Clinical pharmacology of doxazosin in patients with essential hypertension

Flow injection analysis of doxazosin mesylate using UV-detection

A flow injection analysis (FIA) of doxazosin mesylate (DOX) using UV detection is described in this study. The best solvent system was found to be consisting of 0.1 mol l(-1) acetate buffer at pH 4 having 10%MeOH. A flow rate of 1 ml min(-1) was pumped and active material was detected at 365 nm. The calibration equation was linear in the range of 1.3 x 10(-5) to 6.4 x 10(-5) mol l(-1). Limit of detection and limit of quantitation were calculated to be 1.6 x 10(-6) and 4 x 10(-6) mol l(-1) with a RSD 1.27 and 1.16% (n=8), respectively. The proposed method was applied to the determination of DOX in the pharmaceutical preparations. The results were compared with those obtained from UV-Spectrophotometry. The results showed that there is a good agreement between FIA method and UV-Spectrophotometry. The validation studies were realised by the related applications and the results were evaluated statistically. According to the results, insignificant difference was observed between the methods.

Voltammetric determination of doxazosin in tablets using rotating platinum electrode

This study describes the voltammetric behaviour of doxazosin molecule based on the oxidation on the surface of platinum electrode in the stationary and rotating conditions and determine doxazosin in the tablets by differential pulse technique at only rotating condition. The experiments were carried out in the supporting electrolyte consisting of 0.2 M KCl and 0.2 M buffer solution in 10% (v/v) ethanol. The effect of initial potential was investigated and no adsorption effect was observed during use of +500 mV. The influence of pH on the peak current and peak potential was examined and the most symmetrical peaks were obtained at 0.5 M H2SO4 for rotating conditions. In the rotation range of 50-1000 rpm and up to 1.0x10(-5) M doxazosin, the factor affecting the voltammetric current was diffusional. The effect of rate of potential was tested between 2 and 20 mV for the stationary condition and the character of current was found to be diffusional up to 3x10(-5) M concentration of doxazosin solutions. The voltammetric determination of doxazosin in tablets was realised in the optimum rotating system conditions and depending on the statistical evaluations, acceptable results were obtained. Therefore, the method proposed in this study is practical, sensitive and accurate for the analysis of doxazosin in the quality control laboratories.

Effects of doxazosin in the gastrointestinal therapeutic system formulation versus doxazosin standard and placebo in mild-to-moderate hypertension. Doxazosin Investigators' Study Group

The alpha 1-blocker doxazosin is a well-established therapy for hypertension and benign prostatic hyperplasia; however, in its standard form, a multiple-step titration regimen is usually required. The new gastrointestinal therapeutic system (GITS) formulation of doxazosin greatly minimizes the need for titration by changing drug-delivery rate and the pharmaco-kinetic profile. To demonstrate this in hypertensive patients, we assessed the effects of doxazosin GITS 4 or 8 mg once daily versus doxazosin standard 1-8 mg once daily, and placebo, in an integrated analysis of two multicenter, double-blind, randomized, parallel-group trials. Each trial included a 2-week washout period and 12 weeks of therapy. One study compared doxazosin GITS, doxazosin standard, and placebo in 392 patients with mild hypertension [blood pressure (BP) 95-105/ < or = 180 mm Hg]; the other study compared doxazosin GITS with doxazosin standard in 315 patients with mild-to-moderate hypertension (BP 95-115/ < or = 220 mm Hg). The primary outcome measure was the proportion of responders (sitting diastolic BP < 90 mm Hg or 10-mm Hg decrease from baseline 24 h after the dose) at the final visit for the per-protocol population. Mean baseline BP and heart rate were well matched in each group. Approximately 64% of patients with doxazosin GITS (198 of 309 patients) and 68% with doxazosin standard (207 of 304 patients) achieved goal BP response at the final visit versus 36% with placebo (25 of 70 patients; p < 0.05). The majority with doxazosin GITS (60%) remained at the initial 4-mg starting dose. Doxazosin GITS was as effective as doxazosin standard, and both were more effective than placebo in controlling BP in mild-to-moderate hypertension. Doxazosin GITS was well tolerated, and fewer patients with the GITS formulation discontinued therapy because of side effects compared with doxazosin standard or placebo. Syncope was not reported with doxazosin GITS. Whereas the efficacy of doxazosin GITS at 4 or 8 mg is equivalent to that of the standard regimen in this combined analysis, the GITS formulation appears to eliminate the need for titration in most 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.

