Available tubing for peristaltic pumps tend to shed particulates into the solution due to their poor abrasion characteristics. Most commonly used flexible tubing is silicone rubber or polyvinyl chloride (Tygon) tubing. Two newly available tubing are manufactured from a composite of expanded polytetrafluoroethylene (Teflon PTFE) with platinum-cured silicone rubber (Sta-Pure) and a tubing composite of PTFE with fluoroelastomer (Chem-Sure). These are claimed to resist spalling and deliver constant volume when used in peristaltic pumps. The four tubing were compared for spallation. They were also compared for sorption of methylparaben, propylparaben, and benzyl alcohol over a 72 hr study. Spallation studies indicate that Tygon and silicone tubing are prone to damage and shedding of particulates due to abrasion during use in peristaltic pumps while the Chem-Sure and Sta-Pure tubing are resistant to abrasion and spalling and show negligible shedding of particulates over 72 hr use in the peristaltic pump. Chem-Sure shows no spalling after 48 hr. Decrease in volume delivered is expected using Tygon and silicone tubing only. Chem-Sure tubing did not show any preservative losses. Tygon sorbed all preservatives tested to the greatest extent, followed by Silastic and Sta-Pure tubing, in decreasing order of sorption. Propylparaben was sorbed to the greatest extent. The tubing used appear to approach saturation in 24-48 hr. Chem-Sure and Sta-Pure tubing are ideal for use in peristaltic pumps or for general use for any demanding pharmaceutical applications.

Flexible tubings are extensively used in pharmaceuticals, food industry, and in hospitals. This study was undertaken to compare various flexible tubings to determine their sorption characteristics, using methyl and propyl parabens. After 24 h, some tubings showed 100% sorption of propylparaben and over 40% for methylparaben. Significant losses were observed within a few hours using several tubings. For methylparaben, the losses were in the following decreasing order of sorption: Tygon, Clearflo, silicone, Nylotube, and Newtex. For propylparaben, the losses were in the following order: Tygon, Clearflo, silicone, Newtex, and Nylotube. Teflon, Zelite, and Vitube showed little to no losses of methyl and propylparaben over 120 h of study. The silicone tubing, refilled after 120 h with fresh methylparaben or propylparaben solutions, again showed significant losses within a few hours. The tubings show slow desorption when filled with the buffer vehicle. For Silastic tubing, increase in temperature from 25 to 40 degrees C, increase in pH from 3.5 to 6.5, tubing lot to lot variation, or curing with peroxide or platinum had little or no effect on paraben sorption. As expected, the sorption of parabens increased with increasing surface area of Silastic tubing. Results provided can be used to select the best tubings and to minimize paraben losses during production and filling of liquid pharmaceuticals andfood products containing these antimicrobial preservatives.

Earlier studies using methylparaben, propylparaben, and several types of flexible tubing showed that the parabens are sorbed by a number of commonly used tubing. The sorption increased with increase in time of contact and the tubing surface area. The temperature and pH ranges tested did not affect sorption. Current studies evaluated other commonly used antimicrobial preservatives used in oral, parenteral, opthalmic, nasal, and other pharmaceutical products. These preservatives include benzoic acid, sorbic acid, benzyl alcohol, and benzalkonium chloride. Results show that all preservatives, except benzalkonium chloride, are sorbed by several types of flexible tubing. After 24 hr, some types of tubing sorbed over 40% of benzoic acid, benzyl alcohol, and about 30% of sorbic acid. Significant losses were observed within a few hours. No sorption of benzalkonium chloride occurred in the tubing tested. Three different types of fluoropolymer resin tubing, Teflon (flourinated ethylene propylene (FEP), Teflon perfluoroalkoxy) (PFA) and Teflon polytetrafluoroethylene (PTFE, NXT), fluoropolymer FEP laminated Tygon tubing, and Zelite do not sorb any of the preservatives. Silicone tubing shows the highest sorption of preservatives. After 120 hr, as much as 64% of the preservative is sorbed by some tubing. Detailed studies using silicone tubing show that the sorption increases with increase in surface area at 25 degrees C, and increasing the temperature to 40 degrees C shows little change in sorption. At the concentration range generally used in formulations, the concentration of the preservative has no significant effect on sorption. Refilling the tubing with fresh preservative solution after contact with preservative solution for 168 hr still causes extensive sorption of the preservative. Desorption studies indicate that the sorbed preservatives are desorbed in water to a limited extent over 120 hr. Results are important in situations where short or extended interruptions occur in the processing and filling of products. This can lead to decreased and variable results due to residence of the solution in the tubing.

Aqueous liquid formulations of efavirenz, a nonnucleoside inhibitor of reverse transcriptase, have prolonged burning (peppery) taste. Medium-chain triglycerides (MCT) was used as the vehicle to mask the taste and obtain palatable oral liquid formulations containing 20 mg/mL efavirenz. The use of MCT for enhancement of palatability and stability is recommended for drugs that show high solubility and partitioning in this vehicle.