required.
n(nocte)= night, sos (si opus sit)= when necessary, hss (horus sum sumendem) = at the hour of sleep, m (mane) = morning.
You will probably find a complete list on the net somewhere.
johnep