Vascular effects of the dinitrate and moninitrate esters of isosorbide, isomannide and isoidide

NO donors. Part 16: Investigations on structure–activity relationships of organic mononitrates reveal 2-nitrooxyethylammoniumnitrate as a high potent vasodilator

The vasoactive properties of 14 organic mononitrates were investigated in vitro using PGF(2alpha)-precontracted porcine pulmonary arteries. A surprisingly wide range of vasorelaxant potencies was observed (pD(2): 3.36-7.50). Activities showed to be highly sensitive to the molecular structure and the substituents at the molecular carrier of the nitrate group. A correlation between lipophilicity and vasorelaxant potency could not be recognized. 2-Nitrooxyethylammoniumnitrate (1) was found to be slightly superior to the high potency trinitrate GTN.

EFFECT OF ISOSORBIDE DINITRATE ON GASTRIC BLOOD FLOW IN RATS WITH LIVER CIRRHOSIS DETERMINED BY ANALYZING GASTRIC BLOOD FLOW, PORTAL VEIN PRESSURE AND BLOOD GAS

We investigated the effects of isosorbide dinitrate (IDN) on gastric blood flow (GBF), portal venous pressure (PVP) and blood gas of rats with liver cirrhosis (LC) accompanied by portal hypertension. Thirty male Wistar rats (LC in 17 and normal in 13) were used. Before and after IDN administration, GBF, PVP and blood gas in the femoral artery and portal vein were measured. Portal blood oxygen concentration was estimated by calculating the ratio of PO2 in portal blood and that in arterial blood (PpvO2/PaO2) of each rat. The GBF in the LC rats was significantly lower than that in the normal rats. In the LC group, IDN administration significantly increased the GBF. The PpvO2/PaO2 value in the group with LC was significantly lower after IDN administration than that before IDN administration. In the investigation whether changes in PVP or Ppv/PaO2 contributed more to the change in GBF after IDN administration, a significant correlation was found between rates of change in GBF and PpvO2/PaO2 were significantly correlated (r= -0.733, p <0.05). The effect of IDN on changes in the stomach accompanying portal hypertension is mainly attributable to a decrease in preload, which suppresses inflow to the stomach, as reflected by a decrease in PpvO2/ PaO2, rather than to a decrease in afterload on GBF, as reflected by a decrease in PVP.

Plasma concentrations and coronary vasodilation after sublingual and intracoronary administration of isosorbide dinitrate

To investigate the relationship between plasma levels and coronary vasodilation after administration of isosorbide dinitrate (ISDN), the plasma concentration and diameters of six segments of the left coronary artery were measured before and after sublingual (SL) ISDN (5 mg) and left intracoronary (IC) administration of ISDN (3 mg) in 12 patients. After SL-ISDN, the systolic aortic pressure decreased with no significant concomitant changes in heart rate or diastolic aortic pressure. After IC-ISDN, all hemodynamic parameters showed significant changes, and these were greater after IC-ISDN than those after SL-ISDN. The individual mean vasodilation of six segments induced by SL- and IC-ISDN, were 23 +/- 9 and 35 +/- 11% (p < 0.01), respectively. Before SL-ISDN, ISDN was not detected in plasma. After SL- and IC-ISDN, however, the plasma values of the ISDN were 36.1 +/- 53.3 and 101.5 +/- 90.0 ng/ml (p < 0.01), respectively. Thus, both coronary vasodilative responses and plasma ISDN levels after IC-ISDN were significantly greater than those after SL-ISDN. However, neither the individual mean coronary vasodilation nor the hemodynamic changes correlated significantly with plasma ISDN levels. Consequently, with administration of the same dose, the coronary vasodilative response to ISDN did not correlate with plasma levels. Furthermore, IC-ISDN dilutes coronary arteries more effectively than SL-ISDN.

