Tag Archives: Calculation

How to calculate pediatric drug doses?

Calculation of pediatric dosages are many a times cumbersome job for medical practitioners of non-pediatric branches. So, here is a simple way of calculation of pediatric drug doses.

Generally you need to know 2 things before prescribing a medicine – the dosage and the preparation in which it is available in the market.

Let’s try to explore the issue with an example.

Suppose we want to prescribe a paracetamol syrup.

First we have to calculate the dosage. So if we want to give at the dose of 15 mg/kg/dose for a 20 kg weight child the dosage will be 300 mg per dose.

Next we have to see at what strength in the market paracetamol is available. Suppose there is a preparation of paracetamol in which 120 mg paracetamol per 5 ml syrup.

So we have to calculate the amount of dosage of syrup we have to give.

A easy way to count dosage is as following-
Dose calculated/dose available x volume = 300/120 x 5 = 12.5 ml

So, 12.5 ml paracetamol is to be given per dosage to the above mentioned example.

By using the formula above almost any drugs dosage can be derived.

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Intravenous fluid requirement calculations

One common problem encountered by medical students, nursing students and sometimes even to practicing doctors is intravenous (iv) fluid calculation.

There may be various ways to determine how much maintenance fluid to be given intravenously, however the author will discuss here one commonly practiced technique practiceed by certain medical practitioners.

First you should be oriented with the formula depicted below in the diagram –

image
To explain the above diagram –

-For body weight of first 10 kgs we give 100 ml/ kg / day.

-For the next 10 kgs we give 50 ml / kg / day.

-Finally, for the remaining body weight i.e. for those weighing more than 20 kgs we give in the rate of 20 ml / kg / day.

For easy calculations it’s good to memorize the amount of iv fluids which might be needed for an individual weighing 10 and 20 kgs.

For a 10 kg person iv fluid required is 10×100 =1000

For a 20 kg person iv fluid requirement is –
1000 + (10×50)= 1500.

If you remember the above two values you can easily derive iv fluid requirements for various body weights more than 10 and 20 kgs.

Now let us consider some examples –

For a 8 kg child- 8×100= 800 ml per day.

For a 12 kg child – 1000+ (2×50) = 1100 ml per day.

For a 30 kg individual – 1500+ (10×20)= 1700 ml per day.

Lastly, how to determine how much iv fluid to be given in each hour. For this simply divide ➗ the calculated total fluid requirement per day by 24; since 24 hours makes a day.

The above writing is a simplified version for iv fluid requirement calculation made by the author which may not be free from errors. Hence, please cross check the information from reliable sources. ⚠

How to calculate intravenous fluid drop rate?

How to calculate intravenous fluid drop rate?

We will discuss here how to calculate the number of drops of fluid to be given to a patient.

We will do it by an example.

Before we look into the example we should know that 1 ml of fluid is equal to 20 drops.

Now we will begin.

Suppose we need to give a particular drug in the rate of 50ml per hour. So, how many drops should go in one minute?

Since 1 hour is equal to 60 minutes, 50/60=0.8333 ml is to be given in 1 minute

As we discussed above 1ml = 20 drops

So in this case 0.83 x 20=16.6 i.e. about 17 drops to be given in a minute

Quite simple!