Biotransformation of isosorbide dinitrate in humans

A core/shell nanogenerator achieving pH-responsive nitric oxide release for treatment of infected diabetic wounds

Nitric oxide is critical for eliminating infection and promoting regeneration in diabetic wounds. However, clinical uses of nitric oxide are limited by its high activity and lack of specificity in targeting infections. Herein, we develop an intelligent nitric oxide nanogenerator comprising isosorbide dinitrate (ISDN)-coated copper sulfide (CuS)/calcium carbonate (CaCO₃) core/shell nanoparticles (CuS@CaCO₃-ISDN) to target the acidic microenvironment of the infected diabetic wounds. Meaningfully, triggered by acid decomposition of CaCO₃, this nanogenerator can achieve a responsive and accelerated release of nitric oxide from ISDN through enzyme-mimicking redox processes that involve CuS nanoparticles and then inactivate biofilm bacteria through the pathways of oxidative stress and disruption of adenosine triphosphate (ATP)-related energy metabolism. Moreover, after eliminating the infection, the pH-responsive release of nitric oxide can promote the proliferation of blood vessels and tissue regeneration and accelerate diabetic wound closure. This study expands the use of nitric oxide donors in wound treatment by developing the enzyme-mimicking release strategy, and the pH-responsive core/shell nanogenerator is promising for a variety of anti-infection therapeutic applications.

Sale-based estimation of pharmaceutical concentrations and associated environmental risk in the Japanese wastewater system

Information on sales and emission of selected pharmaceuticals were used to predict their concentrations in Japanese wastewater influent through a >300 of pharmaceuticals data sink. A combined wastewater-based epidemiology and environmental risk analysis follow was established. By comparing predicted environmental concentrations (PECs) of pharmaceuticals in wastewater influent against measured environmental concentrations (MECs) reported in previous studies, it was found that the model gave accurate results for 17 pharmaceuticals (0.5 < PEC/MEC < 2), and acceptable results for 32 out of 40 pharmaceuticals (0.1 < PEC/MEC < 10). Although the majority of pharmaceuticals considered in the model were antibiotics and analgesics, pranlukast, a receptor antagonist, was predicted to have the highest concentration in wastewater influent. With regard to the composition of wastewater effluent, the Estimation Program Interface (EPI) suite was used to predict pharmaceutical removal through activated sludge treatment. Although the performance of the EPI suite was variable in terms of accurate prediction of the removal of different pharmaceuticals, it could be an efficient tool in practice for predicting removal under extreme scenarios. By using the EPI suite with input data on PEC in the wastewater influent, the PEC values of pharmaceuticals in wastewater effluent were predicted. The concentrations of 26 pharmaceuticals were relatively high (>1 μg/L), and the PECs of 6 pharmaceuticals were extremely high (>10 μg/L) in wastewater effluent, which could be attributed to their high usage rates by consumers and poor removal rates in wastewater treatment plants (WWTPs). Furthermore, environmental risk assessment (ERA) was carried out by calculating the ratio of predicted no effect concentration (PNEC) to PEC of different pharmaceuticals, and it was found that 9 pharmaceuticals were likely to have high toxicity, and 54 pharmaceuticals were likely to have potential toxicity. It is recommended that this is further investigated in detail. The priority screening and environmental risk assessment results on pharmaceuticals can provide reliable basis for policy-making and environmental management.

In vivo three-dimensional EPR imaging of nitric oxide production from isosorbide dinitrate in mice

Recently, in vivo electron paramagnetic resonance (EPR) spectroscopy and imaging have been widely used to investigate free radical distribution and metabolism in tissues, organs, and whole body of small animals. Endogenous nitric oxide (NO) is an attractive target of this method. In the present study, NO production from a nitrovasodilator, isosorbide dinitrate (ISDN), in live mice was investigated by in vivo EPR spectroscopy and imaging combined with the spin-trapping technique. A highly water-soluble Fe complex with N-(dithiocarboxy)sarcosine (DTCS) was used as an NO-trapping agent. Mice received [14N]-ISDN, and the Fe-DTCS complex subcutaneously exhibited the characteristic triplet EPR signal of the NO adduct [14NO-Fe(DTCS)2]2-. Using [15N]ISDN instead of [14N]ISDN, we were able to observe that the doublet EPR signal stemmed from the 15NO adduct, which directly demonstrated that NO was produced from ISDN. The three-dimensional EPR images of the upper abdomen of living mice showed that the NO adducts were distributed in the liver and the kidneys. This EPR image combined with the ex vivo EPR measurements of the blood suggested that NO production from ISDN occurred in the liver in this experimental condition.

