Steady-state kinetics of ramipril in renal failure

The analysis of ramipril/ramiprilat concentration in human serum with liquid chromatography-tandem mass spectrometry - interpretation of high concentrations for the purposes of forensic toxicology

Ramipril is a popular angiotensin-converting enzyme inhibitor applied in the treatment of hypertension. Its therapeutic effect is oriented on the concentration of the active metabolite ramiprilat. The information about toxic drug levels is missing in the literature. Therefore, the aim of this work was an indication of possible toxic ranges based on the analysis of real samples with high ramiprilat concentrations. For these purposes, an appropriate analytical LC-MS/MS method was developed and validated according to forensic guidelines and applied in the routine. Most real samples targeted for ramipril/ramiprilat were associated with the typical therapeutic drug range of 1-40 ng/mL described in the literature. However, higher drug levels with ramiprilat concentrations above 100 ng/mL could also be observed infrequently in cases of driving under the influence of drugs or attempted suicides. To the best of the author's knowledge, this is the first time antemortem ramipril and ramiprilat concentrations associated with driving under the influence of drugs and suicide attempts were discussed from a forensic point of view. The collected data enabled an indication of the ramiprilat toxic concentration range from about 600 ng/mL to at least 3500 ng/mL. The toxic concentration range discussed can be applied in the forensic practice as a reference for future cases.

Influence of estradiol supplementation on neuropeptide Y neurotransmission in skeletal muscle arterioles of F344 rats

The effects of estradiol on neuropeptide Y (NPY) neurotransmission in skeletal muscle resistance vessels have not been described. The purpose of this study was to determine the effects of long-term estradiol supplementation on NPY overflow, degradation, and vasoconstriction in gastrocnemius first-order arterioles of adult female rats. Female rats (4 mo; n = 34) were ovariectomized (OVX) with a subset (n = 17) receiving an estradiol pellet (OVE; 17β-estradiol, 4 μg/day). After conclusion of the treatment phase (8 wk), arterioles were excised, placed in a physiological saline solution (PSS) bath, and cannulated with micropipettes connected to albumin reservoirs. NPY-mediated vasoconstriction via a Y(1)-agonist [Leu31Pro34]NPY decreased vessel diameter 44.54 ± 3.95% compared with baseline; however, there were no group differences in EC(50) (OVE: -8.75 ± 0.18; OVX: -8.63 ± 0.10 log M [Leu31Pro34]NPY) or slope (OVE: -1.11 ± 0.25; OVX: -1.65 ± 0.34% baseline/log M [Leu31Pro34]NPY). NPY did not potentiate norepinephrine-mediated vasoconstriction. NPY overflow experienced a slight increase following field stimulation and significantly increased (P < 0.05) over control conditions in the presence of a DPPIV inhibitor (diprotin A). Estradiol status did not affect DPPIV activity. These data suggest that NPY can induce a moderate decrease in vessel diameter in skeletal muscle first-order arterioles, and DPPIV is active in mitigating NPY overflow in young adult female rats. Long-term estradiol supplementation did not influence NPY vasoconstriction, overflow, or its enzymatic breakdown in skeletal muscle first-order arterioles.

Assessment of single versus twice daily dosing of ramipril by ambulatory blood pressure monitoring in patients similar to those included in the HOPE study

Ramipril has been used in twice daily dose of 5 mg in most heart failure trials, whereas the dose used in Heart Outcomes Prevention Evaluation (HOPE) study was 10 mg once at bedtime. The HOPE investigators in an ambulatory blood pressure (ABP) substudy observed a fall of nighttime but not daytime blood pressure (BP). We examined the effects of once daily ramipril 10 mg versus 5 mg twice a day. Twenty-nine patients were recruited based on the original criteria for the HOPE study and were given ramipril either in twice-daily dose (5 mg b.d.) or once daily (10 mg o.d.) each morning in randomized, prospective crossover trial. Twenty-four hour ABP recordings were taken just before commencement of ramipril therapy and after treatment with twice-daily and once-daily ramipril. Our results show that ramipril causes a significant reduction of BP over 24-h period as compared with baseline. The mean baseline ABP was 124/73 mm Hg, which reduced to 117/69 mm Hg for the twice-a-day regimen (P<0.001) and 115/68 mm Hg for the once a day regimen (P<0.001). Both regimes effectively lower BP to a similar extent. Ramipril causes significant BP reduction in both once- and twice-daily dosing. The fall in BP after daytime dosing is greater than that observed in the HOPE study (including ABP substudy). Once-daily dosing in the morning seems to be effective in causing a significant reduction in the ABP profile of patients at high-risk of a future vascular event.