Effects of oral and intravenous terazosin and head-up tilt on blood pressure responses in patients with hypertension

Terazosin is a selective alpha1-adrenoceptor antagonist. A double-blind, randomized, placebo-controlled, two-period study evaluated the effects of posture and of oral and intravenous administration of terazosin on blood pressure and heart rate in patients with hypertension. At least one week after withdrawal of all antihypertensive medications, 31 patients with sitting diastolic blood pressure of 95 to 114 mmHg were enrolled in the study. After a 24-hour, single-blind, placebo lead-in phase, the patients were randomized to receive either oral terazosin (1 mg on day 1, 2 mg on day 2, and 5 mg on days 3 and 4), a 12-hour intravenous infusion of terazosin (2.5 mg, 5 mg, or 7.5 mg), or placebo for 4 consecutive days. Head-up tilt (60 degrees for 20 minutes) evaluations were performed before and 0.5, 1.5, 2.5, 6, 12, and 16 hours after start of administration during the placebo lead-in phase and on each of the 4 days of the double-blind treatment phase. Blood pressure and heart rate were monitored every 2 minutes during the 20-minute tilt. Statistically significantly larger mean changes in blood pressure and heart rate were observed with the 7.5-mg intravenous dose of terazosin compared with those after oral terazosin or placebo. With respect to intravenous terazosin, the orthostatic changes were maximal on the first day of the 4-day treatment and increased with increasing doses of terazosin. Maximum orthostatic changes in blood pressure after oral administration of terazosin were not significantly different from those observed with placebo. The most common treatment-emergent adverse events during tilt were dizziness and nausea. Dizziness occurred more frequently with intravenous terazosin than with oral terazosin. The results of this study indicate that oral dose titration of terazosin rather than a slower rate of terazosin infusion minimized the postural effects on blood pressure and associated symptoms during head-up tilt.

Pulse polarographic (constant and increasing) determinations of doxazosin in pharmaceutical tablets

The optimum conditions using DC polarography and the determination of doxazosin employing SIAP and SCAP polarographic techniques are described in this study. All the experiments were conducted in the supporting electrolyte consisting of 20% ethanol (v/v), 0.2 M KCl and 0.2 M acetate buffer at various pH values in order to examine the optimum conditions, and pH 3.5 for the determination of doxazosin. Well-defined curves were obtained in the pH range of 1.5-7.5. The system was diffusional and irreversible at pH 3.5. The calibration studies were performed by using SIAP and SCAP polarography and satisfactory results were observed for all techniques. Since the sensitivity of SIAP and SCAP techniques were higher than the others, the determination of doxazosin was performed in filtered and unfiltered tablet solutions containing 4 mg active material. In the analysis of a tablet, the relative standard deviations (Srel %) of the techniques are in the filtered solutions +/- 0.9 (SIAP), +/- 0.8 (SCAP) and in the unfiltered solutions +/- 0.7 (SIAP), +/- 0.8 (SCAP) and no interference was observed during the analysis. The determination methods proposed in this study appear to be accurate, rapid and practicable. Therefore, these techniques may be suitable for the content uniformity tests.

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.

Doxazosin. An update of its clinical pharmacology and therapeutic applications in hypertension and benign prostatic hyperplasia

Doxazosin is a long-acting alpha 1-adrenoceptor antagonist structurally related to prazosin and terazosin. Its antihypertensive effect is produced by a reduction in the smooth muscle tone of peripheral vascular beds resulting in a decrease in total peripheral resistance without significant effect on cardiac output or heart rate. In benign prostatic hyperplasia, doxazosin's effect of relieving bladder outflow obstruction is produced through a reduction in prostatic tone mediated via alpha 1-adrenoceptor blockade. In most comparative trials doxazosin has proven to be equally effective as the comparator drug in the treatment of mild to moderate hypertension. It has been used in a variety of patient populations including the elderly, Blacks, smokers, and patients with concomitant disease states such as renal dysfunction, hypercholesterolaemia, non-insulin dependent diabetes mellitus (NIDDM) and respiratory disease. Doxazosin has also been used successfully in combination with beta-adrenoceptor antagonists, diuretics, calcium channel antagonists, and angiotensin-converting enzyme inhibitors in patients with hypertension that is uncontrolled with monotherapy. Doxazosin has a beneficial effect on some of the risk factors associated with coronary heart disease including elevated serum lipid levels, impaired glucose metabolism, insulin resistance and left ventricular hypertrophy. Modest decreases in total cholesterol, low density lipoprotein cholesterol and triglycerides are seen with doxazosin therapy while small increases in high density lipoprotein cholesterol and the high density lipoprotein cholesterol/total cholesterol ratio are consistently reported. Some studies have reported an improvement in glucose tolerance although this effect has been more consistently seen in nondiabetic patients than in patients with NIDDM. Additionally, doxazosin produces a similar reduction in left ventricular hypertrophy to other antihypertensive agents. Modelling-based calculations suggest that doxazosin significantly reduces the risk of developing coronary heart disease in patients with mild to moderate hypertension, although this remains to be confirmed in long term prospective studies. Doxazosin appears to be a promising agent in the treatment of urinary symptoms associated with benign prostatic hyperplasia. Similar to other alpha 1-adrenoceptor antagonists, doxazosin treatment produces increases in peak and mean urinary flow rates and improves other objective and symptomatic measures.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of administration and withdrawal of doxazosin on ambulatory blood pressure in patients with essential hypertension

