An overview of prescribing drug dose in paediatric inpatient department, easily explained how to calculate infusion rate

1. Techniques of calculation and
prescribing drug dosage in
pediatric practice
Dr. Paul, Shubhra Prakash
Assistant Registrar
Rajshahi Shishu(children) Hospital

2. Dose of Commonly used drugs
(parenteral)
Drugs Indication with Frequency Preparation
Dose
Aminophylline 5mg/kg/dose stat 125mg/5mL
2.5mg/kg/dose for
maintenance
therapy
Meropenem Other than 8 hourly 500 mg/vial
meningitis
20-30 mg/kg/dose
Meningitis 8 hourly
60mg/kg/dose
Azithromycin 10mg/kg/dose Once daily for 3 500mg/vial
days
Vancomycin 10-15mg/kg/dose 8 hourly 500mg/vial
Dopamine 5 gm/kg/min 200mg/5mL
followed by gradual vial
increase up to

3. Dose of Commonly used drugs
(parenteral)
Drugs Indication with Dose Frequency Preparation
Netilmycin 3mg/kg/dose 12 hourly 50mg/2mL
Phenobarbitone 20mg/kg/dose as 8 hourly 200 mg/ml
loading dose
Maintenance
5-20mg/kg/day in
divided dose
Clarithromycin 15mg/kg/day in2 12 hourly 500mg/vial
divided dose
Phenytoin 20mg/kg/dose as 125 mg/5ml
loading dose
Maintenance
5-20mg/kg/day in
divided dose

4. Relation of Dosage frequency
with weight and age
Dosage frequency of
Gentamycin for an example
Thrice
Twice daily Adult
daily
Children
Once
daily Neonate

5. Age Weigh
t

6. Example
Example I Example II
with with
Meropenem Azithromycin

7. Example I
Case I:
• A 4 months old child weighing 5kg requiring
Meropenem for an indication of meningitis.
How will you calculate the dose and
infusion rate?

8. Basic Calculation
As the indication is meningitis
the baby will receive Injection
Meropenem 60mg/kg/dose 8
hourly.
So the dose for this baby is
300mg/kg/dose

9. Example I with meropenem
As Meropenem is to be infused not less
than 30 minutes, it should be infused
with IV fluid. So for the example case IV
fluid of choice either Normal saline or
Dextrose in aqua or Dexstrose saline is
chosen. A measured volume , suppose
30 ml may be taken as carrier for
meropenem infusion

10. Example I with meropenem
A vial of Meropenem contains 500mg of
active drug in powder format. So it
should be reconstituted with distilled
water. Here comes the measurement of
Dilution. If smaller dose is required the
dilution should be with more amount of
diluents and vice versa.

11. Example I with meropenem
So if dilution is made with 10 ml of D/W
then each ml will contain 50 mg of the
drug, similarly if dilution is made with 5
ml of D/W then each ml will 100 mg of
meropenem. From this diluted drug the
exact dose is taken and poured into
measured infusion fluid and to be
infused.

12. Example I with meropenem
In our example case I the dose is
required 6 ml (if diluted with 10 ml D/W
) or 3 ml (if diluted with 5 ml D/W).
Now this 3 or 6 ml is poured in to
desired amount of fluid to be infused cat
calculated time.

13. Calculation of infusion rate
e.g. 30 ml fluid should be infused over 1
hour.
So infusion rate is 30ml/hr which stands
for 30ml/60min i.e. 0.5ml/min is the
infusion rate.
Then 0.5ml/min means
0.5 X 15 drops/min
=7.5 drops/min (if used with infusion set)
=7.5X 4 drops/min (if used with micro burette
)
= 30 drops/min

14. Calculation of infusion rate
e.g. 30 ml fluid should be infused over
1/2 hour.
So infusion rate is 30ml/30min which
stands for 30ml/60min i.e. 1ml/min is
the infusion rate.
Then 1ml/min means
1X 15 drops/min
=15 drops/min (if used with infusion set)
=15X 4 drops/min (if used with micro burette )
= 60 drops/min

15. Calculation of infusion rate
So in case of infusing 30 ml fluid the
rate will be as follows ( drops/min)
2 hours 1hour 30
minutes
• 15 • 30
• 60

16. Example II
Case II:
• A 7 months old child weighing 8 kg
requiring Azithromycin for an indication
of Acute watery Diarrhea
How will you calculate the dose and infusion
rate?

17. Basic Calculation
As the indication is acute
watery Diarrhoeathe baby will
receive Injection Azithromycin
@ 10mg/kg/day.
So the dose for this baby is
80mg/kg/dose

18. Example II with Azithromycin
As Azithromycin is to be infused over 30
minutes, it should be infused with IV
fluid. So for the example case IV fluid of
choice either Normal saline (as it is
provided with the drug as combipack) or
Dextrose in aqua or Dexstrose saline is
chosen. A measured volume , suppose
30 ml may be taken as carrier for
Azithromycin infusion.

19. Example II with Azithromycin
A vial of Azithromycin contains 500mg
of active drug in powder format. So it
should be reconstituted with distilled
water. Here comes the measurement of
Dilution. If smaller dose is required the
dilution should be with more amount of
diluents and vice versa.

20. Example II with Azithromycin
So if dilution is made with 10 ml of D/W
then each ml will contain 50 mg of the
drug, similarly if dilution is made with 5
ml of D/W then each ml will 100 mg of
Azithromycin From this diluted drug the
exact dose is taken and poured into
measured infusion fluid and to be
infused.

21. Example II with Azithromycin
In our example case II the dose is
required 1.6 ml (if diluted with 10 ml
D/W ) or 0.8 ml (if diluted with 5 ml
D/W).
Now this 0.8 or 1.6 ml is poured in to
desired amount of fluid to be infused cat
calculated time.

22. Example III
Case II:
• A 2 months old child weighing 4 kg
requiring Netilmycin for an indication of
sepsis.
How will you calculate the dose?

23. Example III
Recommended dose of netilmycin in sepsis is
3mg/kg/dose 12 hourly.
•The baby requires 4.5mg/dose of Netilmycin
only.
A vial of Netilmycin contains 50mg/2ml.
•So the baby requires only 0.18 ml of
netilmycin

24. Example III
 Here an insulin syringe of 100 U will
be helpful for the required dose.
 As in 100 unit insulin syringe 1ml=100
unit, 0.18 ml refers to 18 unit.
 So, the dose becomes 18 unit/dose.

25. Thank you all