Urodynamic effects of doxazosin in men with lower urinary tract symptoms and benign prostatic obstruction. Results from three double-blind placebo-controlled studies

OBJECTIVES

Urodynamic investigations provide an objective, quantitative evaluation of urinary function in patients with benign prostatic obstruction (BPO). The effects of doxazosin, a selective alpha 1-adrenoceptor antagonist, on urodynamic measurements were investigated in three double-blind, placebo-controlled clinical studies of the treatment of BPO.

METHODS

302 normotensive and mildly hypertensive men with BPO were evaluated. Patients were randomized to receive doxazosin (1-4 mg o.d.) or placebo for 4-29 weeks.

RESULTS

Doxazosin significantly improved free urinary flow rates compared with placebo. Urodynamic studies confirmed that doxazosin was effective in improving urinary flow, and also showed a reduction in detrusor pressure, resulting in decreased voiding time and increased voided volume. Analysis of pressure-flow data demonstrated a significant reduction in a measure of urethral resistance in doxazosin-treated patients.

CONCLUSION

These results indicate that doxazosin is an important treatment option for patients with troublesome lower urinary tract symptoms and BPO.

Pharmacological evaluation of prazosin- and doxazosin-related compounds with modified piperazine ring

New doxazosin-related compound (1-3) with a N,N'-dimethyl alkanediamine chain replacing the piperazine ring, have been synthesized and their pharmacological properties have been tested together with some prazosin analogues (4-8) bearing either a similar structural modification or a substituted piperazine moiety. In the in vitro study, on alpha 1- and alpha 2-adrenoceptors of rat vas deferens tissues, 1-3 displayed high alpha 1-antagonist activity, 2 and 3 being equipotent to doxazosin but markedly less selective in respect to alpha 2-adrenoceptors. Replacement of the piperazine ring with an alkanediamine chain resulted in a strong fall in alpha 1-selectivity, owing to increased alpha 2-antagonist activity, as in the prazosin-related series. In in vivo studies, the antihypertensive activity of tested compounds was investigated on spontaneously hypertensive rats (SHR) following both intragastric (IG) and intraperitoneal (OP) administration. Among the tested compounds, 7 and 8, which conserved a substituted piperazine ring, proved the most interesting drugs displaying a marked hypotensive effect. The other prazosin- and doxazosin-related compounds, in which an alkanediamine chain replaced the piperazine nucleus, showed an antihypertensive activity markedly lower than that of parent compounds, prazosin (CAS 19216-56-9) and doxazosin (CAS 74191-85-8), although a high alpha 1-antagonist activity in in vitro tests was conserved. These results suggest that the piperazine ring of the prazosin- and doxazosin-related compounds, although not crucial for alpha 1-antagonist activity, may play an important role in the antihypertensive effect, probably by influencing the pharmacokinetic properties of the antagonist.

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.

Blood pressure and blood glucose levels during a cross-over treatment of doxazosin, moduretic and amlodipine in hypertensive patients

A cross-over study comparing the effects of doxazosin, moduretic and amlodipine on fasting blood glucose and blood pressure levels in 9 adult hypertensive Nigerians is presented. The results showed that doxazosin, moduretic and amlodipine were effective in reducing diastolic blood pressure and thus confirmed our previous observation of blood pressure reduction during the monotherapies of these antihypertensive agents. The study further indicated the effectiveness of doxazosin in the management of severe essential hypertension in Nigerian patients. Fasting blood glucose level significantly decreased during doxazosin treatment phase and increased during moduretic phase, while amlodipine treatment did not have any effect on blood glucose level. In conclusion, the cross-over study seem to confirm the effectiveness of doxazosin therapy and its antidiabetic effect in hypertensive patients. The effectiveness of amlodipine therapy in controlling blood pressure was also observed, but no effect on blood glucose level, while moduretic therapy has hyperglycemic effect despite its effectiveness in blood pressure control in African patients.

