Dosing and calculation Flashcards
What unotes should doses be written for paediatrics (& all?)
Mg unless otherwise specified in the BNF
How do you calculate lean body weight? [1]
Body fat weight - actual body weight
In paedatriac intermediate life support, how should you calculate babys weight? [1]
(Age + 4) x 2 (kg)
what does ‘%w/w’ mean? [1]
what does ‘%v/v’ mean? [1]
Explain what ‘%w/v’ means? [1]
Calculate how much sodium bicarbonate is in the following preparation:
’ Sodium bicarbonate 8.4% w/v 100ml’
An 8.4% solution contrains 8.4g in 100ml
How much MgS is in:
‘Magnesium sulfate 20% w/v 20ml ampoule for injection’
Explain how ratios can be used to express drug calculations [2].
1:1000 = 1g in 1000ml
- 1g in 1000ml = 1000mg in 1000ml = 1mg in 1ml
1:10 000 = 1 g in 10 000ml
- 1g in 10,000ml = 1000mg in 10,000ml = 1mg in 10ml = 100microgram in 1ml
In the BNF:
‘Child 3–5 months: 60 mg every 4–6 hours; maximum 4 doses per day”
Therefore max dose: 60x4 = 240mg
What is the standard practise when withdrawing benzodiazepine medication?
Change benzo to equivalent dose of diazepam then carefull reduce the dose of this to zero
He takes 40mg twice a day morphine sulfate. He also takes 20mg morphine sulfate daily PRN.
Covert his 24hr dose of morphine sulfate to a fentanyl patch
Fentanyl 25 micrograms/ hr patch
Fentanyl 37 micrograms/ hr patch
Fentanyl 50 micrograms/ hr patch
Fentanyl 100 micrograms/ hr patch
He takes 40mg twice a day morphine sulfate. He also takes 20mg morphine sulfate daily PRN.
Covert his 24hr dose of morphine sulfate to a fentanyl patch
Fentanyl 25 micrograms/ hr patch
Fentanyl 37 micrograms/ hr patch
Fentanyl 50 micrograms/ hr patch
Fentanyl 100 micrograms/ hr patch
Convert his oral morphine sulfate to diamorphine via sub infusion
What should vancomycin be diluted to a concentration of when dosing? [1]
What should the infusion rate not exceed? [1]
5mg/ml
Should not exceed 10mg/minutes
You need to prescribe 1 gram of vancomycin.
Describe how you decide what size infusion bag you would use [1]
NB: Vancomycin is infused at 5mg/ml
1 g = 1000 mg
Need to dilute to 5mg/ml
Therefore 1000 mg in 1000 ml = 1mg/ml
But we want 5mg/ml so divide 1000ml by 5 = 200ml
BUT bags only come in 250ml
State how you would prescribe the correct infusion rate for vancomycin
What are the steps need to enact when prescribing NAC infusion? [4]
- Find out actual body weight: max weight should use is 110kg
- Add with glucose 5%
-
The total dose regimen is to be prescribed and adminstered in three parts:
- First (loading) dose is given over 1hr in 200ml of glucose 5%
- Second dose given over the next 4hrs, in 500ml of glucose 5%
- The third and final is given over 16hrs, 1 litre of glucose 5% -
Those dose of NAC varies at each steps:
- For the first you need 150 mg/kg
- For the second you need 50 mg/kh
- For the third you need 100 mg / kg
- Thats a total dose of 300 mg/kg over 21 hrs!
Look Up in BNF: Poisoning, emergency treatment
Look up BNF xx
How do you calculate volume required of a paraenteral drug? [1]
Vol = (Dose prescribed x vol of solution) / amount of drug in solution
(same as vol required = what you want / waht youve got) x whats in it
