Nitrate tolerance

Medications and substances as a cause of headache: a systematic review of the literature

Medication- or substance-induced headache is probably an underrecognized entity with numerous etiologies, including prescribed medication, over-the-counter medication, illicit drugs, anesthetic agents, foods, food additives, beverages, vitamins, inhaled substances, and substances used in diagnostic procedures. The author performs a systemic review of the literature to provide an exhaustive description of the relationship between medications and substances and headaches of various types, along with pathophysiologic mechanisms whenever possible. Suggestions for improved identification of this phenomenon and its avoidance are provided. More scientific evaluation of substances and their possible association with headache is required with almost all substances indicated herein.

Inotropic effects of glyceryl trinitrate and spontaneous NO donors in the dog heart

BACKGROUND

In vitro, NO has a biphasic effect on myocardial inotropy. To determine the inotropic effect of NO in vivo, we investigated the activity of glyceryl trinitrate (GTN) and the NO donors S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and sodium-(2)-1-(N,N-diethyl-amino)-diazen-1-ium-1,2-diolat+ ++ (DEA/NO) in dogs.

METHODS AND RESULTS

Eight anesthetized open-chest dogs were instrumented for measurement of left ventricular and aortic pressures (tip manometers) and coronary flow (ultrasonic flow probes). Regional myocardial function was assessed by sonomicrometry as systolic wall thickening (sWT), mean systolic thickening velocity (Vs), and regional myocardial stroke work index (RSW). GTN, SNAP, and DEA/NO were infused into the left anterior descending coronary artery (LAD) to achieve defined coronary plasma concentrations of GTN, SNAP (both 10 to 100 micromol/L), and DEA/NO (2 to 20 micromol/L). All drugs increased LAD flow and myocardial contractile function in the LAD-dependent myocardium within the first 120 seconds. The greatest inotropic effect was noted after infusion of DEA/NO (20 micromol/L), which increased sWT by 9.7+/-3.1% from 28.5+/-2.2%, Vs by 10.3+/-3.4% from 9.1+/-1.1 mm/s, and RSW by 7.1+/-2.1% from 200.0+/-22.1 mm Hg x mm (P<.05). At the same time, systemic hemodynamics remained unchanged. Prevention of the flow response to GTN by external narrowing of the LAD did not influence the inotropic effect of GTN.

CONCLUSIONS

Organic nitrates and NO donors evoke a small but constant positive inotropic effect in vivo that is not caused by coronary vasodilation.

Plasma arteriovenous cGMP difference as a useful indicator of nitrate tolerance in patients with heart failure

BACKGROUND

The present study was performed to evaluate the effects of nitroglycerin (GTN) on plasma arteriovenous cGMP production and to compare its hemodynamic effects in patients with congestive heart failure (CHF). We also estimated the potential clinical value of plasma arteriovenous cGMP production as an indicator of nitrate tolerance.

METHODS AND RESULTS

Plasma arterial and venous cGMP levels, atrial natriuretic peptide level, and hemodynamic parameters were measured before and after GTN infusion in 14 patients with CHF. Although the plasma levels of arterial cGMP and atrial natriuretic peptide decreased immediately after GTN, the plasma level of venous cGMP did not change. GTN infusion caused a dose-dependent increase in plasma arteriovenous cGMP production, and there was a positive correlation between the decrease of pulmonary capillary wedge pressure and the increase of plasma arteriovenous cGMP production immediately after GTN. Hemodynamic tolerance was observed after both 12 and 24 hours, when plasma arteriovenous GMP production was also attenuated.

CONCLUSIONS

These findings indicate that the plasma arteriovenous cGMP difference is a clinical indicator of vasodilatory action of GTN and a useful indicator of nitrate tolerance in patients with CHF.

Risk of rebound phenomenon during nitrate withdrawal

Organic nitrates are first-line drugs in the therapy and prevention of angina. These compounds, are acutely effective yet some formulations demonstrate a rapid decline in effect with chronic use. In this review the mechanisms of development of nitrate tolerance and the different strategies to prevent it are considered. If frequent dosing, high dosages and long acting preparations giving constant 24 h plasma GTN levels are more likely to cause tolerance, nitrate-low periods seem to be effective in restoring the drug's efficacy. Intermittent therapy with GTN patches, an effective way to prevent tolerance, raises the problem of the rebound phenomenon during the removal period. Considerable variations in its occurrence have been reported and in this review the factors that may influence the incidence of the rebound are discussed. The dangers of rebound can be lessened by concomitant anti-anginal drugs or avoiding any abrupt decline in blood nitrate concentrations. The use of beta-blockers or calcium channel blockers during intermittent therapy with GTN patches and oral preparations of isosorbide dinitrate or isosorbide 5-mononitrate seem to be effective for this purpose.