Effect of isosorbide-5-mononitrate on plasma and urine levels of cyclic GMP in relation to exercise in coronary patients compared with control subjects

Nitric oxide (NO) and atrial natriuretic peptide (ANP) relax vascular smooth muscle increasing levels of cyclic guanosine 3':5' monophosphate (cGMP). Nitrovasodilators act as exogenous nitric oxide donors. The aim of this study was to ascertain the response of cGMP to exercise without medication and after the administration of 20 mg of isosorbide-5-mononitrate (IS-5-MN) in coronary patients (n = 8) and healthy control subjects (n = 9). A third group of 10 normal volunteers was studied to test plasma cGMP response to second exercise test without IS-5-MN administration. Plasma cGMP increased significantly in both patients (P < 0.02) and controls (P < 0.01) after the first ergometry. After IS-5-MN administration, plasma cGMP did not increase either before or after exercise. In normal volunteers without IS-5-MN plasma cGMP increased significantly after first (P < 0.004) and second (P < 0.0008) exercise test. In conclusion, plasma cGMP increases during exercise. Administration of IS-5-MN does not raise plasma cGMP and neither does performance of further exercise after its administration.

Portal and systemic haemodynamic response to acute and chronic administration of low and high dose isosorbide-5-mononitrate in patients with cirrhosis

Oral isosorbide-5-mononitrate (Is-5-Mn) was given in doses of 10 and 40 mg acutely and chronically (twice daily for four weeks), allowing a nitrate free interval to 25 patients with cirrhosis. Both 10 mg and 40 mg Is-5-Mn reduced the hepatic venous pressure gradient acutely and chronically, without evidence of tolerance. This was achieved by a reduction in the wedged hepatic venous pressure. The effect on mean azygos blood flow was variable with no significant mean change seen acutely or after chronic use with either dose. The variability was dependent not on the dose used but on the initial azygos flow; the flow in patients with initially low values increased and those with high azygos flows decreased after nitrate challenge. The development of the porto-collateral flow seems an important parameter in predicting haemodynamic response to Is-5-Mn.

Pharmacokinetics of oral L-isoidide mononitrate in rats

L-isoidide mononitrate (L-IIMN) is the most potent mononitrate vasodilator described so far in the literature. Since other mononitrates, such as isosorbide-5-mononitrate and isosorbide-2-mononitrate, have been shown not to be subject to first-pass metabolism, we examined the pharmacokinetics of L-IIMN after oral administration to determine whether this compound also exhibited this behavior. An oral dose of 2 mg kg-1 L-IIMN dissolved in normal saline was given to seven rats. Absorption of L-IIMN after dosing was rapid with an apparent absorption half-life of 9.5 +/- 3.6 min (mean +/- SD). Plasma L-IIMN concentrations peaked between 5 and 20 min after dosing and declined thereafter in an apparently monoexponential manner. The average elimination half-life was 11.9 +/- 1.7 min (mean +/- SD). Oral bioavailability was estimated to be about 50%. Thus, unlike the other mononitrates so far examined in the literature, L-IIMN exhibits incomplete bioavailability. This pharmacokinetic behavior, however, is consistent with its faster systemic clearance compared to other organic mononitrates.

Direct inhibition of platelet function by organic nitrates via nitric oxide formation

This study investigates the mechanisms of platelet inhibition by the nitrate esters isosorbide dinitrate, isoidide dinitrate, isomannide dinitrate, isosorbide 2-mononitrate and isosorbide 5-mononitrate as compared to the spontaneous nitric oxide (NO)-donor linsidomine, the active metabolite of molsidomine. Nitrates and linsidomine dose-dependently inhibited aggregation, ATP secretion and thromboxane formation of washed human platelets at a rank order of potency, identical with that for stimulation of cyclic GMP in cultured rat lung fibroblasts. While linsidomine (0.1 mM) caused a 3-fold platelet cGMP elevation, there was a weak (< or = 30%) but significant cGMP stimulation by organic nitroesters, which was tightly correlated with inhibition of platelet aggregation (r = 0.926, P = 0.008). Zaprinast (2 microM) potentiated, while methylene blue (1 microM) and oxyhemoglobin (10 microM) reversed the antiaggregatory effects. Linsidomine (0.5 microM-0.1 mM) dose-dependently released NO in a cell-free system. No spontaneous NO release was detected with organic nitroesters (0.1 mM). These data suggest that, to some extent, bioactivation of organic nitroesters occurs in platelets, resulting in platelet inhibition via the NO/cGMP system.

