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Biomedical subjects

T J Janssen

Publications and source records attributed to T J Janssen.

14 recordsLinked to original sources
PubMed2000

Visual metrics: discriminative power through flexibility.

An important stage in visual processing is the quantification of optical attributes of the outside world. We argue that the metrics used for this quantification are flexible, and that this flexibility is exploited to optimise the discriminative power of the metrics. We derive mathematical expressions for such optimal metrics and show that they exhibit properties resembling well-known visual phenomena. To conclude, we discuss some of the implications of flexible metrics for visual identification.

Discrimination, Psychological↗
PubMed1992

Bioavailability of lithium from lithium citrate syrup versus conventional lithium carbonate tablets.

The bioavailability of lithium citrate syrup was compared with that of regular lithium carbonate tablets in 18 healthy male human volunteers. Blood samples were collected up to 48 h after dosing. Lithium serum concentrations were determined by means of AAS. The absorption rate following oral administration of the syrup was greater (tmax 0.8 h) than following administration of regular tablets (tmax 1.4 h). Maximum lithium serum concentrations, however, were only about 10 per cent higher after syrup dosing and serum concentrations resulting from syrup and tablets were almost superimposable from 2 h after dosing. The terminal half-life of lithium was found to be 22 h after syrup as well as after tablet dosing. No side-effects were observed during the study. The bioavailability of lithium from syrup relative to tablets was found to be bioequivalent with respect to the maximum lithium serum concentration and the extent of drug absorption (AUC).

Administration, Oral↗
PubMed1990

Pharmacokinetics of rectal diclofenac and its hydroxy metabolites in man.

Diclofenac 100 mg suppository is well absorbed from the gastrointestinal tract of six human volunteers. Plasma concentrations of 4'-hydroxydiclofenac and diclofenac could be measured; the concentrations of the three other metabolites were below the detection limit of the HPLC analysis. The apparent half-lives of diclofenac and 4'-OH-diclofenac are, respectively 1.3 +/- 0.3 h and 4.3 +/- 1.0 h. When the t 1/2 values are derived from the renal excretion rate-time profiles, they are as follows: diclofenac 1.8 +/- 0.9 h, 3'-OH-, and 5-OH-diclofenac 2.3 +/- 1.0 h and 2.5 +/- 0.4 h, respectively, while those of 4'-OH- and 4',5-diOH-diclofenac are, respectively 3.6 +/- 0.5 h and 3.1 +/- 1.3 h. Diclofenac is excreted for 13.6 +/- 6.5%, its renal clearance (Clr) = 3.23 +/- 1.03 ml/min. The main metabolite excreted in the urine is 4'-OH-diclofenac (27.2 +/- 12% dose; Clr = 6.14 +/- 4.04 ml/min). The total body clearance of the parent drug and the apparent total body clearance of the main metabolite are similar, 28.0 +/- 11.9 l/h and 27.5 +/- 10.9 l/h.

Administration, Rectal↗
PubMed1989

Drug-drug interactions affecting fluoroquinolones.

In a three-week study, the metabolism of the bronchodilator theophylline and its major metabolites formed by C-8 oxidation (1,3-dimethyluric acid) and N-demethylation (3-methylxanthine and 1-methyluric acid) was investigated in two healthy volunteers. Metabolic studies were performed following intravenous infusion of a single 6 mg/kg dose of aminophylline. During Week 1, theophylline was given alone (blank period), and during Weeks 2 and 3 it was given during oral coadministration of ofloxacin and enoxacin, respectively. Dosage of each quinolone was 200 mg twice daily for four days, starting three days prior to the theophylline infusion. During enoxacin coadministration, elimination half-lives of theophylline increased from 8.7 to 17.4 hours and from 6.1 to 12.3 hours, respectively. Total body clearance of theophylline decreased in both volunteers, whereas renal clearance did not alter. From this it was concluded that the decreased elimination results from a reduced metabolic clearance. During enoxacin coadministration, the formation of the metabolites 1-methyluric acid and 3-methylxanthine clearly was decreased, whereas the formation of 1,3-dimethyluric acid was less affected compared with the blank period. Interference with theophylline disposition by enoxacin is based predominantly on inhibition of microsomal N-demethylation. Ofloxacin comedication did not cause a change in the plasma parameters or renal excretion of theophylline and its metabolites compared with the blank period.

Adult↗
PubMed1989

Decreased plasma albumin concentration results in increased volume of distribution and decreased elimination of midazolam in intensive care patients.

The pharmacokinetic parameters of 16 patients in the intensive care unit, sedated with midazolam, were evaluated. A large variation was observed in the plasma concentration of midazolam and between the plasma concentration of midazolam and its metabolite 1-hydroxymethylmidazolam glucuronide. The plasma albumin concentration governs the volume of distribution of midazolam. Decreased plasma albumin concentration (25 gm/L) results in an increased volume of distribution and a decreased elimination rate of midazolam. The observed plasma concentration ratio between the parent drug and its metabolite 1-hydroxymethylmidazolam glucuronide is governed by the variables of protein binding, the metabolic rate of midazolam, and the renal clearance of the glucuronide metabolite itself (which can be considered as a measure of the kidney function of the patient).

Adult↗
PubMed1988

The influence of ofloxacin and enoxacin on the metabolic pathways of theophylline in healthy volunteers. A pilot study.

