GLC determination of nitroglycerin and isosorbide dinitrate in human plasma

Clinical pharmacokinetics and pharmacodynamics of glyceryl trinitrate and its metabolites

This review discusses the pharmacokinetics and pharmacodynamics of glyceryl trinitrate (nitroglycerin; GTN) pertinent to clinical medicine. The pharmacokinetics of GTN associated with various dose regimens are characterised by prominent intra- and inter-individual variability. It is, nevertheless, important to clearly understand the pharmacokinetics and characteristics of GTN to optimise its use in clinical practice and, in particular, to obviate the development of tolerance. Measurements of plasma concentrations of GTN and of 1,2-glyceryl dinitrate (1,2-GDN), 1,3-glyceryl dinitrate (1,3-GDN), 1-glyceryl mononitrate (1-GMN), and 2-glyceryl mononitrate (2-GMN), its four main metabolites, remain difficult and require meticulous techniques to obtain reliable results. Since GDNs have an effect on haemodynamic function, pharmacokinetic analyses that include the parent drug as well as the metabolites are important. Although the precise mechanisms of GTN metabolism have not been elucidated, two main pathways have been proposed for its biotransformation. The first is a mechanism-based biotransformation pathway that produces nitric oxide (NO) and contributes directly to vasodilation. The second is a clearance-based biotransformation or detoxification pathway that produces inorganic nitrite anions (NO(2) -). NO(2) - has no apparent cardiovascular effect and is not converted to NO in pharmacologically relevant concentrations in vivo. In addition, several non-enzymatic and enzymatic systems are capable of metabolising GTN. This complex metabolism complicates considerably the evaluation of the pharmacokinetics and pharmacodynamics of GTN. Regardless of the route of administration, concentrations of the metabolites exceed those of the parent compound by several orders of magnitude. During continuous steady-state delivery of GTN, for instance by a patch, concentrations of 1,2-GDN are consistently 2-7 times higher than those of 1,3-GDN, and concentrations of 2-GMN are 4-8 times higher than those of 1-GMN. Concentrations of GDNs are approximately 10 times higher, and of GMNs approximately 100 times higher, than those of GTN during sustained administration. The development of tolerance is closely related to the metabolism of GTN, and can be broadly categorised as haemodynamic tolerance versus vascular tolerance. Efforts are warranted to circumvent the development of tolerance and facilitate the use of GTN in clinical practice. Although this remains to be accomplished, it is likely that, in the near future, regimens will be developed based on a full understanding of the pharmacokinetics and pharmacodynamics of GTN and its metabolites.

Escalating nitrate dose overcomes early attenuation of hemodynamic effect caused by nitrate tolerance in patients with heart failure

This study was performed to examine the hypothesis that an early attenuation of nitrate effect caused by nitrate tolerance can be overcome by dose increase. We compared hemodynamic effects of constant dose (40 to 120 mg) of oral isosorbide dinitrate (ISDN) given every 6 hours for three doses followed by 12 hours of nitrate washout interval with those of escalating dose (40 mg, 80 mg, and 120 mg) in two similar groups of patients with chronic congestive heart failure. Escalating ISDN dose resulted in a progressive increase in ISDN blood level and overcame early attenuation of effect occurring with a constant dose. At peak effect of the third ISDN dose, a significantly greater reduction was seen in mean right atrial pressure (-59% +/- 27% vs -20% +/- 22%, p < 0.01), mean pulmonary artery pressure (-29% +/- 11% vs -11% +/- 15%, p < 0.01) and mean pulmonary artery wedge pressure (-39% +/- 19% vs -19% +/- 23%, p < 0.05) with the escalating dose. These findings demonstrate that early attenuation of hemodynamic effect caused by nitrate tolerance can be overcome by dose escalation.

