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At least 19 recordsLinked to original sources

PubMed1979

Differences in hemodynamic effects of nitroprusside and prazosin in severe chronic congestive heart failure: evidence for a direct negative chronotropic effect of prazosin.

To compare the hemodynamic effects of prazosin and nitroprusside in patients with severe congestive heart failure, nine patients with heart failure refractory to conventional therapy received oral prazosin and intravenous nitroprusside administered so as to produce a similar decrease in left ventricular filling pressure in each patient. By this comparison, both drugs produced similar decreases in mean right atrial pressure, mean pulmonary arterial pressure and systemic and pulmonary vascular resistance. However, with nitroprusside, cardiac index increased more (+0.97 versus +0.73 liters/min per m2, P less than 0.01) and mean arterial pressure decreased less (-13.7 versus -18.3 mm Hg, P less than 0.05) than with prazosin. Both drugs produced similar changes in stroke volume index (+11.7 cc/beat per m2 with nitroprusside and +12.5 with prazosin) and stroke work index (+8.1 g-m/m2 with nitroprusside and +6.6 with prazosin). Therefore, the differences in the hemodynamic responses observed with the two agents were due to the significantly greater decrease in heart rate with prazosin (-8 beats/min) than with nitroprusside (-2 beats/min, P less than 0.05). These clinical data support experimental evidence suggesting that there is a significant negative chronotropic action of prazosin independent of its peripheral vascular effects.

Administration, Oral↗

PubMed1984

Prazosin versus propranolol plus prazosin: a comparison in diuretic-treated hypertensive patients.

The antihypertensive efficacy of prazosin was compared with that of a combination of prazosin and propranolol in 14 patients with essential hypertension. All patients had sitting diastolic blood pressures greater than or equal to 95 mm Hg despite daily therapy with 50 mg of hydrochlorothiazide and 240 mg of propranolol. After a 4-week monitoring period, patients were divided randomly into 2 groups in whom either (1) propranolol was reduced to 120 mg/day (to avoid potential hypotension) and prazosin was added, starting with an initial dose of 1 mg twice daily, or (2) propranolol was tapered and discontinued as prazosin was added. The average doses of prazosin were 7.4 and 7.6 mg/day, respectively. After 12 weeks of therapy, blood pressure was reduced in both groups, and there was no significant difference in the reduction of blood pressure or dose of prazosin in the 2 groups. Mean heart rate increased significantly in both groups (p less than 0.01), but more so in the group of patients who discontinued propranolol therapy. Thus, when a combination of 50 mg/day of hydrochlorothiazide and 240 mg/day of propranolol is insufficient to control hypertension, the addition of prazosin is shown to decrease blood pressure whether or not propranolol is continued.

Aged↗

PubMed1980

Studies on the clinical pharmacology of prazosin. II: The influence of indomethacin and of propranolol on the action and disposition of prazosin.

1 The possibility of pharmacodynamic and pharmacokinetic interactions of prazosin with indomethacin and with propranolol have been studied in healthy subjects. 2 In four out of nine individuals indomethacin considerably attenuated prazosin-induced hypotension, but noradrenaline concentrations were unchanged from the day when blood pressure fell greatly. The effect of prazosin in the other five subjects was not influenced by indomethacin. 3 Indomethacin prevented the rise in plasma renin activity seen following administration of prazosin alone. 4 Propranolol did not prevent the syncope associated with the first dose of prazosin. 5 Propranolol affected neither the absorption nor elimination of prazosin. 6 It is concluded that in certain subjects indomethacin can largely prevent the hypotensive effect of parazosin, possible by increasing adrenergic receptor sensitivity. The theoretical possibility that propranolol could influence prazosin disposition or syncope was not substantiated.

Adult↗

PubMed1998

Erectile response to transurethral alprostadil, prazosin and alprostadil-prazosin combinations.

