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Biomedical subjects

D D Breimer

Publications and source records attributed to D D Breimer.

At least 181 records · Page 10Linked to original sources
PubMed1988

Influence of the rate of hepatic portal vein infusion on hexobarbital pharmacokinetics in the rat.

Pharmacokinetic parameters of hexobarbital were estimated in rats after hepatic portal infusion of a 10-mg dose. Infusion during 10 min resulted in an area under the blood concentration-time curve (AUC) of 556 +/- 83 micrograms.min/ml and a clearance of 83 +/- 13 ml/min.kg, whereas infusion of the same dose during 40 min resulted in values of 272 +/- 36 micrograms.min/ml and 169 +/- 30 ml/min.kg, respectively (mean values +/- SD, n = 3). Infusion during 15 and 20 min provided intermediate values. The decrease of the AUC and the increase of the blood clearance of hexobarbital following decreasing infusion rates clearly indicate nonlinear pharmacokinetics related to the hepatic inflow concentration of hexobarbital.

Animals↗
PubMed1988

Characterization of an "in vitro" blood-brain barrier: effects of molecular size and lipophilicity on cerebrovascular endothelial transport rates of drugs.

The in vitro blood-brain barrier model described consisted of confluent monolayers of bovine cerebrovascular cells in primary cultures. Aim of the study was to investigate whether this type of model exhibits transport characteristics comparable to the in vivo blood-brain barrier and whether the cells in the cultured monolayers were able to form tight junctions, the most typical feature of the in vivo blood-brain barrier. Endothelial permeability of fluorescein-conjugated dextrans with increasing molecular size was correlated to monolayer pore shape, size and abundance by means of a mathematical model. Results showed that the in vitro pores had a longitudinal appearance with an effective pore size of 81 A and fractional pore area of 0.04%. These data indicate that the properties of the in vitro pores and in vivo tight junctions are comparable. The monolayer model was applied successfully to establish a relationship between endothelial permeability and drug lipophilicity, using several beta blocking agents and nonsteroidal anti-inflammatory drugs as model drugs. Results showed a sigmoidal relationship between these parameters, indicating the existence of a threshold lipophilicity for passive transendothelial transport.

Animals↗
PubMed1987

Negligible sublingual absorption of nifedipine.

The sublingual absorption of nifedipine was investigated in 11 healthy volunteers. After the subjects bit a capsule containing 10 mg nifedipine in solution and did not swallow for 20 min (at which time the mouth was washed out), absorption was slow and led to low plasma levels (median 10 ng/ml). After the same subjects bit and swallowed a capsule, absorption was faster and higher plasma levels were achieved 982 ng/ml). Biting a capsule and swallowing its contents is recommended in cardiovascular emergencies.

Absorption↗
PubMed1987

1,2-Dibromo compounds. Their mutagenicity in Salmonella strains differing in glutathione content and their alkylating potential.

The mutagenic activities of several structurally related dibromo compounds were compared in Salmonella strains sensitive to base substitution mutagenesis (TA1535 and/or TA100) and in the glutathione (GSH)-deficient derivative TA100/NG-57, using a preincubation procedure. The compounds tested were 1,2-dibromoethane (DBE), 1,2-dibromopropane (DBP), 1,2-dibromo-1-phenylethane (DBPE) and model compounds for the half-mustards resulting from their conjugation with GSH, i.e. the N-acetyl-S-2-bromoalkyl-L-cysteine methyl esters SBE, SBP, and SBPE, respectively. The alkylating potential of all compounds was assayed with the 4-(p-nitrobenzyl)pyridine (NBP) alkylation test. Five of the compounds showed a good correlation between relative mutagenic activity in TA100 and electrophilic reactivity in the NBP-test, the order of decreasing potency being SBE greater than SBP greater than DBPE greater than DBP. SBPE displayed the highest reactivity in the NBP-test, but was devoid of mutagenic activity. The mutagenic activity of DBE was substantially decreased in the GSH-deficient strain TA100/NG-57 and could be restored by pretreating the cells with GSH. None of the other chemicals showed different mutagenic activities in TA100 and TA100/NG-57. From the results it can be concluded that 2-bromothioethers possess higher alkylating activities than the 1,2-dibromo compounds. Methyl substitution has a deactivating effect on the mutagenic activity. The results with the phenyl-substituted analogue, DBPE, show that a higher alkylating activity does not always lead to a higher mutagenic activity.

Alkylating Agents↗
PubMed1987

Pharmacokinetics in liver disease.

