Pharmacokinetics Of Felodipine Research Articles

Inhibitory effect of 20(S)-protopanaxadiol on cytochrome P450: Potential of its pharmacokinetic interactions in vivo

20(S)-Protopanaxadiol [20(S)-PPD] is a fully deglycosylated ginsenoside metabolite produced by the gut microbiota in the gastrointestinal tract. Although diverse pharmacological effects have been reported, information on the pharmacokinetic interactions of 20(S)-PPD with cytochrome P450s (CYPs) remains limited. Therefore, the inhibitory potential of 20(S)-PPD on CYP enzymes, which mainly contribute to drug pharmacokinetics, was investigated in this study. The inhibitory effect of 20(S)-PPD was strong for CYP3A4 and moderate for CYP2B6 in human liver microsomes. 20(S)-PPD inhibited Cyp3a and Cyp2b in mouse liver microsomes with a potency similar to that in humans. The solubility of 20(S)-PPD in the artificial intestinal fluid was close to IC50 values of Cyp3a and Cyp2b in the mouse intestine. Systemic exposure to buspirone (Cyp3a specific substrate) and bupropion (Cyp2b specific substrate) increased significantly, whereas the area under the plasma concentration–time curve (AUC) ratio of metabolite to parent drug decreased significantly when co-administered with 20(S)-PPD in mice. The pharmacokinetics of felodipine, a widely used anti-hypertensive agent metabolized mainly by Cyp3a, was also altered following 20(S)-PPD treatment in mice. In conclusion, 20(S)-PPD likely affects the in vivo metabolism of CYP3A4 or CYP2B6 substrates, suggesting a need for careful attention when concomitantly administering 20(S)-PPD with other medications. This study will broaden our understanding of ginseng and products containing precursor ginsenosides of 20(S)-PPD for safer and more efficient use in humans.

Severity of coeliac disease and clinical management study when using a CYP3A4 metabolised medication: a phase I pharmacokinetic study

ObjectiveSeverity of coeliac disease depends in part on the extent of small intestinal mucosa injury. Patients with the most abnormal pathology have loss of duodenal villi CYP3A4, a drug-metabolising enzyme...

Pharmacokinetics and drug-drug interaction between enalapril, enalaprilat and felodipine extended release (ER) in healthy subjects.

Since angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists have complimentary mechanisms of action, enalapril, an ACE inhibitor, is used in combination with felodipine, a vascular selective dihydropyridine calcium antagonist, for the treatment of hypertension. The present study was designed to investigate the possible drug-drug interaction between these two agents in Chinese healthy subjects. A randomized, open-label, multiple-dose, 3-treatment, 3-period, 6-sequence cross-over study enrolling 12 healthy subjects (six male and six female subjects) was performed. Plasma pharmacokinetic studies were performed after 5 mg of enalapril and 5 mg of felodipine were administered alone or concomitantly twice per day for six days, and once in the morning of day seven. All 12 healthy subjects (mean [SD] age, 24.3 [2.8] years; body weight, 57.3 [5.7] kg; height, 163.2 [5.2] cm) completed all scheduled pharmacokinetic studies. Geometric mean ratios (with 90% CIs) of AUCτ,ss and Cmax,ss for enalapril administered concomitantly with felodipine vs. enalapril administered alone were 1.025 (0.80-1.25) and 1.065 (0.70-1.43), respectively. Geometric mean ratios (with 90% CIs) of AUCτ,ss and Cmax,ss for felodipine administered concomitantly with enalapril vs. felodipine administered alone were 1.14 (0.97-1.31) and 0.80 (0.65-0.95), respectively. There were no severe or serious drug-related adverse events observed during the study. Our results revealed that the co-administration of enalapril and felodipine affected the pharmacokinetics of felodipine, but not that of enalapril. Although the difference in PK parameters was statistically significant, its clinical significance may be limited, considering safety profile observed in the present study.

Coffee-Antihypertensive Drug Interaction: A Hemodynamic and Pharmacokinetic Study With Felodipine.

