Björn Lemmer

Measurement of hydrophobicity, surface activity, local anaesthesia, and myocardial conduction velocity as quantitative parameters of the non-specific membrane affinity of nine -adrenergic blocking agents.

SummaryIn order to characterize the non-specific membrane affinity of β-adrenergic blocking agents (phenylethanolamino- and phenoxypropanolaminoderivatives), hydrophobicity (i. e. partition coefficients) and surface activity were determined as physicochemical properties of the drugs. Local anaesthetic activity (isolated frog nerve) and effects on myocardial conduction velocity (frog heart) were used as pharmacological parameters. In addition, the hydrophobicity of the β-sympatholytics was calculated according to the method of Hansch and Fujita (1964).1.The nine β-sympatholytics investigated here can be divided into three main groups, according to their physicochemical properties as well as to their nonspecific pharmacological effects. The most active were alprenolol, propranolol, and KL 255; Kö 592, oxprenolol, INPEA, and pindolol were intermediate, while sotalol and practolol were the least active. The activity of the drugs ranged between 3 orders of magnitude in all parameters studied.2.Highly significant correlations were found between the 4 parameters studied. This may indicate that physicochemical properties of the β-sympatholytics are the main determinants of their non-specific pharmacological effects, i. e. of their quinidine-like and/or cardiodepressant effects.3.Structure-activity relationships revealed that the increase of the non-specific membrane affinity of the β-sympatholytics investigated was related to the number of the alkyl- and/or halogen ring substituents, as well as to the length of the alkyl chain of the monosubstituted compounds. Ring substituents containing electronegative N- or O-atoms caused a decrease of membrane affinity.4.The calculated hydrophobicity (Σπ according to Hansch and Fujita) of the drugs investigated here was closely correlated with the partition coefficients determined in an octanol-buffer system. The Σπ-values, on the other hand, correlated significantly with local anaesthetic activity, and with the effects of the drugs on myocardial conduction velocity.5.From the results it is concluded that the non-specific membrane affinity of the β-sympatholytics can be predicted by the determination of their octanol-buffer partition coefficients, or even by simple calculation of their respective Σπ-values.

Circadian rhythms and drug delivery

Abstract Circadian rhythms in the functions of the body are well established, e.g. in cardiovascular (blood pressure, heart rate, blood flow, etc.), pulmonary, hepatic and renal functions. Also the symptoms and onset of disease are not randomly distributed within the 24 hours of a day (e.g. coronary infarction, angina pectoris and asthmatic attacks). It is, therefore, not surprising that also the effects and/or pharmacokinetics of drugs can display significant daily variations. Recent data on the chronopharmaco-dynamics and chronopharmacokinetics of H2-blockers, anti-asthmatics (theophylline, terbutaline), cardiovascular active drugs (propranolol, organic nitrates, nifedipine) are described as representative examples. These data demonstrate that biological rhythms have to be taken into account when evaluating drug delivery systems, galenic formulations and pharmacokinetics as a basis for drug treatment.

PHARMFIT—a Nonlinear Fitting Program for Pharmacology

A new program is presented for nonlinear fitting of data from pharmacological and chronobiological investigations. It contains functions for calculating data from ligand-binding studies and competition experiments, for the analysis of dose-response curves, for pharmacokinetic calculations, and for cosine analysis of harmonic and overlapping rhythms. In addition, it is possible to implement general equations by the user. The program allows data exchange with most spreadsheet, database, and graphics presentation programs, and accepts data from two widely used ambulatory 24-h blood-pressure monitoring systems. The fitting procedure uses the Marquardt-Levenberg algorithm. It calculates the weighted or the unweighted fit together with a great variety of statistics for estimation of goodness of fit. A graphics module permits graphical presentation of the fitted curve. Moreover, fitting of data to different models can be compared for the most likely fit and model discrimination statistics for improvement of further experiments are provided. To demonstrate the chronobiological application of the fitting program PHARMFIT, the analysis of telemetric heart rate data from rats is presented.

Circadian changes in the pharmacokinetics and cardiovascular effects of oral propranolol in healthy subjects.