Transdermal delivery of isosorbide 5-mononitrate from a new membrane reservoir and matrix-type patches

Isosorbide 5-mononitrate (5-ISMN) has a direct relaxing effect on vascular smooth muscle. In the present study we developed matrix and reservoir-type transdermal patches of 5-ISMN. We investigated the usefulness of a new film-forming material isolated from the roots of Salacia macrosperma to serve as rate-controlling membrane for the reservoir-type patches. Matrix-type patches were formulated using polyvinyl chloride. Permeation studies through rat skin were conducted on both types of patches using Teflon cells. The mean +/- SD flux values from the matrix- and reservoir-type patches were 99.55 +/- 22.89 and 31.82 +/- 8.31 micrograms/cm2.hr, respectively.

Pharmacokinetics of isosorbide dinitrate in healthy volunteers after 24-hour intravenous infusion

No studies have examined the pharmacokinetics of isosorbide dinitrate (ISDN) after infusion of long duration, even though such infusions are used in patients. We therefore measured ISDN and its active metabolites, isosorbide-5-mononitrate (IS5MN) and isosorbide-2-mononitrate (IS2MN), in plasma of 9 healthy volunteers who received a continuous intravenous infusion of ISDN for 24 hours at a dose rate that lowered diastolic blood pressure by 10% during the first 30 minutes of infusion. All subjects tolerated the infusion except one who experienced intolerable headache. Five subjects received 1 microgram.min-1.kg-1, one 2 micrograms.min-1.kg-1, and two 4 micrograms.min-1.kg-1 ISDN, whereas the full rate of 6 micrograms.min-1.kg-1 was used continuously in one subject. At all infusion rates the plasma concentrations of ISDN were higher at 24 hours than at earlier times, suggesting that a steady-state condition had not been reached at that time. The same was true for the mononitrate metabolites, which reached higher plasma concentrations and were cleared more slowly than the parent compound after the end of the infusion. Apparent elimination half-lives of ISDN, IS2MN, and IS5MN were 67 +/- 10 minutes, 115 +/- 13 minutes, and 272 +/- 38 minutes, respectively. Comparison of low-rate infusions (1 and 2 micrograms.min-1.kg-1) with high-rate infusions (4 and 6 micrograms.min-1.kg-1) showed that the plasma concentration ratios at 24 hours of mononitrate metabolites to parent drug and apparent plasma clearance of ISDN were almost halved at the higher infusion rates.

Evaluation of bioavailability and pharmacokinetics of two isosorbide-5-mononitrate preparations in healthy volunteers

The objective of this study was to determine both the pharmacokinetic parameters and the bioavailability of two commercial 20-mg isosorbide-5-mononitrate (IS-5-MN) preparations (test and reference preparation) after single oral administration. For this purpose, the test and the reference preparation were examined in 24 healthy male volunteers according to a randomized 2-way cross-over design, blood samples were withdrawn up to 24 hours postadministration, and plasma concentrations of IS-5-MN were quantified by a gas chromatography (GC) method. Both preparations led to peak plasma levels of approximately 360 ng/mL IS-5-MN in the mean 0.76 hour (test) and 0.94 hour (reference preparation) after application; the plasma half-lives were about 5.2 hours, and for the areas under the curve (AUC(0-infinity)), mean values of 2741 (test preparation) and 2742 hour.ng/mL (reference preparation) were found. The statistical comparison (analysis of variance, confidence intervals) of the pharmacokinetic parameters found in the study resulted in bioequivalence of both IS-5-MN preparations. The undesired side effects/concomitant symptoms observed are known to occur after IS-5-MN administration.

A combined single and multiple dose pharmacokinetic study of oral isosorbide-5-mononitrate in healthy volunteers

Pharmacokinetics of 20 mg isosorbide-5-mononitrate (IS-5-MN) after single and multiple administration of two different tablet formulations were investigated in twelve healthy human subjects using an open, randomized, two-way crossover experimental design. Pentacard 20 mg tablets were compared with Ismo 20 mg tablets. After single-dose administration, both preparations caused a rapid increase in IS-5-MN plasma levels with the peak plasma concentration occurring between 0.5 and 1.5 h. For both formulations, the mean plasma half-life was found to be approximately 5 h after a single dose. In steady state during multiple dosing (t.i.d. at 8 h dosing intervals), a reduced elimination rate was observed. In line with this observation, the area under the plasma concentration-time curve (AUC) for one 8 h dosing interval during multiple dosing was higher than the extrapolated AUC after a single dose. Based on statistical evaluation of the various relevant pharmacokinetic parameters calculated from the plasma concentrations occurring after single and multiple dosing, the tablet formulations are judged to be bioequivalent.

