Download File - Health Science CCCHS

Safe Drug Preparation
Two ways to calculate doses
• Basic Calculation & Ratio and Proportion
– Basic Calculation 1st
– Desired dose
on hand dose
In short:
D
_____ X Q
OH
x quantity of on-hand dose
Example 1
• The physician orders aspirin gr 10 q4h
PRN for fever over 101. On hand aspirin
gr 5 tabs.
– Step one: check to see if all measures are in
the same system. No conversion is
necessary. Both measures are in grains
– Step two: use the formula
10 gr
___ x 1 tab = 10 divided by 5 = 2
5 gr
2 x 1 = 2 tabs
Example 2
• Ampicillin 0.5g. The unit dose packet
reads 250mg/cap
– Check to see if all measures are in the same
system 1g = 1000mg
• 0.5g = 0.5 x 1000 = 500mg
• Then use the formula
D
____
OH
500mg
X Q or ____ X 1 cap =
250
• Reduce fraction 500/250 = 50 divided by 25 = 2
2 X 1 = 2 caps
Example 3
• Order: Versed 3 mg IM preoperatively.
On hand are vials labled 5mg per ML
– Check to see if all measures are in the same
system
– Use formula: 3mg
_____ X 1ML = 3 divided by 5 = 0.6
5mg
0.6 X 1ml = 0.6 ml
Ratio
• Ratio describes a relationship between
two numbers.
– Example: 1g : 15gr
Proportion
• A proportion consists of two ratios that are
equal
– Example: 1g : 15gr = 2g : 30gr
Solving problems using ratio and
proportion
•
Known unit of measure : known equivalent = desired unit of measure : unknown equivalent
• Example: 1000 mg : 1 g = 500 mg : xg
– 1000 x = 500 = 500 divided by 1000 = 0.5
X = 0.5g
Example 1 using ratio and
proportion
• Ordered: Demerol 60mg IM on call. The
narcotics draw contains labled Demerol
100mg/2ml
– Verify measures are in same system
– Set up problem:
Dose on hand : know quantity = dose desired : unknown quantity
100mg : 2ml = 60mg : X ml
100X = 120 = 120 divided by 100 = 1.2
X = 1.2ml
Pediatric and Infant doses
• Remember that 1lb = 2.2 kg (always divide
# of lbs by 2.2)
– 33lbs = ? kg
– 24lbs = ? kg
– 66 lbs = ? kg
• Most orders for peds will read: give xmg/kg/24h
Peds example
• Give Demerol 6mg/kg/24h for pain in divided doses every six hours
prn. Demerol is available 50mg/ml. How much Demerol would be
appropriae for a 33lb child every 6 hours?
• 1st convert weight = 33 divided by 2.2 = 15kg
• Next get your daily dose 6mg x 15kg = 90mg in 24 hours
• Next calculate ml needed in 24 hours =
– Dose on hand : know quantity = dose desired : unknown quantity
• 50 mg : 1 ml = 90mg : X ml
50X = 90 = 90 divided by 50 = 1.8
X = 1.8ml in 24 hours
Then calculate the ml per dose (every 6 hours)
24h : 1.8ml = 6h : xml
24X = 10.8 = 10.80 divided by 24 = 0.45
You will give 0.45ml every 6 hours