Platelet cyclic GMP. A potentially useful indicator to evaluate the effects of nitroglycerin and nitrate tolerance

BACKGROUND

The present study was designed to investigate the intracellular production of cyclic GMP (cGMP) in platelets in response to nitroglycerin and to determine the potential clinical value of platelet cGMP as an indicator of the effects of nitroglycerin and nitrate tolerance.

METHODS AND RESULTS

Platelet cGMP levels and the diameters of the coronary arteries before and 2 minutes after intracoronary injection of 200 micrograms nitroglycerin were measured in 15 patients who had previously received nitrates (nitrates group) and in 16 who had not received any nitrates (no-nitrates group). Platelet cGMP levels increased significantly after nitroglycerin injection in the two groups, but plasma cGMP levels and plasma atrial natriuretic peptide levels did not change. The percent increase in platelet cGMP levels and the percent dilatation of the left anterior descending (LAD) and left circumflex (LCx) coronary arteries after nitroglycerin injection were higher in the no-nitrates group than in the nitrates group (platelet cGMP levels: artery, 74.2 +/- 18.3% versus 11.5 +/- 4.2%, P < .01; vein, 73.6 +/- 22.9% versus 9.0 +/- 3.1%, P < .01; coronary dilatation: LAD, 46.7 +/- 6.0% versus 9.9 +/- 2.5%, P < .01, LCx, 51.2 +/- 8.7% versus 6.1 +/- 3.0%, P < .01). The percent increase in platelet cGMP levels was significantly correlated with the percent dilatation of the coronary arteries (LAD: r = .90, P < .01; LCx: r = .92, P < .01) in the no-nitrates group and not in the nitrates group.

CONCLUSIONS

These results indicate that platelet cGMP can be used as an indicator for in situ evaluation of nitroglycerin effects and that patients who have received nitrates develop nitrate tolerance, which affects intracellular production of cGMP and vasodilation in the response to nitroglycerin.

Use of nitrates in ischemic heart disease

The organic nitrates have remarkably diverse actions that are or should be beneficial in patients with ischemic heart disease. These drugs are effective in all the important ischemic syndromes. Preliminary data in patients with acute infarction suggest that the drugs may be truly cardioprotective, resulting in improved mortality. This review has not discussed the role of nitrates in congestive heart failure or LV dysfunction, a subject of great importance. The nitrates are useful adjunctive agents in these syndromes, and the two VeHfT trials support the concept that long-term nitrate administration, in conjunction with hydralazine, may favorably alter the natural history of heart failure. This cardioprotective effect is similar to that suggested for the post-MI patient. The data are not strong enough for definitive conclusions at this time. The clinical benefits of nitrates in decreasing subjective (angina) and objective indices of ischemia in stable and unstable angina, as well as limited data in asymptomatic myocardial ischemia, are unequivocal and are as favorable as those for beta blockers or calcium antagonists. Tolerance is an important problem that unfavorably influences the potential benefits of nitrate therapy. I believe that this problem can be avoided with well-designed dosing regimens. Current research into endothelial biology in health and disease has further supported a physiologic role for the organic nitrates in patients with ischemic heart disease. The nitrate-platelet story, while controversial, is promising and offers another positive rationale for nitrate administration. The concept of nitrates replenishing disordered EDRF release or action is an exciting one. Physicians should feel fortunate to have such a remarkable group of drugs available for their patients.

Comparative evaluation of three dosages of slow-release isosorbide dinitrate (60, 80, 100 mg) in chronic angina of the aged

In a single-blind, placebo-controlled study the acute and chronic antianginal effects of three slow-release (SR) new formulations of isosorbide dinitrate (ISDN 60, 80, 100 mg) have been comparatively evaluated in a group of aged affected by chronic stable effort-induced angina. Compared to placebo, overall the active dose paritetically improved the effort tolerance up to 24 h after the first assumption. In the time course of the trial (2 and 4 weeks) the resting hemodynamic changes induced by the first dose were partially blunted without affecting the exercise related-parameters. Also if plasma levels of ISDN and of its metabolites did not correlate to the degree of physical improvement, the peak increase in effort tolerance was observed under 100 mg treatment. Mild to moderate transient headache was experienced by 50% of actively treated and by 20% of placebo treated patients and no other serious adverse effects have been noted. One may conclude that ISDN in slow-release formulations of 60-100 mg isan effective, safe and well tolerated medication in the management of angina in the aged.