Clinical pharmacokinetics of nitrates

The pharmacokinetics of organic nitrates are discussed with emphasis on the possible clinical relevance. For glyceryl trinitrate, the measurement of plasma concentrations is very difficult. Its pharmacokinetics are unusual, with a very rapid disappearance from plasma, and large intraindividual and interindividual variations. After oral administration, there seems to be a very extensive first-pass hepatic extraction and the plasma concentrations are often below the detection limit; after sublingual administration, glyceryl trinitrate appears in plasma. With transdermal glyceryl trinitrate controlled-release systems, plasma concentrations of glyceryl trinitrate can be maintained over 24 hours, although with fluctuations and important intraindividual and interindividual variability. After administration of glyceryl trinitrate via different routes, glyceryl dinitrates and mononitrates are present in plasma. The pharmacokinetics of isosorbide dinitrate are somewhat easier to understand. The substance disappears less rapidly from the plasma than does glyceryl trinitrate. After oral administration, there is also a hepatic first-pass extraction; the plasma concentrations can be prolonged by administering slow-release products. Sublingual administration leads to higher plasma concentrations than oral administration. Isosorbide dinitrate is metabolized in the organism to isosorbide 5-mononitrate and isosorbide 2-mononitrate, which both have vasodilator activity: after administration of isosorbide dinitrate, the mononitrates, and mainly the 5-mononitrate, reach very high concentrations in plasma. Isosorbide 5-mononitrate has been studied in its own right as an antianginal agent: it is completely absorbed after oral administration; it has a half-life of around 4 hours, and oral standard and controlled-release formulations have been extensively studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized study to evaluate the relation between oral isosorbide dinitrate dosing interval and the development of early tolerance to its effect on left ventricular filling pressure in patients with chronic heart failure

BACKGROUND

Early development of nitrate tolerance has been shown in patients with chronic congestive heart failure (CHF) receiving continuous nitroglycerin therapy. The influence of dosing interval of oral isosorbide dinitrate (ISDN), the nitrate preparation most widely used for the treatment of CHF, has not been investigated.

METHODS AND RESULTS

We performed a prospective, randomized study to evaluate the effect of various regimens of oral ISDN on the development of early tolerance to its effect on left ventricular filling pressure in patients with moderate to severe CHF. Forty-four responders (20% or greater reduction in mean pulmonary artery wedge pressure lasting 1 hour or longer) were divided into four groups of 11 patients each, and randomized to receive their effective ISDN dose (40-120 mg) Q 4 hours, Q 6 hours, Q 8 hours, or t.i.d. (drug given at 0, 6, 12, and 24 hours allowing 12 hours of ISDN washout interval between the third and fourth doses). All groups demonstrated a significant and comparable reduction in LV filling pressure following administration of the first ISDN dose. Early attenuation of hemodynamic response was demonstrated with frequent dosing (Q 4 hours and Q 6 hours) ISDN. Tolerance was with a Q 8-hour regimen as demonstrated by preserved hemodynamic response to each dose. The effect of each dose, however, was short-term, with return of pulmonary artery wedge pressure to baseline level at 2 to 4 hours, resulting in an intermittent effect totaling no longer than 12 hours of the 30-hour study period. The use of a t.i.d. regimen resulted in marked attenuation of response after the third dose with complete restoration of nitrate effect following a 12-hour washout period between the third and fourth doses. ISDN plasma concentration was measured in five patients in each of the Q 4- and Q 8-hour groups. In the Q 4-hour group, plasma levels were significantly higher after administration of the last dose than after the first dose (area under the curve, 242 +/- 216 versus 123 +/- 130 ng/ml, p less than 0.05), and trough levels before administration of the second and the fifth dose (15 +/- 17 and 27 +/- 27 ng/ml, respectively) were both markedly higher than the baseline value of 2 +/- 4 ng/ml.

CONCLUSIONS

Our data demonstrate the development of tolerance and early attenuation of effect on left ventricular filling pressure with frequent oral dosing (Q 4 and Q 6 hours) with ISDN in patients with chronic CHF, which may be related to persistently elevated trough blood levels of ISDN. The development of tolerance can be reversed after a washout period of 12 hours and can be prevented with a Q 8-hour administration. These regimens, however, are limited by an inconsistent effect. Although long-term implications of these findings need further evaluation, the present study demonstrates the difficulty of maintaining a persistent ISDN-mediated reduction in left ventricular filling pressure in patients with chronic, moderate to severe CHF. These results suggest the need to use intermittent ISDN therapy allowing a daily nitrate washout interval and the rationale for combined vasodilator therapy in patients with CHF.

