Computer-aided selection of potential antihypertensive compounds with dual mechanism of action

The prediction of biological activity spectra for substances as an approach for searching compounds with complex mechanisms of action was studied. New compounds with dual mechanisms of antihypertensive action were found by this approach. Biological activity spectra for substances were predicted on the basis of their structural formulas by the computer program PASS. Thirty molecular mechanisms of action of compounds from the MDDR 99.2 database, which cause the antihypertensive effect and can be predicted by PASS, have been identified. The analysis of predictions for compounds with 15 dual antihypertensive mechanisms of action from the MDDR 99.2 database has confirmed high accuracy of prediction. This approach was applied to databases of commercially available compounds (AsInEx and ChemBridge) and allowed us to select four substances that are potential inhibitors of angiotensin converting enzyme (ACE) and of neutral endopeptidase (NEP). At a later time, all these compounds were found to be the inhibitors of both ACE and NEP. The most potent compounds had IC(50) of 10(-7)-10(-9) M for ACE and 10(-5) M for NEP. New combinations of dual mechanisms of action never before found for antihypertensive compounds were predicted.     

玉米降血压肽对体内外血管紧张素转化酶活性的抑制作用

目的研究玉米降血压肽在体内外对血管紧张素转化酶(ACE)的活性抑制作用及机制,为探讨降血压肽的降压机制提供实验依据。方法用反相高效液相色谱法测定玉米降血压肽在体外对ACE的抑制动力学,同时测定多次给药12周后SHR大鼠体内不同组织的ACE活性和血浆AngⅡ浓度。结果玉米降血压肽竞争性抑制ACE活性,IC50为15.0μmol/L,玉米降血压肽能显著降低血清、主动脉和肺ACE活性(P<0.01),而对心、脑、肾的ACE活性抑制作用不显著(P>0.05),同时玉米降血压肽能显著降低血浆中血浆AngⅡ浓度(P<0.01)。结论玉米降血压肽对体内外ACE都有竞争性抑制作用,但在体内不同部位其抑制效果不同,同时其降压作用是通过抑制ACE活性、降低AngⅡ浓度来实现的。     

Biological properties of the angiotensin-converting enzyme inhibitor cilazapril

Cilazapril is the monoethyl ester prodrug form of a potent, specific. long-acting antihypertensive inhibitor of angiotensin-converting enzyme (ACE). The biochemical and pharmacological properties of this compound have been compared with those of captopril and enalapril. In all test systems, cilazapril was the most potent and the longest acting. The active diacid of cilazapril was more potent than the corresponding diacid of enalapril in inhibiting the cleavage of angiotensin I and of Hip-His-Leu by ACE in vitro, in antagonising the angiotensin I-induced contractions of the isolated ileum of the guinea pig, in potentiating the vasodepressor responses to bradykinin, and in reducing the angiotensin I-induced rise in blood pressure of the rat. Parent drug absorption and diacid bioavailability in the rat were higher than for enalapril, and the inhibition of plasma ACE of longer duration. Single doses of cilazapril were more potent than enalapril in lowering the blood pressure of spontaneously hypertensive rats (SHR) and two-kidney renal hypertensive rats. On repeated daily oral dosing to SHR, both compounds had a cumulative antihypertensive effect. The acute antihypertensive effect was enhanced by simultaneous treatment with hydrochlorothiazide.     

Concomitant angiotensin AT1 receptor antagonism and neprilysin inhibition produces omapatrilat-like antihypertensive effects without promoting tracheal plasma extravasation in the rat

