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Pharmacology: Drug Dose Questions
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Gravity
Key Concepts:
Terms in this set (52)
1) calculate volume required
2) calculate concentration required
3) percentage of a drug with given dose
Know that IV fluids are given in two ways: either through an infusion pump or they are gravity fed
4) pump infusion rates (ml/hour) e.g. using the Alaris pump
5) IV fluid via gravity (drops/minute):
this is calculated via
(wanted volume in ml/min) x (drops/ml: this is usually 20 but depending on the gravity IV controller: check the instructions of the equipment)
types of questions
1% = 1 GRAM in 100 ml
so 8.4% = 8.4g/100ml
convert grams to mg
8.4 grams = 8400mg
so the concentration is 8400mg/100ml
this is 84mg/1ml
What is the concentration (in mg/ml) of an 8.4% sodium bicarbonate infusion?
1 in 10,000 = 1 gram in 10,000ml
convert to milligrams so we have 1000mg/10,000ml = the concentration of the solution we have. And we have 10ml of it
so we have 1mg/10ml
You have a 10 ml ampoule of adrenaline 1 in 10,000.
How much adrenaline (in mg) does the ampoule contain?
500mcg = 0.5mg so injection is 0.5mg/2ml
(0.75mg/0.5mg) x 2ml = 3ml of the injection
You have digoxin injection 500 micrograms/2ml
Calculate the volume required for a 0.75mg dose of digoxin
85 x 3 = 255mcg/min
Dose prescribed is 3 micrograms/kg/min
Patient's weight = 85 Kg
What is the dose in microgram/min?
175 units x 85kg = 14875 units required
(14875 units/20,000 units) x 1 = 0.75ml
You need to give a treatment dose of tinzaparin (175 units/kg) to a patient who is 85 kg
You have syringes giving 20000 units/ml which can measure quantities to 0.05ml.
What volume of the drug should be taken up in the syringe?
Golden rule
when using infusion pumps - convert to ml/hour
1) First step: convert 50mg in 500ml to the number of mg in 1ml.
50mg/500ml = 0.1mg/1ml
2) convert mg to mcg
0.1mg = 100mcg
so overall: 100mcg/ml
3)
required dose (mcg)
------------------------------ x 60mins = mcg/hour
what we have (mcg)
10mcg (required) / 100mcg (what we have) = 0.1ml/min
0.1mcg x 60mins =
6ml/hour
you should use a formula to this question.. to make it easier: dose/kg/min has to be converted to mL/hour:
total volume (ml)
----------------------- x dose (mcg/kg/min) x weight x 60
amount of drug (mcg)
remember that units SHOULD BE THE SAME!!!
You have a 500 ml infusion containing 50 mg glyceryl trinitrate.
Dose required is 10 micrograms/min
What is the infusion rate in ml/hour?
1) FIRST: convert 'what we have' to the relevant units of the required dose and then convert it to a concentration per millilitre
what we have is 5mg/ml in 50ml dobutamine
= 5000mcg/50ml
2) SECOND: look at dose required. Multiply this by kg of the patient if that information is shown
40kg x required dose (5 micrograms) = 200 micrograms per minute required
3) THIRDLY: (dose wanted/dose required) x volume
200/5000 x 1ml = 0.04ml per min
4) LASTLY: multiply by 60 to get this in hours
0.04ml x 60 = 2.4ml/hour
12 year old boy is admitted to a paediatric ICU with septic shock. Your are required to give dobutamine at a rate of 5 micrograms/kg/min. Dobutamine is available as 50 ml ampoules at strength 5 mg/ml. The dobutamine solution is to be administered via a syringe pump. The patient weighs 40kg.
At what initial rate of administration should the syringe pump be set in ml/hour
2.5g = 2500mg = 2500000 mcg which is in 250ml
therefore 1ml contains 10000 mcg
----------------------------------------------------------------------
50 x 75kg = 3750 mcg/kg/min dose required total
----------------------------------------------------------------------
(3750/10000) x 1ml = 0.375ml/min
0.375 x 60 = 22.5ml/hour
You have an infusion containing 2.5g esmolol in 250ml sodium chloride 0.9%.
Dose required is 50micrograms/kg/minute
Patient weighs 75kg.
What is the rate in ml/hour?
25mg x 10 = 250mg/dose required 4x a day
(250mg required / 600mg vial) x 2ml = 0.83ml in each dose 4x a day.
you are checking a prescription with a registered nurse for Peter who is 9 months old and weighs 10kg. He is prescribed 25mg/kg/dose of benzylpencillin intravenously, 4 times a day. Each 600mg vial is reconstituted to 2mL. How much should be drawn up for each dose?