Concentrations of isosorbide dinitrate, isosorbide-2-mononitrate and isosorbide-5-mononitrate in human vascular and muscle tissue under steady-state conditions

The concentrations of isosorbide dinitrate (ISDN), isosorbide-5-mononitrate (IS-5-MN) and isosorbide-2-mononitrate (IS-2-MN) were determined in plasma (PL), saphenous vein wall (SV) and pectoral muscle (PM) from 8 patients undergoing coronary bypass surgery. The patients were pretreated for 2 days with ISDN 240 mg per day (standard release formulation) in 4 doses of 40 mg and one dose of 80 mg. The plasma and tissue samples were obtained during the operation, 10-12 h after the last dose. Isosorbide-2-mononitrate and isosorbide-5-mononitrate were present in plasma and tissues in the same concentration ranges with molar concentration ratios of 0.88 (IS-2-MN: PM/PL), 0.85 (IS-5-MN: PM/PL), 0.99 (IS-2-MN: SV/PL) and 1.06 (IS-5-MN: SV/PL). Mean ISDN concentrations in tissue were considerably higher than in plasma; the molar concentration ratios were 4.9 (SM/PL) and 7.21 (SV/PL). The accumulation of ISDN in vessel walls may contribute to its greater vascular action compared to the mononitrates, but it may also facilitate the development of tolerance during long-term treatment.

Relationship between pharmacokinetics and hemodynamic tolerance to isosorbide-5-mononitrate

Healthy male volunteers received three different dose regimens of a controlled-release form of isosorbide-5-mononitrate (IS-5-MN; 60 mg per tablet). Dose regimen I consisted of a single daily dose of 60 mg given for 5 days. Dose regimen II was started with a dose of 60 mg, followed by 30 mg 12 h later and thereafter every 8 h. The last dose, on the 5th day was again 60 mg. In dose regimen III 60 mg followed by 30 mg 6 h later were administered every day for 5 days. The peripheral arterial and venous effects of IS-5-MN during the first and last dosing interval were followed by changes in the finger pulse curve, standing systolic blood pressure, heart rate, and venous distensibility. Plasma concentrations of IS-5-MN were measured frequently following the first and the last dose. Following dose regimen I all hemodynamic effects produced by the first dose were maintained during the study. The maximal plasma concentrations were about 400 ng/ml and the trough value, lower than 100 ng/ml. Following dose regimen II the hemodynamic effects of IS-5-MN and sublingual glyceroltrinitrate were completely abolished on the 5th day. Trough plasma concentrations were approximately 300 ng/ml during the entire study period. Following dose regimen III pronounced hemodynamic effects were seen on the 1st day. However, a significant attenuation of the hemodynamic effects was measured on the 5th day, when trough plasma concentrations were between 100 and 230 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of isosorbide dinitrate, isosorbide-2-nitrate and isosorbide-5-nitrate in renal insufficiency after repeated oral dosage

The pharmacokinetics of isosorbide dinitrate (ISDN) and its two active metabolites isosorbide-2-nitrate (IS-2-N) and isosorbide-5-nitrate (IS-5-N) were studied in 20 patients with normal and impaired renal function after repeated oral doses of standard 20 mg tablets ISDN t.i.d. Blood samples were taken in the steady-state on days 2 and 14, and the plasma concentrations were measured by electron capture capillary gas chromatography. We found a wide variation of pharmacokinetic parameters (AUCss0-8 and t1/2) of ISDN, IS-2-N, and IS-5-N in our patients. No correlation was detected between AUCss0-8 or t1/2 and the degree of renal insufficiency. No drug accumulation was observed after 14 days of administration.

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.

