Simultaneous modeling of bopindolol kinetics and dynamics.

Bopindolol has beta-blocking effects for 96 hr despite a 4-hr t1/2. To investigate the concentration-effect relationship after single and repeated doses. 2-mg oral doses were given once and then daily for 13 days to six healthy subjects. In plasma, no unchanged drug, only the hydrolysis product of bopindolol (referred to as bopindolol concentration) was detectable or could be measured up to 24 hr. Chemical assay by HPLC and determination of total active beta-adrenoceptor blocking material by radioreceptor assay gave identical results. The t1/2 was 4 to 5 hr. Effects, measured as reduction in exercise-induced tachycardia (REIT) and as the isoproterenol dose ratio (DR - 1), were followed for 96 hr. The concentration of bopindolol in plasma (predicted with a one-compartment body model) could be related to the measured effects by classic effect models for 20 t1/2s. Parameter estimates for kinetic end effect models did not differ after single and repeated doses. With the parameters from the single-dose experiment, the time course of the plasma concentration and the effects after the multiple-dose experiment could be adequately predicted for 24 and 96 hr. A deep compartment, an active metabolite, or irreversible destruction of the receptor (accounting for the persistence of the effect) could be excluded. The "dissociation constant" of 100 pmol/l (from DR -1/concentration) and the minimal effective plasma concentration (from REIT/log concentration) of 1 pmol/l suggest that enough receptors are occupied at chemically unmeasurable levels in plasma to induce an effect. The "dissociation constant" determined in vivo is of the same order as that from in vitro radioligand studies.

Ex vivo studies after oral treatment of the beagle with dihydroergotamine.

Plasma concentrations of unchanged dihydroergotamine (DHE) were measured in beagle dogs on days 1 and 7 of a 1 week treatment with daily oral doses of DHE. Responses to both 5-HT and noradrenaline were monitored isometrically on spiral strips from saphenous arteries and femoral veins removed 24 and 72 h after the last oral dosage of DHE. Femoral vein strips were removed from dogs treated for 1 week with daily doses of 0.60 mg/kg DHE p.o. and suspended in organ baths. When stretched to an initial tension of 500 mg, such strips relaxed significantly less than strips taken from control beagles. Furthermore, the vasoconstrictor potencies of both 5-HT and noradrenaline were significantly increased on strips from femoral veins but not on strips from saphenous arteries removed from DHE-treated beagles. About 210 min after suspension in organ baths, femoral vein strips from DHE-treated dogs developed spontaneously an increase in basal tone, a phenomenon which was not observed with saphenous arteries. It is suggested that sensitization of venous smooth muscle to the constrictor activities of endogenous catecholamines and 5-HT contributes to the venoconstrictor activity of DHE. Moreover, the pharmacologic action of orally administered DHE, as assessed by the ex vivo measured changes in sensitivity of vein strips, requires peak plasma levels of more than 0.30 ng/ml. However, the duration and maintenance of the venoconstrictor response is largely independent from continuously elevated plasma DHE levels.

Permanent bile duct cannulation in the monkey. A model for studying intestinal absorption.

Our aim has been to obtain an experimental model where the test animal is subjected to the least amount of stress and restraint, and can serve for the repeated sampling of biliary excretion over a prolonged period of time. By using a special end-piece at the outer terminals of the two cannulas the monkeys could be given full freedom after experimentation. During the course of the study it was found that insertion of the cannula into the common bile duct led to the development of collateral pathways for passage of bile around the point of insertion. This adaption reaction for the restoration of a normal bile channel would seem to be characteristic of Rhesus monkeys, for we did not encounter it in similar experiments on dogs and minipigs. The experimental model described is intended to serve for the determination of intestinal absorption of compounds that are mainly excreted via the bile. Results with radioactive ergotamine are presented.

Dependence of area under the curve on proquazone particle size and in vitro dissolution rate.

The in vitro dissolution and GI absorption of various sieve fractions of proquazone were studied (particle-size ranges of 45-74, 160-300, and 500-1000 micrometer). The dissolution rates of preparations F45, F160, and F500 were determined in vitro in a flow-through assembly in artificial gastric juice at 37 degrees. The time required for 63% of the maximum amount of soluble drug to pass into solution was characterized by the dissolution variable tau D. The in vitro dissolution rates for the preparations differed significantly in the order tau D, F45 less than tau D, F160 less than tau D, F500. After oral administration of 300 mg of the fractions to each of eight rhesus monkeys, the area under the plasma level-time curve (AUC) differed significantly in the order AUC F45 greater than AUC F160 greater than AUC F500. The dissolution rate increased with decreasing particle size. The AUC increased with decreasing particle size and with increasing dissolution rate. These results indicate that the dissolution rate probably determines the extent of absorption when dissolution is rate limiting.

