Search PubMed⌕ Search

Biomedical subjects

B Joos

Publications and source records attributed to B Joos.

29 records · Page 2Linked to original sources
PubMed1987

Determination of teicoplanin concentrations in serum by high-pressure liquid chromatography.

An isocratic reversed-phase high-pressure liquid chromatographic method for the determination of six components of the teicoplanin complex in biological fluid was developed. By using fluorescence detection after precolumn derivatization with fluorescamine, the assay is specific and highly sensitive, with reproducibility studies yielding coefficients of variation ranging from 1.5 to 8.5% (at 5 to 80 micrograms/ml). Response was linear from 2.5 to 80 micrograms/ml (r = 0.999); the recovery from spiked human serum was 76%. An external quality control was performed to compare this high-pressure liquid chromatographic method (H) with a standard microbiological assay (M); no significant deviation from slope = 1 and intercept = 0 was found by regression analysis (H = 1.03M - 0.45; n = 15).

Anti-Bacterial Agents↗
PubMed1985

Effect of standard breakfast on drug absorption and multiple-dose pharmacokinetics of ciprofloxacin.

Ciprofloxacin was administered to 10 volunteers, who received seven oral doses of 250 mg each at 12-h intervals. Volunteers alternately fasted (F) or received a standard breakfast (B) before the morning dose. Pharmacokinetic parameters were derived from high-pressure liquid chromatography data from samples taken after the first and seventh doses and were analyzed in addition for differences caused by food intake. A significant (P less than 0.05) influence of the standard breakfast on the time to the peak was observed. Peak levels (+/- standard deviation) after the first and seventh doses averaged F (fasting): 1.35 +/- 0.17, B (breakfast): 1.02 +/- 0.28 micrograms/ml, and F: 1.41 +/- 0.32, B: 1.17 +/- 0.5 micrograms/ml, respectively. Mean trough concentrations after the first and seventh doses were F: 0.10 +/- 0.03, B: 0.14 +/- 0.03 micrograms/ml, and F: 0.16 +/- 0.05, B: 0.14 +/- 0.04 microgram/ml, respectively. As with the peak, trough concentrations were not affected significantly by food intake or by accumulation over the study period. Breakfast equally did not affect the terminal half-lives, which averaged F: 3.97 +/- 0.67, B: 4.35 +/- 0.88 h after the first dose and F: 4.64 +/- 0.91, B: 3.72 +/- 0.84 h after the seventh dose. Twelve-hour urinary recovery measured by high-pressure liquid chromatography averaged F: 31, B: 30% for the first dose and, in spite of a possible carry-over from the sixth dose, decreased to F: 25, B: 28% after the seventh dosing interval. When measured by bioassay, an increase of urinary recovery between the first dose (F: 38, B: 38%) and the seventh dose (F: 45, B: 45%) was observed. These differences suggest induction of drug metabolism with repeated doses. Ciprofloxacin was well tolerated by the volunteers.

Adult↗
PubMed1985

Comparison of high-pressure liquid chromatography and bioassay for determination of ciprofloxacin in serum and urine.

Ciprofloxacin was given orally to 10 healthy volunteers for seven consecutive doses of 250 mg every 12 h. Serum and urine samples were collected at distinct times between 0 and 96 h and analyzed both by high-pressure liquid chromatography and by a microbiological assay. The detection limits were 0.006 and 0.03 microgram/ml, respectively. For each method, imprecision coefficients of variation were less than 6.1% at various concentrations in serum and urine. The means +/- standard deviations of the absolute values of the relative differences between the two methods were 9.3 +/- 6.8% (n = 225) for serum samples and 58.5 +/- 50.4% (n = 70) for urine samples. Comparison of the concentrations in serum measured with high-pressure liquid chromatography and bioassay by regression analysis yielded a slope which was not significantly different from 1.0 (99.9% confidence limits: 0.984 less than slope less than 1.035). In urine, however, the bioassay results were markedly higher than the high-pressure liquid chromatography values (1.327 less than slope less than 1.698), which indicates the presence of antimicrobially active metabolites. The cumulative 12-h urinary recovery after the first and seventh doses averaged 30.2 +/- 8.5 and 26.4 +/- 4.6%, respectively, by high-pressure liquid chromatography, whereas with bioassay 38.2 +/- 5.9 and 45.5 +/- 5.9% activity was recovered. Protein binding appeared to be neither concentration nor pH dependent and averaged 21.9 +/- 4.1%.