Hemodynamic effects of oral isosorbide-5-mononitrate and dinitrate in ischemic heart failure

Isosorbide-5-mononitrate (ISMN), the main metabolite of isosorbide dinitrate (ISDN) was recently introduced in clinical use. The hemodynamic effects of oral ISMN and ISDN, administered in equal doses, were studied in a randomized, crossover fashion in 20 patients with pump failure of ischemic etiology. Baseline hemodynamic criteria for admission into the study were: pulmonary capillary wedge pressure (PCW) of at least 20 mmHg and systolic arterial pressure (AP) above 90 mmHg. Hemodynamic parameters were serially measured and systemic vascular resistance was calculated up to 6 h postadministration of either ISMN or ISDN single dose (40 mg). Maximal effects obtained were statistically significantly different from baseline. While ISMN and ISDN appeared to be equipotent in reducing the filling pressure, with a maximum effect reached in 60-120 min, the mononitrate maintained its effects for a longer period.

Acute and sustained effects of isosorbide 5-mononitrate in stable angina pectoris

Isosorbide 5-mononitrate (IS 5-MN) is an active metabolite of isosorbide dinitrate and is widely used as an antianginal agent. The acute and subacute (2 weeks) effects of IS 5-MN, 40 mg twice daily, were evaluated in 18 patients with stable angina pectoris using computerized exercise testing and a placebo-controlled, double-blind, randomized trial protocol. There were 2 phases of 2 weeks each in which patients received placebo or active IS 5-MN. Acute testing (8 patients) was performed 2 hours after the first dose and subacute testing 2 hours after the morning dose on day 14. Acute testing showed an increase in exercise time from a mean (+/- standard error of mean) of 8.2 +/- 0.6 minutes to 11.1 +/- 0.5 minutes (p less than 0.001) after a single dose of IS 5-MN. Time to 1 mm of ST depression increased significantly and peak exercise ST-segment depression decreased significantly. Rest and peak exercise heart rate increased significantly during acute testing with IS 5-MN; blood pressure did not change significantly. After 2 weeks of therapy, exercise time had not changed (9.9 +/- 0.6 with placebo to 9.7 +/- 0.6 minutes). The beneficial effects on ST-segment variables were sustained at 2 weeks. The data suggest that there is an attenuation of effect with respect to exercise time and sustained beneficial effect on the ST-segment variables. This may be a result of development of partial tolerance to IS 5-MN after 2 weeks of therapy.

Effects of isosorbide-5-mononitrate on exercise-induced hemodynamic changes in angina pectoris

Hemodynamic effects of isosorbide-5-mononitrate (ISMN) were studied in 14 patients with effort angina pectoris. Hemodynamic and echocardiographic data were obtained by angina-limited supine multistage bicycle ergometer exercise testing before and 120 minutes after single oral administration of 20 mg of ISMN. Compared with control exercise testing, the ST segment at peak exercise showed less depression after administration of ISMN (p less than 0.001). At rest, systolic and diastolic blood pressure decreased significantly after administration of ISMN (p less than 0.001 and p less than 0.01, respectively). At rest and at peak exercise, pulmonary artery wedge pressure (both p less than 0.001), left atrial volume (both p less than 0.001) and left ventricular end-diastolic volume (both p less than 0.05) decreased, whereas cardiac index, pressure-rate product and systemic vascular resistance did not change significantly after administration of ISMN. Average time to peak plasma ISMN concentration was 90 minutes and average peak plasma concentration was 460 ng/ml with an elimination half-life of 7 hours. These data suggest that the main mechanism of the antianginal action of ISMN is a reduction in left ventricular preload followed by diminution of myocardial oxygen requirements.

Isosorbide-5-mononitrate in the treatment of acute left ventricular failure following acute myocardial infarction

Eleven patients with acute left ventricular failure following acute myocardial infarction (mean pulmonary capillary wedge pressure [PCW] greater than 20 mmHg) were entered into an open, haemodynamic study of oral isosorbide-5-mononitrate (ISMN). Left ventricular failure was resistant to intravenous diuretic therapy. No patient received concurrent cardioactive drugs nor further diuretic therapy during the study period. Haemodynamic data were acquired via a flow-directed thermodilution catheter placed in the pulmonary artery. Baseline data were acquired prior to the intravenous administration of an ISMN challenge. Thereafter, oral ISMN (20 mg, 8 hourly) was administered over 48 h. Following intravenous ISMN challenge, mean PCW fell from 26.2 to 17.5 mmHg. Cardiac index fell from 2.4 to 2.3 l/min/m2 due to a fall in heart rate (103 to 96.8 beats/min) as stroke volume and blood pressure were unchanged. At 8 h following ISMN, two patients were withdrawn due to hypotension (systolic pressure less than 85 mmHg). In the remainder, PCW remained acceptable throughout 48 h (13.1 mmHg at 48 h), cardiac output, systemic blood pressure and heart rate showed no further significant change. These data suggest that ISMN is effective in the treatment of acute left ventricular failure following acute myocardial infarction.