A period of abstinence from coffee to permit caffeine elimination appears to enable increased blood pressure on subsequent exposure. We hypothesized that this would offset the antihypertensive effect of the dihydropyridine calcium channel blocker felodipine. A randomized, single-dose, crossover study assessed hemodynamic and pharmacokinetic effects following 2 days without coffee and caffeine-containing foods. Consistently brewed black coffee (2×300ml), felodipine maximum recommended dose (10mg), and coffee plus felodipine were tested in middle-aged normotensive subjects. Pretreatment plasma caffeine concentrations were unquantifiable. After coffee, blood pressure changes (mm Hg) averaged over study hours 1-4 were increased for brachial systolic (7.6, P < 0.001) and diastolic (4.9, P < 0.001) and aortic systolic (7.4, P < 0.001), pulse (3.0, P < 0.05) and augmentation (1.4, P < 0.05) relative to baseline. After coffee plus felodipine, they were higher for brachial systolic (4.0, P < 0.05) and diastolic (3.9, P < 0.001) and aortic systolic (4.6, P < 0.05) compared to felodipine alone. The pressor effects of coffee and its modulation by felodipine were variable among individuals. Coffee containing caffeine (127mg) caused maximum pressor effect. Caffeine and felodipine pharmacokinetics were similar for coffee and felodipine given alone or in combination indicating an interaction having a pharmacodynamic basis. Plasma felodipine concentration-diastolic blood pressure reduction relationship shifted with coffee such that doubling the felodipine concentration would eliminate the pressor effect. However, this may increase the risk of adverse drug events particularly during the timeframe without coffee. Intermittent coffee ingestion might complicate hypertension diagnosis and management for many individuals.

Oral Pharmacokinetics of Felodipine in Mexican Healthy Volunteers: Evidence for Interethnic Differences

Oral Pharmacokinetics of Felodipine in Mexican Healthy Volunteers: Evidence for Interethnic Differences

Evaluation of First-Pass Cytochrome P4503A (CYP3A) and P-glycoprotein Activities Using Felodipine and Hesperetin in Combination in Wistar Rats and Everted Rat Gut Sacs in Vitro

The effects of hesperetin on the pharmacokinetics and the role of P-glycoprotein (P-gp) in the transport of felodipine were investigated in rats and in vitro. Felodipine was administered orally (10 mg/kg) without or with hesperetin (25, 50 and 100 mg/kg) to rats for 15 consecutive days. Blood samples were collected at different time intervals on 1(st) day in single dose pharmacokinetic study (SDS) and on 15(th) day in multiple dose pharmacokinetic study (MDS). The area under the plasma concentration-time curve (AUC0-∞ ) and the peak plasma concentration (Cmax ) of felodipine were dose-dependently increased in SDS and MDS with hesperetin compared to control ( p < 0.001). The half-life (t1/2 ) and mean residence time was longer than the control group in both studies. The role of P-gp determined using everted rat gut sacs in vitro by incubating felodipine with or without hesperetin and verapamil (typical P-gp and CYP3A4 inhibitor). The in vitro experiments revealed that the verapamil and hesperetin increased the intestinal absorption of felodipine (p < 0.01). Concurrent use of hesperetin dramatically altered the pharmacokinetics of felodipine leading to an increase in systemic exposure. The likely mechanism is inhibition of CYP3A4-mediated first-pass metabolism and P-gp in the intestine and the liver.

