Implanted drug delivery systems are being increasingly used to realize the therapeutic potential of peptides and proteins. Here we describe the controlled pulsatile release of the polypeptide leuprolide from microchip implants over 6 months in dogs. Each microchip contains an array of discrete reservoirs from which dose delivery can be controlled by telemetry.

We report the first measurements of the new approach of hydrodynamic fingerprinting. The hydrodynamic fingerprint is the isothermal contour diagram of the hydrodynamic size as a function of pH and pX (the logarithm of the conductivity fitS/cm)). The general applications of fingerprinting are discussed, and we compare hydrodynamic fingerprints with electrophoretic fingerprints on similar systems. The electrophoretic fingerprint is the isothermal isomobility contour diagram in the pH-pX domain. Measurements are reported on five model polystyrene latexes with carboxyl or sulfate surface groups (ranging from 401 to 1050 nm) from the Interfacial Dynamics Corp. We find that the hydrodynamic size depends on pH, pX, and time, and is generally larger than the electron microscopy size. The hydrodynamic fingerprint, like the electrophoretic fingerprint, is a characteristic pattern of a particular colloidal system. The advantages of the colloid system variable pX over the classical ionic strength are illustrated. The fingerprinting approach is a correlation of variables that can be used to spot errors and assess the general

Reproducible releases of a stable solid leuprolide formulation from a multi-reservoir microchip were achieved in vitro. Chronic pulsatile release was subsequently performed in vivo. Comparison of in vitro and in vivo data reveals that pharmacokinetics were controlled by the rate of release from the device.

Clinically relevant formulations of hPTH(1-34) for use with implantable multi-reservoir devices are achievable.

A new technique, hydrodynamic fingerprinting, is presented for the characterization and study of expandable latex dispersions on the basis of their hydrodynamic behavior. In the hydrodynamic fingerprint the hydrodynamic size as measured by photon correlation spectroscopy is presented as a function of two colloidal state variables simultaneously, pH and pλ, where pλ is the logarithm of the conductivity. Hydrodynamic fingerprinting is applied to two methyl methacrylate-ethyl acrylate latexes, one of which contains 2% acrylic acid. It is shown that hydrodynamic fingerprinting can be used to measure expansion properties of colloids, time effects in colloidal solutions, colloidal stability, and the differences in chemistry of the colloid-solution interface. Experimental SectionMaterials. The copolymer latexes were prepared at Union Carbide. The acidic latex, designated latex A170, is an ethyl acrylate, methyl methacrylate, acrylic acid copolymer latex. The composition of the monomer feed in the latex polymerization was 40 parts methyl methacrylate, 58 parts ethyl acrylate, and 2 parts acrylic acid, which was fed over the last half of the feed. Monomer was fed continuously into the reaction vessel at 80 °C in the presence of ammonium persulfate initiator and Aerosol OT. 17 The mean particle diameter for latex A170, determined with the Microtrac UPA particle sizer, was 170 nm, with a standard deviation in the particle size distribution of 23 nm. The Microtrac measurements were made on the concentrated form of the latex, for which the solids weight fraction was 0.37 and the pH was approximately 3.Latex NA143 is the acid-free counterpart of latex A170. The polymerization procedure was the same as that used for latex A170, except that the composition of the monomer feed was 40 parts methyl methacrylate and 60 parts ethyl acrylate. No acrylic acid was present. Latex NA143 was found by the Microtrac UPA to be 143 nm in diameter with a standard deviation of 19 nm. The measurement was made at a pH of 3 and a solids weight fraction of 0.36. Latex NA143 was prepared as a control and was expected to be of constant size.All supporting solutions used for sample preparations were aqueous. The water to be used for solution preparations was distilled twice, the second time in an all glass apparatus. All of the salts were recrystallized from filtered aqueous solutions. The salts were KCl, LiCl, and NaCl, the acid was HCl, and the bases used were KOH, NaOH, and LiOH.