Salbutamol sulfate suppositories: influence of formulation on physical parameters and stability

To prepare and evaluate a suppository dosage form of salbutamol sulfate. The prepared formulae with and without different concentrations of gels were tested for hardness, melting time, content uniformity, and drug release. The stability of some of the selected formulae was assessed.

Salbutamol sulfate was formulated as a rectal suppository with emulsifying fatty bases (suppocire and witepsol) and water-soluble bases (PEG) adopting the molding from a melt technique. Physical characteristics and dissolution profiles of the prepared formulations were determined as the responses. The effects of adding gels, methyl cellulose (MC), and Eudispert (Eud) and their concentrations (1, 3, and 6%) on these responses were also investigated. Formulations showing high rank order were scaled up for shelf-life stability study for one year.

The results showed that all the investigated formulae have acceptable physical characteristics with respect to hardness, melting time (except F7), and uniformity of drug content. The amount of drug dissolved in 100 min of dissolution time was inversely affected by the melting point of the fatty base. The release from PEG bases was found to be molecular weight dependent. Addition of 1% MC or Eud gel increased the release from all the investigated formulae. Increasing gel concentration to 3% then to 6% showed different effects on the release. The degradation of salbutamol sulfate in the investigated formulae was found to be a first-order reaction.

Rectal suppository of salbutamol sulfate could be prepared as an alternative to the oral dosage form to circumvent the first-pass metabolism.