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Biomedical subjects

K Linnet

Publications and source records attributed to K Linnet.

At least 37 records · Page 2Linked to original sources
PubMed1997

Metabolism of the tricyclic antidepressant amitriptyline by cDNA-expressed human cytochrome P450 enzymes.

The metabolism of amitriptyline was studied in vitro using cDNA-expressed human cytochrome P450 (CYP) enzymes 1A2, 3A4, 2C9, 2C19, 2D6 and 2E1. CYP 2C19 was the most important enzyme with regard to the demethylation of amitriptyline, the quantitatively most important metabolic pathway. CYP 1A2, 3A4, 2C9 and CYP 2D6 also participated in the demethylation of amitriptyline. CYP 2D6 was the sole enzyme mediating the hydroxylation of amitriptyline, and (E)-10-OH-amitriptyline was exclusively produced. CYP 2E1 did not metabolize amitriptyline. Concerning the quantitative relations, CYP 2C19 and 2D6 exhibited high affinities with Km values in the range of 5-13 mumol/l, whereas the affinities of 1A2, 3A4 and 2C9 were somewhat lower with Km values ranging from 74 to 92 mumol/l. CYP 2C19 displayed the highest reaction capacity per mole with Vmax equal to 475 mol h-1 (mol CYP)-1. The other enzymes had Vmax values in the range of 90-145 mol h-1 (mol CYP)-1. Allowing for the typical relative distribution of amounts of CYP enzymes in the liver, a simulation study suggested that, at therapeutic doses, on average about 60% of the metabolism depended on CYP 2C19. At toxic doses, CYP 2C19 is expected to be saturated, and CYP 3A4 may now play a dominant role in the metabolism.

Amitriptyline↗
PubMed1997

Hydroxylation and demethylation of the tricyclic antidepressant nortriptyline by cDNA-expressed human cytochrome P-450 isozymes.

The metabolism of nortriptyline was studied in vitro using cDNA-expressed human cytochrome P450 isozymes 1A2, 3A4, 2C19, and 2D6, CYP2D6 was the sole isozyme mediating hydroxylation of nortriptyline, the quantitatively most important metabolic pathway, and only (E)-10-OH-nortriptyline was formed. CYP2D6, 2C19, and 1A2, mentioned in decreasing order of significance, mediated the demethylation reaction of nortriptyline, whereas 3A4 did not participate in the metabolism of nortriptyline. Concerning the quantitative relations, CYP2D6 exhibited a high affinity with respect to hydroxylation and demethylation (K(m) 0.48-0.74 mumol/l), a high hydroxylation capacity (Vmax 130 mol/hr/mol CYP) and a somewhat lower demethylation capacity (Vmax 19 mol/ hr/mol CYP). The affinities of 1A2 and 2C19 were 100-fold lower (K(m) 54-118 mumol/l). The capacity of 1A2 was low (Vmax 6.8 mol/hr/ mol CYP), whereas 2C19 had the highest demethylation capacity (Vmax 93 mol/hr/mol CYP). Taking into account the relative amounts of CYP isozymes present in the liver, about 90% of the metabolism was estimated to depend on CYP2D6, with CYP2C19 and 1A2 mediating the remaining 10%. In subjects lacking the 2D6 isozyme, CYP2C19 and 1A2 are expected to be of major importance for elimination of nortriptyline.

Antidepressive Agents, Tricyclic↗
PubMed1997

Metabolism of clozapine by cDNA-expressed human cytochrome P450 enzymes.

The metabolism of clozapine was studied in vitro using cDNA-expressed human cytochrome P450 (CYP) enzymes 1A2, 3A4, 2C9, 2C19, 2D6, and 2E1. CYP1A2, 3A4, 2C9, 2C19, and 2D6 were able to N-demethylate clozapine. N-Oxide formation was exclusively catalyzed by CYP3A4. CYP2E1 did not metabolize clozapine. With regard to quantitative relationships, CYP1A2, 2C9, 2C19, and 2D6 displayed KM values ranging from 13 to 25 microM, whereas CYP3A4 had a 5-10 times higher KM value. CYP2C19 and 2D6 had the highest Vmax values (149-366 mol/hr/mol CYP). Taking into account the typical relative distribution of amounts of CYP enzymes in the liver, a simulation study suggested that at therapeutic concentrations CYP2C19 and CYP3A4 each accounted for about 35% of the metabolism. At toxic concentrations, the relative importance of CYP3A4 increased.