Effects of sublingual nitrate in patients receiving sustained therapy of isosorbide dinitrate for coronary artery disease

To examine the effects of sublingual isosorbide dinitrate (ISDN) in patients receiving sustained ISDN therapy, 24 patients with coronary artery disease were divided into 2 groups. Group C comprised 12 patients without sustained ISDN therapy and group N included 12 patients with sustained ISDN therapy. Before and during administration of sublingual ISDN in both groups, aortic systolic pressure, left ventricular end-diastolic pressure and coronary artery diameter were examined at cardiac catheterization. During sublingual ISDN, the aortic systolic pressure decreased by 20 +/- 6% (138 +/- 26 to 112 +/- 27 mm Hg, p less than 0.01) in group C and 10 +/- 6% (127 +/- 26 to 113 +/- 23 mm Hg, p less than 0.01) in group N (p less than 0.01, group C vs group N). The left ventricular end-diastolic pressure decreased by 65 +/- 16% (11 +/- 5 to 4 +/- 3 mm Hg, p less than 0.01) in group C and 43 +/- 14% (12 +/- 5 to 7 +/- 3 mm Hg, p less than 0.01) in group N (p less than 0.01, group C vs group N). During sublingual ISDN, the diameters of the proximal and distal segments of the left anterior descending and circumflex coronary arteries increased more significantly in group C than in group N (p less than 0.01, group C vs group N). Thus, sublingual ISDN produced less reduction of aortic systolic pressure and left ventricular end-diastolic pressure, and less dilation of coronary artery diameter in patients receiving sustained therapy with ISDN than in those without sustained therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Resistance to isosorbide dinitrate in patients with severe chronic heart failure: incidence and attempt at hemodynamic prediction

Oral isosorbide dinitrate has been widely used to lower elevated left ventricular filling pressure in patients with chronic heart failure. Although the recommended dose of this drug is 40 mg every 6 h, failure to respond to this dose has been observed in many patients with heart failure. In the present study the incidence of resistance to isosorbide dinitrate was evaluated and an attempt was made to identify baseline hemodynamic predictors for this phenomenon in 50 patients with severe chronic heart failure due to left ventricular systolic dysfunction (mean left ventricular ejection fraction 0.23 +/- 0.08). Twenty-seven (54%) of the 50 patients responded to 40 mg of isosorbide dinitrate (greater than 20% decrease in mean pulmonary artery wedge pressure sustained greater than or equal to 1 h) and 23 patients (46%) failed to respond. Nonresponders to 40 mg of isosorbide dinitrate had a significantly higher baseline right atrial pressure than did responders (14 +/- 5 versus 10 +/- 6 mm Hg, p less than 0.02). In addition, all 7 patients with a baseline right atrial pressure of less than 7 mm Hg and 12 of 14 patients with a baseline right atrial pressure less than 10 mm Hg responded to 40 mg. No significant differences were noted between responders and nonresponders in any other baseline hemodynamic or clinical variables, or in peak isosorbide dinitrate serum levels (32 +/- 19 ng/ml in nonresponders versus 44 +/- 36 ng/ml in responders). Of the 23 nonresponders to 40 mg, 22 received a higher dose (80 to 120 mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of pharmacokinetic and pharmacodynamic properties of the organic nitrates

