Nursing Pharmacology

1. COMPUTATIONS
Prepared by: Rod Taruc, RN, LPT

2. D/H X Q
D – desired dose
H – amount on
HAND/HAVE
Q - quantity

3. CONVERSION
• Conversions to equivalent measures between
systems is necessary when a medication
prescription is written in one system but the
medication label is stated in another.
• Medications are not always prescribed and
prepared in the same system of measurement;
therefore conversion of units from one system to
another is necessary.
• Common conversions in the healthcare setting
include pound to kilograms, milligrams to grains,
minims to drops.

4. CONVERSION
Unit Equivalents
Metric system Equivalents
1 microgram (mcg) 0.000001 g
1 milligram (mg) 0.0001 g or 1000 mcg
1 gram (g) 1000 mg
1 kilogram (kg) 1000 g
1 kilogram (kg) 2.2 lbs
1 milliliter (mL) 0.001 L

5. METHODS
Standard Method
• The commonly used formula for calculating drug dosages.
• Where in:
• D = Desired dose or dose ordered by the primary care provider.
• H = dose on hand or dose on the label of bottle, vial, ampule.
• V = vehicle or the form in which the drug comes (i.e., tablet or
liquid).

7. EXAMPLE: TABLET

8. EXAMPLE: LIQUID
Example:
Order: Acetaminophen 500 mg
On hand: Acetaminophen 250 mg in 5 mL
Desired (D) = 500 mg
On hand (H) = 250 mg
Vehicle (V) = 5 mL
Computation:
500 mg/250mg x 5mL = 10 mL
Answer: 10 mL

9. EXAMPLE: PARENTERAL

10. METHODS
Ratio and Proportion Method
• Considered as the oldest method used for drug calculation
problems.
• For the equation, the known quantities are on the left side, while
the desired dose and the unknown amount to administer are on
the right side.
• Where in:
• D = Desired dose or dose ordered by the primary care provider.
• H = dose on hand or dose on the label of bottle, vial, ampule.
• V = vehicle or the form in which the drug comes (i.e., tablet or liquid).
• X = amount to administer
• Once the equation is set up, multiply the extremes (H and x) and
the means (V and D). Then solve for x.

11. RATIO AND PROPORTION METHOD
H : V = D : x

12. Example:
Order: Erythromycin 750 mg
On hand: Erythromycin 250 mg capsules
Desired (D) = 750 mg
On hand (H) = 250 mg
Vehicle (V) = 1 capsule
Computation:
250 (H) : 1 (V) = 750 (D) : x
Multiply the extremes and the means:
250x = 750
x=3 capsules
Answer: 3 capsules

13. EXERCISES

14. 1. Morphine 45 mg IM, is ordered. morphine is
available as 100mg/ml. How much would the
nurse inject?

15. 2. MD writes an order for Tylenol 160 mg by mouth as
needed every 6 hours for pain for a child. Pharmacy
dispenses you with 80 mg per ml. How many ml will
you administer per dose?*

16. • MD writes an order for Mucomyst 300 mg by mouth
one dose before heart cath. Pharmacy dispenses
you with 600 mg/2 ml. How many ml will you
administer per dose?

17. • MD writes an order for Digoxin Elixir 250 mcg by
mouth daily. Patient’s apical pulse is 65 bpm.
Pharmacy dispenses you with 0.5 mg/2 ml. How
many ml will you administer per dose?

18. • The medication order reads: meperidine 25 mg IM
every 4 hours PRN. The stock is 100 mg per ml. how
much should the nurse administer?

19. • Order: Administer Meropenem 500mg dissolved in
4ml Q4 IV
• Available: Meropenem 250mg/vial
• How many vial of Meropenem do you need to give
to the patient every day?