Dual inhibition of angiotensin-converting enzyme (ACE) and neprilysin (NEP) by drugs such as omapatrilat produces superior antihypertensive efficacy but cause high incidence of angioedema. We examined whether dual inhibition of angiotensin AT1 receptor (ARB) and NEP (ARB-NEPI, valsartan-candoxatril) provides similar efficacy to omapatrilat without the risk of angioedema. Activity of test compounds at the targets was assayed using fluorescence-based enzyme assays (ACE, NEP, aminopeptidase P) or competition binding assays (AT1). Target engagement in vivo (ACE, AT1, and NEP) was quantified by measuring inhibition of angiotensin-pressor responses and potentiation of atrial natriuretic peptide-induced urinary cyclic guanosine monophosphate (cGMP) output in rats. Tracheal plasma extravasation (TPE) was used as a surrogate to assess propensity of compounds to promote upper airway angioedema. Antihypertensive efficacy in renin-dependent and -independent states was measured in spontaneously hypertensive rats and deoxycorticosterone acetate salt hypertensive rats, respectively. Administration of omapatrilat and coadministration of valsartan and candoxatril blocked angiotensin induced vasopressor responses and potentiated atrial natriuretic peptide-induced increase in urinary cGMP output. In spontaneously hypertensive rats, valsartan, omapatrilat, and valsartan-candoxatril combination all produced reduction in blood pressure to a similar extent, whereas candoxatril was ineffective. In deoxycorticosterone acetate rats, omapatrilat, candoxatril, and valsartan-candoxatril combination but not valsartan produced reduction in blood pressure. Antihypertensive doses of omapatrilat produced robust increases in TPE; by contrast, valsartan, candoxatril, or their combination did not increase TPE. Pretreatment with icatibant, a bradykinin B2 antagonist, abolished omapatrilat-induced TPE but not its antihypertensive effects. On the background of NEP inhibition, suppression of the renin-angiotensin system through ARB and ACE inhibition shows a similar antihypertensive efficacy but exerts differential effects on bradykinin metabolism and TPE indicative of reduced risk of angioedema. Thus, dual AT1 receptor blockade and NEP inhibition is potentially an attractive approach to retain the excellent antihypertensive effects of omapatrilat but with a superior safety profile.     

Correlation between the inhibition of renin-angiotensin system and antihypertensive effect of MK-421 and captopril in 2-kidney, 1-clip renal hypertensive rats after single and repeated oral administration of MK-421 or captopril

The angiotensin converting enzyme (ACE) activity in tissues and plasma renin activity (PRA) were measured in 2-kidney, 1-clip renal hypertensive rats (2K-RHR) and normotensive rats after a single and 3-weeks oral administrations of ACE inhibitors such as MK-421 and captopril. In the single dose study, MK-421 (1 and 3 mg/kg) and captopril (3 and 10 mg/kg) inhibited the ACE activities in kidney, aorta and plasma in a dose-dependent fashion. The inhibition of ACE activity in kidney or aorta was observed for a longer time than that in plasma. PRA took a time course reversal to that of plasma ACE activity. In the 3-weeks repeated dose study, the ACE activity in kidney and aorta was strongly inhibited after the administration of each ACE inhibitor, while there was no significant change in lung ACE activity at any time point examined. The plasma ACE activity markedly elevated after the administration of each agent. PRA significantly increased after the administration of either agent, while the plasma angiotensin II level was significantly inhibited. These results indicate that the inhibition of the ACE activity in blood vessel or kidney correlate well with the antihypertensive activity in 2K-RHR after a single and repeated administration of both ACE inhibitors, but not well with the inhibition of plasma ACE activity.     

Angiotensin-converting enzyme inhibitors: new orally active 1,4-thiazepine-2,5-diones, 1,4-thiazine-2,5-diones, and 1,4-benzothiazepine-2,5-diones possessing antihypertensive activity

The preparation of a series of 1,4-thiazepine-2,5-diones, 1,4-thiazine-2,5-diones, and 1,4-benzothiazepine-2,5-diones and their ability in inhibiting the activity of angiotensin-converting enzyme (ACE) in vitro and in vivo were examined. These compounds are assumed to act as prodrugs since they undergo rapid ring-opening reactions to give the corresponding biologically active free SH compounds when incubated with rat plasma or when treated with aqueous 0.1 N HCl or phosphate buffer (pH 7.4). The thiazepines 23-25 and 30 are potent inhibitors of ACE when administered po to rats and are comparable in potency to captopril (1). The most active thiazines in rats, po, were 42 and 45. Of the benzothiazepines studied, 22a was the most active in inhibiting ACE in the conscious normotensive rat, ID50 = 0.15 mg/kg, po. The acute antihypertensive effects of oral administration of a number of these compounds on mean arterial pressure and heart rate were studied in spontaneously hypertensive rats (SHR) maintained on a sodium-deficient diet.     