Isosorbide 5-mononitrate effects on isolated rabbit aorta and vena cava: relationship between cyclic GMP and relaxation of vascular smooth muscle

The effects of isosorbide 5-mononitrate (5-ISMN) on vascular smooth muscle tone and cyclic GMP levels in isolated rabbit aorta and vena cava were compared. 5-ISMN induced concentration-dependent relaxation of noradrenaline-contracted strips of aorta and vena cava. 5-ISMN was over 100 times more potent in eliciting relaxation in vena cava than in aorta. Unlike 5-ISMN, 8-bromo cyclic GMP produced concentration-dependent relaxation with similar potency in both strips. The relaxation induced in both strips by 5-ISMN but not by 8-bromo cyclic GMP was inhibited by pretreatment with 5 X 10(-5) M methylene blue. The 5-ISMN-induced changes in tone of both strips were closely associated with those in cyclic GMP levels. 5-ISMN increased the cyclic GMP levels of both strips in a concentration-dependent manner. 5-ISMN was also considerably more potent in increasing cyclic GMP levels in vena cava than in aorta. This 5-ISMN-induced increases in cyclic GMP levels of both strips were inhibited by pretreatment with methylene blue. These results suggest that cyclic GMP could be involved in the 5-ISMN-induced relaxation of smooth muscle from both aorta and vena cava. Furthermore, the finding that 5-ISMN was more active on vena cava than on aorta both to cause relaxation and increase cyclic GMP levels indicates that cyclic GMP-mediated vasodilatation may be responsible for the pharmacological action of 5-ISMN in vivo.

Pharmacokinetics and metabolism of isosorbide-dinitrate after intravenous and oral administration

The bioavailabilities of a conventional and two slow release 20 mg isosorbide dinitrate (ISDN) formulations were compared after oral administration in a three way cross-over study in 8 male volunteers. In a further group of 6 male volunteers the pharmacokinetics and metabolism of ISDN were investigated after intravenous infusion of a median dose of 14.1 mg for 2.5 h. A new analytical procedure was developed for the determination of isosorbide-5-mononitrate-2-glucuronide (IS-5-MN-2-Glu) and of isosorbide (IS). Kinetic data analysis on a molar basis was performed by the program package KIN-PAK providing model independent parameters. The median elimination half-lives of ISDN, IS-5-MN, IS-2-MN and IS-5-MN-2-Glu were 0.7, 5.1, 3.2 and 2.5 h, respectively. The systemic clearance of ISDN was 3.71/min and the distribution volume 2521 (3.1 l/kg). Apart from IS-5-MN-2-Glu, with a renal clearance of 5.9 l/min which suggested substantial glucuronidation in the kidney, the renal clearances of ISDN, IS-5-MN, IS-2-MN and the corresponding amounts excreted were negligible. 27.8% of the administered ISDN was excreted as IS-5-MN-2-Glu (8.7%) and IS (19.1%). Calculations based on the two mononitrate metabolites formed from ISDN showed an incomplete recovery of 84.1%, leading to the assumption that a simultaneous denitration to IS must have occurred. The rate of denitration at each nitro group in ISDN was almost twice as high as for the same position in the corresponding mononitrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Isosorbide dinitrate plasma concentrations and bioavailability in human subjects after administration of standard oral and sublingual formulations

The bioavailability of isosorbide dinitrate from formulations containing 5, 10, and 20 mg in tablets and 10 mg in solution for oral use and 5 mg in tablets for sublingual use, has been compared. When adjusted for dose, the peak mean plasma drug concentrations after oral administration were similar (e.g., 9.2 ng/mL after a 10-mg tablet) and about one-half that obtained after sublingual administration. Drug concentrations declined monoexponentially with mean half-lives ranging from 25-36 min. The relative bioavailability of isosorbide dinitrate from the oral formulations was not significantly different (p greater than 0.05) over the dose range studied, whereas the relative bioavailability after sublingual administration was about twice as great (p less than 0.01) as that after oral administration. The plasma drug concentration-time profile after administering the 5-mg sublingual tablet was similar to that obtained after administering orally a solution containing 10 mg, indicating that the latter should be as clinically effective as the former.

