Rising multiple-dose pharmacokinetics of labetalol in hypertensive patients

The randomised Oslo study of renal denervation vs. Antihypertensive drug adjustments: efficacy and safety through 7 years of follow-up

PURPOSE

The blood pressure (BP) lowering effect of renal sympathetic denervation (RDN) in treatment-resistant hypertension shows variation amongst the existing randomised studies. The long-term efficacy and safety of RDN require further investigation. For the first time, we report BP changes and safety up to 7 years after RDN, compared to drug adjustment in the randomised Oslo RDN study.

MATERIALS AND METHODS

Patients with treatment-resistant hypertension, defined as daytime systolic ambulatory BP ≥135 mmHg after witnessed intake of ≥3 antihypertensive drugs including a diuretic, were randomised to either RDN (n = 9) or drug adjustment (n = 10). The initial primary endpoint was the change in office BP after 6 months. The RDN group had their drugs adjusted after 1 year using the same principles as the Drug Adjustment group. Both groups returned for long-term follow-up after 3 and 7 years.

RESULTS

The decrease in office BP and ambulatory BP (ABPM) after 6 months did not persist, but gradually increased in both groups. From 6 months to 7 years follow-up, mean daytime systolic ABPM increased from 142 ± 10 to 145 ± 15 mmHg in the RDN group, and from 133 ± 11 to 137 ± 13 mmHg in the Drug Adjustment group, with the difference between them decreasing. In a mixed factor model, a significantly different variance was found between the groups in daytime systolic ABPM (p = .04) and diastolic ABPM (p = .01) as well as office diastolic BP (p<.01), but not in office systolic BP (p = .18). At long-term follow-up we unveiled no anatomical- or functional renal impairment in either group.

CONCLUSIONS

BP changes up to 7 years show a tendency towards a smaller difference in BPs between the RDN and drug adjustment patients. Our data support RDN as a safe procedure, but it remains non-superior to intensive drug adjustment 7 years after the intervention.

Gender differences in labetalol kinetics: importance of determining stereoisomer kinetics for racemic drugs

STUDY OBJECTIVE

To evaluate the impact of gender on labetalol kinetics.

DESIGN

Part of a randomized, crossover study.

SETTING

Academic medical center.

PATIENTS

Nineteen hypertensive patients (14 men, 5 women; 6 blacks, 13 whites).

INTERVENTIONS

Participants had labetalol dosages titrated to a specific antihypertensive response, then underwent ambulatory blood pressure monitoring (ABPM) and a pharmacokinetic study. Labetalol plasma concentrations were measured by high-performance liquid chromatography (HPLC) and labetalol stereoisomer ratios were determined in a single plasma sample by chiral HPLC, both with fluorescence detection.

MEASUREMENTS AND MAIN RESULTS

Labetalol concentrations were 80% higher in women (area under the concentration-time curve [AUC]/dose x 1000: 6.79 +/- 2.11 in women vs 3.82 +/- 1.37 hr/L in men, p<0.05), yet both genders had a similar antihypertensive response by 24-hour ABPM. Dose-corrected AUC (AUC/dose x 1000) for labetalol's stereoisomers in women and men, respectively, were S,R-labetalol 7.55 +/- 1.47 and 4.83 +/- 1.54 hr/L (p<0.05), S,S-labetalol 8.23 +/- 2.93 and 4.65 +/- 1.78 hr/L (p<0.05), R,S-labetalol 6.99 +/- 3.30 and 4.25 +/- 2.35 hr/L (p=0.11), and R,R-labetalol 3.91 +/- 2.57 and 3.55 +/- 3.08 hr/L (NS).

CONCLUSION

The higher labetalol concentration in women than in men was explained largely by differences in inactive and alpha1-blocking stereoisomers. However, concentrations were similar between genders for the beta-blocking stereoisomer (R,R-labetalol), possibly explaining the similarity in antihypertensive response to the drug. This study highlights the importance of determining stereoisomer kinetics for agents administered as racemates, particularly when relating concentrations to pharmacologic response.

Effect of time of administration on the pharmacokinetics and tolerance of doxazosin in healthy male volunteers

A randomized, open-label, two-way crossover study of 24 normotensive, healthy male volunteers with nocturia was conducted to compare morning and evening administration of doxazosin in terms of pharmacokinetics and tolerance. In both the morning and evening phases, participants received doxazosin 1 mg once daily for 10 days, followed by 2 mg once daily for 5 days. Pharmacokinetic data were evaluated from blood samples serially collected for 72 hours after drug administration on the last day of each phase. Vital signs and adverse events were recorded throughout the study. Mean peak plasma concentrations (C(max)) were 16.98 and 15.76 ng/mL after morning and evening administration, respectively. Corresponding mean values of area under the plasma concentration-time curve (AUC0-24) were 227.90 and 253.66 ng.hr/mL, respectively. Statistical analysis of the log-transformed values for C(max) and AUC0-24 indicated that morning and evening administration of doxazosin were bioequivalent. There were no statistically or clinically significant differences between phases for mean apparent half-life (t1/2) or total body clearance. There were no clinically relevant differences in blood pressure or in pulse rate between phases, and no occurrences of orthostatic hypotension. The incidence of adverse experiences during morning and evening administration was similar. Morning and evening administration of doxazosin are equivalent and have similar tolerance profiles.

