Tablet Twinning | Tablet Coating Defect

Twinning is a tablet coating defect that is not observed in all coating processes but is observed during the coating operation of capsule-shaped tablets in pharmaceutical industries. This tablet coating defect is related to the tablet shape and we can define this defect as,

Twinning is a tablet coating defect in which tablets bind with each other along flat surfaces and look like a pair of tablets so known as twins & this tablet coating defect is called Twinning.

In this article, we will discuss why tablet twinning occurs during the coating process & how we can prevent this tablet coating defect.




Tablet Shape

As we discussed earlier tablet shape is a major contributor to this tablet coating defect and is usually observed in capsule-shaped oblong tablets.


  • A change in tablet shape can resolve this problem.
  • If we want to use capsule-shaped tablets then use that design where we have a small degree of curvature on tablet edges.
  • It will help to prevent tablet twining by reducing the side-to-side contact area for tablets.

Nature Of Coating Suspension

If we are using polymers that give tackiness to the tablet coating formulation then it may result in tablet twinning.


  • Use anti-adherent in the coating formulation to reduce tackiness.

Solvent Evaporation

Tablet twining is observed when applied solvent is not properly evaporated and due to this poor solvent evaporation over wetting of tablets occurs which results in tablet twinning.


  • Increase the inlet air temperature to properly evaporate the solvent.
  • Reduce the spray rate.
  • Increase spray guns to the bed distance.

Spray Rate

The higher spray rate may also be the main contributor to tablet twinning because due to the high spray rate tablets may become over-wet if drying is not proper.


  • Reduce the coating solution spray rate.
  • Increase the Inlet air temperature & tablet bed temperature.

Droplet Size

The droplet size of applied spray depends on the automization air pressure. If automization air pressure is low, droplet size will be large and it may result in tablet twinning defect due to inappropriate drying of the tablets.


  • Increased automation air pressure to reduce the spray droplet size.

Spray Gun To Tablet Bed Distance

If spray guns to tablet bed distance is reduced it may result in a tablet coating defect known as twinning.

The reason is that due to a reduction in the distance the tablets are overwett and are not properly dried so resulting in twinning defect.


  • Increase the distance between spray guns and tablet bed.
  • Increase tablet bed temperature by increasing the inlet air temperature.

Tablet Bed Temperature

If our tablets are not properly warmed during the tablet coating process then the applied coating solution will not properly be evaporated and may result in tablet twinning defects.


  • Increase inlet air temperature to increase the tablet bed temperature.
  • Reduce the spray rate.

Pan Speed

Pan speed is also a main logical contributor to the twinning defect & the reason is that if pan speed is low the contact time between tablets is increased & it increases the chance of twinning.

Due to low pan speed the amount of applied spray over tablets is also increased due to less coating pan rotations and it results in overwetting of tablets & ultimately a tablet coating defect known as tablet twinning in case of capsule shaped tablets.


Increase the speed of the coating pan and it will reduce the tablet-to-tablet contact time.

By increasing the coating pan rotations the stay time of tablets below the spray shower is also reduced so tablets are not over wet and are properly dried.


When we talk about tablet coating defects the tablet twinning defect is observed in capsule-shaped tablets due to the imbalance of applied spray rate and drying capacity due to which our tablets are attached or aligned side by side and look like a twin.By creating harmony between applied spray rate, inlet air temperature, and coating pan speed we can prevent this tablet coating defect.

Also Read

  1. Sticking And Picking During Tablet Coating
  2. Color Variation Defect In Coated Tablets
  3. Weight Gain Defect In Coated Tablets
  4. Basis of Tablet Coating.
  5. Tablet Coating formulation.
  6. Technical Aspects of Tablet Coating Process.