[Effect of 1-alpha blockader on maximal oxygen consumption and physical endurance in hypertensive men]

The effect of alpha 1 adrenoceptor blockade (doxazosin, 4 mg daily) on maximal oxygen uptake (VO2 max) and physical endurance capacity in 16 mildly hypertensive, athletic men was investigated in a randomized, placebo-controlled, double-blind, two-period of 4 weeks, cross-over study. The maximal work load obtained during graded bicycle ergometer exercise and the VO2 max were reduced by 16 +/- 3 W (mean +/- SE) and 3 +/- 1 ml x kg-1 x min-1 on doxazosin (p < 0.001 for both), and the running time on 5000 m track increased by 43 +/- 12 sec (p < 0.05). Thus, alpha 1-blockade moderately reduces VO2 max and physical endurance capacity in mildly hypertensive athletic men. However, lower systolic blood pressure (9 +/- 4 mm Hg, p < 0.05) immediately after running, and unchanged heart rate suggest a safer performance of exercise.

Doxazosin in the treatment of benign prostatic hyperplasia in normotensive patients: a multicenter study

A 16-week, double-blind, placebo controlled, dose titration study was done on 100 normotensive patients age 45 years or older to determine the efficacy and safety of doxazosin, a selective alpha 1-adrenoceptor antagonist, in the treatment of benign prostatic hyperplasia (BPH). Of the 41 efficacy evaluable patients 88% underwent dose titration to a maximum of 8 mg. doxazosin once daily. Maximum and average urinary flow rates increased significantly above baseline with doxazosin (2.9 ml. per second and 1.4 ml. per second, respectively) compared with placebo (0.7 ml. per second and 0.3 ml. per second, respectively). A significant effect on maximum flow rate was noted as early as week 2 of double-blind treatment at the initial efficacy evaluation. Doxazosin was superior to placebo in patient and investigator assessments of total, obstructive and irritative BPH symptoms. The onset of efficacy for total patient-assessed symptoms was significant for doxazosin compared to placebo 4 weeks after the start of the treatment regimen. Statistically significant decreases in mean blood pressure of 4 to 6 mm. Hg were noted with doxazosin compared with placebo. Adverse events, primarily mild to moderate in severity, were reported in 44% of patients given doxazosin and 30% of those given placebo. Our results strongly demonstrate that doxazosin is significantly superior to placebo in the treatment of BPH in normotensive patients, with the patient experiencing significant relief early after initiation of therapy.

Functional tolerance to alpha-adrenergic receptor blockade in the spontaneously hypertensive rat highlights the multifunctional role of vascular angiotensin II in the development of hypertension

Treatment of spontaneously hypertensive rats (SHR) with alpha-adrenoceptor antagonists failed to alter the development of hypertension in this animal model. However, agents such as captopril (CAP) and losartan (LOS) which interfere with the renin-angiotensin system effectively prevented the development of hypertension. When tolerance occurred in the presence of doxazosin (DOX) or phenoxybenzamine, there was an enhanced sensitivity to the blood pressure lowering influence of LOS. In the presence of CAP, at a dose that did not retard the development of blood pressure in the SHR, DOX treatment significantly offset the development of hypertension in this strain. These results suggest that a functional tolerance to agents that interfere with the sympathetic nervous system is mediated by the renin-angiotensin system. Angiotensin-converting enzyme inhibition was associated with a normalization of the enhanced contraction of the mesenteric vascular bed seen in preparations from the SHR and a suppression in the development of the vascular amplifier. The results suggest that the sympathetic nervous system is unable to maintain an elevated blood pressure in the SHR during interference with the functioning of the renin-angiotensin system. Conversely, under conditions of alpha-adrenoceptor blockade, angiotensin II can maintain an elevated blood pressure in the SHR.