Clozapine↗
PubMed1996

[Serious drug interaction between clozapine-Leponex and fluvoxamine-Fevarin].

A 67 year-old woman in steady-state treatment with clozapine 150 mg/24 h was co-medicated with 100 mg/24 h of fluvoxamine. During the next months the patient suffered from nausea and occasionally vomited, but these symptoms were ascribed to fluvoxamine, and as she mentally improved, both treatments were continued. Two months after the start of fluvoxamine her serum clozapine concentration was 7570 nmol/l or 7.5 fold higher than before fluvoxamine was added. The woman was admitted to hospital, suffering from abdominal pain, dehydration and fever (38.5 degrees C). Serum creatinine concentration was increased, but normalized during hydration. After 18 days care the woman felt well and was discharged from hospital. The case report shows that certain combinations of selective serotonin reuptake inhibitors and neuroleptic drugs should either be avoided or the serum concentrations of the drugs closely followed.

Aged↗
PubMed1996

[Citalopram and desmethylcitalopram for psychiatric patients].

Serum samples were selected randomly from blood samples drawn in the morning for other reasons in patients treated with citalopram, and the serum concentrations of citalopram (S-citalopram) and its major metabolite desmethylcitalopram were determined. A total of 44 patients, 13 males and 31 females, with a median age of 38.5 years (range 18-89) entered the study. In 17 patients given 20 mg/day of citalopram the S-citalopram was (median and range) 153 nmol/l (83-237). In 24 patients treated with citalopram 40 mg/day the S-citalopram was 240 nmol/l (range 0-360). In one serum sample no S-citalopram could be detected (non-compliance) and in another sample S-citalopram was just above the detection limit (about 3 nmol/l). The latter may at least partly be due to treatment with 600 mg/day of carbamazepine, which is known to accelerate the metabolism of other drugs. The serum concentration of the major metabolite desmethylcitalopram averaged 28% of S-citalopram and is most likely without clinical importance. It is concluded that determination of S-citalopram may be considered if there is doubt about the compliance of the patient, in drug interaction cases or if the clinical effect is poor. If high S-citalopram

Adolescent↗
PubMed1996

Simplified high-performance liquid chromatographic method for the determination of citalopram and desmethylcitalopram in serum without interference from commonly used psychotropic drugs and their metabolites.

A simplified method for the determination of racemic citalopram and its main metabolite desmethylcitalopram in serum using HPLC was developed. The compounds were extracted with heptane-isoamyl alcohol (98:2) and subsequently transferred into phosphate buffer pH 2.5 for direct injection into the HPLC apparatus. The analytes were separated with an acetonitrile-phosphate buffer, pH 2.5-tetraethylamine mobile phase on a C18 column and measured by UV detection at 240 nm. Within the typical range of serum concentrations (30-100 ng/ml) the inter-day variation was < 6% for both compounds. Possible analytical interference from a number of commonly coadministered psychoactive drugs and their metabolites was studied by extracting sera from patients receiving these drugs. Interference was not a problem for the developed method.

Artifacts↗
PubMed1996

Steady-state serum concentrations of the neuroleptic perphenazine in relation to CYP2D6 genetic polymorphism.

