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M103 > W3 Pharmaceutical calculations > Flashcards

W3 Pharmaceutical calculations Flashcards

inc lecture and workshop notes

1
Q
  • od
  • tds, tid
A

once daily
three times a day

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2
Q

bd, bds, bid
qds, qid

A

twice a day
four times a day

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3
Q

ii qds prn mdu

A

two tablets, four times a day, when required, as directed

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4
Q

i, ii and iii
Examples?

A

1,2,3 tablet (s) Eye drops, inhalations etc

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5
Q

om, mane, am
on, nocte, pm

A

In the morning
At night

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6
Q

Prn,sos

A

When required/if necessary

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7
Q

Mdu, ud

A

As directed/use as directed

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8
Q

qld
qod, alt
Mitt. Mitte, send

A

Once daily
On alternate days
Total quantity

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9
Q

qh, q1h
q2h
q4h or qqh
q12h
stat.

A

Hourly
Every two hours
Every four hours
Every twelve hours
Immediately

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10
Q

1 kilogram in grams?

A

1000 grams (g)

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11
Q

1 gram in milligrams?

A

1000 milligrams (mg)

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12
Q

1mg in mcg?

A

1000 micrograms (mcg)

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13
Q

1mcg in nanograms?

A

1000 (ng)

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14
Q

Which are bigger?
Nanograms
milligrams
micrograms

A

Milligrams > Micrograms > Nanograms
10- 3 > 10-6 > 10-9

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15
Q

1 litre in millilitres
1mL in microlitres?

microlitres is NOT mL (millilitres)

A

1L= 1000 millilitres
1mL=1000 microlitres

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16
Q

What are solid dosage forms measured in?

A

grams, milligrams,micrograms

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17
Q

What are non-solid dosage forms measured in?

A

milligrams/mL
e.g. 100mg/5ml or 10mg/ml

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18
Q

Non solid dosage forms:

What do (% w/v) (% v/v) (%w/w) mean??

A
  • weight in volume (% w/v): % = g per 100ml [e.g. 2% = 2g per 100ml]
  • volume in volume (% v/v): % = ml per 100ml [e.g. 2% = 2ml per 100ml]
  • weight in weight (% w/w): %= g per 100g
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19
Q

Non solid dosage forms:

What do (% w/v) (% v/v) (%w/w) mean??

A
  • weight in volume (% w/v): % = g per 100ml [e.g. 2% = 2g per 100ml]
  • volume in volume (% v/v): % = ml per 100ml [e.g. 2% = 2ml per 100ml]
  • weight in weight (% w/w): % = g per 100g [e.g. 2% = 2g per 100g]
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20
Q

Ratios:
What is; 1:1000 and 1:10,000

A

1:1000= 1g in 1000ml
1:10,000= 1g in 10,000ml

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21
Q

What is the definition of dose?

A

The amount of medicine taken by/administered to a patient in order to achieve a therapeutic outcome.

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22
Q

1)A patient is prescribed amoxicillin capsules 250mg 1 tds x 7 days.

a. How many capsules should we dispense?
b. How many grams of amoxicillin do they take if they complete the course?

The same patient needs amoxicillin suspension 250mg/5ml instead of capsules.
a. How many millilitres of suspension would we dispense to cover the full course?
b. What strength (%w/v) is this suspension?

A

a: 21 capsules
b: 21x250= 5,250mg= 5.25g

a. 5ml x 3 x 7 =105mL
b. 250mg/5mL
100/5= 20
250x20= 5,000
5000mg/100mL
so, 5g/100mL so 5% w/v

23
Q

Doses based on renal function:
When does a dose need to be decreased?
What can renal function be expressed as? (2)

A

When there is a reduction in kidney function
eGFR- estimated Glomerular Filtration Rate
Creatinine clearance

24
Q

Creatinine clearance; things to remember (3):

A

Creatinine clearance (ml/min) = (140-age) x weight x constant/ serum creatinine

Do brackets first
Constant is different for males and females:
1.23 for male and 1.04 for female (micro mol/l)
Age in years, weight in kg,

25
Q

Mrs Mitra is a 67 year old patient who weighs 70kg. Her recent bloods show a serum creatinine of 90 micromol/L
constant=

Work out her creatinine clearance: (use GpHC approved calculator)

Creatinine clearance (ml/min) = (140-age) x weight x constant/ serum creatinine

A

59.05

26
Q

“Parts” in formulae and dilutions:
(for info)

A
  • Industrial methylated spirit (IMS), BP
  • spirit (L) 95 parts
  • wood naphtha (L) 5 parts
    For IMS above, the formula adds up to 100 parts.