Some general pharmacokinetic principles, relevant to understand and predict altered disposition of drugs in liver disease, are reviewed. It is appropriate to differentiate between high- and low-clearance drugs as to the influence of hepatic dysfunction. On intravenous administration high-clearance drugs generally show reduced systemic clearance predominantly caused by decreased liver blood flow, whereas on oral administration a considerable increase in systemic availability may occur caused by reduced enzyme activity and (in cirrhosis) bij portacaval shunting. Low-clearance drugs are sensitive to reduced enzyme activity and reduced protein binding. It seems that oxidative reactions are far more affected than conjugation reactions in liver disease. Large inter-patient variability exists in the kinetics of a drug in any type of hepatic disease. The conventional liver-function tests are of no value in predicting altered drug disposition.

Humans↗
PubMed1987

Variability in drug metabolism: importance of genetic constitution.

In man wide variability exists in the rate of metabolism of drugs and among factors which contribute to this phenomenon genetic constitution is of major importance. The metabolism of a number of drugs is subject to polymorphism and the frequency distribution of particular pharmacokinetic parameters shows bimodality, with poor (PM) and extensive metabolizers (EM). Acetylation of a number of drugs is known to be polymorphic and the incidence of poor metabolizers varies markedly among different populations. Debrisoquine and sparteine are frequently applied model substrates for the characterization of a polymorphism in oxidative metabolism. Polymorphic drug oxidation may have important clinical implications, because when standard dosage regimens are applied plasma concentrations will reach far above the maximum acceptable in poor metabolizers and consequently side effects may arise. Regarding the multiplicity of the drug oxidizing enzyme system (cytochrome P-450) it could be of interest to combine model substrates in a cocktail to be able to characterize human subjects simultaneously for a number of independent polymorphisms.

Acetylation↗
PubMed1987

Correlation of apparent intrinsic clearances of simultaneously administered S (+) and d3R (-) hexobarbital in the rat.

Pseudoracemic hexobarbital (HB), consisting of equal molar fractions of S (+) HB and deuterium-labeled R (-) HB, d3 R (-) HB, was administered orally to rats in a dose of 50 mg/kg. Concentrations of both enantiomers in blood were measured by an enantioselective mass fragmentographic assay. Clearance data of S (+) HB and d3 R (-) HB were correlated in untreated rats, and in rats pretreated with 3-methylcholanthrene (MC), carbon tetrachloride (CCl4), and different doses of phenobarbital (PB). Although in the different groups some variation in the clearance ratio of S (+) HB over d3 R (-) HB was found, the clearance of S (+) HB was generally up to a factor of five higher than the clearance of d3 R (-) HB, except for the CCl4-treated rats. From the present data it can be tentatively concluded that S (+) HB and R (-) HB are metabolized by similar (PB-inducible) cytochrome P-450s in control and PB- and MC-pretreated rats and that clearance data obtained with racemic HB following different pretreatments may be employed as a reflection of (PB-inducible) cytochrome P-450 activity.

Animals↗
PubMed1987

Lamotrigine, a new anticonvulsant: pharmacokinetics in normal humans.

The pharmacokinetics of lamotrigine, a new anticonvulsant, were studied in three studies in normal volunteers. In the first study, five subjects received oral doses of lamotrigine up to 240 mg. A linear relationship was observed between dose administration and both peak drug concentration and AUC. In a second study 10 subjects received 120 mg lamotrigine and the mean (+/- SD) of the elimination half-life (t1/2) was 24.1 +/- 5.7 hours and of volume of distribution/bioavailability 1.2 +/- 0.12 L/kg. Saliva concentrations were 46% of the plasma concentration. Total urinary recovery of drug over 144 hours was 70.5% of the oral dose. A glucuronide conjugate accounted for 89.4% of the urinary recovery. In a third study the kinetics of repeated administration were studied. Fifteen subjects were randomized to lamotrigine (n = 10) or placebo (n = 5) and received multiple doses over 7 days. The overall plasma elimination t1/2 calculated from data during the 7 days was 25.5 +/- 10.2 hours. Observed pharmacokinetics on multiple administration obeyed closely those predicted from the single-dose experiment, suggesting the absence of autoinduction of metabolism. No clinically important side effects or changes in central nervous system or cardiovascular system variables, hematology, biochemistry, or urinalysis occurred during the 7 days.

Anticonvulsants↗
PubMed1987

Rate of increase in the plasma concentration of nifedipine as a major determinant of its hemodynamic effects in humans.

