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  • 1
    ISSN: 1432-1041
    Keywords: Amobarbital ; pentobarbital ; barbiturates ; gas chromatography ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Gas chromatographic methods are described for the assay of amobarbital and pentobarbital in 500 µl samples of plasma, in concentrations down to 250 ng/ml. After ether extraction at pH 5.5, the barbiturates are reextracted into an alkaline solution of trimethylanilinium hydroxide and are determined quantitatively by gas chromatography as their dimethylated derivatives. The method has been used successfully in volunteers receiving therapeutic doses of these bariturates.
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  • 2
    ISSN: 1432-1041
    Keywords: Pentobarbital ; diphenylhydantoin ; salicyclic acid ; protein binding ; erythrocytes ; cell equilibration ; temperature effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The binding of pentobarbital, diphenylhydantoin and salicylic acid to cells in blood was found to be independent of total drug concentration within therapeutic levels. Salicylic acid displaced pentobarbital and diphenylhydantoin from plasma protein binding sites, but high levels of salicylic acid had no effect on the distribution of the other two drugs to washed blood cells. Thus, in whole blood the presence of salicylic acid decreased the fraction of pentobarbital or diphenylhydantoin bound to plasma protiens and increased the fraction of the drug in plasma water and in blood cells. Diphenylhydantoin was shown not to be bound irreversibly to blood cells and equilibration in between the inside and outside of the cells was found to be rapid (within 5 min), even at high concentrations. Binding to washed blood cells was the same at 37°C and 25°C, in contrast to plasma protein binding. It is pointed out that these effects may cause certain analytical errors, resulting in changes in plasma concentration if plasma is separated at a low temperature.
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  • 3
    ISSN: 1432-1041
    Keywords: fluoride ; renal clearance ; urinary pH ; fluoride kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Five healthy subjects were each given fluoride 3.0 mg (F) as sodium fluoride tablets on two occasions — during production of acid urine, induced by giving NH4Cl, and during production of alkaline urine obtained by giving NaHCO3. Frequent plasma and urine samples were taken up to 12 h and were analyzed with a F− sensitive electrode. Control experiments without F administrations were also performed to permit calculation of net F concentration in plasma and urine. The urine F excretion was lower during acid than alkaline diuresis. Pharmacokinetic analysis of the net plasma F concentrations showed that the apparent plasma half-life of F was longer when urine was acid (4.3±0.6 h: SD; n=5) than when it was alkaline (2.4±0.4 h). This could be explained by changes in the renal clearance of F, which was always lower with an acid (61.5±8.1 ml/min) than an alkaline (97.8±10.4 ml/min) urine. The apparent extra-renal clearance, which mainly represents clearance to the bone-pool, was also significantly higher during production of alkaline (109.2±20.2 ml/min) than of acid (86.3±21.3 ml/min) urine. It is suggested, that increased reabsorption of non-ionic hydrogen fluoride (HF) is responsible for the decreased renal clearance during acidic conditions.
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  • 4
    ISSN: 1432-1041
    Keywords: Protein binding ; foetus ; infant ; newborn ; antibiotics ; anticonvulsants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The binding to human plasma proteins of ampicillin, α-azidobenzylpenicillin, benzylpenicillin, phenobarbital and diphenylhydantoin was studied by equilibrium dialysis of labelled compounds. Human foetal and neonatal plasma had very low binding capacities for all five drugs as compared with plasma from adults. Hyperbilirubinemia in the neonatal period further decreased the binding capacity. The age dependence of drug binding activity should be taken into account when analysing pharmacological effects in foetuses and newborn children.
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  • 5
    ISSN: 1432-1041
    Keywords: busulphan ; leukaemia ; high-dose pharmacokinetics ; metabolism ; bone marrow transplantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetics of high-dose busulphan was studied in adult patients with acute myeloblastic leukaemia after oral doses of 1 mg·kg−1 every 6 h for 4 days. The mean steady-state plasma concentration was 1080 ng/ml−1 during the treatment. Individual steady-state concentrations after the last dose on average were 32% lower than those predicted from total AUC measurements following the first dose. Mean elimination half-life in plasma was 2.3 h after the last dose and 3.4 h after the first dose which suggests that busulfan may increase its own metabolic rate on repeated treatment. The cerebrospinal fluid/plasma concentration ratio of busulphan was 1.3. Busulphan showed insignificant protein binding in plasma (7.4%). About 2% of the dose was excreted unchanged in the urine. For the first time sulpholane, 3-hydroxysulpholane and tetrahydrothiophene 1-oxide were identified as urinary metabolites of busulphan in man.
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  • 6
    ISSN: 1432-1041
    Keywords: fluoride ; bioavailability ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of milk products on the gastrointestinal absorption of fluoride from sodium fluoride tablets was studied in five healthy subjects. Two different diets were tested: (1) 250 ml standardized milk (3% fat) and (2) 500 ml of milk, 3 pieces of white bread with cheese and 150 ml of yoghurt. The 100% bioavailability of sodium fluoride tablets during fasting was greatly decreased by coadministration of milk products: with Diet 1 the absolute bioavailability calculated from combined plasma and urine data was in the range 50–79% and with Diet 2 it ranged from 50–71%. It is suggested that the decreased bioavailability produced by dairy products should be taken into account when establishing fluoride dosage regimens for prophylaxis of caries.