Antihypertensive effect of repeated oral administration of MK-0521 in 2-kidney Goldblatt hypertensive dogs

MK-0521 and captopril were orally administered to acute (6 to 8 days after unilateral renal artery constriction) and chronic (2 to 2.5 months after the constriction) 2-kidney Goldblatt hypertensive dogs for 7 to 21 days. MK-0521 lowered the blood pressure to similar extents in the acute and chronic stages of hypertension. The antihypertensive effect of MK-0521 was dose-dependent and persistent even after its cessation. Captopril also produced an antihypertensive effect, although the effect in the chronic stage of hypertension was less prominent than that in the acute stage of hypertension. MK-0521 was more inhibitory on the renin-angiotensin system than captopril. In the acute stage of hypertension, the dogs treated with MK-0521 had increased angiotensin converting enzyme (ACE) activity, while they had decreased plasma angiotensin II level and elevated plasma angiotensin I level and plasma renin activity. These results clarified the inhibitory effect of MK-0521 on ACE. In contrast, in the chronic stage of hypertension, MK-0521 showed no depression of plasma angiotensin II. There were no significant changes in daily urinary volume, and renal clearances of sodium, potassium and creatinine. These results suggest that the major mechanism of the antihypertensive effect of MK-0521 in 2-kidney Goldblatt hypertensive dogs is an inhibition of the ACE. In addition, the different effects in the acute and chronic hypertensive dogs suggest that some differences exist in the mechanisms of maintaining blood pressure between the two stages of 2-kidney Goldblatt hypertensive dogs.     

Angiotensin I-converting enzyme (ACE) inhibition and antihypertensive effects of EU-5476, a new,potent, and long-acting ACE inhibitor

EU-5476 is a new, orally active angiotensin I-converting enzyme (ACE) inhibitor. In vitro, EU-5476 produced a concentration-dependent inhibition of ACE purified from rabbit lung (IC₅₀ = 0.084 μ). Inhibition showed complex kinetics and was reversible as determined by equilibrium dialysis. EU-5476 inhibited plasma ACE in mice (93.8% inhibition at 5 μmol/kg) and produced dose-dependent inhibition of plasma ACE in dogs (ID₅₀ = 2.52 μmol/kg) after oral administration. In acute aortic coarctate hypertensive rats, EU-5476 administered orally produced dose-dependent decreases in blood pressure (ED₃₀ = 0.53 μmol/kg). The magnitude and duration of blood pressure reduction in hypertensive rats were similar to those of plasma ACE inhibition in dogs, suggesting that plasma ACE inhibition per se is one of the mechanisms of the antipertensive action of EU-5476. Comparative studies showed that EU-5476, like enalapril, was more potent and longer acting than captopril in producing plasma ACE inhibition and an antihypertensive response. EU-5476 is a potent and long-acting, orally effective ACE inhibitor potentially useful in the treatment of hypertension.     

Reduction of the antihypertensive effect of captopril induced by prostaglandin synthetase inhibition

The effects of prostaglandin synthetase inhibition by indomethacin on blood pressure and hormonal variations induced by captopril were studied in eight patients with essential hypertension and in six nonhypertensive subjects. Captopril antihypertensive effect and captopril-induced plasma renin increase were almost totally abolished by a short-term administration of indomethacin (50 mg t.i.d.). These results support the hypothesis that prostaglandins contribute to the antihypertensive effects of ACE inhibitors. It may be of clinical importance that anti-inflammatory drugs that inhibit PG-synthetase can also blunt the antihypertensive action of ACE inhibitors.     

