Pharmacokinetics and tissue distribution of the anticholinergics tiotropium and ipratropium in the rat and dog.

Ipratropium, a current treatment for chronic obstructive pulmonary disease (COPD) and tiotropium, a longer acting anticholinergic bronchodilator currently being developed for COPD are structurally related to atropine. In this study, the intravenous (i.v.), oral (p.o.) and intratracheal (i.tr.) single dose pharmacokinetics (PK) of tiotropium and ipratropium were determined in rat and dog. In rats, concentration-time profiles of tiotropium and ipratropium after single i.v. bolus administration of 7-8 mg kg(-1) are similar. Both drugs are highly cleared (Cl between 87 and 150 ml min(-1) kg(-1)) and extensively distributed into tissues (volume of distribution V(ss) between 3 and 15 l kg(-1)). In dogs, this holds also true for both drugs (Cl between 34 and 42 ml min(-1) kg(-1), V(ss) between 2 and 10 l kg(-1)), although different dose regimen were applied (i.v. bolus of 0.08 mg kg(-1) vs. infusion of 0.1 mg kg(-1) h(-1) for 3 h). Tiotropium plasma concentrations increased linearly in rats over a wide dose range following single i.v. administration. Both ipratropium and tiotropium showed a comparable terminal elimination half-life in rat urine (21-24 h) after single i.v. administration, which was much longer than the corresponding half-life in plasma (6-8 h). Whole body autoradiography in rats revealed a broad and rapid tissue distribution of [(14)C]tiotropium radioactivity after single i.v. administration. A comparable distribution pattern has also been reported earlier for ipratropium.

Tiotropium (Spiriva): mechanistical considerations and clinical profile in obstructive lung disease.

Inhaled antimuscarinics, often called anticholinergics in clinical medicine, are established as first line bronchodilators in COPD. Tiotropium has been developed as a new generation antimuscarinic following ipratropium. Tiotropium is a specific, highly potent antimuscarinic, demonstrating very slow dissociation from muscarinic receptors. Dissociation from M2-receptors is faster than from M3 or M1, which in functional in vitro studies, appeared as kinetic receptor subtype selectivity of M3 and M1 over M2. The high potency and slow receptor dissociation found its clinical correlate in significant and long lasting bronchodilatation and bronchoprotection in patients with COPD and asthma. In asthma, protection against methacholine challenge exceeded the study period of 48 hours. In COPD, bronchodilatation of about 80% of the plateau was demonstrated after the first dose. Following chronic once daily inhalation for 28 days, the improvement in pulmonary function was sustained and there was a further increase in peak effects, but more importantly a rising baseline, achieving steady state within 2 weeks. Tiotropium achieves very stable long lasting effects with comparatively low variation of bronchodilatation between peak and trough (the level before the next administration). Stable 24 hour effectiveness profiles the compound as the first once daily bronchodilator. Clinical correlates of kinetic receptor subtype selective blockade remain to be shown. Plasma levels of tiotropium at trough are in the low pg/ml range and are unlikely to explain the sustained effectiveness in the airways. Slow dissociation from muscarinic receptors is likely to be responsible for the long duration of action.

Effects of clonidine in a primed rat model of acute hepatic porphyria.

Acute hepatic porphyrias can be induced by several drugs and acute attacks of porphyrias are often associated with severe hypertension. Therefore it is important to know if an antihypertensive drug used has porphyrogenic potency or not. As previously demonstrated in normal rats the alpha-receptor blocker clonidine (CAS 4205-90-7) has no significant influence on the porphyrin metabolism. Pretreatment of rats with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or allyl-isopropyl-acetamide (AIA) induces hepatic delta-aminolaevulinic acid synthase (ALA-S) and increases the urinary excretion of porphyrin precursors (ALA and PBG) comparable to the latent phase of acute hepatic porphyrias in humans. Clonidine did not induce hepatic ALA-S or urinary excretion of ALA or PBG in normal as well as in DDC or AIA pretreated rats. Moreover the induction of P4501A1 (7-ethoxyresorufin-O-deethylase) by DDC was abolished by simultaneous application of clonidine. From these findings one can probably conclude that clonidine is a safe drug in human acute hepatic porphyria.

Pharmacokinetics and pharmacodynamics of beta 2-agonists (in the light of fenoterol).

