Tolerance to the circulatory effects of oral isosorbide dinitrate. Rate of development and cross-tolerance to glyceryl trinitrate

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)

Sustained effect of and lack of development of tolerance to controlled-release isosorbide-5-mononitrate in chronic stable angina pectoris

Tolerance has been shown to develop when nitrate preparations are used in such a manner as to produce plasma levels within the therapeutic range continuously over a 24-hour period. However, a period of reduced or low nitrate plasma levels of a few hours per day may limit or completely prevent tolerance development. In 18 patients with chronic stable angina pectoris, a single 60-mg daily dose of a controlled-release preparation of isosorbide-5-mononitrate (ISMN) was compared with the administration of 30 mg, 4 times daily, of immediate-release isosorbide dinitrate (ISDN) in a double-blind, randomized, placebo-controlled, crossover study. The comparisons were carried out on the first day of therapy and after 11 to 14 days of continuous therapy to assess the duration of effectiveness and the development of tolerance. On short-term therapy, both drugs produced a significant improvement in treadmill walking times to moderate angina in comparison with placebo. The values for ISMN were 87 +/- 99 seconds (23%) at 12:30 P.M., 72 +/- 91 seconds (19%) at 5 P.M. and 51 +/- 81 seconds (13%) at 8:30 P.M. For ISDN, the respective values were 71 +/- 83 seconds (19%), 89 +/- 98 seconds (24%) and 79 +/- 87 seconds (21%). There were no significant differences between drugs. Plasma nitrate levels for each drug paralleled the improvements in exercise performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of effects of isosorbide-5-mononitrate on hepatic hemodynamics in HBsAg-positive cirrhosis

We conducted a randomized controlled hemodynamic study to evaluate the effect of placebo and 20 mg isosorbide-5-mononitrate, a long-acting organic nitrate, in 19 patients with HBsAg-positive cirrhosis by the simultaneous measurement of portal venous pressure and wedged hepatic venous pressure. Baseline values for the two groups were similar. One hour after oral administration of 20 mg isosorbide-5-mononitrate in 10 patients, mean arterial pressure, mean pulmonary arterial pressure and pulmonary capillary wedge pressure significantly decreased from 92 +/- 13 (mean +/- S.D.) to 82 +/- 14 mmHg, from 12.9 +/- 4.5 to 9.3 +/- 2.4 mmHg and from 6.9 +/- 3.4 to 4.3 +/- 1.8 mmHg, respectively. However, both portal venous pressure gradient (from 18.1 +/- 3.6 to 17.5 +/- 3.0 mmHg) and hepatic venous pressure gradient (from 17.8 +/- 5.2 to 16.6 +/- 5.3 mmHg) remained unchanged during the study. In six patients who received 20 mg isosorbide-5-mononitrate twice daily for 7 days, hepatic venous pressure gradient remained unaltered as compared to basal and 1-hr values. There was no significant change in cardiac index, heart rate or systemic vascular resistance in either immediate (1-hr) or delayed (7-day) studies. Three patients (30%) developed mild headache or dizziness and two patients (20%) demonstrated systolic hypotension (less than mmHg) during the immediate study. This study shows that isosorbide-5-mononitrate appears to have no effect in treating portal hypertension in patients with HBsAg-positive cirrhosis. In addition, the isosorbide-5-mononitrate may affect the systemic circulation more than the portal circulation.

Nitrate tolerance in angina pectoris

Tolerance to the hemodynamic and antianginal effects of the organic nitrates develops rapidly during therapy. This has been documented with a variety of nitrate preparations and with different routes of administration. Dosing strategies designed to provide therapeutic plasma nitrate concentrations throughout the 24 hours of the day are regularly associated with the development of tolerance. Recent information indicates that dosing schedules providing a nitrate-free period will permit continued efficacy of the organic nitrates without tolerance development. This can be accomplished in several ways. With oral preparations of isosorbide dinitrate, medication can be given 3 times daily, omitting the evening dose. Buccal nitroglycerin is usually given 3 times daily after meals, and this has been shown not to be associated with tolerance. Likewise, preliminary studies suggest that removal of the nitroglycerin patches for a period of several hours each day will prevent the development of tolerance. Much needs to be learned about the nitrate-free period. With oral isosorbide dinitrate, it appears that 12 hours is required, but this could be substantially less with nitroglycerin preparations. It is also possible that several short periods with low nitrate levels each day would suffice. Thus, simply increasing the interval between dosing of oral preparations may provide an adequate, low, nitrate-free period.

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.

Dose-ranging study of isosorbide-5-mononitrate in chronic congestive heart failure treated with diuretics and angiotensin-converting enzyme inhibitor

The hemodynamic response of isosorbide-5-mononitrate (IS-5-MN) to the addition of the widely used therapy of diuretic drugs and the maximally tolerated dose of enalapril for heart failure was assessed in 8 patients with congestive heart failure (CHF) (New York Heart Association class II and III). The diuretic therapy was furosemide, 40 to 80 mg/day, with or without amiloride, 5 to 10 mg/day. The dose of enalapril was 5 to 20 mg/day. Four hours after the administration of the morning dose of enalapril, a Swan-Ganz catheter was positioned in the pulmonary artery. Patients received increasing doses of IS-5-MN to produce a satisfactory decrease in pulmonary capillary wedge pressure. Two of the first 3 patients studied had a large reduction in blood pressure when given 10 mg of IS-5-MN. Subsequent patients were therefore given an initial dose of 5 mg, the total dose being 5 to 20 mg over 2 hours. Results at baseline and 1 hour after the final dose of IS-5-MN are expressed as mean +/- standard deviation. Both pulmonary artery systolic and diastolic pressures decreased significantly (p less than 0.05) by 12.2 +/- 8.9/4.2 +/- 5.2 mm Hg, from 47.2 +/- 16.0/21.6 +/- 6.0 mm Hg to 35.0 +/- 15.2/17.4 +/- 9.3 mm Hg. Pulmonary capillary wedge pressure decreased by 8.6 +/- 4.4 mm Hg, from 22.1 +/- 5.4 to 13.6 +/- 7.5 mm Hg (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of tolerance to nitroglycerin in the arterial and venous circulation of dogs