In Vitro to in Vivo Extrapolation and Physiologically Based Modeling of Cytochrome P450 Mediated Metabolism in Beagle Dog Gut Wall and Liver

The beagle dog is a widely used in vivo model to guide clinical formulation development and to explore the potential for food effects. However, the results in dogs are often not directly translatable to humans. Consequently, a physiologically based modeling strategy has been proposed, using the dog as a validation step to verify model assumptions before making predictions in humans. One current weakness in this strategy is the lack of validated tools to incorporate gut wall metabolism into the dog model. In this study, in vitro to in vivo extrapolation factors for CYP2B11 and CYP3A12 mediated metabolism were established based on tissue enzyme abundance data reported earlier. Thereafter, physiologically based modeling of intestinal absorption in beagle dog was conducted in GastroPlus using V(max) and K(m) determined in recombinant enzymes as inputs for metabolic turnover. The predicted fraction of absorbed dose escaping the gut wall metabolism (F(g)) of all five reference compounds studied (domperidone, felodipine, nitrendipine, quinidine, and sildenafil) were within a two-fold range of the value estimated from in vivo data at single dose levels. However, further in vivo studies and analysis of the dose-dependent pharmacokinetics of felodipine and nitrendipine showed that more work is required for robust forecasting of nonlinearities. In conclusion, this study demonstrates an approach for prediction of the gut wall extraction of CYP substrates in the beagle dog, thus enhancing the value of dog studies as a component in a strategy for the prediction of human pharmacokinetics.

Pharmacokinetics of felodipine extended-release tablets in healthy Taiwanese subjects: a retrospective review

The objective of this study was to investigate the pharmacokinetics of felodipine (CAS 72509-76-3) in healthy male Taiwanese subjects. This is a retrospective review of five felodipine pharmacokinetic studies completed in Taiwan. A total of 100 evaluable healthy Taiwanese males were enrolled in these studies. The subjects received 5 mg (n = 80) or 10 mg (n = 20) of Plendil (felodipine extended-release tablets; felodipine ER) once daily for 6 days. The mean +/- SD t(max,ss,) CG(max,ss) and AUG(tau) of dose normalized to 10 mg felodipine was 3.32 +/- 1.33 h, 13.12 +/- 5.34 nmol/L and 136.33 +/- 63.18 nmol x h/L, respectively. By using Kolmogorov-Smirnov's test and probit plots, the results indicated that the frequency distribution of AUC/dose, C(min)/dose and CL/F was bimodal. Compared to data from the literature, the mean C(max,ss) and AUG(tau) of 5 mg felodipine in healthy young Taiwanese subjects were similar to or slightly lower than data from Swedish, Danish, Turkish and Canadian studies in healthy young subjects who received 10 mg felodipine. Comparable C(max) values and approximately 30% lower AUC values were observed when comparing the 5 mg Taiwanese data to data in healthy elderly German subjects who also received 5 mg felodipine. Taiwanese subjects might have lower CYP3A4 activity to metabolize felodipine, which is similar to the phenomenon observed with nifedipine.

Different Roles of Pummelo Furanocoumarin and Cytochrome P450 3A5*3 Polymorphism in the Fate and Action of Felodipine

Herein we aim to test if pummelo furanocoumarins can inhibit cytochrome P450 (CYP) 3A both in vitro and in vivo, and to explore the influence of CYP3A5*3 (GenBank AC005020: A22893-->G) polymorphism in the pharmacokinetics and pharmacological response to felodipine. Fruit juices of pummelo grapefruit (Citrus paradisi Macf., G), 'Guanximiyou' (C. grandis Osbeck vs. Guanxi, P) and 'Changshanhuyou' (C. changshanhuyou Y.B. Chang, H) were selected by screening Citrus fruit juices for their furanocoumarin contents and their inhibition of testosterone 6beta-hydroxylation in human liver microsomes. Twelve healthy male Chinese were administered 250 mL G, P, H or water (W) alternatively with 26-mumol (10-mg) plain tablet felodipine, and were observed for 12 h. G had more furanocoumarins and at higher levels than P while H had none, and their potencies for in vitro CYP3A inhibition were in the order as G > P > H. The geometric mean and 90% confidence intervals of pharmacokinetic parameters for human oral felodipine with G, P, H and W were respectively as follows: peak plasma concentration (nmol.L(-1)), 37 (32-44), 25 (21-29), 19 (16-22) and 18 (15-21); area under the plasma concentration-time curve (nmol.h.L(-1)), 118 (103-136), 84 (73-97), 64 (56-74) and 59 (51-68). Subjects showed higher heart rates with G than with H or W. CYP3A5*3 polymorphism showed no significant effect on felodipine pharmacokinetics and related hemodynamic changes. This work supports the hypothesis that CYP3A inhibition by furanocoumarins caused pummelo fruit juice-drug interaction; while the role of CYP3A5 in the population pharmacokinetics of felodipine and blood pressure response appear to be limited.