Labetalol pharmacokinetics in pregnancy-induced hypertension

Pharmacokinetic parameters of oral labetalol were studied in eight women with pregnancy-induced hypertension in the third trimester of pregnancy. Labetalol exhibited rapid absorption; peak serum concentrations of 881 +/- 219 ng/ml occurred at 20 minutes after labetalol ingestion. The terminal elimination half-life (mean, 1.7 +/- 0.27 hours) was found to be shorter than that reported for normotensive volunteers or nonpregnant hypertensive patients (mean, 6 to 8 hours). A mean apparent oral elimination clearance of 21.8 ml/min/kg compared favorably with that seen in other pregnant and nonpregnant populations. Food delayed the time to peak serum concentration to approximately 60 minutes. Labetalol was detected in fetal cord samples and amniotic fluid samples at concentrations approximately 50% and 16% that of simultaneous maternal vein samples, respectively.

Effects of age on the elimination of labetalol

Labetalol is an alpha 1- and beta-adrenergic antagonist currently used in the treatment of hypertension. Studies which have evaluated the effects of age on its pharmacokinetics have yielded conflicting results. The purpose of this study is to comprehensively re-evaluate the effect of age on the elimination of labetalol. Data were obtained from 4 single-dose and 3 multiple-dose studies of the pharmacokinetics of the drug. An analysis of covariance was performed on the single-dose data to determine whether the type of subject evaluated (normotensive vs hypertensive), type of assay methodology used and/or age were significant factors affecting labetalol clearance estimates. A similar covariance procedure was used for the multiple-dose data, to assess whether the type of subject, duration of treatment and/or age were significant variables affecting labetalol elimination. Subsequent to the analysis of covariance, linear regression and correlation analysis was used to evaluate the effects of age on labetalol clearance. A modest though significant relationship was observed between the apparent oral clearance of the drug and age; it appeared slightly stronger when clearance was normalised for bodyweight. No relationship was found following multiple doses of the drug. Hence, age does not appear to be a significant factor affecting the oral clearance of labetalol, particularly in individuals receiving the drug in the long term.

Labetalol. A reappraisal of its pharmacology, pharmacokinetics and therapeutic use in hypertension and ischaemic heart disease

Since labetalol was first reviewed in the Journal (1978), its scope of therapeutic use has expanded and become better defined. Labetalol is an adrenoceptor blocking drug with combined alpha- and beta-blocking properties. These result in a more favourable haemodynamic profile for labetalol compared with 'pure' beta-blockers or pure alpha-blockers, but also contribute to a wider range, but not an overall increased incidence, of adverse effects. The drug is effective and well-tolerated in patients with all grades of hypertension, but is of particular value in special subgroups such as Black patients, the elderly and patients with renal hypertension. While comparative studies are not extensive, available data show that the drug reduces blood pressure to a similar extent, and in a similar proportion of patients, as 'pure' beta-blockers such as propranolol, pure alpha-blockers such as prazosin, calcium antagonists (nifedipine, verapamil), and centrally acting drugs (clonidine and methyldopa). Labetalol is very effective in hypertensive pregnant women and in hypertensive crises, where it provides good control of blood pressure without serious adverse effects, and where few therapeutic options exist. Few controlled studies have investigated the use of labetalol in deliberate induction of hypotension or prevention of hypertension during anaesthesia, and also in patients with ischaemic heart disease. However, available evidence suggests a role for labetalol in these indications and further studies should aid in clarification of its efficacy in these areas. Thus, with its broad scope of therapeutic use in hypertension labetalol remains an important therapeutic option, and the drug may well find an additional place in the treatment of myocardial ischaemia if further evidence confirms encouraging preliminary findings.

Interindividual and intraindividual variability in labetalol pharmacokinetics

The between-subject and within-subject variability in the pharmacokinetics of labetalol at steady state were determined. Sixteen nonobese normal volunteers (mean age, 27 years) received five different formulations of labetalol orally on five different occasions every 12 hours for five doses. A 7-day washout separated each administration phase. Plasma concentration-time data for labetalol were obtained over the 24-hour period after the fifth dose in each phase. Labetalol concentrations in plasma were measured using high-performance liquid chromatography (HPLC). Pharmacokinetic parameters for each subject after each study phase were estimated. The mean V beta/F, Vdss/F, TBC/F, t1/2 beta, and AUC tau 0 for each subject ranged between 18.1 and 161.9 L/kg, 7.1 and 53.9 L/kg, 1.3 and 5.72 L/hr/kg, 6.9 and 11.0 hours, and 154 and 520 micrograms.hr/L, respectively, indicating large interindividual variability. Considerable intraindividual variability in each of the pharmacokinetic parameters was also observed. These data indicate that a larger number of subjects will be required to detect "significant" differences in the disposition of labetalol.