Pharmacodynamic modeling of the in vitro vasodilating effects of organic mononitrates

The in vitro dose-relaxation curves of four isomeric organic mononitrates: L-isoidide mononitrate (L-IIMN), isosorbide-2-mononitrate (IS-2-MN), isomannide mononitrate (IMMN), and isosorbide-5-mononitrate (IS-5-MN), were determined with rat aorta rings. These mononitrates relaxed vascular tissue in a concentration-dependent manner. Based upon the EC50 obtained from the Hill equation, the relative potency of L-IIMN: IS-2-MN: IMMN: IS-5-MN was 43.2:12.2:2.3:1. The Hill exponential coefficients were identical (value of about 1.5) in these four isomeric mononitrates, suggesting that they are likely to have a common mechanism of action. For all four isomers, relaxation was fairly immediate after addition of the tested compound into the tissue bath, with a 2- to 3-min-delay to reach steady-state effect. The rates of relaxation were then used to construct a pharmacodynamic model that described the time course of relaxation for these compounds. This theoretical analysis suggested that in vitro nitrate action is mediated by a catenary process, consistent with published biochemical evidence that suggests a series of reactions involving metabolic activation to nitric oxide, production of cyclic GMP, and myosin light-chain phosphorylation to produce relaxation. Via this pharmacodynamic model, the half-lives of nitric oxide and cGMP in the smooth muscle cells were estimated to be 15.2 and 23.1 sec, respectively, consistent with literature reports. Results from the present study indicated the potential use of in vitro pharmacodynamic modeling in confirming mechanism(s) of drug action obtained through biochemical or other methods.

Structure activity relationship of organic nitrates: an exploratory hypothesis via molecular models

An exploratory attempt to explain the structure/activity relationship of organic nitrates was initiated. In addition to the partition coefficient, a new empirical parameter, F(5.8A), was used in this correlation. This new parameter denotes the number of times that two oxygen atoms in the molecule can be arranged at a distance of 5.8A. Vasodilating potencies (EC50s) and partition coefficients of 11 organic nitrates were obtained from a literature report, while their corresponding F(5.8A) values were obtained from manual determination using two molecular models, viz: CPK and Drieding. Via linear regression comparisons, we showed that F(5.8A) was a better physicochemical parameter than the partition coefficient in explaining the differences in the observed pharmacologic activity. When the two parameters were combined, greater than 90% of the variability of the potency was accounted for. These results suggest that the pertinent protein (most likely the activating enzyme) for organic nitrate activity may contain at least two 'oxygen-philic' attachment sites which are separated by a distance of 5.8A.

Do nitrates differ?

1. The organic nitrates all share a common biochemical and physiological mechanism of action. 2. The organic nitrates differ substantially in their pharmacologic potency and pharmacokinetics. In vitro potency differences appear larger than the corresponding in vivo activities. 3. The duration of action of organic nitrates, after a single immediate-release dose, is governed by the pharmacokinetics of the drug. However, the duration of action of available sustained-release preparations, whatever the nitrate or formulation, is limited to about 12 h, due to the development of pharmacologic tolerance. 4. Nitrates do not appear to differ in their production of undesirable effects.

Gas chromatographic analysis of isomeric organic mononitrates in plasma

A specific, sensitive and precise capillary gas chromatographic method using electron-capture detection was developed for the determination of four isomeric vasodilating organic mononitrates, viz. L-isoidide mononitrate (L-IIMN), isosorbide-2-mononitrate (IS-2-MN), isomannide mononitrate (IMMN) and isosorbide-5-mononitrate (IS-5-MN), in rat plasma. With a sample size of 100 microliters of rat plasma, the detection limits were found to be between 0.5 and 2 ng/ml for these mononitrates, and the absolute recovery was found to range from 83 to 90%. The within-day coefficients of variation for the assay of the four isomers were less than 5%, while the between-day coefficients of variation were less than 10%. Because of the short retention times of these isomers in this assay, routine analyses of about sixty plasma samples per day can be carried out. The possibility of in vivo interconversion among these four isomers in rats was investigated after individual administration of each isomer. No interconversion was found based on examination of plasma samples. The gas chromatographic method was applied to the pharmacokinetic studies of these four isomers in rats; at an intravenous dose of 2 mg/kg, the biological half-lives of L-IIMN, IMMN, IS-2-MN and IS-5-MN were found to be 13.2, 25.2, 54.6 and 112 min, respectively.

The sorption of isosorbide-5-mononitrate to intravenous delivery systems

The sorption of isosorbide-5-mononitrate, diluted in 0.9% NaCl or 10% glucose solutions, to intravenous delivery systems was investigated. Infusion bags, burettes, a syringe, infusion tubings and end-line filters were tested in static and in dynamic experiments. No clinically significant sorption was detected during those experiments. The use of PVC tubings of different hardness did not influence the results.