Pharmacokinetics of SMS 201-995 in healthy subjects.

The pharmacokinetics of a new somatostatin derivative, SMS 201-995, was investigated in a group of eight healthy subjects. SMS 201-995 was given intravenously in doses of 25 micrograms, 50 micrograms, 100 micrograms, and 200 micrograms and also subcutaneously in doses of 50 micrograms, 100 micrograms, 200 micrograms, and 400 micrograms in accordance with a randomized Latin-square design. Blood samples were taken up to 8 h. The tolerability of SMS 201-995 was very good. Routine blood chemistry variables remained normal. After intravenous administration of SMS 201-995 initial half-lives ranging from 9 +/- 2 min to 14 +/- 4 min and second half-lives of from 72 +/- 22 min to 98 +/- 37 min were calculated for the different doses. SMS 201-995 was rapidly absorbed after subcutaneous injection with a half-life ranging from 5.3 +/- 2.2 min to 11.7 +/- 7.6 min. The disposition half-life was from 88 +/- 20 min to 102 +/- 16 min for the different doses. Cp(tmax) and AUC (0 - infinity) increased dose-dependently after both routes of administration, pointing to linear pharmacokinetics for SMS 201-995. On the basis of its good tolerability, slow plasma clearance, and long action, SMS 201-995 represents a valuable tool for further clinical studies.

Venoconstrictor effects of dihydroergotamine after intranasal and intramuscular administration.

A parenteral formulation of dihydroergotamine (DHE) is the only galenical form now available for the treatment of acute attacks of migraine in which a rapid onset of action is required. A recently developed nasal spray of DHE has been compared with intramuscular DHE for its venoconstrictor activity. In a randomised double-blind, cross-over trial, 9 healthy male volunteers received a single dose of DHE 1 mg intranasally, DHE 0.5 mg i.m. or placebo (intranasally and i.m.) on three different occasions, with an interval of at least 1 week between doses. Both active treatments, but not placebo, produced marked venoconstriction as shown by reduced compliance of superficial hand veins. The effect persisted for more than 8 h. The maximum venoconstrictor effect of 1 mg DHE intranasally was 40 +/- 12% (mean +/- SEM) and after 0.5 mg i.m. it was 52 +/- 15%. The time course of the venoconstrictor effect was similar after both routes of administration. Blood pressure and heart rate changes in these normotensive subjects were almost identical after dihydroergotamine and placebo. The results suggest that the nasal spray could be used as an alternative to parenteral DHE, permitting self-administration of the drug for the treatment of acute attacks of migraine.

Dihydroergotamine: pharmacokinetics, pharmacodynamics, and mechanism of venoconstrictor action in beagle dogs.

Dihydroergotamine (DHE) elicits selective and long-lasting venoconstrictor activity, although the drug disappears rapidly from the blood. Therefore, a comparative study on the pharmacokinetic and pharmacodynamic properties of DHE was performed in beagle dogs. In addition, the mechanism of the venoconstrictor activity of DHE was investigated in vivo. Changes in the diameter of the saphenous vein and plasma level-time curves of DHE and its metabolites were determined in conscious beagle dogs. After both intravenous and oral administrations of DHE, the venoconstrictor response is of markedly longer duration than would be expected on the basis of the half-life for elimination of DHE from blood. The experimental data support the suggestion that the long duration of the DHE-induced venoconstriction is due to an extremely slow dissociation of the drug from its receptor sites on the venous smooth muscle cell, and to the formation of active metabolites. Using the antagonists ketanserin, pizotifen, and rauwolscine, evidence is presented that the venoconstrictor activity of DHE is mediated through stimulation of 5-HT receptors; there is no evidence of involvement of alpha-adrenoceptors.

Ergotamine in plasma and CSF after i.m. and rectal administration to humans.