The purpose of this study was to define the effects of nitroglycerin on venous tone and to investigate the time course of nitroglycerin tolerance in the peripheral circulation. The changes in the arterial and venous circulation resulting from an intravenous infusion of nitroglycerin (5 micrograms/kg per min) after 5 minutes (acute infusion) were compared with those changes that occurred after 2 hours (chronic infusion) of the same infusion in six splenectomized, ganglion-blocked dogs. Hemodynamics, blood volume and venous and arterial compliance were measured during each infusion. Nitroglycerin initially decreased mean arterial pressure from 81.5 +/- 2.0 to 57.6 +/- 2.7 mm Hg (p less than 0.01). Central blood volume decreased from 21.1 +/- 1.4 to 15.9 +/- 1.1 ml/kg (p less than 0.01), while total blood volume and unstressed vascular volume did not change. In the acute study, nitroglycerin increased venous compliance 33% from 1.75 +/- 0.14 to 2.32 +/- 0.16 ml/mm Hg per kg (p less than 0.01) and arterial compliance 33% from 0.049 +/- 0.007 to 0.065 +/- 0.007 ml/mm Hg per kg (p less than 0.01). At the end of the 2 hour infusion, arterial pressure increased and was now unchanged from control. Central blood volume had returned to baseline, 17.8 +/- 0.9 ml/kg. Total blood volume and unstressed vascular volume remained unchanged. With the long-term infusion, both arterial and venous compliance decreased (p less than 0.02) to 0.050 +/- 0.006 and 1.50 +/- 0.06 ml/mm Hg per kg, respectively, such that neither value was different from control. Nitroglycerin levels remained constant throughout.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction and circumvention of nitrate tolerance applying different dosage intervals

There is increasing evidence that constant nitrate plasma levels, as induced by at least three-times-daily ingestions of isosorbide dinitrate in sustained-release form, lead to an attenuation or even complete loss of the anti-ischemic effects (nitrate tolerance). Therefore, the dependence of tolerance development on dosage intervals according to once-daily and twice-daily ingestions was assessed. Tablets of isosorbide dinitrate (80 mg) in sustained-release form were administered once-daily at 8 A.M. (dosage interval 24 hours) or twice-daily at 8 A.M. and 8 P.M. (dosage interval 12 hours), as well as at 8 A.M. and 2 P.M., respectively (maximal dosage interval 18 hours). A total of 34 patients with angiographically proven coronary artery disease, a history of stable, exercise-dependent angina pectoris, and a reproducible, exercise-induced ST-segment depression of at least 0.15 mV (1.5 mm), who initially showed a response to 80 mg of isosorbide dinitrate, were enrolled. The anti-ischemic effects of isosorbide dinitrate on exercise-induced ischemia were objectively determined by the measurement of exercise-induced ST-segment depression before as well as two, six, and 12 hours after the ingestion at the first and the 15th day of the studies. Since the dosage interval of 12 hours resulted in constant plasma levels, the initially beneficial anti-ischemic effects of isosorbide dinitrate were considerably attenuated after two weeks of treatment. In contrast, the once-daily regimen with its intermittent peaks and valleys of nitrate plasma levels showed identical anti-ischemic effects at the 15th day as compared with the first day. Ingestions at 8 A.M. and 2 P.M. also circumvented the development of nitrate tolerance, however, combined with an even more pronounced anti-ischemic effect after 12 hours as compared with the once-daily regimen. Thus, the circumvention of nitrate tolerance requires a daily "nitrate-poor" interval. The best compromise between a maximal possible anti-ischemic effect and the circumvention of tolerance development was found for the "eccentric" dosage regimen in which the tablets were ingested in the morning and early afternoon.

Tolerance to organic nitrates in ischemic heart disease

The development of tolerance to organic nitrates in patients with ischemic heart disease is reviewed, with particular interest in alterations to both the hemodynamic and antiischemic effects over time. The article primarily focuses on how tolerance is defined, what biochemical mechanisms are involved when this condition occurs, which agents have been associated with the development of tolerance, and what can be done to prevent or reverse the condition in patients taking nitrates for ischemic heart disease. From a historical perspective, tolerance to organic nitrates has been a recognized phenomenon since the last century. The role that blood-level determinations and nitroglycerin pharmacokinetics have in the development of tolerance is discussed, and an extensive overview of currently marketed organic nitrate preparations and a few others available only through approved investigational protocols is presented. The role of cross-tolerance is discussed as is the role that nitrate-free intervals play in partially or completely reversing the effects of tolerance during chronic nitrate therapy. Additionally, a discussion of which specific nitrate formulation are least likely to have tolerance associated with their use is included, such as short-acting nitrate formulations with the exception of the intravenous dosage form. Finally, buccal nitroglycerin is presented as another new formulation that appears to be associated with minimal tolerance in studies already completed.

Hemodynamic effects of oral isosorbide-5-mononitrate and dinitrate in ischemic heart failure

Isosorbide-5-mononitrate (ISMN), the main metabolite of isosorbide dinitrate (ISDN) was recently introduced in clinical use. The hemodynamic effects of oral ISMN and ISDN, administered in equal doses, were studied in a randomized, crossover fashion in 20 patients with pump failure of ischemic etiology. Baseline hemodynamic criteria for admission into the study were: pulmonary capillary wedge pressure (PCW) of at least 20 mmHg and systolic arterial pressure (AP) above 90 mmHg. Hemodynamic parameters were serially measured and systemic vascular resistance was calculated up to 6 h postadministration of either ISMN or ISDN single dose (40 mg). Maximal effects obtained were statistically significantly different from baseline. While ISMN and ISDN appeared to be equipotent in reducing the filling pressure, with a maximum effect reached in 60-120 min, the mononitrate maintained its effects for a longer period.