Glyceryl trinitrate (nitroglycerin), isosorbide dinitrate and isosorbide mononitrate are, in various formulations, available for clinical use. The pharmacokinetics of glyceryl trinitrate are complex and only 1% of the drug administered orally can be detected in the plasma due to a pronounced arteriovenous concentration gradient, hydrolysis in the blood, and rapid denitration in the liver. There is a poor and usually transient correlation between plasma concentrations and therapeutic effects, due in part to the complex pharmacokinetics of glyceryl trinitrate, but primarily due to development of tolerance during continuous administration, either via the intravenous or cutaneous route. Isosorbide dinitrate kinetics are complicated by its extensive metabolism into 2- and 5-mononitrates, which are pharmacologically active, and which also accumulate more than the parent drug during long term treatment. These facts, combined with development of tolerance during long term therapy, preclude the establishment of a concentration-response relationship. Isosorbide-5-mononitrate has ideal and dose-linear kinetics and is nearly 100% bioavailable after oral administration. However, tolerance develops during long term therapy, and therefore a relationship between plasma concentrations and clinical effects cannot be established. On the basis of available data, plasma concentrations of various nitrates do not reliably predict clinical effects.

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.

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.

Determination of isosorbide dinitrate biotransformation in various tissues of the rabbit by capillary column gas-liquid chromatography

A selective and sensitive capillary column gas-liquid chromatographic procedure has been developed for the simultaneous determination of isosorbide dinitrate (ISDN) and its mononitrate metabolites in rabbit blood and tissue homogenates. The method has a limit of detection of 0.1 ng ml-1 for ISDN, 1 ng ml-1 for isosorbide 5-mononitrate (5-ISMN), and 2 ng ml-1 for isosorbide 2-mononitrate (2-ISMN). The day-to-day coefficients of variation were 2.5, 6.8, and 11.3 per cent for ISDN, 5-ISMN, and 2-ISMN, respectively. The within-day coefficients of variation were 2.7, 4.9 and 6.5 per cent for ISDN, 5-ISMN, and 2-ISMN, respectively. The procedure was used to determine the biotransformation of ISDN (2 X 10(-7) M) to 5-ISMN and 2-ISMN by various rabbit tissue homogenates. The relative rate of biotransformation of ISDN was liver greater than lung approximately equal to intestine greater than kidney greater than blood approximately equal to skeletal muscle, with the lung and intestine homogenates being about two-thirds as active as liver homogenates. These results indicate that extrahepatic biotransformation of ISDN, especially by lung and intestine, may contribute to the systemic clearance of ISDN in the rabbit.

Pharmacokinetics and pharmacodynamics of isosorbide dinitrate

It has long been believed that organic nitrates, including isosorbide dinitrate (ISDN), are completely metabolized during their first passage through the liver and that oral therapy with this class of compounds is thus irrational. In the past few years, convincing data have been obtained in patients showing that intact ISDN is significantly bioavailable to the systemic circulation after oral administration; the oral bioavailability is about 20% relative to an intravenous dose and about 45% relative to a sublingual dose, with the balance metabolized to isosorbide mononitrates. These pharmacologically active metabolites have longer biologic half-lives than ISDN and are thus believed to contribute to the sustained duration of action of this drug. After acute dosing, changes in the pharmacologic effects of ISDN mirror those in plasma concentration. However, after long-term therapy, partial nitrate tolerance develops despite elevated plasma ISDN concentrations. Available evidence suggests that during sustained dosing, nitrate metabolism is generally reduced throughout the body; thus reduced hepatic and peripheral tissue metabolism raises plasma ISDN concentrations while reduced vascular tissue metabolism decreases the metabolic activation (perhaps to nitrosothiols?) necessary for vascular relaxation.

[Anti-angina effectiveness of isosorbide dinitrate in an acute trial and following continuous 4-week therapy with 40 mg 6 times a day]

