Calculations of medicine: Nursing perspective

Calculations of medication

1. Calculations &
Legal framework
By C.Settley
Compiled by C Settley

2. Calculations &
Legal framework
Outcomes:
•Students must be able to
administer medication according to
the correct principles
Compiled by C Settley

3. LEGAL FRAMEWORK
•Figure 13.1 pg230
•Pg230-232
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4. Drug calculations
•Nursing as a profession requires that
you will often be called upon to
administer or supervise the
administration of all types of medicines.
•This means that you will have to be able
to possess a certain amount of
mathematical skills.
•The required level is not high, but
attaining it is necessary to ensure that
the safety of patients is not
compromised.
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5. •When a measurement is very large or very
small, using the unit on it's own becomes
impractical. If we had a drug that was very
potent, a patient may only require a tiny
amount.
•If this was just one millionth of a gram, this
could be written as 0.000001g but this can
easily be misread. It would be very easy to
confuse it with 0.00001g for example.
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6. •By using prefixes the same quantity could be written as 1mcg or as 1
microgram, either of which is clearer to read.
•By definition, 1 gram = 1000 milligrams and 1 milligram =1000
micrograms.
•There might be times where you will have to convert a quantity from
one unit to another, e.g. mg to g.
•Consider the number and the units separately. If the units describing a
quantity get bigger, you will have numerically less of them.
•If the units get smaller you will have more of them.
•What you need to do is to balance
the number and the units.
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7. •Here is an example:
Convert 500mg into grams
•Consider the 500 and the mg as two separate parts.
•The mg is to be changed to g so the units are to become one thousand
times bigger.
•The number of these units is made one thousand times smaller to
compensate.
•To make a number one thousand times smaller, consider the number as
a decimal (ie500.0) then move the decimal point three places to the
left, giving .5000 which in its standard form would be rewritten as 0.5.
•So 500mg can be rewritten as 0.5g
•To convert the other way, use the same idea in reverse.
•If the units get smaller the number gets bigger.
•Just remember to balance the dimensions of the
units against the number of units.
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8. Conversion: Examples
•300mg = 0.3g
•0.5g = 500mg
•750micrograms = 0.75 mg
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9. Dosage calculations
•On a drug round, you may be given the total dose a patient is to
receive. The nurse's task will be to find out the amount of drug in each
tablet and then to calculate how many tablets to give the patient.
•Example A patient is prescribed 120mg of Verapamil but the tablets are
available as 40mg each. How many tablets are required ?
The formula is: Dosage requiredx Volume
Dosage in stock 1
120 mg x Volume
40 mg 1
= 3 tablets
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10. Dosage calculations: Exercise
•500mg is prescribed, tablets are 250mg each:
how many tablets will you give?
The formula is: Dosage requiredx Volume
Dosage in stock 1
500 mg x Volume
250 mg 1
= 2 tablets
Compiled by C Settley

