Plasma isosorbide dinitrate concentrations in human subjects after administration of standard and sustained-release formulations

Saliva: a challenging human fluid to diagnose brain disorders with a focus on Alzheimer's disease

Biomarkers are molecules of biological processes that help in both the diagnosis of human diseases and in follow-up assessments of therapeutic responses. Biomarkers can be measured in many human fluids, such as blood, cerebrospinal fluid, urine, and saliva. The -omics methods (genomics, RNomics, proteomics, and metabolomics) are useful at measuring thousands of markers in a small volume. Saliva is a human fluid that is easily accessible, without any ethical concerns. Yet, saliva remains unexplored in regard to many human disease biomarkers. In this review, we will give an overview on saliva and how it can be influenced by exogenous factors. As we focus on the potential use of saliva as a diagnostic tool in brain disorders (especially Alzheimer's disease), we will cover how saliva is linked to the brain. We will discuss that saliva is a heterogeneous human fluid, yet useful for the discovery of biomarkers in human disorders. However, a procedure and consensus that is controlled, validated, and standardized for the collection and processing of saliva is required, followed by a highly sensitive diagnostic approach.

Nitric Oxide as a Central Molecule in Hypertension: Focus on the Vasorelaxant Activity of New Nitric Oxide Donors

Cardiovascular diseases include all types of disorders related to the heart or blood vessels. High blood pressure is an important risk factor for cardiac complications and pathological disorders. An increase in circulating angiotensin-II is a potent stimulus for the expression of reactive oxygen species and pro-inflammatory cytokines that activate oxidative stress, perpetuating a deleterious effect in hypertension. Studies demonstrate the capacity of NO to prevent platelet or leukocyte activation and adhesion and inhibition of proliferation, as well as to modulate inflammatory or anti-inflammatory reactions and migration of vascular smooth muscle cells. However, in conditions of low availability of NO, such as during hypertension, these processes are impaired. Currently, there is great interest in the development of compounds capable of releasing NO in a modulated and stable way. Accordingly, compounds containing metal ions coupled to NO are being investigated and are widely recognized as having great relevance in the treatment of different diseases. Therefore, the exogenous administration of NO is an attractive and pharmacological alternative in the study and treatment of hypertension. The present review summarizes the role of nitric oxide in hypertension, focusing on the role of new NO donors, particularly the metal-based drugs and their protagonist activity in vascular function.

A comparison of organic and inorganic nitrates/nitrites

Although both organic and inorganic nitrates/nitrites mediate their principal effects via nitric oxide, there are many important differences. Inorganic nitrate and nitrite have simple ionic structures and are produced endogenously and are present in the diet, whereas their organic counterparts are far more complex, and, with the exception of ethyl nitrite, are all medicinally synthesised products. These chemical differences underlie the differences in pharmacokinetic properties allowing for different modalities of administration, particularly of organic nitrates, due to the differences in their bioavailability and metabolic profiles. Whilst the enterosalivary circulation is a key pathway for orally ingested inorganic nitrate, preventing an abrupt effect or toxic levels of nitrite and prolonging the effects, this is not used by organic nitrates. The pharmacodynamic differences are even greater; while organic nitrates have potent acute effects causing vasodilation, inorganic nitrite's effects are more subtle and dependent on certain conditions. However, in chronic use, organic nitrates are considerably limited by the development of tolerance and endothelial dysfunction, whereas inorganic nitrate/nitrite may compensate for diminished endothelial function, and tolerance has not been reported. Also, while inorganic nitrate/nitrite has important cytoprotective effects against ischaemia-reperfusion injury, continuous use of organic nitrates may increase injury. While there are concerns that inorganic nitrate/nitrite may induce carcinogenesis, direct evidence of this in humans is lacking. While organic nitrates may continue to dominate the therapeutic arena, this may well change with the increasing recognition of their limitations, and ongoing discovery of beneficial effects and specific advantages of inorganic nitrate/nitrite.

