Clinical pharmacology of ramipril

Impact of methylation of acyl glucuronide metabolites on incurred sample reanalysis evaluation: ramiprilat case study

Background: Reanalysis of incurred samples showed that the bioanalytical method for the quantification of ramipril and ramiprilat was generating irreproducible results for ramiprilat. Results: An additional peak interfering with ramiprilat was observed in the incurred samples but not in the calibrant and quality control samples. A similar interference was detected for ramipril, but it was chromatographically separated. Interferences were produced during sample preparation, which involves strong cation exchanger cartridges. The interfering products corresponded to the methylation of ramipril and ramiprilat glucuronide. Conclusion: Following this discovery, a reproducible method was developed and successfully validated for ramipril and ramiprilat. Additional stability tests were performed in the presence of glucuronide and diketopiperazine metabolites of ramipril and ramiprilat to demonstrate the method specificity.

The prospective, randomized investigation of the safety and efficacy of telmisartan versus ramipril using ambulatory blood pressure monitoring (PRISMA I)

OBJECTIVE

To compare the efficacy and safety of once-daily telmisartan and ramipril on blood pressure (BP) reductions during the last 6 h of the dosing interval.

PATIENTS AND METHODS

In a prospective, randomized, open-label, blinded-endpoint study using ambulatory BP monitoring, 801 patients with mild-to-moderate hypertension were randomly assigned to once-daily treatment with telmisartan 80 mg for 14 weeks or ramipril 5 mg for 8 weeks and then force titrated to ramipril 10 mg for the last 6 weeks. Primary endpoints were the reduction from baseline in the last 6-h mean ambulatory systolic BP (SBP) and diastolic BP (DBP). Secondary endpoints included changes in 24-h, morning, daytime and night-time mean ambulatory BP and ambulatory BP response rates.

RESULTS

Telmisartan 80 mg produced greater reductions in the last 6-h mean ambulatory SBP and DBP compared with ramipril 5 mg (P < 0.0001) and 10 mg (P < 0.0001), and was superior to ramipril for all secondary ambulatory SBP and DBP endpoints (P < 0.05). Ambulatory BP response rates (24-h mean ambulatory SBP/DBP < 130/80 mmHg or reduction from baseline > or = 10 mmHg) were greater with telmisartan 80 mg (P < 0.01) than with ramipril 5 and 10 mg. Ramipril was associated with a higher incidence of treatment-related cough (5.7 versus 0.5% for telmisartan).

CONCLUSIONS

Telmisartan was significantly more effective than ramipril in reducing BP throughout the 24-h dosing interval and particularly during the last 6 h, a time when patients appear to be at greatest risk of cerebro- and cardiovascular events. Both drugs were well tolerated, although ramipril was associated with a higher incidence of cough.

Inhibition of angiotensin-converting enzyme and phosphodiesterase type 5 improves endothelial function in heart failure

ACE (angiotensin-converting enzyme) inhibitors and PDE5 (phosphodiesterase type 5) inhibitors have each been reported to improve endothelial function in cardiovascular disease patients, but the comparative and combined effects of these two classes have not been studied previously. We sought to characterize the acute effects of ramipril alone, sildenafil alone, or their combination on endothelial function in patients with CHF (chronic heart failure). CHF subjects (n=64) were randomized to receive placebo, 10 mg of ramipril alone, 50 mg of sildenafil alone or a combination of ramipril and sildenafil in a double-blind manner. FMD (flow-mediated dilation) of the brachial artery was determined by high-resolution ultrasound imaging before and at 1, 2 and 4 h after administration of the study drug. Ramipril alone increased FMD at 4 h compared with placebo (+2.3+/-1.3%, P=0.02). Sildenafil alone increased FMD at 1, 2 and 4 h compared with placebo (+3.9+/-1.4, +4.6+/-1.8 and +3.7+/-1.3% respectively, all P<0.02). Sildenafil in combination with ramipril increased FMD at 1, 2 and 4 h when compared with placebo (+3.5+/-1.5, +4.5+/-1.8 and +4.8+/-1.3% respectively, all P<0.03). Ramipril and sildenafil both acutely improved FMD in patients with CHF, with additive effects evident at 4 h during combination therapy. Therefore further work to characterize chronic effects of combined ACE and PDE5 inhibition on endothelial function are warranted.