11. Dosage calculations: Exercise
•50mg is prescribed, tablets are 12.5mg each:
how many tablets will you give ?
The formula is: Dosage requiredx Volume
Amount in stock 1
50 mg x Volume
12.5 mg 1
= 4 tablets
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12. Dosage calculations: Exercise
•1mg prescribed, tablets are 500micrograms:
how many tablets will you give?
The formula is: Dosage requiredx Volume
Amount in stock 1
Conversion: 1 mg= 1000 mcg/ 500 mcg= 0.5 mg
1000 mg x Volume
500 mg 1
= 2 tablets
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13. Drugs in liquid form
•When drugs are in liquid form, the availability
is given in terms of the concentration of the
solution or suspension.
•As an example, pethidinehydrochloride is
available as 50mg/ml. This means that 50
milligrams of pethidinehydrochloride is
dissolved in every millilitreof liquid.
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14. Example
•A drug is available as 25mg/ml and 75mg are
required. What volume will be given in ml?
•Answer: The amount prescribed is 75mg and the
amount per measure is 25mg.
Now 75 divided by 25 is 3 so we need three measures.
But each measure is one
milliliter so we should give 3ml.
•DO EXERCISE!
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15. Prescriptions
•Nurses’ actions regarding the
handling of medication is
governed by
•Nursing Act (No. 33 of 2005)
•SANC regulations e.g. Scope of
Practice
•Medicine and Related Substances
Act(No. 101 of 1965 as amended)
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16. Legal prescriptions
•In terms of Medicines & Related Substances Act(1965 as amended)
•Name, qualifications, practice number and address of the prescribing practitioner.
•Name and address of the patient.
•Date of issue.
•Approved generic name.
•Dosage form.
•Strength in dosage form and quantity to be supplied.
•Instructions for the administration of specified dosage form and frequency.
•Signature must be handwritten.
•Legible.
•The following must also appear on the prescription chart:
•Age (especially children
•Gender
•Weight / BMI
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17. Legal prescriptions by
telephone
•Dispenser needs to verify the authenticity.
•Record must be kept.
•Original prescription must be obtained
within seven working days.
•Verbal instruction-treatment not to exceed
7 days. Schedule 5/6 max treatment 48
hours and signed by prescribing
practitioner within 72 hours.
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18. What are scheduled drugs?
•Scheduled substances:
Figure 14.1 –pg242
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19. Managing pharmaceutical stock(pg232)
•Aspects of stock management:
–Ordering
–Receiving
–Issuing
–Reordering
•Ineffective management 
–Wastage of essential drugs and money
–Decrease in quality of care to patient
•Proper stock management and drug control 
successful management of the
nursing unit andfacility.
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20. Checklist for effective stock management
(pg232)
•Find / develop a structured system to manage
stock effectively.
•Regularlyupdate minimum and maximum levels
(or reorder levels).
•System for proper stock control prevents
losses(theft,expired, damaged)
•A dedicated reg. nurse to be
responsible; must also maintain open
lines of communication.
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21. •Identify fast moving items and ensure
sufficient supply
–Adjust minimum-maximum stock levels
–Determine effective reordering schedule
•Receiving items
–Specific method for unpacking / rotating stock
to prevent expired stock
–Two principles
•FIFO–First in first out
•FEFO-Firtexpired first out
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22. •Identify stock that is about to expire
–System in place to check expiry dates regularly
–Return short dated stock to pharmacy 3 months
before expiry date (especially if not used frequently)
•Assign regular, fixed dates for checking
ward stock and storage conditions
•Standard operating procedures (SOPs),
guidelines and policies must be in place
AND all staff must know where to findit ,
and how to implement it uniformity and
less chance of mistakes.
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23. •Storage of drugs and other pharmaceutical
stock must be clearly marked.
•Preparations for internal or externaluse
must be separately stored.
•Inflammable agents should also be
separately stored.
•Keep drug cabinets and medicine trolleys
locked.
•Use correct procedures for control
of schedule 5 and 6 drugs.
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24. Cold chain management (pg233)
•Somedrugs are thermo-labile (temperature
sensitive must be kept at a low temperature =
fridge).
•The ward/unit must have a dedicated fridge for
these drugs e.g. insulin, muscle relaxants, vaccines
•Only the correct items may be kept in this fridge
(not the patient’s cold drink!)
•The fridge should be placed in a cool place, not
indirect sunlight.
•The fridge must also be connected to a dedicated
electric plug.
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25. •The temperature should be kept between 2 and
8°C.
•Temperature readings should be done twice a
day to verify this.
•The fridge should be cleaned regularly.
•There should be a maintenance plan.
•Thermo-labile drugs must be placed in the fridge
immediately on receipt from the pharmacy
•Remove drugs from fridge
immediately before use
Compiled by C Settley

26. Medicine administration pg235
•The 5 R’s of medication administration
–Right patient
–Right medication
–Right dose
–Right time
–Right route
NB. Medication administration done
under the supervision of a R/N
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27. 1. The right patient
Identify identifyidentify!
Patient
Prescription chart
Medication
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28. 2. The right medicine
•Prescribing is dr’sresponsibility
•But nurse must have adequate knowledge
of drug administered
•Bothdr. & nurse accountable
•Nurse accountable, even if incorrect
prescription
•NB is the prescription legible and legal
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29. •Ask questions
–Why is drug prescribed?
–Expected effect (observations to do)?
–Dosage appropriate?
–Any allergies?
–Possible drug interactions?
–Special instructions?
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30. 3. The right dosage
•Correct dose calculated using
correct formula where applicable
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31. 4. The right route
•Use routeprescribed
•Oral route preferred where possible
•Oral route
–Patient must be able to swallow
–For nasogastric tube administration check whether
tablets may be crushede.g. enterically coated tablets
•IV drugs
–Compatibility of drug with IV fluid
–Use correct diluents
–Simultaneous administration of more than one drug
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32. 5. The right time
Check prescription for
correct
Time (time of day)
Frequency
Dosage interval
Interaction with food
Interactionwith other drugs
Compiled by C Settley