Study on adrenergic function after development of tolerance to ethylene glycol dinitrate (EGDN) in rats

The effects of sustained exposure to ethylene glycol dinitrate (EGDN; 50 mg.kg-1.2, 10 days) on heart rate (HR) and mean arterial blood pressure (MAP), isolated strips from aorta and vena cava, catecholamine (CA) and DOPAC levels in brain, heart, adrenals and plasma, and synaptosomal uptake of noradrenaline (NA) have been investigated in rats. Aortic strips showed a decreased responsiveness to EGDN and were more sensitive to NA than were control strips 2, 24 and 96 hrs after cessation of EGDN. Acute cumulative doses of EGDN induced a decrease in MAP at all time intervals but 2 hrs after cessation of chronic EGDN-treatment, while NA induced a dose-dependent increase in MAP. MAP was lower 2 hrs after cessation of EGDN, than in the control rats, while HR was higher. After 24 hrs, MAP was slightly higher than in the controls and HR was still elevated. EGDN induced a decrease in the accumulation of L-DOPA and DOPAC in all brain structures measured, which was especially prominent 2 hrs after cessation of EGDN. The levels of CA's and DOPAC in peripheral tissues did generally not change significantly, although there was a tendency to a decrease. L-DOPA, NA and adrenaline (A) in plasma decreased significantly, while DOPAC and dopamine (DA) increased. No consistent effects on uptake of NA into synaptosomes could be distinguished. However, the amount of protein was generally lower at all times after cessation of EGDN. It is suggested that prolonged exposure to EGDN not only induces tolerance at the cellular level, but also interferes with arterial smooth muscle sensitivity to NA and with resetting of MAP and HR. The decrease in the synthesis and turnover of CA's and DOPAC in the brain indicated a decrease in nervous activity, which is reflected by a corresponding decrease of NA and A levels in plasma.

Usefulness of twice-daily isosorbide-5-mononitrate in preventing development of tolerance in angina pectoris

Development of tolerance to nitrates during long-term therapy is a major concern. It has been suggested that isosorbide-5-mononitrate (IS-5MN), an active metabolite of isosorbide dinitrate, administered twice daily 12 hours apart does not lead to development of tolerance. The duration of effects of IS-5MN at a dose of 20 and 40 mg and of placebo was studied in patients with angina pectoris who responded to nitrates after the first dose (n = 12) and after 1 week of twice-daily therapy (n = 9). The study was double-blind, randomized and crossover in design. Compared with placebo values, after the first dose of 20 and 40 mg IS-5MN, exercise duration was higher at 2 hours (p less than 0.001) and 6 hours (p less than 0.02). After 1 week of twice-daily therapy at these doses, exercise duration increased at 2 hours (p less than 0.05) but not at 6 or 10 hours after the dose. After the first dose of 20 and 40 mg IS-5MN, standing systolic blood pressure decreased at 2 hours (p less than 0.02). Blood pressure did not change significantly after chronic therapy. Tolerance to antianginal effects during twice-daily therapy with 20 and 40 mg of IS-5MN developed despite higher plasma IS-5MN concentrations at 2 and 6 hours during twice-daily therapy than after the first dose. The tolerance during twice-daily therapy with IS-5MN was characterized by a reduced peak effect at 2 hours and shortened duration of action compared with first-dose effects.

Comparison of nifedipine and isosorbide dinitrate when added to maximal propranolol therapy in stable angina pectoris

A study was performed to compare isosorbide dinitrate and nifedipine as adjunctive therapy in 14 patients with coronary artery disease and stable angina pectoris taking maximal beta-blocking drugs. Drug titration phases ensured maximal therapy of propranolol, isosorbide or nifedipine. The combination of nifedipine and propranolol was more effective than the combination of isosorbide and propranolol in reducing angina and increasing exercise capacity (323 vs 416 seconds, p less than 0.005) during exercise treadmill testing. Nifedipine produced a greater reduction in systolic blood pressure at submaximal exercise than isosorbide. Global and regional ejection fraction at rest and exercise was assessed with radionuclide ventriculography. The substitution of nifedipine for isosorbide depressed the global ejection fraction at rest (0.61 to 0.56 p less than 0.05) and produced a slight improvement in exercise ejection fraction (0.47 to 0.51, difference not significant). The decrease in ejection fraction from rest to exercise was 0.14 to 0.04 with nifedipine (p less than 0.005). The benefit of nifedipine compared with isosorbide occurred in regions with marked exercise-induced ischemia. In patients treated with maximal beta-blocking therapy, nifedipine is an effective alternative to isosorbide as a combination agent with propranolol. The salutary effects of nifedipine included afterload reduction with exercise and possible improvements in coronary blood supply.

Effect of intervals between doses on the development of tolerance to isosorbide dinitrate

We studied the development of tolerance to isosorbide dinitrate in 12 patients with chronic stable angina pectoris. The effect of 30 mg of isosorbide dinitrate on treadmill exercise performance was assessed before and at one, three, and five hours after a single dose. As compared with placebo, the drug increased treadmill walking time until the onset of angina and until the development of moderate angina over the five-hour observation period (P less than 0.05). The patients then received 30 mg of isosorbide dinitrate twice, three times, and four times daily for a period of one week, and exercise performance was assessed before and at one, three, and five hours after the final morning dose. During sustained treatment two and three times daily, treadmill walking time was longer throughout the five-hour testing period than during the placebo phase (P less than 0.05). In contrast, during treatment four times daily, treadmill walking time was prolonged at one hour (P less than 0.05) but not at three and five hours after the last dose. We conclude that tolerance to the clinical effects of isosorbide dinitrate develops with a sustained dosage of 30 mg four times daily, but not when the drug is given two or three times daily.

Duration of effects and tolerance of slow-release isosorbide-5-mononitrate for angina pectoris

Isosorbide-5-mononitrate (IS-5MN) is an active metabolite of isosorbide dinitrate, but unlike its parent compound, is nearly 100% bioavailable after oral administration. Once-a-day therapy with a slow-release formulation of IS-5MN is used widely in Europe for 24-hour prophylaxis of angina pectoris. In a randomized, crossover, double-blind, placebo-controlled study, the duration of effects of 50 and 100 mg of slow-release IS-5MN were evaluated after the first dose and after once-a-day therapy for 1 week in 9 patients with stable angina pectoris. Compared with placebo values, standing blood pressure decreased (p less than 0.001) and exercise time to the onset of angina and total exercise duration increased (p less than 0.008 and p less than 0.003) at 4 hours, but not at 20 or 24 hours after first dose of 50 and 100 mg of slow-release IS-5MN. After once-a-day therapy for 1 week, no improvement in exercise duration or reduction in ST-segment depression was seen after 50 or 100 mg of slow-release IS-5MN at 4, 20 or 24 hours despite high plasma IS-5MN concentrations. Thus, despite therapeutic plasma concentrations, 50 and 100 mg of slow-release IS-5MN did not exert antianginal or anti-ischemic effects at 20 and 24 hours after the first dose and at 4, 20 and 24 hours after sustained once-a-day therapy for 1 week.

