This article is part of PharmTech's supplement "Injectable Drug Delivery."

More than two billion prefilled syringes are developed and used each year. The rise of the prefilled syringe as the preferred container for injectable drugs began with Sanofi and Rhône-Poulenc Rorer's successful introduction of syringes for heparins to the European market in the early 1980s. The prefilled syringe market has expanded considerably because of factors such as the growth of biopharmaceuticals, the need to eliminate overfills, the need for precise delivery volumes, the desire for convenient delivery, the quest for cost effectiveness, and the goal of reducing dosage errors (1–4).

Figure 1: Daikyo Crystal Zenith prefillable syringes (Daikyo Seiko, Tokyo). (IMAGES ARE COURTESY OF WEST)

Many chronic diseases such as multiple sclerosis and rheumatoid arthritis require the self-administration of injectable treatments. This need has increased interest in combination-drug delivery systems that are safe, convenient, and help improve the administration process.

Pen injectors and multidose cartridges were created for patients who need frequent injections. These devices were limited to specific therapies such as diabetes and growth hormones, which often require weighed dosages or dose titration. Although pen injectors were designed for frequent injections and for patients who require variable dose capabilities, they are not ideal for chronic users of fixed-dose medications, including patients suffering from impaired dexterity. The need for a safe, reliable, easy-to-use, single-dose injection system for these patients soon became apparent.

Figure 2: ConfiDose autoinjector (West, Lionville, PA). (IMAGES ARE COURTESY OF WEST)

Traditional systems' performance problems

Autoinjector systems traditionally use 1-mL glass prefilled syringes. These systems have been successful, but they have notable limitations, including performance problems. Recent studies have shown that silicone oil, which is used to increase lubricity in syringe systems, is often distributed unevenly, thus leaving certain areas of the prefilled syringe surface with insufficient lubrication (5). The inconsistent silicone-oil coating can significantly affect the piston-travel and glide forces in autoinjectors. In 2006, commercial lots of a drug product delivered by an autoinjector that contained a glass prefilled syringe were recalled in several European countries because of problems with slow or incomplete delivery of the drug (6). Uneven silicone coating may increase travel forces and cause failures such as incomplete injections.