Monolithic matrix tablets of ambroxol hydrochloride were formulated as sustained release tablets employing hydroxypropyl methylcellulose polymer, and the sustained release behaviour of the fabricated tablets was investigated. Sustained release matrix tablets containing 75 mg ambroxol hydrochloride were developed using different drug polymer ratios of hydroxypropyl methylcellulose. Tablets were prepared by direct compression. Formulation was optimized on the basis of acceptable tablet properties and in vitro drug release. The resulting formulation produced robust tablets with optimum hardness, consistent weight uniformity and low friability. All tablets but one exhibited gradual and near-completion sustained release for ambroxol hydrochloride, and 98-101% released at the end of 12 h. The results of dissolution studies indicated that formulation F-V (drug to polymer 1:1.47), the most successful of the study, exhibited drug release pattern very close to theoretical release profile. A decrease in release kinetics of the drug was observed on increasing polymer ratio. Applying exponential equation, all the formulation tablets (except F-V) showed diffusion-dominated drug release. The mechanism of drug release from F-V was diffusion coupled with erosion (anomalous).
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