SummaryFour subjects were synchronized with activity from 07 to 23 h and were given a single oral dose of 80 mg racemic propranolol at fixed times (08, 14, 20 and 02 h) at weekly intervals.ANOVA revealed significant circadian changes in the peak propranolol concentration (Cmax), with a maximum at 08 h and a minimum at 02 h after drug intake; tmax was not dependent on the circadian phase. The elimination half-life varied significantly with the time of day, being shortest at 08 h (3.3 h) and longest at 20 h (4.9 h). The stereospecificity of the propranolol pharmacokinetics was not dependent on the time of drug intake. No circadian variation was found in the maximum decrease in heart rate, but the time to peak effect was dependent on the time of drug intake; tmax was 2.3 h at 08 h and 7.0 h at 02 h. Thus, the time to peak drug concentration did not coincide with the time to peak effect on heart rate at different times of day. Circadian changes were also found in the systolic blood pressure and in the double product.The results show a significant daily variation in the pharmacokinetics and cardiovascular effects of propranolol. However, chronokinetics cannot explain the circadian changes in the effects of the drug. It is concluded that circadian variation in sympathetic tone and vascular reactivity is mainly responsible for the circadian changes in the effects of propranolol.

Reduced basal and stimulated (isoprenaline, Gpp(NH)p, forskolin) adenylate cyclase activity in Alzheimer's disease correlated with histopathological changes

Cyclic adenosine monophosphate (cAMP) is an adenylate cyclase borne second messenger involved in basic metabolic events. The beta-adrenoceptor sensitive adenylate cyclase was studied in post-mortem hippocampi of controls and Alzheimer patients. Virtually identical subsets of each hippocampus homogenate were stimulated by 100 mumol isoprenaline, Gpp(NH)p and forskolin, respectively, in presence of an ATP-regenerating system. The determination of cAMP formed was carried out by means of a radioassay. The observed significant 50% reduction in basal as well as in stimulated adenylate cyclase activity in Alzheimers disease is negatively correlated with semiquantitative evaluations of amyloid plaques (P less than 0.05) but not with neuritic plaques, neurofibrillary tangles or neuropil threads. This reduction in enzyme activity is obviously not due to simple cell loss alone. It is likely that the crucial point of the observed functional disturbance is at the level of the catalytic unit of the adenylate cyclase, since the same degree of reduction is maintained at all steps of the signal cascade.

Diurnal rhythm in the central dopamine turnover in the rat

SummaryUnder controlled conditions of environmental light and darkness of 12:12 h the turnover of dopamine and noradrenaline in brain of male Wistar rats was studied at different times of the day. The turnover was calculated from the decline of the amine concentrations either after inhibition of the tyrosine-hydroxylase with H 44/68 (200 mg/kg, i.p.) or after inhibition of the dopamine-β-hydroxylase with FLA 63 (40 mg/kg s.c.). Whereas the noradrenaline turnover showed only slight but not significant variations within 24 h, the turnover of the central dopamine exhibited significant variations with increased turnover rates in the second half of the light and first half of the dark period. Thus, diurnal variations have to be taken into account when studying the effects of drugs on the turnover of biogenic amines in the central nervous system.

Chronopharmacokinetics and Cardiovascular Effects of Nifedipine

Circadian phase dependency in pharmacokinetics and hemodynamic effects on blood pressure and heart rate of different galenic formulations of nifedipine (immediate-release, sustained-release, and i.v. solution) were studied in healthy subjects or in hypertensive patients. Pharmacokinetics of immediate-release but not sustained-release and i.v. nifedipine were dependent on time of day: immediate-release nifedipine had higher Cmax (peak concentration) and shorter tmax (time-to-peak concentration) after morning than evening application, and bioavailability in the evening was reduced by about 40%. Circadian rhythm in estimated hepatic blood flow as determined by indocyanine green kinetics may contribute to these chronokinetics. A circadian time dependency was also found in nifedipine-induced effects on blood pressure and heart rate as monitored by 24-h ambulatory blood pressure measurements. In conclusion, the dose response relationship of oral nifedipine is influenced by the circadian organization of the cardiovascular system as well as by the galenic drug formulation.

Recent advances in chronopharmacokinetics: methodological problems

Chronopharmacokinetics deals with the study of the temporal changes in absorption, distribution, metabolism and elimination and thus takes into account the influence of time of administration on these different steps. In the last decade, numerous studies have been devoted to chronokinetics: recent advances will be reviewed in the first part. As representative examples, the main chronokinetic changes of anaesthetics, cardiovascular active drugs and antiinflammatory drugs in men are listed. Temporal changes can be involved at each step of the sequence of pharmacokinetic processes: temporal variations in drug absorption from the gastro-intestinal tract, in plasma protein binding and drug distribution, in drug metabolism (temporal variations in enzyme activity, hepatic blood flow) and in renal drug excretion may play a role. Thus, the time of administration of a drug is an important source of variation which must be taken into account in kinetic studies and particular methodological aspects of chronokinetics are needed. In a chronopharmacokinetic study many factors of variation must be controlled: factors related to the drug itself (influence of food, galenic formulation, drug interactions), subject related-factors (age, gender, pathology, posture, exercise, synchronization) and factors related to the conditions of the administration (single or repeated dosing, constant rate delivery, route of administration). In conclusion, there are some instances in which a chronokinetic study is needed: 1) when possible daily variations in pharmacokinetics may be responsible for time dependent variations in drug effects, 2) when drugs have a narrow therapeutic range, 3) when symptoms of a disease are clearly circadian phase-dependent (e.g. nocturnal asthma, angina pectoris, myocardial infarction, ulcer disease) 4) when drug plasma concentrations are well correlated to the therapeutic effect in case the latter is circadian phase-dependent. Variables influencing pharmacokinetics such as fasting, meals and meal times, galenic formulation, posture, activity-rest, have to be controlled according to the aim of the investigation. The main aim of chronokinetic studies is to control the time of administration which among others, can be responsible for variations of drug kinetics but also may explain chronopharmacological effects observed with certain drugs.