Saliva concentrations of isosorbide dinitrate, isosorbide 2-mononitrate and isosorbide 5-mononitrate

Correlations between saliva and plasma concentrations of isosorbide dinitrate (ISDN), and its active metabolites, isosorbide 2-mononitrate (2-ISMN) and isosorbide 5-mononitrate (5-ISMN) were examined. In the case of 5-ISMN (r = 0.98, P less than 0.01), saliva concentrations are probably reliable indices of the plasma concentrations of this drug and their measurement should provide a useful non-invasive procedure to assess compliance during the clinical use of products containing either ISDN or 5-ISMN: it may also be helpful in assessing the clinical pharmacokinetics of 5-ISMN. Less satisfactory correlations were obtained for ISDN (r = 0.84) and 2-ISMN (r = 0.83).

Pharmacokinetics of nicorandil, a new coronary vasodilator, in dogs

The kinetic disposition of nicorandil, N-[2-( nitroxy )ethyl]-3- pyridinecarboxamide (1), and its main metabolic product, N-[2-(hydroxy)-ethyl]-3- pyridinecarboxamide (II), was studied after administering intravenous and oral doses (2.5 mg/kg) of nicorandil to the same beagle dogs. The plasma concentrations were measured using a high-performance liquid chromatographic method. The pharmacokinetic data derived from intravenous administration of nicorandil were: t1/2, 0.73 plus/minus 0.11 h; Vdarea , 0.67 plus/minus 0.04 L/kg; and total plasma clearance, 13.50 plus/minus 1.05 mL/min/kg. After oral administration, nicorandil was rapidly absorbed (tmax, 0.58 plus/minus 0.11 h). The oral bioavailability was calculated as 0.72 plus/minus 0.07. The metabolic formation of the corresponding alcohol after intravenous and oral administration of the parent compound appeared to occur quite efficiently, and its elimination half-life (3.09 plus/minus 0.25 and 3.69 plus/minus 0.88 h after intravenous and oral administration of nicorandil, respectively) was longer than that of the parent compound. Since the dose employed in this study was much higher than the expected therapeutic doses, whether such a good bioavailability after a lower dose of the drug would be obtained in humans remains unanswered.

Determination of the two mononitrate metabolites of isosorbide dinitrate in human plasma and urine by gas chromatography with electron-capture detection

This paper describes a sensitive method for the determination of 2-isosorbide mononitrate and 5-isosorbide mononitrate as metabolites of isosorbide dinitrate at concentrations down to 2 ng/ml of 2-isosorbide mononitrate in both plasma and urine, and 5 ng/ml and 10 ng/ml of 5-isosorbide mononitrate in plasma and urine, respectively. The two mononitrate metabolites are extracted at basic pH into ethyl acetate, which is then evaporated to dryness. The residue is dissolved in a basic aqueous solution, which is washed with heptane and then re-extracted into ethyl acetate. The metabolites are quantitated by gas chromatography, using a 63Ni electron-capture detector. Conjugates of 2- and 5-isosorbide mononitrate are determined in urine after enzymatic hydrolysis.

Sex-related difference in the metabolism of isosorbide dinitrate following incubation in human blood

Isosorbide dinitrate (ISDN) (at a concentration of 100 ng/ml) was incubated aerobically at 37 degrees in whole blood from five male and five female normal volunteers. Following incubation of the blood samples for 0, 30, 60, 120, 240 and 360 min, the samples were centrifuged and the plasma was assayed for ISDN. A linear relationship was observed between the logarithm of the concentration of ISDN remaining and incubation time, and there was a significant difference between the T1/2 of ISDN in blood from males (90.6 min) and females (161.4 min). Very little ISDN metabolism was observed when ISDN was incubated with plasma rather than whole blood. When erythrocytes, resuspended in saline, were incubated with ISDN, there was a time-dependent loss of ISDN from the saline incubation medium. Investigation of the soluble fraction obtained after hemolysis of these erythrocytes also showed a time-dependent loss of ISDN. The saline incubation medium contained sufficient concentrations of the two major ISDN metabolites (isosorbide 2- and 5-mononitrate) to account for the observed disappearance of ISDN. The results indicate that ISDN is metabolized in the cellular compartment of blood and that the metabolic rate in males is greater than that in females.

