Single-layer The Elementary Osmotic Pump (EOP) was developed by
ALZA in 1974, and was the first practical example of an osmotic pump based drug release system for oral use. It was introduced to the market in the early 1980s in Osmosin (
indomethacin) and Acutrim (
phenylpropanolamine), but unexpectedly severe issues with GI irritation and cases of
GI perforation led to the withdrawal of Osmosin.
Multi-layer Both the EOP and CPOP were relatively simple designs, and were limited by their inability to deliver poorly
soluble drugs. Methylphenidate's short
half-life required multiple doses to be administered each day to attain long-lasting coverage, which made it an ideal candidate for the OROS technology. Multiple candidate
pharmacokinetic profiles were evaluated and tested in an attempt to determine the optimal way to deliver the drug, which was especially important given the puzzling failure of an existing extended-release formulation of methylphenidate (Ritalin SR) to act as expected. The zero-order (flat) release profile that the PPOP was optimal at delivering failed to maintain its efficacy over time, which suggested that acute tolerance to methylphenidate formed over the course of the day. This explained why Ritalin SR was inferior to twice-daily Ritalin IR, and led to the
hypothesis that an ascending pattern of drug delivery was necessary to maintain clinical effect. Trials designed to test this hypothesis were successful, and ALZA subsequently developed a modified PPOP design that utilized an overcoat of methylphenidate designed to release immediately and rapidly raise serum levels, followed by 10 hours of first-order (ascending) drug delivery from the modified PPOP design. This design was called the Push-Stick Osmotic Pump (PSOP), and utilized two separate drug layers with different concentrations of methylphenidate in addition to the (now quite robust) push layer. ==List of OROS medications==