Methods for the quantitation of nitroglycerin and its metabolites in human plasma

Liquid Chromatographic Method Development for Quantification of Inorganic Nitrite and Nitrate Impurities from Nitroglycerin Drug Substance by Using Ion-Pair Reagents with Liquid-Liquid Extraction Technique

A large number of laboratory studies have reported Nitrite (NO2-) and Nitrate (NO3-) to be among the most common degradation products of the high-explosive Nitroglycerin drug substance. A novel, simple, robust and rapid reversed-phase high-performance liquid chromatography method has been developed for quantification of inorganic Nitrite and Nitrate impurities from Nitroglycerin drug substance. Successful separation was achieved in isocratic elution, using Inertsil C8-3, (250 × 4.6 mm, 5.0 μm) column, with mobile phase consisting of pH 7.0 tetrabutyl ammonium hydrogen sulfate buffer, methanol and acetonitrile (96:02:02, v/v/v). Flow rate was monitored at 2.0 mL min-1 and ultraviolet detection at 220 nm. The present work describes the role of an ion-pair reagent in the separation of polar compounds and liquid-liquid extraction technique for separation of polar and non-polar compounds. Nitroglycerin was subjected to various stress conditions to demonstrate the stability-indicating power of the method. The performance of the method was validated as per present International Council for Harmonisation (ICH) guidelines for specificity, linearity, accuracy, precision, ruggedness and robustness. The developed method can be a valuable alternative to the current ion-exchange chromatographic method mentioned in the literature. To the best of our knowledge, a rapid Liquid Chromatography (LC) method, which separates inorganic Nitrite and Nitrate impurities of Nitroglycerin, disclosed in this investigation was not published elsewhere.

Simultaneous determination of nitroglycerin and dinitrate metabolites in metabolism studies using liquid chromatography-mass spectrometry with electrospray ionization

We have developed a liquid chromatographic-mass spectrometric method for the simultaneous determination of nitroglycerin (NTG) and its active metabolites, glyceryl 1,2-dinitrate (1,2-GDN) and glyceryl 1,3-dinitrate (1,3-GDN), for metabolism studies in cell cultures. 1,2,4-Butanetriol-1,4-dinitrate was chosen as an internal standard. Using a linear gradient of water/methanol containing 0.025 mM NH(4)Cl, the compounds were eluted within 12.5 min on an Allure Aqueous C(18) column (100 mm x 2.1 mm). Detection and quantification was achieved with multiple reaction monitoring in the negative ion mode. Intra- and inter-day variabilities for simultaneous determination of the three nitrates were below 10 and 18%, respectively, over a range of NTG and GDN concentrations of 0.5-15 ng/ml. The lower limit of quantification was found to be about 0.01 ng on column. Application of this method was illustrated through in vitro metabolism studies of NTG in culture media bathing LLC-PK1 cells and human vascular smooth muscle cells (HA-VSMC) at 37 degrees C. The degradation half-life of NTG was found to be 4.5 +/- 0.4 h and 39.2 +/- 0.02 h, respectively, for LLC-PK1 cells versus HA-VSMC. At 5 h, the 1,2-GDN versus 1,3-GDN metabolite distribution ratio in the bathing medium was found to be 1.5 +/- 0.1 and 0.2 +/- 0.02 for LLC-PK1 and HA-VSMC cells, respectively. With this method, the degradation half-life of NTG in rat plasma at 37 degrees C was shown to be 26.8 +/- 1.8 min, consistent with previous values obtained using gas chromatography.

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.

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.

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.

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.

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.

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.