Ten patients with angiographically proven coronary heart disease, stable exercise-induced angina pectoris, and reproducible ST-segment depression were treated with isosorbide dinitrate (ISDN) tablets in daily doses of 240 mg (6 X 40 mg) and placebo (PL) for 28 days each on the basis of a randomized double-blind protocol with intraindividual cross-over. ISDN treatment resulted in a sustained reduction of anginal attacks with a weekly mean rate ranging from 1.4 (3rd week) to 3.9 (4th week) as compared to 10.2 (2nd week) to 11.7 (4th week) during placebo treatment (P less than 0.001). Ischemic response during stress testing (sum of ST-segment depressions) was significantly improved during ISDN treatment as compared to placebo. Day 1: 56% (P less than 0.01); day 7: 30% (P less than 0.01); day 28: 49% (P less than 0.001). Heart rate and arterial blood pressure in the upright position were different between ISDN and placebo on day 1 and day 7 of the treatment phases (P less than 0.02), but not on day 28. Nitrate responsiveness with regard to blood pressure and heart rate was restored after a drug-free interval of 2 days. The plasma concentrations for ISDN and the mononitrate metabolites exhibited a constant ratio during the treatment period. Thus, therapy with 6 X 40 mg ISDN per day resulted in a sustained reduction of anginal attacks and preserved improvement of ischemic ST-segment depression during exercise in upright position.

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.

Nitroglycerin concentration in plasma: comparison between transdermal therapeutic system and ointment

This double-blind cross-over study evaluates in 12 male volunteers the time course of nitroglycerin concentration in plasma with use of the TTS-nitroglycerin, a controlled-release transdermal dosage form for nitroglycerin, and compares the bioavailability of nitroglycerin delivered from the transdermal system with that from three successive applications of 0.5 inch of 2% nitroglycerin ointment placed at 8 hr intervals over 10 cm2 of skin. The mean amounts of nitroglycerin available when subjects wore the TTS-nitroglycerin or received successive applications of ointment were 15.8 mg +/- 1.8 (SE) and 9.8 mg +/- 0.8, respectively. Mean plasma concentrations for both treatments ranged from 10-18 pg/ml-cm2. The normalized areas under the curves--353 and 410 pg/hr/ml-cm2, respectively--did not differ significantly. The ratio of clearance from the two dosage forms was 0.98 +/- 0.12. All subjects experienced mild-to-moderate side effects of nitrate therapy with both dosage forms and also decrease in blood pressure and increase in heart rate.

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.

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.

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 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.

Dose-response relation of antianginal activity of isosorbide dinitrate

Eleven men with angiographic evidence of coronary heart disease and stable, exercise-induced angina pectoris were given placebo (P) or isosorbide dinitrate (ISDN) in a daily dose of 30, 120, 240 or 480 mg, in a randomized single-blind trial. The daily doses were administered 6 times a day as single oral doses of 5, 20, 40 and 80 mg. Each dose or placebo was given for 7 days. Before therapy was begun, and on the seventh day of each treatment period, an exercise ECG with standardized level and duration of exercise was recorded. Subsequently, a 4-week treatment period with 480 mg/day was carried out at the end of which another stress test was performed. The was followed by a final 2-week placebo period. The frequency of anginal attacks per week tended to decrease with increasing nitrate doses, but decreased significantly only after the highest dose (480 mg/day) compared with placebo. Continuation of therapy with 480 mg/day maintained the reduced rate of anginal attacks. The ischemic response, expressed as the sum of ST-segment depressions in the exercise ECG, revealed a dose-dependent reduction of 26% (30 mg/day), 39% (120 mg/day) (p less than 0.01), 63% (240 mg/day) (p less than 0.01) and 72% (480 mg/day) (p less than 0.01), respectively. At the end of the 4-week treatment period with 480 mg/day, antianginal efficacy was found to be moderately reduced, showing a 56% reduction of ischemic response compared to the placebo trial. The time of onset of angina during exercise testing was also delayed in relation to the dosage given.(ABSTRACT TRUNCATED AT 250 WORDS)

Controlled, eight-hour haemodynamic study of a sustained-release formulation of isosorbide dinitrate in moderate left ventricular failure