ACE inhibition improves cardiac NE uptake and attenuates sympathetic nerve terminal abnormalities in heart failure

Cardiac sympathetic nerve terminal dysfunction plays an important role in the downregulation of myocardial beta-adrenoceptors in heart failure. To determine whether chronic angiotensin-converting enzyme (ACE) inhibition improved cardiac sympathetic nerve terminal function and hence increased myocardial beta-adrenergic responsiveness, we administered ACE inhibitors to dogs with chronic right-sided heart failure (RHF) produced by tricuspid avulsion and pulmonary artery constriction. The RHF animals exhibited fluid retention, elevated right heart filling pressures, blunted inotropic response to isoproterenol, and reduced beta-adrenoceptor density. These changes were accompanied by decreases in right ventricular norepinephrine (NE) uptake and neuronal NE histofluorescence and tyrosine hydroxylase immunoreactive profiles. ACE inhibitors had no effect on the production of heart failure but greatly reduced the attenuation of cardiac NE uptake, neuronal NE histofluorescence, and tyrosine hydroxylase immunoreactive profiles. ACE inhibition also improved the inotropic response to isoproterenol and restored myocardial beta-adrenoceptor density. The changes probably are caused by reduction of cardiac NE release by ACE inhibition and may contribute to the beneficial effects of ACE inhibitor therapy in patients with chronic heart failure.

Clinical pharmacokinetics of vasodilators. Part I

Understanding the mechanism of action and the pharmacokinetic properties of vasodilatory drugs facilitates optimal use in clinical practice. It should be kept in mind that a drug belongs to a class but is a distinct entity, sometimes derived from a prototype to achieve a specific effect. The most common pharmacokinetic drug improvement is the development of a drug with a half-life sufficiently long to allow an adequate once-daily dosage. Developing a controlled release preparation can increase the apparent half-life of a drug. Altering the molecular structure may also increase the half-life of a prototype drug. Another desirable improvement is increasing the specificity of a drug, which may result in fewer adverse effects, or more efficacy at the target site. This is especially important for vasodilatory drugs which may be administered over decades for the treatment of hypertension, which usually does not interfere with subjective well-being. Compliance is greatly increased with once-daily dosing. Vasodilatory agents cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO) or by inhibiting myosin light chain kinase. They are divided into 9 classes: calcium antagonists, potassium channel openers, ACE inhibitors, angiotensin-II receptor antagonists, alpha-adrenergic and imidazole receptor antagonists, beta 1-adrenergic agonist, phosphodiesterase inhibitors, eicosanoids and NO donors. Despite chemical differences, the pharmacokinetic properties of calcium antagonists are similar. Absorption from the gastrointestinal tract is high, with all substances undergoing considerable first-pass metabolism by the liver, resulting in low bioavailability and pronounced individual variation in pharmacokinetics. Renal impairment has little effect on pharmacokinetics since renal elimination of these agents is minimal. Except for the newer drugs of the dihydropyridine type, amlodipine, felodipine, isradipine, nilvadipine, nisoldipine and nitrendipine, the half-life of calcium antagonists is short. Maintaining an effective drug concentration for the remainder of these agents requires multiple daily dosing, in some cases even with controlled release formulations. However, a coat-core preparation of nifedipine has been developed to allow once-daily administration. Adverse effects are directly correlated to the potency of the individual calcium antagonists. Treatment with the potassium channel opener minoxidil is reserved for patients with moderately severe to severe hypertension which is refractory to other treatment. Diazoxide and hydralazine are chiefly used to treat severe hypertensive emergencies, primary pulmonary and malignant hypertension and in severe preeclampsia. ACE inhibitors prevent conversion of angiotensin-I to angiotensin-II and are most effective when renin production is increased. Since ACE is identical to kininase-II, which inactivates the potent endogenous vasodilator bradykinin, ACE inhibition causes a reduction in bradykinin degradation. ACE inhibitors exert cardioprotective and cardioreparative effects by preventing and reversing cardiac fibrosis and ventricular hypertrophy in animal models. The predominant elimination pathway of most ACE inhibitors is via renal excretion. Therefore, renal impairment is associated with reduced elimination and a dosage reduction of 25 to 50% is recommended in patients with moderate to severe renal impairment. Separating angiotensin-II inhibition from bradykinin potentiation has been the goal in developing angiotensin-II receptor antagonists. The incidence of adverse effects of such an agent, losartan, is comparable to that encountered with placebo treatment, and the troublesome cough associated with ACE inhibitors is absent.