Determination of isosorbide as a metabolite of isosorbide dinitrate in human urine by capillary gas chromatography with electron-capture detection

A method for the determination of isosorbide as a metabolite of isosorbide dinitrate at concentrations down to 200 ng/ml in human urine is described. After addition of a known amount of isomannide as internal standard to 50 microliter of urine, both compounds are extracted at basic pH into chloroform-isopropanol (4:1, v/v), which is then evaporated to dryness. They are then derivatized with heptafluorobutyric anhydride, and isosorbide is quantitated by capillary gas chromatography with electron-capture detection. A conjugate of isosorbide is determined in urine after enzymatic hydrolysis.

Clinical pharmacokinetics of organic nitrates

Plasma concentrations of glyceryl trinitrate (nitroglycerin), isosorbide dinitrate and isosorbide 2- and 5-mononitrates in man have been measured after administration via different routes. Appropriate precautions have to be taken in the administration of these agents (to avoid loss during intravenous infusion), and in their sampling and assay. Pharmacokinetic calculations based on plasma concentrations should be viewed with caution, as the data on which these calculations are based are often very limited, and the very rapid disappearance of for example glyceryl trinitrate from plasma makes the choice of an appropriate kinetic model and exact calculations difficult. Glyceryl trinitrate disappears from plasma within a few minutes, and a high apparent volume of distribution and a very high systemic clearance are found. After oral administration, plasma concentrations are very low; with sublingual or cutaneous administration, higher plasma concentrations can be obtained, suggesting a high first-pass extraction after oral administration, but quantitative data on bioavailability are lacking. For isosorbide dinitrate the systemic clearance, although high, is lower than for glyceryl trinitrate; disappearance from the plasma is slower and plasma concentrations after different routes of administration are much higher. Here too, quantitative data on bioavailability are lacking. High plasma concentrations of isosorbide 2-mononitrate and isosorbide 5-mononitrate are found in plasma after administration of isosorbide dinitrate. These metabolites have a good bioavailability, and half-lives of around 2.5 hours for isosorbide 2-mononitrate and 5 hours for isosorbide 5-mononitrate. Only very limited data are available about the influence of disease states and interactions with food and other drugs on the kinetics of the organic nitrates. It is very difficult to correlate the effects of the nitrates to their plasma concentrations; counter-regulation, development of tolerance, and the presence of metabolites could disturb the interpretation of such a relationship. It is at present impossible to predict the pharmacological effects or the efficacy of organic nitrates on the basis of their plasma concentrations.

Pharmacokinetics of intravenous isosorbide-dinitrate

The kinetics of isosorbide dinitrate (ISDN) after i.v. administration and the absolute availability of an oral slow release preparation (SR) were studied in young healthy volunteers. ISDN and the 2- and 5-mononitrates of isosorbide (2-MN, 5-MN) were determined by GLC. After i.v. administration plasma levels of ISDN declined biexponentially and could be adequately described by an open two compartment body model. Distribution half-life was extremely rapid (2-5 min). Terminal disappearance had a half-life of 67 (62-75) min (mean, range). Total plasma clearance was 1.6 (1.2-2.2) litres X min-1, thus approaching liver blood flow. Nevertheless, absolute systemic availability (F) or oral ISDN amounted to 22% (16-29%). Assuming that oral ISDN is completely absorbed and blood levels do not exceed serum levels, an upper limit of hepatic clearance (liver blood flow 1.5 litres X min-1 X (1-F/100)) can be estimated, which is significantly smaller (p less than 0.05) than the measured clearance. This finding is best interpreted by assuming that ISDN is partly eliminated by extrahepatic routes, which is further substantiated by a different pattern of metabolites after i.v. and oral dosing. Whereas after i.v. administration more 2-MN is produced, 5-MN is the main metabolite after oral ISDN. Since the glutathione-S-transferases are found in the cytosol of most cells, it seems likely that other organs than the liver contribute to the metabolism of ISDN.