Efficacy of continuous and intermittent transdermal treatment with nitroglycerin in effort angina pectoris: a multicentric study. The Collaborative Nitro Group

Eighty-eight patients (84 men and 4 women; mean age 59.3 years) with stable exercise-induced angina pectoris were enrolled in this within-patient, placebo-controlled study aimed at comparing the efficacy of the continuous and intermittent (12 hour on, 12 hour off) application of transdermal nitroglycerin. Eighty-one patients completed the study. After a 1-week placebo run-in period, during which the stability of angina was assessed on a bicycle ergometer, the patients received continuous treatment (two 10 mg/24 hour patches twice daily, at 8 a.m. and 8 p.m.), intermittent treatment (two 10 mg/24 hour patches at 8 a.m. and two placebo patches at 8 p.m.) and placebo (two placebo patches twice daily, at 8 a.m. and 8 p.m.), each given for one week in a double-blind randomised sequence, according to a 3 x 3 latin-square design. A cycloergometric exercise test was performed at the end of each period of treatment, 4 and 10 hours after the application of the morning patch. In comparison with placebo, both schedules of the active treatment induced a significant increase in both the ischemic (duration of exercise to 1 mm ST segment depression) and the angina threshold (duration of exercise to mild angina) at the 4th and at the 10th hours after-dosing. A significant difference was also found between continuous and intermittent treatment at the same times of observation, in favour of the intermittent schedule. The limited number of anginal attacks recorded during placebo prevented any clinical evaluation of the treatments. This study shows that the efficacy of transdermal nitroglycerin is more pronounced when it is given following an intermittent schedule.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of oral isosorbide-5-mononitrate in patients with ischemic heart failure

This study compared the pharmacokinetics of orally administered isosorbide-5-mononitrate (20 mg) in patients with and without signs of ischemic heart failure after acute myocardial infarction. The central venous pressure was used as a parameter of global myocardial function and to separate 17 patients into two groups with normal (group I: CVP less than 6 cmH2O; Killip class I; n = 9) and elevated (group II: CVP greater than or equal to 6 cmH2O; Killip class II-III; n = 8) pressure. As compared to subjects with normal CVP patients with hemodynamic impairment showed a markedly lower peak concentration of isosorbide-5-mononitrate levels (475 +/- 32 vs 663 +/- 38 ngml-1; p less than 0.01; mean +/- SEM) which occurred delayed (32 +/- 6 vs 55 +/- 9 s; p less than 0.05). Reduced cardiac function also resulted in a prolonged elimination of isosorbide-5-mononitrate as was suggested by the diminished elimination rate constant (0.14 +/- 0.01 vs 0.18 +/- 0.01 h-1; p less than 0.05). Thus, in patients with ischemic heart failure cardiac performance influences both the absorption and apparent elimination phase of oral isosorbide-5-mononitrate.

Tolerance to intravenous nitroglycerin in patients with congestive heart failure: role of increased intravascular volume, neurohumoral activation and lack of prevention with N-acetylcysteine

To better understand the mechanism of nitrate tolerance in patients with congestive heart failure, 13 patients received a 24 h infusion of nitroglycerin (1.5 micrograms/kg body weight per min) with or without N-acetylcysteine (225 mg/kg per 24 h). The infusions were separated by a 24 h nitrate-free interval. By the end of the nitroglycerin infusion, mean arterial pressure had returned to baseline values and there was a significant increase in ventricular filling pressures and systemic vascular resistance compared with values after 1 h of treatment. The simultaneous infusion of N-acetylcysteine had no effect on these changes. Although a strict fluid restriction of 1.5 liters/day was maintained for 1 week before and throughout the study, after 24 h of nitroglycerin infusion there was a significant and similar degree of hemodilution whether nitroglycerin was infused alone (9.1 +/- 4.3%) or with N-acetylcysteine (8.7 +/- 4.1%). This hemodilution corresponded to an increase in intravascular volume of 745 +/- 382 ml, most of which occurred during the 1st h. Plasma renin activity increased and plasma atrial natriuretic peptide decreased during the infusion. The results of this study suggest that nitrate tolerance is multifactorial. In addition to the previously described pharmacologic tolerance to the effect of nitroglycerin on vascular smooth muscle, a capillary fluid shift from the extravascular to intravascular space appears to be involved, especially during the 1st h of the infusion. A third mechanism, reflex neurohumoral activation, also seems to contribute to the genesis of nitroglycerin tolerance.

