From Brewer:
Q.S Quantum sufficit. Two letters appended to prescriptions, and meaning as much as
is required to make the pills up. Thus,after giving the drugs in minute proportions, the
apothecary is told to “mix these articles in liquorice q.s”

Also used in chemistry in directions for preparing reagents, to indicate final volume.

...and also to indicate how many refills. "QS i year" means as many refills as wanted/needed, up to one full year from the date of writing. Some prescription plans need a three-month supply per prescription; others refuse to go beyond 30 days. I have no way of knowing the patient's policy, so QS it is...

It's the "health insurance" (quotes intentional) policy, not the patient's. Just thought I'd throw that in, as I'm grappling with this problem right now.

what are all those other Latinisms like "nocte", etc. which physicians use to show how to take drugs??

a c - ante cibum - before meals
b i d - bis in die - 2 times a day
b i n - bis in nocte - 2 times a night
h s - hora somni - at bedtime
I M - intramuscularly
I V - intravenously
o d - omni die - every day
o h - omni hora - every hour
o m - omni mane - every morning
o n - omni nocte - every night
p c - post cibum - after meals
P O - per os - by mouth
p r n - pro re nata - when required
q d - quaque die - every day
q h - quaque hora - every hour
q2h - every 2 hours q3h - every 3 hours, etc
q i d - quater in die - 4 times a day
q s - quantum satis - sufficient quantity
s c - subcutaneously
S L - sub linguam - under the tongue
S O S - si opus sit - if necessary (once only)
t i d - ter in die - 3 times a day
t i n - ter in nocte - 3 times a night

that's EXACTLY what I meant, boronia, ta muchly!

Does your reference give an expansion of "ut d," instruction to a pharmicist meaning "as directed"?

Ut D. I had a scary experience with prescription directions. The hospital had a stupid policy
of having some medications given to patients actually made in chem lab.
A private physician had written an order for a young girl to be given a vaginal douche
based on something almost as bad as corrosive sublimate. I was covering for three interns
who claimed they were ill conveniently at Xmas. I was in a hurry, and asked her if she
knew how it was to be taken. She was too bashful to discuss it, and just said yes.
The private physicians were awful touchy about interns talking to their patients, so
I just handed her the stuff. She went home and drank it. A special providence made
her vomit it and rinse quickly enough that stricture of esophagus did not develop.

I just looked it up in the Compendium of Pharmaceuticals and Specialties, which does not include the original Latin. Ut dict. (or u.d.) means 'as directed'. Oh - just saw that 'P.P.A.' means 'shake the bottle first' - who knew?

Dear Boronia: your shake well reminded me. When sulfa drugs first came out, a drug company
most of whose sales were in the South, where liquid medicines were preferred to tablets was
faced with problem of making a solution of sulfanilamide. A clever chemist read that it dissolved
well in a solvent that was also used as antifreeze in automobile radiators. It was very toxic.
A significant number of fatalities resulted.

I finally remembered the name of solvent: diethylene glycol.

My mother, loved antibiotics, since they cured her case of chorea, and allowed her to have a normal life after 20 years of being chronically ill. Then, one day after a shot of penicillin, she said "I don't feel righ..." and passed out... Our doctor was a good one, reacted quickly, and 24 hours later she was right as rain. and as much as possible, he avoided giving us antibiotics..

So sulfa drugs became the drugs of choice. I now associate sulfur with good things... my response is a learned one. burning, dry, sore throat, that hurt even when you sipped water,was soon cooler, moister and less painful with every teaspoon full of the sulfur elixir. I even came to like the chalky consistency...

so i don't smell "rotten eggs" when i smell a sulfur compound, i smell "feeling better"...