The renin-angiotensin system and angiotensin converting enzyme (ACE) inhibitors

Anaesthetists will encounter increasing numbers of patients who are receiving long-term treatment with ACE inhibitors for hypertension, congestive heart failure and prophylactically following myocardial infarction. Our understanding of the physiology and pharmacology of the renin-angiotensin system has dramatically increased in the last decade, and has led to the discovery of endogenous renin-angiotensin systems which may be physiologically more important than the better understood circulating system. There are several reports of adverse interactions between anaesthesia and ACE inhibitors, manifested as hypotension and bradycardia, which may be delayed until the postoperative period. The mechanism behind them is not understood and, as yet, no published studies have attempted to address this issue. It is possible, however, that dehydration associated with the pre-operative fast may play an important role. ACE inhibitors may, in the future, prove to be useful in the subspecialties of cardiac and vascular anaesthesia, where they might be used in an attempt to preserve cardiac function following periods of ischaemia and cardiopulmonary bypass, and to avoid renal damage following aortic cross-clamping. Meanwhile, it would seem prudent to exercise caution when anaesthetising patients taking ACE inhibitors and to be fully prepared to treat the hypotension and bradycardia which may occur.

Acute haemodynamic effects and pharmacokinetics of ramipril in patients with heart failure. A placebo controlled three-dose study

The aim of the present study was primarily to evaluate the haemodynamic effects of the ACE-inhibitor ramipril which is active via its metabolite ramiprilat. Ramipril 1.25, 2.5 and 5 mg and placebo was administered orally to 4 groups of 12 patients with heart failure (NYHA III) in a double-blind randomised, parallel study. Haemodynamics were monitored for 24 h and blood was sampled and urine collected for up to 96 h. In the placebo-treated group the cardiac index (CI) was significantly increased (15.8%) and right atrial pressure decreased (26.6%). Ramipril 1.25 mg had insignificant haemodynamic effects compared to placebo and the 2.5 mg dose had significant effects on some haemodynamic variables. Ramipril 5 mg had pronounced and sustained effects on pulmonary artery pressure, which fell by 43.7%, and pulmonary capillary wedge pressure (PCWP; -59.1%); systemic vascular resistance was also decreased 21%. A significant effect on CI was only seen after 2.5 mg ramipril (+7.4%). The mean maximal degree of ACE inhibition was 73.2, 90.4 and 98.5%, respectively, after the three doses of ramipril. Complete inhibition of ACE-activity was seen at a mean plasma concentration of ramiprilat of 4.7 ng.ml-1. The degree of inhibition declined with a half life of about 75 h. There was a significant relation between the degree of ACE-inhibition and change in PCWP but not with the change in SVR. Ramipril was mainly eliminated in the form of ramiprilat and inactive metabolites.

24-hour blood pressure profiles in hypertensive patients administered ramipril or placebo once daily: magnitude and duration of antihypertensive effects. Ramipril Multicenter Study Group

Ramipril is a new, potent nonsulfhydryl inhibitor of angiotensin converting enzyme. The magnitude and duration of its antihypertensive effect were evaluated in a multicenter, placebo-controlled, randomized clinical trial conducted in 100 patients with mild to moderate essential hypertension. Ramipril significantly reduced both supine and standing blood pressures measured 24 h after dosing. Automated blood pressure monitoring showed that ramipril significantly reduced systolic and diastolic pressures for 24 h after dosing. The peak effect occurred between 3 and 6 h after dosing, with approximately 50% of this effect retained after 24 h. Ramipril was well tolerated; there was no significant difference between active drug and placebo in the overall incidence of side effects. Ramipril is an effective and well-tolerated antihypertensive agent, which reduces both supine and standing blood pressure over the entire 24-h period after dosing.