The effect of both administration and withdrawal of doxazosin on patients with essential hypertension was evaluated by twenty-four-hour ambulatory blood pressure (BP) monitoring. Six hypertensive men were treated with doxazosin starting at 1 mg/day, and the dosage was titrated at weekly intervals up to a maximum of 8 mg/day. The twenty-four-hour BP profile was monitored noninvasively before treatment, in the fourth week of treatment, and on days 2 and 7 after the discontinuation of doxazosin. The average twenty-four-hour systolic and diastolic BPs (SBP and DBP) were lowered by doxazosin treatment and returned to the pretreatment levels within two days of doxazosin withdrawal. Doxazosin treatment produced a significant decrease in the daytime SBP and DBP but not in the nighttime BP values. The daytime BP decrease was no longer detected on days 2 and 7 after drug withdrawal. The twenty-four-hour pulse rate was not influenced by either doxazosin administration or discontinuation. The plasma norepinephrine concentration and plasma renin activity were increased by doxazosin treatment and were decreased by drug withdrawal. There was no rebound hypertension following doxazosin withdrawal. Thus, the present study using twenty-four-hour BP monitoring showed that doxazosin treatment reduced the daytime BP in patients with essential hypertension and that this reduction was abolished within two days after doxazosin discontinuation.

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.

Doxazosin withdrawal and ambulatory blood pressure monitoring in normotensive subjects

The effect of doxazosin withdrawal on normotensive subjects was examined by ambulatory blood pressure monitoring (ABPM) during twenty-four hours. Eight normotensive volunteers were treated with doxazosin for four weeks. ABPM was done the day before withdrawal and on the second and seventh days after withdrawal. The average systolic and diastolic BP were not altered by doxazosin withdrawal either on day 2 or day 7, but pulse rate (PR) decreased on day 2 and day 7. Daytime PR decreased on day 2, but both daytime and nighttime PR decreased on day 7. On withdrawal of doxazosin, the plasma norepinephrine concentration decreased and the plasma renin activity tended to decrease. Neither overshooting hypertension nor cardiovascular event was related to doxazosin withdrawal was observed. It is concluded that, in normotensive subjects, discontinuation of doxazosin may result in bradycardia without hypotension or signs of withdrawal syndrome.

Effects of doxazosin on blood pressure, renin-angiotensin-aldosterone and urinary kallikrein

Doxazosin, a new quinazoline-derivative postsynaptic alpha 1-adrenoceptor antagonist, was studied in this randomized, double-blind, placebo-controlled 12-week study. Its effects on blood pressure (BP), heart rate, metabolic functions and renal hormones were analyzed after administration of a single oral morning dose in a 3-phase fashion when administered to 17 patients (11 women, 6 men, 21 to 59 years) with mild to moderate uncomplicated essential hypertension. After titrating the antihypertensive effective dose biweekly from 1 to 8 mg/day and a mean end titration-point dose of 4.14 +/- 0.1 mg (mean +/- standard error of the mean) at week 8 of treatment, it was adjusted to maintain diastolic BP at levels less than or equal to 90 mm Hg for up to 12 weeks of treatment when, at a final mean dose of 4.35 +/- 0.2 mg/day, BP decreased in all patients by a mean 31 +/- 3/17 +/- 2 (supine) and 39 +/- 3/15 +/- 3 (standing) mm Hg (p less than 0.005) with no increase in heart rate and no "first-dose phenomenon." Neither the renin-aldosterone system nor electrolyte excretion was significantly affected. Renal function and metabolic parameters also remained unchanged. Urinary kallikrein excretion was augmented 2.47-fold (p less than 0.002). There was good tolerance; 1 patient discontinued the study because of dry nose. These results suggest that long-term monotherapy with doxazosin is an effective and safe antihypertensive agent for mild to moderate essential hypertension that stimulates urinary kallikrein excretion.

Doxazosin in the treatment of essential hypertension in general medical practice in Latin America

This Latin American study assessed in the general practice setting the efficacy and tolerance of once-daily doxazosin in the treatment of mild or moderate essential hypertension (sitting diastolic blood pressure, 95 to 115 mm Hg). Patients (n = 220) were treated with doxazosin for 12 weeks as monotherapy or in combination with other antihypertensive agents. At the final visit, doxazosin produced a mean change in sitting systolic/diastolic blood pressure of -18.4/-14.4 mm Hg, at a mean daily dose of 4.3 mg. One hundred sixty-three (77.6%) of the 210 evaluable patients were considered a therapeutic success. Lipid analyses identified a statistically significant (p = 0.02) reduction in total serum cholesterol (4.85%) and an overall decrease in triglyceride levels (5.12%). According to the Framingham Heart Study equation, doxazosin produced a highly significant (p less than 0.001) 20% reduction in the calculated probability of developing coronary heart disease in 10 years. Of the 220 patients evaluated, 54 (24.5%) reported side effects that were considered related to treatment. Ten (4.5%) patients reported side effects unrelated to treatment and 37 (16.8%) reported events of unknown relationship. Most side effects were mild or moderate and were tolerated or disappeared with continued treatment. Nine patients (4.1%) were discontinued from therapy and in 13 (5.9%) the dose was reduced. The most prevalent side effects were headache and dizziness. The investigator's overall assessment of antihypertensive efficacy was excellent or good for 176 patients (80.4%); tolerance was considered excellent or good in 193 patients (88.5%).(ABSTRACT TRUNCATED AT 250 WORDS)

