Application of high-pressure liquid chromatography and thermal energy analyzer to analysis of trinitroglycerin and its metabolites in blood

Improved gas chromatographic assay for the simultaneous determination of nitroglycerin and its mono- and dinitrate metabolites

A sensitive, specific capillary gas chromatographic-electron-capture detection method for the simultaneous determination of nitroglycerin (GTN), 1,2- and 1,3-glyceryl dinitrate (1,2-GDN and 1,3-GDN, respectively) and 1- and 2-glyceryl mononitrate (1-GMN and 2-GMN, respectively) is reported. The minimum quantifiable concentration for GTN, GDNs and GMNs is 0.4 ng/ml in plasma, with extraction recoveries for GMNs greater than 76% and for GTN and the GDNs greater than 95%. Over the full range of quantifiable concentrations the inter-run assay precision and accuracy were less than 13 and 11%, respectively, for all five nitrates. Similar intra-run assay precision and accuracy values were found. The method was employed in the preliminary in vitro examination of GTN, GDN and GMN kinetics in human blood. Following addition of GTN to human blood, the ratio of 1,2-GDN to 1.3-GDN maximum concentrations (Cmax) was ca. 7:1, reflecting preferential denitration of the GTN molecule at the primary positions, while the Cmax ratio for 2-GMN to 1-GMN in this system was ca. 6:1, representing a highly selective if not specific primary denitration of the 1,2-GDN molecule. Following the intravenous administration of 1,2-GDN to five healthy male volunteers, 2-GMN/1-GMN Cmax ratios averaged 8.8:1, representing a highly selective but not specific formation of 2-GMN from the 1,2-GDN molecule. The assay will find utility in in vitro studies attempting to address the molecular pharmacology of GTN and its metabolites, and in in vivo clinical pharmacology studies attempting to address the relationship between pharmacokinetics and pharmacodynamics of GTN and its metabolites.

Assay of glyceryl trinitrate, isosorbide dinitrate, and their metabolites in plasma by large-bore capillary column gas-liquid chromatography

Two large-bore capillary columns, one with dimethyl polysiloxane (HP-1) as the stationary phase and the other with phenyl (50 per cent) methyl (50 per cent) polysiloxane (DB-17), were used to develop gas-liquid chromatographic (GLC) assays for measuring isosorbide dinitrate (ISDN), glyceryl trinitrate (GTN), and their metabolites. ISDN, isosorbide-2-mononitrate (2-ISMN), and isosorbide-5-mononitrate (5-ISMN) in plasma, ranging in concentration from 1 to 300 nM, and GTN, glyceryl-1,2-dinitrate (1,2-GDN), and glyceryl-1,3-dinitrate (1,3-GDN), ranging in concentration from 3 to 60 nM in plasma, were analysed on both columns. GLC analysis yielded baseline resolution of the analytes. The method using the dimethyl polysiloxane column gave a lower limit of detectability for GTN of 0.75 nM (signal/noise (s/n) = 2), and the procedure using the phenyl-methyl column provided a lower limit of detectability for ISDN of 81 pM (s/n = 2). The large-bore column GLC procedures exhibited shorter retention times for both ISDN and GTN than those previously reported for capillary-column assays. The chromatographic resolution of analytes and column efficiency of the large-bore capillary columns were comparable to the results previously found using capillary-column GC. The assays for ISDN and GTN have been shown to be appropriate for pharmacokinetic studies in volunteers and patients. We determined that the HP-1 column is appropriate for the analysis of GTN and metabolites, and the DB-17 column is suitable for analysis of ISDN and its metabolites. We conclude that the use of large-bore capillary columns provides rapid and reliable GLC assays for organic nitrates.

Simultaneous determination of nitroglycerin and its dinitrate metabolites by capillary gas chromatography with electron-capture detection

A sensitive gas chromatographic-electron-capture detection method for the simultaneous determination of the antianginal drug nitroglycerin (GTN) and its dinitrate metabolites (1,2-GDN and 1,3-GDN) was developed. Human plasma samples (1 ml) spiked with 2,6-dinitrotoluene as the internal standard were extracted once with 10 ml of a methylene chloride-pentane mixture (3:7, v/v). Using this solvent system, less contaminants are extracted into the organic phase from plasma, resulting in cleaner chromatograms and prolonged column life. A break point was observed on the standard curves of GTN and GDNs. The two linear regions for the detectable concentrations of GTN are 0.025-0.3 and 0.3-3 ng/ml and for 1,2-GDN and 1,3-GDN they are 0.1-1 and 1-10 ng/ml. The limits of detection by this method for GTN, 1,2-GDN and 1,3-GDN in plasma are 0.025, 0.1 and 0.1 ng/ml, respectively.