An attempt was made to study the kinetics of penetration of ergotamine across the blood-brain barrier. A single therapeutic dose of ergotamine was given to 18 hospitalized patients; eight patients received 0.5 mg i.m., three patients 4 mg rectally, and seven patients 2 mg rectally. Plasma samples were drawn between 0.25 and 72 h and one CSF sample was taken from each patient between 0.5 and 6.5 h after administration. The ergotamine concentrations were measured using a RIA method. The 0.5 mg intramuscular injection showed the highest plasma levels of ergotamine, with a mean peak concentration of 1.27 ng/ml reached at 0.5 h. The 4 mg rectal administration resulted in mean plasma ergotamine levels of 0.44 ng/ml in the time interval of 0.75-2 h. The 2 mg ergotamine rectally resulted in mean plasma levels of 0.15-0.17 ng/ml 1-8 h after administration of ergotamine. Neither the plasma samples taken after 10 h nor the CSF samples had ergotamine concentrations above the detection limit of the RIA method (0.1 ng ergotamine/ml).

Steady state pharmacokinetics of hydrolysed bopindolol in young and elderly men.

Steady-state pharmacokinetic parameters of the new, long-acting beta-adrenoceptor blocker bopindolol have been measured in 17 young and 20 elderly healthy men. The t 1/2 beta and the AUC(0----24 h) of hydrolysed bopindolol (the active metabolite) were both increased (40% and 26%, respectively) in the elderly subjects but tmax, Cmax and CL/f were not altered. However, after adjusting the parameters to allow for the different average body weights of the two groups, Cmax and CL/f became significantly different (+29% and -30%, respectively). AUC(0----24 h) was increased by 41%. The changes of up to 41% in pharmacokinetic parameters were smaller than the alterations of 50-100% usually seen when titrating doses of antihypertensive drugs. The clinical relevance of the effects was not examined, but similar changes have been reported for other beta-blockers which did not appear to be clinically relevant and did not affect the dosage required to treat hypertension.

Non-equilibrium method for the radioimmunoassay of clozapine in the presence of metabolites.

Cross-reactions with metabolites are an ever-recurring problem encountered in the use of radioimmunoassay techniques to determine active compounds in biological material. Metabolites may interfere with the assay of the parent drug to a variable extent. Taking 8-chloro-11-(4-methyl-1-piperazinyl)-5H-dibenzo[b,e][1,4]diazepine (clozapine as an example, it was shown that the extent to which the antiserum produced interacts with the parent drug and the metabolites can be estimated by determining the equilibrium constants and the kinetics. In the present case, therefore, it was advantageous to carry out the radioimmunoassay in disequilibrium, i.e. in order to differentiate the metabolites from the parent drug, the sample was incubated with the antiserum for 10 min, after which the labelled antigen was added and the reaction mixture again incubated for a brief, exactly timed interval. It was shown that cross-reactions did not occur in mixtures of clozapine and its N-demethyl and N-oxide metabolites in the propor tions 1:1:2 over a range of concentration of 1.5-48 ng clozapine per 100 microliter human plasma. The equilibrium constants measured with the clozapine goat antiserum were as follows: clozapine 1.2 X 10(8) M-1, the N-demethyl metabolite 4.6 X 10(7) M-1 and the N-oxide metabolite 3.7 X 10(7) M-1 (pH 7.5 and 20 degrees C).

Interindividual variation of beta-adrenoceptor blocking drugs, plasma concentration and effect: influence of genetic status on behaviour of atenolol, bopindolol and metoprolol.

Ten healthy subjects whose genetic oxidative phenotype had been determined (6 extensive and 4 poor metabolizers of the debrisoquine-sparteine type of polymorphism) received single oral doses of 3 beta-blockers: atenolol, bopindolol and metoprolol. The plasma concentrations and the extent of the decrease in exercise-induced tachycardia were determined. The oxidative polymorphism was only significant for substances that had a high hepatic first pass metabolism, such as metoprolol. The metabolic pathway under genetic control was highly stereoselective. This observation must be taken into account when assessing the relation between the plasma concentration and effect of these drugs, which are often administered as racemic mixtures.

A new radioimmunoassay of thioridazine and its comparison with a high performance liquid chromatographic method and another radioimmunoassay.

A new radioimmunoassay (RIA) procedure for the determination of thioridazine in plasma is described. Antiserum was produced in rabbits immunized with N-(2-carboxyethyl)desmethylthioridazine-protein conjugate. The developed RIA procedure can measure as low as 80 pg of thioridazine in a 200-microliter human plasma sample with a coefficient of variation of less than 5%. This RIA procedure was compared with previously reported RIA and high performance liquid chromatographic (HPLC) methods by determining plasma concentrations of thioridazine in samples from human volunteers over 72 h after administration of single 50-mg oral doses of thioridazine hydrochloride. There was a good correlation between the assay values (n = 55) determined by the new RIA and HPLC methods (r2 = 0.916), and the slope of the regression line was not significantly different from 1.0 (p greater than 0.60, 95% confidence limits 0.981 +/- 0.081 when RIA values were plotted on the y axis, and HPLC values on the x axis; p greater than 0.10, 95% confidence limits 0.934 +/- 0.080 when HPLC values were plotted on the y axis and RIA values on the x axis). Also, the plot of the differences between these two assay values against the average of the assay values showed that the differences were independent of the concentration range studied. Similar favorable statistical comparisons were obtained when the assay values (n = 44) determined for thioridazine by the two RIA procedures were compared with one another.

