Doxazosin GITS versus standard doxazosin in mild to moderate hypertension

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.

Controlled‐Release Doxazosin as Combination Therapy in Hypertension: The GATES Study

Doxazosin gastrointestinal therapeutic system (GITS) or placebo was added to the antihypertensive therapy of uncontrolled hypertensive patients in a prospective, randomized, double-blind trial. Patients received doxazosin GITS 4 mg/d (n=89) or placebo (n=86) for 6 weeks in addition to entry antihypertensive medication. Doxazosin GITS was increased to 8 mg/d after 2 or 4 weeks if patients did not respond (sitting blood pressure <140/90 mm Hg and 10/10-mm Hg decrease from baseline). Reductions from baseline in sitting and standing blood pressures were greater with doxazosin GITS than placebo at all time points (p</=0.017) except Week 1 sitting systolic pressure (p=0.068). The response rate was greater in the doxazosin GITS group (37.3%) than the placebo group (10.7%; p<0.001). With the exception of postural hypotension (7% compared with 0.0%), the frequency of adverse events was similar for doxazosin GITS and placebo. Doxazosin GITS was effective as combination antihypertensive therapy with the major classes of antihypertensive agents.

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

OBJECTIVE

To evaluate extended-release doxazosin gastrointestinal therapeutic system (GITS) as add-on therapy in patients with treated, but uncontrolled hypertension.

METHODS

A 16-week, open, noncomparative, multicenter, prospective study of patients with hypertension (> or = 140/> or = 90 mm Hg). Doxazosin GITS 4 mg/d was added to entry medication and increased to 8 mg/d at Week 4 in cases of inadequate blood pressure (BP) control.

RESULTS

A total of 3631 patients (40% women) with mean age of 62.4 +/- 0.2 years were included. Proportion of patients reaching goal (< 140/< 90 mm Hg) after 4 weeks of add-on therapy with doxazosin GITS was 39% and increased to 61% at Week 16. Systolic and diastolic BP (mean +/- SEM) decreased, respectively, from 161.6 +/- 0.2 and 95.1 +/- 0.1 mm Hg at baseline to 142.2 +/- 0.2 and 84.1 +/- 0.1 mm Hg at Week 4 (P < 0.0001) and 136.8 +/- 0.2 and 80.6 +/- 0.2 mm Hg at Week 16 (P < 0.0001). Adverse events occurred in 108 patients (3.0%), with 57 (1.6%) related to the study treatment. In 17 patients (0.5%), serious adverse events were described, but only one was related to the study drug.

CONCLUSIONS

Doxazosin GITS as add-on therapy achieved target blood pressure and was well tolerated in patients with hypertension uncontrolled by previous regimens. Doxazosin GITS efficacy and tolerability was achieved in combination with all classes of antihypertensives tested.