Glyceryl-1-nitrate pharmacokinetics in healthy volunteers

The plasma kinetics and urinary excretion of glyceryl-1-nitrate (G-1-N), a metabolite of glyceryl trinitrate with antianginal potential, were investigated in 10 healthy male volunteers, after intravenous infusion and oral administration of 20 mg G-1-N. The apparent volume of G-1-N distribution was 601 corresponding to 0.761 kg-1 body weight, on average. It is suggested that total body water is the principal biological correlate of the hydrophilic drug. Mean intravenous clearance was 283 ml min-1 or 3.61 ml min-1 kg-1. The average of elimination half-lives were 2.50 +/- 0.36 (s.d.) h after the intravenous and 2.54 +/- 0.40 (s.d.) h after the oral dose. Inter-subject variances of pharmacokinetic parameters were low compared to variances reported for glyceryl trinitrate. The coefficient of intra-subject variation of the elimination half-lives was 8.8%. 5.5% (i.v.) and 5.4% (p.o.) of the administered dose were excreted into urine up to 48 h after the administration. 1% (i.v.) and 1.5% (p.o.) were in the conjugated form. The oral dose was rapidly and almost completely absorbed. The oral bioavailability on the basis of areas under the curve amounted to 88.6% on the average. For clinical use, owing to its high oral bioavailability, long residence in the body, inactivation by metabolic conversion, and good predictability of kinetic parameters, G-1-N offers advantage over glyceryl trinitrate.

Determination of the two dinitrate metabolites of nitroglycerin in human plasma by capillary gas chromatography with electron-capture detection

This paper describes a sensitive method for the specific determination of 1,2-glyceryl dinitrate and 1,3-glyceryl dinitrate as metabolites of nitroglycerin at concentrations down to 250 pg/ml plasma. After addition of a known amount of 2-isosorbide mononitrate as internal standard, plasma is introduced onto an Extrelut cartridge and the compounds of interest are eluted with dichloromethane. The glyceryl dinitrates are then quantitated by capillary gas chromatography with electron-capture detection.

Gas chromatographic assay of glycerol mononitrates in biological samples

A new gas chromatographic analysis of glycerol 1-nitrate and glycerol 2-nitrate is described. The method is suitable for a variety of biological samples and can detect down to the low nanogram range. An extract of the sample to be analysed is treated with phenylboronic acid. The glycerol mononitrates rapidly form cyclic boronates, with five- and six-membered rings, respectively, which can then be separated by gas chromatography and detected by an electron-capture detector.

Clinical pharmacokinetics of glyceryl trinitrate following the use of systemic and topical preparations

Glyceryl trinitrate has been used for more than a century for the treatment of angina pectoris and, more recently, for the treatment of congestive heart failure. The introduction of transdermal delivery systems has renewed the controversy regarding the efficacy of the drug, mainly in the light of the development of tolerance. With concentrations of the order of 1 microgram/L or less, the measurement of glyceryl trinitrate in plasma is not easy: gas chromatography with electron capture detection has been used widely but recently gas chromatography-mass spectrometry has provided satisfactory results. Assay problems are most likely to be responsible for some of the unexpected results reported. Further factors which may confound the results of the study of plasma concentrations are the rapid metabolism of glyceryl trinitrate in blood in vitro, adsorption to containers and infusion sets, and the uptake and/or metabolism in vessel walls. From the intravenous infusion data, the large interindividual variability in plasma concentrations of glyceryl trinitrate is apparent. The plasma half-life is about 2 to 3 minutes; plasma clearance values reported vary from 216 to 3270 L/h, indicating extensive non-hepatic metabolism. With transdermal administration, mainly with the transdermal controlled delivery systems, plasma concentrations of glyceryl trinitrate appear to be maintained for up to 24 hours, with large interindividual variations. Despite the ability to maintain, for example with the transdermal delivery systems, relatively constant concentrations of glyceryl trinitrate, it has not been possible to find a relationship between plasma concentrations and pharmacological or clinical effects. This is in part due to the attenuation of the effects with time; from the available data it is clear that this attenuation occurs at a pharmacodynamic level (reflex adaptation and tolerance) and not at the pharmacokinetic level.