The pharmacokinetic parameters of theophylline and its major metabolites were measured in two healthy volunteers, after the administration of theophylline alone and during co-medication with ofloxacin, 200 mg twice daily, or enoxacin, 200 mg twice daily. During enoxacin co-medication, elimination half-lives of theophylline increased from 8.7 h to 17.4 h and from 6.1 to 12.3 h, respectively. As the renal clearance of theophylline did not change, the decreased elimination of theophylline during enoxacin co-medication must result from a reduced metabolic clearance. Enoxacin co-medication caused a clearly decreased formation of the metabolites 1-methyluric acid and 3-methylxanthine, formed by N-demethylation, whereas the C-8 oxidation of theophylline was less influenced compared to the blank. Enoxacin's interference with the theophylline disposition is predominantly based on the inhibition of the microsomal N-demethylation. Ofloxacin co-medication did not induce a change in the plasma parameters or renal excretion of theophylline and its metabolites.

Adult↗
PubMed1988

Bioavailability of ambroxol sustained release preparations. Part II: Single and multiple oral dose studies in man.

The bioavailability of a new ambroxol sustained release preparation (75 mg) based on a dialyzing membrane for controlled release was studied in healthy volunteers after single and multiple oral dose in comparison with a standard sustained release formulation in a cross-over study under carefully controlled conditions. Plasma concentrations of ambroxol were measured by means of a HPLC method. Based on AUC data both preparations are found to be bioequivalent, but show different plasma concentration profiles. The test preparation showed a more pronounced sustained release profile than the reference preparation (single dose) resulting in significantly higher steady state plasma levels.

Adult↗
PubMed1988

The pharmacokinetic profile of naproxen suppository in man.

After a rectal dose of 500 mg in a suppository, naproxen is 6-O-demethylated (20%) and glucuronidated (40%), the metabolites are subsequently excreted renally. The elimination half-life is 15.2 +/- 2.6 h. Ten out of 22 subjects show biphasic elimination kinetics with half-lives of 7 and 15 h, respectively. There is a wide range in the percentage of the dose that is glucuronidated and demethylated (20-70%). This variation does not deviate from a normal distribution.

Adult↗
PubMed1986

Clinical pharmacokinetics of carbamazepine and its epoxy and hydroxy metabolites in humans after an overdose.

In five cases of carbamazepine (CBZ) intoxication, the time curves of the plasma concentration and of the renal excretion rate of carbamazepine and its metabolites carbamazepine 10,11-epoxide (CBZ-epoxide) and trans-10,11-dihydro-10,11-dihydroxy-CBZ (CBZ-diol) were measured. Pseudo-steady-state or plateau-like plasma concentration-time curves were observed when doses of 12 or 18 g of CBZ were ingested. Hemoperfusion lowers the plasma concentration of CBZ and its metabolites by affecting the half-life. The effect of hemoperfusion is reduced by the continuous absorption from the gastrointestinal tract and redistribution from the tissues. The renal clearances of CBZ and of CBZ-epoxide are low (1 and 8 ml/min, respectively); both are flow dependent. The renal clearance of CBZ-diol is approximately 160-350 ml/min and is independent of the urine flow. Although urine stimulation increases the renal clearance of CBZ by 100%, the overall amount excreted increases only 1-2% of the dose. Protein binding of CBZ is approximately 80%, of CBZ-epoxide 50%, and of CBZ-diol 70%.

Adult↗
PubMed1983

The effect of the molecular structure of closely related N1-substituents of sulfonamides on the pathways of elimination in man. The acetylation-deacetylation equilibrium and renal clearance related to the structure of sulfadiazine, sulfamerazine and sulfadimidine.

Sulfadiazine, sulfamerazine, sulfadimidine and their corresponding N4-acetyl derivatives were administered to man. The percentages of acetylation and deacetylation, protein binding, half-lives of elimination and apparent and true renal clearance values were measured. Methyl substitution in the N1-pyrimidine ring favours acetylation by an additional N-acetyltransferase isoenzyme present in 'fast' acetylators only. Methyl substitution in the N1-pyrimidine ring favours renal clearance of the N4-acetylsulfonamide derivatives. The N1-substituent probably reinforces the binding of the N4-acetyl group to the active tubular transport mechanism. The renal clearance of these sulfonamides is not dependent on the structure of the N1-substituent.

Acetylation↗
PubMed1981

Reimbursement for durable medical equipment.

The use of durable medical equipment in the home, while not a recent development, was formally recognized by the Congress with the passage of the original Medicare legislation. Since that time the statute has been amended to provide for a more workable, economical, and desirable interface among the administrative, supplier, and user communities. To assist in achieving this end, a research project was begun in October 1976 that has yielded data on Federal expenditures for reimbursement of rental and purchase costs of this equipment. Data were extracted from the Beneficiary History Files of five Part B carrier in 11 geographic areas covering the period 1976-1977. These data included the type of equipment; rental or purchase decision; submitted charges; allowed charges, and reimbursement by Medicare. Some 1.3 million individual records, from approximately 400,000 beneficiaries, were tabulated and analyzed. The exploratory nature of this research has provided a benchmark for future research and policy considerations. This article details various characteristics of the data collected for the project.

Equipment and Supplies↗