Newer ACE inhibitors. A look at the future

Available information indicates that about 78 new molecules belonging to the class of angiotensin converting enzyme (ACE) inhibitors are under investigation, and that at least 11 or 12 of the newer ACE inhibitors will be available for clinical use. The newer ACE inhibitors can be classified, according to the zinc ion ligand of ACE, into 3 main chemical classes: sulfhydryl-, carboxyl- and phosphoryl-containing ACE inhibitors. All the newer sulfhydryl-containing ACE inhibitors differ from captopril since they are prodrugs, and among them alacepril and probably moveltipril (altiopril, MC 838) are converted in vivo to captopril. When compared with captopril, they show a slower onset and a longer duration of action, and obviously the same route of elimination. Zofenopril, a prodrug that is converted in vivo to the active diacid, shows a greater potency, a similar peak time and a longer duration of action than captopril and, unlike captopril, partial elimination through the liver. The newer carboxyl-containing ACE inhibitors are prodrugs which are converted in vivo to active diacids. Like enalaprilat, they are excreted via the kidney; the exception is spirapril, which is totally eliminated by the liver. Compared to enalapril, benazepril shows an earlier peak time and a slightly shorter terminal half-life, cilazapril and ramipril have an earlier peak time and even longer terminal half-life, perindopril shows similar peak time and terminal half-life, while delapril, quinapril and spirapril show an earlier peak time and a shorter half-life. The phosphoryl-containing ACE inhibitors belong to a new chemical class. Fosinopril is a prodrug which is converted to the active diacid in vivo, shows a relatively late peak time, a long terminal half-life, and is eliminated partially by the liver. SQ 29852, the only newly developed ACE inhibitor which is not a prodrug, seems to be more effective than captopril, with a much longer lasting effect and elimination through the kidney. When the differences in potency between these drugs are compensated by dosage adjustment, all the newer ACE inhibitors are expected to exert a similar amount of inhibition of circulating ACE, and therefore to inhibit to a similar extent the generation of circulating angiotensin II and the breakdown of bradykinin. Obviously they may differ in timing and the duration of circulating ACE inhibition according to their pharmacokinetic properties. With regard to the possibility that they may stimulate prostaglandin synthesis, it is suggested that this action, which does not seem to be specific to this drug class, plays only a minor role in their antihypertensive action; the hypothesis that the sulfhydryl group exerts an additional stimulating action remains to be proved.(ABSTRACT TRUNCATED AT 400 WORDS)

Ramipril. A review of its pharmacological properties and therapeutic efficacy in cardiovascular disorders

Ramipril is a long acting angiotensin converting enzyme (ACE) inhibitor, which exhibits similar pharmacodynamic properties to captopril and enalapril. Like enalapril it is a prodrug, which is hydrolysed after absorption to form the active metabolite ramiprilat which has a long elimination half-life, permitting once daily administration. In hypertensive patients daily doses in the range 2.5 to 20 mg are usually effective in reducing high blood pressure and maintaining satisfactory control during long term treatment. Patients who do not respond adequately to monotherapy with ramipril usually respond with the addition of a diuretic such as hydrochlorothiazide or piretanide. Ramipril 5 to 10 mg once daily shows comparable antihypertensive efficacy to usual therapeutic dosages of captopril, enalapril and atenolol in patients with mild to moderate essential hypertension. Preliminary data indicate that ramipril may be effective in indications such as severe essential hypertension and renal hypertension. It has also displayed beneficial effects in patients with moderate to severe congestive heart failure. Ramipril has been well tolerated and exhibits an adverse effect profile typical of ACE inhibitors as a class. In conclusion, ramipril will likely represent a useful alternative ACE inhibitor for use in patients with hypertension or congestive heart failure.

Ramiprilat attenuates the local release of noradrenaline in the ischemic myocardium

