Tablet Coating Problems and their Solutions in Pharmaceuticals

Some Common Tablet Coating Problems & Solutions in Pharmaceuticals

There are various problems in pharmaceutical tablet coatings we are discussing some of them here and providing their possible solutions.

• Poor Tablet Design (e.g. fine embossing, flat surfaces)
• Physical Damage (e.g. overloading the coater, loading/ unloading operations)
• Over-wetting - the suspension droplets hit the tablet surface whilst still wet and the drying air does not dry quickly enough. This can lead to surface pitting.
• Spray Drying - the suspension droplets hit the tablet surface after the moisture has been removed. This can lead to lack of / poor adherence of the coat.

TABLET-TO-TABLET COLOR VARIATION

Possible Causes and Solutions:

•  Too little coating applied - Increase quantity of coating applied

•  Inadequate mixing of tablets during coating - Increase pan speed and/or improve baffle system

•  Poor opacity (or hiding power) of coating - Reformulate coatings to improve opacity or use an opacified white pre-coat (for coloured tablet cores)

•  Solids content of coating liquid is too high - Reduce solids content of coating liquid

•  Insufficient number of spray guns - Increase number of spray guns

•  Poor spray pattern bed distribution - Ensure gun position is correct and provides optimum bed coverage

•  Pan speed too low - Increase pan speed

TWINNING

Possible Causes and Solutions:                                

•  Spray rate too high - Reduce spray rate and/or increase efficiency atomizing      

•  Pan speed too low - Increase pan speed

•  Inappropriate tablet shape - Select new tablet shape that minimizes chances of flat  surfaces coming into contact during application of coating liquid (e.g. avoid capsule-shaped tablets with straight edges or thick side walls)                   

•  Tacky coating formulation - Reformulate the suspension

•  Spray guns too close to tablet bed - Increase gun to tablet bed distance

CRACKING

Possible Causes and Solutions:

• Low mechanical strength of coating, inadequate plasticiser or pigmentation - Select formulation with improved mechanical strength characteristics.
• Core has significantly different thermal expansion characteristics than coating - Avoid use of mineral-type fillers (e.g. carbonate, calcium sulphate, carbonate) where possible
• Extended elastic recovery of core after submitting them to compaction - Extend holding period for tablets prior to coating process

Related: Film Coating Process of Tablets in Pharma Manufacturing

PEELING

Possible Causes and Solutions:

•  Low mechanical strength of coating - Select formulation with improved strength

•  Poor adhesion of coating to tablet surface - Select formulation for improved adhesion characteristics

•  Excess lubricant usage in formulation - Use an excipient with good lubrication properties like STARCH 1500

ORANGE PEEL ROUGHNESS

Possible Causes and Solutions:

•  Viscosity of coating liquid too high - Reduce solids content of coating liquid /viscosity

•  Poor atomisation of coating liquid - Increase atomizing air pressure / volume  (n.b. excessive atomisation may exacerbate spray drying)

LOGO BRIDGING

Possible Causes and Solutions:

•  Inadequate adhesion of the film coating - Select formulation for improved adhesion characteristics

•  Surface characteristics of the product - Modify core formulation to include more coated (e.g. hydrophobic substrate) hydrophilic ingredients (where possible)

•  Inappropriate design of logo(e.g. too detailed or too fine) - Select a different logo design (with increased area within the debussing and  modified angles)

•  Insufficient plasticiser in film / high internal stress - Reduce spray rate / increase drying rate

PICKING / STICKING

Possible Causes and Solutions:

•  Spray rate too high - Reduce spray rate

•  Inadequate drying conditions - Improve drying conditions

•  Pan speed too low - Increase pan speed

•  Inadequate atomisation of coating - Increase atomizing air pressure / volume
liquid

•  Poor distribution of coating liquid - Select formulation for improved adhesion  characteristics

LOGO INFILLING

Possible Causes and Solutions:

•  Inappropriate design of logo(e.g. too detailed or too fine) -  Select a different logo design (with increased area within the debussing and modified angles)                     

•  Logo "disappearance" can be due to erosion of tablet surface around logo of tablet - Reduce erosion potential by reformulating core, changing logo design or modifying curvature of faces

•  Logo Bridging - See solutions for Logo Bridging

•  In-filling of logo with spray-dried coating material - Reduce spray-drying potential by:
- increasing spray rate

            - reducing inlet air temperature / air flow

            - reducing atomising air pressure

            - reducing distances between spray guns and surface of tablet bed

CORE EROSION

Possible Causes and Solutions:

•  Inherent softness or high friability - Improve mechanical strength of core by increasing of core compaction force, modifying core formulation or changing process by which core is produced (e.g. use granulation process instead of direct compaction

•  Excessive pan speed in coating process - Reduce pan speed

•  Spray rate too low - Increase spray rate

•  Low solids content of spray - Select formulation with high solids solution content

•  Premature swelling of hydrophilic disintegrant in formulation - Replace super disintegrant with less hydrophilic super disintegrant like STARCH 1500

EDGE CHIPPING / EROSION

Possible Causes and Solutions:

•  Low mechanical strength of coating - Select formulation with improved mechanical strength

•  Excessive pan speed - Decrease pan speed

•  Low solids content in coating liquid - Increase solids content of coating liquid

•  Low spray rate - Increase spray rate

•  Sharp edges on tablets - Replace or use modified punch design (use dual radius punch tips)

•  Worn tablet punches - Refurbish or replace punches

•  Low tablet hardness / friability - Improve mechanical strength of core by increasing compaction force, changing tablet shape, modifying core formulation or changing process by which core is produced (e.g. use granulation process instead of direct compaction)

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