As an example of beta 2-agonists fenoterol was used in this study on 27 patients with chronic obstructive airways diseases (COAD). After refraining from any kind of bronchodilator during 12 h the patients were given the drug in a crossover design in three groups. Using aerosol inhalation, intravenous route and nasal instillation we measured the response of airway resistance, intrathoracic gas volume and fenoterol plasma concentrations. The plethysmographic measurement of airways resistance (Rt) and intrathoracic gas volume showed comparable results of bronchodilation (at different dosages) for each of the routes. Even the onset of action was nearly the same with all the different routes. The amount of bronchodilatation was in the range of 59% of the initial Rt values. The duration of bronchodilatation was much longer after metered dose inhalers (MDI) inhalation ( > 4 h) than after intravenous routes. The duration after nasal administration was in between. The infusion maintains its effect only as long as the infusion is given. The bronchodilation response induced by fenoterol reaches the same values with different routes of administration and depends on the amount of decrease of airway obstruction. The highest plasma concentrations were reached with the intravenous boluses. Immediately after injection the concentration decreased rapidly. The maximum plasma concentrations after MDI were around 20% of that after the intravenous route for the same bronchodilatation. The heart rate is a function of the plasma concentration. At low concentrations such as after aerosol inhalation of 200 micrograms the influence on the heart rate is not significant. After aerosol inhalation the effect at the receptor can be calculated to be > 7 times stronger than seen from any plasma concentration after intravenous administration. It is assumed that there are structures near the beta 2-bronchodilator receptor which are responsible for the long-lasting effect that is observed only after aerosol inhalation. These depot structures cannot be reached from the plasma in concentrations needed under in vivo conditions. Loss of these structures shortens the duration of the bronchodilator effect. In respect to effect/side effect relationship, more frequent administration of smaller doses may be the best method for administering beta 2-agonists as aerosols in patients with COAD. For many patients with severe forms of this disease, individual optimal dosage with MDI has to be defined following repeated measurements of the airway obstruction so as to achieve the best possible bronchodilatation.

Influence of clonidine on the porphyrin metabolism in female rats.

Effects of different doses of clonidine (CAS 4205-90-7) (15, 150, or 300 micrograms/kg body weight) over a period of 3, 14, or 64 days on the activities of delta-aminolevulinic acid synthase (ALA-S) and the P450 dependent isoenzymes aminopyrine-N-demethylase (ADM), 7-ethoxycoumarin-O-deethylase (7-ECO-D), and 7-ethoxyresorufin-O-deethylase (7-ERO-D) as well as on the hepatic porphyrin and P450 content were studied in female rats. Additionally, the urinary excretion of total porphyrins, and porphyrin precursors delta-aminolevulinic acid (ALA) and porphobilinogen (PBG) and the plasma clonidine level were measured. No changes in the activity of ALA-S and in the hepatic and urinary porphyrin, ALA and PBG contents were observed. An increase in the activities of ADM in the short and median term application of clonidine and of 7-ERO-D in the long term application was detected. It is concluded from these findings that clonidine has no effect on the porphyrin biosynthesis, but has an influence on the activities of P450 dependent isoenzymes ADM or 7-ERO-D.

Ba 679 BR, a novel long-acting anticholinergic bronchodilator.

The use of anticholinergics in antiobstructive therapy is well established in pulmonary medicine. We sought to improve the duration of action of inhaled antimuscarinics. A newly developed compound, Ba 679 BR (abbreviated Ba 679) proved to be a highly potent muscarinic antagonist in guinea pig tracheal rings. Its binding to human receptors (Hm1, Hm2, Hm3) was characterized by KD-values in the 10(-10) M concentration range. Assessment of the dissociation rate of complexes of labelled Ba 679 and human muscarinic receptors revealed very slow dissociation in comparison to ipratropium. The half-lives in hours were: Ba 679-Hm3: 34.7, -Hm1: 14.6, -Hm2: 3.6; ipratropium-Hm3: 0.26, -Hm1: 0.11, -Hm2: 0.035. The duration of action in vivo was determined by means of acetylcholine-induced bronchospasms in dogs following inhalation of the drugs. Ba 679 demonstrated a significantly longer duration of protection than an equipotent dose of ipratropium. The plasma levels following inhalation in dogs declined rapidly and are unlikely to reflect the duration of the pharmacological activity. In summary, Ba 679 represents a novel type of antimuscarinic bronchodilator with a long duration of action, most likely due to its slow dissociation from Hm3-receptors. In addition, the drug showed "kinetic receptor subtype selectivity" by having a more rapid dissociation from Hm2 than from Hm1 and Hm3 receptors.

