Objectives: The antiretroviral efavirenz decreases serum levonorgestrel (LNG) concentrations among LNG implant users. Our primary objective was to compare LNG concentrations between LNG implant users who were or were not taking efavirenz, for up to 33 months after implant initiation. Our secondary objective was to evaluate the pregnancy rate among LNG implant users on efavirenz.

The diffusion coefficients of sonicated calf-thymus DNA and an oligonucleotide fragment have been measured via an electrochemical strategy. The complex [Os(bpy)(2)(dppz)](2+) (bpy = 2, 2'-bipyridine, dppz = dipyridophenazine) has been synthesized as a simple, single-electron intercalating redox couple. The free complex undergoes a kinetically reversible single-electron oxidation to the corresponding Os(III) complex at an applied potential of 0.72 V vs Ag/AgCl, which is insufficient to achieve electrocatalytic DNA oxidation. Upon addition of DNA, the complex binds via intercalation to a two-base-pair site with binding constant K-b = 4 x 10(6) M(-1), as reflected in the changes in the photophysics of the Os(II)-dppz chromophore. Changes in the voltammetric current upon binding reveal a slight limitation on heterogeneous charge-transfer kinetics (k = 5 x 10(-4) cm s(-1)) and a dramatic limitation on mass transfer of bound complexes. Normal pulse voltammetry gives diffusion coefficients of sonicated calf-thymus DNA and (dA)(20).(dT)(20) equal to 2.0 x 10(-6) and 1.2 x 10(-6) cm(2) s(-1), respectively; each agrees with values reported for light-scattering experiments and theoretical calculation.