Early tolerance to hemodynamic effects of high dose transdermal nitroglycerin in responders with severe chronic heart failure

Transdermal systems for delivery of nitroglycerin have been shown to provide sustained blood levels of the drug for at least 24 hours. Investigations of hemodynamic effects of transdermal nitroglycerin in patients with heart failure have demonstrated a transient reduction in pressure lasting less than the expected 24 hours. These findings could be due to the development of circulatory tolerance to the vasodilatory effects of nitroglycerin or to insufficient drug dosing. In the present study, we compared the hemodynamic effects of the first and the second doses of high dose (120 mg) transdermal nitroglycerin given 24 hours apart in 11 responders (greater than or equal to 20% reduction in mean pulmonary artery wedge pressure lasting greater than or equal to 2 hours). Initiation of nitroglycerin therapy resulted in a significant reduction in mean right atrial pressure lasting for 14 hours and in a reduction in mean pulmonary artery and mean pulmonary artery wedge pressures lasting 24 hours. After administration of the second dose, mean right atrial pressure at 2 hours (9 +/- 5 versus 7 +/- 4 mm Hg), 4 hours (8 +/- 5 versus 6 +/- 4 mm Hg) and 8 hours (8 +/- 5 versus 6 +/- 3 mm Hg) was higher than after the first dose (p less than 0.05). Both mean pulmonary artery and mean pulmonary artery wedge pressures were significantly higher after the second nitroglycerin dose.(ABSTRACT TRUNCATED AT 250 WORDS)

The haemodynamic and anti-ischaemic effects of a single tablet of 80 mg isosorbide dinitrate in slow-release formulation and a review of nitrate tolerance

There is increasing evidence that relatively constant plasma nitrate concentrations induced by 3-times-daily administration of isosorbide dinitrate can lead to an attenuation or even complete loss of the drug's anti-ischaemic effects (nitrate tolerance). We therefore assessed the dependence of nitrate tolerance development from the haemodynamic and anti-ischaemic effects of a slow-release tablet formulation of isosorbide dinitrate 80 mg, administered according to different daily dosage regimens in patients with angina. It was found that a once-daily regimen, with its consequent peak and trough plasma nitrate concentrations, is capable of protecting against exercise-induced myocardial ischaemia for about 12 hours with the circumvention of nitrate tolerance.

Isosorbide-5-mononitrate and isosorbide dinitrate retard in the treatment of coronary heart disease: a multi-centre study

A multi-centre study was carried out in 200 coronary patients to compare the efficacy and tolerance of isosorbide dinitrate retard (40 mg) and isosorbide-5-mononitrate (20 mg) with regard to the frequency of anginal attacks and consumption of sub-lingual (short acting) nitrates. After receiving treatment for 2 weeks with isosorbide dinitrate retard at a dosage of 2 or 3 tablets per day, only those patients continued the study who had a weekly average of 4 or more anginal attacks during this basal period. The selected patients were divided in 4 groups of 50 patients and received treatment for a further 4 weeks with either isosorbide dinitrate retard at a dosage of 2 tablets (Group D2) or 3 tablets (D3) per day or isosorbide-5-mononitrate at a dosage of 2 tablets (Group M2) or 3 tablets (Group M3) per day. A progressive improvement in symptoms was seen at the end of 2 and 4 weeks with both drugs. The greater therapeutic benefits were obtained in patients in Group M2; the greater difference was observed between Group M2 and D2 (p less than 0.01) and there were also significant differences (p less than 0.05) between Groups M2 and D3 and between Groups M3 and D3. Analysis of the results showed that the more frequently angina attacks had occurred during the basal period, the greater was therapeutic benefit obtained with isosorbide-5-mononitrate compared to isosorbide dinitrate retard at the end of the study. Heart rate at the end of the study showed a slight tendency to increase over initial levels in all groups. In contrast, systolic blood pressure decreased very significantly in all groups (p less than 0.001). Diastolic blood pressure also decreased in all groups but only to a highly significant degree in patients treated with isosorbide-5-mononitrate (p less than 0.001) and the two sub-groups M2 and M3 (p less than 0.005). In patients treated with isosorbide dinitrate retard, the reduction in diastolic pressure was only statistically significant when the 100 patients in the group were considered as a whole (p less than 0.05), while this was not the case for the two sub-groups D2 and D3. The most frequent side-effect was headache, which improved gradually. During treatment there was a progressive dissociation between reduction in the intensity and frequency of this adverse effect and the increasing anti-anginal action of the nitrates.

Nitrate tolerance. A relevant clinical problem?

Tolerance to nitrates has been shown to develop rapidly during therapy in experimental animals and in man. Although tolerance to the haemodynamic effects was originally considered to be of no clinical significance, it has now been demonstrated to have a major effect on the management of patients with angina. The mechanism of tolerance is not clear, but the hypothesis that it is related to depletion of reduced sulfhydryl groups, with resultant decreased production of S-nitrosothiols and cyclic guanosine monophosphate, is not supported by our investigation. Although the mechanism of action is unknown, dosage strategies providing intermittent therapy with nitrates appear to be effective in preventing nitrate tolerance.