A novel transdermal patch incorporating isosorbide dinitrate with bisoprolol: in vitro and in vivo characterization

The combination therapy of nitrate and selective beta-adrenoceptor antagonist has shown benefits for treatment of hypertension and heart disease than either drug alone. The objectives of the present study were to define effects on the anti-hypertension activity and pharmacokinetics of a novel transdermal patch incorporating isosorbide dinitrate (ISDN) with bisoprolol (BP). The 3:2 ratio of ISDN to BP (mg/mg) in the transdermal patches exhibited better anti-hypertension effect synergistically with a similar inhibiting heart rates effect to that of BP alone in renovascular hypertensive rats, and was therefore selected as a final formulation. The in vitro transdermal penetration of both ISDN and BP from the patches displayed a zero-order process, and the penetration rate constants were 7.4 microg/(cm(2)h) for ISDN, and 5.9 microg/(cm(2)h) for BP, respectively. After transdermal administration at single dose or multiple doses, the synergistic anti-hypertension effect was confirmed in spontaneously hypertensive rats also. The effect of each patch lasts for 3 days, and increased with the total dose of two drugs (2mg/cm(2), ISDN:BP=3:2, mg/mg), showing a dose dependant manner. After transdermal administration to rabbits, the absolute bioavailabilities were 33.6% for ISDN, and 31.3% for BP, respectively. The maximal concentrations (C(max)) of both drugs were significantly reduced while the areas under the plasma concentration-time curve (AUC), and mean residence times (MRT) were evidently increased and extended, respectively. As a patient-friendly, convenient, and multi-day dosing therapeutic system, the transdermal patches incorporating ISDN and BP could be promising for prevention and treatment of hypertension.

[Fast-disintegration oral tablets having sustained release property]

Fast-disintegrating (FD) tablets containing nicorandil-loaded dry emulsions were prepared and their controlled-release properties were examined and compared with the plain FD tablets (FD tablets without dry emulsions) and commercial tablets. The dry emulsions were prepared with myristyl alcohol and stearyl alcohol and their property was modified by mixing the ratio of the two alcohols. Disintegration time of the prepared FD tablets was sufficiently fast (i.e., 12 to 23 s). In vitro release of nicorandil from the FD tablets containing the dry emulsions was sustained over 6 h, while that from plain FD and commercial tablets was complete within 5 min. In vivo absorption of nicorandil from the tablets was evaluated by oral administration in beagle dogs. FD tablets containing dry emulsions showed a similar AUC, lower Cmax, and delayed Tmax compared to the plain FD and commercial tablets. These results suggest that the dry emulsion-loaded FD tablets can be utilized to improve the sustained-release property of active drugs.

Plasma disposition and hemodynamic effects of a single oral dose of isosorbide dinitrate in human males and females

The goal of the present work was to determine the plasma disposition and hemodynamic effects of isosorbide dinitrate (ISDN) in human males and females. Fourteen healthy human volunteers took part in the study; seven males, 21.7 +/- 2.5 y (SD), and seven females, 20.7 +/- 3.4 y. Measurements of forearm blood flow (FBF), vascular conductance (FVC), and venous capacitance (Cv) were obtained by venous occlusion plethysmography, whereas blood pressure was measured by automatic sphygmomanometry. Blood samples were taken through a catheter placed in the antecubital vein at 0, 15, 30, 45, 60, 90, 120, 360, 480, 720, and 1440 min following a single 10 mg oral dose of ISDN. Plasma concentrations of ISDN and its mononitrate metabolites, isosorbide-2-mononitrate (2-ISMN) and isosorbide-5-mononitrate (5-ISMN), were determined by large bore capillary column gas-liquid chromatography. Hemodynamic measurements were made at corresponding experimental times up to 480 min. No differences were observed in the disposition of ISDN, 2-ISMN or 5-ISMN between the male and female volunteers. In addition, the plasma concentrations of ISDN and its mononitrate metabolites did not consistently correlate with the hemodynamic changes of the individual subjects. Diastolic blood pressure was significantly decreased for a 0.5 h period starting at 30 min, which was the time at which plasma ISDN concentrations peaked, and which preceded the time when the plasma concentrations of 2-ISMN and 5-ISMN were maximal. These observations indicate that, for a single 10 mg oral dose of ISDN, there were no gender-dependent differences in the plasma disposition of the parent drug or its mononitrate metabolites, and the vascular changes responsible for the decrease in diastolic blood pressure in these volunteers occurred in vascular beds other than those of skeletal muscle as represented by forearm blood flow.

