A double-blind and cross-over comparison of once daily doxazosin and placebo with steady-state pharmacokinetics in elderly hypertensive patients

Clinical correlation of maximal urinary flow rate and plasma doxazosin concentrations in the treatment of benign prostatic hyperplasia. Multicenter Study Group

OBJECTIVES

To investigate the relationship among doxazosin dose, plasma concentration, and clinical response in 248 hypertensive men with benign prostatic hyperplasia (BPH) in a 16-week, placebo-controlled, double-blind study.

METHODS

After a 2-week placebo run-in period, patients were randomized to treatment with either doxazosin (titrated to doses of 2, 4, 8, or 12 mg once daily) or placebo. After 6, 10, and 14 weeks, plasma concentrations of doxazosin were measured at 2 to 6 hours (peak) and approximately 24 hours (trough) after dosing. Changes in maximal urinary flow rate (Qmax) compared with baseline were measured at the same time points. Patients recorded their symptoms in a daily diary and completed a questionnaire at weeks 2, 8, and 16 to assess both obstructive and irritative BPH symptoms. In addition, BPH symptoms were assessed by the investigator at each study visit.

RESULTS

Steady-state peak and trough plasma doxazosin concentrations were achieved by 6 weeks of therapy and were maintained between 6 and 14 weeks of active treatment. Peak and trough plasma concentrations increased linearly within the dose range of 2 to 12 mg and were positively correlated with a corresponding mean improvement in Qmax (P = 0.001 and P = 0.008, respectively), consistent with a 24-hour once-daily dosing of doxazosin. Clinical response to doxazosin plateaued at peak and trough plasma concentrations of between 60 and 80 ng/mL and 25 ng/mL, respectively, corresponding to a dose of 8 mg daily. Patient assessment of obstructive BPH symptoms showed significant improvement in the 4- and 8-mg doxazosin treatment groups compared with placebo.

CONCLUSIONS

In patients with BPH, both doxazosin plasma concentration and Qmax increased linearly with increasing dose, in the range of 2 to 8 mg daily. The maximal therapeutic dosage of doxazosin would appear to be 8 mg in this group of BPH patients. Further studies are required to support these findings.

Clinical pharmacokinetics of vasodilators. Part II

Stimulating cardiac beta 1-adrenoceptors with oxyfedrine causes dilatation of coronary vessels and positive inotropic effects on the myocardium. beta 1-adrenergic agonists increase coronary blood flow in nonstenotic and stenotic vessels. The main indication for the use of the phosphodiesterase inhibitors pamrinone, mirinone, enoximone and piroximone is acute treatment of severe congestive heart failure. Theophylline is indicated for the treatment of asthma, chronic obstructive pulmonary disease, apnea in preterm infants ans sleep apnea syndrome. Severe arterial occlusive disease associated with atherosclerosis can be beneficially affected by elcosanoids. These drugs must be administered parenterally and have a half-life of only a few minutes. Sublingual or buccal preparations of nitrates are the only prompt method (within 1 or 2 min) of terminating anginal pain, except for biting nifedipine capsules. The short half-life (about 2.5 min) of nitroglycerin (glyceryl trinitrate) makes long term therapy impossible. Tolerance is a problem encountered with longer-acting nitric oxide donors. Knowledge of the pharmacokinetic properties of vasodilating drugs can prevent a too sudden and severe blood pressure decrease in patients with chronic hypertension. In considering the administration of a second dose, or another drug, the time necessary for the initially administered drug to reach maximal efficacy should be taken into account. In hypertensive emergencies urapidil, sodium nitroprusside, nitroglycerin, hydralazine and phentolamine are the drugs of choice, with the addition of beta-blockers during catecholamine crisis or dissecting aortic aneurysm. Childhood hypertension is most often treated with angiotensin-converting enzyme (ACE) inhibitors or calcium antagonists, primarily nifedipine. Because of the teratogenic risk involved with ACE inhibitors, extreme caution must be exercised when prescribing for adolescent females. The propagation of health benefits to breast-fed infants, combined with more women delaying pregnancy until their fourth decade, has entailed an increase in the need for hypertension management during lactation. Low dose hydrochlorothiazide, propranolol, nifedipine and enalapril or captopril do not pose enough of a risk of preclude breastfeeding in this group. The most frequently used antihypertensive agents during pregnancy are methyldopa, labetalol and calcium channel antagonists. Methyldopa and beta-blockers are the drugs of choice for treating mild to moderate hypertension. Prazosin and hydralazine are used to treat moderate to severe hypertension and hydralazine, urapidil or labetalol are used to treat hypertensive emergencies. The use of overly aggressive antihypertensive therapy during pregnancy should be avoided so that adequate uteroplacental blood flow is maintained. Methyldopa is the only drug accepted for use during the first trimester of pregnancy.

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.

The promises and perils of treating the elderly hypertensive

Recently published clinical trials have shown clear benefits of the treatment of hypertension in the elderly. Therefore, millions of elderly patients will be considered in need of antihypertensive therapy. In addition to the promises that such therapy offer, there are multiple perils involved in the treatment of elderly patients.

Antihypertensive therapy in the geriatric patient: II. A review of the alpha1-adrenergic blocking agents

The prevalence of hypertension increases with age. Multiple physiologic factors are involved in the development of hypertension in the elderly. Alpha1-adrenergic blocking agents lower blood pressure through a reduction in total peripheral resistance. Prazosin, terazosin, and doxazosin have been shown to be equally effective in reducing blood pressure in older persons. The bioavailability, terminal elimination half-life, and volume of distribution of prazosin is increased in the elderly. Hybrid drugs, such as ketanserin, urapidil, and indoramin are also effective in lowering blood pressure. Ketanserin seems to have a greater effect on blood pressure reduction in persons older than 60 years of age. Alpha1-adrenergic blockers may be used safely in patients with diabetes, asthma, and hyperlipidemia.