Adult↗
PubMed1984

Variability of ceftriaxone pharmacokinetics in hospitalized patients with severe infections.

The pharmacokinetic behavior of ceftriaxone was studied in 60 patients with severe community- or hospital-acquired infections. Serum concentrations one to three hours after a 30-minute intravenous infusion appeared to be dose related. The mean two-hour levels were 110, 138, and 146 mg/liter, and trough values averaged 54.9, 28.5, and 16.1 mg/liter after doses of 1.0, 2.0, and 3.0 g, respectively. At 24 hours, values were at least 10 mg/liter in all but seven patients. The serum half-life of ceftriaxone in all patients and for all dosage regimens varied from 3.5 to 59.4 hours. In patients with normal renal function (serum creatinine 1.30 mg/dl or less) the mean half-life was 8.2 hours. In patients with moderate (creatinine 1.34 to 1.83 mg/dl) and severe (creatinine 2.40 mg/dl or greater) renal insufficiency, the mean serum half-lives were 12.8 and 12.4 hours, respectively. In six patients who had severe renal failure and concomitant hepatic dysfunction, half-lives ranged from 23.7 to 59.4 hours. Single daily doses of 2.0 g of ceftriaxone produced adequate serum concentrations. Dose reductions are recommended in patients with both renal and hepatic dysfunction.

Adolescent↗
PubMedDate not supplied

Ciprofloxacin-induced hematuria.

We used ciprofloxacin, a quinolone-derivative, to treat a lung infection due to Pseudomonas aeruginosa in an adult cystic fibrosis patient. On three different occasions the use of ciprofloxacin was associated with the development of an asymptomatic hematuria with red blood cell casts. The mechanism responsible for this hematuria is presently unknown, but clinicians should be aware of this potential adverse effect of ciprofloxacin.

Adult↗
PubMedDate not supplied

Variability of serum concentrations of trimethoprim and sulfamethoxazole during high dose therapy.

Serum kinetics of trimethoprim and sulfamethoxazole were studied in 23 patients during oral and i.v. treatment of Pneumocystis carinii pneumonia. Daily doses of 15-22 mg/kg trimethoprim and 75-110 mg/kg sulfamethoxazole were given every 6 h. Despite administration of a loading dose of twice the regular dose, serum trough concentrations continuously rose from 12 h to 96 h by 63% for trimethoprim and 102% for sulfamethoxazole. After 4-6 days mean trough concentrations of trimethoprim and sulfamethoxazole were 7.7 +/- 3.0 and 198 +/- 74 mg/l, with individual values of < 4.6 and < 103 mg/l in two patients and > 11.4 and > 307 mg/l in two others. Patients treated orally or i.v. had similar serum levels. However, large interindividual variability was observed despite weight-specific dosing. Administration of a loading dose did not prevent accumulation of serum levels of trimethoprim and sulfamethoxazole over several days of treatment.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Effects of ambient oxygen tension on flight performance, metabolism, and water loss of the honeybee.

Although the metabolic rate of resting insects is relatively insensitive to atmospheric O2 tensions, metabolic rates during flight increase by 20- to 100-fold above resting levels. In this study we test whether O2 delivery limits metabolic rate during unladen hovering flight of the honeybee, Apis mellifera. Below 10 kPa PO2, wing-stroke frequency decreased, and at 5 kPa, bees could not fly. However, for PO2's ranging from 39 to 10 kPa, metabolic rate and wing-stroke frequency were unaffected by PO2. Evaporative water loss rates increased by 40% at the lowest O2 tensions, which suggests that flying honeybees compensated for decreasing ambient PO2 by modulating convective ventilatory flow. Under normal sea-level conditions, O2 delivery does not limit flight metabolic rate in unladen, hovering honeybees and does not limit maximal metabolic rate. At altitudes above 3,000 m, the convective component of O2 delivery may, however, limit flight metabolic rate and flight capacity in honeybees.

Animals↗