A multicenter study of doxazosin in the treatment of patients with mild or moderate essential hypertension and concomitant intermittent claudication

This study assessed the efficacy and safety of once-daily doxazosin in the treatment of patients (n = 19) with mild or moderate essential hypertension (sitting diastolic blood pressure [DBP] 95 to 114 mm Hg) and concomitant intermittent claudication (Doppler ankle/arm ratio of less than 0.80 and walking tolerance of less than 700 m on the treadmill). After 14 weeks of treatment with doxazosin, a significant (p less than 0.05) reduction in systolic blood pressure and DBP was observed. Mean blood pressures were reduced from 170/100 mm Hg at baseline to 161/93 mm Hg at the end of treatment. Minor changes in heart rate occurred, which with continued treatment were not statistically significant from baseline. In 12 of 16 (75.0%) efficacy-evaluable patients blood pressure was normalized (DBP to less than or equal to 90 mm Hg with an greater than or equal to 5 mm Hg reduction from baseline) with a mean daily dose of 7.6 mg/day. Doxazosin improved the hypertension severity category in 13 of 16 (81.3%) patients. The blood pressure ratios between both the thighs and arms and ankles and arms showed no statistically significant changes after treatment with doxazosin. Thigh blood flow at rest and the reactive hyperemia after 3 minutes of arterial occlusion did not change statistically. There was a tendency for pain-free distance to improve. Laboratory data were not significantly changed after treatment with doxazosin. Of the 19 patients studied, 5 reported mild or moderate side effects that were either tolerated or disappeared with continued treatment. No patient had therapy withdrawn and no patient required a dose reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Doxazosin: a study in a cohort of patients with hypertension in general practice--an interim report

The objective of this study was to assess the safety and efficacy of doxazosin in a substantial cohort of hypertensive patients drawn from general practice. A total of 4027 patients entered the study, 1472 of whom (36.6%) were untreated hypertensive patients. Patients were not advised to change diet, smoking habit, or life-style during the study. Twenty-one percent were cigarette smokers, and concurrent diabetes was present in 2.3%. Baseline blood cholesterol exceeded 200 mg/dl (5.2 mmol/L) in 90% and 250 mg/dl (6.5 mmol/L) in 56% of patients. The mean decrease in blood pressure produced by doxazosin was 22/15 mm Hg after 10 weeks of therapy; there was a mean decrease in heart rate of 1 beat/min. The mean maintenance dose for all patients was 3.1 mg/day. Side effects considered related or possibly related to treatment were reported in 705 patients. Treatment was discontinued in 233 patients (5.8%) because of adverse events related or possibly related to treatment with doxazosin. Doxazosin produced a significant (p less than 0.001) decrease in total cholesterol, low-density lipoprotein cholesterol, and triglyceride levels and a significant increase in high-density lipoprotein cholesterol and the ratio of high-density lipoprotein:total cholesterol. The potential reduction in 10-year coronary heart disease risk (according to the Framingham equation) was calculated to be 20.4%.

Doxazosin for the treatment of chronic congestive heart failure: results of a randomized double-blind and placebo-controlled study

In this study we evaluated the effects of once-daily administration of oral doxazosin in patients with chronic congestive heart failure (CHF). After a stabilization period of at least 2 weeks with digitalis and diuretics, 73 patients with chronic CHF were randomized to receive additionally either doxazosin or placebo in double-blind fashion. Patients underwent weekly dose adjustments with increasing doses of doxazosin (1, 2, 4, 8, and 16 mg daily) or placebo for 5 weeks, and 67 were evaluated for 12 additional weeks on maximally tolerated doses of blinded study drugs. Treatment groups were evaluated with respect to symptoms of heart failure, indexes of quality of life and left ventricular function, frequency and type of arrhythmia, adverse events, and mortality rates. Doxazosin (11.9 +/- 0.9 mg) given once daily produced a favorable trend in the investigators' and patients' assessments of symptomatic change. Doxazosin was associated with a significantly higher level of voluntary submaximal exercise and a favorable trend on left ventricular ejection fraction (increase of 9.8% of the baseline value vs 2.7% with placebo; p = NS). During the 3-month steady-dosing period, patients treated with doxazosin had a significant (p less than 0.004) reduction in ventricular arrhythmias and significantly fewer morbid and mortal cardiac events (including episodes of worsening heart failure severe enough to prompt discontinuation of the study, myocardial infarction, and death). Doxazosin was well tolerated, producing no major side effects and only a slightly higher frequency of minor treatment-related side effects compared with placebo (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

A long-term study of doxazosin in the treatment of mild or moderate essential hypertension in general medical practice