Doxazosin for the treatment of benign prostatic hyperplasia in patients with mild to moderate essential hypertension: a double-blind, placebo-controlled, dose-response multicenter study

A total of 248 hypertensive patients 45 years old or older with benign prostatic hyperplasia (BPH) was included in this 16-week, multicenter, double-blind, placebo-controlled, parallel-group dose-response study. Doxazosin, a selective alpha 1-adrenoceptor antagonist, produced a significant increase in maximum urinary flow rate (2.3 to 3.6 ml. per second) at doses of 4 mg., 8 mg. and 12 mg., and in average flow rate (8 mg. and 12 mg.) compared with placebo. The increase in maximum flow rate was significant with doxazosin versus placebo within 1 week of initiating double-blind therapy. Doxazosin compared to placebo significantly decreased patient-assessed total, obstructive and irritative BPH symptoms. Blood pressure was significantly lower with all doxazosin doses compared with placebo. Adverse events, primarily mild to moderate in severity, were reported in 48% of patients on doxazosin and 35% on placebo. Our results strongly support the use of doxazosin as a nonoperative therapeutic alternative in the management of uncomplicated BPH. Doxazosin would also be particularly useful in the management of patients who have BPH and hypertension.

[Efficacy and tolerance of doxazosin in the treatment of isolated systolic hypertension in hypertensive patients over 60 years of age]

Isolated Systolic Arterial Hypertension (ISAH) is the most frequent form of AHT in the aged population, resulting in an increase of the cardiovascular risk, mainly at the cerebrovascular level. In this open non-comparative study, we analyze the effect of doxazosin, an alpha-adrenergic blocker in 40 patients older than 60 years, diagnosed of isolated systolic hypertension. After 2 weeks of lavage, the patients received treatment with doxazosin according to a monotherapy scheme, with progressive increase of the dose, from 1 to 16 mg/day during a period of 14 weeks. Doxazosin significantly reduces the systolic and diastolic arterial pressure (p < 0.001) with a therapeutical response in 86.5% of the cases, using an average dose of 3.4 mg/day and without observing modifications in the heart rate. This drug improves the lipidic profile, with a reduction of the plasmatic levels of total cholesterol and cholesterol linked to low density proteins (LDL) with p < 0.05 and a reduction of triglycerides. Among the 40 patients included in the study, 10 (25%) referred side effects; there were 2 drop-outs (5%) and the dose had to be reduced in 2 patients (5%). In conclusion, doxazosin shows its antihypertensive effectiveness in the treatment of isolated systolic hypertension in patients older than 60 years and it is well tolerated by most of the patients, improving at the same time the lipidic profile. Hence, it contributes to the reduction of the cardiovascular morbidity-mortality in this group of patients.

Terazosin and doxazosin in normotensive men with symptomatic prostatism: a pilot study to determine the effect of dosing regimen on efficacy and safety

In this pilot study, the effect of dosing schedule on the efficacy and safety of the long-acting alpha 1-adrenergic blockers, terazosin (TER) and doxazosin (DOX), was evaluated in 43 consecutive normotensive men (mean age 59.6 years) with symptoms of prostatism. Patients were randomized to one of four treatment groups: (1) TER 5 mg once in the morning (AM; n = 10), (2) TER 5 mg once in the evening (PM; n = 11), (3) DOX 4 mg once AM (n = 11), and (4) DOX 4 mg once PM (n = 11). Patients were titrated to their final dose over 3 weeks. Parameters evaluated included Boyarsky symptom score (Sx), peak uroflow (Qmax), blood pressure and occurrence of adverse events. Once stabilized, patients were seen at 3-month intervals; follow-up ranged from 4 to 17 months (mean 9.7). Clinical improvement as determined by Sx and Qmax was similar for all four treatment groups. Mean decreases in Sx at 3 months were 4.6, 5.4, 4.9, and 5.0 for TER-AM, TER-PM, DOX-AM, and DOX-PM, respectively. Mean peak uroflow increased 3.0, 3.1, 2.8, and 3.1 ml/s for TER-AM, TER-PM, DOX-AM, and DOX-PM, respectively (p < 0.05 vs. baseline). Eight patients (18%) were withdrawn from the study because of adverse events (fatigue 1, asthenia 1, headache 3, dizziness 4): 5 during the titration phase (TER-AM: 2, DOX-AM: 2, TER-PM: 1) and 3 during the treatment phase (TER-AM: 2, DOX-AM: 1). In these 8 patients, the mean decreases in sitting and standing blood pressure were approximately 7/5 and 10/8 mm Hg, respectively. These data suggest that efficacy of TER and DOX was similar at the dosages employed and not affected by the dosing schedule. Adverse events in this small population were significantly decreased (p < 0.05) by dosing in the PM. These preliminary results suggest that a larger prospective study is warranted to determine (1) the comparative efficacy of TER and DOX in the treatment of symptomatic benign prostatic hyperplasia and (2) optimal timing of the medication.