Specific 3H radioimmunoassay with a monoclonal antibody for monitoring cyclosporine in blood.

A specific radioimmunoassay involving a mouse monoclonal antibody to cyclosporine has been developed for monitoring the parent drug in blood. Pretreatment with methanol removes cyclosporine from the erythrocytes. The limit of detection is about 12 micrograms/L, sample volume is 50 microL of blood, and within- and between-assay CVs are less than 7%. Assay results correlated well with those obtained by "high-performance" liquid chromatography (HPLC) for liver (n = 42), for heart (n = 64), for bone-marrow (n = 36), and for kidney (n = 140). For blood specimens obtained from patients treated with cyclosporine postoperatively for as long as 65 months, the mean RIA/HPLC ratio in all with transplant indications was close to 1. Therefore, the specific radioimmunoassay apparently can be used instead of HPLC to measure the parent drug in blood.

Pharmacokinetics of a long-acting bromocriptine preparation (Parlodel LA) and its effect on release of prolactin and growth hormone.

The pharmacokinetics and endocrine actions of a long-acting form of bromocriptine (Parlodel) were examined in a controlled study in 10 healthy volunteers receiving a single i.m. injection of 50 mg. Six further subjects took bromocriptine 1.25 mg t.i.d. for 3 days p.o. In the subjects given the slow release preparation, the plasma bromocriptine concentrations increased sharply to a maximum of 1.65 mg/l 2 h after injection. This fast release process was followed by slow clearance with a half-life of 16 days. The substance was still detectable in plasma 35 days postinjection. Plasma prolactin (PRL) fell rapidly from a mean of 5.6 ng/ml to reach significantly lower levels at 60 and 120 min. Inhibition was maintained for up to 35 days, when plasma PRL was still significantly below the values recorded at baseline and in the control group. Plasma GH peaked at 3.6 ng/ml at 120 min and subsequently declined slowly to stabilize between 1.4 and 2.2 ng/ml for about 12 h, falling to below the 1 ng/ml limit for the remainder of the study period. In contrast, individuals receiving oral bromocriptine exhibited a significant elevation following the first dose and an equivalent increment after the morning dose on Day 3. Thus, the results show a prolonged inhibitory effect on PRL of this long-acting bromocriptine preparation in parallel with its slow plasma clearance. The stimulant effect on GH secretion is short lived, presumably due to desensitisation of specific receptors.

Description of the time course of the prolactin suppressant effect of the dopamine agonist CQP201-403 by an integrated pharmacokinetic-pharmacodynamic model.

Six male volunteers (mean age 24 years) received a single oral dose of 0.025 mg CQP201-403 and placebo in a randomised double-blind crossover design. Fifteen plasma samples were collected over 48 h and were assayed by radioimmunoassay for drug substance and prolactin (PRL). Three of the samples were drawn during sleep on the first study day. The pharmacological effect (E%) of CQP201-403 was expressed as reduction in plasma PRL levels. The pharmacokinetic (PK)-pharmacodynamic (PD) model consisted of two kinetic compartments and an effect compartment linked to the central compartment. A sigmoid Emax model (Hill equation) described the relationship between the drug concentration in the effect compartment and E%. Curve-fitting of PK and PD data provided individual parameter estimates which served to generate computer-simulated PK and PD profiles after single and multiple doses in order to: investigate the in vivo concentration-effect relationship; evaluate the consequence of dosage reduction on the steady-state PD profile; and study the robustness of the response to changes in drug potency and bioavailability.

Plasma bromocriptine levels, clinical and growth hormone responses in Parkinsonism.

