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

Determination of isosorbide-5-mononitrate in human plasma by high-resolution gas chromatography

A method for the determination of isosorbide-5-mononitrate (5-ISMN) in human plasma by capillary gas chromatography with electron-capture detection was developed and applied to clinical samples. 9-Fluorenone was used as an internal standard, ethyl acetate was employed for liquid-liquid extraction. The advantage of the extraction procedure is the possibility of a direct injection of the plasma extract, without solvent removal/reconstitution of the sample. The precision and accuracy of the method were satisfactory in the concentration range 10-1600 ng/ml. The lower limit of quantification was 10 ng/ml.

Simultaneous determination of isosorbide dinitrate and its mononitrate metabolites in human plasma by capillary gas chromatography with electron-capture detection

A method for the simultaneous determination of isosorbide dinitrate (ISDN) and its mononitrate metabolites (2- and 5-ISMN) in human plasma by capillary gas chromatography with electron-capture detection was developed. Two internal standards were used: isomannide dinitrate (IMDN) for the determination of ISDN and isomannide mononitrate (IMMN) for the determinations of 2- and 5-ISMN. After addition of the internal standards, the compounds were isolated from plasma by solid-liquid extraction. They were determined by gas chromatography using an electron-capture detector. The reproducibility and accuracy of the method were found suitable in the range of concentrations 2.5-83 ng/ml for ISDN, 2.6-208 ng/ml for 2-ISMN and 2.3-1010 ng/ml for 5-ISMN. The limit of quantitation (LOQ) was about 2.5 ng/ml for each compound. The method was applied to clinical samples.

Investigation of a possible pharmacokinetic interaction between ibopamine and isosorbide-5-mononitrate

The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.

Nitrates in the elderly. Pharmacological considerations

Although a significant proportion of patients receiving nitrates are elderly, surprisingly little published work is available describing the pharmacokinetics and pharmacodynamics of these agents in elderly patients. The lack of pharmacokinetic data is related to the difficulty in assaying nitrates and there are at present no definitive data describing the effect of aging on their bioavailability or elimination. A common finding in old age is of decreased hepatic first-pass metabolism. This would affect isosorbide-2-mononitrate and isosorbide-5-mononitrate less than isosorbide dinitrate and nitroglycerin (glyceryl trinitrate). Venous responsiveness to nitrates does not appear to alter with age, so that pharmacodynamic properties would not be expected to alter. However, decreased baroreflex function causes an increased tendency for posturally related side effects to occur. Mechanisms of tolerance are likely to be unaltered but any possible alteration in quantitative aspects of tolerance has not been studied. Nitrate therapy in the elderly would benefit from systematic investigation. At the moment, therapy needs to be titrated to the individual patient, with care taken to avoid age-related side effects by careful initiation of therapy and appropriate reviews of each patient.

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.

Influence of exercise on plasma concentrations of isosorbide dinitrate

As the fall in hepatic blood flow caused by exercise is expected to decrease the elimination of high extraction drugs, the influence of exercise on the fate of the anti-anginal drug isosorbide dinitrate has been assessed. Isosorbide dinitrate 10 mg was given orally, after an overnight fast, on 2 different days to 7 healthy volunteers and the plasma concentrations of the parent compound and its mononitrate metabolites were measured. Heavy bicycle exercise from the 45th to the 105th min after intake of the drug on one of the experimental days did not change the plasma isosorbide dinitrate concentrations as compared to those on the rest day. The concentrations of both mononitrates were lower on the exercise day, but the difference was already present before the exercise started.

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.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

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)

Determination of isosorbide 5-mononitrate in human plasma by capillary column gas chromatography

An electron-capture gas chromatographic method for the determination of isosorbide 5-mononitrate in human plasma using a capillary column is described. Isosorbide 5-mononitrate and the internal standard (isosorbide dinitrate) are extracted from the alkalinized plasma with ether. The lower limit of detection for isosorbide 5-mononitrate is 1 ng/mL of plasma.

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.

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.

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.

Determination of isosorbide dinitrate and its mononitrate metabolites in human plasma by high-performance liquid chromatography-thermal energy analysis

An accurate and sensitive method for the simultaneous determination of isosorbide dinitrate and its 2- and 5-mononitrates in human plasma has been developed. Following extraction of 3.0 ml of plasma with 12.0 ml of dichloromethane-ethyl acetate (1:1) the extract is subjected to high-performance liquid chromatography employing a Zorbax NH2 column. The eluent stream is introduced into a thermal energy analyser, employing chemiluminescence as a specific means of detection. The minimum quantifiable level of the compound in plasma is 200 pg/ml allowing the quantitation of isosorbide dinitrate in human plasma following single oral administration. Nitroglycerin is employed as internal standard.

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.