Sensitive and Rapid Quantification of Felodipine by High-performance Liquid Chromatography-tandem Mass Spectrometry (HPLC-MS/MS) and Its Pharmacokinetics in Healthy Chinese Volunteers

To investigate the pharmacokinetics of felodipine in the plasma of healthy Chinese volunteers, 30 healthy volunteers received a single oral dose of 5 mg of extended release felodipine tablets. The felodipine was extracted from the matrix with a liquid-liquid extract procedure and analyzed by high-performance liquid chromatography-tandem mass spectrometry in the multiple reaction monitoring(MRM) mode using an electrospray ion source with positive ion detection. The method was validated over a felodipine concentration range of 0.05–10.00 ng/mL in human plasma. Its main pharmacokinetic parameters values were; ρ max = (1.67 ± 0.84) ng/mL, occurring at (3.93 ± 2.49) h; the plasma elimination half-life; (23.08 ± 9.48) h and the area under the plasma concentration versus time curve: (29.94 ± 14.39) ng h/mL. The validation results demonstrated that this method showed a satisfactory precision and accuracy across the calibration range. The procedure involved minimal drug administration, sample preparation, and a 2.5-min chromatographic run time. It was well suited to clinical studies of the drug involving large numbers of samples.

A furanocoumarin-free grapefruit juice establishes furanocoumarins as the mediators of the grapefruit juice–felodipine interaction

Grapefruit juice (GFJ) enhances the systemic exposure of numerous CYP3A4 drug substrates, including felodipine, by inhibiting intestinal (but not hepatic) first-pass metabolism. Furanocoumarins have been identified as major CYP3A4 inhibitors contained in the juice, but their contribution to the GFJ effect in vivo remains unclear. To ascertain whether furanocoumarins mediate the GFJ-felodipine interaction, a furanocoumarin-free GFJ was created and tested against orange juice and the original GFJ with respect to the oral pharmacokinetics of felodipine. With the use of food-grade solvents and absorption resins, furanocoumarins were removed (approximately 99%) from whole GFJ, whereas other major ingredients (flavonoids) were retained. In an open, 3-way, randomized crossover design, 18 healthy volunteers ingested felodipine (10 mg) with 1 of the 3 juices (240 mL). Blood was collected over 24 h. At least 1 wk elapsed between juice treatments. The median and range of the area under the curve and the maximum concentration of felodipine were significantly (P < 0.001) greater with consumption of GFJ [110 (range: 58-270) nmol . h/L and 21 (7.6-50) nmol/L, respectively] than with that of orange juice [54 (29-150) nmol . h/L and 7.6 (3.4-13.9) nmol/L, respectively] or furanocoumarin-free GFJ [48 (23-120) nmol . h/L and 8.3 (3.0-16.6) nmol/L, respectively]. GFJ, orange juice, and furanocoumarin-free GFJ did not differ significantly (P > 0.09) in median time to reach maximum plasma concentration [2.5 (1.5-6), 2.8 (1.5-4), and 2.5 (2-6) h, respectively] or terminal half-life [6.6 (4.2-13.6), 7.8 (4.4-13.2), and 6.8 (2.6-14.4) h, respectively]. Furanocoumarins are the active ingredients in GFJ responsible for enhancing the systemic exposure of felodipine and probably other CYP3A4 substrates that undergo extensive intestinal first-pass metabolism.