Evaluation of the efficacy and duration of action of isosorbide mononitrate in angina pectoris

The magnitude and duration of the antianginal and anti-ischemic effects of isosorbide mononitrate (IS-5-MN), 20 mg, were determined in 10 patients with chronic stable angina pectoris. An exercise test (treadmill, Bruce protocol) was performed before and at 1, 6, 8 and 10 hours after oral administration of the drug. The patients were randomly assigned to receive IS-5-MN or placebo, and after 1 week of therapy were crossed over to the other formulations. The drug increased the exercise duration from 321 to 455 seconds at 1 hour (p less than 0.001). Time to moderate angina increased from 237 to 324 seconds (p less than 0.05) and time to ST depression greater than or equal to 1 mm increased from 150 to 307 seconds (p less than 0.01) at 1 hour. Placebo had no effect on any of the exercise parameters. Although partially attenuated at 6 hours, the effect of IS-5-MN remained statistically significant even at 8 hours, but not at 10 hours. It is concluded that the duration of action of a single tablet of IS-5-MN, given orally, is 8 hours.

Coronary artery dilation and hemodynamic responses after isosorbide dinitrate therapy in patients with coronary artery disease

The response to sublingual isosorbide dinitrate (ISDN) was studied in 10 men with suspected coronary artery disease undergoing coronary arteriography. A Swan-Ganz catheter was placed in the pulmonary artery to record hemodynamic response. Diseased coronary segments were identified during routine Judkins selective coronary angiograms. Sublingual isosorbide dinitrate (ISDN) (5 or 10 mg) was then given with the catheters in place. Multiple sequential single-view coronary angiograms and pulmonary and systemic hemodynamic responses were recorded over 30 minutes after drug administration. At 30 minutes, there was a 53% reduction (p less than 0.01) in pulmonary capillary wedge pressure and a 15% decrease (p less than 0.05) in systemic and pulmonary vascular resistance, with a net 13% decrease (p less than 0.01) in cardiac output and 20% decrease (p less than 0.01) in mean arterial pressure. Quantitative arteriography demonstrated substantial dilation of luminal cross-sectional area in both normal and diseased coronary arterial segments. Normal epicardial segments were grouped according to luminal area (1 to 4, 4 to 8 and more than 8 mm2) and demonstrated maximal area dilation at 10 minutes of 55% (p less than 0.01), 29% (p less than 0.01) and 16% (p less than 0.05), respectively. Diseased epicardial segments (stenosis 50% or greater) dilated 51% (p less than 0.01) at 10 minutes. Calculated stenosis resistance decreased 40% (p less than 0.01). Diseased segments in small and middle-sized arteries (1 to 8 mm2) are 4 times more reactive than those in larger arteries (more than 8 mm2), with peak dilation of 77 vs 21% (p less than 0.01) at 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

A study into the mucosal absorption of isosorbide dinitrate at different intraoral sites

This study measured the absorption of isosorbide dinitrate (ISDN) into the systemic circulation after application of tablets to the buccal, palatal, or sublingual mucosa in six healthy subjects. After 1 minute serum levels were detectable by gas liquid chromatographic analysis from buccal and sublingual sites. Levels progressively increased, peaking at 5 minutes, and then progressively decreased during the 30-minute sampling period. At most of the time periods serum levels were greater from sublingual sites than from buccal sites. ISDN levels were not detected at any time in any subject after application to the palatal mucosa. As with the skin, the keratinized layer of the oral mucosa may be an important barrier to absorption. The findings appear relevant to the delivery of drugs via the oral mucosa for systemic effect.