This study assessed the long-term (54 weeks) antihypertensive efficacy and safety of doxazosin in the treatment of mild or moderate essential hypertension, defined as sitting and standing diastolic blood pressure of 95 to 114 mm Hg. Of the 153 patients who successfully completed an initial 14-week trial, 61 continued uninterrupted into a 40-week extension study. Optimal antihypertensive efficacy was achieved by week 12 and maintained in all patients for the duration of 1 year. The final mean sitting blood pressure was 148/84 mm Hg and was reduced from a mean baseline level of 173/102 mm Hg. Occasional decreases in heart rate were observed, but these were not considered to be clinically relevant (1 to 3 beats/min). The mean final dose of doxazosin for patients evaluable for efficacy was 2.4 mg/day; 91.7% of patients were taking less than or equal to 4 mg/day. No increase in daily maintenance dose was observed from the initial phase to the long-term extension study. After 1 year of treatment, 93.3% of patients were considered a therapeutic success (sitting diastolic blood pressure greater than or equal to 10 mm Hg reduction from baseline or less than or equal to 90 mm Hg with greater than or equal to 5 mm Hg reduction). In no patients was there a worsening in the severity category of the hypertension. Total serum cholesterol concentrations were reduced significantly (6.6% p = 0.03) at the end of week 14. Reductions in total serum cholesterol levels persisted throughout the extension study, with a final reduction of 5.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

The place of simultaneous pharmacokinetic pharmacodynamic modeling in new drug development: trends and perspectives

The potential applications in drug development of pharmacokinetic-pharmacodynamic modeling are numerous: optimal medication regimen, design of galenic forms, identification of specific effects of metabolites and enantiomers. Nevertheless, this methodology is presently under-used, as appears from an analysis of the literature. We examine this point as well as progress in both non-invasive pharmacodynamic measurement and specific experimental design that could lead to a future extension of PK-PD in toxicology and phase I drug development.

Concentration-effect relationships and individual responses to doxazosin in essential hypertension

1. This study investigates aspects of the pharmacokinetics, pharmacodynamics and concentration-effect relationships in 10 patients with essential hypertension during acute and chronic treatment with doxazosin, an alpha 1-adrenoceptor antagonist. 2. Following the first dose of doxazosin (2 mg) there were significant reductions in blood pressure, increases in heart rate and in plasma noradrenaline, and parallel rightward shifts of the phenylephrine pressor response curves, consistent with alpha-adrenoceptor antagonism. There was no significant change in the pressor response to angiotensin II. 3. Using an integrated kinetic-dynamic model, individual blood pressure responsiveness was characterised as the fall in blood pressure (mm Hg) per unit drug concentration. Responsiveness to the first dose of doxazosin was directly correlated with the responsiveness after 1 and 6 weeks treatment although there was a systemic reduction (of approximately 30%) which occurred during the first week of treatment. 4. Neither the acute nor long-term responsiveness to doxazosin was related to age, plasma renin activity, plasma noradrenaline or the pretreatment sensitivity to phenylephrine. There was a significant relationship between responsiveness and the height of the initial (pretreatment) blood pressure. 5. Integration of pharmacokinetic and pharmacodynamic data provides a reproducible index of responsiveness which can be used to investigate the consistency of the long-term anti-hypertensive response, to identify factors which influence the magnitude of the response, and to optimise the choice of dose and dose interval.

Clinical pharmacotherapeutics of doxazosin

Doxazosin is the latest in a series of highly selective postsynaptic alpha 1-adrenoceptor inhibitors. It is readily absorbed, with high bioavailability and a relatively long plasma half-life, neither of which property is influenced by age. This accounts for the prolonged pharmacologic activity of doxazosin following a single oral dose. Its prime pharmacodynamic activity resides in its ability to counter sympathetic vasoconstriction of the systemic arteriolar resistance vessels and venous capacitance system, which enables the drug to target the major pathophysiologic abnormality in hypertension, i.e., the generalized systemic arteriolar constriction. The widespread vasodilation induced by doxazosin relieves both cardiac preload and afterload and, consequently, reduces left ventricular wall stress and myocardial oxygen consumption. In hypertension, doxazosin reduces blood pressure both at rest and during exercise by reduction of systemic vascular resistance without precipitating substantial reflex cardiac stimulation. The effects are maximal on the standing blood pressure between two and four hours after ingestion; due to doxazosin's relatively slow absorption, postural hypotension is infrequent. Its antihypertensive activity is maintained over 24 hours following a single oral dose, and the optimal dose range is 2 to 8 mg once daily. The antihypertensive efficacy of doxazosin has been shown to be comparable with that of other alpha-adrenoceptor inhibitors, beta-blocking drugs, diuretics, calcium antagonists, and angiotensin-converting enzyme inhibitors. In contrast to other conventional antihypertensive drugs, a unique feature of alpha-adrenoceptor-inhibiting drugs, including doxazosin, is their ability to reduce the plasma concentrations of triglycerides, total cholesterol, and low-density lipoprotein cholesterol and to increase high-density lipoprotein cholesterol concentration. This contrasts with the opposite effect on lipid levels induced by hydrochlorothiazide and atenolol seen in comparative studies. Side effects show no predilection for any organ system, and the overall incidence of such effects compares well with those of other commonly used antihypertensive drugs. This unique combination of antihypertensive efficacy and favorable effect on blood lipid levels indicates that once-daily treatment with doxazosin holds considerable promise in the treatment of hypertension, both from the point of view of its antihypertensive efficacy and also from its primary preventative potential.