Comparative and combined efficacy of doxazosin and enalapril in hypertensive patients

Twenty patients with essential hypertension were randomised to a 7-week period of dose titration with doxazosin, 1-8mg/day or enalapril, 5-20mg/day. In a further 7-week period the dosage level reached with the initial drug was halved, and titration with the second agent was carried out. Blood pressure responses at the end of each treatment period were assessed by clinic measurements made 24 hours post-dose. In the first treatment period, enalapril (mean dose 19mg/day) reduced serum free ACE activity by 40% and had a greater effect than doxazosin (mean dose 5.2mg/day) on clinic supine blood pressure (systolic and diastolic). In the second period, the addition of enalapril to doxazosin was associated with a significant fall in clinic standing blood pressure (systolic and diastolic), despite the doxazosin dose reduction and consequent decrease in median plasma doxazosin concentration (from 10.6 to 5.2ng/ml). Alternatively, when doxazosin was added to enalapril, free ACE activity remained 40% decreased despite enalapril dose reduction, and blood pressure was not further affected. Plasma renin activity was increased by enalapril. No changes were observed in plasma aldosterone or lipid concentrations with either drug. The combination of doxazosin and enalapril was well tolerated and lowered blood pressure overall. Judged by clinic measurements 24 hours post-dose, most of the antihypertensive effect was attributable to the enalapril component. However, ambulatory blood pressure monitoring 0-12 hours post-dose in a subset of patients suggested a contribution of doxazosin earlier in the dose interval.

Nighttime dosing of doxazosin has peak effect on morning ambulatory blood pressure. Results of the HALT Study. Hypertension and Lipid Trial Study Group

In this study the effects of a single daily dose (average 8.9 mg) of doxazosin (an alpha-adrenergic blocker) given at night were evaluated in 111 patients with mild hypertension. Patients were studied first on no medication, and a second time after being treated for up to 16 weeks with doxazosin. Blood pressure was measured by noninvasive ambulatory monitoring at the beginning and end of the study. There was a sustained reduction of both systolic and diastolic pressure throughout the day and night, but the greatest reduction occurred in the morning hours. Since the peak treatment effect was later than predicted from previous pharmacokinetic studies, it is suggested that the timing of the peak effect may depend on the prevailing level of alpha-adrenergic tone, as well as on the pharmacokinetics of the drug.

Differential effects of doxazosin on clinic and ambulatory pressure according to age, gender, and presence of white coat hypertension. Results of the HALT Study. Hypertension and Lipid Trial Study Group

In this study the effects of a single daily dose of doxazosin (an alpha-adrenergic blocker) given at night were evaluated in 112 patients with mild hypertension. Patients were studied first on no medication, and a second time after being treated for up to 16 weeks with doxazosin. Blood pressure (BP) was measured by noninvasive ambulatory monitoring at the beginning and end of the study. Before treatment, the white coat effect (clinic-ambulatory BP) was greater in women than in men (significant for systolic pressure but not diastolic), and greater in elderly (aged over 65 years) than in younger patients (significant for both systolic and diastolic pressure). Clinic and ambulatory BP were reduced to a similar extent in men and women by doxazosin, but in the elderly the fall in clinic BP was associated with a much smaller fall of ambulatory BP. In patients with white coat hypertension (elevated clinic but normal ambulatory BP) doxazosin lowered clinic but not ambulatory BP, while in those with sustained hypertension it lowered both.

