[Discrimination of Hearing Disorder by Means of CLS and OAE in Vestibular Schwannoma]. / KLS und OAE zur Differenzierung der Hörstörung bei Vestibularisschwannom.

INTRODUCTION: Currently a sensitive early diagnosis of small vestibular schwannoma is only possible by using magnetic resonance imaging (MRI). OBJECTIVES: The main objective was a differentiation of the cochlear and retrocochlear component of small vestibular schwannoma with the help of categorial loudness scaling (CLS) and the growth function of otoacoustic emissions (DPOAE I/O-functions). MATERIAL AND METHODS: 34 patients (gr. 1: 17 patients with vestibular schwannoma ≤15 mm, gr. 2: 17 matched patients with an inner ear hearing disorder) were examined. Besides audiological standard procedures they also underwent CLS according to the Würzburger auditory field and a generation of DPOAE I/O-functions was conducted on the probands. RESULTS: The gradients of the loudness growth function as part of the CLS and the DPOAE I/O-functions showed with few exceptions [500 Hz at 0-10 dB HL during CLS (p=0,040)] no significant differences between the groups (all p>0.05). A recruitment verification with the help of CLS was possible for tumors starting at a size of 5.45,mm at 3,000 and 4,000 Hz, respectively for tumors exceeding the size of 6.85 mm at 6,000 Hz with 100% sensitivity but only low specificity. CONCLUSIONS: A differentiation between a vestibular schwannoma and a mere cochlear hearing disorder with only the help of CLS and DPOAE I/O-functions is not possible. The results corroborate the thesis of an additional cochlear component even in small vestibular schwannoma. The implementation of CLS to determine cochlear deficits linked to vestibular schwannoma seems to be medically sensible if the tumor size exceeds 5 mm. According to the diagnostic method used to determine vestibular schwannoma MRI remains the first choice procedure.

Determination of linezolid in human serum and urine by high-performance liquid chromatography.

An HPLC method is described for the determination of the new oxazolidinone antibiotic linezolid (I) in human biofluids. After precipitation of serum proteins with perchloric acid the protein free supernatant was separated by isocratic reversed-phase chromatography on a Nucleosil-100 5C18 column. The mobile phase consisted of a mixture of acetonitrile: sodium acetate buffer: water (180:100:720, v/v) adjusted to pH 3.7. Urine was diluted with aqueous buffer solution. The column eluate was monitored at 250 nm. Validation of the method yielded satisfactory results for serum (and urine); detection limit 0.07 mg/l (2.4), lower limit of quantitation 0.14 mg/l (4.7), linear range 20 mg/l (500), imprecision within series (c.v.) 1.8-2.5% (0.8-1.0), imprecision between series (c.v.) 1.8-9.3 (0.4-9.3), recovery 99-102% (93-103). Comparison of HPLC results with results obtained using a quantitative microbiological assay yielded acceptable agreement both for serum and urine. The method was successfully used in a pharmacokinetic study with human volunteers.

Determination of a new cephalosporin, SCE-2787, in serum and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of a new-broad spectrum cephalosporin (I, SCE-2787) has been developed. The analyte was extracted from serum by precipitation of serum proteins with acetonitrile. Acetonitrile was extracted from the protein-free supernatant by dichloromethane. Urine was simply diluted with mobile phase. Separation was performed by ion-pair chromatography on a reversed-phase column (Nucleosil 5C18; 125 mm x 4.0 mm I.D.; 5 microns average particle size). The guard column was Perisorb RP18 (30 mm x 4.0 mm I.D.; 30-40 microns particle size). The mobile phase was acetonitrile-buffer solution containing 15 mM heptanesulphonic acid (pH 3.2) (4.5:95.5, v/v). Detection was performed at 235 nm with a diode-array detector, which also served to record ultraviolet spectra. The assay was sensitive, precise, accurate and fast. Specificity was controlled by on-line recording the ultraviolet spectrum of I and also by enzymic degradation with beta-lactamase. No interferences were observed during the analysis of serum and urine of healthy volunteers in pharmacokinetic studies.

Determination of sparfloxacin in serum and urine by high-performance liquid chromatography.

A specific and sensitive analytical method for the determination of sparfloxacin in serum and urine is described. Serum proteins are removed by precipitation with acetonitrile after the addition of ofloxacin as an internal standard. The supernatant solvent is evaporated in a vacuum concentrator and the dry residue is redissolved in the mobile phase. Separation is performed on a cation-exchange column (Nucleosil 100 5SA, 125 x 4.0 mm I.D., 5 microns particle size) protected by a guard column (Perisorb RP-18, 30 x 4.0 mm I.D., 30-40 microns particle diameter). The mobile phase consisted of 750 ml of acetonitrile and 250 ml of 100 mmol/l phosphoric acid (v/v) to which sodium hydroxide had been added. The final concentration of sodium was 23 mmol/l and the pH was 3.82. Sparfloxacin and ofloxacin were determined by spectrofluorimetry (excitation wavelength 295 nm; emission wavelength 525 nm). The flow-rate was 1.5 ml/min and the retention times were 4.7 (sparfloxacin) and 8.0 (ofloxacin) min. Validation of the method yielded the following results for serum: detection limit 0.05 mg/l; precision between series 10.4-3.6%; recovery 99.5-100.0%; comparison with a microbiological assay c(bioassay) = 1.035c(HPLC) - 0.06. The test organism was Bacillus subtilis ATCC 6633. For urine the results were: detection limit 0.5 mg/l; precision between series 7.8-5.0%; recovery 97.0-97.8%; method comparison c(bioassay) = 1.092c(HPLC) - 1.09. No interferences were observed in human volunteers. The method can also be applied to stool samples.

Determination of cefmenoxime in human body fluids by high-performance liquid chromatography.

A rapid and reliable method for the quantitative determination of cefmenoxime in serum and urine by reversed phase high-performance liquid chromatography is described. Serum was deproteinized with acetonitrile. Urine was diluted with dilute acetic acid (17.5 mmol/l). Separations were performed in isocratic mode using a C18 type column and a precolumn packed with Perisorb RP/8. The eluant consisted of a mixture of acetonitrile and 25.0 mmol/l acetic acid in a ratio of 32/69 (vol/vol). In normal subjects cefmenoxime was well separated from endogenous compounds and various added drugs. Its complete separation was confirmed by selective degradation with beta-lactamase from Bacillus cereus and UV spectrophotometry. The detection limit was 0.3 mg/l at a detection wave-length of 254 nm. Peak areas gave linear results up to concentrations of 500 mg/l. Within-batch precision (coefficient of variation) ranged from 1.1 to 6.2%. Recovery rates varied from 99.0 to 103.3%. Results of a standard microbiological assay correlated well with those obtained by the present HPLC method. Eight healthy volunteers who were given a single intravenous dose of 1 g cefmenoxime excreted 86.3 +/- 5.8% of the unchanged drug within 24 h in urine.