Pharmacokinetics of oral glycerol-1-nitrate

The plasma kinetics and urinary excretion of glycerol-1-nitrate (G-1-N), a water soluble metabolite of glycerol trinitrate with anti-anginal potential, have been investigated in healthy human volunteers following oral doses of 10, 20 and 40 mg tablets and 20 mg as drops. In all volunteers G-1-N was rapidly absorbed. The mean concentration-time curves peaked 40 min after administration of tablets at 144 ng/ml (10 mg), 308 ng/ml (20 mg) and 573 ng/ml (40 mg). After the drops the peak of 324 ng/ml occurred at 1 h. The areas under the G-1-N concentration-time curve and the G-1-N peak heights were linear with dose. Tablets and drops can be regarded as bioequivalent with respect to area under the curve and elimination half-life. The bioavailability of the 20 mg tablet relative to the 20 mg drops was 98.6% in terms of area under the curve. The mean apparent half-life of G-1-N elimination from plasma was 2.69 +/- 0.67 h (n = 46). The mean residence time of G-1-N in the body was 4.65 h compared to 0.28 h for glycerol trinitrate after buccal administration. Female volunteers were found to have significantly lower areas under the curve than male volunteers. The difference was probably due to differences in body weight. Renal excretion does not play an important role in the elimination of oral G-1-N from the body. An overall average of 5.42% of the G-1-N dose was excreted in the urine; free drug accounted for 4.02% and conjugated drug for 1.40%.

Quantitative determination of nitroglycerin in human plasma by capillary gas chromatography with electron-capture detection

A sensitive method for the selective determination of nitroglycerin at concentrations down to 50 pg/ml in human plasma is described. After the addition to plasma of a known amount of butane-1,2,4-triol trinitrate as internal standard, both compounds are extracted into hexane. Nitroglycerin is then quantitated by capillary gas chromatography with electron-capture detection.

Determination of nitroglycerin and its dinitrate metabolites in human plasma by high-performance liquid chromatography with thermal energy analyzer detection

A highly selective and sensitive high-performance liquid chromatographic assay employing a thermal energy analyzer as the detector for nitroglycerin and its dinitrate metabolites in human plasma has been developed. Prior to chromatography the method employs a simple one-stage extraction step. Nitroglycerin and its dinitrate metabolites are then chromatographed on a 10-micron nitrile bonded phase column using an internal-external standard method. The nitroglycerin and its 1,2,3-propanetriol-1,3- and -1,2-dinitrate metabolites (glyceryl-1,3- and -1,2-dinitrate) have a retention time of 8.5, 10.5, and 11.5 min, respectively at a flow rate of 2.0 mL/min for a mobile phase of 5% v/v acetone in n-hexane. The limits of sensitivity were 0.05 ng/mL for nitroglycerin and 0.25 ng/mL for the dinitrate metabolites. Linearity of response was observed over the 0.1-2.0-ng/mL range for nitroglycerin and 0.5-10.0-ng/mL range for the dinitrate metabolites. Blood level data from a pilot study with human volunteers in receipt of an oral form of nitroglycerin is presented.

Determination of picogram nitroglycerin plasma concentrations using capillary gas chromatography with on-column injection

A specific, sensitive, and precise capillary gas chromatographic (GC) assay capable of analyzing picogram concentrations of nitroglycerin in human plasma was developed. The analytical procedure involves a double extraction of 1 mL of plasma with pentane, after the addition of internal standard (1 ng of 2,6-dinitrotoluene), followed by evaporation and reconstitution in 50 microL of heptane. The extract (1 microL) was injected onto a capillary column using the on-column injection technique. The GC oven temperature was programmed from 120 degrees C to 180 degrees C at a rate of 5 degrees C/min. The oven temperature was then programmed to 250 degrees C and was maintained for 10 min. The nitroglycerin and internal standard retention times were 8.6 and 11.4 min, respectively. The position of the end of the capillary column inside the detector is a critical determinant of sensitivity: the column exit must be positioned such that nitroglycerin adsorption to the detector is minimized (i.e., sensitivity maximized). The assay limit of quantitation was 25 pg/mL (CV = 7.6%) using 1 mL of plasma. This GC assay, specific for nitroglycerin in the presence of its metabolites, isosorbide dinitrate, and several other drugs, may be used to quantitate plasma levels obtained after therapeutic nitroglycerin doses.