(15mcg/600mcg) x 1 = 0.025ml atropine required
John, a young infant, requires 15 micrograms of atropine. There is 600 micrograms in 1mL. How much do you give?
25mg x 13 = 325mg/dose = required
(325mg/500mg) x 4ml = 2.6ml
You are checking a prescription with a registered nurse for Eimear who weighs 13kg. She is prescribed 25mg/kg/dose of benzylpencillin IV, 3 times a day. Each 500mg vial is reconstituted to 4mL. How much should be drawn up for each dose?
75/250 x 5 = 1.5ml atropine required
Becky, a young infant, requires 75 micrograms of atropine. There is 250 micrograms in 5mL. How much do you give?
1200 x 5 = 6000mcg/dose
6000mcg = 6mg/dose
6/50 x 2ml (volume in the vial) = 0.24ml
You are checking a prescription with a registered nurse for Bob who weighs 5kg. He is prescribed 1200mcg/kg/dose of benzylpencillin IV, 4 times a day. Each 50mg vial is reconstituted to 2mL. How much should be drawn up for each dose?
80/50 x 2ml (in the stock) = 3.2ml
A patient has been prescribed 80 milligrams. The stock available is 50mg / 2mL. What volume is required?
remember that IV infusion is calculated in ml/hour however this questions asks about no. of drops/min
250ml in 4 hours
250ml in 240 minutes
1.04ml/min
1.04 x 15 drops = 16 drops/ml total required
A unit of blood is to be transfused over 4 hours. The volume of blood is 250 mL. The drip rate of the infusion set is 15 drops per mL. Calculate the number of drops per minute the transfusion requires to be set at.
firstly convert the hours to minutes
8 hours = 480 minutes
500ml in 480 minutes
1.04ml/min required
1.04 x 20 = 21 drops required per minute
A patient is to receive 500ml of Hartmann's solution over 8 hours. The intravenous set delivers 20 drops per millilitre. At what rate (in drops per minute) should it drip?
75mcg x 5 = 375mcg in this 25ml bottle
375mcg = 0.375mg in this bottle
Drug Labels
A suspension contains carbamazepine 75mcg/5ml. How many milligrams would be in a 25ml bottle?
250g should be given for each dose
if tablets are 125mg each then 2 tablets are required for each dose 6-hourly.
1g of drug A is to be given per day in 4 equally divided doses. Capsules are 125mg. How many capsules should be given at each dose?
750mcg = 0.75mg
(0.75/1mg) x 1ml = 0.75ml benzatropine IM
note: benzatropine is an anticholinergic drug used in patients to reduce the side effects of antipsychotic treatment. Benzatropine is also a second-line drug for the treatment of Parkinson's disease.
a patient is prescribed 750mcg benzatropine IM and ward stock contains benzatropine 1mg/ml. How much should you administer?
1l = 1000ml
(1000ml/100ml) x 1 hour = 10 hours
should finish at 8pm
a patient is to receive Nutrison multifibre 1litre via PEG tube at a rate of 100ml/hour commencing at 8am with a break between 12-2pm. What time should it finish?
60x5mg = 300 mg required of amiodarone in 100ml of 5% glucose over 20mins
amiodarone 5mg per kg body weight in 100ml 5% glucose over 20 mins is prescribed. The patient weighs 60 kg. What is the dose required?
1% = 1 gram in 100ml
so 2.5% = 2.5 grams in 100ml
equivalent to 2500mg in 100ml
(100mg/2500mg) x 100ml = 4ml required
thiopentone 2.5% infusion is prescribed. What volume is required to administer a dose of 100mg?
1 in 10,000 = 1
g
in 10,000ml = 1000
mg
/10000ml
= 1000000
mcg
/10000ml
1000000/10000 = 100mcg/1ml
so 100 micrograms in 1ml
convert 1:10000 ratio to mcg/ml
1 in 1000 = 1 gram in 1000ml
= 1000mg in 1000ml
= 1mg/1ml
adrenaline 1:1000 injection is available.
The prescribed dose is 1ml.
How many mg in 1ml?
(125/500) x 2ml = 0.5ml volume to be added
digoxin 125 microgram in 100ml sodium chloride 0.9% is to be prescribed over 1 hour.
500 microgram digoxin in 2ml ampoules are available.
What volume is to be added to 100ml sodium chloride?
volume(ml)/drug amount (mg)
60/30 = 2ml containing 1mg of the drug
so 1.25mg is 1.25 x 2 = 2.5ml/hour
diamorphine 30mg in 60ml 0.9% sodium chloride over 24 hours using a syringe pump is prescribed.
