Coating is an important part of pharmaceutical product manufacturing. It's increase the patient acceptance and tablet quality also.


Benefits of tablet and granule coating:

  • Improve the visual quality
  • Modifying drug release characteristics
  • Facilitating handling
  • Improve the product stability
  • Mask the unpleasant taste and odor
  • Increasing the ease to swallow by patient


Coating types:

  • Sugar coating
  • Press coating (compressed coating)
  • Film coating: Conventional and Functional
    • Conventional Film coating: Immediate release/ Non-enteric coating
    • Functional Film coating: Delayed release (Enteric coating), Extended release (Sustained release coating)

Sugar Coating:

  • Larger weight gain (30-50%), High degree of elegant, Multi-stage process.
  • Steps:
  • Sealing: Water impermeable polymer (Shellac, CAP)
  • Sub Coating: Bulking agent ( Talc, Calcium carbonate)
  • Smoothing: Sucrose syrup
  • Coloring: Titanium dioxide
  • Polishing: Beeswax, Carnauba wax
  • Printing: Indelible ink

Press Coating:
  • An adhesive coating that allows even small quantities of immediate release powders to be press coated onto controlled release coated dosage form
  • Used mainly to separate chemically incompatible materials 
  • Used in pulsatile drug delivery system (Fast and rate controlled)

Film Coating:
  • Thickness: 20-100 ┬Ám
  • 2-3% weight gain only
  • Logo or break line is possible
  • Automatic
  • Usually single stage
  • High adaptability to GMP
  • Control release is possible
  • Materials used: Film formers, Solvents, Plasticizers, Colorants, Opacifier
  • Sophisticated equipments are used

Particular attention must be paid during sugar coating:
  • Hardness
  • Friability
  • Lamination tendency

Problem arise during coating:
  • Chipping
  • Cracking
  • Non-drying
  • Twinning
  • Uneven color
  • Blooming
  • Sweating
  • Picking
  • Twinning
  • Orange peel
  • Chipping
  • Cracking
  • Bridging
  • Peeling

Polymers used in conventional film coating:
  • HPMC
  • HPC
  • HEC
  • MC
  • EC
  • Na-CMC
  • PVP
  • PEG
  • Ethylacrylate methylmethacrylate copolymer

Polymers used in enteric coating:
  • CAP
  • CAT (Cellulose acetate trimellate)
  • PVAP (Polyvinyl acetate phthalate)
  • HPMCP
  • HPMCAS (Hydroxypropyl methylcellulose acetate succinate)

Factors influence the quality of film coating:
  • Tablet core
  • Coating liquid
  • Solid contents of coating liquid
  • Process drying
  • Spray equipment
  • Spray rate
  • Pan speed

Aqueous vs. Organic film coating:

Aqueous
  • Water is the most common solvent used
  • Non-toxic, No significant safety issue
  • Dry slower
  • Can’t be used for moisture sensitive products
  • Can’t impact on smell and taste

Organic
  • Different organic solvents are used
  • Toxic, Significant safety issue
  • Dry faster (due to volatile solvent)
  • Can be used for moisture sensitive products
  • Can impact on smell and taste


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