Filling and packaging of liquid dosage form
The method used for filling a liquid dosage form depends on following:
• Characteristics of the liquid (viscosity, surface tension, foaming ability)
• Type of package
• Production output
Three basic methods are used for filling of liquid dosage forms:
1. Gravimetric filling
2. Volumetric filling
3. Constant level filling
Gravimetric filling:
In this, a particular weight of liquid is filled into the container. This type of filling is rare in use because it can be used only for highly viscous liquid or to fill large size containers.
Volumetric filling:
In this, a given volume of liquid is filled into the container using the displacement piston action. Each filling station is equipped with a measuring piston and cylinder. The fill amount is measured by the stroke of the piston which can be varied from machine to machine.
Disadvantages:
• Highly viscous liquids can block the piston causing loss of fill accuracy
• Highly thin liquids can cause dripping of the drops from the filling point of machine
• If container is oversized then filling appears loose and if container is undersized then filling appears overfill, hence container to be filled should have uniform size
Constant level filling:
In this, each container is filled to the same level hence it is also called as fill-to-a- level method. It uses the container for controlling the filling of each unit which means that any change in size of the container causes change in the net fill per unit.
Methods for constant level filling:
In older days, the siphon method was used. But due to slowness of this method, slight modifications in siphon method are used which are following:
• Vacuum filling
• Gravity-vacuum filling
• Pressure-vacuum filling
Problems associated with liquid filling machines:
• Excessive foaming ability:
It can be minimized by following:
• Reduction in turbulence of the liquid
• Using the closed system to prevent the entry of air or other gases that help in foaming
• Use of defoaming devices
• Decrease in speed of machine
