Stuck with Pre-Reg exam calculations?

[Bulletproof]

Hey,

I'm stuck with some calc. qs. Would really appreciate the help!

1. In the TPN unit, you are required to prepare 60mmol of Potassium ions in 3.5 litres of TPN, 2 bags are required for the patient. Please calculate the total amount of Potassium 15% injection that is required.

a) 20mls
b) 30mls
c) 40mls
d) 50mls
e) 60mls



2. What weight of a drug Y, containing 20% w/w moisture, should be added when preparing a 20L batch of an aqueous solution formulation with a final concentration of 3% w/v anhydrous drug Y?


a) 250g
b) 500g
c) 750g
d) 1250g
e) 1500g

3) A doctor has asked you to predict the concentration of a drug with a half-life of 16 hours. On admission, the patient’s serum contains 84 micrograms/ml of the drug, could you please predict the plasma concentration at 24 hours?

a) 45
b) 41.5
c) 35
d) 33.5
e) 31.5

Also can you explain how you got the answers? I'm so confused about half life qs.

Cheers!

[shan]

Hey,

I'm stuck with some calc. qs. Would really appreciate the help!

1. In the TPN unit, you are required to prepare 60mmol of Potassium ions in 3.5 litres of TPN, 2 bags are required for the patient. Please calculate the total amount of Potassium 15% injection that is required.

a) 20mls
b) 30mls
c) 40mls
d) 50mls
e) 60mls

CHECK BNF : HOW MANYmmol OF POTTASSIUM IN 15% SOLUTION THEN THE ANSWER IS SIMPLE

2. What weight of a drug Y, containing 20% w/w moisture, should be added when preparing a 20L batch of an aqueous solution formulation with a final concentration of 3% w/v anhydrous drug Y?


a) 250g
b) 500g
c) 750g
d) 1250g
e) 1500g

Answr : 750G.20L= 20000 MLS. 100MLS WILL HAVE 3g, SO 20000MLS WILL HAVE 600g. NOW THE GIVEN POWDER HAS 20 % MOISTURE MEANING 100g POWDER HAS 80g OF ANHYDROUS DRUG SO TO GET 600g OF ANHYDROUS DRUG YOU NEED 600 x 100 / 80 = 750g.

3) A doctor has asked you to predict the concentration of a drug with a half-life of 16 hours. On admission, the patient’s serum contains 84 micrograms/ml of the drug, could you please predict the plasma concentration at 24 hours?

a) 45
b) 41.5
c) 35
d) 33.5
e) 31.5

Also can you explain how you got the answers? I'm so confused about half life qs.

SMPLE. HALF LIFE = AFTER A GIVEN PERIOD THE DRUG'S CONCENTRATION IS REDUCED BY HALF. SO IF HALF LIFE IS 16 Hrs THEN AFTER 16HRS THE DRUG IN THE BODY IS 84/2=42. NOW START WITH 42 AND YOU WILL SEE THAT AFTER 16Hrs THE CONC WILL BE 21. SO AFTER 8 HOURS IT WILL BE 21 + HALF OF 21 (10.5). hENCE THE ANSWER IS 24Hrs = 16 + 8 Hrs = 21 + 10.5 = 31.5

Cheers!

cHECK ALL THE RED BOLD LETTERS AS ANSWERS

[Bulletproof]

Thank you very much :-)

[Fleegle]

Threads such as this one seriously undermine my confidence in the presumed 'knowledge' of future pharmacists.

Fleeg.

[Nik]

Hey,

I'm stuck with some calc. qs. Would really appreciate the help!

Would have been good to see your ideas rather than relying on someone else to come up with the answers. It was very generous of Shan to give you asnwers AND explanations.

[little girl]

hi everyone, I am stuck on this calculation, please can some-one guide me through how to attempt it because I have no clue how to start

you have in your pharmacy a cream containing 0.5% w/w hydrocortisone. You have been requested to use this cream as a base and to add in sufficient calamine such that the final concentration in the new cream will be 10.0% w/w. What is the concentration of hydrocortisone in the new cream?

A - 0.3 w/w
B - 0.45%
C - 0.5% w/w
D - 0.05% w/w
E - 0.045% w/w

Thank you!

[little girl]

Sorry answer B should be 0.45 w/w

Is this right?

As the new cream will be 10% calamine, the hydrocortisone will make up 90% of the rest of it....but don't really know what to do next

[johnep]

Regret example of poor maths teaching in schools. Start at the end.
ie 100grms of finished cream contains 10 grm of calamine. Therefore 90 grms of 0.5% cream left.
0.5/100 x 90 = 0.45
All simple proportion. When I was teaching maths in a school, I told the pupils that if they could do proportions and percentages, would make money.
Thus, To start 100 grm cream contains 0.5grm
Therefore, 1 grm .. .. 0.5/100
and 90 grm .. .. 0.5/100 x 90

As the meercat would say Seemples!
johnep

[little girl]

Thank you johnep! My maths is so bad!!!

[johnep]

I just hope you are a tech and not a pre reg. Simple errors of concentration have killed many people in hospital, eg sodium phosphate soln given in 10 x concentration. Used to be many deaths from concentrated potassium chloride solns in ward cupbds. You need to do one calculation each day.
johnep