Effect of in vitro organic nitrate tolerance on relaxation, cyclic GMP accumulation, and guanylate cyclase activation by glyceryl trinitrate and the enantiomers of isoidide dinitrate

Previously, it was shown that the D enantiomer of isoidide dinitrate was 10-fold more potent than the L enantiomer and 10-fold less potent than glyceryl trinitrate for stimulating cyclic GMP accumulation and relaxation of isolated rat aorta. In the present study, these organic nitrates were tested for their ability to induce tolerance to organic nitrate-induced relaxation, cyclic GMP accumulation, and guanylate cyclase activation in rat aorta in vitro. To compensate for the differences in vasodilator potency, tolerance was induced by incubating isolated rat aorta with concentrations of organic nitrates 1,000-fold greater than the EC50 for relaxation. Under these conditions, the EC50 for relaxation was increased significantly for each organic nitrate and to a similar degree on subsequent reexposure. These data suggest that the potential for inducing in vitro tolerance to relaxation was the same for the three organic nitrates tested. When activation of soluble guanylate cyclase by these compounds was assessed, the enantiomers of isoidide dinitrate were equipotent, but less potent than glyceryl trinitrate, suggesting that the site of enantioselectivity is not guanylate cyclase itself. In blood vessels made tolerant to organic nitrates by pretreatment with glyceryl trinitrate, vasodilator activity, cyclic GMP accumulation, and guanylate cyclase activation were attenuated on reexposure to each organic nitrate. In addition, differences in the potency of the three organic nitrates and the enantioselectivity of isoidide dinitrate for relaxation were abolished in tolerant tissue, whereas the potency difference between glyceryl trinitrate and isoidide dinitrate for activation of guanylate cyclase was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent developments in the use of nitrates for treatment of angina pectoris

Organic nitrates are effective in the treatment and prophylaxis of angina pectoris. The major clinical problem of tolerance may be avoided if the daily plasma concentrations of the active metabolite, isosorbide-5-mononitrate are maintained at 100-300 ng/ml. The most promising development in achieving this is the use of sustained release preparations.

Comparative evaluation of isosorbide-5-mononitrate and nitroglycerin in chronic congestive heart failure

The hemodynamic effects of isosorbide-5-mononitrate (IS-5-MN) and nitroglycerin were compared in 10 patients with chronic congestive heart failure (CHF). Both drugs were given intravenously, at an infusion rate individually titrated to achieve a maximal increase in cardiac output and a maximal decrease in pulmonary capillary wedge pressure. Both drugs produced the typical hemodynamic responses to nitrates, the most prominent of which were decreases in pulmonary capillary wedge, pulmonary arterial and right atrial pressures, and an increase in cardiac output. Several differences in the response to these 2 drugs were observed. Pulmonary capillary wedge pressure was reduced from 31.5 +/- 3.0 to 19.6 +/- 5.0 mm Hg with nitroglycerin and to 15.0 +/- 3.12 mm Hg with IS-5-MN. Both the absolute and the percent decrease with IS-5-MN were significantly greater (p less than 0.05) than those observed with nitroglycerin. Mean systemic arterial pressure was reduced from 89.2 +/- 11.3 to 79.8 +/- 10.8 with IS-5-MN (difference not significant) and to 67.5 +/- 7.7 mm Hg with nitroglycerin (p less than 0.01). The difference, both in absolute and percent reductions, was statistically significant. Thus, in patients with chronic CHF, IS-5-MN produced a greater decrease in pulmonary capillary wedge pressure (the major beneficial effect of nitrates in this condition) and a smaller decrease in systemic arterial pressure (the potentially deleterious effects of nitrates). These findings indicate a potential advantage of IS-5-MN over nitroglycerin in patients with CHF, particularly in those with CHF of ischemic etiology.

The bioavailability of oral nitroglycerin

In the 1970's, the efficacy of oral nitroglycerin therapy was seriously challenged, primarily on the basis of animal studies showing complete first-pass hepatic metabolism of nitroglycerin. Today, it is generally accepted that high oral doses of nitroglycerin do show antianginal efficacy. It has been suggested that this efficacy results from saturation of hepatic metabolism by the large oral doses administered, although the experimental evidence in humans purporting to support this may be questioned. In the present investigation, the bioavailability of oral nitroglycerin when administered in a capsule dosage form and as a solution was determined. Oral doses of nitroglycerin were less than 1% bioavailable. However, substantially high concentrations of the relatively low activity dinitrate metabolites were measured in plasma. We hypothesize that the activity of oral nitroglycerin preparations may result from high concentrations of the dinitrate metabolites, although this was not directly tested in the bioavailability studies described here.

