Radiation dosimetry estimates for the PET serotonin transporter probe 11C-DASB determined from whole-body imaging in non-human primates.

The radiotracer 3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile labelled in the N-methyl position (11C-DASB) is a selective radioligand for the in vivo quantification of serotonin transporters (SERTs) using positron emission tomography (PET). The current study quantified the distribution of activity in two rhesus monkeys after the injection of approximately 333 MBq (9 mCi) 11C-DASB. Whole-body images were acquired at 22 time points for a total of 120 min following injection of the radioligand. Source organs were identified at each time point from both tomographic images (using multiple regions of interest on each tomograph for each organ) and a single planar image (using a single region of interest for each organ). The peak activities in planar images in the five identified source organs (expressed as per cent injected dose (ID)) were lungs (24% ID at 1.5 min), kidneys (6.5% ID at 4 min), liver (8% ID at 3 min), brain (4% ID at 5 min) and spleen (0.42% ID at 3 min). Mono-exponential fitting of activity overlying the bladder suggested that approximately 14% of activity was excreted via the urine. The radiation burden to the body was calculated from residence times of these source organs and then scaled to corresponding human values. The calculated effective dose from tomographic and planar images was 6.0 and 6.4 microGy x MBq(-1) (22.3 and 23.7 mrad x mCi(-1)), respectively. The planar analysis was much easier to perform, and generally yielded slightly higher (i.e., more conservative) estimates of radiation burden than the tomographic analysis. The estimated radiation burden of 11C-DASB is relatively modest and would allow multiple scans per research subject per year.

Oxidative degradation study of nitrendipine using stability indicating, HPLC, HPTLC and spectrophotometric method.

The objective of this study is to develop validated stability indicating HPLC (A), HPTLC (B) and spectrophotometric (C) method for the estimation of nitrendipine. The stability indicating capability of the assays is proved using forced degradation, by exposing drug solution to sunlight, acidic and alkaline medium. The chromatogram and UV spectrum showed nitrendipine well resolved from the degradation product. Degradation of drug is found faster in acidic (0.1 N hydrochloric acid) medium as compared to alkaline (0.1 N sodium hydroxide) medium at 100 degrees C. Also, photodegradation is studied, with special emphasis on the effect of solvents like methanol (1), chloroform (2), dichloromethane (3), acetone (4) and ethyl acetate (5), on the rate of photodegradation. The degradation of title compound followed first order kinetics in all cases. Estimation of the drug is carried out by the stability indicating methods mentioned, using one point standardization within the linearity range of interest. The methods are compared in respect of performance precision and accuracy. Major route of degradation in all cases is found to be oxidation and degradation product is confirmed as dehydronitrendipine by the use of relevant UV, IR and 1H NMR spectrometry.