Acute and sustained effects of isosorbide 5-mononitrate in stable angina pectoris

Isosorbide 5-mononitrate (IS 5-MN) is an active metabolite of isosorbide dinitrate and is widely used as an antianginal agent. The acute and subacute (2 weeks) effects of IS 5-MN, 40 mg twice daily, were evaluated in 18 patients with stable angina pectoris using computerized exercise testing and a placebo-controlled, double-blind, randomized trial protocol. There were 2 phases of 2 weeks each in which patients received placebo or active IS 5-MN. Acute testing (8 patients) was performed 2 hours after the first dose and subacute testing 2 hours after the morning dose on day 14. Acute testing showed an increase in exercise time from a mean (+/- standard error of mean) of 8.2 +/- 0.6 minutes to 11.1 +/- 0.5 minutes (p less than 0.001) after a single dose of IS 5-MN. Time to 1 mm of ST depression increased significantly and peak exercise ST-segment depression decreased significantly. Rest and peak exercise heart rate increased significantly during acute testing with IS 5-MN; blood pressure did not change significantly. After 2 weeks of therapy, exercise time had not changed (9.9 +/- 0.6 with placebo to 9.7 +/- 0.6 minutes). The beneficial effects on ST-segment variables were sustained at 2 weeks. The data suggest that there is an attenuation of effect with respect to exercise time and sustained beneficial effect on the ST-segment variables. This may be a result of development of partial tolerance to IS 5-MN after 2 weeks of therapy.

Isosorbide dinitrate: relationship between pharmacokinetics and brachial artery hemodynamics in essential hypertension

Pharmacokinetics of isosorbide dinitrate (ISDN) and brachial arterial hemodynamics have been studied in 15 patients with sustained essential hypertension. The hemodynamic study was performed by using a pulsed Doppler device enabling evaluation of the diameter of the brachial artery with an error of less than 10%. After intravenous administration until plateau concentrations were reached, the ISDN infusion was stopped in order to study the disappearance curve of the drug and the pharmacokinetic parameters. ISDN caused a significant decrease in systolic pressure, a significant increase in arterial diameter, and no change in heart rate. Brachial hemodynamics were not correlated with the plasma concentration in the steady state or the area under the disappearance curve. In contrast, the changes in arterial diameter during perfusion were significantly correlated with the apparent distribution volume, a finding that might indirectly reflect the affinity of ISDN for vascular tissues.

Cardiovascular effects of isosorbide dinitrate infused intravenously into anaesthetized dogs

The cardiohaemodynamic response and the development of tolerance to isosorbide dinitrate (ISDN) were examined in anaesthetized, open-chest dogs. ISDN, infused intravenously (i.v.) for 2 h at a rate of 10 or 30 micrograms/kg per min, decreased systemic blood pressure (systolic, mean and diastolic; SBP), left ventricular (LV) systolic and end-diastolic pressure, LVdP/dt max, pressure-rate product and coronary blood flow. No significant changes in heart rate (HR) and coronary vascular resistance were observed. Intravenous ISDN significantly attenuated the vasodilator effect of bolus intracoronary (i.a.) glyceryl trinitrate (GTN, 1 micrograms), and ISDN (30 micrograms), whereas that of bolus i.a. nicorandil (mononitrate, 20 micrograms) remained unaffected. Just after acute tolerance towards i.a. ISDN was provoked 1 h after starting ISDN infusion (30 micrograms/kg per min, i.v.), the combined infusion of ISDN (i.v.) and nicorandil (30 micrograms/kg per min) was instigated for a further hour. Also, 1 h after the onset of vehicle infusion (i.v.), the combined infusion of vehicle and nicorandil (30 micrograms/kg per min, i.v.) was started. There were essentially no significant differences between the corresponding values concerning the coronary vascular responses obtained from the two combined infusion groups.

Nitrate tolerance

Nitrates are widely used in anginal prophylaxis. In spite of the fact that the concept of nitrate tolerance was first put forward many years ago, the question of tolerance has remained controversial. There is widespread agreement that tolerance does occur to the effects of nitrates on arterial pressure. In contrast, tolerance to the venous and pulmonary effects is disputed. Similarly, the possibility of tolerance to the antianginal effects remains at issue. In this review, I discuss the factors which may have contributed to conflicting results in different studies, in particular recent findings on the rapidity of onset and reversal of tolerance. Tolerance develops rapidly on initiation of treatment and disappears equally rapidly on its discontinuation. In addition, tolerance appears to be a function of plasma nitrate profile. It is most likely to occur when plasma nitrate levels are constant and least likely when nitrate levels fluctuate. Furthermore, the provision of a daily nitrate free interval may protect against the development of tolerance. I then discuss the implications of these findings for patient management. They suggest that nitrate prophylaxis should not be used continuously, if this can be avoided. Rather, prophylaxis should be tailored to the individual to provide protection at times of maximum susceptibility, while allowing nitrate levels to fall at other times. The adequacy of antianginal protection with drug regimens incorporating a nitrate free interval requires further assessment. Similarly, the possibility that a nitrate free interval might lead to withdrawal effects and exacerbation of angina needs to be excluded.

Influence of transdermal nitrates on exercise capacity in patients with stable angina

Twenty patients completed a double-blind cross-over study to determine the influence of a transdermal preparation of Nitroglycerin on exercise performance in stable angina. Angiographically proven two or three vessel coronary disease was present in all. After a base-line exercise test the active device was titrated to efficacy or side effects and the number of patches thereafter remained constant (2-6 patches per day; mean 3.5). Patients were randomly allocated to active treatment or placebo, and further exercise tests were performed at 2 hours and 26 hours after application of the device. Patients were then crossed over after one days rest to the opposite treatment group, and exercise studies repeated. Two hours after application of transdermal nitroglycerin total exercise duration increased (mean 14.0 minutes) compared to placebo (12.5 minutes) and control (12.0 minutes) (p less than 0.05). This effect was maintained at 26 hours. Exercise time to anginal threshold (angina + 1.5 mm ST segment depression) was increased at 2 hours and 26 hours with active drug by 11% compared to placebo and by 22% in comparison to control. Double product of heart rate and blood pressure was not significantly different in treated and placebo groups. Oral nitroglycerin consumption assessed during the titration phase was reduced by 71%. It is concluded that transdermal nitroglycerin significantly increases exercise capacity in patients with stable angina, with an effect that is maintained over a 24-hour period using a single dose application.

