Tablet coating and its problems

The following objectives are achieved by the coating:

Protecting tablets and capsule contents from stomach acid

Protecting the stomach from drugs that damage the stomach wall, such as coated aspirin

Creating a slow-release drug

Masking the smell and taste of medicine

Helps maintain tablet shape

Ideally, the tablet material should be released gradually, making the drug available to the digestive tract. The tablet coating can be specially formulated to dissolve the drug at a specific rate, allowing it to be absorbed after digestion.

Tablet coating process and its control

The tablet coating process is carried out in a pressure-controlled, mesh drum. Angled blades are installed inside it to mix the tablets. The tablets are lifted by the blades and directed towards the center. The surface of the tablets is covered with the coating solution.

 The solution sprayed on the tablet surfaces is dried by the hot air entering the machine. The air flow is regulated in terms of volume and temperature so that the drying is done in a controlled manner and at the same time the pressure inside the machine is negative compared to the room to create a separate and isolated condition for the preparation operation of the tablet coating machine.

A tablet coating machine usually consists of a spray nozzle, a coating chamber, a non-homogeneous coating solution tank, a peristaltic pump, a fan, filters, and connecting pipes. The tablet coating process usually includes the following phases:

1- Select the instructions for the desired batch

2- Weighing materials-loading 

3- Warm up 

4- Spraying 

5- Cooling 

6- Emptying the product

Some of the problems encountered in the tablet coating process and ways to solve them:

A large number of problems can arise during tablet coating operations, some of which we will describe and possible methods for solving.

Tablet-To-Tablet Color Variation

Problem: Using too little veneer material 

Solution: Increase the amount of coating

Problem: Insufficient mixing of tablets during tablet coating

Solution: Increase Pan speed or upgrade the baffle system .

Problem: Low opaqueness of the tablet coating material

Solution: Reformulation of the tablet coating to increase the opaqueness using an opaquer and using a pre  – coating system for colored  tablets . 

Problem: The solid portion of the coating solution is too high.

Solution: Reduce its amount in the coating solution

Problem: Insufficient number of nozzles on the device

Solution: Increase the number of nozzles 

Problem: Improper spray distribution pattern on tablets

Solution: Ensure the correct location of the nozzles

Pan speed is low/Increase Pan speed

Tablets sticking together ( twinning )

Problem: The intensity and amount of spray is too high.

Solution: Reduce the speed of the spray or increase the powderiness of the spray.

Problem: Pan speed is too slow

Solution: Increase Pan Speed

Problem: Improper tablet shape

Solution: Choosing the right shape for the pills that reduces the chance of twinning (reducing the amount of contact surface) 

Problem: Coating suspension solution is sticky 

Solution: Change the formulation of the coating suspension 

Problem: Nozzles are too close to the tablet bed

Solution: Increase the distance between the nozzles and the tablet.

CRACKINGCracking

The tablet core has a different coefficient of thermal expansion after coating. Avoid mineral fillers-calcium carbonate-sulfate as much as possible.

Problem: Low amount of forming material 

Solution: Change the tablet coating formulation

peeling

Problem: Low adhesion and strength of the coating solution

Solution: Change the formulation of the tablet surface coating, it has low adhesion (select a formulation to increase adhesion)

Problem: Too much lubricant in the formulation

Solution: Use a supplement with lubricating properties (such as Starch 1500 ).

ORANGE PEEL ROUGHWESS

Problem: The viscosity of the coating solution is too high.

Solution: Reduce solids, reduce coating viscosity

Problem: The tablet coating liquid does not powder well.

Solution: Increase the pressure of powdering the tablet coating solution in tablet sprays

Problem: Inappropriate product logo design

Solution: Change the logo design

Problem: Insufficient amount of plasticiser in the coating

Solution: Reduce coating spray speed – increase drying rate

 IndentationPicking/Sticking

Problem: The spray rate of the coating solution is too high. 

Solution: Reduce the amount and speed of coating solution spray.

Problem: Pan speed is too slow

Solution: Increase Pan Speed

Problem: Insufficient powder pressure of the coating solution

Solution: Increase the pressure to powder the tablet coating solution

Problem: Improper distribution of coating solution

Solution: Choose the right formulation to increase adhesion.

LOGO INFILLING

Problem: Inappropriate logo design

Solution: Choosing the right design

Problem: LOGO is filled with coating material