Release kinetics of salbutamol sulphate from wax coated microcapsules and tableted microcapsules

Microcapsules of salbutamol sulphate were prepared using beeswax and carnauba wax as coating materials. In vitro release kinetics were studied following the zero order, first order and Higuchi equations. Beeswax alone was not effective but beeswax and carnauba wax combinations were suitable in controlling the in vitro release of the drug. Microcapsules were compressed into tablets to get a controlled release oral dosage form. Release from tableted microcapsules was significantly more prolonged than the respective batches of the microcapsules. Best data fit with the highest correlation coefficient for the tableted microcapsules was obtained for first order.

Equilibrium and kinetic studies of the interactions of salmeterol with membrane bilayers

The interaction of salmeterol with model membranes has been studied with regard to equilibrium and kinetic behavior, including determination of the membrane-based partition coefficient, the rate of dissociation of salmeterol from membranes, and the rate of association. These data were obtained in various membrane preparations and under various conditions (e.g., temperature, cholesterol content). The compound is very lipophilic, compared with other beta 2 agonists such as salbutamol, and has a rapid association rate and a moderate dissociation rate. The equilibrium data support the assertion that the salmeterol action measured in perfused tissue involves an exo-site for nonspecific binding that may be identified with or related to the lipid bilayer. The kinetic data in unilamellar and multilamellar liposomes of synthetic lipids further suggest that the approach to the exo-site and the active site may involve components in the native system other than the lipid bilayer in which the beta 2 receptor is located. These additional components may explain the slow onset and the extraordinarily long duration of action.

Quantitative evaluation of aqueous isopropanol enhancement of skin flux of terbutaline (sulfate). I. Ion associations and species equilibria in the formulation

It has been reported previously that saturated terbutaline sulfate in aqueous isopropanol significantly enhances the terbutaline flux through human skin in vitro. This paper demonstrates that the effect of isopropanol on the permeant species in the formulation contributes to the flux enhancement. This demonstration is based on studies involving measurements of conductivity and pKa as well as NMR spectroscopy in isopropanol-water mixtures. Increasing isopropanol concentration inhibits the proton dissociation of terbutaline and results in the ion associations between the protonated terbutaline and its counterion, sulfate anion. The species present in the formulation include protonated terbutaline, the negatively charged terbutaline-sulfate (1:1) ion pair, and the neutral terbutaline-sulfate (2:1) ion triplet. The results of the studies provide the basis for a quantitative evaluation of the species equilibria in solutions of terbutaline sulfate. The saturated terbutaline sulfate in 60% isopropanol produces the maximum concentration of the neutral ion triplet. This result is almost parallel to the terbutaline skin flux, which maximized at 60-80% isopropanol.

Update on the physical-chemical compatibility of cromolyn sodium nebulizer solution: bronchodilator inhalant solution admixtures

Cromolyn sodium nebulizer solution, 1% (wt/vol), is physically and chemically compatible (stable) for at least 90 minutes when mixed in vitro with a new formulation (metabisulfite-free) of metaproterenol sulfate solution, an inhalant solution of albuterol sulfate or an atropine sulfate inhalant solution. Similarly, cromolyn sodium does not adversely affect the stability of the individual bronchodilator drugs in the admixtures. Since cromolyn sodium is compatible in admixtures with these bronchodilator drugs, adding these agents to cromolyn sodium nebulizer solution should have no negative influence on the effectively administered dose of either active ingredient.

Osmolality and pH of anti-asthmatic drug solutions

Mixtures of different drugs are frequently used in aerosol solution for treatment of asthma. These drugs have different pH and osmolality values as stock solutions. It has been suggested that acidity and osmolality interact in provoking bronchoconstriction and cough. Therefore, pH and osmolality of anti-asthmatic drug solutions and mixtures were measured in the nebulizer at 0, 1, 2, 5, 10 and 15 minutes of nebulisation, pH of fenoterol, ipratropium bromide, salbutamol and disodium cromoglycate ranged between 2.0 and 5.7 and did not change during nebulisation. Nearly all drug solutions were hypoosmolar and the osmolality increased during nebulisation with 11 to 62%. Therefore, it is suggested to dilute these drugs with saline 0.9% and to restrict nebulisation time to 10 minutes, since the most striking increase of osmolality was noted after 10 minutes.