Hemodynamic factors limiting the response to transdermal nitroglycerin in severe chronic congestive heart failure

To clarify the continuing controversy concerning the use of transdermal nitroglycerin (TDN), the shortterm hemodynamic responses to sublingual, oral and transcutaneous nitrates were evaluated and compared in 22 patients with severe chronic congestive heart failure. Sixteen patients showed favorable hemodynamic effects with TDN, but the doses needed to achieve this response varied greatly: 10 mg/24 hours in 6 patients, 20 mg/24 hours in 5 patients, 40 mg/24 hours in 3 patients and 60 mg/24 hours in 2 patients. Of the 6 remaining patients, 3 did not respond to high-dose TDN even though they showed marked effects after sublingual and oral nitrate administration; 3 others did not respond to any nitrate formulation by any route. TDN produced immediate increases in cardiac index and decreases in right and left ventricular filling pressure, mean arterial pressure and systemic vascular resistance (p less than 0.01). These effects, however, became rapidly attenuated within 3 to 6 hours; after 18 to 24 hours, only modest decreases in right and left ventricular filling pressures were observed. After removal of TDN treatment, rebound decreases in cardiac index and rebound increases in mean arterial pressure and systemic vascular resistance occurred, but right and left ventricular filling pressures returned to pretreatment values without rebound changes. Isosorbide dinitrate, 40 mg orally, produced hemodynamic effects that were greater in magnitude than effects seen after administration of TDN (p less than 0.05 to 0.01), but 4 patients in whom tolerance to TDN developed showed reversible cross tolerance to oral isosorbide dinitrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrate tolerance

The nitrate group of drugs is one of the most commonly used therapeutic modalities. The application of the nitrates is generally directed at ameliorating the symptoms of occlusive coronary artery disease (angina) and/or congestive heart failure. Although studies are available that attempt to refute the concept of nitrate-induced tolerance in angina pectoris, well-designed and well-controlled reports are appearing that convincingly establish the occurrence of one or more expressions of tolerance (e.g., shorter duration of action, loss of intensity of effect) with long-term dosing in this clinical setting. The type and degree of tolerance to nitrate therapy in angina pectoris depend on a number of pharmaceutic-pharmacokinetic considerations, including route of administration, dose strength, dosing frequency, and magnitude and duration of drug delivery. Reports concerning the development of tolerance to nitrates in congestive heart failure are also somewhat conflicting. However, one form and dose of nitrate therapy has been studied rather extensively: isosorbide dinitrate at 40 mg orally every 6 hours. The administration of this preparation over 3 months to a population with heart failure resulted in the development of tolerance to the systemic arterial-arteriolar effects, whereas the pulmonary vascular and venous dilative effects were maintained throughout the long-term dosing period. Exercise tolerance improved for the long-term isosorbide dinitrate group compared to the group receiving long-term placebo therapy. The mechanism(s) of tolerance to the nitrates is not known; altered disposition of reduced sulfhydryl groups at receptor and intracellular sites is the leading hypothesis.

Efficacy of transdermal glyceryl trinitrate in the treatment of chronic stable angina pectoris

A study was carried out to assess the efficacy of a new transdermal preparation of glyceryl trinitrate (Transiderm-Nitro 5) in the 24 hour prophylaxis of angina and to determine the duration of effect of a single patch application. Twelve men with chronic stable angina were studied in a randomised, placebo controlled, double blind trial. By serial treadmill exercise testing a therapeutic effect was shown at three hours; the exercise time to angina and to 1 mm ST segment depression and the total exercise time were all significantly increased. At 24, 48, and 72 hours, however, no therapeutic effect was observed. Recent studies have shown a similar lack of effect at 24 hours for various forms of transdermal delivery systems. It is suggested that this lack of effect is due to the rapid onset of tolerance probably as a result of the constancy of blood concentrations obtained by this method of administration.

Failure of transdermal nitroglycerin to improve exercise capacity in patients with angina pectoris

Sixteen patients with stable angina pectoris were studied in a double blind crossover manner utilizing treadmill exercise testing with the direct measurement of total body oxygen uptake, 1 and 24 hours after application of a 20 cm2 transdermal nitroglycerin system and identical placebo. Testing was performed after a 3 day lead-in period of treatment with either an active patch or placebo. Points of analysis were peak angina and the submaximal work load occurring at 4 minutes of exercise. No statistically significant differences were observed between nitroglycerin and placebo treatment in any of the rest hemodynamic or peak angina variables at 1 or 24 hours. A significant increase in the rate-pressure product at the submaximal work load was observed 1 hour after transdermal nitroglycerin relative to placebo application. However, no significant differences were observed in any of the other measured variables at the submaximal work load, 1 or 24 hours after nitroglycerin application. The once daily application of a 20 cm2 transdermal nitroglycerin system was ineffective in altering the exercise capacity of patients with angina pectoris. The lack of efficacy at 1 hour appears to be due to inadequate nitroglycerin blood levels; at 24 hours it may be due to tolerance.

Isosorbide dinitrate and glyceryl trinitrate: demonstration of cross tolerance in the capacitance vessels

Cross tolerance to the arterial effects of sublingual glyceryl trinitrate (GTN) has been demonstrated in subjects taking oral isosorbide dinitrate (ISDN). To determine if cross tolerance also develops in the venous system, the effects of 0.6 mg of GTN on venous capacitance were assessed before (stage A) and during (stage B) therapy with ISDN. Venous capacitance was assessed using the radionuclide blood pool method, with relative changes in regional blood volume measured in the forearm in 6 patients and the splanchnic circulation in 4 patients. Heart rate, blood pressure and blood volume were measured before and at 1-minute intervals for 10 minutes after GTN; there was less than 2% variability in regional blood volume during 6 control measurements. During stage A, 5 minutes after GTN, systolic blood pressure (mean +/- standard deviation) decreased by 14% (from 125 +/- 15 to 107 +/- 19 mm Hg, p less than 0.01) and heart rate increased by 17% (from 68 +/- 14 to 80 +/- 17 beats/min, p less than 0.001), while regional blood volume increased to 101 +/- 2% at 1 minute (difference not significant [NS]), 111 +/- 2% at 5 minutes (p less than 0.001) and 107 +/- 3% at 10 minutes (p less than 0.01) relative to baseline measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrate cross-tolerance: effect of sublingual isosorbide dinitrate and nitroglycerin during sustained nitrate therapy