To make 200L of IMS, you would use
* 95L x 2 = 190L of spirit
* 5L x 2 = 10L of wood naphtha

27
Q

Differentiate between “parts” and “to
parts”

Example 1
* calamine powder 1 part
* aqueous cream to 10 parts

Example 2
* calamine powder 1 part
* aqueous cream 10 parts

A

Example 1: Equivalent to:
1g
9g
Total: 10g and (1g/10g) x 100% = 10% w/w

Example 2:
Equivalent to:
1g
10g
Total: 11g and (1g/11g) x 100% = 9.09% w/w

28
Q

A prescription calls for 10ml qds x 7 days. How many millilitres do you supply?

A

=280 ml

10x4x7

29
Q

A patient takes digoxin tablets 250 micrograms od. How many milligrams of digoxin do they take in a month (28 days)?

A

= 7 milligrams

250 x 28= 7000mcg / 1000= 7mg

30
Q

A patient uses chloramphenicol eye drops 1% (w/v), 1 drop q2h (during waking hours – for this example 16 hours per day) for two days and 1 drop qds for the next three days. Each drop is 0.05ml.

i) How many millilitres has the patient used?
ii) How many milligrams has the patient used?

A

i) (9x2) +(4x3)= 30 eye drops x0.05ml
= 1.5ml

ii) 1.5ml
1% w/v= 1g in 100ml
1.5/100= 0.015g so 15 milligrams

8 can be used instead of 9

31
Q

How many grams of active ingredient are contained in 1L of a 5% w/v solution?

A

=50g

  • 5%w/v = 5g/100mL
  • (1000mL/100mL) x 5g = 50g
32
Q

What strength, expressed as w/v, is paracetamol suspension 120mg/5ml?

A

= 2.4% w/v

  • w/v means g/100mL
  • (100mL/5mL) x 120mg = 2400mg = 2.4g
  • If there are 2.4g in 100mL, strength is 2.4%w/v
33
Q

How many grams of amoxicillin would a patient take in total if they were prescribed:
Amoxicillin Capsules 500mg tds x 5 days?

A

=7.5g

  • 500mg tds means 500mg three times a day = 1500mg daily
  • Given for 5 days = 7500mg = 7.5g
34
Q

What volume of adrenaline 1 in 1000 would need to be administered to provide a 300mcg dose?

A

=0.3ml

  • 1 in 1000 means 1g in 1000ml
  • 1g in 1000ml = 1000mg in 1000ml = 1mg/ml = 1000mcg/ml
  • Want 300mcg, so (300mcg/1000mcg) x 1ml = 0.3ml
35
Q

How much of each ingredient is required to make 250ml of Chalk Mixture, Paediatric BP?
* chalk 20g
* tragacanth powder 2g
* cinnamon water, conc 4ml
* syrup 100ml
* chloroform water, double strength 500ml
* water to 1000ml

A

Need 250ml/1000ml = 0.25 times (a quarter) of each ingredient.

  • chalk 50g
  • tragacanth powder 0.5g or 500mg
  • cinnamon water, conc 1ml
  • syrup 25ml
  • chloroform water, double strength 125ml
  • water to 250ml
36
Q

When may we need to change to strength of a medicine?
Reasons for decreasing and increasing?

A

Decrease – e.g. for administration to a child or an older patient or for preparation of a medicine to give to a patient from a stock solution. This is done by dilution.

Increase – e.g. to make a product that is stronger than the one we have available. This is done by admixing (the action of adding one ingredient to something else)

37
Q

When we dilute:
the amount of active ingredient inc/dec ..?
the concentration inc/dec ..?

A

Stays the same
Decreases

38
Q

We have a 20% w/v of stock solution and want to make 200ml of a 5% w/v solution.
-How much stock solution and how much diluent do we need?

2 methods to work out; C1V1=C2V2 or First principles

A

Stock- 20% w/v = 20g in 100ml

Product- 5% w/v= 5g in 100ml (200ml)
10g active ingredient in 200ml x2

so 50ml of stock (half) is needed for 10g and 150ml diluent to make 200ml

39
Q

You have a 25% stock solution and need to make 1L of a 1% preparation. How much stock solution and how much diluent do you need?

A

40ml stock and 960ml of diluent

Using the equation C1V1 = C2V2
25% x V1 = 1% x 1000ml So, V1 = (1%/25%) x 1000ml =40ml

40
Q

You need to make 50ml of a 7.5% w/v solution. You have a 12% w/v solution in stock. How much stock and how much diluent do you need?

A

31.25ml stock and 18.75ml of diluent

Using the equation C1V1 = C2V2
12% x V1 = 7.5% x 50ml
So, V1 = (7.5%/12%) x 50ml = 31.25ml
18.75 diluent

41
Q

You need to make a 150ml of a 1.25mg/5ml solution. You have a 1.5% w/v solution in stock. How much stock and how much diluent do you need?