Effectiveness of doxazosin in systemic hypertension

Most alpha-receptor blocking drugs require divided daily administration because of a short plasma half-life. This multicenter study examined the effectiveness and safety of once-daily administration with doxazosin, a quinazoline analog alpha 1-receptor blocking drug with a plasma half-life of 19 hours. Patients with diastolic blood pressure (BP) of 90 to 115 mm Hg entered 4 weeks of single-blind placebo therapy and then were randomized to double-blind treatment with doxazosin (63 patients) or placebo (67 patients). After 10 weeks of titration, standing arterial BP was lowered by 14/11 mm Hg with doxazosin and by 0.5/0.9 mm Hg with placebo (p less than 0.001). Measured hourly for 12 hours after the dose, all standing and supine arterial BP values were significantly lower in the doxazosin group at each hour. Pulse rate increased slightly in both groups int he double-blind phase, but the increase with doxazosin never significantly exceeded that of placebo. Dizziness was the most common complaint with doxazosin, but syncope did not occur. Side effects were mild and transient and did not necessitate withdrawing any participants from the study. Body weight increased by 1.5 kg in the doxazosin group and decreased by 0.2 kg in the placebo group (p less than 0.01). Safe and effective in once-daily administration, doxazosin is suitable for initial therapy in mild and moderate hypertension.

Doxazosin: a newly developed, selective alpha 1-inhibitor in the management of patients with pheochromocytoma

Although surgical removal is the therapy of choice in patients with pheochromocytoma, medical management is necessary in the preoperative preparation of these patients and in inoperable cases. An alpha-adrenoceptor-blocking agent is routinely used as initial therapy to control hypertension, with a beta-blocker used as a second-step agent to control tachycardia when indicated. Doxazosin, a selective alpha 1-inhibitor used as an antihypertensive agent for the reduction of coronary heart disease risk in hypertensive patients, appears to be a good agent to control blood pressure with minimal changes in heart rate. The aim of this study was to assess the antihypertensive efficacy and safety of doxazosin when used alone or in conjunction with a beta-blocker in 24 patients with pheochromocytoma. Overall excellent or good antihypertensive efficacy was assessed by physicians in 19 of 24 patients (79.2%) enrolled in the study. Doxazosin monotherapy was effective in eight of 12 patients (66.7%), and combined therapy with a beta-blocker was effective in 11 of 12 patients (91.7%). The mean pulse rate remained constant throughout therapy. Adverse reactions were minor and transient and occurred in only three patients. Urinary and plasma catecholamine levels tended to decrease or remained unchanged during doxazosin therapy. There were no clinically hazardous abnormalities or problems in hematologic and biochemical laboratory data. Overall, doxazosin was considered very useful or useful in 83.3% of patients. In conclusion, doxazosin appears to be an excellent agent for the management of hypertension associated with pheochromocytoma.

Doxazosin versus atenolol: a randomized comparison of calculated coronary heart disease risk reduction

Doxazosin is a selective alpha 1-inhibitor for the reduction of calculated coronary heart disease (CHD) risk in hypertensive patients. Atenolol, although a widely used beta-blocker, appears to adversely affect blood lipids by increasing triglycerides and decreasing high-density lipoprotein (HDL) cholesterol. The aim of our study was to compare doxazosin and atenolol for their therapeutic efficacy in reducing CHD risk (decrease in blood pressure and effect on lipid distribution) and toleration. Patients with mild-to-moderate hypertension were randomized into two groups of 20 patients to receive once-daily atenolol (100 mg) or doxazosin (2 to 8 mg) for 8 weeks. Doxazosin was as effective as atenolol in reducing supine and standing blood pressure. Unlike atenolol, doxazosin did not produce a marked bradycardia. Doxazosin therapy produced favorable modifications in plasma lipid profiles by decreasing triglycerides and total cholesterol and by increasing HDL cholesterol and HDL/total cholesterol ratio. A reverse in this lipid profile was seen with atenolol. Therefore doxazosin may reduce calculated CHD risk more effectively than atenolol, based on the Framingham equation.