Sustained beneficial effect of a seventy-two hour intravenous infusion of nitroglycerin in patients with severe chronic congestive heart failure

To determine whether a 72-hour infusion of nitroglycerin produces hemodynamic improvement in patients with severe congestive heart failure and to assess the contributing role of various possible causes of hemodynamic tolerance to nitroglycerin, 19 patients received an infusion of nitroglycerin 1.5 micrograms/kg/min for 72 hours. In a subgroup of patients (n = 10), there was an increase in stroke work index and a decrease in ventricular filling pressures throughout the infusion and even after it was discontinued. Tolerance to the hemodynamic effects of nitroglycerin was partially reversed 8 hours after the infusion was stopped. Neurohumoral changes occurred but appeared to play only a minor role in the development of nitroglycerin tolerance. However, hematocrit fell 9 +/- 5%, which suggests that an increased intravascular volume contributed to tolerance. In summary: (1) a 72-hour infusion of nitroglycerin improves ventricular function in some patients with severe heart failure; (2) volume shifts from the extravascular to the intravascular compartments may, at least in part, be responsible for nitroglycerin tolerance; and (3) reflex neurohumoral activation may also play a small role in nitrate tolerance.

Anti-ischemic and antianginal effects of 60 mg isosorbide-5-mononitrate in patients treated chronically after myocardial infarction

25 patients with stable angina pectoris after acute myocardial infarction were given single and maintenance doses of isosorbide-5-mononitrate (IS-5-MN) in a controlled-release formulation. For evaluation of the efficacy of this treatment, a score based on exercise tests and patient's complaints including additional antianginal medication were used 4 weeks after the acute event. For assessment of anti-ischemic effect non-invasive parameters including heart rate, arterial blood pressure, changes in ST segments, frequency of premature ventricular beats and systolic time intervals were used before medication, 5 h after the initial dose and 7 days after maintenance therapy. The therapeutic concept of interval treatment was found to be effective. Nitrate tolerance did not develop. Measurements of plasma levels under steady-state conditions revealed minimum values of 100 ng/ml and maximum levels of 460 ng/ml which is in between the threshold for anti-ischemic effect and development of nitrate tolerance, respectively.

Individual responses to transdermal nitrates after chronic administration in angina pectoris

The aim of this study was to investigate whether, and to which extent, sustained treatment with transdermal nitroglycerin plasters may lead to the development of tolerance in patients with effort-induced angina pectoris. Ten patients, all men, mean age 62.7 years, took part in a double-blind, cross-over, acute study, comparing the transdermal therapeutic system of nitroglycerin 10 mg/24 hours with placebo. Patients were then treated for 1 month with the active drug in single-blind condition, and finally they took part in a further acute study identical to the first. Cycloergometric exercise tests were carried out 4 hours after dosing. In comparison with placebo, the active drug significantly (P less than 0.01) increased ischaemic threshold (ST depression = 1 mm) after both acute (from 299 +- 92 to 413 +- 120 sec) and chronic treatment (416 +- 107 sec). The same results were obtained for exercise duration to peak exercise (acute study: from 336 +- 65 to 482 +- 90 sec; chronic treatment: 466 +- 118 sec). The final acute study confirmed the stability of angina, showing that the improvement in exercise tolerance after chronic treatment was entirely due to the pharmacological effect of the drug. In terms of single patient response to the active treatment, 7 of the 10 patients showed an improvement in exercise tolerance after both acute and chronic treatment, while in 3 patients no antianginal effect was observed. These results suggest that nitrate tolerance cannot be considered an inevitable finding in patients chronically treated with transdermal patches.