Pharmacokinetics of isosorbide dinitrate in rhesus monkey, cynomolgus monkey, and baboon

At 2 min after intravenous injection of isosorbide dinitrate (1 mg/kg), mean plasma drug concentrations were 565 +/- 66 (SD), 586 +/- 43, and 1572 +/- 253 ng/ml in the rhesus monkey, cynomolgus monkey, and baboon, respectively. Following a relatively short distribution phase, mean plasma concentrations declined with half-lives of 62, 23, and 24 min in these three species, respectively. The time course of plasma concentrations could be described by a two-compartment open model, although a one-compartment open model was adequate for obtaining some pharmacokinetic parameters. Statistically significant differences among the species were observed in areas under the plasma concentration-time curves, plasma half-lives, and volumes of distribution. The pharmacokinetics kinetics of isosorbide dinitrate in baboons most closely resembled those in humans.

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.

A standard approach to compiling clinical pharmacokinetic data

A standard format for a Clinical Pharmacokinetic Summary is proposed. It consists of a heading, tables, notes, and references for each drug reviewed. The table presents a unified and logical set of clinically useful population pharmacokinetic parameters. They concern four major areas: absorption, distribution, elimination, and the relationship of concentration to effect. Within each major group, parameters dealing with extents and rates of processes are given. Each such parameter is really two: a population mea value (for example, average volume of distribution) and the standard deviation of individual values about this mean. The first value allows individual predictions of dosage or drug level to be made; the second allows computation of the likely proximity of subsequently observed quantities to those predictions. The table presents single consensus values for each population parameter, rather than a list of values. A procedure for computing these consensus values, and for revising them in the light of new data, or reinterpreted old data, is given. Examples of Summaries are given. The method appears applicable to a variety of drugs. We suggest our approach as a standard one for preparing Clinical Pharmacokinetic Summaries, and urge our colleagues to consider it for that purpose.

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.

Measurement of plasma concentrations of isosorbide dinitrate

Concentrations of the vasodilator isosorbide dinitrate (ISDN) in human plasma can be measured with good sensitivity (about 0.2--0.5 ng ml-1) using electron-capture gas chromatography after a one-stage extraction. The mean recovery of ISDN from plasma was 83 per cent +/- 9 standard deviation (S.D.). The precision of the method for the measurement of ISDN in plasma ranged from +/- 14 per cent at 1 ng ml-1 to +/- 7 per cent at 5 ng ml-1 to +/- 4 per cent at 50 ng ml-1. The 95 per cent confidence limits of the least-squares regression calibration line forced through the origin were +/- 100 percent at 1 ng ml-1, +/- 11 per cent at 10 ng ml-1, and +/- 8 per cent at 30 ng ml-1. The method has been used to assay many samples withdrawn after doses of drug at therapeutic levels to normal subjects.

Pharmacokinetics of isosorbide dinitrate after intravenous infusion in human subjects

Plasma concentrations of isosorbide dinitrate have been measured after intravenous infusion of drug at a rate of 5.0 mg h-1 for 150 min and after single equal oral doses of 12.5 mg of drug in solution to two normal human subjects. During the infusion, uneven plateau concentrations were approached after 30 min. The calculated average steady-state plasma levels were 258 ng ml-1 and 514 ng ml-1 in the two subjects respectively. The half-life of elimination of isosorbide dinitrate after termination of the infusion was 9--10 min. After oral doses, peak plasma levels of 26.6 ng ml-1 and 12.7 ng ml-1 occurred at 10 min and 20 min in the two subjects respectively. The terminal half-life of drug after the oral doses was much longer than the elimination half-life (about 10 min), and was associated with the absorption phase. Fairly good agreement was obtained between the observed concentrations and those predicted by a one-compartment open model. The systemic availability of isosorbide dinitrate after the oral doses was up to only 3 per cent of the equal doses infused, indicating that presystemic elimination processes accounted for very large proportions of the oral doses. The systemic clearances of drug after infusion of 0.32 l min-1 and 0.16 l min-1 were unexpectedly low for a drug of reported high liver extraction ratio.

Improved method for the rapid determination of isosorbide dinitrate in human plasma and its application in pharmacokinetic studies

A rapid, accurate and highly sensitive method was developed for the determination of isosorbide dinitrate in human plasma. Concentrations in the lower nanogram and subnanogram range are determined by a one-step extraction of 2 ml plasma, containing 4 ng/ml nitroglycerine as internal standard, with 5.5 ml n-pentane. The extract is subjected to gas--liquid chromatography--electron capture detection analysis. The lower limit of quantitation is 200 pg/ml, but concentrations as low as 50 pg/ml are still detectable. The method allows the quantitative determination of isosorbide dinitrate plasma levels in man following a 5 mg sublingual administration up to four hours after application.

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.

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.