A multicenter study of doxazosin in the treatment of severe essential hypertension

The antihypertensive efficacy and safety of doxazosin, a selective alpha 1-inhibitor, were assessed in 33 severely hypertensive patients. The study involved three phases: a 1-day baseline period, a 32-day period in which patients received doxazosin, 1 to 16 mg, once daily, and a 4-week maintenance period. All patients were considered therapy successes (sitting diastolic blood pressure either less than or equal to 90 mm Hg or greater than or equal to 10 mm Hg reduction) at a mean daily dose of 8.1 mg. Twenty-seven patients (82%) achieved good blood pressure control (sitting diastolic blood pressure less than or equal to 90 mm Hg) at a mean dose of 6.7 mg once daily. By the final treatment visit, mean systolic/diastolic blood pressures in the sitting and supine positions were significantly reduced by 40/29 and 37/28 mm Hg from a mean baseline of 180/121 and 181/121 mm Hg to final visit values of 140/91 and 144/92 mm Hg, respectively (p less than 0.05). Eleven patients experienced one or more side effects that were mild or moderate and disappeared or were tolerated with continued therapy. During the study no abnormal laboratory test findings were identified by the investigators. The investigators' global assessment of the efficacy and toleration of once-daily doxazosin therapy was excellent or good for 31 (94%) patients and fair for the remaining two patients.

Clinical experience with doxazosin in general medical practice

The antihypertensive efficacy, lipid effects, and safety of doxazosin, a selective alpha 1-inhibitor for the reduction of coronary heart disease (CHD) risk in hypertensive patients, was assessed in a general medical practice setting. Seven hundred seventy-one patients were entered into the study, which involved three phases: (1) a 2-week baseline period, (2) an 8-week period in which patients received doxazosin, 1 to 8 mg once daily, and (3) a 4-week maintenance period. From baseline to final visit there was a highly significant 27% reduction (p less than 0.001) in calculated CHD risk based on the Framingham equation as a consequence of doxazosin's favorable effects on both blood pressure and serum lipid levels. Efficacy and toleration of doxazosin therapy were good to excellent in most patients. The investigators' global assessment of efficacy of once-daily doxazosin therapy was excellent or good for 82% of patients and fair or poor for only 18% of patients. After 12 weeks, 83% of the patients were considered therapy successes (sitting diastolic blood pressure either less than or equal to 90 mm Hg or greater than or equal to 10 mm Hg reduction not reaching less than or equal to 90 mm Hg) at a mean daily dose of 3.5 mg. Seventy-one percent achieved "normalized" blood pressure control (sitting diastolic less than or equal to 90 mm Hg with a decrease of greater than or equal to 5 mm Hg) at a mean dose of 3.1 mg once daily. By the final treatment visit, systolic/diastolic blood pressures of efficacy evaluable patients were reduced by 20.6/15.3 and 21.0/15.4 mm Hg from a mean baseline of 166/104 and 165/104 mm Hg in the sitting and standing positions, respectively (p less than 0.05). Total cholesterol was significantly decreased (p less than 0.01). Most side effects were mild or moderate and disappeared with or were tolerated on continued therapy. The investigators' global assessment of patient toleration of doxazosin treatment was excellent or good for 89% of the 763 patients evaluated and fair or poor for only 11% of patients. The most commonly reported side effects were headache (8%) and dizziness (7%). No clinically significant laboratory changes were apparent, and no trends were observed with regard to organ systems or correlations with dose or duration of treatment.

Pharmacotherapeutic stature of doxazosin and its role in coronary risk reduction

In hypertension the primary pathophysiologic abnormality is a generalized increase in the peripheral vascular resistance as a result of concentric narrowing of the systemic arterioles, as a result of alpha 1-receptor stimulation. Such stimulation is attenuated by the selective alpha 1-inhibitor doxazosin. The pharmacologic attributes of doxazosin are translated into direct relaxation of the peripheral arteriolar resistance vessels and venous capacitance system, particularly those with a high alpha-adrenoceptor population. The direct effects of such vascular dilatation are immediately beneficial to the heart in reducing systemic and pulmonary vascular pressures that reduce left ventricular wall stress and myocardial oxygen consumption. In clinical studies doxazosin has been found to have a plasma half-life of 19 to 22 hours, of which a single daily dose is sufficient to control hypertension. The antiatherogenic changes in the blood lipid profile resulting from long-term treatment with doxazosin can also be expected to advance its primary prevention potential in hypertensive patients, which is in marked contrast to the potentially disadvantageous changes in the blood lipid profile that follow treatment with beta-blockers and thiazide diuretics. The therapeutic efficacy of doxazosin has been confirmed, irrespective of hypertension severity, age and race of the patient, or the presence of renal impairment or diabetes mellitus. Its side-effect profile is not substantially different from that of placebo or other antihypertensive drug treatment. Given its unique actions regarding antihypertensive efficacy, together with favorable effects on blood lipids, doxazosin probably holds more promise for the prevention of precocious coronary heart disease in hypertensive patients than any other currently available antihypertensive agent.

