1. Safe Drug Preparation

3. Two ways to calculate doses
Basic Calculation & Ratio and Proportion
Basic Calculation 1st
Desired dose x quantity of on-hand dose
on hand dose
In short: D
_____ X Q OH

4. Example 1
The physician orders aspirin gr 10 q4h PRN for fever over 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 gr
___ x 1 tab = 10 divided by 5 = 2
5 gr 2 x 1 = 2 tabs

5. 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 mg
____ X Q or ____ X 1 cap = OH
Reduce fraction 500/250 = 50 divided by 25 = 2
2 X 1 = 2 caps

6. 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

7. Ratio Ratio describes a relationship between two numbers.
Example: 1g : 15gr

8. Proportion A proportion consists of two ratios that are equal
Example: 1g : 15gr = 2g : 30gr

9. Solving problems using ratio and proportion
Known unit of measure : known equivalent = desired unit of measure : unknown equivalent
Example: mg : 1 g = 500 mg : xg
1000 x = = 500 divided by 1000 = 0.5
X = 0.5g

10. 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

11. 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

12. 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 = = divided by 24 = 0.45
You will give 0.45ml every 6 hours