Pharmacokinetic/dynamic correlation of pulmonary and cardiac effects of fenoterol in asthmatic patients after different routes of administration.

Pulmonary and cardiac effects of the beta 2-adrenergic drug fenoterol were studied in 27 asthmatic patients using an integrated pharmacokinetic/dynamic (PK/PD) approach. Airway resistance (Rf), intrathoracic gas volume (IGV), heart rate, and plasma levels were monitored after placebo, injection (12.5 and 25 micrograms), nasal instillation (400 micrograms), inhalation (200 and 400 micrograms), and infusion (200 micrograms/180 min with or without loading dose). The pharmacokinetics were best described by an open three-compartment model with a terminal half-life of 200 min (gamma = 0.23 +/- 0.08 L/hr), a volume of distribution at steady state of 1.9 +/- 0.8 L/kg, and a clearance of 0.86 +/- 0.32 L/hr/kg, with 14 and 9% absorbed after nasal and pulmonary administration, respectively. For the noninhalation regimens, a PK/PD correlation linked the concentration in the shallow pharmacokinetic compartment to the investigated effects via an Emax relationship, resulting in three to five times higher EC50 values (concentration necessary to achieve half-maximal effect) for the heart rate than for the beta 2-mediated effects on IGV and Rf. In contrast, pulmonary effects after inhalation could not be incorporated into the correlation, indicating that these effects are induced locally after inhalation. Intrapatient variability for EC50 and Emax was approximately 90%.

Clenbuterol plasma concentrations after repeated oral administration and its effects on cardio-respiratory and blood lactate responses to exercise in healthy Standardbred horses.

To evaluate the effects of clenbuterol on cardio-respiratory parameters and blood lactate relation to exercise tolerance, experimental horses performed standardized exercise tests on a high-speed treadmill before and after administration of the drug. Clenbuterol was administered in feed to six healthy Standardbreds at a dose rate of 0.8 micrograms/kg b.wt twice daily for 5.5 days. Each horse was tested twice, without and with a respiratory mask, during two consecutive days. One week elapsed between the baseline tests without drug and the tests with clenbuterol treatment (each horse served as its own control). The results show an unchanged heart rate response to exercise 2 h after the last clenbuterol administration. The blood lactate response and the arterial oxygen tension during exercise did not differ before and after drug treatment. The oxygen uptake as well as pulmonary ventilation relative to the work load performed was essentially unaffected. The arterial pH during exercise was significantly increased (P less than 0.05) following clenbuterol treatment. Plasma levels of clenbuterol were maximal 2 h post-administration with values between 0.45 and 0.75 ng/ml. The plasma half-life of elimination was 10.4 h (+/- 2.25 SD). In conclusion, clenbuterol did not cause any major effects on the cardio-respiratory and blood lactate parameters studied in healthy horses performing submaximal exercise tolerance tests.

[Pharmacokinetics of clonidine following intravenous administration of high doses for the treatment of delirium tremens]. / Pharmakokinetik von clonidin nach intravenöser Gabe hoher Dosen zur Behandlung des Delirium tremens.

Concentrations of clonidine (CAS 4205-09-7. Catapresan) were measured in the plasma and the urine of 6 patients with delirium tremens who received 1.8-13.8 mg clonidine on the third treatment day. There was a linear correlation between the daily dose of clonidine and the steady state concentration of clonidine in the plasma, even with the high doses of clonidine used in this study. The total clonidine clearance was 29-62% lower than in normal volunteers. The renal clearance were 49-75% lower than normal. The renal excretion of the non-metabolized clonidine was significantly lower than the normal range. The creatinine clearance on the other hand was only slightly reduced. The present study gives first hints that the metabolic clearance of clonidine in patients with delirium tremens is not decreased remarkably.

Radioimmunological determination of fenoterol. Part II: Antiserum and tracer for the determination of fenoterol.

