Effect of Doxazosin Gastrointestinal Therapeutic System on Patients with Uncontrolled Hypertension: The ASOCIA Study

Enantioselective pharmacokinetics of doxazosin and pharmacokinetic interaction between the isomers in rats

In this study, the stereoselective pharmacokinetics of doxazosin enantiomers and their pharmacokinetic interaction were studied in rats. Enantiomer concentrations in plasma were measured using chiral high-pressure liquid chromatography (HPLC) with fluorescence detection after oral or intravenous administration of (-)-(R)-doxazosin 3.0 mg/kg, (+)-(S)-doxazosin 3.0 mg/kg, and rac-doxazosin 6.0 mg/kg. AUC values of (+)-(S)-doxazosin were always larger than those of (-)-(R)-doxazosin, regardless of oral or intravenous administration. The maximum plasma concentration (Cmax ) value of (-)-(R)-doxazosin after oral administration was significantly higher when given alone (110.5 ± 46.4 ng/mL) versus in racemate (53.2 ± 19.7 ng/mL), whereas the Cmax value of (+)-(S)-doxazosin did not change significantly. The area under the curve (AUC) and Cmax values for (+)-(S)-doxazosin after intravenous administration were significantly lower, and its Cl value significantly higher, when given alone versus in racemate. We speculate that (-)-(R)-doxazosin increases (+)-(S)-doxazosin exposure probably by inhibiting the elimination of (+)-(S)-doxazosin, and the enantiomers may be competitively absorbed from the gastrointestinal tract. In conclusion, doxazosin pharmacokinetics are substantially stereospecific and enantiomer-enantiomer interaction occurs after rac-administration.

Doxazosin selectively potentiates contraction to serotonin via 5-HT₂A receptors in longitudinal muscle strips of the rabbit gastric body

The aims of this study were to examine the effects of doxazosin on contractile responses to 5-hydroxytryptamine (5-HT), carbachol, and histamine, and to compare them with those of prazosin, alfuzosin, and terazosin, and then characterize a pharmacological profile of the 5-HT-induced contractile response using preparations of isolated longitudinal muscle strips from the rabbit gastric body. The results from these preparations showed that the contraction response to 5-HT, but not to carbachol or histamine, was found to be dose-dependently potentiated by doxazosin and its enantiomers. The specific potentiation effect on 5-HT was not observed in the preparations that were treated with prazosin, terazosin, or alfuzosin. The contractile response to 5-HT and its potentiation by doxazosin were not affected by treatment with phenoxybenzamine. However, 5-HT-induced contraction was competitively antagonized by nefazodone (with pA₂ value of 8.64 ± 0.17), and was almost completely inhibited by treatment with indomethacin. In conclusion, doxazosin, but not prazosin, alfuzosin, or terazosin, selectively potentiates 5-HT-induced contraction in the rabbit gastric body strips via an α₁-adrenoceptor-independent mechanism, without chiral recognition of its enantiomers. Additionally, the contraction to 5-HT was found to be mediated via 5-HT(₂) receptors, and was similar to PGs synthesis in the preparations.

Time to re-appraise the role of alpha-1 adrenoceptor antagonists in the management of hypertension?

The role of alpha-1 adrenoceptor antagonists (alpha-blockers) in the management of hypertension continues to evolve. Recent data support their use as add-on therapy in uncontrolled hypertension when used in combination with all other major classes of antihypertensive drug and there is increasing evidence suggesting that they have modest but significant beneficial effects on lipid and glucose metabolism. The availability of extended-release formulations has contributed to an excellent tolerability profile. New data from an observational analysis of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) suggest that doxazosin gastrointestinal therapeutic system (GITS) used as a third-line antihypertensive agent lowered blood pressure and caused modest reductions in plasma lipids. Furthermore, use of doxazosin in ASCOT was not associated with an increased risk of heart failure, in contrast to the earlier finding of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). Overall, currently available data support the use of alpha-blockers as safe, well tolerated and effective add-on antihypertensive drugs, which have additional favourable metabolic effects.

Extended-release doxazosin for treatment of renal transplant recipients with benign prostatic hyperplasia

We studied living-related donor renal transplant recipients with benign prostatic hyperplasia (BPH). No prisoners were used in the study either as donors or recipients. We sought to assess the effectiveness and safety of extended-release doxazosin for treatment of renal transplant recipients with BPH.

METHODS

Forty-six recipients were diagnosed with BPH. Their transplanted kidney functions were stable. They received 4 or 8 mg/d of extended-release doxazosin orally. After 2, 4, 12, and 24 weeks, changes in the International Prostate Symptom Score (IPSS), quality of life (QoL), peak urinary flow rate (Q(max)), residual urine, blood pressure, renal graft function, and trough immunosuppressant concentrations were analyzed by a prospective, self-calibrated method.

RESULTS

The effectiveness rate of extended-release doxazosin in renal transplant recipients with BPH was 63.04% (29/46). Compared with their status before they took doxazosin, IPSS and residual urine decreased significantly, whereas Q(max) and QoL increased significantly at 2, 4, 12, and 24 weeks after treatment (P < .01). In 15 renal transplant recipients with hypertension, systolic blood pressure (SBP) and diastolic blood pressure (DBP) significantly decreased at 2, 4, 12, and 24 weeks after treatment (P < .01); blood pressure became normal in 10 patients (66.67%). The differences in renal graft function and trough concentration of immunosuppressants before versus after treatment were not significant.

CONCLUSION

Extended-release doxazosin treatment was effective and safe in renal transplant recipients with BPH. The drug not only had no influence on renal graft function and trough concentrations of immunosuppressant, but improved hypertension in these patients.

