Sugar Coating Process and its Problems in Pharmaceuticals

Sugar coating is rarely used in pharmaceuticals these days but this has its importance so the problems and their solutions are given billow related to the pharmaceutical sugar coating.

Sugar Coating is-

•  Relatively low tech and low capital costs and low complexity

•  Cheap, readily available and acceptable ingredients (sugar & water)

•  Provides an attractive, smooth & glossy finish

•  Good for taste masking and easing swallowing

•  High expertise / experience of operator required

•  More difficult to automate / more labor intensive

•  Long process  time (up to 20 hours)

•  Does not allow for embossing, so identification must be by printing if required

•  Results in  a large increase in tablet size and weight

Sugar Coating - The Process

•  Involves the successive application of sucrose based solutions in a coating pan

•  It can be automated in a modern coating machines but the traditional approach has been a manual operation using an open (conventional) pan and ladling the solution on tablets

Sugar Coating - A Typical Multi-stage Process

•  Sealing
    –  application of a sealant to protect the tablet cores from water applied during subsequent stages
    –  over application can give disintegration issues
    –  sealants are typically water insoluble film forming materials applied in an organic solution
    –  examples of sealants are
        -  shellac in combination with polyvinyl pyrrolidone (PVP) to prevent hardening with age
        -  polyvinyl acetate phthalate
        -  cellulose acetate phthalate
        -  acrylate polymers

•  Subcoating
    –  sugar coated tablets have completely smooth edges and the subcoat is gradually built up to achieve this profile
    –  Method 1
        -  apply gum / sucrose solution followed by dusting with powder then drying
        -  repeat until desired profile is achieved
    –  Method 2
        -  apply suspension of dry powder in gum / sucrose solution followed by drying
        -  repeat until desired profile is achieved
        -  gums used include gelatin, acacia , starch or PVP
    –  powders used include calcium carbonate or talc
    –  solids content in the solution is as high as possible to keep drying times low
    –  the compressed core should have as “rounded” a profile as possible to assist in the process

•  Smoothing (or Grossing)
    –  after Sub coating the tablet surfaces are generally rough
    –  a more dilute sucrose solution is applied to make the surface smooth

•  Colouring
    –  water soluble dyes demand a high degree of skill in application and have longer coating times
    –  Easier to use and give more consistent results with shorter coating times

•  Polishing
    –  gives an attractive finish to the tablets
    –  beeswax or carnuba wax is applied in an organic solvent
    –  sometimes a wax or canvas lined pan is used to assist in the polishing action.

•  Printing
    –  the thickness of the coat would obliterate any embossing so if markings are required the tablets are printed with edible printing inks

Related: Film Coating Process in Pharmaceuticals

Some common sugar coating problems

S.No.	Problem/Possible Causes	Solutions
1.	Chipping of Coating
a.	Less/absence of polymer	Add polymer
b.	Excessive use of insoluble fillers and pigments	Reduce Quantity of fillers
2.	Cracking of the coating
a.	Expansion of tablet core during / after coating by moisture absorption / stress relaxation	- Use seal coat - Extend the time between compaction and sugar coating
3.	Non Drying of Coating
a.	Excess level of invert sugar present	Avoid excess heating of sucrose syrup under acidic conditions
4.	Twinning
a.	Flat surface/high edge walls	Modify tablet punch design
5.	Uneven Colour
a.	Poor distribution of coating liquid	Improve mixing & add sufficient liquid.
b.	Colour migration due to under drying or too rapid drying	Use pigments and optimize drying conditions.
c.	Uneven surface of sub coat layer	Achieve requisite smoothness during sub coat application.
d.	Washing back of pigment colour coating	Avoid excessive quantities of coating liquid.
e.	Excessive drying between colour application (colour layer erosion)	optimize drying
6	Blooming and Sweating
a.	Residual moisture in finished coated tablets	Dry to get appropriate level of moisture at each application and at the end.
7	Marbling
a.	Uneven coating surface	Achieve smooth coating surface prior to polishing.