A radioimmunological method for the determination of the concentration of fenoterol in biological samples is described. The mixture of antibodies against the enantiomers of fenoterol obtained with the selected hapten shows a high affinity for racemic fenoterol and for the monoiodo125-fenoterol used as a tracer, which is also present as a racemate. The limit of detection of the radioimmunoassay for fenoterol (racemate) in biological samples (plasma, urine) is 10-20 pg/ml. The precision and accuracy of the radioimmunoassay, in the presence of racemic fenoterol, are sufficient for an analysis and meaningful interpretation of samples from human pharmacokinetic studies. A relationship between the cross-reactivity of the antibodies against fenoterol and a preferred conformation of the fenoterol molecule in aqueous solution is discussed.

[Maternal plasma concentrations in multiple oral fenoterol treatment]. / Mütterliche Plasmakonzentrationen bei multipler oraler Fenoterolbehandlung.

Reports on the clinical effectiveness of oral treatment with beta-sympathomimetic fenoterol are quite divergent in their conclusions. The aim of this study was to determine the plasma levels of fenoterol in steady state during tocolytic treatment with high oral doses. Nine pregnant women with clinically indicated tocolysis were given a 5 mg dose of fenoterol in tablet form eight times per day at prescribed hours. During the first four days, in the late afternoon just before and again one hour after the intake, a blood sample was taken to determine the fenoterol concentration by radioimmunoassay. In addition, uterine activity, blood pressure, heart rate, and tremor were periodically checked while the patient was under observation. The fenoterol levels in the plasma ranged from 130 to 200 pg/ml; the steady state concentration remained relatively constant throughout the observation period. It is not certain, that by taking the blood sample one hour after the tablet was swallowed, the maximal concentration was found. However, with the given doses, nearly the same fenoterol levels were measured in the blood as with low doses of intravenously administered fenoterol.

[Oral tocolytic therapy with clenbuterol--clinical facts]. / Orale Tokolyse mit Clenbuterol--clinische Fakten.

Clenbuterol is a betamimetic agent with a marked effect on the adrenergic beta-2-receptors relevant for tocolysis. The influence on beta-1-receptors of the heart, resulting in cardiovascular side effects is far less. The substance is resorbed almost completely enterally and has a half-life of 34 hours. Consequently, ingestion intervals of 12 hours are possible, resulting in a good acceptance of the tocolytic, therapy and a noticeable improvement of the patients compliance. Clenbuterol was applied in 37 cases in the course of a clinical test. Initially, the dose was 0.04 mg b.i.d., after 24 hours 0.02 mg b.i.d. In cases of cervix-effective, premature labor, an objectively measureable tocolytic effect was achieved. Subjectively reported side effects, i.e. palpation, tachycardia and tremor, were noticeably weaker than under fenoterol therapy. There was no indication of clenbuterol-related cardiotoxicity regarding continuous measurement of heart-specific enzymes, i.e. CK-MB and serum myoglobin. No pathologic alterations were found in the EKGs. Therefore, regarding indications and contraindications for beta-adrenergic agents, clenbuterol appears to have good tocolytic properties, with the advantages of less cardiac side effects, better compliance and a better dose-effect-ratio compared with the common oral tocolysis with fenoterol.

[Oral tocolytic therapy with clenbuterol--determination of the plasma level]. / Orale Tokolyse mit Clenbuterol--Plasmaspiegelbestimmungen.

12 pregnant women with premature labor received tocolytic treatment with clenbuterol tablets. Initially, 2 clenbuterol tablets (40 micrograms each) were to be given as loading dose (application interval = 12 hours), then a dose reduction was planned (40 micrograms), to be followed by a maintenance dose of 20 micrograms. The mean values of plasma levels of clenbuterol hydrochloride during the day ranged between 0.266 and 0.328 ng/ml on testing days 2 to 8, without significant statistical variation. Therefore, the loading dose lead to the desired rapid steady state of the plasma level. The applied dosage plan with clenbuterol tablets for oral therapy of premature labor proved to be ideal, both clinically as well as pharmacokinetically. After reaching an effective plasma level, only 20 micrograms b.i.d. is sufficient as maintenance dose, resulting in excellent patient compliance compared with oral fenoterol therapy (max. application interval: 4 hours).

Radioimmunological determination of fenoterol. Part I: Theoretical fundamentals.

A general solution is given for the system of equations describing coupled mass equilibria having m antibodies with one binding site, or with several mutually independent binding sites of equal intrinsic affinity (immunoglobulin (Ig) G antibodies) and n monovalent antigens. Based on this a formula is given with which it is possible to calculate the minimum association constant of the antibody and the minimum specific radioactivity of the tracer in a radioimmunoassay when the detection limit is given and the assay conditions are established. The model m = 2 and n = 4 describes the behaviour of a system which is based on a mixture of stereoselective antibodies and a racemic tracer. The effect of the enantiomer ratio of an optically active ligand on this system is demonstrated.