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

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

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

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

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)

First-pass elimination. Basic concepts and clinical consequences

First-pass elimination takes place when a drug is metabolised between its site of administration and the site of sampling for measurement of drug concentration. Clinically, first-pass metabolism is important when the fraction of the dose administered that escapes metabolism is small and variable. The liver is usually assumed to be the major site of first-pass metabolism of a drug administered orally, but other potential sites are the gastrointestinal tract, blood, vascular endothelium, lungs, and the arm from which venous samples are taken. Bioavailability, defined as the ratio of the areas under the blood concentration-time curves, after extra- and intravascular drug administration (corrected for dosage if necessary), is often used as a measure of the extent of first-pass metabolism. When several sites of first-pass metabolism are in series, the bioavailability is the product of the fractions of drug entering the tissue that escape loss at each site. The extent of first-pass metabolism in the liver and intestinal wall depends on a number of physiological factors. The major factors are enzyme activity, plasma protein and blood cell binding, and gastrointestinal motility. Models that describe the dependence of bioavailability on changes in these physiological variables have been developed for drugs subject to first-pass metabolism only in the liver. Two that have been applied widely are the 'well-stirred' and 'parallel tube' models. Discrimination between the 2 models may be performed under linear conditions in which all pharmacokinetic parameters are independent of concentration and time. The predictions of the models are similar when bioavailability is large but differ dramatically when bioavailability is small. The 'parallel tube' model always predicts a much greater change in bioavailability than the 'well-stirred' model for a given change in drug-metabolising enzyme activity, blood flow, or fraction of drug unbound. Many clinically important drugs undergo considerable first-pass metabolism after an oral dose. Drugs in this category include alprenolol, amitriptyline, dihydroergotamine, 5-fluorouracil, hydralazine, isoprenaline (isoproterenol), lignocaine (lidocaine), lorcainide, pethidine (meperidine), mercaptopurine, metoprolol, morphine, neostigmine, nifedipine, pentazocine and propranolol. One major therapeutic implication of extensive first-pass metabolism is that much larger oral doses than intravenous doses are required to achieve equivalent plasma concentrations. For some drugs, extensive first-pass metabolism precludes their use as oral agents (e. g. lignocaine, naloxone and glyceryl trinitrate).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Use of isosorbide dinitrate saliva concentrations for biopharmaceutical investigations

The concentration of isosorbide dinitrate in paired samples of plasma and mixed saliva was monitored for up to 24 hr after oral administration of 60 mg of sustained-release isosorbide dinitrate to eight healthy volunteers. Measured isosorbide dinitrate plasma concentrations were mainly in the range of 0.1-10 ng/ml. Isosorbide dinitrate was excreted into saliva resulting in a mean (+/- SD) saliva-plasma concentration ratio of 0.68 +/- 0.37. A significant correlation between concentrations of isosorbide dinitrate in saliva and plasma was found (p less than 0.01). The sustained-release properties of the administered formulation were confirmed from the concentrations of isosorbide dinitrate found in both saliva and plasma. Saliva-plasma ratios were independent of the absolute concentrations of isosorbide dinitrate but showed a slight tendency to decrease with time. The principal factor relating saliva and plasma isosorbide dinitrate concentrations appeared to be the degree of plasma protein binding of the drug.

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

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

Plasma concentrations and bioavailability of isosorbide dinitrate and pindolol from a combination formulation

The plasma concentrations and bioavailability of sustained-release isosorbide dinitrate and standard-release pindolol have been compared after administration of these drugs in combination and alone. Bioavailability parameters of isosorbide dinitrate and pindolol obtained after administration of the drugs in combination were not significantly different (P greater than 0.05) to those obtained after administration of either drug alone. Two peaks of mean concentrations of isosorbide dinitrate occurred in plasma after administration of 30 mg of this drug in combination with 7.5 mg pindolol (4.4 ng ml-1 at 1 h and 4.5 ng ml-1 at 5 h), or alone (5.9 ng ml-1 at 2 h and 5.7 ng ml-1 at 5 h). In each case, plasma concentrations of isosorbide dinitrate were maintained during at least 8 h, whereas the drug was not detected in plasma at 2.5 h after administration of a standard-release formulation. The peaks of mean concentrations of pindolol were 39.7 ng ml-1 at 1.5 h after administration of 7.5 mg drug in combination with isosorbide dinitrate and 38.0 ng ml-1 at 1 h administration of the drug alone. Concentrations of pindolol in plasma declined with a half-life of 3 h.

