Geotrichum septicemia

Although disseminated geotrichosis is an unusual disease (to our knowledge, only six cases have been reported), Geotrichum candidum is not a very virulent fungus. In our case, there was neutrophillic phagocytosis of the arthrosphores of G candidum, with rapid clearance of the fungus from the plasma of a chronically ill patient whose immune defenses were still intact.     

Strategies for the assessment of matrix effect in quantitative bioanalytical methods based on HPLC-MS/MS

In recent years, high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection has been demonstrated to be a powerful technique for the quantitative determination of drugs and metabolites in biological fluids. However, the common and early perception that utilization of HPLC-MS/MS practically guarantees selectivity is being challenged by a number of reported examples of lack of selectivity due to ion suppression or enhancement caused by the sample matrix and interferences from metabolites. In light of these serious method liabilities, questions about how to develop and validate reliable HPLC-MS/MS methods, especially for supporting long-term human pharmacokinetic studies, are being raised. The central issue is what experiments, in addition to the validation data usually provided for the conventional bioanalytical methods, need to be conducted to confirm HPLC-MS/MS assay selectivity and reliability. The current regulatory requirements include the need for the assessment and elimination of the matrix effect in the bioanalytical methods, but the experimental procedures necessary to assess the matrix effect are not detailed. Practical, experimental approaches for studying, identifying, and eliminating the effect of matrix on the results of quantitative analyses by HPLC-MS/MS are described in this paper. Using as an example a set of validation experiments performed for one of our investigational new drug candidates, the concepts of the quantitative assessment of the "absolute" versus "relative" matrix effect are introduced. In addition, experiments for the determination of, the "true" recovery of analytes using HPLC-MS/MS are described eliminating the uncertainty about the effect of matrix on the determination of this commonly measured method parameter. Determination of the matrix effect allows the assessment of the reliability and selectivity of an existing HPLC-MS/MS method. If the results of these studies are not satisfactory, the parameters determined may provide a guide to what changes in the method need to be made to improve assay selectivity. In addition, a direct comparison of the extent of the matrix effect using two different interfaces (a heated nebulizer, HN, and ion spray, ISP) under otherwise the same sample preparation and chromatographic conditions was made. It was demonstrated that, for the investigational drug under study, the matrix effect was clearly observed when ISP interface was utilized but it was absent when the HN interface was employed.     

Structure-based design of inhibitors specific for bacterial thymidylate synthase

Thymidylate synthase is an attractive target for antiproliferative drug design because of its key role in the synthesis of DNA. As such, the enzyme has been widely targeted for anticancer applications. In principle, TS should also be a good target for drugs used to fight infectious disease. In practice, TS is highly conserved across species, and it has proven to be difficult to develop inhibitors that are selective for microbial TS enzymes over the human enzyme. Using the structure of TS from Lactobacillus casei in complex with the nonsubstrate analogue phenolphthalein, inhibitors were designed to take advantage of features of the bacterial enzyme that differ from those of the human enzyme. Upon synthesis and testing, these inhibitors were found to be up to 40-fold selective for the bacterial enzyme over the human enzyme. The crystal structures of two of these inhibitors in complex with TS suggested the design of further compounds. Subsequent synthesis and testing showed that these second-round compounds inhibit the bacterial enzyme at sub-micromolar concentrations, while the human enzyme was not inhibited at detectable levels (selectivities of 100-1000-fold or greater). Although these inhibitors share chemical similarities, X-ray crystal structures reveal that the analogues bind to the enzyme in substantially different orientations. Site-directed mutagenesis experiments suggest that the individual inhibitors may adopt multiple configurations in their complexes with TS.     

Pharmacokinetics of nicotine carbomer enemas: a new treatment modality for ulcerative colitis

BACKGROUND: Ulcerative colitis is largely a disease of nonsmokers, and transdermal nicotine is of therapeutic value in the active disease. Because side effects are common, we developed a topical enema formulation of nicotine. OBJECTIVE: To study the pharmacokinetics of nicotine complexed with a polyacrylic carbomer and administered by enema to eight healthy volunteers and to eight patients with active ulcerative colitis, verified sigmoidoscopically. PATIENTS AND METHODS: All 16 subjects were nonsmokers. The mean age for normal subjects was 33 years; the mean for patients with ulcerative colitis was 60 years. Median stool frequency for patients with ulcerative colitis was four daily. Patients were taking 5-amino salicylic acid compounds and five were taking oral prednisolone (median dose, 12 mg daily). Nicotine, 6 mg, complexed with carbomer 974P, 400 mg, was administered in a 100 ml enema after an overnight fast, with serial blood measurements taken over 8 hours. Serum nicotine and cotinine were measured by gas liquid chromatography. Area under the concentration-time curves were calculated by the trapezoidal method, and the terminal elimination half-life was derived by extrapolation of the log-linear terminal phase. RESULTS: With the exception of nicotine time to reach peak concentration, which was longer in patients (median of 60 minutes compared with 45 minutes; p < 0.005), other comparisons between normal subjects and patients showed no statistically significant difference, although there was considerable inter-subject variation. Maximum concentration of nicotine, 8.1 +/- 3.5 ng/ml, in the 16 subjects occurred after a median of 60 minutes (range, 30 to 180 minutes); maximum cotinine concentrations of 60.4 +/- 11.5 ng/ml occurred after 4 hours. Side effects in five subjects were mild (four subjects) or moderate (one subject) and included lightheadedness, nausea, and headache; these five subjects were female lifelong nonsmokers of low body weight. CONCLUSION: Because most of the active ingredient of nicotine is converted to continine on the first pass through the liver, substantial concentrations can be achieved at the site of disease with only modest rises in serum nicotine, which are responsible for side effects; cotinine has low pharmacologic activity. Topical administration of nicotine may be useful treatment for distal ulcerative colitis.