The Effect of Core and Coating Composition on Drug Release from Directly Compressed Time-Controlled Release Tablets - Pharmaceutical Technology

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The Effect of Core and Coating Composition on Drug Release from Directly Compressed Time-Controlled Release Tablets
The authors prepared and tested press-coated tablets with various weight ratios of ethylcellulose to hydroxypropylcellulose (HPC) and various ratios of two different batches of HPC as an outer coating shell and fillers in core tablets. The tablets were examined for changes in time lag and release patterns of salbutamol sulfate.

Pharmaceutical Technology

Figure 8
A 50:50% w/w combination of HPC HF and HPC EXF formed a tougher gel-like structure upon contact with the dissolution medium. Because tablets containing Avicel PH 101 as a filler were hydrophobic, they required more time to hydrate upon contact with the dissolution medium to diffuse out salbutamol sulfate from the gell-like structure of the outer shell. The hydration and disintegrant properties of Starlac present in the core tablet resulted in a rapid drug release and a slower lag time compared with the formulation containing Avicel PH 101 as filler. The pressure generated upon the swelling of Ac-Di-Sol with Avicel PH 101 as filler was not sufficient to break the outer shell because of the tough gel-like structure formed on the outer shell. Obviously, the erosion of the outer-coating shell of the core tablet containing Starlac was lower than when Avicel PH 101 was used as as filler (see Figure 9).

Figure 9
A photograph of the formulation containing 50:50% w/w HPC HF to HPC EXF at the 20th hour also suggests the proper hydration effect of the core and shows the possible mechanism of release of salbutamol sulfate from this formulation (see Figure 10). Formulation containing a higher weight ratio of HPC HF to HPC EXF showed more delay in the release of salbutamol sulfate and an increase in the time lag to start the release of salbutamol sulfate.


Various drug-release mechanisms were observed by incorporating different polymers into the outer shell and different core compositions. By deepening the knowledge of polymeric materials' behavior in dosage forms and, in particular, their application in the press-coating of different core compositions such as those proposed in this study, a safe and more accurate targeting of the drug from dosage forms can be achieved.

Figure 10

Shilpa P. Chaudhari and Praveen D. Chaudhari* are professors of pharmaceutics at Padm. Dr. D.Y. Patil Institute of Pharmaceutical Sciences and Research, Pune University, India, tel. +91 9850179873, fax +91 22 27421097,
Chetan J. Mistry is a research scientist at the Torrent Research Centre, India. Manohar J. Patil, PhD, is head of the Department of Pharmacognosy at Padm. Dr. D.Y. Patil Institute of Pharmaceutical Sciences and Research. Nilesh S. Barhate is a research and development officer at Blue Cross Laboratories, India.

*To whom all correspondence should be addressed.

Submitted: Sept. 26, 2006. Accepted: Oct. 11, 2006.

Keywords: controlled release, coating, excipients, direct compression, formulation, solid dosage forms, tableting


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