Ambulatory blood pressure monitoring in paediatric patients treated by regular haemodialysis and peritoneal dialysis

Ambulatory blood pressure monitoring (ABPM) has been shown to be more representive of blood pressure (BP) levels than casual BP measurements in adult patients treated by haemodialysis (HD). In this study we compared ABPM using the oscillometric SpaceLabs 90207 monitor with casual BP measurements in 35 paediatric patients [17 treated by peritoneal dialysis (PD) and 18 by DH]. Heart rate and plasma concentrations of atrial natriuretic peptide were also measured. No correlations were found between ABPM and casual BP measurements, except for systolic day-time BP in PD patients (r=0.63). Seventy percent of PD and 33% of HD patients were regarded as hypertensive when evaluated by ABPM, while casual BP measurements demonstrated hypertension in 47% (P<0.05) of PD patients and in 44% (NS) of HD patients. One-third of patients were reclassified by ABPM either from normotensive to hypertensive (7/19) or from hypertensive to normotensive (5/16). BP assessed by ABPM was higher in PD than in HD patients. The physiological decline of BP at night was significant and more prouounced in PD than in HD patients. In HD patients day-time BP did not differ between the 1st and the 2nd interdialytic day, but increased in the night hours before the following dialysis session. A positive correlation was found between day-time BP and pre-dialysis plasma atrial natriuretic peptide in both treatment groups. In conclusion this study demonstrates that casual BP recordings are not representative of average BP in dialysed paediatric patients. ABPM is useful in the diagnosis and treatment of hypertension in children with endstage renal disease.

Chronopharmacokinetics of beta-receptor blocking drugs of different lipophilicity (Propranolol, metoprolol, sotalol, atenolol) in plasma and tissues after single and multiple dosing in the rat

SummaryComparative pharmacokinetic studies with the β-receptor blocking drugs propranolol, metoprolol, sotalol and atenolol, differing greatly in lipophilicity, and their main route of elimination were performed in light-dark-synchronized rats after equimolar single (6 μmoles/kg) or multiple (6x6 μmoles/kg) drug application. Drug concentrations were determined in plasma and various target organs of the drugs, e.g. heart, muscle, lung and brain, after drug application in the light period (L) and dark period (D), respectively. After single drug administration pharmacokinetic parameters of all drugs depended on the L and D conditions. Elimination half-lives in plasma and organs were shorter during D than during L. No L-D-differences were found in initial drug concentrations of the hydrophilic drugs sotalol and atenolol. In contrast, C0-values of the lipophilic propranolol in highly perfused organs (muscle, lung, brain) and of metoprolol in muscle tissue were significantly higher in D than in L. No obvious temporal dependency was found in other pharmacokinetic parameters (AUC, plasma clearance,Vdβ) with the exception inVdβ of propranolol. Due to the different physico-chemical properties of the compounds inter-drug-differences in pharmacokinetic parameters including drug accumulation into lung and brain tissue were observed. Multiple drug dosing abolished the circadian-phase-dependency in the elimination half-lives of the drugs due to an increase in D. Only for the highly lipophilic propranolol half-lives in highly perfused organs were still shorter in D than in L. It is concluded that L-D-differences in drug half-lives after single dose application are mainly due to circadian variations in drug elimination with a higher hepatic (propranolol, metoprolol) or renal (sotalol, atenolol) elimination in the activity period of rats during D. Additional studies with propranolol on heart rate of conscious rats revealed that a maximum in β-receptor blockade was achieved at 10 μmoles/kg in L but not in D. Thus, it is assumed that abolition of circadian-phase-dependency in half-lives after 6x6 μmoles/kg of the drugs may be due to the longer lasting and more pronounced β-receptor blockade after multiple drug dosing over a period of several hours in D. Thereby, liver-flow-dependent elimination of propranolol and metoprolol and renal elimination of sotalol and atenolol is reduced to base-line levels found in L.