Download View the Sample

Drug Calculations
1. Mrs Jones is ordered 1.6 mg/day of drug A, to be given in four equally divided doses. Each
dose of medication is?
Formula and Workings: drug A/4 = X
1.6 mg/4 = X
0.4 mg = X
Answer: Each dose of medication must be 0.4 mg.
2. She is also to have 125 mcg of drug B. Stock in the ward is 0.25 mg tablets. How much should
she be given?
Formula and Workings: Convert 0.25 mg to mcg: 0.25 mg x 1000= 250 mcg
Desired dose/ drug on hand = x
125 mcg/ 250 mcg
=x
½ or 0.5 tablet
=x
Answer: Mrs Jones must be given 0.5 or ½ tablet.
3. Stock of drug C is 0.6 g tablets. Mrs Jones is to have 600 mg of this drug BD. How often will
she have this medication?
Formula and Workings: 0.6 g x 1000= 600 mcg.
Answer: Mrs. Jones will have this medication twice daily or 2/24.
4. With reference to Q3, How many tablets should Mrs Jones be given?
Formula and Workings: 2/24 means that medication will be given twice per day.
Answer: Mrs. Jones should be given two tablets per day.
5. Mrs Jones is to have 375 mg of drug D. Stock in the ward is 0.75 g tablets. How many tablets
should she be given?
Formula and Workings: Convert grams to mg: 0.75 g= 750 mg
Stock dose/ desired dose * quantity = x
750mg/375 mg * 1tab = x
2 tablets
=x
Answer: Mrs. Jones must receive two tablets. 2 tablets must be given to her.
6. When you visit Rachel after handover, she asks for Panadol to relieve her headache.
She is permitted 1 gram of paracetamol 4/24 PRN for mild to moderate pain. Stock is
500 mg tablets. How should this order be interpreted?
Formula and Workings: Convert gram to mg: 1gram= 1000mg
Stock dose/ desired dose * quantity = x
1000mg/500 mg * 1tab = x
2 tablets
=x
Answer: Rachel must be given 2 tablets in order to meet the drug ordered for her.
7. An intravenous infusion of 1 L of 0.9% sodium chloride is in progress. The drop factor
for the giving set is 20 drops/ml and the line is dripping at the rate of 40 drops/minute.
What volume of fluid/hour would Rachel receive from this rate of flow?
Formula and Workings: 20 drops:1 ml = 40 drops: x
X= 2ml
2 ml/min x 60 min/ hr = 120 ml/hr
Answer: The volume of fluid that Rachel would receive with a dripping rate of 40 drops/minute
is 120 ml/hr.
8. How long (in hours and minutes) would you expect this infusion to last?
Formula: 1000 ml = 1000 ml x 1 hr
= 8.33 hours or 8 hours and 30 minutes.
120ml/hr
120 ml
Answer: The infusion is expected to last for 8 hours and 30 minutes.
9. How much fluid will the registered nurse need to add to the vial to achieve a
concentration of 100 mg/ml?
Formula and Workings: Convert 1 gram to mg: 1 gram x 1000 = 1000mg
1000mg / 10ml = 100 mg/ml
Since 1 gram displaces 0.7 ml, then,
10 ml – 0.7 ml = 9.3 ml.
Answer: The nurse must add 9.3 ml to the vial to achieve the concentration of 100mg/ml.
10. How many mg/dose should Rachel receive from the order?
Formula and Workings: Convert grams to milligrams: 3 grams x 1000 = 3000mg
3000 mg/ day = 500 mg/dose
6 doses/day
Answer: Rachel will receive 500 mg/dose.
11. Intravenous frusemide 30 mg has been ordered. If available stock is 20 mg/ml, how much
should the registered nurse give him?
Formula and Workings: stock dose: quantity on hand = desired dose: desired quantity
20 mg: 1ml = 30mg: x
20 mg(x) = 30mg(ml)
X = 30/20 ml
X = 1.5 ml
Answer: The nurse must give him 1.5 ml of 20mg/ml furosemide.
12. Intravenous Lanoxin is due and he is to have 125 mcg BD. If stock available is 0.5 mg/2ml,
how much should the registered nurse draw up?
Formula and Workings: Convert mg to mcg:0.5mg x 1000= 500 mcg
stock dose: quantity on hand = desired dose: desired quantity
0.5 mg:2 ml = 125mcg: x
500 mcg(x) = 125 mcg(2ml)
X
= 250/500 ml
X
= 0.5 ml
Answer : The nurse must draw up is 0.5 ml.
13. Intramuscular Stemetil 10 mg has been ordered. What is the volume required for this order, if
available stock is 12.5 mg/ml?
Formula and Workings: stock dose: quantity on hand = desired dose: desired quantity
12.5 mg:1ml = 10mg: x
12.5mg(x) = 10mg(ml)
X
= 10/12.5 ml
X
=0.8 ml
Answer: The volume required for this order is 0.8ml.
14. Mr Blacker asks for medication for chest pain which has not been relieved by his
Anginine tablets. He is seen by the doctor and is to have 12 mg of subcutaneous morphine. If
stock is 15 mg/ml, what is the volume to be drawn up?
Formula and Workings: stock dose: quantity on hand = desired dose: desired quantity
15mg:1ml
= 12mg: x
15mg(x)
= 12mg(ml)
X
= 12/15 ml
X
=0.8 ml
Answer: the volume that the nurse must draw up is 0.8ml
15. The antibiotic Gentamicin 120 mg is to be given intravenously. Stock available is 40mg/ml.
How much should the registered nurse draw up?
Formula and Workings: stock dose: quantity on hand = desired dose: desired quantity
40mg: 1ml = 120mg: x
40mg(x) = 120mg (ml)
X
= 120/40 ml
X
= 3 ml
Answer: the nurse must draw up 3ml in order to provide the 120mg Gentamicin ordered.