1. Noradrenaline is administered by continuous intravenous infusion to treat hypotension. 2. The initial infusion rate for a 70kg patient is 10-20 ml/hour, equivalent to 0.4-0.8 mg/hour of noradrenaline base. 3. The dose is then titrated in steps of 0.05-0.1 μg/kg/min according to blood pressure, with the aim of achieving a systolic BP of 100-120 mmHg.

1. CALCULATION OF DOSES - 2
PH 2.4
DEMONSTRATE CORRECT METHOD
OF CALCULATION OF DRUG DOSAGE
IN PATIENTS, INCLUDING THOSE
USEDIN SPECIAL SITUATIONS

2. Intravenous infusions
• Intravenous (IV) infusions are sterile, aqueous preparations
administered intravenously in relatively large volumes.
They are used to extend blood volume and /or provide
electrolytes, nutrients or medications.
• An administration set is attached to an intravenous bottle
or bag to deliver the fluid into a patient’s vein. The set may
be standard (macrodrip) or pediatric (microdrip).
Depending on the particular set used, the drip rate can
vary from 10 to 15 drops/mL for standard sets to 60
drops/mL for microdrip sets.
• The passage of an infusion solution into a patient’s vein of
entry may be assisted by gravity (the solution is hung on a
stand well above the portal of entry) or by electronic
volumetric infusion pumps.

3. Intravenous Admixtures
• The preparation of an intravenous admixture
involves the transfer of one or more additives to a
large-volume parenteral fluid.
• Additives may include therapy-specific medications,
antibiotics, electrolytes, vitamins, trace minerals and
other agents.
• Some drugs which are produced by the manufacturer
as a dry powder need reconstitution shortly before
use.
• These drugs are frequently then given to patients
intravenously by adding them to an intravenous
infusion fluid.

4. • Some drugs will have a significant displacement
volume, which would have to be allowed for
when reconstituting the solution.
• Subsequent calculations include working out how
much drug solution should be added to an
infusion fluid, what concentration, in mg/mL, is
produced, then working out the speed of
infusion, in terms of either mg/min or mL/min
and how this is achieved when it is being
administered by means of a giving set.

5. Example calculation
1. An ampoule of flucloxacillin contains 250 mg of
powder with instructions to produce a 5 mL
solution with water for injections. What volume of
this solution should be added to 500 mL of saline
infusion to provide a dose of 175 mg? What is the
concentration, in mg/mL, produced ?
 250 mg in 5 ml = 50 mg per mL. Therefore, volume
for 175 mg:
175
50
= 3.5 mL

6. • In preparing the infusion, 3.5 mL is added to 500 mL of normal saline
infusion. This produces a total volume of 503.5 mL. Therefore there is
175 mg in 503.5 mL (not 500 mL). Division obtains the concentration of
the resulting infusion:
concentration of flucloxacillin =
=0.35 mg/mL
note: whenever a solution is added to a pre-prepared infusion, the
volume of two solutions must be added together to give the total
volume of the resulting infusion.
175
503.5

8. Rate of flow of Intravenous Fluids
• On medication orders, the physician specifies the rate of flow of
intravenous fluids in mililiters per minute, drop per minute,
amount of drug (as milligrams per hour), or, more frequently, as
the approximate duration of time of administration of the total
volume of the infusion.
• Following equation finds use in rate-of-flow calculation:
Rate of flow(drops/minute)=
• In common usage are macro sets that deliver 10,15, or 20
drops/milliliter and microdrip or minidrip sets that deliver 60
drops/milliliter.
𝐕𝐨𝐥𝐮𝐦𝐞 𝐢𝐧𝐟𝐮𝐬𝐢𝐨𝐧 𝐦𝐋 × 𝐃𝐫𝐢𝐩 𝐬𝐞𝐭( 𝐝𝐫𝐨𝐩𝐬/𝐦𝐋)
𝐓𝐢𝐦𝐞(𝐦𝐢𝐧𝐮𝐭𝐞)

9. • Paediatric Phenytoin sodium dose 6mg/kg/day administered in 3 equal
doses. Pt. weight is 5kg. Calculate the dose.
• 6mg x 5 = 30mg = three eq. dose = 10mg TDS
• Syrup = 125mg/5 ml
• How many ml/dose - 5ml = 125 mg
• 125mg = 5ml
• 10mg = 5/125 = 0.6ml
• 1 standard dropper = 20 drops/ml
• = 12 drops.