Effect of dosing regimen on efficacy and safety of doxazosin in normotensive men with symptomatic prostatism: a pilot study

OBJECTIVES

In this pilot study, the effect of dosing schedule on the efficacy and safety of the long-acting alpha 1-adrenergic blocker doxazosin (DOX) was evaluated in 48 consecutive, normotensive men (mean age, 61.2 years) with symptoms of prostatism.

METHODS

In this titration to fixed dose study, patients were randomized into 1 of 4 treatment groups: (1) 4 mg DOX once in the AM (n = 12); (2) 4 mg DOX once in the PM (n = 12); (3) 8 mg DOX once in the AM (n = 12); and (4) 8 mg DOX once in the PM (n = 12). Parameters evaluated included Boyarsky symptom score (Sx), peak uroflow (Qmax), blood pressure, and occurrence of side effects. Once stabilized, patients were seen at 3-month intervals; follow-up ranged from 3 to 19 months (mean, 7.7).

RESULTS

Clinical improvement as determined by Sx and Qmax was similar for AM and PM groups with either 4 or 8 mg of DOX. Mean decreases in Sx at 3 months were 4.6, 4.2, 5.1, and 5.2 and at 6 months were 4.7, 4.7, 5.3, and 5.4 for the 4 mg AM, 4 mg PM, 8 mg AM, and 8 mg PM, respectively. Mean peak uroflow at 3 months increased 2.7, 2.9, 3.2, and 3.3 mL/s and at 6 months increased 2.6, 3.0, 3.4, and 3.5 mL/s for the 4 mg AM, 4 mg PM, 8 mg AM, and 8 mg PM, respectively (p < 0.05). Six patients (13%) were dropped from the study because of side effects (2 for fatigue, 2 for headache, 2 for dizziness): 5 during the titration phase (4 mg AM: 2; 8 mg AM: 2; 8 mg PM: 1), and 1 during the treatment phase (8 mg AM).

CONCLUSIONS

These data suggest that evening dosing does not diminish efficacy yet may enhance toleration of DOX. These preliminary results suggest that a larger prospective study is warranted to determine the optimal dosing and timing of DOX in the management of symptomatic benign prostatic hyperplasia.

Doxazosin versus nitrendipine: a double-blind comparative study in patients adhering to a sodium-restricted diet

The aim of this double-blind parallel-group study was to compare the effects of doxazosin, a selective alpha 1-adrenoceptor antagonist with a long plasma half-life, with nitrendipine, a long-acting calcium-entry blocking drug. Following a 4-week placebo period, 26 patients with mild-to-moderate essential hypertension were randomly allocated to treatment with either doxazosin (n = 12) or nitrendipine (n = 14). Over a period of 10 weeks, doses were titrated to obtain a standing diastolic pressure below 90 mmHg. Thereafter, optimal doses were continued for another 4 weeks. Both drugs were administered once daily; median doses were 4 mg/day for doxazosin and 10 mg/day for nitrendipine. During the titration period three patients in the doxazosin group and one in the nitrendipine group dropped out from the study; one patient on doxazosin was considered a nonresponder. Twenty-one patients completed the study. The percentage of patients showing an adequate hypotensive effect (standing diastolic pressure below 90 mmHg) at the end of the study was similar in the two groups (42% vs. 50% in the intention-to-treat analysis and 56% vs. 54% in the per-protocol analysis). Casual, basal, and standing blood pressure and heart rate did not differ between groups throughout the study; serum lipids and blood glucose remained unchanged. We conclude that doxazosin and nitrendipine given as monotherapy are equally effective in mild to moderate hypertension.