In a randomized, single-blind, crossover study, 10 patients with stable, exercise-induced angina pectoris were studied during sustained therapy with oral isosorbide dinitrate (ISDN). Circulatory changes and exercise performance were evaluated before and 6 hours after therapy with oral ISDN. One-half hour after this therapy, sublingual ISDN or nitroglycerin (NTG) was administered and exercise testing repeated. Treadmill walking time 6 hours after oral ISDN was similar to the control value. Subsequent administration of sublingual ISDN improved walking time from 429 +/- 156 to 513 +/- 166 seconds (p less than 0.005), whereas after NTG improved from 411 +/- 159 to 480 +/- 158 second (p less than 0.005). The improvement in walking time with ISDN (23%) and NTG (18%) and the absolute walking times were not different. The standing systolic blood pressure decreased from 124 +/- 23 to 112 +/- 22 mm Hg (p less than 0.02) after therapy with sublingual ISDN and 122 +/- 23 to 110 +/- 24 mm Hg (p less than 0.005) after administration of NTG. This study demonstrates that (1) during sustained ISDN therapy, walking time returns to control values by 6 hours; (2) administration of either sublingual ISDN or NTG results in significant circulatory changes and improvement in walking time; and (3) the changes in circulatory and exercise variables after administration of NTG in patients taking sustained ISDN therapy cannot be taken as evidence of an absence of cross-tolerance between these agents.

Pharmacokinetic determinants of nitrate action

An update on some of the recent studies relating to organic nitrate pharmacokinetics and pharmacodynamics is presented. The systemic clearance of nitroglycerin was found to be unaffected by portacaval shunting in animals. Thus, the liver only plays a minor role in the metabolism of systemic nitroglycerin. Organic nitrates are extensively taken up by blood vessels in which metabolic activation can occur to produce vascular activity. During sustained therapy, nitrate metabolites may decrease the systemic and hepatic clearance of the parent drug, thus increasing its plasma concentration. Metabolites could also decrease the extent of metabolism in vascular tissues, thus contributing to vascular nitrate tolerance. Therefore, during long-term angina therapy when metabolites are present, the same plasma nitrate concentration may produce less effects compared with that obtained after acute dosing. Nitrate action was shown to be possibly dependent on the rate of drug input. An alternate dosing mode is proposed that speculatively may provide an improvement in producing and maintaining nitrate action in long-term angina therapy.

Hemodynamic effects of vasodilators and long-term response in heart failure

Hemodynamic responses to vasodilators are commonly assessed when starting long-term vasodilator treatment in patients with chronic left ventricular failure, although the relation between short- and long-term responses is not established. Thus, short- and long-term hemodynamic responses to placebo and vasodilators (isosorbide dinitrate, minoxidil and enalapril or captopril) were measured and long-term clinical efficacy was assessed by changes in exercise capacity after 1 to 5 months of vasodilator administration (plus digitalis and diuretic agents) in 46 patients with New York Heart Association functional class II to IV heart failure caused by cardiomyopathy. There were no significant changes in hemodynamics or exercise capacity during placebo treatment. After initial doses and during long-term administration of vasodilator drugs, hemodynamics were significantly improved. After long-term vasodilator treatment, maximal oxygen uptake during exercise increased by 2.9 +/- 5.7 ml/min per kg from a control value of 14.1 +/- 5.6 ml/min per kg (p less than 0.01), and exercise duration also increased by 1.8 +/- 3.5 minutes (p less than 0.01). Changes in maximal oxygen uptake, however, did not correlate with short-term changes in pulmonary wedge pressure (correlation coefficient [r] = -0.14), cardiac index (r = -0.01) or systemic vascular resistance (r = -0.20). Long-term hemodynamic changes also failed to correlate with changes in exercise capacity. Baseline hemodynamics, cardiac dimensions and left ventricular ejection fraction before vasodilator administration all failed to correlate with baseline exercise capacity or with long-term changes in exercise capacity. Thus, hemodynamic measurements at initiation or during follow-up of vasodilator therapy do not relate to long-term clinical efficacy assessed by exercise capacity in patients with chronic left ventricular failure. Therefore, the rationale for making invasive hemodynamic measurements before initiating long-term vasodilator therapy for heart failure is questioned.

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.

Treatment of coronary heart disease with isosorbide mononitrate ('Elantan' 20): a multi-centre study in hospital and general practice

An open, multi-centre clinical trial was carried out in 537 hospital patients and 2138 general practice patients to evaluate the efficacy and tolerance of isosorbide 5-mononitrate in the treatment of angina pectoris. Prior to entry into the trial, angina attack frequency and acute glyceryl trinitrate consumption were assessed during previous, in most cases unsatisfactory, anti-anginal therapy. After a treatment-free washout period of 3 days, graded multi-stage exercise testing was performed and then treatment started with 20 mg isosorbide mononitrate 3-times per day. Exercise testing was repeated after 14 days' therapy and, in the case of the hospital patients, also 4 to 5 hours after the first dose of isosorbide mononitrate. At the end of the 14-day treatment period, angina attack frequency and glyceryl trinitrate consumption were again assessed. Similar results were obtained for both hospital and general practice patients. Changing to isosorbide mononitrate resulted in a marked reduction in angina frequency, with complete elimination of angina attacks in approximately half of the patients; nocturnal angina, present in approximately 20% of the patients during previous therapy, virtually disappeared during isosorbide mononitrate therapy. Exercise tolerance and performance improved in the majority of patients, with a marked increase in the number of patients able to exercise to the level at which some symptom other than angina pectoris caused them to stop. ST-depression during exercise and exercise-induced arrhythmias also showed clear reductions during isosorbide mononitrate therapy. Tolerance to isosorbide mononitrate was good, the expected 'nitrate headaches' being the only common side-effect reported. The results were such that continuation of treatment with isosorbide mononitrate after the trial was recommended by the attending physician in 77% of the hospital patients and 87% of the general practice patients.

