APPENDIX D
APPENDIX D
drug calculations
Read the following information carefully before attempting the examples and exercises.
TABLETS
Formula method
Required dose
= No. of tablets to be given
Stock dose
Ratio method
Required dose : Required tablet
Stock dose : Stock tablet
Required dose Required tablet
=
Stock dose Stock tablet
Note: Units for the required dose and stock dose must be the same. The stock dose is the mass
you have available to you. The required dose is the mass that needs to be given to the client.
EXAMPLE
A client is ordered 150 mg soluble aspirin. ‘Disprin’ tablets containing 300 mg aspirin are
available. How many tablets will you give?
Formula method Ratio method
150mg 150mg : × tablet
= No. of tablets to be given
300mg 300mg : 1 tablet
= 0.5 tablet 150mg × tablet
=
300mg 1 tablet
= 0.5 tablet
DRIP RATES
Total volume mL
=
Total hours hr
Drops per minute (dpm)
Macro drip Volume × Drop factor (20)
= dpm
Time (hr) 60 min
Micro drip Volume × Drop factor (60)
= dpm
Time (hr) 60 min
Note: Drop factor for macro drip = 20 drops/mL; micro drip = 60 drops/mL.
APPENDIX D
, EXAMPLE
A client is ordered an intravenous infusion of 1000 mL normal saline to run over
24 hours, using a macro drip. Calculate the drip rate.
1000 20
× = 13.8
24 60
= 14 dpm
MEDICATION DOSAGES
For intravenous and intramuscular injections.
Formula method
Required dose Stock volume
× = Volume to be given
Stock dose 1
Note: Units for the required dose must be the same. Units for the required volume and stock
volume must be the same.
Ratio method
Required dose : Required volume
Stock dose : Stock volume
Required dose Required volume
=
Stock dose Stock volume
Note: Units for the required dose and stock dose must be the same. Units for the required
volume and stock volume must be the same.
EXAMPLE
(i) You are required to give 6 mg morphine. In your stock ampoule there is 15 mg per 1 mL.
How much of the ampoule will you need?
Formula method Ratio method
6 mg 1 mL 16 mg : × mL
× = 0.4 mL 15 mg : 1 mL
15 mg 1
16 mg × mL
=
15 mg 1 mL
= 0.4 mL
EXAMPLE
(ii) You are required to give 30 units insulin. In your stock vial there is 100 units per 1 mL.
How much do you require?
Formula method Ratio method
30 units 1 mL 130 units : × mL
× = 0.3 mL 100 units : 1 mL
100 units 1
130 units × mL
=
100 units 1 mL
= 0.3 mL
APPENDIX D
APPENDIX D
drug calculations
Read the following information carefully before attempting the examples and exercises.
TABLETS
Formula method
Required dose
= No. of tablets to be given
Stock dose
Ratio method
Required dose : Required tablet
Stock dose : Stock tablet
Required dose Required tablet
=
Stock dose Stock tablet
Note: Units for the required dose and stock dose must be the same. The stock dose is the mass
you have available to you. The required dose is the mass that needs to be given to the client.
EXAMPLE
A client is ordered 150 mg soluble aspirin. ‘Disprin’ tablets containing 300 mg aspirin are
available. How many tablets will you give?
Formula method Ratio method
150mg 150mg : × tablet
= No. of tablets to be given
300mg 300mg : 1 tablet
= 0.5 tablet 150mg × tablet
=
300mg 1 tablet
= 0.5 tablet
DRIP RATES
Total volume mL
=
Total hours hr
Drops per minute (dpm)
Macro drip Volume × Drop factor (20)
= dpm
Time (hr) 60 min
Micro drip Volume × Drop factor (60)
= dpm
Time (hr) 60 min
Note: Drop factor for macro drip = 20 drops/mL; micro drip = 60 drops/mL.
APPENDIX D
, EXAMPLE
A client is ordered an intravenous infusion of 1000 mL normal saline to run over
24 hours, using a macro drip. Calculate the drip rate.
1000 20
× = 13.8
24 60
= 14 dpm
MEDICATION DOSAGES
For intravenous and intramuscular injections.
Formula method
Required dose Stock volume
× = Volume to be given
Stock dose 1
Note: Units for the required dose must be the same. Units for the required volume and stock
volume must be the same.
Ratio method
Required dose : Required volume
Stock dose : Stock volume
Required dose Required volume
=
Stock dose Stock volume
Note: Units for the required dose and stock dose must be the same. Units for the required
volume and stock volume must be the same.
EXAMPLE
(i) You are required to give 6 mg morphine. In your stock ampoule there is 15 mg per 1 mL.
How much of the ampoule will you need?
Formula method Ratio method
6 mg 1 mL 16 mg : × mL
× = 0.4 mL 15 mg : 1 mL
15 mg 1
16 mg × mL
=
15 mg 1 mL
= 0.4 mL
EXAMPLE
(ii) You are required to give 30 units insulin. In your stock vial there is 100 units per 1 mL.
How much do you require?
Formula method Ratio method
30 units 1 mL 130 units : × mL
× = 0.3 mL 100 units : 1 mL
100 units 1
130 units × mL
=
100 units 1 mL
= 0.3 mL
APPENDIX D
