Thermal Characterization of Drug/Polymer and Excipient/Polymer Interactions in Some Film Coating Formulation

Abstract

Some probable consequences of the dissolution/migration of a major solid dosage component in or into an applied film coating during or after a film coating operation have been investigated using free films of hydroxypropyl methylcellulose (HPMC) and polyvinyl alcohol (PVA) incorporating small amounts of either lactose (a diluent) or ephedrine hydrochloride (a drug). Intrinsic features of the films such as softening, glass transition, crystallinity and melting were examined by differential scanning calorimetry and thermomechanical analysis. Generally, the results indicate that ephedrine hydrochloride exhibited plasticizing activity in both HPMC and PVA films. On the other hand, incorporation of lactose produced an opposite effect (stiffening) in PVA films as demonstrated by increased glass transition temperature and crystallinity. On the basis of these findings, it was proposed that the undesired presence of a component of a solid dosage core in the applied film coating could significantly alter its end-use properties such as diffusivity and the incidence of film coating defects. It was also shown that the application of the relationship of Moelter & Schweizer (1949) in the evaluation of the plasticizer efficiency of non-homologous additives could pose problems of interpretation.

A Dissolution-Diffusion Model and Quantitative Analysis of Drug Controlled Release from Biodegradable Polymer Microspheres

“…It suggests that a strong interaction exists between nifedipine and PLGA 50:50. Meanwhile, the peak melting temperatures remain unchanged for drug loaded PLA microspheres and it indicates that no interaction between nifedipine and PLA or the interaction is weak (Okhamafe and York, 1989;David et al, 1999). 4.…”

Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

“…They interpose themselves between the individual polymer strands thus breaking down, to a large extent, polymer±polymer interactions and thereby lowering the Tg (Bodmeier & Paeratakul 1994). Plasticization improves the mechanical properties of the ®lms and lowers the incidence of ®lm-coating defects such as cracking, edge splitting and bridging of intagliation (Okhamafe & York 1989). However, it may also have drawbacks such as an increase in ®lm diffusivity of moisture and of drugs.…”

“…Furthermore, the Tg is affected by storage conditions (Aulton 1995), water content (Hancock & Zogra® 1994;Wang et al 1997) and the addition of plasticizers (Selinger & Brine 1988; Van der Voort Maarschalk et al 1998;Hogan 1995). Therefore, the Tg of polymers is a critical factor not only in the ®lm formation during coating (Okhamafe & York 1988Keshikawa & Nakagami 1994) but also in compaction (Van der Voort Maarschalk et al 1998) and drug release (Okhamafe & York 1989;Dressman et al 1995).…”

Effects of calcium salts on thermal characteristics of hydroxypropyl methylcellulose films

“…Okhamafe and Iwerbor et al [13] reported that the highly water-soluble additives citric acid and urea affect the moisture permeability of films based on HPMC and polyvinyl alcohol (PVA). In addition, Okhamafe and York et al [14,15] reported that small amounts of ephedrine hydrochloride have a plasticizing effect on both HPMC and PVA films. The nature and degree of plasticizer/polymer interactions have a significant influence on film properties.…”