Antihypertensive action of a new angiotensin converting enzyme inhibitor, (R)-3-[(S)-1-carboxy-5-(4-piperidyl)pentyl]amino-4-oxo-2,3,4,5-tetr ahy dro-1,5-benzothiazepine-5-acetic acid (CV-5975), in various hypertensive models

The antihypertensive activity of a new angiotensin converting enzyme (ACE) inhibitor, CV-5975, (R)-3-[(S)-1-carboxy-5-(4-piperidyl)pentyl] amino-4-oxo-2,3,4,5-tetrahydro-1,5-benzothiazepine-5-acetic acid, was examined in normotensive rats and various hypertensive animal models. In spontaneously hypertensive rats, CV-5975 (1 to 10 mg/kg, p.o.) had a dose-related, sustained antihypertensive action, which was more potent and longer than that of enalapril. The potency and duration of action of CV-5975 was intensified when it was administered repeatedly or combined with hydrochlorothiazide. CV-5975 (1 mg/kg, p.o.) inhibited the ACE activity of plasma and tissues; inhibition on the ACE activity of the aorta, kidney, and brain was marked when CV-5975 was administered repeatedly. In 2-kidney, 1 clip hypertensive rats (1 to 10 mg/kg, p.o.) and dogs (0.3 and 1 mg/kg, p.o.), CV-5975 had a marked, sustained antihypertensive action, which was more marked than that of enalapril. In normotensive rats (10 mg/kg), 1-kidney, 1 clip hypertensive rats (3 and 10 mg/kg), and hyporeninemic DOCA/salt hypertensive rats (1 to 10 mg/kg/day), CV-5975 administered orally once or repeatedly reduced blood pressure, whereas enalapril did not. These results indicate that CV-5975 is a potent and long-lasting antihypertensive agent, the action of which is mediated primarily by inhibiting ACE activity and partly by some unknown mechanisms.     

Pharmacogenomics of angiotensin converting enzyme inhibitors in renal disease--pathophysiological considerations

Angiotensin converting enzyme (ACE) inhibitors preserve native kidney function in patients with renal disease better than other antihypertensive drugs, most likely because they more effectively reduce proteinuria. The plasma concentration of the ACE inhibitors target is, at least in part, under genetic control. A polymorphism of the ACE gene based on the presence or absence of a 287 base pair element in intron 16 accounts for 47% of the total phenotypic variance in the plasma ACE levels of healthy individuals. Unfortunately, pharmacogenetic studies performed so far do not provide a clear answer as to whether the efficacy of the reduction of proteinuria by ACE inhibitors is influenced by the ACE genotype - probably because these studies were not primarily designed to answer this question. This paper will try to outline some aspects that should be considered before an appropriate study on this topic is initiated.     

Effect of captopril on converting enzyme activity in chemically sympathectomized, spontaneously hypertensive rats

Effect of subacute angiotensin converting enzyme (ACE) blockade on the converting enzyme activity (ACE activity) in plasma, aorta, lung, kidney and whole brain was evaluated in chemically-sympathectomized (with 6-hydroxydopamine) normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) using captopril given peripherally via the intraperitoneal (i.p) route and centrally through intracerebroventricular (i.c.v.) administration. Daily i.p. injection of 25 mg/kg for 8 days reduced the blood pressure of both WKY rats and SHR, and the ACE activity in the aorta, lung and plasma of both WKY rats and SHR were correspondingly depressed. The brain ACE activity remained unaltered in both strain of rats. The ACE activity in the kidney of WKY was depressed, while that of SHR remained unchanged. These observations are independent of peripheral sympathectomy with 6-hydroxydopamine (6-OHDA). Daily central captopril administration at a dose of 2 mg/kg, i.c.v., for 8 days significantly reduced the blood pressure of SHR but not WKY rats, whereas the ACE activity of the whole brain of both WKY and SHR were depressed. Central sympathectomy with 6-OHDA did not alter these responses. It is concluded that captopril exerts its antihypertensive effect not only via reduction of the ACE activity in the plasma and lungs as reported earlier, but also that of other organs, principally the aorta, and that these effects are independent of the sympathetic nervous system.     

