Germany's BASF has been awarded a US patent covering a new coating agent, binder and/or film-forming excipient, based on polyether-containing polymers, which can be used in pharmaceutical formulations.
Film coatings are used in solid pharmaceutical preparations for a wide variety of reasons, such as to make them easier to swallow and to mask unpleasant tastes, to increase the stability of the active ingredient and to allow product differentiation by the use of different dyes. The coating may also be used to change the properties of the medicine, for example by altering the rate of release of the active ingredient.
The new patent (No 6,579,953), awarded on June 17, notes that the polyether-based polymer technology used in the invention is suitable for both immediate- and sustained-release formulations and overcomes many of the limitations posed by currently-used excipients.
In the case of instant-release forms, the disintegration of the tablet and the release of the active ingredient from the presentation should be unaffected by the coating, which must dissolve rapidly in gastric fluid yet have high tensile strength so it can withstand mechanical effects like those occurring during pharmaceutical processing, especially packaging, and during transport and storage.
Pharmaceutical formulators often use hydroxypropylmethylcellulose to coat immediate-release dosage forms, but this allows only low film concentrations to be used, resulting in relatively long processing times and high costs, according to the patent.
In addition, HPMC has other disadvantages, relating to its wetting characteristics, adhesiveness on the tablet surface, pigment binding capacity, rate of dissolution and in the difference in disintegration time between film-coated tablets and the core. Moreover, the low elasticity of HPMC films frequently leads to the film-coated tablets splitting open on storage in moist conditions, as a consequence of the swelling of the core.
For sustained-release formulations, current approaches include the use of cores which are coated with a film which is insoluble in water but is semi-permeable or contains pores through which the medicinal substance diffuses, or by embedding the medicinal substance in matrices.
The excipients normally employed for this purpose are HPMC, hydroxypropylcellulose, alginic acid or alginates and xanthan, but once again these have significant limitations, according to the patent. These include deficient flow properties which makes direct tabletting difficult and the dependence of the release of medicinal substance on the salt content and pH of the release medium. The use of xanthan results in tablets whose hardness is low, while tablets made with alginates have only slight release-slowing properties and can show a wide variability between batches.
BASF claims its polymer compounds do not have the disadvantages of currently-used excipients. In addition, they are suitable for use as binding agents and avoid the problems with hardness and friability that can occur with alternatives such as maltodextrin or polyvinylpyrrolidones. Other binders such as starch paste and HPMC can be employed only in low concentrations because of their high viscosity.
In addition, the polymers can also be used to produce solutions and sprays that form a film when applied to the skin or mucous membrane. This makes them useful for wound treatment preparations and spray-on dressings, as well as for transdermal delivery of active ingredients, according to BASF. The polymers are also flexible so the use of plasticisers, which is undesirable for toxicological and pharmacological reasons, is not required.