The relevance of the rate of increase in the plasma concentration of nifedipine for the drug's hemodynamic effect was investigated in healthy volunteers. Nifedipine was given intravenously according to two regimens, each designed to produce the same steady-state concentration, but attained gradually (within 5 to 7 hours) with one regimen and rapidly (within 3 minutes) with the other. The mean steady-state concentrations obtained were 31.7 +/- 5.2 (SD) ng/ml and 29.4 +/- 9.8 ng/ml, respectively (not significant). With the gradual regimen, heart rate was unchanged and diastolic blood pressure was lowered gradually by approximately 10 mm Hg. With the rapid regimen, heart rate increased immediately and remained elevated for the duration of the infusion, whereas diastolic blood pressure did not change significantly. At the end of the gradual-rise regimen, the infusion rate was increased tenfold for 10 minutes, promptly resulting in tachycardia and a paradoxical rise in diastolic blood pressure. These divergent hemodynamic responses of the gradual- and rapid-rise regimens could well be related to differences in baroreceptor activation. It is concluded that the hemodynamic response to nifedipine is influenced by the rate of increase of its concentration in plasma.

Adult↗
PubMed1987

Pharmacokinetics and hemodynamic effects of long-term nifedipine treatment in hypertensive patients.

In six patients with essential hypertension, pharmacokinetics and pharmacodynamics of nifedipine were investigated during 6 weeks of treatment. On day 1 nifedipine was infused intravenously (6.0 mg within 60 min), and on day 2 oral nifedipine treatment (20-mg tablets, twice daily) was started. Patients came to the hospital once weekly, when blood samples were taken and blood pressure and heart rate were assessed prior to tablet intake and 3 h later. After 6 weeks of oral treatment the intravenous infusion experiment was repeated. At the first intravenous nifedipine infusion a total systemic plasma clearance of 671 +/- 240 ml/min (mean +/- SD), an elimination half-life of 95 +/- 36 min, and a volume of distribution of 60.2 +/- 11.9 L were found. Protein unbound fraction of nifedipine amounted to 4.6 +/- 0.3%. After 6 weeks of oral treatment half-life was almost doubled (p less than 0.05), whereas in most patients the volume of distribution had slightly increased and systemic plasma clearance was decreased. Using a sigmoidal model, hemodynamic effects were fitted to nifedipine plasma concentrations. After 6 weeks the maximal effect of intravenous nifedipine on both systolic and diastolic blood pressures had significantly decreased. In four patients the potency had decreased considerably. During oral nifedipine treatment the mean plasma half-life was 5.8 +/- 1.0 h; trough concentration was 11.3 +/- 4.1 ng/ml and peak concentrations were 36.8 +/- 14.3 ng/ml. During chronic treatment heart rate was not significantly changed, whereas systolic and diastolic blood pressures were significantly reduced (p less than 0.02 and less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

The disposition of antipyrine and its metabolites in young and elderly healthy volunteers.

1 Oxidative metabolism of antipyrine (AP) was compared in 11 elderly (greater than 65 years) and 12 young (less than 40 years) volunteers. All subjects were non-smokers, consumed little if any alcohol and were in good health. 2 After a single dose of AP 500 mg, its clearance from saliva and profiles of the parent drug and its major metabolites in urine were determined using high-performance liquid chromatography. 3 Mean total AP clearance from saliva was lower in the elderly (P less than 0.05). Mean weight-normalised volume of distribution was also smaller (P less than 0.01) so that elimination half-life in the elderly was not significantly different from that in the young. 4 The percentage dose excreted in 48 h urine as norantipyrine (NORA) and its clearance for production were lower in the elderly (P less than 0.001 and P less than 0.01 respectively). Urinary 3-hydroxymethylantipyrine (HMA) and free antipyrine were present in greater quantities in 48 h urine in the elderly (P less than 0.001 and P less than 0.05) while the amounts of 4-hydroxyantipyrine (OHA) were almost identical in the two age groups. 5 The findings suggest that there is a selective impairment of N-demethylation in the elderly which may have important implications for dosage of elderly patients with drugs metabolised by this route.

Adult↗
PubMed1987

Nifedipine. Relationship between pharmacokinetics and pharmacodynamics.