Doxazosin in the treatment of patients with mild or moderate hypertension and mild or moderate renal insufficiency

The antihypertensive efficacy and safety of doxazosin, a selective alpha 1-inhibitor, were assessed in 23 hypertensive patients with renal insufficiency. The study involved three phases: (1) a 2-week baseline period, (2) a 10-week period during which patients received doxazosin, 1 to 16 mg, once daily, and (3) a 4-week maintenance period. After 14 weeks of active treatment, systolic/diastolic blood pressures of efficacy evaluable patients were reduced by 8.9/9.2 and 4.6/9.1 mm Hg to final values of 153/90 and 149/91 mm Hg in the supine and standing positions, respectively. The mean dose of the efficacy evaluable patients was 9.8 mg/day. Eleven patients experienced one or more side effects, most of which were mild or moderate and disappeared or were tolerated with continued therapy. No clinically significant laboratory changes were apparent, and no trends were observed with regard to organ systems or correlations with dose or duration of treatment. There were no significant differences in serum creatinine levels between baseline and final visits. The overall lipid profile indicated a decrease in total cholesterol with increases in high-density lipoprotein cholesterol and the high-density lipoprotein/total cholesterol ratio. From baseline to final visit there was a highly significant reduction of 19% (p less than 0.05) in calculated risk scores for coronary heart disease on the basis of the Framingham equation.

A comparative study of doxazosin versus atenolol in mild-to-moderate hypertension

Doxazosin, a quinazoline derivative, is a selective alpha 1-inhibitor that reduces calculated coronary heart disease risk by lowering blood pressure while favorably affecting blood lipid levels. The aim of this study was to compare the efficacy and toleration of doxazosin with atenolol, one of the most frequently used cardioselective beta-blockers in Italy. Forty patients with mild-to-moderate hypertension were treated with either atenolol (100 mg) or doxazosin (mean dose, 3.3 mg) once daily for 8 weeks. Both drugs significantly reduced supine and standing systolic and diastolic blood pressures. Atenolol induced marked bradycardia, whereas doxazosin had very little effect on heart rate. Doxazosin produced a favorable effect on blood lipid levels by decreasing triglyceride and total cholesterol levels and increasing high-density lipoprotein cholesterol and high-density lipoprotein total cholesterol ratio. Atenolol had exactly the opposite effect on blood lipid levels. Both drugs had equivalent toleration profiles. It was concluded that doxazosin was as effective as atenolol in reducing elevated supine and standing blood pressures. In addition, doxazosin had a beneficial effect on lipid profiles and minimal effect on heart rate. Therefore doxazosin may reduce calculated coronary heart disease risk in hypertensive patients.

New alpha 1-adrenergic receptor antagonists for the treatment of hypertension: role of vascular alpha receptors in the control of peripheral resistance

The pharmacology, clinical efficacy and safety of new alpha-adrenergic receptor antagonists for the treatment of hypertension was reviewed (Table XIV). Although all these agents block alpha 1 receptors, some of them have additional effects on histamine, serotonin, dopamine, and alpha 2 receptors. These other actions account for the differences in the side effect profiles observed, i.e., increased incidence of central nervous system side effects found with indoramin, ketanserin, and urapidil, as well as for some additional beneficial effects of ketanserin (i.e., antiplatelet aggregation activity). The magnitude of BP reduction observed with antagonists of alpha 1-adrenergic receptors is modest. In most studies, the degree of BP reduction is comparable to that of prazosin, but less than that achieved with thiazide diuretics, beta-receptor antagonists, or methyldopa. Studies on the comparative efficacy and safety of new alpha 1 antagonists with converting enzyme inhibitors or calcium-channel blockers are not available. In general, alpha 1 antagonists produce greater reductions in standing than in supine BP, an effect due to the venodilatory action of these drugs. New alpha 1 antagonists appear to have equal efficacy in black and white hypertensive individuals. Their comparative efficacy and safety in young vs elderly hypertensive individuals requires further investigation. No information about the possible development of tolerance during treatment with new alpha 1 blockers was encountered. The effects of alpha 1 antagonists on HR are variable and depend on how long after the oral dose the measurements were obtained. In most studies, no significant HR changes are noticed for readings obtained 24 hours post dose; whereas tachycardia has been observed at the time of peak hypotension. Since alpha 1 antagonist-induced tachycardia is most likely of reflex nature, i.e., mediated to an increase in sympathetic activity, the increased HR may be associated with increases in myocardial contractility and in myocardial oxygen consumption. Consequently, a 24-hour HR monitoring during treatment with alpha 1 antagonists should be required for evaluation of new agents. The hemodynamic, humoral, and hormonal effects of the newer alpha 1-receptor antagonists are comparable to those of prazosin. The most consistent finding is a reduction in total peripheral resistance associated with either no change or with only small increases in cardiac index. These agents have been shown either not to change or to increase renal blood flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Doxazosin in patients with hypertension

The antihypertensive effects and steady-state pharmacokinetics of doxazosin, as well as the bioequivalence of four dosage forms, were studied in 25 hypertensive patients. For an 8 mg daily dose mean Cmax at steady-state for all patients was 108 ng/ml; the mean tmax was 1.8 h. The mean terminal elimination half-life was 22 h. The four tablets containing 1, 2, 4, or 8 mg of doxazosin were bioequivalent in delivering the 8 mg dose. In patients with mild to moderate hypertension, 26-day treatment with doxazosin resulted in blood pressure reduction of 10/7 mmHg in the supine and 13/18 mmHg in the standing position. Adverse effects were generally mild and of brief duration.