A key element to this process is the spray-dry technology that produces the pigment–polymer solid dispersion. This process
(Xfast, BASF) provides high surface area, solid-dispersion granules consisting of pigment embedded in the coating polymer
matrix. These properties of the solid-dispersion granules, combined with the high water solubility of the polyvinyl alcohol–polyethylene
glycol copolymer, allow for the fast redispersion into water. Once dispersed using a standard propeller mixer, the coating-systems'
coating suspensions are ready to be used in the film-coating process in approximately 20 min.
The Kollicoat IR copolymer offers additional benefits in film-coating applications. The low viscosity, water-soluble copolymer
of polyvinyl alcohol and polyethylene glycol provides color film-coatings that exhibit high elasticity. Elasticity is important
when dealing with applications where a more flexible film coating is needed to eliminate film cracking that can result when
using more brittle coating ingredients. The copolymer's low viscosity allows for increased manufacturing productivity by using
high solids-content suspensions of 20% and higher. The adhesive properties of the polyvinyl alcohol–polyethylene glycol copolymer
result in film-coated tablets with excellent logo definition. The copolymer also is internally plasticized, which eliminates
the potential for plasticizer migration.
Color selection. The color system (Kollicoat IR Coating System, BASF) uses 102 preformulated color options (Color Fan, BASF). A color–combination
formula is provided for each color square. As a result, film-coating formulation–development work is not necessary, and color
evaluation on a solid oral-dosage form can be completed using the preformulated formulation.
An important part of the color system is the software, which is used to expand the color options by using preformulated recipes
to create new colors by adjusting the amounts of base global colors found in a given formulation. For example, a preformulated
color can be made lighter or darker by either increasing or decreasing the percentage of one of the formula components, or
a wholly new color can be created by adding a new color component or removing one from the original formula. The new color
is displayed as a color square on a computer monitor, and the resulting formula can be evaluated in the laboratory either
by film casting or coating a tablet.
Alternative color measurement
. A color-measurement spectrophotometer can be used to measure the color of another product, a tablet or capsule, for example,
in order to match that color. The CIE color scale can be used to generate L*a*b* color values, which define color in a color space. The L* axis represents the color scale from black to white, and the a* and b* axes represent color values from green to red and blue to yellow, respectively. The L*a*b* color values generated are used by the software to provide the closet color match. Manual pigment manipulation and combination
are not needed to determine a specific color match. The software provides a measured starting point based on the combination
of formulations in the coating system.
Regulatory considerations.
The software can provide regulatory guidance for products marketed in the United States, European Union, and Japan with regards
to pigment levels on a final dosage form. By factoring in tablet dimensions, specific coating weight gain, colorant concentrations,
and daily product dosing, the software determines whether a specific coating formulation exceeds current colorant limits in
the US, the EU, and Japan. Using this regulatory software tool, a color formulation can be created and evaluated without having
to prepare a test formulation or perform a coating trial. If a specific coating-formulation color exceeds colorant limits,
the formulation and color can be adjusted using the software before actual color-coating work is completed in the laboratory.
Conclusion
The application of the new color system (Kollicoat IR coating system) illustrates how pharmaceutical excipient technologies
can be combined to make new color options for immediate-release film coatings. The system also is a good tool to increase
productivity and reduce the development time encountered in manual color systems.
Phil Butler is a technical sales manager for BASF, 100 Campus Drive, Florham Park, NJ 07932, tel. 973.245.6378, fax. 973.245.6843, philip.butler@basf.com
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