To be given at 1.25mg per hour.
How many ml per hour should be given?
remember infusions calculated in ml/hour
volume(ml)/drug amount (units)
50/50 = 1ml per 1 unit
that is 4ml per 4 units
insulin 50 international units in 50ml 0.9% sodium chloride is prescribed for administration from
a syringe pump, starting at 4 international units per hour.
calculate a set rate?
so remember
(dose wanted/dose we have) x volume we have
so (7.5mg/5mg) x 5ml = 7.5ml = the volume needed for a dose of 7.5mg (prescription)
the prescription is asking us to make this up to 25ml glucose 5% solution so we should get a 25ml syringe and draw up 7.5ml of midazolam and make up 25ml
25ml - 7.5ml = 17.5ml of 5% glucose solution to be added to make up our 25ml volume syringe
The syringe now contains 25ml of solution containing 7.5mg midazolam
0.5 microgram per kg per minute midazolam is prescribed for a 1kg baby, to run at 0.1ml per hour.
The prescription asked for 7.5mg midazolam in 25ml glucose 5% solution.
Ampoules of midazolam 5mg in 5ml are available
Prepare the volume required
(5mg/20mg) x 2ml = 0.5ml of actual drug required
so 20ml (total volume) - 0.5ml (drug volume) = 19.5ml (normal saline volume)
you are asked to prescribe 5mg of hydralazine in 20ml 0.9% NaCl. Vials contain 20mg/2ml
steps in preparing your medication
volume total to make up = 20ml
1mg/ml is basically a 1:1 ratio so the concentration and volume in the vial will remain the same
vial contains 2ml of drug. 20-2 = 18ml NaCl 0.9% added to the syringe
you are asked to prepare 1mg/ml dilution of hydralazine in 20ml 0.9% NaCl. Vials contain 20mg/2ml
how much normal saline should be added
1:1000 = 1 gram in 1000ml
= 1000mg in 1000ml
(0.5mg/1000mg) x 1000 = 0.5ml required
an adult male is to be given IM injection of 0.5mg of adrenaline 1:1000 for treatment of suspected anaphylaxis
what is the volume required?
15x48 = 720mg required over 15 mins
720/10 x 1ml = 72 ml required over 15 minutes
A 25-year-old woman is nil by mouth following an appendicectomy. She requires a single dose of paracetamol for pain relief. She will not accept treatment in the form of suppositories and a decision is made to use the IV route. The recommended IV dose of paracetamol is 15 mg/kg given over 15 minutes. She weighs 48 kg.
Paracetamol intravenous infusion is available in vials containing 10 mg/mL.
What total volume of paracetamol intravenous infusion should she be given?
11ml/hour
A 67-year-old man weighing 84 kg develops cardiogenic shock following a myocardial infarction. You are required to give an IV infusion of dopamine hydrochloride 3.5 micrograms/kg/minute. Dopamine hydrochloride is supplied at a concentration of 1.6 mg/mL in glucose 5% solution.
Calculate the IV infusion rate
4/5 = 0.8ml
A 42-year-old man weighing 66 kg requires a dose of haloperidol 4mg IM to treat an exacerbation of schizophrenia. Haloperidol is supplied for injection as a 5 mg/mL solution.
What volume of the supplied solution should the patient be given?
Whenever infusion fluids are to be administered via
GRAVITY FLOW
AS OPPOSED TO INFUSION FLOW, the fluid administration rate must be converted to
drops/minute
. Checking how many drops the fluid administration set delivers per mL is a vital part of the associated prescribing calculation.
- 2400 ml/day required. This needs to be converted to minutes
- 100ml/hour
- 1.666ml/min
x 15ml = 25 drops per minute.
A 33-year-old woman weighing 60 kg is "nil by mouth" awaiting surgery. You are required to give sodium chloride 0.9% IV at a rate of 40 mL/kg/day. The fluid administration set delivers 15 drops/mL.
At what rate should the IV fluid be given via the administration set? Report your answer to the nearest drop/minute.
drip rate = drops/min
100ml/30mins required
= 3.3ml/min
3.3 x 10 = 33 drops/min
Calculate the drip rate for 100 mls of IV fluids to be given over a half hour via a giving set which delivers 10 drops/ml.
1000ml in 9 hours
1.85ml/min
1.85 x 15 = 28 drops/min
One litre of 0.9% NaCl is charted over 9 hours. The drop factor is 15. Calculate the number of drops per minute.
