Transcript Pharmacy Technician*s Course. LaGuardia Community College

Dosage Calculations
 The elements of the prescription can be curtailed
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down to several elements
Dose is the amount of drug taken at one time
Q is a variable that represents the quantity or units
that consists of a dose of a medication. i.e. 2 tablet give
a 650 mg dose if each dose is 325 mg.
F is the frequency of administration per day i.e. BID
N is the number of days, or the “day supply”
T is the total quantity to dispense
Q*F*N=T
Example One
 Renagel ® Sig: iii TID AC for 30 days with 11 refills.
 Q= 3, F=TID, N= 30 days therefore T=3*3*30= 270
tablets
 Renagel® is the brand name of sevelamer chloride
which a drug given to patient with end stage renal
disease to lower their phosphate levels in the blood.
Example Two
 i.e. Timoptic® sig: instill 1 gtt OU BID. Dispense 5 ml
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ophthalmic container.
What is the day supply?
T= 5ml* 20 gtt/1 ml= 100 gtt
Remember Q is the quantity per dose which should
take into account the route of administer OU is both
eyes so Q=2 gtt
Q= 2, F= BID, T=100 what is N?
Answer: 2*2*N=100 or N= 25 days
Example three
 Amoxicillin 250 mg/5 ml suspension
 Sig: ii tsp tid for 14 days
 What is the total quantity to dispense?
 Q= ii tsp
 Tsp=teaspoon so ii tsp is 2 teaspoons
 2 teaspoons * (5 ml /one teaspoon)= 10 ml
 F=tid or three times a day, N=14 days
 Q*F*N= 10*3*14
 420 ml
Example Four
 Phoslo® Sig: 1,334 mg tid ac with 6 refills
 What is the total quantity needed to fill this Rx for one
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month? For the full 7 months?
Q= 2 (1,334 mg * (1 tab/667 mg)= 2)
F= tid is 3 times a day
N=30 days
T= 2*3*30=180 tablets
T for 7 months = 180 * 7= 1,260 tablets
Insulin Example
 Novolin N sig: inject 10 units bid and 20 units qhs
dispense one vial (10 ml)
 Commercially Novolin N is available as a 100 unit/ml,
10 ml vial size. Novolin N is human insulin neutral
protamine suspension where is a type of long acting
insulin.
 When the prescription is written with composition
instructions (i.e. 2 parts- bid dosing and qhs dosing)
calculate quantity per day (q/d).
 What is the days supply of this Rx?
Insulin Example
 Quantity per day is 10 units bid which is 20 units
 20 units qhs is 20 units
 Adding both is 40 units/days
 (q/d)*Days supply= total quantity
 Total quantity is 100 units/ml*10 ml= 1,000 units
 Day supply = total quantity/(q/d) or 1,000/40 or 25
days
Pediatric Dosing
 Pediatric dosing includes dosing for neonates, infants
and children up to about 12 years of age
 Neonates and infants metabolize drugs differently that
adults often slower in neonates. Kidney function and
renally cleared drugs are removed more slowly
 Drugs applied topically on the skin are absorbed much
better on neonates and infants than adults because of
increased surface area and thinner stratum corneum
 Caution must always be exercised in these
circumstances
Drugs that dangerous in children
Drug
Potential Fatal Dose
Benzocaine (Ora Base or Ora Gel)
2 ml of 10% ointment
Camphor (Icy Hot)
5 ml of 20% oil
Chlorpromazine (Thorazine ®)
One 200 mg tablet
Codeine
Three 60 mg tablets
Sulfonylurea
Two 5 mg tablets of Glyburide
Imipramine
One 150 mg tablet
Iron Tablets (sweet flavored)
10 tablets of 325 mg
Theophylline
One 500 mg tablet
Verapamil
One 240 mg tablet
Pediatric Dosing Formulas
 Fried’s Rule: PD (pediatric dose)=Age (months)/150X
adult’s dose
 Young’s Rule : PD= Age (years)/(age (years)+12)Xadult
dose
 Clark’s rule: PD= weight (lbs)/150Xadult dose