The advent of hypromellose capsules has greatly simplified capsule coating using aqueous systems due to good polymer to polymer interaction and adhesion. Furthermore, hypromellose does not soften nor become brittle when aqueous film coating is applied. Cole et al.  reported the successful coating of hypromellose capsules with two types of pH-sensitive polymers viz. Eudragit® L 30 D-55 or Eudragit® FS 30D and confirmed the in vivo release using gamma scintigraphy. Optical microscopy showed a contiguous coat of uniform thickness around the capsule shell (Fig. 14.8).
Dissolution tests confirmed that the capsule coated with either 6 or 8 mg cm2 Eudragit® L 30 D-55 did not release the drug acetaminophen over 2 h at pH 1.2, but released rapidly at pH 6.8. Capsules that were coated with either 6, 8 or 10 mg cm2 Eudragit® FS 30 D did not release the drug at either pH 1.2 for 2 h nor pH 6.8 for an additional hour but released at pH 7.4. Gamma-scintigraphy studies in human volunteers confirmed that:
• Neither type of coated capsule disintegrated in the stomach.
• Eudragit® L 30 D-55-coated capsules disintegrated completely in the small intestine.
• Eudragit FS 30 D-coated capsules disintegrated between the mid distal small intestine and the proximal colon.
This study illustrated the potential for intestinal targeting through coated hypromellose capsules .
Fig. 14.8 Optical micrographs of HPMC capsules coated with Eudragit® L 30 D-55. (Top) Cross-section of domed end of capsule coated with 10 mg cm2 Eudragit® L 30 D-55. (Bottom) Longitudinal cross-section through a capsule coated with 6 mg cm2 Eudragit L 30 D-55 
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