Advances in film coating

Pharmaceutical Technology Europe interviews Xavier Parissaux, Product and Project Manager at Roquette, about the factors driving innovation in film coating.

What developments have been made in pharmaceutical film coatings in recent years?

Xavier ParissauxBecause of the constraints weighing on it, the pharmaceutical industry is very conservative. Novelty is often employed only in very specific cases (mainly due to stability issues) when all opportunities of using a well‑known, well‑established material or product have failed. Consequently, traditional coated tablets still maintain their popularity and no major change has really occurred in the dosage form area except for the introduction of orally dispersible films (ODFs), first in the US and more recently in Europe. The proof of concept of this novel dosage form has been demonstrated by the food industry with breath freshners, and there is also growing interest from the pharma industry in different kinds of film forming agents, as evidenced by the increasing number of composition patents.

When looking at improvements in the area of film coating, it is important to distinguish between the functional coating, which modifies the release profile of the API (enteric coating, colon targeting etc.), and non functional coating, which does not modify the relase profile of the API.

With regards to functional coatings, most of these are non-water soluble and the challenge for coating manufacturers, therefore, was to stop using organic solvents (used to enable aqueous suspension) because of their negative impact on the environment. With the tightening of residual solvent limits, there is still interest in reducing the use of organic solvents, but progress has been slow.

For non‑functional coatings, innovations have been limited because commonly used cellulosic derivatives and polymetacrylate coatings continue to provide satisfactory results for most uses. Innovation has also been frozen because of the patent situation in the coating business; many patents expired around 2006 and since then few companies have come up with innovations, preferring to concentrate on ‘me too’ products instead.

One major improvement that has taken place, however, is the shortening of the coating process length. This improvement was brought about by using coating solutions with a high solid content; the amount of solid applied per time unit is higher in high solid content solutions than in low solid content solutions, thus the time required for the overall coating process is reduced and so too is the cost.

How do different film coatings compare with one another?

Cellulosic derivatives are used in the majority of already marketed products, but more recently developed coatings, such as PVA and modified pea starch, will become more widespread as new developments using these coatings receive marketing authorisation. One of the primary attractions of these newer coatings is that they enable manufacturers to use a high, dry solid content coating solution that significantly reduces coating times compared with the majority of cellulosic derivatives. Other comparisons between the different coatings include:

• Inertness: the chemical nature of polymers influences their inertness. Literature does not report any incompatibility phenomenon of starch with other ingredients, compared with PVA and cellulosic derivatives, which do have incompatability issues.¹
• Moisture barrier: PVA in itself presents higher moisture barrier properties compared with cellulosic derivatives and starch; however, when adding plasticiser and other ingredients to the formulation this difference is reduced.
• Organoleptic properties: Everybody remembers the taste and odour of HPMC after experiencing it once (like old paper). PVA smells and taste like plastic where as starch is neutral in term of taste and odour.

What effect has new coating materials had on processing equipment?

With new coating materials that can be used at a higher solid concentration to reduce coating times, one of the most important questions is “how do we increase the frequency of nucleus passing through the spray while avoiding abrasion/stress of/on nucleus?” To meet this challenge, spray nozzles are now equipped with an anti-bearding system. The shorter coating process that can be achieved using new coating materials has helped to decrease this phenomenon.

Roquette’s LYCOAT film-forming polymer can enable the formulation of films that dissolve on the tongue for immediate action of the active ingredient. Can you tell us more about this technology and its benefits?

Technologies for ODF manufacture are quite different compared with film coating, which explains why different grades of Lycoat can be used; we have different grades of Lycoat that are either readily soluble in cold water or that need to be cooked in order to be solubilised and our different grades have different viscosities. ODFs are either extruded or casted, with both processes having their own advantages and drawbacks from both technical and economical points of view. The clear benefit that I see with ODF manufacture technologies is a continuous or semi continous process that provides a higher level of robustness compared with other manufacturing processes, such as tabletting, for solid dosage forms with regards to interlinking between friability, hardness, disintegration time and the dissolution profile of a tablet, as well as other parameters that can affect each single criteria such as lubrication, speed of the equipment, etc. Moreover, it is possible to reach the level of homogeneity of a liquid dosage form while retaining the stability and handling of a solid dosage form.

What industry trends do you believe will shape the future of the film coatings market?

With the increasing potency and sensitivity of APIs, there is a constant need for inert materials that, as well as avoiding incompatibility issues, also protect drugs from degradation caused by environmental factors, such as moisture, light, heat and oxygen. However, designing such a material will be a challenge for the industry.

Pharmaceuticals tend to follow what’s happening in the food industry; therefore, I believe that marketing departments of pharma companies will follow the ‘clean labelling trend’ that is being pursued in the food industry (the clean labelling concept avoids the presence of non natural names in the ingredient list of the finished product, such as food additives numbers) and will push formulators to use as many natural ingredients as possible. Getting rid of organic solvents remains a topic of interest and getting rid of any solvent with dry coating could also be part of the future.

References

1. R. C. Rowe (Ed.), Handbook of Pharmaceutical Excipients Sixth Edition (Pharmaceutical Press, UK, July 2009).