The capsule is one of the most commonly used oral solid dosage forms in which medication is closed in a shell made of gelatin.

Hard Gelatin shells are usually used to fill

Powders

Granules

Pellets or beads

Granules for hard gelatin shell filling can be manufactured by wet granulation or dry granulation method. Powders for capsule filling can be mixed by a simple mixing process or are available as ready to fill form.

Beads or pellets are also used to fill in hard gelatin capsules and these beads are usually available as ready to fill, meaning most pharmaceutical companies take manufactured pellets or beads from other suppliers and fill in the pharmaceutical industries using semi-automatic or fully automatic capsule filling machines.

Now the main question is how do we know how much powder, granules or pellets fill in a capsule shell?

We will learn the answer to this question in two portions.

In the first portion, we will learn to calculate the weight of powders or granules for capsules filling.

In the second portion, we will learn to calculate the weight of pellets or beads for filling the hard gelatin shell and this calculation is very important because about 70% people does not know this calculation.

Before starting to learn calculations we will first learn a basic difference between the following two terms

Filling weight of capsules

Filled weight of capsules.

Filling weight

Filling weight is the weight of powders, granules or pellets which are to be filled in the capsule shell.

Filled weight

Filled weight is the weight of fully locked or sealed capsules.

In simple words, filled weight is the weight of the product to be filled in the capsule shell plus the weight of an empty hard gelatin shell.

How to calculate the filling weight of capsules for Granules?

Now we will learn calculation by the practical example as follow,

Example

Suppose we have to fill a granular product Z having API strength as 50 mg into a capsule shell and the batch size of final granules (Including API+other excipients) is 60 kilograms and it is required to fill 300,000 capsules from 60kg.

Solution

To calculate the filling weight of capsules mean amount of granules to be filled in a shell we will use following formula

Batch Size( in milligrams) ÷ Batch Size (In numbers)

Note:

To convert kilograms into milligrams first we will multiply kilograms to 1000 and the answer will be in grams and then we will multiply grams with 1000 to get milligrams.

Put values in the above formula,

60×1000×1000 ÷ 300,000= 200 mg

Result

So our answer is 200 mg means we will fill 200 mg granules in a hard gelatin shell to produce 300,000 capsules from 60 kg.

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How to calculate the filled weight of capsules for Granules?

Now after calculating the filling weight of capsules we will learn to calculate the filled weight of capsules.

Filled weight is calculated by using the following formula

Filled Weight=Filling Weight+Empty Shell Weight

It is cleared from the above formula that for the filled weight we need two values one is filling weight and the other is empty shell weight.

We have learnt in the above portion about the calculations of filling weight so now will learn how to find empty shell weight.

Empty shell weight means the weight of a single hard gelatin shell when it is empty.

For this, we can simply find out the weight of a single shell by putting it on weighing balance but for more precise results we weigh100 capsules and take their average weight.

Suppose we have calculated the average weight of 100 capsules shell as 75 mg and in above portion we have calculated the filling weight of a capsule as 200 mg so now we will calculate the filled weight by using the formula

Filled Weight=Filling Weight+Empty Shell Weight

Put values

Filled Weight=200mg+75mg

=275 mg

So our filled weight for one capsule will be 275 mg and filled weight of 300,0000 capsules will be

300,000×275=82.5 kg

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How to calculate the filling weight of capsules for Powders?

The filling weight of capsules for powders is calculated by the same formula as used for the calculation of granules

Batch Size( in milligrams) ÷ Batch Size (In numbers)

How to calculate the filled weight of capsules for Powders?

The filled weight of capsules for powders is calculated by the same formula as used for the calculation of filled weight for granules

Filled Weight=Filling Weight+Empty Shell Weight

How to calculate the filling weight of capsules for Pellets?

This portion includes the most important calculation where we will learn about basic calculations of pellets filling weight.

Coated Pellets are usually used as ready to fill pellets.

Example

Now we will discuss the examples of enteric-coated pellets.

