Film coating is a commonly applied technique for the production of pharmaceutical products in order to achieve different requirements such as sustained- or controlled- release formulations.
Film coating techniques are characterized by the deposition of a uniform film onto the surface of a substrate. Because of the capability of depositing a variety of coating materials onto solid cores, this process has been widely used to make modified-release dosage forms starting from different formulations, such as tablets, granules, pellets, and capsules.
Nevertheless, very few cores possess the optimal physico-chemical properties needed by conventional coating processes. These properties include (1) suitable compaction, impaction, and attrition strengths to avoid ruptures during the coating process; (2) approximately spherical shape to obtain good flow and rolling properties in the coating equipment; and (3) suitable size, size distribution, and density as required by the coating process. Obviously, as different types of coating equipment are used, the handling of the cores and consequently the requirements of the cores for the various equipment should also be different.
Cores are usually prepared using one of the following processes: compaction, surface-layering, or agglomeration. Among these methods, the surface-layering technique is an appealing approach. Generally, this pelletization method involves the use of inert substrates, such as sugar spheres, and their enlargement by intermittently spraying a binder solution and applying the active substance powder in a rotating coating pan or in a fluidized bed.
In spite of interesting possibilities offered by the powder layering technique, it still presents some drawbacks as follows:
1. The powder layering process requires a great deal of repetition of wetting and powdering operations and is thus time consuming; moreover, undesired agglomeration and adhesion of the pellets to the wall of the coating equipment can occur.
2. The powder layering technique requires specialized equipment such as a rotary-tangential fluidized bed or modified rotating pans.
3. In the literature there are few or no complete studies aimed to determine whether a relationship exists between the formulation and process parameters and the physical, technological, and biopharmaceutical properties of the pellets. Some works on the traditional method of building up cores by conventional pan coating are reported, but the layering technique used was discontinuous and without automation.
In this respect, the recent and specialized coating equipment of the GS system represents an interesting new approach allowing the use of a fully automatized aqueous-based system for powder layering on starting cores. The system is based on a rotating non-perforated pan, equipped with patented air supply (two perforated swords) and volumetric powder feeding unit. The most attractive features of this powder layering system are the uniform distribution of the powder on cores and the high drying efficiency of the binder solution, as well as the easy-to-clean pan and the possibility of applying the successive functional film coating using the same equipment. The critical aspects involved in the process of layering activated-surface powder using the aqueous binder solution are the decreased adhesiveness of the binder on cores due to the presence of a wetting agent and the high latent heat of vaporization of water used as a binder vehicle.
The aim of the present study was to evaluate the influence of the formulation and operating conditions on the pellet preparation by GS pan layering. For instance, the following parameters were considered: (1) size of the starting cores; 2) type of micronized powder with particular attention to its flowing properties and wettability; (3) binder type and concentration; (4) application rate of the sprayed binder solution and powder; (5) presence of wetting, flowing, and anti-sticking agents; (6) pan speed; (7) spray gun position and atomization degree; (8) inlet air and bed temperatures; (9) air cap type; and (10) size of the pellets.
Ibuprofen was used as poorly soluble drug model (solubility in water: 0.07 g/l), because until now, no formulation of this drug had been developed based on pellets and using only aqueous solvents.
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