Comparison of the effects of doxazosin and atenolol on target organ damage in adults with type 2 diabetes mellitus and hypertension in the CARDHIAC study: a 9-month, prospective, randomized, open-label, blinded-evaluation trial

OBJECTIVE

The CARDHIAC (CARduran en pacientes Diabéticos con HIpertensi'on Arterial no Controlada) trial examined the effects of doxazosin gastrointestinal therapeutic system (GITS) and atenolol on 3 separate measures of target-organ damage--left ventricular mass index (LVMI), carotid intima media thickness (IMT), and urinary albumin excretion (UAE)--in patients with type 2 diabetes mellitus and hypertension.

METHOD

This trial had a prospective, open-label, blinded-evaluation design and a duration of 9 months. Patients whose blood pressure (BP) was uncontrolled (systolic BP > or = 130 mm Hg and/or diastolic BP > or = 80 mm Hg) despite at least 1 month of treatment with a renin-angiotensin blocker and diuretic were randomly allocated to receive doxazosin GITS 4 mg or atenolol 50 mg once daily in addition to their existing treatment. Seated BP was measured at study visits at 1, 3, 6 and 9 months; if the BP goal was not achieved at any visit, the dose of doxazosin or atenolol was titrated upward to 8 or 100 mg, respectively. Treatment compliance (pill count) and adverse reactions were monitored at each visit. Each patient underwent echocardiography and Doppler ultrasonography at baseline and at the end of the study for evaluation of the change in LVMI. The change in carotid IMT was evaluated by carotid ultrasound examination at the same time points. UAE also was measured at baseline and the end of the study.

RESULTS

Sixty patients (100% white; 51% female; mean [SD] age, 63.4 [7.5] years; body mass index, 28.2 [3.4] kg/m(2)) were randomized to receive doxazosin GITS (n=32) or atenolol (n=28). At baseline, mean BP was 150.2 (10.6)/90.1 (7.3) mm Hg in the doxazosin group and 153.1 (13.8)/92.3 (6.1) mm Hg in the atenolol group (P=NS). At the end of the study, BP had decreased by 10.1 (3.2)/5.2 (1.3) mm Hg in the doxazosin group and 12.2 (4.2)/6.3 (2.1) mm Hg in the atenolol group (both, P<0.001 vs baseline; P=NS between groups). Heart rate at the end of the study was 78(6) beats/min in the doxazosin group (P=NS vs baseline) and 66(7) beats/min in the atenolol group (P<0.01 vs baseline and between groups). LVMI decreased by 10.8 in the doxazosin group (P=0.001 vs baseline) and 4.2% in the atenolol group (P=NS vs baseline; P=0.03 between groups). The changes in carotid IMT and UAE were not statistically significant between groups.

CONCLUSIONS

In this study in hypertensive patients with type 2 diabetes, LVMI was significantly decreased in doxazosin-treated patients relative to baseline and compared with atenolol-treated patients. The differences in carotid IMT and UAE were not statistically significant between groups.

Add-on therapy with a nighttime dose of doxazosin in patients with uncontrolled hypertension: effects on autonomic modulation of the cardiovascular system

This study was designed to determine whether or not the addition of a single nighttime dose of doxazosin in extended-release form (GITS; gastrointestinal therapeutic system) would affect the autonomic modulation of the cardiovascular system in patients with uncontrolled hypertension treated with a multi-drug regimen. Resting 5-min noninvasive finger blood pressure and ECG signals, as well as 24-h Holter ECGs, were recorded in 30 patients with uncontrolled hypertension on multi-drug treatment before and after 16-week add-on therapy with doxazosin GITS. Cardiovascular autonomic modulation was evaluated by spectral analysis of heart rate variability (HRV) and a cross-correlation method for spontaneous baroreflex sensitivity (BRS) in 5-min resting recordings, and by the analysis of Poincaré plots and phase-rectified signal averaging of the duration of cardiac cycles in 24-h ECG recordings. This combined therapy significantly reduced systolic pressure (19.4+/-3.5 mmHg; p<0.0001), diastolic blood pressure (9.4+/-2.0 mmHg; p=0.0003), and pulse pressure (10.0+/-2.8 mmHg; p=0.0021). Concomitantly, there was a significant increase in resting spontaneous BRS (p=0.0191) and increases in 24-h short-term (p=0.0129) and total (p=0.0153) HRV, but with no significant change in heart rate or other measures of HRV. The improvements in HRV and BRS were observed mainly in patients already treated with thiazide diuretics. There was a significant association (r=0.49; p=0.0065) between the degree of change in diastolic blood pressure and short-term HRV caused by the combined treatment. The addition of 4 mg doxazosin GITS to multi-drug antihypertensive therapy is associated with an improvement in cardiovascular autonomic control.

Add-on therapy with doxazosin in patients with hypertension influences arterial stiffness and albuterol-mediated arterial vasodilation

AIMS

Doxazosin is an antihypertensive agent with largely unknown effects on arterial stiffness and vasodilation. The aim of this study was to determine the effect of the addition of doxazosin extended-release (ER) to the standard management of hypertension in patients with inadequately controlled blood pressure (BP) on arterial stiffness and arterial vasodilation.

METHODS

Twenty patients with inadequately controlled hypertension were treated with 4 mg doxazosin ER daily for 16 weeks as an adjunct to their existing antihypertensive regimen.

RESULTS

Doxazosin ER add-on therapy was associated with significantly reduced systolic (P < 0.0001) and diastolic (P = 0.0003) BP, improved arterial stiffness (determined by digital volume pulse analysis (P = 0.048) and albuterol-mediated arterial vasodilation (P = 0.030).

CONCLUSIONS

Add-on therapy with 4 mg of doxazosin ER daily reduces BP and arterial stiffness and improves arterial vasodilation in response to adrenergic stimulation.