The availability of specific chemical assays and the development of appropriate biological models have made it feasible to study the relationship between the pharmacokinetics and the pharmacodynamics of nifedipine, a relationship that is presumed to be sigmoidal for most effects. In healthy volunteers the haemodynamic effects of a single dose of nifedipine are markedly influenced by the pharmaceutical preparation and the rate of drug input. When the plasma concentration of nifedipine increases rapidly, such as after an intravenous bolus injection or rapidly disintegrating capsules, there is a marked increase in heart rate and little or even no effect on blood pressure. On the other hand, when the drug is given as a slow intravenous infusion or as a sustained release tablet and when the capsules are taken together with food, the decrease in blood pressure is accompanied by few or no changes in heart rate. Furthermore, it has been shown that not only haemodynamic effects of nifedipine, but also oesophageal motor function may be used as a quantifiable pharmacological effect. For patients with angina pectoris, a plasma concentration range that is associated with optimal treatment has not been defined, since large inter-individual variations in the nifedipine plasma concentration were observed in effectively treated patients. For patients with hypertension, significant sigmoidally shaped correlations between blood pressure reduction and nifedipine plasma concentrations following single or multiple doses have been demonstrated. The concentration-effect parameters were very similar to those found for normotensive subjects. After 6 weeks of treatment the potency of the drug had decreased, which might indicate the development of some tolerance. In patients with severe renal impairment, the maximal effect of nifedipine on diastolic blood pressure was more than doubled, which cannot be explained by differences in pharmacokinetics; therefore these patients appear to be more sensitive at the pharmacodynamic level. In patients with liver cirrhosis, the pharmacokinetics of nifedipine were quite different due to reduced protein binding and reduced enzyme activity; in patients with a portacaval shunt, considerable increased bypassing of the liver during the first pass after oral administration was observed. When corrected for free drug concentrations, the concentration-effect relationship for these patients is essentially the same as that found for healthy subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Humans↗
PubMed1987

Pharmacokinetics of lignocaine and bupivacaine in surgical patients following epidural administration. Simultaneous investigation of absorption and disposition kinetics using stable isotopes.

The pharmacokinetics of lignocaine (lidocaine) and bupivacaine following epidural administration were studied in 12 surgical patients using a stable isotope method. Shortly after epidural administration of the agent to be evaluated, a deuterium-labelled analogue was administered intravenously. Plasma concentrations of the unlabelled and the deuterium-labelled local anaesthetics were determined using gas chromatography and mass fragmentography. The pharmacokinetic behaviour of both agents was consistent with a 2-compartment open model and two parallel first-order absorption processes. The mean distribution and elimination half-lives were 12 minutes and 100 minutes for lignocaine, and 22 minutes and 143 minutes for bupivacaine. The mean volumes of the central compartment and the mean steady-state volumes of distribution were: lignocaine, 43L and 99L; bupivacaine, 33L and 68L. Total plasma clearances averaged 0.95 L/min (57 L/h) for lignocaine and 0.52 L/min (31.2 L/h) for bupivacaine. The half-lives, characterising the fast and slow absorption processes, were 9.3 and 82 minutes for lignocaine, and 7.0 minutes and 362 minutes for bupivacaine; the fractions of the doses absorbed in the fast and slow processes were lignocaine 0.38 and 0.58, bupivacaine 0.28 and 0.66, respectively. The results indicate that the local anaesthetics are completely absorbed from the epidural space into the general circulation. The initial absorption rates of both local anaesthetics appear to be similar, but, later, the absorption of bupivacaine proceeds much more slowly than the absorption of lignocaine.

Absorption↗
PubMed1986

Influence of salicylate and anaesthesia on the rectal absorption of theophylline in rats.

The effect of sodium salicylate and anaesthesia on the rectal absorption of theophylline was evaluated in rats. Theophylline proved to be slowly but completely absorbed on rectal infusion in conscious rats, compared with intravenous infusion. Pentobarbital anaesthesia did not influence absorption. In contrast to literature data, the results with salicylate showed that rectal absorption of theophylline was not enhanced.

Anesthesia↗
PubMed1986

Microsomal and cytosolic epoxide hydrolase in Drosophila melanogaster.

Subcellular fractions from Drosophila melanogaster and rat liver were investigated on their epoxide hydrolase activity. Both microsomes and the post-microsomal supernatant of Drosophila appeared to contain epoxide hydrolase activity using styrene-7,8-oxide as the substrate. Based on body weight, these activities were in the same order of magnitude. Rat liver cytosol was able to catalyze the hydrolysis of styrene oxide only if the glutathione S-transferase activity was blocked.

Animals↗