Scaling-Up the Coating Process

SCALING-UP THE COATING PROCESS General Factors to Consider 

In a somewhat simplistic way, the scale-up of a coating process typically involves  

Irrespective of the type of coating process used, the potential process changes that commonly occur on scale-up include  

Many of these parameters are quite predictable, especially when applying some of the thermodynamic concepts described earlier. The increased processing time, which brings with it increased exposure to stressful conditions (both mechanical and as a result of environmental conditions used in the process, especially when that process is aqueous-based) is much more 

In each of these cases, there is a certain financial cost associated with potential product loss, reprocessing, and work in process. 

---

Despite the apparent variety expressed by these options, aqueous systems hold a dominant position in the pharmaceutical industry at this time. As a consequence, serious constraints are often imposed on the products being coated, the coating formulations used, and the coating processes that are adopted, with the result that scaling up the coating process can present serious challenges. 

Scaling-up the optimized process Using the optimized coating process as a basis, procedures were developed which enabled the process to be scaled... 

Table 16 Details of Coating Procedures Used in Scaling-Up the Wurster Process...

An important fact to be recognized, however, is that an extensive database relating to the coating process in question has been established, and key process variables (including their interactive effects) have been identified, providing a sound platform from which to begin the scale-up process. 

From the foregoing discussion, there are clearly many issues to be confronted when scaling up the pan-coating process. Evidently, the more definitive data that are developed initially, the less likely that major problems will occur later on, especially problems that could inevitably delay a product launch and cost much in the way of lost revenues, particularly when dealing with a potentially blockbuster drug product. 

Scaling-up the optimized enteric-coating process Based on the results... 

Summary of scale-up issues Scaling-up the fluid-bed process clearly faces many hurdles that are both similar and, at the same time, different from those faced with pan-coating processes. Additional complexity stems from the nature of the substrate that is likely to be coated in the fluid-bed process, as well as the fact that, very often, the applied coating has a very important role to play in drug delivery. 

Figure 17 Drug release characteristics of pellets coated on various scales of the Wurster process when the laboratory-scale process, used as the basis for scale-up, has been fully optimized.

Up to this point, the issue of process scale-up has been dealt with in terms of technology transfer from a small- to intermediate- to full production-scale processes. In each case, the coating process is a batch process that gets progressively larger. 

As with pan coating, the key to successfully scaling up the fluid bed process involves the design of a completely optimized laboratory-scale process on which key decisions can be based. As discussed earlier, Turkoglu and Sakr [8] have provided an appropriately relevant example of how such an optimized fluid bed process (in this case, a tangential-spray process) may be designed. 

The equation allows for modeling the coating process and predicting process conditions. Table 12 displays the parameters for scale-up that was performed in the lab to evaluate process conditions for a launch site. 

The number of experimental variables available with chemical polymerization is greatly reduced because no electrochemical cell or electrodes are employed. The range of dopant counterions (A-) that may be incorporated into the PPy backbone during polymerization has also, until recently, been generally limited to ions associated with the oxidant. However, chemical polymerization remains of interest for processing purposes because it may be easier to scale up this batch process and it results in the formation of powders or colloidal dispersions. Furthermore, it is possible to use chemical deposition to coat other nonconducting materials. 

---