Grapefruit juice–felodipine interaction: Mechanism, predictability, and effect of naringin

Grapefruit juice produces a marked and variable increase in felodipine bioavailability. The pharmacokinetics of felodipine and its single primary oxidative metabolite, dehydrofelodipine, were studied after drug administration with 200 ml water, grapefruit juice, or naringin in water at the same concentration as the juice in a randomized crossover trial of nine healthy men. With grapefruit juice, mean +/- SEM felodipine area under the plasma concentration-time curve (AUC) and peak plasma concentration (Cmax) were 206% +/- 23% (range, 123% to 330%, p < 0.01) and 170% +/- 24% (range, 127% to 310%, p < 0.02), respectively, compared with water. Dehydrofelodipine/felodipine ratios for AUC (1.5 +/- 0.2 versus 2.2 +/- 0.2, p < 0.001) and felodipine Cmax (1.5 +/- 0.2 versus 2.2 +/- 0.2, p < 0.001) were reduced, consistent with inhibition of presystemic felodipine metabolism. Intersubject changes in felodipine and dehydrofelodipine AUC supported inhibition of both primary and secondary metabolic steps as a mechanism. The interaction could not be predicted from baseline pharmacokinetics with water and did not result in more consistent bioavailability among individuals. Naringin solution produced much less of an interaction, showing that other factors were important.

Pharmacokinetics of Felodipine in Chronic Hemodialysis Patients

Five chronic hemodialysis patients (1 woman and 4 men, aged, 46-68 yr) were given an oral dose of 10 mg felodipine followed by 0.057 mg [3H] felodipine IV. After 5 hours, a hemodialysis treatment lasting 4 hours was performed. Blood and dialysate flows were 200 mL/min and 500 mL/min, respectively. Capillary dialyzers with 1.3 m2 cellulose acetate membrane were used. The pharmacokinetic characteristics and reduction in diastolic BP were similar to those in hypertensive patients with normal renal function and in uremic patients who were not treated with dialysis. There was no measurable removal of felodipine by hemodialysis. Dialyzer clearance of radioactive metabolites was about 10 mL/min, and only 8.9% of the dose was eliminated by the treatment. The half-life of radioactive metabolites was 10 days (6-14 days) in three patients dialyzed thrice weekly. Since the metabolites are biologically inactive, no adjustment of dose is required in hemodialysis patients.

A population study of the pharmacokinetics of felodipine.

1. The pharmacokinetics of felodipine was studied after continuous oral administration of 5 or 10 mg conventional tablets to a population of 140 male and female Caucasian subjects, of which 67 were hypertensive patients and 73 were healthy volunteers. In addition, 42 of these individuals received felodipine intravenously. 2. With increasing age the area under the felodipine plasma concentration vs time curve (AUC), the maximum plasma concentration (Cmax), and the terminal elimination half-life of felodipine increased, while the plasma clearance of felodipine decreased. The bioavailability and steady state volume of distribution and the time to Cmax were not consistently influenced by age. 3. The ratio of the AUC of the primary pyridine metabolite of felodipine and that of unchanged drug decreased with increasing age. 4. Neither Cmax, AUC nor the half-life of felodipine were related to body mass index. 5. The distribution of AUC for felodipine, as well as the ratio of the AUC of this first metabolite to that of unchanged felodipine, was unimodal. Thus, the presence of a sizable group of individuals, with a clinically significant different metabolism of 1,4-dihydropyridine due to genetic factors is unlikely. 6. The pharmacokinetics of felodipine did not seem to differ between hypertensive patients and healthy volunteers, when adjusted for age. Neither was there a difference between patients taking beta-adrenoceptor antagonists and those who did not. 7. As a group the elderly had higher total concentrations of unchanged felodipine in plasma compared with younger individuals. The variation in plasma concentrations of felodipine between individuals is, however, only partially explained by age. In clinical practice this emphasizes the need for dose titration of felodipine.

