Definition of q.d. (on prescription)
q.d. (on prescription): Seen on a prescription, q.d. (or qd) means
one a day (from the Latin quaque die). The abbreviation is
sometimes written without a period in capital letters as 'QD'.
However it is written, it is one of a number of hallowed
abbreviations of Latin terms that have been traditionally used in
prescriptions to specify the frequency with which medicines should
be taken.
Other examples include:
b.i.d. (bid or BID) is twice a day; b.i.d.. stands for 'bis in die'
(which means, in Latin, twice a day).
t.i.d. (or tid or TID) is three times a day ; t.i.d. stands for
'ter in die' (in Latin, 3 times a day).
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