Proof of the linearity of the pharmacokinetics of alinidine in man.

The pharmacokinetics of alinidine was investigated in two groups of volunteers: Group I (N=5) received on two occasions single doses of 14C-labelled drug given orally (40 mg) or intravenously (10 mg); Group II (N=6) received single oral doses 10, 30, or 90 mg dissolved in 20 ml water. The samples from Group I were analysed by two different and independent methods (RIA and counting total radioactivity). The results obtained by the two methods were identical, since the compound was not metabolized. The plasma concentrations and renal excretion data obtained from both groups were individually fitted to an open three compartment model. Independent of the route of administration and of the doses given, similar pharmacokinetic parameters were calculated for each group and each trial. The half lives of the distribution and elimination phases were t1/2 alpha: 36-41s, t1/2 beta: 9.9-11.1 min and t 1/2 gamma: 2.7-3.8h. There was a linear relationship between the dose administered and the resulting areas under the plasma concentration curves (AUC). Following a lag period (tau =0.19-0.22h), the peak plasma concentration was reached 0.6-1.2h after oral administration. Oral alinidine was 100% bioavailable.

Pharmacokinetic comparison of etilefrine to its prodrug, the stearic acid ester of etilefrine.

The relative bioavailability of a prodrug of etilefrine, its stearic acid ester, was determined by means of plasma levels and renal excretion. The comparison of the plasma levels and renal excretion was carried out in a cross-over design in six subjects. 3H-etilefrine (20 mg) and 3H-2-etylamino-1-(3-stearoylphenyl)ethanol hydrochloride (44.42 mg) were administered orally in equimolecular amounts. The stearic acid ester of etilefrine does not appear in the blood; the ester is split even during absorption. The relative bioavailability of the stearic acid ester of etilefrine, which was determined from the comparison of the areas under the plasma level and the renal excretion, amounts to 51% related to etilefrine. The investigation of the renal excretory products after administration of etilefrine and its prodrug showed the same metabolic pattern. The sulfuric acid ester of etilefrine is the main metabolite. In addition to etilefrine, two basic metabolites are excreted. According to mass- and NMR-spectrometric findings, these two metabolites are two isomeric tetrahydroisoquinolines which formally developed by condensation of etilefrine with formaldehyde. These tetrahydroisoquinolines are excreted free and conjugated with sulfuric acid.

[Plasma levels, renal excretion and metabolism of orciprenaline after administration in sustained-release form (author's transl)]. / Plasmaspiegel, renale Ausscheidung und Metabolismus von Orciprenalin nach Verabreichung als Depotpräparat.

A newly developed sustained-release form of orciprenaline-sulfate (Alupent) was tested in 13 patients. Determination of 3H-radioactivity in blood, urine and faeces was used to elucidate its pharmacokinetic properties. Maximum plasma levels of radioactivity were obtained between 8 and 12 h after administration. 10.7 +/- 2.5% of the administered radioactivity were excreted in urine over a period of 72 h. Orciprenaline was mainly excreted as the sulfate-conjugate. Approximately five percent of the radioactivity were excreted as 4,6,8-trihydroxy-N-isopropyl-tetrahydroisoquinoline--the condensation product of formaldehyde and orciprenaline.

[Metabolite isolation for mass spectrometrical determination of new drugs (author's transl)]. / Isolierung von Metaboliten neuer Arzneimittel zur massenspektrometrischen Strukturaufklärung.

Only very minute concentrations of metabolites of highly effective and consequently low dosed drugs can be detected in urine. In order to identify the structure of these compounds they must be concentrated by a factor up to 1:10(6). Isolation of metabolites, especially when present as conjugates, becomes more complicated the greater the polarity. In this paper some methods for isolation are presented using column- and thin-layer chromatography as well as extraction and dialysis, finally their practical application and their most effective combination are described. Priority must be given to solving two problems: firstly, a rough pre-purification is necessary to eliminate physiological components from the urine such as salts, urea, etc., and secondly, the mixture of metabolites has to be separated into single metabolites. Examples are given to demonstrate the practicability of these methods for the isolation and structural identification of metabolites belonging to varying structural classes.