A

2.5ml stock, 147.5ml diluent

1.25mg/5ml = 25mg/100ml = 0.025g/100ml = 0.025% w/v Then, V1 = (0.025%/1.5%) x 150ml = 2.5ml

42
Q

You have a 10ml of a 4% solution. How many 1ml ampoules of a 1 in 1000 solution could you make?

A

1 in 1000 = 1g in 1000ml = 0.1g/100ml = 0.1% w/v
4% x 10ml = 0.1% x V2
So, V2 = (4%/0.1%) x 10ml = 400ml
400 x 1ml ampoules

If we can make 400ml of 1 in 1000 solution, we can fill 400 x 1ml amps

43
Q

Multiple/Serial Dilutions:

What weight of active ingredient is required to produce 1000ml of a solution such that, when 2.5ml is diluted to 50ml with water, it gives a 0.25% w/v solution?

A

= 50g

Stock Solution Product
5% w/v 0.25% w/v = 0.25g per 100ml
= 5g per 100ml

20x dilution

  • 0.25% = 0.25g/100ml, so final product 50ml contains 0.125g (as it did
    2.5ml before dilution)
  • So: if there is 0.125g in 2.5ml of original solution, we need:
    (1000ml/2.5ml) x 0.125g = 50g to make 1000ml of stock

method 2:
* Diluted 50ml/2.5ml = 20 times
* Original solution must therefore be 20 x 0.25% w/v = 5% w/v
* 5% w/v = 5g/100ml
* So, need: (1000ml/100ml) x 5g = 50g active ingredient to make 1000ml

44
Q

What weight of active ingredient is required to produce 250ml of a solution such that, when 10ml is diluted to 200ml, we have a 1% w/v solution?

A

Solution is diluted 200ml/10ml = 20 times
* So, original solution is 20 x 1% w/v = 20% w/v
* 20% w/v = 20g in 100ml
* To make 250ml, need (250ml/100ml) x 20g = 50g
or 20g x 2.5=50g

45
Q

What are the different types of dose?

A

Single dose, Daily dose, Daily divided dose, Weekly dose

46
Q

Examples of doses based on weight: (for info)

A
  • Can often be for children, but also for specific medicines in adults.
  • Expressed as mg/kg or mcg/kg for weight
    e.g. Paracetamol
  • Expressed as mg/m2 or mcg/m2 for BSA
  • Often there is an accompanying maximum dose that should not be exceeded.
47
Q

For infusions: the dose if often expressed as:

A

mg/kg/min or mcg/kg/min

48
Q

A patient, weight 68kg, has been diagnosed with viral encephalitis and requires aciclovir at a dose of 10mg/kg every 8 hours. What total dose is required?

A

68kg x 10mg/kg = 680mg every 8 hours

49
Q

A child aged 2, weight 12kg, has asthma and requires a 3 day course of steroids. The dose of prednisolone would be 1-2mg/kg od. What dose range could be administered?

A

12-24 mg od x 3 days

50
Q

The maintenance dose of sodium valproate for epilepsy in children is 30mg/kg daily in two divided doses.

i) What is the dose in mg for a 12kg child?
ii) Sodium valproate is available as a 200mg/5ml oral solution. What is the dose in ml?

A
  1. 12kg x 30mg/kg = 360mg per day
    In two divided doses, this is 180mg bd
  2. (180mg/200mg) x 5ml = 4.5ml bd
51
Q

Example (BSA) - Aciclovir [Refer to BNF]

A 9-year-old child with a BSA calculated at 1.2m2 requires an I/V infusion of aciclovir. What is the 8-hourly dose?

A

1.2m2 x 500mg/m2 = 600mg every 8 hours

52
Q

Refer to BNF: Dopamine Hydrochloride
- What is the maximum dose of dopamine that can be given to a 70kg adult patient?
-Dopamine infusion vials contain 200mg/5ml. What volume of dopamine should be used to provide a 6-hour infusion?

A

a. 70 x 5mcg = 350mcg/min
b. 350mcg x 60 (minutes) x 6 (hours) = 126,000 mcg = 126mg
Need: (126mg/200mg) x 5ml = 3.15ml

53
Q

A 75kg patient requires an atenolol intravenous infusion after admission for an arrythmia [Refer to BNF Hypertension]

  1. What dose of atenolol is required initially?
  2. Atenolol is available as 5mg/10ml solution for injection ampoules. How much should be added to the infusion solution for a single dose?
A
  1. 75kg x 150mcg = 11,250mcg (11.25mg) over 20 minutes
  2. (11.25mg/5mg) x 10ml = 22.5ml

M103 (46 decks)

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