Pharmacological studies on (4S)-1-methyl-3-[(2S)-2-[N-((1S)-1-ethoxycarbonyl-3-phenylpropyl)amino] propionyl]-2-oxo-imidazolidine-4-carboxylic acid hydrochloride (TA-6366), a new ACE inhibitor: I. ACE inhibitory and anti-hypertensive activities

TA-6366 and its active metabolite 6366A inhibited swine renal angiotensin converting enzyme (ACE) activity with IC50s of 9900 and 2.6 nM, respectively. TA-6366 (0.05-0.5 mg/kg, p.o.) inhibited the angiotensin I (AT-I)-induced pressor response in rats. 6366A augmented bradykinin (BK)-induced contraction of guinea pig ileum more potently than captopril. However, when the augmentation on BK-induced hypotension in rats was used as an indicator, TA-6366 was less active than captopril. TA-6366 increased plasma renin activity and plasma AT-I concentration. Oral administration of TA-6366 lowered the blood pressure in two-kidney one-clip renal hypertensive rats at 0.5 to 2 mg/kg and in spontaneously hypertensive rats (SHRs) at 2 to 10 mg/kg. The antihypertensive effect of TA-6366 was approximately 5 times more potent than that of captopril and almost as potent as that of enalapril. In SHRs, the antihypertensive action of TA-6366 was intensified in potency when administered repeatedly. The duration of action was longer than those of captopril and enalapril. However, TA-6366 had no substantial effect on the blood pressure in DOCA/saline hypertensive rats. These results indicate that TA-6366 is a potent and long lasting antihypertensive agent and that its antihypertensive action is attributable to the inhibition of ACE.     

Comparative pharmacology of the angiotensin II receptor antagonists

The non-peptide angiotensin II (AII) receptor antagonists are a new class of compounds that are continuing to be developed as therapeutic agents for the treatment of hypertension, heart failure (HF) and chronic renal disease (CRD). Several of these compounds are currently available for therapeutic use in the USA and the European community with several more in clinical trials and in development. Compounds in this new class are as effective as angiotensin converting enzyme (ACE) inhibitors in treating hypertensive patients and appeared to have a similar therapeutic profile to ACE inhibitors in patients with HF and CRD. One clinical advantage of the AII receptor antagonists over ACE inhibitors is an improved side-effect profile with the absence of the persistent dry cough associated with ACE inhibitor therapy. To date, it is clear that the AII receptor antagonists are effective antihypertensive agents. Clinical trials are currently in progress to determine the therapeutic efficacy of these drugs in the treatment of HF and progressive renal disease.     

Angiotensin converting enzyme inhibitory activity of MK-0521 in vivo and antihypertensive effect of its single oral administration on blood pressure and effect on the renin-angiotensin system in 2-kidney Goldblatt hypertensive dogs

Angiotensin converting enzyme (ACE) inhibitory activity of MK-0521 in dogs and the effects of its single oral administration on blood pressure and the renin-angiotensin system in 2-kidney Goldblatt hypertensive dogs were compared with those of captopril and MK-421. MK-0521 at 0.001-0.1 mg/kg, i.v., or 0.01-1 mg/kg, p.o., attenuated the pressor effect of angiotensin I without affecting that of angiotensin II and augmented the depressor effect of bradykinin. The potency of MK-0521 to reduce the pressor effect of angiotensin I was 9.8 times that of captopril by intravenous administration, and by oral administration, it was 15.9-32.1 times that of captopril and approximately 3 times that of MK-421. When administered orally, the onset of action and the time to peak effectiveness were more rapid than those of MK-421, but slower than those of captopril. Duration of the action of MK-0521 was longer than that of captopril and equal or longer than that of MK-421. The inhibition of ACE was well correlated with serum MK-0521 levels. MK-0521 produced a dose-dependent antihypertensive effect in 2-kidney Goldblatt hypertensive dogs at over 0.3 mg/kg, p.o., without affecting the heart rate. The antihypertensive effect of MK-0521 was persistent and approximately 3 times more potent than that of captopril. MK-0521 inhibited the serum ACE activity and increased the plasma renin activity, while it had a tendency to decrease plasma aldosterone level. These changes were parallel to the time course of the antihypertensive effect. These results suggest that the main mechanism of the antihypertensive effect of MK-0521 is the suppression of angiotensin II production due to the inhibition of the ACE.     