Pharmacokinetics of isosorbide dinitrate and its mononitrate metabolites after intravenous infusion

Plasma concentrations of isosorbide dinitrate (ISDN) and its two active metabolites 2-isosorbide mononitrate (2-ISMN) and 5-isosorbide mononitrate (5-ISMN) have been measured during and for 6 hr after intravenous infusion at a rate of 2.5 mg/hr during 1.75 hr in six cardiac patients, by a capillary gas chromatographic method. Data were analyzed by simultaneous modeling of the observed kinetics of the three compounds. Two or three phases were detected on the postinfusion ISDN concentration-time curves. ISDN concentrations declined with a mean terminal half-life of 2.81 hr +/- 0.7 SD. The mean systemic clearance of ISDN (2.9 L/min +/- 0.7 SD) and its mean total volume of distribution (259 L +/- 48 SD) were relatively high. Plasma 5-ISMN concentrations were 5- to 6-fold greater than those of 2-ISMN during the whole observation period. Maximum levels of 2-ISMN (6.7 ng/ml +/- 0.9 SD) and of 5-ISMN (27 ng/ml +/- 6 SD) occurred within a few minutes after the end of infusion. The mean half-lives of 2-ISMN (1.59 hr +/- 0.19 SD) and of 5-ISMN (3.78 hr +/- 0.79 SD) estimated by the model were smaller than those calculated by a model-independent method (2.95 hr +/- 0.41 SD and 5.98 hr +/- 2.22, respectively), but were in good agreement with those reported in the literature following separate administration of both metabolites to man. This study shows how such modeling can distinguish between metabolite formation and elimination processes and allow the determination of metabolite half-lives after administration of the precursor drug.

Isosorbide dinitrate sublingual therapy for inferior myocardial infarction: randomized trial to assess infarct size limitation

To assess the potential of isosorbide dinitrate sublingual therapy for limiting myocardial infarct size, 41 patients with inferior acute myocardial infarction (AMI) were studied. Twenty patients were randomly assigned to the control group and 21 to the treatment group. Patients in the treatment group received 10 mg of isosorbide dinitrate every 2 hours for 72 hours. To estimate infarct size, QRS scoring, peak creatine kinase (CK) serum levels and CK curves were used. There were no significant differences between the 2 groups in maximal or cumulative activity of CK or QRS score (percent of left ventricle infarcted: 16% in the control group, 17% in the treatment group). In both groups the QRS score increased significantly by 13 hours after AMI, and the increase was highly significant by 19 to 23 hours. Thus, sublingual isosorbide dinitrate at the dosage given did not reduce infarct size in patients with inferior AMI.

Determination of isosorbide dinitrate and its mononitrate metabolites in human plasma using Extrelut purification and capillary column gas-liquid chromatography

A rapid, accurate and sensitive method for the determination of isosorbide dinitrate (internal standard: isomannide dinitrate) and its 2- and 5-mononitrate metabolites (internal standard: isoidide mononitrate) in 1.0 ml of human plasma has been developed. Before chromatographic quantitation by gas-liquid chromatography with electron-capture detection, isosorbide nitrates were purified by Extrelut chromatography (recovery about 90%), eliminating most of the endogenous interferences. Routine limit of quantitation and reproducibility were 0.5, 2.0 and 10.0 ng/ml and 6, 8 and 7% for isosorbide dinitrate and the 2- and 5-mononitrates, respectively. This method allowed the behaviour of this vasodilating drug and its metabolites to be studied in humans.