10. Example calculation
1. A medication order calls for 1000 mL of D5W to be
administered over an 8 hr period. Using an IV
administration set that delivers 10 drops/mL, how many
drops per minute should be delivered to the patient?
 Volume of fluid = 1000 mL
8 hours = 480 minute
= 2.08 mL/min
2.08 mL/min X 10 (drops/ml) = 20.8 or 21 drops per minute
1000(mL)
480 (minute)

12. • A pt. weighing 80kg needs a bolus dose of Heparin for start of treatment.
• A) Calculate the bolus dose if dose is 80U/kg.
• 80units x 80kg = 6400 units = 1.25 ml ( 1 ml = 5000units)
• B) Calculate the dose for infusion @18U/kg/hr for 6hr for maintenance.
• 18units x 80kg x 6 = 8640 units = 1.5ml
• Children – 50U /kg = loading dose,
• 15-25 U/kg i.v. infusion = Maintenance Dose.

13. HEPARIN DOSE ADJUSTED ACCORDING TO APTT( Test
performed before 4-6hr of every i.v. injection or s.c. injection)
• Normal aPTT = 30-40sec.
• aPTT should be maintained at 1.5-2 times the patient’s pre treatment Aptt or CT
2-3 times the control value.
• Adult – prevention of thromboembolism – Low dose heparin before surgery. 5000
units deep s.c. injection – 2hr before surgery, 5000 units 8hr after surgery.
A) Calculate the bolus dose of Heparin
Pt – 80kg – initial bolus = 80 units/kg
Dose = 80x 80 = 6400 units
B) Calculate dose for first 6 hours
Infusion rate = 18units/kg/hr = 18units x 80kg x 6 hr = 15040 units.
1ml = 5000 I.U = 3ml in 5% glucose or 0.9% Sodium Chloride i.v / s.c inj.

14. 2. A doctor requires an infusion of 1000 mL of 5% dextrose to
be administered over an 8-hour period. Using an IV giving set
which delivers 10 drops/mL, how many drops per minute
should be delivered to the patient?
 First convert the time into minutes:
8 hour= 8 X 60 min = 480 min
 Next calculate how many mL/min are required:
= 2.08 mL/min
 Then calculate the number of drops this requires:
2.08 mL/min X 10 drops/min = 21 drops/min
1000
480

15. Adrenaline in Anaphylaxis
• 1 ml= 1mg adrenaline for i.m. use
• >12yr = 0.5 mg i.m.( 0.5ml 1:1000 solution)
• 6-12 yr = 0.3 mg i.m .( 0.3ml 1:1000 solution)
• 6months-6yr = 0.15 mg i.m .( 0.15ml 1:1000 solution)
• <6months = 0.01mg/kg i.m .( 0.01ml/kg 1:1000 solution)
• I.V – 1:10,000 solution ( 1ml = 1mg)
• Overdose = increase in B.P.
• Drug is rapidly inactivated. Treatment is mainly supportive.
• Alpha blocker - Phentolamine – 5-10mg i.v
• Beta blocker – Propranolol – 2.5- 5mg i.v

16. Posology and method of administration
of Nor-adrenaline
• Initial rate of infusion:
• When diluted as recommended in section 6.6 (the concentration of the
prepared infusion is 40 mg/litre noradrenaline base (80 mg/litre
noradrenaline tartrate)) the initial rate of infusion, at a body weight of 70
kg, should be between 10 ml/hour and 20 ml/hour (0.16 to 0.33
ml/min). This is equivalent to 0.4 mg/hour to 0.8 mg/hour noradrenaline
base (0.8 mg/hour to 1.6 mg/hour noradrenaline tartrate). Some
clinicians may wish to start at a lower initial infusion rate of 5 ml/hour
(0.08 ml/min), equivalent to 0.2 mg/hour noradrenaline base (0.4
mg/hour noradrenaline tartrate).

17. • Titration of dose:
• Once an infusion of noradrenaline has been established the dose should
be titrated in steps of 0.05 -0.1 µg/kg/min of noradrenaline base
according to the pressor effect observed. There is great individual
variation in the dose required to attain and maintain normotension. The
aim should be to establish a low normal systolic blood pressure (100 -
120 mm Hg) or to achieve an adequate mean arterial blood pressure
(greater than 65 - 80 mm Hg – depending on the patient's condition).

18. Noradrenaline Infusion Solution
40 mg/litre (40 µg /ml) noradrenaline base
Patient's Weight Posology (µg/kg/min)
noradrenaline base
Posology (mg/hour)
noradrenaline base
Infusion Rate
(ml/hour)
50kg .05 .15 3.75
.10 .30 7.5
.25 .75 18.75
.5 1.5 37.5
1 3 75
60kg .05 .18 4.5
.10 .36 9
.25 .90 22.5
.5 1.8 45
1 3.6 90