The aim of the study was to assess the duration of the haemodynamic effects of a new sustained-release oral formulation of isosorbide dinitrate (ISDN). Twenty patients (17 men and 3 women; mean age 60 years) with acute myocardial infarction (10 anterior, 10 inferior) complicated by moderate left ventricular failure took part in a randomized controlled trial. Ten patients were randomly assigned to the placebo group and 10 to the ISDN group, who received 40 mg sustained release isosorbide dinitrate. Haemodynamic variables were measured before treatment, after 0.5 and 1 h and then every 2 hours up to the 8th hour after treatment. There was no significant change in any haemodynamic parameter in the placebo group, during the study period. In the ISDN group there was a significant fall in pulmonary artery diastolic pressure at 4 and 8 h, from 19.0 +/- 1.0 mm Hg to 16.5 +/- 1.2 mm Hg and 15.5 +/- 0.8 mmHg, respectively. The mean pulmonary capillary wedge pressure fell progressively from 17.9 +/- 1.0 to 12.5 +/- 1.2 mmHg at 2 h (p less than 0.001 in comparison with the placebo group. The fall remained significant up to 8 h. There was no statistically significant change in heart rate, cardiac index, systemic blood pressure or systemic and pulmonary vascular resistances. On the whole the cardiac index remained unchanged. There were numerous individual variations of cardiac index in relation to the initial mean pulmonary capillary wedge pressure and the magnitude of its fall following administration of ISDN. The change in cardiac index was inversely correlated with the control cardiac index (r = -0.69, p less than 0.02).

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 nitroglycerin and long-acting nitrate esters

The current literature on the human pharmacokinetics of nitroglycerin, isosorbide dinitrate, and isosorbide mononitrates is briefly reviewed and evaluated. The pharmacokinetics of nitroglycerin are unusual in that its systemic clearance is extremely large and that there is a distinct arterial-venous gradient in plasma concentration. These features had created substantial difficulties in the documentation and interpretation of nitroglycerin plasma concentrations and pharmacokinetics. Studies with isosorbide dinitrate showed that this nitrate is absorbed as intact drug at about 20 percent of a comparable intravenous dose, firmly disproving a previous belief that orally administered nitrate is completely degraded by presystemic metabolism. The current data suggest that plasma nitrate concentration may relate to some of its pharmacologic effects after short-term dosing, but the concentration-response relationship is complex after long-term dosing. Studies of nitrate pharmacokinetics in their presumed sites of action, namely, the vasculature, appear to be useful for the further understanding of the mechanism of action for these vasodilators.

Pharmaceutical considerations of nitroglycerin

During the past few years, there have been rapid changes in the pharmaceutical uses of nitroglycerin. New dosage forms and new delivery systems have become available, which have resulted in potential confusion to all concerned with the proper use of these systems. The goal of this review is to prevent confusion and to bring all the relevant information together. The various analytical techniques available for quality control of the dosage forms and for the study of the pharmacokinetics are reviewed, with the intent of enabling the reader to identify pertinent references rapidly. The interaction of nitroglycerin with packaging and plastic delivery devices is also reviewed so that the reader can make informed choices. Finally, the clinical pharmacy and pharmacokinetics are reviewed so as to bring the reader up to date in that area. After reading this article, the areas of nitroglycerin research that still need to be explored should be apparent.

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.

Pharmacokinetic studies of various preparations of glyceryl trinitrate

1 The pharmacokinetics and pharmacodynamics of five pharmaceutical preparations of glyceryl trinitrate (GTN) have been studied in six healthy volunteers. 2 Peak plasma GTN levels of 1.4 +/- 0.1 ng/ml were achieved at 3 min after sublingual administration (0.5 mg); 2.8 +/- 0.6 ng/ml and 2.5 +/- 0.3 ng/ml at 2 h and 4 h after Nitrocontin (6.4 mg) and Sustac (6.4 mg) respectively; 2.7 +/- 0.1 ng/ml and 2.5 +/- 0.2 ng/ml at 30 min after the cream (23 mg) and ointment (35 mg) respectively. 3 The mean times to reach half peak plasma GTN levels were 4.2 +/- 0.7 min after sublingual GTN, 6.5 +/- 0.9 h after Nitrocontin, 4.1 +/- 0.7 h after Sustac, 46.1 +/- 10.2 min after the ointment and 50.2 +/- 39.2 min after the cream. 4 Plasma nitrate (NO3) levels were undetectable after sublingual administration; peak NO3 levels were 0.48 +/- 0.03 microgram/ml at 4 h after Nitrocontin, 0.45 +/- 0.02 microgram/ml at 6 h after Sustac, 0.68 +/- 0.04 microgram/ml at 6 h (end of study) after the ointment and 0.63 microgram/ml at 4 h after the cream. 5 Plasma nitrite (NO2) was undetectable after sublingual GTN and peak NO2 levels were 0.48 +/- 0.04 microgram/ml at 2 h after Nitrocontin, 0.48 +/- 0.02 microgram/ml at 2 h after Sustac, 0.69 +/- 0.02 microgram/ml at 1 h after the ointment and 0.64 +/- 0.02 microgram/ml at 1 h after the cream. 6 Blood pressure (BP) declined throughout the 11 min of the study after sublingual GTN but did not change significantly after Nitrocontin or Sustac. After the ointment and the cream BP fell to the lowest level 30-60 min after administration and remained low throughout the 6 h of the study. 7 Heart rate (HR) increased to a maximum 5 min after sublingual administration with no significant increase after Nitrocontin or Sustac. After the ointment and the cream HR increased gradually to a maximum 30-60 min after administration remaining high throughout the rest of the study.