PURPOSE: Transurethral alprostadil has been shown to be efficacious in many men with erectile dysfunction. We compared transurethral alprostadil and prazosin alone, and in combination to treat this disorder. MATERIALS AND METHODS: In this double-blind, placebo controlled study the erectile responses to transurethral alprostadil, prazosin and alprostadil-prazosin combinations were assessed in 234 men 26.8 to 81.5 years old with complete organic erectile dysfunction. Patients self-administered a random sequence of 7 doses in the clinic in 4 weeks. The erectile response was assessed using categorical and visual analog scales. RESULTS: Full penile enlargement or rigidity was achieved by 165 of the 234 men (70.5%) after at least 1 active dose of medication. The most effective alprostadil dose (500 microg.) resulted in full penile enlargement or rigidity in 51.8% of administrations, whereas the most effective prazosin dose (2,000 microg.) and placebo resulted in a similar response in 12.7 and 2.7%, respectively (p <0.001). The 500/2,000 microg. alprostadil/prazosin combination, which resulted in full enlargement or rigidity in 58.9% of doses, was only slightly better than the most effective dose of alprostadil alone (500 microg.). However, combinations of 125/500 and 250/500 microg. alprostadil/prazosin were more effective (p <0.01) than 125 and 250 microg. alprostadil given alone, respectively. The most common side effect of therapy was penile pain, which rarely led to study discontinuation. Hypotension most commonly developed at the higher alprostadil-prazosin combination. CONCLUSIONS: Transurethral alprostadil and alprostadil-prazosin combinations produced erections in men with complete organic erectile dysfunction. This combination therapy may be an option in patients who do not respond to transurethral alprostadil alone.

Adrenergic alpha-Antagonists↗

PubMed1976

Studies with prazosin--a new effective hypotensive agent. I. Open clinical study of prazosin in combination with other antihypertensive agents.

The use of prazosin, a new antihypertensive agent, in combination with other conventional antihypertensive agents, in a hospital outpatient clinic setting, was studied in a mixed group of 104 hypertensive patients. Prazosin effectively lowered the lying and standing blood pressure in the majority of patients whose blood pressure was uncontrolled or poorly controlled before the introduction of prazosin. Blood pressure control was adequately maintained in patients who were given prazosin because of the occurrence of side effects of other antihypertensive medication. No significant change in renal function attributable to prazosin was found in patients with normal or impaired renal function.

Adult↗

PubMed2004

Structural characterization of prazosin hydrochloride and prazosin free base.

The three-dimensional solid-state structures of prazosin hydrochloride, C19H22N5O4+.Cl- (A), and prazosin free base, C19H21N5O4 (B), have been determined by synchrotron X-ray powder diffraction. A and B crystallize in triclinic P-1 and monoclinic Cc space groups, respectively, with one structural unit per asymmetric part. In A and B, the prazosin molecule adopts different conformations, which do not correspond to those obtained by DFT optimizations of protonated and free prazosin.

Hydrogen Bonding↗

PubMed1977

Open studies with prazosin in the treatment of essential hypertension. Prazosin Research Group in Japan.

The clinical usefulness of prazosin was investigated in 67 patients with mild to moderate essential hypertension for 6 to 12 weeks. The daily doses were increased from 3 to 9 mg according to the responses of the patients. The average reduction of mean arterial blood pressure by 6 weeks' prazosin treatment was 13-4 +/- 1-7 mm Hg. Thirty-three patients (49-3%) showed good or excellent responses to prazosin. Serious side effects or laboratory abnormalities did not appear in this trial, through postural dizziness was found in 6-0%. Prazosin seems to be a useful antihypertensive agent in the treatment of patients with mild or moderate essential hypertension.

Adult↗

PubMed1978

Studies with prazosin--a new effective hypotensive agent. III. An acute double-blind cross-over study comparing the effects of single doses of prazosin and hydrallazine in combination with propranolol and a diuretic.

The duration of action of a single dose of prazosin and hydrallazine on blood pressure and heart rate was studied in 16 hypertensive patients whose blood pressure was not adequately controlled by a combination of a thiazide diuretic and a beta-adrenergic blocking agent, and had required the addition of either prazosin or hydrallazine. Observations over an eight-hour period, after a single dose of either 3 mg of prazosin, or 75 mg of hydrallazine, in identical capsules, with cross-over study one week later, showed significant reductions in blood pressure within the first hour after oral administration of either agent. This reduction in blood pressure persisted for four to six hours after hydrallazine and six to seven hours after prazosin administration. Tachycardia was more pronounced and prolonged after hydrallazine administration and side effects were more common.

Adult↗

PubMedDate not supplied

Disposition of a new rate-controlled formulation of prazosin in the treatment of hypertension during pregnancy: transplacental passage of prazosin.