Acute and Steady‐State Pharmacokinetics and Antihypertensive Effects of Felodipine in Patients with Normal and Impaired Renal Function

Eighteen patients (14 men and 4 women, aged 36-74 years) treated with metoprolol for a month were included in the study. Twelve had impaired renal function (IRF) with a glomerular filtration rate (GFR) of 7.5-77.1 mL/min and six having normal renal function (NRF) with a GFR of 84.9-113.0 mL/min. Plasma and urine concentrations of felodipine and metabolites, heart rate, and blood pressure were recorded over 24 hours on day 1 after an oral dose of 10 mg felodipine and 0.04 mg 3H-felodipine IV and repeated on day 29 during continuous treatment with felodipine, 10 mg bid. The bioavailability of the oral dose on day 1 and day 29 was 13% and 12.5%, respectively. The terminal plasma half-life (t1/2) on day 29 was 22 hours and systemic clearance was 490 mL/min on day 1 and 434 mL/min on day 29 (NS). There were no differences in these parameters between NRF and IRF. The protein binding determined by equilibrium dialysis in the six patients with the lowest GFR was 99.74% on day 1 and 99.73% on day 29 and did not differ significantly from previously reported values in healthy subjects. The mean supine blood pressure before the acute dose of felodipine was 164/96 mm Hg in the IRF patients and 145/95 mm Hg in the NRF patients. A maximum decrease of 37/22 mm Hg and 32/19 mm Hg, respectively, was seen within 1.5 hours after dose and at 12 hours the reduction was 12/9 and 15/10 mm Hg, respectively, compared to baseline values. At steady state the morning blood pressure before dose was 152/87 mm Hg in the IRF patients and 129/86 mm Hg in the NRF patients. Similar maximum decreases and effects at 12 hours were seen after dose on day 29 as on day 1. Data on the effect on diastolic blood pressure and plasma felodipine concentrations were well fitted to the Emax model. The maximum reduction in diastolic blood pressure using this model was 27% and the plasma concentration leading to 50% of the maximum effect was 6.2 nmol/L. In conclusion, renal disease does not affect the pharmacokinetics of felodipine. The pharmacokinetic and pharmacodynamic effects of felodipine are not altered during steady state. The renal excretion of inactive metabolites is reduced in IRF. However, the accumulation of metabolites in the blood does not affect the protein binding or the clearance of felodipine. No dosage adjustment of felodipine seems to be necessary in patients with hypertension and renal impairment.

The influence of infusion rate on the hemodynamic effects of felodipine

The hemodynamic effects of the calcium entry blocker felodipine were studied during and after different infusion rates. Eight healthy normotensive volunteers had their individual pharmacokinetics of felodipine determined, and they subsequently entered a double-blind, randomized, crossover study. Individualized infusions of felodipine were given by a computerized infusion pump to reach plasma concentrations of 6 ng/ml (15.6 nmol/L) after 20 minutes, to be sustained for 8 hours (fast infusion) or the same plasma concentration after 8 hours (slow infusion). Control infusions with saline and vehicle were given. Blood pressure, heart rate, ECG conduction times, and baroreceptor sensitivity by the Valsalva test were measured, as well as the plasma concentrations of felodipine. The infusion system used produced the expected plasma concentration-time profiles with higher plasma concentrations after the fast infusion until 8 hours. Both slow and fast infusion increased heart rate (p less than 0.05) and produced a similar decrease in diastolic blood pressure (p less than 0.05). Slow infusion therefore reduced blood pressure more effectively. The tachycardia after the fast infusion was more pronounced during the first hour of the infusion but was indistinguishable from the slow infusion later, when plasma concentrations were still significantly different. Baroreceptor responsiveness was diminished by both felodipine treatments. There was no obvious difference in side effects caused by the two infusion regimes. The initial tachycardia after felodipine can be diminished by a slow rate of administration of the drug with a similar effect on blood pressure.

Biliary secretion of felodipine metabolites in man after intravenous [14C]felodipine

The biliary secretion of [14C]felodipine in 4 healthy human subjects was studied by use of the multiple marker dilution principle with double lumen tubes placed in the stomach and intestine. Insignificant amounts of 14C activity were recovered from gastric aspirates. The individual recovery from intestinal aspirates varied from 2.9 to 8.5% of the dose of radioactivity over the period of 4.5 h after dosing. Less than 0.1% was identified as unchanged felodipine. The results show that biliary secretion is a minor route of elimination of felodipine or its metabolites. Bile collection for 4.5 h had no significant effect on the pharmacokinetics of felodipine, although the 72 h urinary recovery of radioactivity tended to be lower when bile was collected (59%) than in the control experiment (66%).