1500ml/4 hours
6.25ml/min
6.25 x 10 = 62.5 drops/min --> this is an interesting answer because obviously you cannot say half a drop! so you would have to round it up that 0.5 to include the whole drop so it would be 63 drops/min
One and a half litres of 0.9% NaCl is required to be given over 4 hours. Using a giving set which delivers 10 drops/ml how many drops per minute will need to be given?
2000ml/5 hours
6.666ml/min
6.666 x 10 = 67 drops/min
calculate the drip rate for 2 litres of IV Fluids to be given over 5 hours via a giving set which delivers 10 drops/ml.
1000ml/8 hours
= 2.08/min
2.08 x 10 = 21 drops/min
Ordered: 1 litre of Dextrose 5% in water over 8 hours using a giving set which delivers 10 drops/ml. Calculate the rate in drops/minute.
100ml/hour
1.666ml/min
x 15 = 25 drops/min
You are required to administer 100 mls of IV Fluids over 1 hour. The drop factor is 15. How many drops per minute are required to start the flow off at the correct rate?
500ml/135 minutes
3.7 x 15 = 55.5 = 56 drops/min
3 litres of normal saline is charted over 12 hours. The drop factor is 15. The IV has been running for 9 hours and 45 minutes. 500 mls remain. How many drops per minute are needed so that the IV finishes in the required time?
100ml/2 hours
0.8333ml/min
0.8333 x 60 = 50 drops/min
calculate the drip rate for 100 mls of IV Fluids to be given over 2 hours via a giving set which delivers 60 drops/ml.
35mg/50 x 1 = 0.7ml
A client is ordered 35 milligrams of codeine phosphate by subcutaneous injection. 50 milligrams in 1 millilitre of liquid for SC Injection is available. How much will you administer?
50/125 x 5ml = 2ml
A client is ordered 50mg of Amoxicillin trihydrate orally. 125mg in 5ml of Syrup is available. How much should you administer?
3ml
you order 30 mg of furosemide IV. The vial contains 10 mg in 1ml of liquid for IV Injection is available. How much volume should you administer?
you want = 10
you got = 5
(10/5) x 1ml = 2 ml from the vial
you are asked to prescribe 10 mg every 4 hours of morphine sulphate s/c to patient in severe pain. How much volume should you give from the vials given?
Alaris infusion pump is shown on the picture and delivers fluid in ml/hour
1000ml in 12 hours
83.3ml/hour = infusion rate of the pump required
a patient requires 1 L of 5% Dextrose to be given over 12 hours. What should you set on the thing shown in this picture?
ATROPINE
IV 500 micrograms every 3-5 minutes; maximum 3 mg per course
you are given Atropine 1mg/1ml ampules. How much atropine should you give to the patient?
500/1000mcg x 1 = 0.5ml from the ampule.
a patient on the ward complains of weakness and dizziness. PMH: recent MI, hypothyroidism that is well controlled. O/e: unremarkable except for irregular HR
you perform an ECG revealing no P waves and an irregularly irregular rhythm
first initial drug to prescribe to this patient?
140 mg
Dose = 10 mg/kg
Body weight = 14 kg
Total daily dose = 10 mg/kg × 14 kg = 140 mg
DONT BE FOOLED!! it says the dose is 'daily' FOR 3 days. Ignore how long it was given for (3 days) because the question is asking about the 'daily dose' alone.
A 4-year-old girl is brought to the GP with a persistent cough that has recently become productive. She is dyspnoeic and has a slight fever. Her records show a history of adverse reactions to penicillins. A prescription is required for oral azithromycin 10 mg/kg daily for 3 days. The patient's body weight is 14 kg.
What daily dose of azithromycin should be prescribed?
(Write your answer in the box below)
1) available dose = 25 mg / mL in 10mL ampoules
so there is 250mg/mL in one ampule
this is diluted into a 500mL solution so the concentration is now 250mg in 500mL
this is 0.5mg / mL
2) required dose = 60kg x 500mcg = 30000 mcg/hour
this is 30mg / hour
3) (30 / 0.5) x 1mL = 60 ml / hour
4) 60 / 60 = 1mL /min
A 37-year-old woman (weight 60 kg) presents to hospital with severe asthma. She is given a loading dose of aminophylline 300 mg IV and now requires this to be followed by a maintenance aminophylline IV infusion at a rate of 500 micrograms/kg/hr. Aminophylline is available in 10 mL ampoules in a strength of 25 mg/mL. An infusion fluid is prepared by diluting one ampoule of aminophylline solution to a total of 500 mL in sodium chloride 0.9% solution.
At what rate (mL/min) should the aminophylline infusion be delivered?
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