Prazosin (PRZ) in conventional tablet form (P-CT) has the disadvantages of a relatively short terminal half-life, a slight solubility in water and the well-recognized adverse effect of symptomatic orthostatic hypotension. The pharmacokinetic study of a new rate-controlled formulation of prazosin (Prazosin-Gastrointestinal System: P-GS) was performed in 9 pregnant women during the third trimester of pregnancy. Patients had persistent elevation of blood pressure. The subjects gave their informed consent for oral administration of 1 daily dose of 5 mg P-GS at 8 a.m. A first analysis period on day 1 enabled definition of the initial pharmacokinetic behavior of the drug, while the aim of a second was to evaluate its fate at plateau. The clinical course of both mother and fetus was subsequently monitored. This was an open, non-randomized study, each patient serving as her own control. For 3 patients, we aimed to determine the possible transplacental passage of PRZ at delivery. PRZ levels were measured by HPLC and data were analysed by noncompartmental linear pharmacokinetic methods. The data show: (i) P-GS was well tolerated by all patients and there were no significant changes in fetal heart rate during the study. (ii) A significant decrease in diastolic blood pressure was observed after the 36th hour following the first dose of P-GS while a reduction in systolic blood pressure was observed on day 4. (iii) An approximated relative bioavailability (f'P-GS) of 36.5% was calculated. P-GS appears to have a lower bioavailability than P-CT in women of similar gestational age. (iv) Both Cmax and AUC0-->infinity are significantly increased at plateau. Further, terminal half-life is increased with regard to the value determined with P-CT. No accumulation of PRZ was noted at steady-state. (v) P-GS is an example of an oral zero-order absorption product that offers one approach to control and improve the outcome of hypertensive therapy during pregnancy. This treatment could represent an alternative to methyldopa as a first treatment of pregnancy-associated hypertension. (vi) There is a slight transplacental passage of the drug (of the order of 10-20%).

Adrenergic alpha-Antagonists↗

PubMed1993

Preliminary evidence for the mechanism underlying the development of tolerance to prazosin in congestive heart failure: the alpha-agonistic properties of dobutamine unmasked by prazosin treatment.

The hemodynamic effects of acute and chronic treatment with different vasodilators were assessed in patients with chronic heart failure of New York Heart Association (NYHA) class III-IV. Each of 24 patients was randomly allocated; 6 to each of four groups: isosorbide dinitrate, dihydralazine, captopril, or prazosin. In addition, we evaluated the hemodynamic response to dobutamine by using increasing infusion rates of 2.5, 5.0, and 10.0 micrograms/kg/min at the start and end of a 3-month period of chronic therapy with either vasodilator. Dobutamine caused a dose-dependent increase in cardiac index and a decrease in mean pulmonary artery pressure (PAP) at the start of the vasodilatory treatment and maintained the effects during a 3-month period of chronic treatment with either isosorbide dinitrate, dihydralazine, or captopril. After 3-month therapy with 6 mg/day prazosin, however, mean PAP was increased above pretreatment value and dobutamine caused a further increase in PAP, thus reversing the initial effects. The dobutamine-induced increase in cardiac index remained virtually unchanged. We conclude that the reversal of the effects on PAP after chronic treatment with prazosin may be, at least in part, due to upregulation of alpha 1-adrenoceptors. This appears to be unmasked by the alpha 1-adrenoceptor agonist of the (-)-enantiomer of the racemic mixture of (+/-)-dobutamine.

Adrenergic alpha-Agonists↗

PubMed1983

Dissociation of presynaptic alpha 2-adrenoceptors following prazosin administration: presynaptic effect of prazosin.

Evidence has been obtained that prazosin possesses a presynaptic alpha 2-adrenoceptor blocking action in the rat was deferens preparation stimulated at 1 Hz. In the presence of prazosin yohimbine failed to affect the presynaptic alpha 2-adrenoceptor stimulatory effect of 1-noradrenaline while the effect of xylazine was almost completely abolished. It is therefore suggested that there are two kinetically different prejunctional alpha 2-adrenoceptor sites.

Animals↗

PubMed1998

Design, synthesis, and biological activity of prazosin-related antagonists. Role of the piperazine and furan units of prazosin on the selectivity for alpha1-adrenoreceptor subtypes.