29-week doxazosin treatment in patients with symptomatic benign prostatic hyperplasia. A double-blind placebo-controlled study

In a placebo-controlled study, the safety and efficacy of the selective alpha 1-adrenoceptor-blocking agent doxazosin 4 mg once daily in the symptomatic treatment of benign prostatic hyperplasia (BPH) were evaluated. One hundred patients were primarily included in a 9-weeks study, and after this 75 patients accepted to continue in the present 20 weeks extension. Of the patients in the doxazosin-group (DG) 61% reported overall improvement against 53% in the placebo-group (PG)--(p = 0.56). In the DG, 49% of obstructive symptoms were improved compared to 27% in the PG (p < 0.01), and a reduction of 60% of irritative symptoms was found in the DG against 36% in the PG (p < 0.01). Daytime frequency was reduced by median 1.5 in the DG and remained unchanged in the PG (p < 0.01). Nocturia was reduced by median 1 and 0.5 respectively (p = 0.06). Maximum urinary flow rate (MFR) was improved by median 1.5 ml/s in the DG, while it deteriorated by median 0.5 ml/s in the PG (p < 0.05), Considering postvoid residual urine volume, cystometry variables (first sensation and bladder capacity), changes in sexual function and adverse events there was no difference between the two groups. In conclusion, doxazosin 4 mg once daily in long-term treatment of patients with BPH reduces both obstructive and irritative symptoms, daytime voiding frequency and although only slightly, significantly augments MFR without interference with sexual function and without other serious adverse effects.

Alteration of response to neuropeptide Y in the nucleus tractus solitarius of spontaneously hypertensive rats

In normotensive rats, microinjections of neuropeptide Y (2.5 to 25 pmol) into the unilateral nucleus tractus solitarius elicited dose-dependent vasodepressor and bradycardiac responses accompanied by an inhibition of sympathetic nerve firing. After microinjections of the alpha 2-adrenergic receptor antagonist yohimbine (100 ng) into the nucleus tractus solitarius, the depressor and bradycardic responses to the injection of neuropeptide Y (25 pmol) into the nucleus tractus solitarius were significantly attenuated. In contrast, pretreatment with the alpha 1-adrenergic receptor antagonist doxazosin (200 ng) injected into the nucleus tractus solitarius did not alter these responses. In spontaneously hypertensive rats, microinjections of neuropeptide Y (25 pmol) into the nucleus tractus solitarius also elicited depressor and bradycardic responses that were significantly less than those of normotensive Wistar-Kyoto rats. However, pretreatment with yohimbine (100 ng) in the nucleus tractus solitarius did not diminish these depressor responses in spontaneously hypertensive rats. Depressor responses to neuropeptide Y, which was administered after yohimbine pretreatment, were also less in Wistar-Kyoto rats than in spontaneously hypertensive rats. The results suggest that the depressor and bradycardic responses elicited by neuropeptide Y were accompanied by the inhibition of sympathetic nerve activity. These responses may be mediated in part by alpha 2-adrenergic receptor in the nucleus tractus solitarius. The impairment of alpha 2-adrenergic receptor-mediated responses to neuropeptide Y in spontaneously hypertensive rats may contribute to the development of hypertension.

Placebo-controlled trial of doxazosin in management of patients with hypertension and hypercholesterolaemia

The blood pressure (BP)- and lipid-lowering activities of the alpha 1-antagonist, doxazosin, were investigated in hypertensive, hypercholesterolaemic patients. Thirty-one patients satisfactorily completed the study, and there was no significant difference between doxazosin and placebo in terms of reported adverse events. After 3-month treatment, BP was significantly reduced by doxazosin by 24/14 mm Hg supine and by 33/22 mm Hg erect as compared with corresponding reductions of 2/9 and 2/2 mm Hg with placebo. There were concomitant improvements in the plasma lipid profile with, in particular, significant net reductions of 30% for triglycerides and 20% for apoprotein B. There was no adverse effect on glucose metabolism. The principal aim of this study was assessment of the clinical utility and acceptability of doxazosin in a heterogeneous population of patients with several cardiovascular risk factors. The results confirm that doxazosin is an effective antihypertensive agent that has modest additional beneficial effects on the plasma lipid profile.