Treatment of coronary heart disease with isosorbide mononitrate ('Elantan' 20): a multi-centre study in hospital and general practice

An open, multi-centre clinical trial was carried out in 537 hospital patients and 2138 general practice patients to evaluate the efficacy and tolerance of isosorbide 5-mononitrate in the treatment of angina pectoris. Prior to entry into the trial, angina attack frequency and acute glyceryl trinitrate consumption were assessed during previous, in most cases unsatisfactory, anti-anginal therapy. After a treatment-free washout period of 3 days, graded multi-stage exercise testing was performed and then treatment started with 20 mg isosorbide mononitrate 3-times per day. Exercise testing was repeated after 14 days' therapy and, in the case of the hospital patients, also 4 to 5 hours after the first dose of isosorbide mononitrate. At the end of the 14-day treatment period, angina attack frequency and glyceryl trinitrate consumption were again assessed. Similar results were obtained for both hospital and general practice patients. Changing to isosorbide mononitrate resulted in a marked reduction in angina frequency, with complete elimination of angina attacks in approximately half of the patients; nocturnal angina, present in approximately 20% of the patients during previous therapy, virtually disappeared during isosorbide mononitrate therapy. Exercise tolerance and performance improved in the majority of patients, with a marked increase in the number of patients able to exercise to the level at which some symptom other than angina pectoris caused them to stop. ST-depression during exercise and exercise-induced arrhythmias also showed clear reductions during isosorbide mononitrate therapy. Tolerance to isosorbide mononitrate was good, the expected 'nitrate headaches' being the only common side-effect reported. The results were such that continuation of treatment with isosorbide mononitrate after the trial was recommended by the attending physician in 77% of the hospital patients and 87% of the general practice patients.

Tolerance to isosorbide dinitrate: rate of development and reversal

The circulatory response and plasma concentrations of isosorbide dinitrate (ISDN) were determined in 10 patients with chronic, stable angina after administration of 5 mg of sublingual ISDN during the control stage, after 48 hr of therapy with 15 mg of ISDN orally every 6 hr, and subsequently after a 48 hr period when ISDN was substituted by placebo four times daily. Initially, sublingual ISDN induced major reductions in both supine and standing systolic and diastolic blood pressure, but after 45 hr of therapy with oral ISDN, there was a significantly diminished vasodepressor response in both positions. Subsequently, when placebo was substituted for ISDN, the circulatory response initially seen was restored within 21 hr. Plasma ISDN concentrations after the test sublingual dose were slightly higher after 48 hr of oral ISDN dosing (i.e., the tolerant state) than at the start of the study. This suggests that tolerance is unlikely to be caused by reduced bioavailability or accelerated elimination of ISDN. It is possible that tolerance is related to accumulation of ISDN metabolites. The attenuation of the circulatory response to ISDN may be related to the altered antianginal efficacy commonly seen during sustained therapy with ISDN.

Absorption and excretion of isosorbide dinitrate and isosorbide-2-mononitrate in dogs

In a crossover design four male dogs were given orally or i.v. [14C]isosorbide dinitrate (ISDN) or [14C]isosorbide-2-mononitrate (2-ISMN) at a dose of 1 mg kg-1 (70-80 microCi). Virtually all of the oral dose was absorbed and all of the radioactivity was excreted in the urine. The profile of serum radioactivity was similar after all drug administrations. ISDN was rapidly denitrated, giving rise to isosorbide-5-mononitrate (5-ISMN) as a major metabolite, and 2-ISMN as a minor metabolite. The apparent elimination half-life from serum of 2-ISMN and 5-ISMN was 2-3 h. More than 50% of the serum radioactivity after [14C]2-ISMN was due to unchanged drug. The apparent volume of distribution of 2-ISMN averaged 8.3 litres. The results show that, in contrast to ISDN, administration of 2-ISMN resulted in relatively high unchanged drug levels in the serum; the disposition of radioactivity after [14C]ISMN was however similar to that after [14C]ISDN. The findings support the concept that the concentrations of ISDN, 2-ISMN and 5-ISMN in the blood are inversely related to the rates of denitration, and that the vascular activity of the nitrates of isosorbide relates to the rates of their dinitration.