The cost effectiveness of ACE inhibitors as first-line antihypertensive therapy

BACKGROUND: Current hypertension guidelines differ in their recommendations for first-line antihypertensive therapy. OBJECTIVE: To evaluate the cost effectiveness of ACE inhibitor therapy as antihypertensive first-line therapy as compared with conventional antihypertensive therapy with beta-adrenoceptor antagonists or diuretics. STUDY DESIGN: Cost-effectiveness analysis based on data from randomised trials and observational studies comparing the effectiveness of ACE inhibitor and conventional antihypertensive therapy, we constructed a Markov model to compare four strategies in the management of uncomplicated hypertension: (i) prescribing ACE inhibitor therapy to all patients; (ii) prescribing conventional therapy to all patients; (iii) individualised antihypertensive therapy based on the presence or absence of left ventricular hypertrophy on electrocardiography (ECG); or (iv) individualised antihypertensive therapy based on the presence or absence of left ventricular hypertrophy on echocardiography. METHODS: Cost data were derived from the medical literature and focus groups, and utility values were derived from patients on antihypertensive monotherapy. All costs were calculated in 1999 Canadian dollars, but are reported in US dollars according to the 1999 purchasing power parity rate for medical and healthcare. The effectiveness of ACE inhibitor therapy in the presence of left ventricular hypertrophy was derived from observational studies. The time horizon was over a lifetime. PERSPECTIVE: Third-party payer. PATIENTS/PARTICIPANTS: A cohort of men aged 40 years without cardiovascular comorbidity requiring antihypertensive drug therapy. MAIN OUTCOME MEASURES AND RESULTS: In the baseline analysis, all four strategies resulted in expected discounted QALYs that differed from each other only at the third decimal point (i.e. less than 0.003). Given the uncertainties in the variable estimates and the small size of the differences, these differences are extremely small and unlikely to represent real differences. Even accepting the small gains as real, the resulting cost-effectiveness ratios are unattractively high: $US 200,000 per QALY gained for the echocardiography strategy (compared with ECG), and $US 700,000 for the "ACE inhibitor for all" strategy (compared with ECG). The incremental cost effectiveness of prescribing ACE inhibitor therapy to everybody was never less than $US 100,000/QALY in the sensitivity analysis. CONCLUSIONS: Prescribing ACE inhibitors as antihypertensive first-line therapy in patients without cardiovascular morbidity cannot be recommended at the present time unless the acquisition costs of ACE inhibitors become substantially more attractive.     

Antihypertensive activity of alacepril, an orally active angiotensin converting enzyme inhibitor, in renal hypertensive rats and dogs