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.

Mechanism of the potentiation of vasoconstriction by neuropeptide Y in arterioles from the submucosa of the guinea-pig small intestine

1. Neuropeptide Y (NPY; 3-100 nmol/L) caused a concentration-dependent potentiation of constriction in response to noradrenaline or the thromboxane mimetic U46619 in arterioles from the submucosa of the guinea-pig small intestine. 2. In arterioles permeabilized by exposure to the alpha-toxin of Staphylococcus aureus and maintained in Ca(2+)-buffered medium, NPY potentiated the contractile effects of Ca2+. The magnitude of the potentiation was the same as in intact arterioles. 3. Exposure of arterioles to 1 mumol/L nifedipine to inhibit Ca2+ influx or to 20 mumol/L cyclopiazonic acid to abolish Ca2+ uptake into internal stores had no effect on the potentiating action of NPY.

ACE inhibitors. Differential use in elderly patients with hypertension

High blood pressure (BP) in the elderly must not be ignored as a normal consequence of aging. The criteria for the diagnosis of hypertension and the necessity to treat it are the same in elderly and younger patients. The aim of treatment of elderly hypertensive patients is to decrease BP safely and to reduce risk factors associated with cerebrovascular, cardiovascular and renal morbidity and mortality. The treatment of elderly hypertensive patients should be adjusted according to the needs of the individual, based upon age, race, severity of hypertension, co-existing medical problems, other cardiovascular risk factors, target-organ damage, risk-benefit considerations and costs. In addition to the elevated BP, other cardiovascular risk factors include smoking, glucose intolerance, hyperinsulinaemia, dyslipidaemia, hypercreatininaemia, peripheral vascular disease, left ventricular hypertrophy, and microalbuminuria (or albuminuria). Thus, the choice of initial antihypertensive therapy in elderly hypertensive patients should be based not only on the expected response, but also on the effects of therapy on lipid, potassium, glucose and uric acid levels, and left ventricular anatomy and function. Co-existing medical conditions (such as asthma, diabetes mellitus, heart failure, renal failure, gout, coronary artery disease, hyperlipidaemia and peripheral vascular disease) are major determinants for the selection of antihypertensive medications. With previous therapies (diuretics, beta-blockers, etc.), good BP control in the elderly was associated with clear and statistically significant reductions in stroke-related morbidity and mortality, but the overall effects on cardiovascular and renal complications of hypertension was either more variable or less obvious. Angiotensin converting enzyme (ACE) inhibitors are not only efficacious antihypertensive agents in the elderly, but also appear promising in counteracting some of the cardiovascular and renal consequences of hypertension. They are well tolerated and have a relatively low incidence of adverse effects. ACE inhibitors possess ancillary characteristics that are potentially beneficial for many elderly patients, including reduction of left ventricular mass, lack of metabolic and lipid disturbances, no adverse CNS effects, no risk of induction of heart failure, and a low risk of orthostatic hypotension. Since ACE inhibitors may improve perfusion to the heart, kidney and brain, they are well worth considering for the treatment of elderly patients with hypertensive target organ damage, especially in patients with heart failure, and diabetic patients with early nephropathy.

Effect of neuropeptide Y on endotoxin-induced suppression of the response to various agonists in conscious rats

Hypotension during endotoxic shock is related to reduced vascular responsiveness to vasoconstrictors. Neuropeptide Y (NPY) is known to potentiate the pressor response to some agonists, and NPY infusion has been shown to improve hemodynamics and survival in endotoxemic rats. We therefore studied the effect of NPY infusion on the suppressed pressor effect of norepinephrine (NE), angiotensin II (AII), vasopressin (VP), and endothelin (ET) in conscious endotoxemic rats. Chronically cannulated conscious rats were infused with a non-hypotensive dose of endotoxin (LPS, 10 micrograms/10 microliters/min) throughout the experiment. Infusion of NPY, 40 pmol/10 microliters/min was started 15 minutes before the LPS infusion, and continued for 65 minutes. Five minutes after the termination of NPY infusion, increasing agonist doses were administered i.v. to construct dose-response curves. Each experiment included one control group where saline replaced LPS, and one control group where saline replaced NPY. LPS infusion caused suppression of the pressor responses to all four agonists, as expressed by ED50 and by decreased pressor response to the individual agonist doses. In addition, LPS infusion altered the bradycardic response to AII and ET. NPY infusion prior to the administration of NE, AII and VP resulted in partial reversal of the LPS-induced suppressed responsiveness to these agonists. NPY infusion had no effect on the response to ET in either control or endotoxemic rats. Partial reversal of the suppressed responsiveness to the three agonists by NPY infusion may contribute to the observed NPY-induced improvement of blood pressure and survival rate during endotoxic shock.