Isosorbide 5-mononitrate pharmacokinetics in humans

When isosorbide 5-mononitrate was intravenously infused at a rate of 4 mg h-1 for 2.5 h to five human subjects, its concentrations in plasma increased slowly to 185 ng ml-1 +/- 5 per cent C.V. at 2.5 h and a steady-state plasma level was not reached during the infusion. When the infusion was discontinued, plasma drug concentrations declined with an elimination half-life of 4.2 h +/- 6 per cent C.V. The systemic clearance after the infusion doses was 132 ml min-1 +/- 18 per cent C.V. and the volume of distribution was 48.4 +/- 16 per cent C.V. After equal oral doses of 10 mg, the peak plasma isosorbide 5-mononitrate concentration of 191 ng ml-1 +/- 16 per cent C.V. was reached at 1.1 h +/- 30 per cent C.V., and plasma levels declined with a terminal half-life of 4.9 h. The complete systemic availability of isosorbide 5-mononitrate indicated that pre-systemic elimination after the oral doses was negligible. A one-compartment open model appeared adequate to describe the plasma level data after intravenous infusion and oral dose. After single oral doses of 10 mg isosorbide dinitrate, the peak plasma concentration of the 5-mononitrate metabolite of 72 ng ml-1 +/- 27 per cent C. V. occurred at 1.7 h +/- 41 per cent C.V. Approximately 50 per cent (range 22--68 per cent) of the oral dose of isosorbide dinitrate circulated in plasma as the 5-mononitrate metabolite. The pharmacokinetics of isosorbide mononitrates are markedly different to those of the parent dinitrate and these differences follow from the greater systemic availability and volume of distribution of the mononitrates.

Fate of isosorbide dinitrate and mononitrates in patients with renal failure

Isosorbide dinitrate 10 mg, isosorbide 5-mononitrate 5 mg and isosorbide 2-mononitrate 5 mg were administered orally to subjects with and without renal failure, and the plasma concentrations of isosorbide dinitrate and of both the mononitrates were measured. There was no striking difference in plasma concentration as a function of time between subjects with and without renal failure, except for a somewhat higher isosorbide 5-mononitrate concentration after administration of this metabolite to uraemic patients.

Pharmacokinetics of intravenous and oral isosorbide - 5 - mononitrate

The pharmacokinetics of isosorbide-5-mononitrate (IS-5-MN) has been studied in two groups of healthy volunteers after oral (n = 20) and intravenous (n = 11) administration of 20 mg, which had previously been proved to be as effective as 20 mg sustained-release isosorbide dinitrate (ISDN). IS-5-MN in serum was measured by gas chromatography using capillary columns. The kinetic calculations were carried out with a newly developed model, which assumes a virtual volume of distribution dependent on time. IS-5-MN is rapidly (invasion half-life 4.1 min) and completely absorbed from the gastro-intestinal tract without any first pass metabolism. The maximum concentration of 480 micrograms/l was reached 1.2 h after oral administration of 20 mg. The substance was distributed throughout the total body water (distribution coefficient: 0.62), and was eliminated with a terminal t1/2 of 4.1 and 4.6 h after oral and intravenous administration, respectively. Total body clearance was 115ml/min. Thus, IS-5-MN is unlike ISDN with respect to the absence of first-pass metabolism and an 8-times longer half-life. The consequences for therapy are discussed.

Effects and pharmacokinetics of isosorbide dinitrate in normal man

18 subjects were given isosorbide dinitrate (ISDN) 5 mg sublingually and serum concentrations of ISDN, 2-isosorbide mononitrate (2-ISMN) and 5-isosorbide mononitrate (5-ISMN) were measured, as well as changes in digital plethysmographic amplitude, heart rate, ECG, blood pressure and Schellong's test. ISDN was rapidly absorbed and metabolized, having an elimination half-life of 29 min. Its metabolites 2-ISMN and 5-ISMN had longer half-lives of 1.75 and 7.6 h respectively. The amplitude of the alpha-wave of the digital plethysmograph did not change significantly either in the pre-drug period or after placebo administration. It increased within 4 min of administration of ISDN, and reached a maximum after 14 min; the effect lasted for about 2 h. ISDN lowers blood pressure and increases heart rate in most volunteers, but in 3 of the 18 subjects severe hypotension occurred, accompanied by severe, reversible bradycardia, which was probably due to vagal reflexes initiated by the markedly diminished ventricular enddiastolic volume (LVEDV) and pressure (LVEDP). No correlation could be demonstrated between the serum concentration of ISDN and/or its vasoactive metabolites and changes in plethysmographic amplitude.

Simultaneous determination of isosorbide dinitrate and its mononitrates in human plasma by capillary column GLC

A previously described electron-capture GLC method for determination of isosorbide dinitrate in human plasma was adapted for the simultaneous determination of isosorbide dinitrate, isosorbide 2-mononitrate, and isosorbide 5-mononitrate using a capillary column. Quantitation was done with two internal standards. The lower limits of detection were approximately 0.5 ng/ml of plasma for isosorbide dinitrate, 2 ng/ml for isosorbide 2-mononitrate, and 20 ng/ml for isosorbide 5-mononitrate.