Kinetics of isosorbide dinitrate and relationships to pharmacological effects

1 The inter-relationships among oral isosorbide dinitrate (ISDN) dose, drug pharmacokinetics and pharmacological effects were studied in 12 angina patients following single and chronic doses of 15, 30, 60 and 120 mg. 2 Significant accumulation of intact ISDN in plasma was observed after four times a day dosing at 30, 60 and 120 mg for 1 week. 3 The area under the plasma concentration v time curve (AUC), form 0-6 h, was shown to be proportional to dose following single doses. In contrast, AUC increased disproportionately to dose after chronic dosing. 4 Pharmacokinetic correction provided modest improvements in the dose-response relationships of ISDN. 5 Adverse hypotensive effects were observed in five patients after the single 60 mg dose. These patients showed statistically higher AUC and lower intrinsic clearance of ISDN at doses of 15, 30 and 60 mg compared to those who did not develop adverse effects. A possible relationship exists, therefore, between lower drug clearance and hypersensitivity to ISDN.

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.

Availability of isosorbide dinitrate, diazepam and chlormethiazole, from i.v. delivery systems

The loss of isosorbide dinitrate from aqueous solutions stored in plastic infusion bags and/or infused through plastic giving sets was investigated. During simulated infusions, the loss of isosorbide dinitrate was found to be flow-rate dependent. The clinical and pharmacokinetic significance of this loss is discussed. Infusion o isosorbide dinitrate from a glass syringe through high density polyethylene tubing overcame the loss associated with its administration via plastic infusion bags and intravenous giving sets. This method was also applied successfully to minimise the previously reported loss of diazepam and chlormethiazole during infusions.

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.

Effects and pharmacokinetics of isosorbide dinitrate in normal man

18 subjects were given isosorbide dinitrate (ISDN) 5 mg sublingually and serum concentrations of ISDN, 2-isosorbide mononitrate (2-ISMN) and 5-isosorbide mononitrate (5-ISMN) were measured, as well as changes in digital plethysmographic amplitude, heart rate, ECG, blood pressure and Schellong's test. ISDN was rapidly absorbed and metabolized, having an elimination half-life of 29 min. Its metabolites 2-ISMN and 5-ISMN had longer half-lives of 1.75 and 7.6 h respectively. The amplitude of the alpha-wave of the digital plethysmograph did not change significantly either in the pre-drug period or after placebo administration. It increased within 4 min of administration of ISDN, and reached a maximum after 14 min; the effect lasted for about 2 h. ISDN lowers blood pressure and increases heart rate in most volunteers, but in 3 of the 18 subjects severe hypotension occurred, accompanied by severe, reversible bradycardia, which was probably due to vagal reflexes initiated by the markedly diminished ventricular enddiastolic volume (LVEDV) and pressure (LVEDP). No correlation could be demonstrated between the serum concentration of ISDN and/or its vasoactive metabolites and changes in plethysmographic amplitude.

Measurement of plasma concentrations of isosorbide dinitrate

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

Pharmacokinetics of isosorbide dinitrate after intravenous infusion in human subjects

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

Plasma concentrations of isosorbide dinitrate after cutaneous and sublingual doses to human subjects

After application of 100 mg (nominal dose) isosorbide dinitrate as an ointment to the skin of human subjects, mean drug concentrations were 1 to 2 ng/ml for 1.5 hour and reached a peak of 6.2 ng/ml at 6 hours. Thereafter, mean concentrations declined slowly to 2.9 ng/ml at 12 hours and 1.2 ng/ml at 24 hours. After a sublingual dose of 5 mg isosorbide dinitrate, mean drug concentrations reached a peak of 15.9 ng/ml at 0.5 hour and declined with a half-life of about 50 minutes. The mean bioavailability of isosorbide dinitrate from the ointment was estimated as 30 per cent of that from the sublingual tablet when corrected for differences in dose/body weight ratio. The results demonstrate that concentrations of isosorbide dinitrate in plasma can be maintained for relatively long periods when the drug is applied to the skin.