Steady-state serum concentration to dose ratios of the neuroleptic agent perphenazine were related to CYP2D6 metabolizer status for 96 psychiatric inpatients: 88 extensive metabolizers and eight poor metabolizers. The median concentration per dose of the poor metabolizer group (0.195 nmol/L per milligram) was about twice the median (0.098 nmol/L per milligram) of the 56 extensive metabolizers without interacting medicine (p < 0.01). The rest of the extensive metabolizers (n = 32), who were comedicated with drugs that compete with perphenazine for metabolism by CYP2D6, had an intermediate median value of 0.140 nmol/L per milligram. The range of concentration/dose values for the total extensive metabolizer group extended from 0.025 to 0.688 nmol/L per milligram, that is, an almost thirtyfold variation. The concentration/dose range of the eight poor metabolizer subjects was 0.096 to 0.750 nmol/L per milligram. Serum levels not corrected for dose overlapped to a large degree among the groups, with a total range from 0.5 to 12 nmol/L. This study points toward a limited information value of CYP2D6 genotyping in the context of therapeutic drug monitoring of perphenazine.

Adolescent↗
PubMed1996

Extreme values of the concentration/dose ratio as a risk factor of obtaining suboptimal nortriptyline serum concentrations.

Using nortriptyline as an example of a typical tricyclic antidepressant, I studied the relation between the steady-state concentration/dose ratio (C/D) and the performance of therapeutic drug monitoring (TDM), with a focus on the frequency of serum concentrations located in the therapeutic interval. A TDM database comprising 1,214 patients, of whom 619 patients had more than one sample taken, was used. The median C/D value for the patients was 4.05 [nM]/mg with 5th and 95th percentiles of 1.80 and 9.60, respectively. A total of 18.6% of the patients with C/D values below the 5th percentile had serum concentrations in the therapeutic interval at the first occasion, increasing to 49% for the average of the succeeding samples. These values were lower than those for the total group, 60.4 and 68.9%, respectively. For those with C/D values exceeding the 95th percentile, 36.2% had initial serum concentrations in the therapeutic interval, increasing to 66.3% for the average of succeeding samples. Only 11 patients (0.9%) had very high initial serum concentrations (> 1,200 nM). Thus patients with low C/D values are at risk of being underdosed, even after successive samples, whereas adequate dose correction is more likely to be implemented for those with average or high C/D values. Saturation kinetics for those with low C/D values was not a problem of clinical significance. Neither was lack of steady-state at the first occasion a problem for those with high C/D values (suspected poor metabolizers).

Adult↗
PubMed1996

Influence of Cyp2D6 genetic polymorphism on ratios of steady-state serum concentration to dose of the neuroleptic zuclopenthixol.

One hundred and nineteen psychiatric patients undergoing therapeutic drug monitoring (TDM) of the neuroleptic zuclopenthixol were genotyped with regard to Cyp2D6. Twelve patients (10.1%) were of the poor metabolizer genotype. The extensive metabolizers comprised 58 patients receiving no potentially interacting drugs and 38 patients concomitantly treated with other drugs competing for metabolism by Cyp2D6. Information on the rest (11 patients) was missing. The median steady-state serum concentration-to-dose ratio (C/D) of the PM group (2.00 nmol/L/mg) was close to that of the EM group receiving potentially interacting drugs (1.80) and approximately 60% higher than that of the remaining EM group (1.25) (p < 0.01). When judging the clinical importance of this difference, the total group variability in C/D of nearly 10-fold should be kept in mind (0.5-4.2 nmol/L/mg). In terms of serum concentrations not corrected for dose, the three groups had about similar levels, with median values from 16 to 21 nmol/L. We consider that TDM adequately takes into account dose adjustments for both EM and PM subjects in the context of this neuroleptic.

Adolescent↗
PubMed1995

Serotonin depletion decreases serotonin transporter mRNA levels in rat brain.

In order to study the impact of serotonin depletion on gene expression of the serotonin transporter (5-HTt) we measured 5-HTt mRNA levels by Northern blot in rats treated with p-chlorophenylalanine methyl ester (PCPA) for 10 days. Six rats received PCPA i.p. only, and another 6 rats receiving 0.9% NaCl served as controls. An additional group of 6 rats received both PCPA i.p. and imipramine, 5 mg/kg/day by osmotic minipumps. 5-HTt mRNA levels decreased to 81.1% (P = 0.05) and 76.0% (P = 0.05) of the control level for PCPA treated animals without and with concomitant imipramine treatment, respectively. The average level of the PCPA treated groups was 78.6% (P = 0.03). The isolated effect of 21 days of imipramine treatment was a 5-HTt mRNA level of 89.4%, which was not significantly different from the control level. In conclusion, 5-HTt gene expression is suppressed in the serotonin depleted state. A decreased synaptic reuptake of 5-HT may be interpreted as a compensatory mechanism aiming at preserving adequate synaptic 5-HT levels in a generally deficient state.