1. Plasma bromocriptine levels following separate oral doses of bromocriptine 12.5, 25, 50 and 100 mg have been determined in ten subjects with parkinsonism. 2. There was considerable variation between peak plasma bromocriptine levels in individual subjects after similar doses of bromocriptine. Peak levels occurred 30--210 min after dosage (mean 102 min). Peak clinical response, peak rise in plasma growth hormone level and fall in blood pressure followed shortly after peak bromocriptine levels occurred. 3. The shape of the plasma-time curve for bromocriptine was similar with all dosages. 4. There was no significant relationship between peak plasma bromocriptine levels, peak clinical response, peak increase in growth hormone and peak fall in blood pressure. However, the degree of improvement in the signs of parkinsonism was related to plasma bromocriptine levels was achieved. 5. Metoclopramide 60 mg pretreatment had no consistent effect upon plasma bromocriptine levels, the clinical or hormonal response.

Pharmacokinetic investigation of oral and i.v. dihydroergotamine in healthy subjects.

A new radioimmunoassay (RIA) for the specific measurement of dihydroergotamine (DHE), sufficiently sensitive for the determination of low plasma concentrations, has been used to investigate the pharmacokinetics of unchanged DHE. In a randomized cross-over trial, eight healthy male volunteers received single doses of DHE 5 mg, 10 mg and 20 mg orally and 0.1 mg and 0.5 mg intravenously. It was possible to determine plasma concentrations and urinary excretion of DHE over the following 48 h. A long terminal plasma elimination phase of unchanged DHE (half-life 15 h) was found. A similar terminal elimination half-life was also calculated from urine data. The multi-exponential decline in plasma DHE with a long terminal half-life suggests that distribution into a deep compartment contributes to the long-lasting effect of the drug. Plasma protein binding was 93%. Despite extensive tissue distribution (Vz = 33 l/kg) and a high plasma clearance (CLP = 2 l/min), dose-independent linear pharmacokinetics was observed. The present assay was at least 20-times more specific than the polyvalent RIA used previously and appears suitable to explore the pharmacokinetics of unchanged DHE in patients on low-dose therapy. The long terminal elimination half-life of DHE only reported previously in studies using 3H-labelled drug, and considered to be due to metabolites, was also true for the parent compound. This, in addition to the sustained pharmacological activity of the 8'-hydroxy metabolite already shown, provides a further explanation for the long duration of action of DHE in animals and man.

Immunoassay of ergotamine and dihydroergotamine using a common 3H-labelled ligand as tracer for specific antibody and means to overcome experienced pitfalls.

A highly sensitive radioimmunoassay for the determination of ergotamine and dihydroergotamine is described. The limit of detection is about 9 pg/mL blood plasma for both compounds. The specificity of the gamma-globulin, which was prepared from rabbit antiserum, was investigated in the presence of compounds synthesized as possible metabolites. It was found that the tricyclic peptide moiety common to both molecules is an essential structural feature for binding to the gamma-globulin. From dilution experiments with the radioactively labelled compound it followed that ergotamine and to a lesser extent also its dihydro derivative are adsorbed on various tube wall materials using known buffer solutions. A practically insuperable obstacle is rearrangement of ergotamine under the experimental conditions, forming a stereoisomer by inversion at the C-8 position. The equilibrium of ergotamine in equilibrium ergotaminine found in human plasma remains stable under the incubation conditions of the radioimmunoassay.

Relationship between plasma concentrations and cardiac beta-adrenoceptor blockade--a study with oral and intravenous bopindolol.

Bopindolol, an esterified beta-adrenoceptor blocking drug, was administered to nine healthy male volunteers in oral (1 mg and 4 mg) and intravenous (1 mg) doses. Plasma concentrations determined using a radio-receptor assay (RRA) and high pressure liquid chromatography (h.p.l.c.) yielded almost identical results, indicating that hydrolysed bopindolol, the major metabolite, is responsible for the pharmacological activity of the drug. After intravenous administration the half-life for the formation of the hydrolysis product was about 0.3 h. The elimination of hydrolysed bopindolol from the plasma, determined with a one-compartment model occurred with a half-life of about 4 h. There were indications for a longer beta phase of elimination with a half-life of about 8 h, which, owing to the relative insensitivity of the method for concentrations present after more than 24 h, could not be determined exactly. The absolute bioavailability of the active compound is about 70%. Cardiac beta-adrenoceptor blockade was determined as the reduction in exercise-induced tachycardia. With oral doses the maximum effect was reached after 3 h (-29 beats min-1 after 1 mg, -40 beats min-1 after 4 mg). After intravenous administration most of the effect was present after 0.5 h but the maximum effect (-33 beats min-1) was only reached at 3 h. Bopindolol possesses a long duration of action: after 48 h 33% of the maximum effect of the oral dose of 4 mg was still present.(ABSTRACT TRUNCATED AT 250 WORDS)