Commonly used pellets which are filled in the majority of pharmaceutical industries are enteric-coated

Here we will take the example of esomeprazole enteric-coated pellets and as we know that it is available in two strengths as 20 mg and 40 mg so we will calculate the filling weight of both of these strengths.

If we look at the label claim provided by the vendor for esomeprazole it is usually mentioned as 8.5% and 22.5% for esomeprazole 20 mg and 40 mg respectively.

Now first we will discuss what is the meaning of 8.5% and 22.5% then we will learn how we will decide how much weight of pellets should be filled in the shell to give a 20 mg and 40 mg effect?

What is 8.5% and 22.5% Meaning?

The statement 8.5% and 22.5% means that our pellets are not 100% pure but they contain excipients along with their API and are 8.5% and 22.5% pure for Esomeprazole 20 mg and 40 mg respectively.

In other words, if we have 100 mg of esomeprazole enteric-coated pellets then 8.5% means out of 100 mg we have 8.5 mg of Esomeprazole and the remaining 91.5 mg are the excipients.

In the same way if we have 100 mg of esomeprazole enteric-coated pellets then 22.5 % means out of 100 mg we have 22.5 mg of Esomeprazole and the remaining are excipients.

We can also say that the assay or the potency of our beads is 8.5% or 22.5%.

Calculation

Calculate filling weight for esomeprazole 20 mg while vendor claims that pellets contain 8.5% of enteric-coated esomeprazole.

Solution

We will find filling weight by two methods for easy and conceptual learning.

Method 1 for 8.5% & 20 mg Strength

Method 1 is a simple unit rule calculation to find a filling weight for esomeprazole 20 mg and is as follow,

8.5 mg esomeprazole is present in 100 mg pellets so

8.5 mg esomeprazole =100 mg pellets

1 mg esomeprazole = 100÷8.5

as we want to calculate 20 mg of esomeprazole so

20 mg esomeprazole = 100÷8.5×20

=235. 29 mg

Results

It means that if we fill 235.29 mg of 8.5% pellets it will be equivalent to 20 mg of esomeprazole or the filling weight of esomeprazole 20 mg will be 235.29 mg if vendor claim is 8.5%.

Method 2 for 8.5% & 20 mg Potency

This method is based on the assay of the pellets.

So as from above statement it is clear that assay is 8.5% for 20 mg so now we will make it 100% for 20 mg as follow

Required Strength÷Assay×100

Put values

20/8.5×100=235.29

Results

So the filling weight is 235.29 mg.

Esomeprazole 40mg Calculation

Calculate filling weight of esomeprazole 40 mg while vendor claims that pellets contain 22.5% of enteric-coated esomeprazole.

Solution

We will find filling weight by two methods for easy and conceptual learning.

Method 1 for 22.5% & 40 mg

Method 1 is simple unit rule calculation for 40 mg and is as follow

22.5 mg esomeprazole is present in 100 mg so

22.5 mg esomeprazole =100 mg pellets

1 mg esomeprazole = 100÷22.5

as we want to calculate 40 mg of esomeprazole so

40 mg esomeprazole = 100÷22.5×40

=177.77 mg

Results

It means that if we fill 177.77 mg of 22.5% pellets it will be equivalent to 40 mg of esomeprazole or the filling weight of esomeprazole 40 mg will be 177.77 mg if the supplier or vendor claimed 22.5% pellets.

Method 2 for 22.5% & 40 mg

It will be based in term of assay of the pellets so as from above statement it is clear that assay is 22.5% for 40 mg so we will make it 100% for 40 mg as follow

Required Strength÷Assay×100

Put values

40/22.5×100=177.77 mg.

Learn Other Calculations:

How to calculate the filled weight of capsules for Pellets?

The filled weight of capsules for pellets is calculated by the same formula as used for the calculation of filled weight for powders or granules which is as follow

Filled Weight=Filling Weight+Empty Shell Weight.

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