The effects of the converting enzyme inhibitors ramiprilat and enalaprilat on ischemia-induced release of noradrenaline (NA) were examined in the isolated perfused rat heart, submitted to 30 min of total flow restriction followed by 5 min of reperfusion. Ramiprilat (2.6 nM-2.6 microM) caused a concentration-dependent decrease in the efflux of NA at reperfusion. The maximal effect (about 70% reduction) was observed at a concentration of 26 nM. In contrast, enalaprilat (10 nM-10 microM) caused no reduction in NA efflux until at a high concentration (10 microM, NA efflux reduced by about 20%). Moreover, the prodrugs ramipril and enalapril (added to the perfusion medium) were without any significant effects on ischemia-induced NA release. Both the angiotensin II receptor antagonist saralasin (0.1 microM) and bradykinin (0.1 and 1 nM) caused marked reductions in ischemic NA efflux. However, when indomethacin (10 microM) was added to the perfusion medium, the effects of bradykinin (1 nM) and ramiprilat (26 nM) on NA efflux were abolished. Likewise, in the presence of angiotensin II (0.1 microM) the effect of ramiprilat was no longer evident. The magnitude of cellular injury, expressed as efflux of creatine kinase during reperfusion, was reduced by bradykinin (0.1 and 1 nM) and by ramiprilat (by about 55% at 2.6 microM). It is concluded that ramiprilat, at therapeutically relevant concentrations, attenuates the ischemia-induced mobilization of NA via a reduction in local angiotensin II production and/or bradykinin degradation. The lack of effect of enalaprilat in this model may reflect differences between converting enzyme inhibitors regarding tissue accumulation or the potency of local enzyme inhibition.

Acute and chronic effects of ramipril and captopril in congestive heart failure

We studied the acute and long-term effects of ramipril and captopril in 12 patients with moderate to severe congestive heart failure using an open, parallel design. Drug doses were titrated. Compared with baseline values, maximal haemodynamic and humoral effects after the first dose of both angiotensin converting enzyme inhibitors were similar, but the effects of ramipril (5 mg) demonstrated a slower onset of action and a significantly longer duration than captopril (12.5 mg). After 3 months of treatment a single dose of 5 mg ramipril showed the same 24-hour haemodynamic profile as after the first dose, but the hypotensive effect was less marked. There was no plasma accumulation of ramiprilat. Serum creatinine and potassium remained stable, except for one patient whose renal function deteriorated on captopril treatment. Complex ventricular arrhythmias occurred in 11 patients and were unaffected after treatment with ramipril or captopril. Two patients died suddenly during ramipril therapy and one patient during captopril therapy. In summary, ramipril is an effective, long-acting angiotensin converting enzyme inhibitor, producing long-term haemodynamic effects in patients with congestive heart failure. Using an individualised dosage scheme, neither long-lasting hypotension nor deterioration of renal function occurred. No effect on ventricular arrhythmias was seen.

Comparisons in vitro, ex vivo, and in vivo of the actions of seven structurally diverse inhibitors of angiotensin converting enzyme (ACE)

1. Seven drugs (captopril, zofenopril, enalapril, ramipril, lisinopril, fosinopril, and SQ 29,852) were compared in vitro in homogenates of aorta, brain, heart, lung, and kidney and in sera of spontaneously hypertensive rats (SHR) both with respect to potencies of their active moieties as inhibitors of angiotensin-converting enzyme (ACE), and, where applicable, rates of hydrolysis of their prodrug ester functions. 2. In ex vivo dose-response and time-course studies, the inhibitory effects of the seven drugs on tissue ACEs and their relative distributions to SHR tissues were compared following oral administration. 3. The relative potencies of the inhibitory moieties of the drugs (in parentheses) and the normalized 'equiactive' oral doses employed for time-course studies were: SQ 29,852 (1.0), 100 mg kg-1; captopril (3.5), 30 mg kg-1; enalapril (12), 20 mg kg-1; fosinopril (13), 25 mg kg-1; zofenopril (20), 10 mg kg-1; lisinopril (24), 10 mg kg-1; and ramipril (51), 5 mg kg-1. 4. Following oral administration of the drugs to SHR, the degree and duration of ACE inhibition in aorta and lung correlated with the antihypertensive actions, with ramipril, lisinopril, and zofenopril producing effects of the greatest magnitude and duration. 5. Ramipril and enalapril did not inhibit brain ACE ex vivo; captopril and zofenopril had modest but short-lasting effects; and fosinopril, lisinopril, and SQ 29,852 had long-lasting inhibitory actions, which, with the latter two, were delayed in onset. 6. All of the drugs produced significant inhibition of kidney ACE, with ramipril and fosinopril having somewhat weaker effects, perhaps due to biliary routes of excretion. 7. Captopril, fosinopril, and particularly zofenopril inhibited cardiac ACE ex vivo with degrees and durations that were marked compared with those of the other drugs; preliminary studies with isolated hearts suggest a possible relationship between inhibition of cardiac ACE and preservation of cardiac function subsequent to ischaemia.