Common dosage abbreviations

Bottles in Childers Pharmaceutical MuseumEver seen a prescription like this … 2mL a.c. omni mane ? Or 5mL q.3h ? Medical and herbal dosage terminology is often derived from old Latin, however it is still commonly used. Here is a list of the most common abbreviations and how to decipher them.

CAUTION: Remember clarity is essential – if you are writing a prescription which somebody else may view and not understand, it is far better to forgo the abbreviations and write it longhand. It might be more tedious, but one of the biggest causes of adverse reactions to medicines is incorrect dosage, so it is better to avoid confusion and err on the side of clarity.

UPDATE 7 August 2015: clarification of the once daily abbreviations


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Dosing Frequency
alt. hor.alternate hoursalternis horis
q.h.every hourquaque hora
q. 2 h.every 2 hoursquaque 2 hora
q. 3 h.every 3 hoursquaque 3 hora
q. 4 h.every 4 hoursquaque 4 hora
o.d.every day (preferred in the UK as opposed to q.d.)omni die
q.d. or q.1.d.every dayquaque die
alt dieb.every other dayalternis diebus
b.d. , b.i.d. twice a daybis in die
b.i.n.twice a nightbis in noctis
t.d.s.three times a dayter die sumendum
t.i.d.three times a dayter in die
q.d.s.four times dailyquater die sumendum
q.i.d. four times a dayquater in die
Specific Time
a.c.before foodante cibum
p.c.after food post cibum
alt. noct.alternate nightsalternis noctes bedtimehora decubitus
manein the morningmane
o.m.every morningomni mane the nightnocte
o.n.every nightomni nocte
non rep.not to be repeatednon repetatur
p.r.n.whenever necessary pro re nata oncestatim


Copyright Ian Breakspear, 2014