Animals↗
PubMed1995

[Results of urinary control analyses of narcotic addicts on methadone therapy. An evaluation in the county of ]rhus in 1993].

Urinary control results were evaluated for 230 drug addicts in methadone therapy in the county of Arhus for 1993. Nine point nine percent of the initial samples were positive for opiates, dropping to 5.9% for subsequent samples, suggesting that urinary control has consequences. Two point four percent of the initial samples were negative for methadone decreasing to 1.3% for later samples. Fifty percent were positive for cannabinols and 15-20% for benzodiazepines, whereas only 1.4% was positive for amphetamine. Looking at the serial pattern for the patients, it turned out that 41% had one or more samples positive for opiates during the methadone treatment period, and 14% were occasionally negative for methadone. For comparison, urine samples from 461 clients not in methadone treatment were also studied. A similar abuse pattern was recorded for these samples.

Adult↗
PubMed1995

Methaemoglobinaemia among neonates in a neonatal intensive care unit.

After detection of a few clinical cases of methaemoglobinaemia (methb) in our NICU, a prospective clinical study was undertaken to determine the extent of the problem and to identify the causes. Consequently, during the following 8 months all haemoglobin tests included simultaneous measurements of methb on an OSM 3 hemoximeter (Radiometer): 8% (n = 33) of 415 neonates were found to be methb positive (defined as > or = 6% methb). Mean methb was 19% (range 6.5-45.5%). Maximum methb concentrations were found on day 4-31 postpartum (mean 12 days) and the number of days with a positive methb sample ranged from 1 to 18 days (mean 6 days). About 40% of the neonates born at 25-30 weeks of gestation and 60% with a birth weight < 1000 g were methb positive. Also, there was a negative correlation between the size of the methb positive concentration and gestational age (r = -0.38, p = 0.02). Measurements of C-reactive protein and leucocytes, NADH reductase, pH, Cl, nitrate and nitrite were carried out in methb positive patients. The tests were repeated 1 week after cessation of methb. The only significant difference was an increase in NADH reductase at the second measurement. Likewise, a wide range of clinical parameters were registered and they occurred with a higher frequency among the methb positive patients when compared with a methb negative control group matched with regard to gestational age and the closest possible birth weight. The mean birth weight of methb positive patients was 1170 g and that of negative controls 1380 g (p < 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)

Birth Weight↗
PubMed1995

Comparison of the kinetic interactions of the neuroleptics perphenazine and zuclopenthixol with tricyclic antidepressives.

Using data from a therapeutic drug monitoring database, kinetic interactions between the neuroleptics zuclopenthixol and perphenazine and tricyclic antidepressives were studied. Out of 290 patients monitored for amitriptyline and 611 patients monitored for nortriptyline, 77 patients were comedicated with perphenazine and 50 patients with zuclopenthixol. Comedication with perphenazine increased the median steady-state serum concentration to daily dose ratio (C/D) of nortriptyline by 30-45%, whereas the median C/D of amitriptyline was unaffected. On the contrary, median C/D values of nortriptyline and amitriptyline were not significantly influenced by comedication with zuclopenthixol. Thus, in accordance with previous studies, perphenazine increases the concentration of tricyclic antidepressives to a moderate extent. Zuclopenthixol, on the other hand, does not exert any impact under routine therapeutic drug monitoring, even though the drug is known to partly depend on metabolism by the isozyme cytochrome P450 2D6.

Adolescent↗
PubMed1994

An HPLC-GC/MS reference method for serum total cholesterol with control for ester hydrolysis.