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  • 7
    ISSN: 1432-1041
    Keywords: sulpiride ; pharmacokinetics ; serum clearance ; renal clearance ; bioavailability ; healthy volunteers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetics of sulpiride was studied in 6 healthy volunteers after intravenous and oral (tablets) administration of 100 mg. An open two- and in two subjects a three-compartment model was applied following intravenous administration. The average total distribution volume during the terminal slope was 2.72±0.66 l/kg and total systemic clearance was 415±84 ml/min. The serum half-life of the terminal slope following intravenous administration averaged 5.3 h (range 3.7–7.1 h) according to the two-compartment model. In two subjects the half-lives were 11.0 and 13.9 h when the three-compartment model was applied. Determination of urinary excretion rates of unchanged sulpiride indicated a half-life of 7.15 h. Following intravenous administration, 70±9% of the dose was recovered unchanged in urine within 36 h; the mean renal clearance was 310±91 ml/min. Sulpiride was absorbed slowly, with peak concentrations appearing between 3 and 6 h after oral administration. The recovery of unchanged drug in urine following oral administration was 15±5% of the dose, with a mean renal clearance of 223±47 ml/min. The bioavailability determined from combined plasma and urine data was only 27±9%. The low bioavailability was probably due to incomplete absorption.
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  • 8
    ISSN: 1432-1041
    Keywords: pethidine ; norpethidine ; analgesic ; singledose kinetics ; plasma concentrations ; drug disposition ; geriatric patients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Pethidine was given as a single intravenous dose for premedication before minor surgery. Two groups of subjects were studied, old patients aged more than 65 years, and young patients aged 18–30 years. Blood samples were taken at fixed intervals for 30 h after the injection, and the plasma concentrations of pethidine and its major metabolite norpethidine were analyzed by gas chromatography. In comparison with the young the old patients had a lower plasma clearance for pethidine (9.13±2.50 versus 16.18±5.15 ml/min/kg), slower elimination rate β (0.101±0.036 versus 0.211±0.146), and a larger AUC (1935±554 versus 1092±277 h · ng/ml) but a similar volume of distribution (5.69±1.54 versus 5.38±1.75 l/kg). Norpethidine appeared later and reached its peak concentration later in the old patients than in the young. In several old patients it was still present at a plateau level after 30 h. The present study emphasizes that both parent drug and active metabolite must be taken into consideration when drug therapy is evaluated. The data do not provide pharmacokinetic support for a reduction in the dose of pethidine if it is given as a single intravenous dose. However, when repeatedly administered, it is advisable to reduce the total daily dose.
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  • 9
    ISSN: 1432-1041
    Keywords: cloxacillin ; flucloxallin ; maternal — fetal distribution ; whole blood levels ; erythrocyte content ; plasma binding ; bilirubin effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The distribution of cloxacillin and flucloxacillin in whole blood from seven newborn infants and their mothers was determined in vitro by equilibrium dialysis at 37°C. Seven healthy, non-pregnant women of reproductive age served as controls. The distribution of the penicillins to erythrocytes was the same in the infants as in the adults. It was significantly lower in the presence of plasma albumin than when plasma was replaced by isotonic phosphate buffer. The plasma protein binding of cloxacillin and flucloxacillin in 22 infants was significantly lower than in the controls, but was slightly higher than in the mothers. A significant correlation between binding of cloxacillin and flucloxacillin in the same individual suggested that the two drugs were bound to similar sites. During the first postnatal week binding in infant plasma decreased. This change was correlated with an increase in the bilirubin levels. In the mothers, the binding increased during the first week after delivery. On the basis of the distribution data, maternal to fetal plasma and whole blood concentration ratios at equilibrium were calculated. These ratios were lower for flucloxacillin (medians 0.770 and 0.821, respectively) than for cloxacillin 0.996 and 1.094). Accordingly, at equilibrium somewhat higher levels of flucloxacillin should appear on the fetal than on the maternal side, whereas the concentrations of cloxacillin would be expected to be approximately the same.
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  • 10
    ISSN: 1432-1041
    Keywords: geriatrics ; pethidine ; drug disposition in blood ; erythrocytes ; age effect ; plasma protein binding ; red cell binding ; intracellular concentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The distribution of3H-pethidine in whole blood was compared in old (63–86 years;n=11) and young (19–25 years,n=12) subjects using equilibrium dialysis. The plasma protein binding was 52.7±3.3% (mean ± SD) in the old subjects and 51.8±3.1% in the young; the difference was not statistically significant. Studies on isolated plasma protein fractions showed that the main pethidine-binding protein wasα 1-acid glycoprotein. Accordingly, the degree of pethidine binding is likely to be affected by inflammatory disease rather than by age. The distribution of pethidine to blood cells showed no age-related difference; the ratio between whole blood and plasma concentrations was 0.99 in old and 0.98 in young subjects. In whole blood from old and young subjects, 43% and 41% of pethidine was present in erythrocytes, 27% and 26% in plasma water whereas 30% and 29% was bound to plasma proteins. The mean ratio between pethidine in cells and plasma water (2.01) indicates binding of the drug in or on the blood cells. These in vitro results do not support the previous theory that a decrease in intracellular pethidine distribution in old age was the reason for the reported higher plasma levels. A slower elimination rate remains the most likely explanation for the increased plasma concentration of pethidine in old patients.
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