Vascular responses to neuropeptide Y in the rat: effect of age

Neuropeptide Y (NPY) is co-released with norepinephrine (NE) from sympathetic neurons, which innervate blood vessels, and acts to potentiate NE-induced smooth muscle contraction. This study sought to determine if vascular levels of NPY-like immunoreactivity or the contractile effects of NPY are altered by age in segments of isolated blood vessels from Fischer 344 and Brown Norway-F344-F-1 rats. Tissue extracts of femoral and tail arteries of Fischer 344 rats, aged 6, 12, 20, and 24 months, were analyzed for NPY content by radioimmunoassay. Neither blood vessel showed a significant age-related difference in NPY content. Contractile responses of the tail artery to adrenergic transmural nerve stimulation (TNS) were compared in the same age groups. No significant age-related differences in contractile responses to TNS were observed in either rat strain. NPY, at concentrations of 1 and 10 nM, both potentiated and prolonged the contractile response to TNS; 6-month-old F-344 rats were significantly less responsive to the effects of NPY. However, advancing age from 12 to 24 months did not alter the responses to NPY in either rat strain. We conclude that an age-dependent increase in the contractile responses to NPY occurs from age 6 to 12 months, and this responsiveness to NPY is maintained through senescence.

NPY is not a primary mediator of the acute thyroid blood flow response to sympathetic nerve stimulation

It has been suggested that thyroid blood flow is regulated by both sympathetic and parasympathetic nerves. The purpose of our experiments was to study the role of neuropeptide Y (NPY) in the sympathetic neural control of thyroid blood flow. Sympathetic nerve fibers to the thyroid contain both norepinephrine (NE) and NPY. Therefore, NE (15 nmol iv bolus) and NPY (12 or 1.7 nmol/kg body wt iv infusion; 4 min) were administered to anesthetized male rats (250-300 g) either alone or together, with or without an alpha-adrenergic receptor blocker (phentolamine; 10 mg/kg body wt iv bolus). Experiments were also performed in which the cervical sympathetic trunks were stimulated (30 Hz, 10 V; 0.5 ms; 2 min) with or without phentolamine. Thyroid blood flow was monitored continuously by laser-Doppler blood flowmetry. Results are expressed as thyroid vascular conductance (TVC). NE or NPY at both doses decreased TVC relative to that in control saline-infused rats (P < 0.05). No potentiation of the NE effect by NPY was observed when the first dose of NE was injected 2 min after a high or low dose of NPY. However, the effect of a second dose of NE, injected 15 min after the end of the low dose of NPY, was prolonged compared with the effect of a second dose of NE in saline-infused rats. Phentolamine blocked the effect of NE but not that of NPY. Stimulation of the cervical sympathetic trunks decreased TVC (P < 0.01 vs. sham), and this effect was completely blocked by phentolamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacokinetics of angiotensin converting enzyme (ACE) inhibitors in renal failure

Arterial hypertension occurs frequently in patients with chronic renal failure. Antihypertensive treatment of arterial hypertension with angiotensin converting enzyme (ACE) inhibitors has been shown to be effective with a low incidence of adverse effects compared with other drug classes. Furthermore, treatment with ACE inhibitors may slow the progression of renal function impairment in certain groups of patients, such as those with diabetes. Most ACE inhibitors are prodrugs which are converted by hepatic esterolysis to an active diacid metabolite. Only captopril and lisinopril have sufficient oral bioavailability and are given as active drugs. ACE inhibitors can be subdivided into 3 classes with regard to the active group: the majority of ACE inhibitors are carboxyl-containing drugs, a new class of ACE inhibitors possess a phosphoryl-group and captopril and related compounds are sulfhydryl-containing drugs. The predominant elimination pathway of ACE inhibitors is excretion via the kidneys. Therefore, renal insufficiency is associated with reduced elimination of most ACE inhibitors and, thus, altered pharmacokinetic properties. This is most evident in chronic renal failure when glomerular filtration rates (GFR) are < 30 to 40 ml/min (1.8 to 2.4 L/h). As renal clearance decreases, the peak plasma concentration and area under the plasma concentration-time curve of the active drugs or diacids are increased and time to peak concentrations and half-life are prolonged. However, there are large between-drug differences in the changes in pharmacokinetic parameters, resulting in different degrees of drug accumulation after consecutive administration. This leads, for example, to high accumulation rates for drugs such as lisinopril, or cilazaprilat. In contrast, fosinopril, which is also excreted to a large extent by the hepatobiliary pathway, does not seem to accumulate in renal failure. In general, pharmacokinetics and conversion of prodrugs seem to be slightly affected in chronic renal failure; however, these changes do not appear to be clinically relevant. Efficiency of clearance for prodrugs or active drugs and their respective metabolites by haemodialysis or peritoneal dialysis varies considerably. For some ACE inhibitors, such as captopril or enalapril, the high elimination fraction by haemodialysis necessitates a supplemental dose after dialysis. Other ACE inhibitors, such as quinapril or cilazapril, are only poorly eliminated by haemodialysis or peritoneal dialysis. Dosage recommendations for treatment with ACE inhibitors in chronic renal failure depend on the specific pharmacokinetic properties of the various agents. For most ACE inhibitors, dosage adjustment is recommended in moderate and severe impairment of renal function, with resultant dosages being 25 to 50% of those recommended for patients with normal renal function.