Oral pharmacokinetics of felodipine in patients with congestive heart failure: variable prediction using intravenous data.

Peak and trough concentrations after 8 weeks oral therapy with felodipine, a vasodilating calcium antagonist of the dihydropyridine group, were predicted from intravenous pharmacokinetic data before therapy in 11 patients, randomly allocated to felodipine treatment 10 mg b.i.d., during a placebo controlled study in patients with congestive heart failure. Peak concentrations were well predictable, but trough levels varied between a good agreement in some patients to a large underestimation in others. Predictability was significantly correlated with half life, plasma clearance and distribution volume of the intravenous pharmacokinetic study. After 8 weeks chronic oral therapy no significant differences could be detected between the oral pharmacokinetics of predictable (n = 6) and unpredictable (n = 5) patients. This demonstrates that felodipine kinetics change during felodipine treatment. Differences in the distribution of blood flow before therapy combined with an interindividual variability in blood flow response during therapy is probably responsible for the observed impossibility to calculate trough levels, and thus oral dosage schedules, from intravenous pharmacokinetic data in patients with congestive heart failure.

Haemodynamic effects and pharmacokinetics of felodipine at rest and during exercise in hypertensive patients treated with metoprolol or atenolol.

A study has been performed in thirteen patients with essential hypertension, WHO Class I-II, and a diastolic blood pressure greater than or equal to 95 mmHg, on beta-blocker (metoprolol or atenolol) monotherapy, who were also given felodipine 10 mg b.d. for 28 days. The acute and steady state blood pressure response at rest and during exercise, and the pharmacokinetics of felodipine and metoprolol, were examined. Felodipine in combination with the beta-blocker reduced the systolic and diastolic blood pressures acutely and at steady-state. The duration of the effect was longer at steady-state. There was a significant correlation between the plasma concentration of felodipine and the change in blood pressure. The increase in systolic blood pressure during exercise was of the same magnitude before and after felodipine administration. No change in resting supine heart rate was found after the administration of felodipine. There was no significant differences in the pharmacokinetics of felodipine during long-term treatment, except for the trough plasma concentration, which was increased at steady-state, even though cumulation of felodipine and its metabolite did not occur. There was a significant decrease in the maximal plasma concentration and AUC of metoprolol after 28 days of treatment with felodipine, but its elimination half-life was not changed. The adverse reactions reported during this study were those generally seen after dihydropyridines and, except for two patients who were withdrawn after the first study day, the effects were well tolerated.

Pharmacokinetics of felodipine in patients with liver disease.

Nine patients (6 males, 3 females) with biopsy-proven liver cirrhosis participated in an open, cross-over, three centre study of the effect of impaired liver function on the pharmacokinetics of felodipine. Two of the nine patients had undergone porto-caval anastomosis. Each patient was given 0.75 mg i.v. and 10 mg p.o. on separate occasions. The results of this study have been compared with published data from younger subjects and elderly hypertensive patients. The mean peak plasma concentration normalized to a dose of 10 mg (Cmax 46 nmol/l) was twice as high in the cirrhotic patients as in the healthy subjects, but the bioavailability, f, (17.0%) was comparable. Subjects with a porto-caval shunt did not have higher f than the mean for the group. The volume of distribution at steady-state, Vss, was significantly lower than in the healthy subjects. Protein binding was significantly lower in the patients with cirrhosis: 99.46% compared to 99.64% in the healthy subjects. The weight-corrected clearance was 1/3 of the value in healthy subjects. No correlation between systemic availability and oral clearance was found, so it is proposed that felodipine is metabolized both in the liver and also in the gut wall. The results suggest that at least the starting dose should be reduced in patients with severe liver disease.