Application of high-performance liquid chromatography with synchronized accumulating radioisotope detector to analysis of glyceryl trinitrate and its metabolites in rat plasma

A new, sensitive, and specific high-performance liquid chromatographic method for the quantitative analysis of [14C]glyceryl trinitrate and its four metabolites in plasma is described. The drugs are extracted from 0.05 ml of plasma with methanol and analyzed by high-performance liquid chromatography using a synchronized accumulating radioisotope detector. The limit of detection is 0.2 ng per injection. The within-day coefficient of variation is 5.9% at a concentration of 27.0 ng per ml of plasma. The method was applied to single-dose pharmacokinetics of glyceryl trinitrate in rat.

Measurement of plasma concentrations of vasodilators and metabolites by the TEA Analyzer

The determination of therapeutic levels of glyceryl trinitrate (GTN), isosorbide dinitrate (ISDN), pentaerythritol tetranitrate (PETN), and their metabolites in human plasma was conducted using the TEA Analyzer interfaced to a high-performance liquid chromatograph (HPLC-TEA). Chromatographic separation of these compounds was accomplished under isocratic HPLC conditions. The sensitivity of the instrument was established to be 0.1 ng for each of the three nitrate esters. At the 5 ng ml-1 plasma fortification level, the precision of the method gives mean relative standard deviations (RSD) of +/- 10.2 per cent, +/- 6.5 per cent, and +/- 5.9 per cent for GTN, ISDN, and PETN, respectively. The recoveries for the nitrate esters and their metabolites from human plasma over the range 1-50 ng ml-1 are presented. The specific and sensitive HPLC-TEA method developed in this study provides a reliable and rapid assay for the routine analysis for metabolism or bioavailability studies of nitrate esters and their metabolites in plasma of blood, with a detection limit as low as 1 ng ml-1.

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.

Gas chromatographic mass spectrometric determination of 1,2,3-propanetrioltrinitrate (nitroglycerin) in human plasma using the nitrogen-15 labelled compound as internal standard

A method for the quantitative determinatio of 1,2,3-propanetrioltrinitrate (nitroglycerin) in human plasma by gas chromatography mass spectrometry has been developed. After addition of 1,2,3 and methyl acetate (90 : 10). The extracts are purified by partition between, first, the extraction solvent and a mixture of acetonitrile and water (60 : 40) and, secondly, the resultant aqueous phase and benzene. THe solvent is evaporated to a small volume before injection. The fragment ions at m/z 46 and 47 are monitored for the measurement of the [NO2]+ and [15NO2]+ ions using electron impact ionization. The mean recovery (%) +/- SD in blind plasma samples spiked with amounts in the concentration range 0.35-3.52 nmol 1(-1), was 97.4 +/- 9.0 (n = 58). Within a day, recovery experiments gave rise to coefficients of variation of 9.6, 6.4 and 2.7% at the levels 0.44, 0.88 and 11 nmol 1(-1), respectively. Concentrations in plasma down to about 0.2 nmol 1(-1) (50 pg ml-1) could be estimated. Percent recovery of duplicate determinations in the range 0.5-1.96 nmol 1(-1) +/- SD was 99.4 +/- 6.0 (n = 80).

Quantitative determination of nitroglycerin in human plasma by capillary gas chromatography negative ion chemical ionization mass spectrometry

A quantitative method for determination of nitroglycerin in human plasma was developed. Nitroglycerin and the internal standard (butane-1,2,4-triyl trinitrate) were extracted from plasma with pentane. The extracts were analysed by gas chromatography mass spectrometry using fused silica capillary columns and electron capture negative ion chemical ionization. The quantitation limit of the method was about 50 pg ml-1. Linear calibration curves were obtained in the range of 50-1600 pg ml-1. Precision at the level of 100 pg ml-1 was 4%.