Plasma concentrations of isosorbide dinitrate and its metabolites after chronic high oral dosage in man

1 We have previously reported that vasodilator headache due to isosorbide dinitrate (ISDN) can be circumvented by using small 'priming' doses for an induction period of 1-2 weeks, after which it is possible to increase to dose rapidly to 360-720 mg, daily without recurrence of headache and without toxicity. The present study corroborates this earlier finding. 2. Chronic oral administration of doses of ISDN of this order of magnitude results in prolonged high plasma concentrations of the parent compound, as well as higher levels of the metabolites 2-ISMN and 5-ISMN. 3. It is our thesis that chronic high oral dosage of ISDN saturates the intrahepatic biotransformation process, and allows high concentrations of ISDN and its metabolites to enter the systemic circulation.

Plasma isosorbide dinitrate concentrations in human subjects after administration of standard and sustained-release formulations

After sublingual administration of 5 mg of isosorbide dinitrate, mean plasma concentrations (+/-SD) peaked (8.9+/-3.1 ng/ml) at 15 min after dosing and declined with a half-life of 30 min. After oral administration of 5 mg, mean concentrations peaked (3.1+/-0.7 ng/ml) at 30 min and declined with a half-life of 40 min. After oral administration of 20 mg in a sustained-release tablet, mean concentrations initially peaked (1.4+/-1.2 ng/ml) at 40 min, declining to 0.9+/-0.5 ng/ml after 8 hr. Mean concentrations were maintained above half the mean peak level during 10 hr. Because of probable rapid first-pass metabolism, the bioavailability of isosorbide dinitrate after administration of the oral dose of the standard tablet was 58% of that from the sublingual dose, and the bioavailability from the sustained-release tablet was 47% of that from the sublingual dose of the standard tablet. The time course of mean plasma concentration data could be described by a one-compartment model; but a more complex model, taking the pass effect into account, probably is needed for a better description of the pharmacokinetics of isosorbide dinitrate.

Comparative effects of nitroglycerin and isosorbide dinitrate on coronary collateral vessels and ischemic myocardium in dogs

To determine the effect of isosorbide dinitrate or ischemic myocardium, this agent was administered to dogs with well developed coronary collateral vessels 8 to 14 weeks after embolization and subsequent occlusion of the left anterior descending coronary artery. After thoracotomy the left coronary artery was cannulated and perfused with blood from the femoral artery. The distal left anterior descending artery was cannulated to monitor peripheral coronary pressure. Regional contractile force in the normal left circumflex and potentially ischemic left anterior descending regions was measured with isometric strain gauge arches sewn to the epicardium. Moderate decreases in coronary perfusion pressure averaging 27 mm Hg produced selective ischemia in the myocardium beyond the site of occlusion of the left anterior descending artery. Under these conditions the average increase in peripheral coronary pressure produced by intracoronary injection of isosorbide dinitrate was 9.0 mm Hg, whereas contractile force in the ischemic region increased by 30 percent. The contractile force was unchanged in the normal regions. Therefore, isosorbide dinitrate can dilate coronary collateral vessels and improve contractile force in ischemic areas. Intracoronary injection of nitroglycerin had similar effects. The durations of responses to isosorbide dinitrate and nitroglycerin were remarkably similar: 6.4 and 6.7 minutes, respectively. Although isosorbide dinitrate can directly dilate coronary collateral vessels, its effects are not longer lasting than those of nitroglycerin.

Concentrations of the vasodilator isosorbide dinitrate and its metabolites in the blood of human subjects

An oral dose of 5 mg of 14C-isosorbide dinitrate was rapidly absorbed, biotransformed and excreted by human subjects. Peak whole blood concentrations of radioactivity were reached after 1.5 to 2 hours and declined relatively slowly. The radioactivity in whole blood mainly represented metabolites, isosorbide mononitrates. The peak concentrations found were 4.5, 11.7 and 34.3 ng/ml of isosorbide dinitrate, isosorbide 2-mononitrate and isosorbide 5-mononitrate, respectively, in the blood of one subject and 5.9, 15 and 61.3 ng/ml, respectively, in the blood of another subject. However, concentrations of the metabolites declined relatively slowly during 6 h after the oral urine of the first day (ca. 78%). The results showed that isosorbide mononitrates were available to contribute to the pharmacological action.