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.

Analysis of acetylcholine-induced relaxation of rabbit isolated middle cerebral artery: effects of inhibitors of nitric oxide synthesis, Na,K-ATPase, and ATP-sensitive K channels

The functional importance of membrane hyperpolarization through activation of ATP-sensitive K channels, or activation of the Na,K-ATPase, was investigated for acetylcholine (ACh)-induced relaxation of the rabbit isolated middle cerebral artery (MCA) precontracted with uridine triphosphate. Incubation with glibenclamide (1 microM), a known blocker of ATP-sensitive K channels, or precontraction with a high concentration of KCl (50 mM) had no effect on ACh-induced relaxation. Similarly, inhibition of the Na,K-ATPase with ouabain (10 microM) or incubation with a potassium-free solution had either no or only a small effect on ACh-induced relaxation. In contrast, NG-nitro-L-arginine (NOLAG) (1 to 10 microM), a structural analogue of L-arginine and an inhibitor of nitric oxide synthesis, produced concentration-dependent although apparently noncompetitive inhibition of ACh-induced relaxation. This inhibition was partially reversed by application of L-arginine (100 microM), a putative precursor for nitric oxide synthesis. It is concluded that membrane hyperpolarization induced by activation of ATP-sensitive K channels or Na,K-ATPase does not play a major functional role in ACh-induced relaxation of rabbit MCA. The potent inhibitory actions of NOLAG would suggest that the major mechanism of ACh-induced relaxation is by release of nitric oxide as in other cerebral and peripheral arteries.

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)

Changes in the levels of neuropeptide Y-LI in the external jugular vein in connection with vasoconstriction following subarachnoid haemorrhage in man. Involvement of sympathetic neuropeptide Y in cerebral vasospasm

NPY is a putative neurotransmitter mainly co-localized with noradrenaline in sympathetic fibers which innervate the cerebral vasculature. The origin of most of the perivascular NPY fibers seems to be in the superior cervical ganglion. To investigate involvement of Neuropeptide Y (NPY) mechanisms in subarachnoid haemorrhage (SAH), twenty patients with SAH were investigated. NPY-LI (-like immunoreactivity) levels in the external jugular vein were assessed using radioimmunoassay in blood samples collected post-operatively (or after SAH in non-surgical patients) on days 1,2,3, 5,7 and 9. These levels were compared with the clinical course and blood flow velocity changes monitored with ultrasonic Doppler equipment from both middle cerebral arteries (MCA) and both internal carotid arteries (ICA). Compared to NPY-LI levels in 14 controls (mean 116 +/- 3 pmol/1), increased levels (up to 253 pmol/l) and a close relationship between velocities and NPY-LI levels were found in a subpopulation of the SAH patients. When comparing the mean haemodynamic index (V MCA/ipsilateral V ICA) and mean NPY-LI levels in each of the 20 patients, a correlation of r = 0.75, p = 0.0001 was found. Increased NPY-LI were found (131 +/- 8 pmol/l) when simultaneous Doppler velocity recordings showed vasoconstriction (Haemodynamic index greater than 5) compared with samples taken when the haemodynamic index was less than 5, p less than 0.05. When MCA velocity exceeded 120 cm/sec. increased levels were found (129 +/- 9 pmol/l) compared with the conditions when MCA velocity was less than 120 cm/sec (113 +/- 5 pmol/l), p = 0.06. The results indicate a possible NPY involvement in cerebral vasoconstriction after SAH.