Prazosin-related quinazolines 4-20 were synthesized, and their biological profiles at alpha1-adrenoreceptor subtypes were assessed by functional experiments in isolated rat vas deferens (alpha1A), spleen (alpha1B), and aorta (alpha1D) and by binding assays in CHO cells expressing human cloned alpha1-adrenoreceptor subtypes. The replacement of piperazine and furan units of prazosin (1) by 1, 6-hexanediamine and phenyl moieties, respectively, affording 3-20, markedly affected both affinity and selectivity for alpha1-adrenoreceptor subtypes in functional experiments. Cystazosin (3), bearing a cystamine moiety, was a selective alpha1D-adrenoreceptor antagonist being 1 order of magnitude more potent at alpha1D-adrenoreceptors (pA2, 8.54 +/- 0.02) than at the alpha1A- (pA2, 7.53 +/- 0.01) and alpha1B-subtypes (pA2, 7.49 +/- 0. 01). The insertion of substituents on the furan ring of 3, as in compounds 4 and 5, did not improve the selectivity profile. The simultaneous replacement of both piperazine and furan rings of 1 gave 8 which resulted in a potent, selective alpha1B-adrenoreceptor antagonist (85- and 15-fold more potent than at alpha1A- and alpha1D-subtypes, respectively). The insertion of substituents on the benzene ring of 8 affected, according to the type and the position of the substituent, affinity and selectivity for alpha1-adrenoreceptors. Consequently, the insertion of appropriate substituents in the phenyl ring of 8 may represent the basis of designing new selective ligands for alpha1-adrenoreceptor subtypes. Interestingly, the finding that polyamines 11, 16, and 20, bearing a 1,6-hexanediamine moiety, retained high affinity for alpha1-adrenoreceptor subtypes suggests that the substituent did not give rise to negative interactions with the receptor. Finally, binding assays performed with selected quinazolines (2, 3, and 14) produced affinity results, which were not in agreement with the selectivity profiles obtained from functional experiments. This rather surprising and unexpected finding may be explained by considering neutral and negative antagonism.

Adrenergic alpha-Antagonists↗

PubMed1989

Beneficial effects of pinacidil on blood lipids: comparisons with prazosin and placebo in patients with hypertension. Pinacidil-Prazosin and Pinacidil-Placebo Research Groups, Lilly Research Laboratories.

In two randomized, double-blind clinical trials comparing pinacidil with prazosin and with placebo in patients with hypertension, a number of statistically significant and potentially beneficial effects on blood lipids were detected in the patients taking pinacidil. Patients treated with pinacidil exhibited significant average decrements from baseline in concentrations of total and low-density lipoprotein cholesterol and triglycerides and a significant average increment in high-density lipoprotein cholesterol. The mean effects seen in the pinacidil group were significantly greater than those in the placebo group for both total cholesterol (-9.8 vs +4.2 mg/dl, p less than 0.001) and triglycerides (-21.6 vs +8.6 mg/dl, p less than 0.001). The effects seen in patients given pinacidil were also significantly greater than those seen in the patients treated with prazosin for both high-density lipoprotein cholesterol (+3.6 vs -1.0 mg/dl, p = 0.002) and triglycerides (-14.8 vs +30.3 mg/dl, p less than 0.001). Negative effects of hydrochlorothiazide and propranolol on blood lipids were not apparent in patients given pinacidil. Thus, pinacidil treatment of hypertension is associated with a beneficial effect on blood lipids, which may be of clinical significance.

Antihypertensive Agents↗

PubMed1987

[Slow elimination of a prazosin metabolite compared to prazosin kinetics after its intravenous administration to rabbits].

Serum concentration profiles of prazosin and its metabolite 2-(1-piperazinyl)-4-amine-6,7-dimethoxyquinazoline after intravenous bolus administration to rabbits (0.5 mg/kg) were shown to be biphasic. Rapid decline related to distribution was followed by a terminal slope lasting for up to 24 hours. Prazosin level in this phase decreased, its elimination half-life being about 9 hours, while the metabolite serum level was almost constant between 4 and 24 hours and averaged 0.9 mumol/l. This is in keeping with the earlier suggested extremely low elimination rate of this metabolite. Enterohepatic recirculation may account for this phenomenon, as well as a significant rise in the metabolite serum concentration I hour after the injection.

Animals↗

PubMed1977