rhythm-adjusted peak), amplitude (one-half of the peak-trough difference) ..... agents by thin-layer chromatography and high-performance liquid chromatography ...
European Journal of Clinical Pharmacology
Eur J Clin Phalanacol (1988) 33 : 619-624
© Springer-Verlag t988
Circadian Changes in the Pharmacokinetics and Cardiovascular Effects of Oral Propranolol in Healthy Subjects B. Langner and B. Lemmer Center of Pharmacology, J.W. Goethe-University, Frankfurt/Main, Federal Republic of Germany
Summary. Four 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 (Cm~_0,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. Key words: propranolol; isomers, chronopharmacokinetics, cardiovascular effects, circadian changes, healthy volunteers
Pronounced daily variation in the cardiovascular effect (on heart rate and blood pressure) of beta-receptor blocking drugs is known to occur in hypertensive patients and in those suffering from coro-
nary heart disease [1-5, for review see 61. These carcadian changes in drug effects could be due to daily variation in the pharmacokinetics and/or in the susceptibility of the cardiovascular system to the drug. In rats active at night circadian variation in the pharmacokinetics of various beta-receptor blocking drugs has been described [7-9]. In man circadian variation has been described in the pharmacokinetics of (+__)-propranolol [10]. In order to find out whether or not the chronokinetics of propranolol contributed to its chronodynamics, the pharmacokinetics and cardiovascular effects on heart rate and blood pressure have been investigated in healthy subjects after ingestion of (+_)-propranolol at four different times of the day. Since the specific beta-receptor blocking activity of propranolol is restricted to the (-)-enantiomer, the plasma concentrations of both stereo-isomers were determined by HPLC.
Subjects and Methods Four healthy volunteers, 3 men and 1 woman, aged 23-42 years, weighing 60-74 kg, participated in the study. They were members of the department and were considered healthy on the basis of medical history and physical examination. Informed consent was obtained. Subjects were synchronized with physical activity from 0%23 h and nocturnal rest in bed from 23-07 h. Each subject ingested racemic propranolol 80 mg (Dociton) with 100 ml mineral water at 08 h, 14 h, 20 h and 02 h, with a one week wash-out between each study. On each occasion propranolol was taken always one hour after a light meal consisting of 2 slices of bread with marmelade and cheese and 200 ml mineral water; the meals were eaten at 07, 13, 19 and 01 h, additional meals were only allowed 5 h after drug intake.
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B. Langner and B. Lemmer: Circadian Changes in Propranolol Kinetics and Effects
Blood samples were taken by venepuncture 0, 1, 2, 4, 6, 8 and 10 h after drug intake. Heart rate and blood pressure in the sitting position were measured at the same times with an electronic device (Sanoquell). Circadian control values of heart rate and blood pressure in each subject were measured over a 24-h period on a separate occasion. Drug effects were calculated in relation to the individual circadian controls. Plasma concentrations of the propranolol enantiomers were determined by HPLC following chiral derivatization to [11, 12]. The HPLC system consisted of a constant flow p u m p (Gynkotek, 600/200), an autosampler (Waters, WISP710B), a reversedphase column (Knauer, 1 0 c m × 4 m m , Hypersil ODS 5 gm), a spectrofluorometer with a 150 W Xenon lamp (Kontron, SFM 22) and a computing integrator (Spectra Physics, SP4100). After nonstereospecific extraction of alkalized plasma with heptane: butanol (80: 20), derivatization with the chiral reagent R-(+)-a-methylbenzyl-isocyanate [13, 14] (Aldrich Chemical Company, Milwaukee, USA) in dry chloroform: dimethylformamide (9:1), produced diastereoisomers from the propranolol enantiomers. The diastereomers were separated on a non-chiral reversed-phase C18-column and detected fluorometrically (ex/em: 285/338) in a 15-rain run; peak heights were measured. Calibration curves were linear in the relevant concentration range of 0-120 ng ( +)-propranolol. The correlation coefficients were 0.997 + 0.003 and 0.996_+ 0.004 for ( - ) - and (+)-propranolol, respectively ( ,7 _+SD, n = 16). The detection limit was 1-2 ng/ml plasma;
the separation factor a=1.131_+0.004 ( 2 + S D , n = 16); and the intra assay variance was 4.7% and 5.7% for ( - ) - and (+)-propranolol, respectively. The pharmacokinetic variables assessed were: peak serum concentration (Cm~x), time to peak concentration (tm~), the apparent terminal elimination half-life (t~ p), and the area under the serum concentration from zero time to 10 h (AUC). The apparent oral clearance was calculated as administered dose/ kg b.w. divided by AUC.
Statistical Analysis Unless otherwise stated, mean values __,SEM were calculated. In order to test for daily variation analysis of variance (ANOVA) was used, and to take into account interindividual differences, ANOVA was also calculated for the individual results of each as a percentage of the corresponding 24-h mean. ~llae two-tailed paired t-test was used to test differences in the effects of propranolol. Twenty-four-hour control values of heart rate and double product (mean arterial blood pressure x heart rate) were submitted to a single cosinor analysis for rhythm quantification [15]. The rhythm was characterized by its acrophase (circadian time of rhythm-adjusted peak), amplitude (one-half of the peak-trough difference) and mesor (rhythm-adjusted 24-h mean), and the hypothesis that the amplitude differed from zero was tested with p < 0.05. The calculations followed Vokac [15] and were done on an Apple II e computer. For the ANOVA a HP85 computer was used.
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Fig. 1. Circadian phase-dependency of the plasma concentrations of (-)-propranotol and the heart rate lowering effect as % of the circadian control values (see Table 3). Group mean __+SEM for 4 healthy volunteers. Racemic propranolol 80 mg p.o. was taken at 08:00 h, 14:00 h, 20:00 h or 02:00 h
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24 20 Time of d o y (h)
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B. Langner and B. Lemmer: Circadian Changes in Propranolol Kinetics and Effects Table 1. Pharmacokinetics of (-)-propranolot after oral intake of 80 mg (±)-propranolol at 4 different times of the day
ANOVA
Time of drug intake (h)
Parameter
Crna~(ng. m1-1) t ~ (h) Cmax/tmax (ng.ml -~-h -t) % (h) AUC (ng.ml -a.a0 h) Clearance (ml.min-l-kg-1)
08:00 h
14:00 h
20:00 h
02:00 h
F(3/12 )
p
38.6 _+11.2 2.5:2 0.50 17.9± 6.4 3.3 ± 0.43 196:247 61 ±15
20.0+ 6.5 3.5 + 0.50 7.5+ 3.9 4.2+ 0.50 106 +30 t13 ±24
26.2+ 5.3 3.0_+ 0.58 10.6±_ 3.7 4.9:2 0.21 140 :223 76 __+12
18.4_+ 4.4 3.5 ± 0.96 7.1± 2.4 4.4± 0.58 92 __+22 131 __+35
3.67 t.33 3.55 6.05 3.20 2.62
