Solubilization of rapamycin

The solubilization of rapamycin, a poorly water soluble investigational immunosuppressive drug, by facilitated hydrotropy is presented. Partially water-miscible aromatic solutes (such as benzyl alcohol, benzoate, or benzoic acid) can be solubilized by water-miscible cosolvents, such as ethanol and propylene glycol. Once solubilized, the partially miscible aromatic solute becomes a solubilizing agent. This technique yielded a dramatic (>1000-fold) increase in the aqueous solubility of rapamycin.

Systemic delivery of insulin via an enhancer-free ocular device

Sodium insulin and zinc insulin ocular devices are developed for the systemic delivery of insulin. The devices consist of Gelfoam (absorbable gelatin sponge, USP) as an insulin carrier and do not contain any surfactant or absorption enhancer. Sodium insulin was dissolved in either distilled water, 30% ethanol, or 10% acetic acid for either eyedrop or device preparations. Because of its low solubility in water and aqueous ethanol solution, zinc insulin was dissolved in 10% acetic acid-water solution for eye devices preparation. Commercially available Humulin R was selected as another source of zinc insulin and was used as an eyedrop as well as one device preparation. Only 10% acetic acid solution-treated insulin devices produce significant blood glucose reduction. The dose of insulin used in this study is < 50% of that used in the reported insulin devices.

Effect of Brij-78 on systemic delivery of insulin from an ocular device

An ocular insert is developed for the controlled systemic delivery of insulin. Commercially available Gelfoam absorbable gelatin sponge, USP, is used in the fabrication of the ocular insert in the form of a matrix system. Two eyedrop formulations and 13 eye device formulations were evaluated. The efficacy of insulin ocular delivery was quantitated by monitoring the changes in its pharmacological response (i.e., blood glucose lowering). The in vivo results from devices containing 0.5 or 1.0 mg of insulin with 20 micrograms of polyoxyethylene-20-stearyl ether (Brij-78) give a substantial improvement in insulin activity and a significant prolongation in its duration compared with the eyedrops. In addition, the mean blood glucose concentration returns to nearly normal levels within 60 min after the removal of the device. Overall, the application of the Gelfoam device makes it feasible to obtain a prolonged systemic delivery of insulin within the desired therapeutic levels without the risk of hypoglycemia.

Studies in phlebitis VIII: evaluations of pH solubilized intravenous dexverapamil formulations

Injectable and infusion formulations of dexverapamil are evaluated for their potential to produce phlebitis. The evaluation technique utilizes two independent in vitro methods and two in vivo methods to screen a pH solubilized drug for its potential to induce phlebitis due to precipitation at the injection site. One method is based upon a theoretical calculation that simulates the change of solubility upon dilution. Its predictions are confirmed by the second method which consists of an in vitro precipitation experiment. Thermal and visual evaluations are then obtained from an in vivo rabbit ear injection. Dexverapamil formulations that have low buffering capacity are shown to contribute to the incidence of phlebitis to a greater extent than the properly buffered formulations. The calculation and the in vitro precipitation experiment are found to be useful in formulating pH solubilized parenterals. They enable the formulator to optimize pH, drug concentration, and buffer concentration without the need for animal studies. The results of this study show the importance of selecting a buffer that provides adequate buffer capacity in the formulations.

Studies in phlebitis. VII: In vitro and in vivo evaluation of pH-solubilized levemopamil

We describe a computational model and an in vitro experiment for assessing whether or not a pH-solubilized drug has the potential to precipitate upon dilution with blood. The computational model enables an efficient means of selecting buffer concentration and pH, and the in vitro test provides a simple experimental validation. Both means of screening are applied to the formulation of the weakly basic drug levemopamil-HCI. A buffered formulation of levemopamil is chosen from the computational model and shown to be free of precipitation upon dilution in vitro and to not produce phlebitis in the rabbit ear model. In comparison, an unbuffered formulation at the same pH and drug concentration precipitates in vitro and causes significant phlebitis in vivo. The results of this study reinforce the importance of buffering parenteral formulations instead of simply adjusting the pH of the formulation.

Effect of pH on injection phlebitis

Formulation pH has been reported to be responsible for the incidence of phlebitis. In this study, the effect of pH on injection phlebitis is investigated. Buffers of varying pHs were examined for their ability to produce phlebitis in rabbits. Thermal measurements as well as visual evaluations were used for phlebitis quantitation. The results show that formulation pH between 3.0 and 11.0 does not contribute to the incidence of phlebitis when administered as an iv bolus injection.