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).

Rectal absorption of nitroglycerin in the rat: avoidance of first-pass metabolism as a function of rectal length exposure

Nitroglycerin administered orally undergoes substantial presystemic elimination. It was shown recently that first-pass hepatic metabolism of high clearance drugs can be substantially avoided via rectal administration. In applying this concept to nitroglycerin in rats, it was found that unrestricted rectal instillation of nitroglycerin (at 3.5-mg/kg dose) gave a mean +/-SD bioavailability of 26.7 +/- 7.0% (n=6) compared to 1.8 +/- 0.9% (n=5) from oral dosing. This mode of dosing did not lead to complete avoidance of first-pass metabolism of nitroglycerin in rats. When the rectal exposure length to nitroglycerin was restricted to 3.5 cm from the anus, the mean +/-SD bioavailability increased to 83.5 +/- 74.5% (n=14). However, the variability in bioavailability was extremely large. When the rectal exposure length was restricted to 2.0 cm from the anus (at 1.75-mg/kg dose), nitroglycerin bioavailability was estimated at 91.2 +/- 30.4% (n=6). The plasma nitroglycerin concentrations (greater than 5 min) obtained after this mode of administration were similar to those achieved after intravenous dosing. The data showed that substantial avoidance of presystemic nitroglycerin metabolism can be achieved via rectal administration. This avoidance can be nearly complete if nitroglycerin is limited in exposure to only the lower rat rectum. It was also demonstrated that sustained (at least 24 hr) nitroglycerin delivery via the rat rectal route was feasible with an experimental osmotic minipump. This delivery system also produced nearly complete bioavailability for nitroglycerin in the rat.

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%.

Nitroglycerin stability: effects on bioavailability, assay and biological distribution

The solution, absorptive, and adsorptive properties of nitroglycerin are related to problems encountered in the intravenous use of solutions of the drug and in its assay in biological tissues. Solutions of the drug in usual intravenous fluids are quite stable to hydrolysis under neutral conditions. Loss to plastic intravenous delivery set components by rapid adsorption and slower absorption processes present a significant clinical problem. Assay of the drug and its major metabolites is complicated by problems of extraction related to the solubility of nitroglycerin, its metabolites and substances in the plasma. Loss of nitroglycerin incubated with red blood cells is a very rapid process (half-life 4.0 min. at 10 ng/ml). The mechanism appears to be a physical process rather than an enzymatic one. The loss to blood cells and perhaps other biological materials should be considered in an analysis of the distribution of the drug.