Currently used isotope-dilution mass spectrometry methods for serum total cholesterol are performed without control in each sample for completeness of hydrolysis of cholesterol esters. In order to monitor this step in the analysis, we developed a method based on both high-pressure liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). 13C3-cholesterol and cholesteryl [1-14C] oleate were added to serum that was saponified and extracted into hexane. The extract was subjected to HPLC with collection of the fractions corresponding to cholesterol and cholesteryl oleate. The radio-activity of the latter was counted in order to estimate the nonhydrolysed fraction that on average amounted to less than 0.1% for commonly used ester hydrolysis procedures. The cholesterol fraction was subjected to GC/MS for quantitation using the traditional isotope-dilution principle. Evaluation of accuracy by assaying sera from the National Institute of Standards and Technology showed a deviation from the target value of < 1% with a coefficient of variation of < or = 1.0%. In conclusion, the present reference method for serum total cholesterol assures results based on complete hydrolysis of the cholesterol ester fraction.

Calibration↗
PubMed1993

[Paraclinical examination programs in Danish hospitals prior to minor surgical procedures].

Using a questionnaire, paraclinical test programs prior to minor surgery were recorded for Danish hospitals. Sixty-one out of 66 departments of surgery completed the questionnaire. Most of the departments used a basic test program for younger subjects and an extended one for elderly subjects. The most commonly used investigations were in descending order: analysis of urine for glucose, albumin and hemoglobin, B-Hemoglobin, blood typing, P-Creatinine, and P-Potassium and Sodium. In elderly persons, ECG and a chest radiograph were used rather frequently in addition. The number of tests ranged from zero to nine (median three) for younger patients and from two to ten (median six) for elderly subjects. The estimated costs of the programs ranged from zero to 1092 Danish crowns (109 pounds) (median 185) for younger patients and from 71 to 1676 Danish crowns (167 pounds) (median 714) for elderly patients. In conclusion, the variation in the extent and estimated costs of preoperative test programs used in Danish hospitals is considerable.

Adult↗
PubMed1993

Effect of the biological matrix on the urinary testosterone/epitestosterone ratio measured by gas chromatography/mass spectrometry in doping analysis.

Testosterone doping in sport is detected by measurement of an increased testosterone/epitestosterone (T/E) ratio in urine. The critical limit is 6. The present study concerns calibration curves for the T/E ratio measured by gas chromatography/mass spectrometry (electron impact) according to the guidelines of the International Olympic Committee. Testosterone (T) and epitestosterone (E) are measured as trimethylsilyl (TMS)-enol-TMS ethers in selected ion monitoring mode using m/z 432 with methyltestosterone (MT) (m/z 446) as internal standard. Calibration curves corresponding to T/E = 1, 6 and 12 prepared directly, i.e. without extraction of T and E, were non-linear. The non-linearity was caused by an increase of the relative molar response of T with respect to the internal standard MT with increasing concentration level. A mean increase of 82% was observed from T/E = 1 to T/E = 12 (E fixed). Adding T/E corresponding to 1/1, 6/1 and 12/1 to urine without endogeneous hormone content resulted in an almost linear calibration curve along the diagonal, with only a slight increase of the relative molar response of testosterone (16% from T/E = 1 to 12). Apparently, the biological matrix stabilizes the relative molar response over a wide concentration range. At a molar ratio of about 1/1 for T/MT, the relative molar response for direct measurement of T is identical to that observed in the presence of urine matrix, which is explained on the basis of a simple mathematical model. The practical conclusion of this study is that, contrary to the present-day practice, calibration curves for the T/E ratio should be based on T/E added to blank urine taken through the extraction procedure. Otherwise, the T/E ratio of urine sample is systematically easily underestimated by 30% or more.

Animals↗
PubMed1993

Analytical goals for accuracy and precision of plasma creatinine determinations evaluated by reference method measurements.

Using approaches based on "medical needs" and biological variation, goals for analytical accuracy were assessed to 0.072-0.15 expressed as relative deviations, and goals for analytical precision were estimated to 0.022-0.14 expressed as relative standard deviations. A representative clinical method was evaluated using a reference method. On this basis, it is concluded that accuracy goals are fulfilled at high but not at low levels, and that precision goals are met according to medical needs but not with respect to biological variation.

Chemistry, Clinical↗