Alacepril (1-[(S)-3-acetylthio-2-methylpropanoyl]-L-prolyl-L-phenylalanine, DU-1219) showed a dose related and long lasting antihypertensive effect in renal hypertensive rats (two-kidney, one-clip), a typical renin dependent hypertensive model. The maximum hypotensive potency of alacepril (1-30 mg/kg) after single oral administration was slightly weaker than that of captopril (1-30 mg/kg). Judging from the AOC (area over the antihypertensive curve) value, the overall antihypertensive activity of alacepril was 3 times more potent than that of captopril on a weight basis. The long lasting antihypertensive effect of alacepril in renal hypertensive rats was also confirmed by once daily successive oral administration (1-2 mg/kg/d). In renal hypertensive dogs, alacepril (3 mg/kg) showed a stable and sustained hypotensive effect, and its duration of action was longer than that of captopril. Although alacepril did not possess a significant in vitro angiotensin converting enzyme (ACE) inhibitory activity, orally given alacepril (5.6-56.1 mg/kg) produced a potent and prolonged in vivo ACE inhibition which was estimated by suppression on angiotensin-I (310 ng/kg i.v.) induced pressor response in conscious normotensive rats. The prolonged in vivo ACE inhibitory activity of alacepril (5.6 mg/kg) was also observed in conscious normotensive dogs. These results suggest that the disposition and metabolism of orally given alacepril are responsible for the prolonged ACE inhibition and, concomitantly, for exerting the long lasting antihypertensive effect. Consequently, alacepril is a novel orally active ACE inhibitor having a potent and prolonged antihypertensive activity, and these properties suggest that alacepril is favorable for the treatment of hypertension.     

Pharmacokinetics and pharmacodynamics of benazepril in hypertensive patients with normal and impaired renal function.

The pharmacokinetics and pharmacodynamics of benazepril, an angiotensin converting enzyme (ACE) inhibitor, were investigated after administration of a single oral 5-mg dose and 7 more doses on consecutive days to hypertensive patients with normal renal function (NRF) and those with impaired renal function (IRF). The antihypertensive effect of benazepril was observed as early as 30 min after a single dose, and those effects during consecutive dosing were also sustained for 24 h with a lesser diurnal variation in blood pressure (BP). The time to peak (Tmax) and the apparent elimination half-life (t1/2) for benazepril were 0.6-0.7 h and 0.4-0.8 h, respectively. Tmax for its diacid was 1.5-2.4 h in both groups. The area under the plasma concentration-time curve to 24 h (AUC0-24h) for the diacid was significantly greater in the IRF group than in the NRF group. After consecutive dosing of benazepril, AUC0-24h and plasma peak level (Cmax) were significantly increased in the IRF group. Serum ACE activity was markedly suppressed for 24 h after administration, and the inhibition was closely related to plasma diacid levels. A significant inverse correlation was observed between creatinine clearance and the AUC for the diacid. These results suggest that benazepril is rapidly bioactivated to diacid and exhibits rapid onset and long-lasting antihypertensive effects. Dosage reduction might be required to minimize unnecessary drug accumulation in patients with severe IRF.     

Pharmacokinetic and pharmacodynamic study of imidaprilat, an active metabolite of imidapril, a new angiotensin-converting enzyme inhibitor, in spontaneously hypertensive rats

The pharmacokinetics and pharmacodynamics (PK/PD) of imidaprilat, an active metabolite of imidapril, a new angiotensin-converting enzyme (ACE) inhibitor, were investigated. Imidapril was infused subcutaneously for 4 weeks via an osmotic pump implanted under the skin in the back of male spontaneously hypertensive rats (SHRs). Plasma concentration of imidaprilat, systolic blood pressure (SBP), and plasma ACE activity were determined periodically. The plasma concentration of imidaprilat increased in proportion to the infusion rates and was maintained for 4 weeks. The SBP and ACE activity did not decrease in proportion to the infusion rates due to the saturation of the pharmacologic effects, but these actions also were maintained for 4 weeks. The PK/PD of imidaprilat were not influenced by aging of SHRs. The antihypertensive action in subcutaneous infusion of imidapril was as potent as that in oral administration at the same dose, although the maximum plasma concentration of imidaprilat in subcutaneous infusion was one-eightieth times of that in oral administration. The action was also maintained 28 times longer than that in oral administration, indicating that subcutaneous infusion is useful as an administration route. Furthermore, good correlation between plasma imidaprilat concentration and SBP was observed in subcutaneous infusion, indicating that plasma concentration may be a useful marker of pharmacologic action.