Relation of time course of plasma nitroglycerin levels to echocardiographic, arterial pressure and heart rate changes after sublingual administration of nitroglycerin

Despite the widespread use of nitroglycerin, a relation between plasma nitroglycerin concentrations and the associated cardiovascular effects has not been well established. It was hypothesized that nitroglycerin levels may help predict the hemodynamic responses. With use of a recently developed nitroglycerin assay technique, the relation between the time course of plasma nitroglycerin levels and echocardiographic changes after sublingual administration of 0.6 mg of the drug was evaluated in 12 normal volunteers. Mean plasma nitroglycerin levels were maximal at 2 (1.1 +/- 0.3 ng/ml) and 5 (1.4 +/- 0.6 ng/ml) minutes, when the changes in mean heart rate (+17 +/- 7 and +12 +/- 3 min-1) and decreases in echocardiographic left ventricular diastolic (-4.2 +/- 0.8 mm at 5 minutes) and systolic (-3.1 +/- 0.6 mm at 5 minutes) dimensions were also maximal. Parallel changes were noted in left atrial dimension, ventricular velocity of circumferential fiber shortening and systolic blood pressure, but not in diastolic blood pressure. These findings demonstrate the existence of a close relation between plasma nitroglycerin levels and variables that reflect the known responses to this drug.

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.

First data on effects and pharmacokinetics of isosorbide-5-mononitrate in normal man

Isosorbide-5-mononitrate (IS-5-MN) 5, 10, 20, 30, 40 and 50 mg were administered orally to 2 healthy male volunteers. The pharmacological effect was determined using digital pulse plethysmography and the orthostatic tilting test, and at the same time side effects were monitored. The threshold of oral activity of IS-5-MN was found to be 5 mg. The maximum response was reached with doses of 20-30 mg. The duration of action of this dose was approximately 8 h. Higher doses did not lead to any further increase, but rather to a decrease in the pharmacological response, while the side-effects, such as headaches, dizziness and nausea, became more prominent. In a randomized, double-blind, three-way cross-over study in 11 female volunteers IS-5-MN 30 mg proved to be more potent with respect to pharmacological activity than sustained released ISDN 20 mg (isosorbide dinitrate), whereas there was no difference in side-effects. Thus, it can be estimated that IS-5-MN 20 mg is approximately equivalent to 20 mg sustained released ISDN. IS-5-MN is rapidly absorbed after oral administration and the maximum concentration in serum was reached 1.2 +/- 0.2 h after doses of 10 to 50 mg. The pharmacokinetics showed dose-linearity. The compound was eliminated with an average half life of 4.04 +/- 0.16 h, which is appropriate for a reasonably prolonged duration of action without the need for a sustained release formulation.

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.

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

A highly selective and sensitive analytical procedure for the determination of trinitroglycerin and four metabolites in whole blood was developed. Trinitroglycerin and its metabolites were extracted from whole blood with ethyl acetate and analyzed by high-pressure liquid chromatography using the thermal energy analyzer detector. Linearity of response was observed over the 1-1000-ng range. The applicability of this method to the analysis of whole blood from dogs orally dosed with trinitroglycerin is described.

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.

Loss of nitroglycerin from aqueous solution into plastic intravenous delivery systems

The mechanism of potential loss of nitroglycerin stored in plastic and glass containers was studied from an equilibrium and kinetic approach. Plastic strips equilibrated with dilute aqueous solutions of neat nitroglycerin showed that the drug was lost by absorption. Drug loss was followed by an electron-capture GLC assay. The same assay of control solutions in glass showed no drug loss in 48 hr at pH 5.7. The kinetics of nitroglycerin absorption and desorption were determined using synthesized 14C-labeled drug. Absorption can be quantified using a diffusion model, where the concentration in the aqueous phase falls with time. Curve fitting yielded an average diffusion coefficient in plastic of 2.05 x 10(-9) cm2/sec and a partition coefficient of 104 (plastic-water) at 30 degrees. Temperature-dependence studies of absorption showed that the diffusion coefficient followed an Arrhenius relationship with an energy requirement of 19.6 kcal/mole, whereas effects on the partition coefficient were negligible. Nitroglycerin desorption from plastic disks under sink conditions into water can be quantified by assuming a diffusion model where the concentration at the surface of a plane sheet remains constant. Nonlinear least-squares curve fitting generated a diffusion coefficient of 1.14 x 10(-9) cm2/sec for the desorption process at 30 degrees.