PRINT also can help extend a drug carrier's elimination half life, thus keeping it in the body longer (1). The more deformable a drug particle is, the more easily it can bypass biological barriers such as the lung and spleen, and the longer its elimination half-life. Rigid particles tend to get stuck in small capillaries.

DeSimone's team made particles that were 1.5 µm thick and 6 µm in diameter to mimic the properties of red blood cells. "We systematically varied the degree of deformability. When we matched the degree of deformability of a red blood cell, we had a 30-fold increase in elimination half life. We had a four-day elimination half-life for a 6-µm diameter particle, which is really unheard of," says DeSimone.

Because the PRINT technique offers enhanced control over particle properties, including size, shape, chemistry, and surface area, it could enable a wider range of release rates for injectable drugs compared with manufacturing techniques, such as emulsions, says DeSimone. The method also allows manufacturers to load particles with more types of drugs than other techniques do, including hydrophilic, hydrophobic, and biomacromolecules. He adds that PRINT can modify the particle matrix easily, thus establishing the desired release profile. "The precise control over numerous particle parameters is what makes PRINT so versatile," says DeSimone.

Several options for controlled-release injectable dosage forms, though effective, require somewhat complicated formulations that present unique manufacturing challenges. Injectable controlled-release drugs are traditionally in liquid form because of the constraints of the standard needle-and-syringe delivery method, which limits formulation options.

The ability to retain a solid formulation offers several advantages, not least in terms of stability. The injection of solid doses is not a new concept; drug implants have been around for some time. AstraZeneca's Zoladex (goserelin), for example, was introduced more than 20 years ago. Used to treat prostate cancer, the 10.8-mg implant must be injected by a healthcare professional through a 14-gauge needle with an aseptic technique. "Not particularly pleasant," says Charles Potter, chief technical officer at specialty pharmaceutical company Glide Pharma. However, the formulation does offer sustained release over a 12-week period and makes such injections relatively infrequent.

Taking the idea of an implant one step further, Potter asked, "Why not use the drug as the needle? If the formulation can be made solid enough, it can be formed into a sharp point." That premise is the basis of Glide Pharma's Solid Dose Injector (SDI) technology, which uses a solid, homogenous mixture of drug and excipient.