Clinical pharmacokinetics in heart failure. An updated review

Pharmacokinetics is the study of the effect that the body has on drug absorption, distribution, metabolism and excretion. The pharmacokinetics of a specific drug are assessed by the volume of distribution, bioavailability, clearance and elimination half-life. Elimination half-life is directly related to the volume of distribution and inversely related to clearance. Any 1 or more of these parameters may be altered by physiological changes such as ageing, or disease states such as congestive heart failure. Congestive heart failure is associated with hypoperfusion to various organs including the sites of drug clearance, i.e. the liver and kidneys. It also leads to organ congestion as seen in the liver and gut. The main changes in drug pharmacokinetics seen in congestive heart failure are a reduction in the volume of distribution and impairment of clearance. The change in elimination half-life consequently depends on whether both clearance and the apparent volume of distribution change, and the extent of that change. Pharmacokinetic changes are not always predictable in congestive heart failure, but it seems that the net effect of reduction in the volume of distribution and impairment of clearance is that plasma concentrations of drugs are usually higher in patients with congestive heart failure than in healthy subjects. The changes in pharmacokinetics assume importance only in the case of drugs with a narrow therapeutic ratio (e.g. digoxin) and some of the antiarrhythmics such as lignocaine (lidocaine), procainamide and disopyramide. This necessitates reduction in both the loading and maintenance doses. Prolongation of the elimination half-life leads to delay in reaching steady-state, and therefore dose increments must be made more gradually. Plasma concentration measurements of the drugs concerned are a good guide to therapy and help to avoid toxicity. Pharmacokinetic changes are of less importance in the case of drugs with immediate clinical response, e.g. diuretics and intravenous vasodilators such as nitrates and phosphodiesterase inhibitors. The dose in the latter group can be titrated to the desired effect. Not all adverse reactions to drugs that may occur in heart failure are the result of alterations in pharmacokinetics; rather, some may be due to important drug interactions. An interaction may occur directly e.g. reduction of renal clearance of digoxin by captopril and quinidine; or indirectly, e.g. through diuretic-induced hypokalaemia, which exacerbate arrhythmias associated with digoxin and antiarrhythmics such as quinidine and procainamide.

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.

Sustained-release isosorbide mononitrate (50 mg): optimization of a once-daily dosage form for long-term treatment of angina pectoris

A capsule formulation containing 50 mg of isosorbide mononitrate has been developed, 30% of which is in a nonsustained-release form to ensure rapid attainment of initial plasma levels. The remaining 70% is in a sustained-release form that ensures a long-lasting effect and the convenience of once-daily dosing. This formulation of sustained-release isosorbide mononitrate (Elantan LA 50 mg) provides plasma levels greater than 100 ng/ml for 17 hours after oral administration. For the remaining 7 hours, the nitrate plasma level ranges between 50 and 100 ng/ml.

Nitrates

Nitroglycerin and the long-acting nitrates are playing an increasingly important role in cardiovascular medicine. These agents are recommended in all of the various anginal syndromes and are as effective as the beta-blockers and calcium channel antagonists. There is a definite place for nitrate therapy in treating the complications of acute myocardial infarction. These drugs are also highly effective as unloading therapy in congestive heart failure. The mechanisms of action of the nitrates are reviewed in this article. Information is provided regarding nitrate efficacy in all the major clinical syndromes in which these drugs are used. Finally, appropriate dosing strategies are suggested that should eliminate the potential problem of nitrate tolerance.

Prevention of tolerance to nitroglycerin patches by overnight removal

This investigation assesses the extent of tolerance development with nitroglycerin patches and whether tolerance might be prevented by overnight patch removal. On commencing therapy, active patches significantly prolonged exercise time (3.5 hours after patch application) in comparison with placebo, with an accompanying reduction in ST-segment depression at maximal common workload. Patients then received continuous or 12-hour-daily intermittent patch therapy, in a double-blind fashion, for 7 days. Exercise testing was repeated before and after active patch application, on the eighth day of each treatment phase. During continuous therapy, beneficial effects on exercise time and ST depression were abolished. By contrast, during intermittent therapy, prolongation of exercise time and reduction in ST-segment depression still occurred, on testing 3.5 hours after active patch application. These results confirm previous studies showing a high degree of tolerance during continuous therapy with nitroglycerin patches and suggest that tolerance can be prevented by 12-hour-daily intermittent therapy.

Tolerance to glyceryl trinitrate patches: prevention by intermittent dosing

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Immunoscintigraphy of metastases with radiolabelled human antibodies

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