Hemodynamic and clinical response to three-day infusion of sulmazol (AR-L 115 BS) in severe congestive heart failure

Sulmazol (AR-L 115 BS) is a new positively inotropic drug with arterial and venous vasodilating properties. We studied the effects of sulmazol (three-day infusion) on clinical tolerance, hemodynamics, and blood gas levels in ten patients with severe chronic heart failure. The hemodynamic monitoring included a Swan-Ganz catheter in the pulmonary artery and a radial catheter. Blood gas levels were determined on samples of arterial and mixed venous blood. After 24 hours of infusion, there was a significant increase in cardiac index (2 to 2.5 L/min/sq m; p less than 0.005) and a significant decrease in pulmonary wedge pressure (28 to 19 mm Hg; p less than 0.001) and in right atrial pressure (7 to 4 mm Hg; p less than 0.001) without significant changes in heart rate and systolic blood pressure. These beneficial effects lasted during the three days of infusion. Oxygen delivery was significantly increased (350 to 443 ml/min/sq m; p less than 0.005) without significant change in arterial oxygen tension. The side effects included nausea, vomiting, anorexia, and mild thrombocytopenia. We conclude that sulmazol is a potent drug which may improve severely deteriorated left and right ventricular function in patients with chronic refractory heart failure without affecting the heart rate and the systolic blood pressure.

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.

Symptoms, haemodynamics, and exercise capacity during long term treatment of chronic heart failure. Experience with pirbuterol

An open study of long term treatment with an oral beta 2 agonist (pirbuterol 20 mg three times daily) was undertaken in 63 patients with severe chronic heart failure. During three months of treatment 20 (32%) patients died, of whom 16 were taking the drug at the time of death. Mortality was related to initial functional class (New York Heart Association classification: 23% in grade III and 75% in grade IV). Concomitant treatment with digoxin did not affect mortality. The drug was well tolerated by most patients but unwanted side effects necessitated withdrawal of the drug in six (10%). Thirty-five patients were continuing to take the drug after three months, of whom 22 reported symptomatic improvement and only four deterioration. There was a relation between symptomatic improvement and increase in exercise capacity. At initial haemodynamic assessment a single dose of pirbuterol increased the cardiac index by 34% and the stroke index by 21%. Left ventricular filling pressure fell by 23% and systemic vascular resistance by 22%. Haemodynamic reassessment after three months of continuous treatment in 29 patients showed maintained improvement in the group as a whole, although individual variation was considerable. There was no apparent relation between haemodynamic improvement and improvement in exercise duration and symptoms. Severe heart failure has a poor prognosis. Identification of those patients who may derive benefit from treatment with a particular drug is not yet possible.

New perspectives on therapeutic application of nitrates as vasodilator agents for severe chronic heart failure

Although nitrates produce marked decreases in ventricular filling pressures in patients with severe heart failure, their therapeutic value has long been believed to be limited because they were thought to exert minimal arterial dilating effects. Recently, however, new conceptual approaches to vasodilator drugs have been developed that have challenged this traditional view. These new perspectives indicate that nitrates exert dilator actions on both the arterial and venous circulations, and reduce both preload and afterload; such balanced circulatory responses are particularly evident when large doses of these drugs are used. Cardiac output increases markedly with nitrates in patients with a greatly increased systemic vascular resistance before treatment or with significant mitral regurgitation. The major reason for the limited increases in cardiac output noted in previous studies is the inclusion of patients with heart failure whose pretreatment values for cardiac output were within normal limits; in these persons nitrates markedly activate neurohumoral vasoconstrictor mechanisms that counteract the arterial dilating actions of these drugs. Long-term nitrate therapy attenuates exercise-induced increases in pulmonary venous pressures, which permit patients to undergo repeated submaximal exercise with fewer symptoms; this improves physical conditioning and exercise capacity, even in the absence of drug-related changes in cardiac output. The long-term hemodynamic and clinical benefits of nitrates in heart failure have been confirmed by two independent randomized double-blind placebo-controlled clinical trials.

Regression of myocardial cellular hypertrophy with vasodilator therapy in chronic congestive heart failure associated with idiopathic dilated cardiomyopathy

Forty-nine patients with idiopathic dilated cardiomyopathy (IDC) were evaluated to determine the hemodynamic and morphologic effects of vasodilator therapy. Hydralazine (225 mg/day, H), isosorbide dinitrate (160 mg/day, I), and combination H + I therapy were compared with placebo (P) at baseline and after 3 months of continuous therapy. Thirty-three randomly assigned patients completed the study. Hemodynamic parameters included the echocardiographic percent change of left ventricular diameter (% delta D), the systolic time intervals ratio of preejection period to left ventricular ejection time (PEP/LVET), the pulmonary capillary wedge pressure, mean pulmonary artery pressure, cardiac index, systemic vascular resistance, and pulmonary vascular resistance. An endomyocardial biopsy was performed at baseline and after 3 months; the myocardial cell diameter of 50 cells per biopsy was measured. During the 3-month study 5 patients died; there was not a significant difference among the groups in the number of deaths. The % delta D and PEP/LVET did not change in the P or I groups but did improve significantly from baseline in the H and H + I groups. The pulmonary capillary wedge and mean pulmonary artery pressures and the pulmonary vascular resistance did not change in the P or H groups but did decrease significantly in the I and H + I groups. The P and I groups did not have improvement in systemic vascular resistance or cardiac index, whereas the H group had a decrease in systemic vascular resistance and an increase in cardiac index from 2.5 +/- 0.4 to 3.1 +/- 0.4 liters/min/m2 (p less than 0.05). The H + I group also had a decrease in systemic vascular resistance; the cardiac index increased from 2.3 +/- 0.4 to 3.1 +/- 0.4 liters/min/m2 (p less than 0.01). Myocardial cell diameter did not change in the P or I group. Cell diameter of the H group decreased from 25.4 +/- 3.1 microns at baseline to 23.1 +/- 3.8 microns (p less than 0.05) after 3 months of continuous therapy. The H + I group decreased its cell diameter from 23.9 +/- 3.7 to 22.2 +/- 2.2 microns (p less than 0.05). Compared with P and H, patients treated with I alone or H + I had a significant reduction of preload. In contrast to P and I, H alone and H + I elicited improvement in parameters of inotropy and afterload, and this improvement was accompanied by a reduction in cell diameter. Chronic therapy of heart failure with H and H + I effects a persistent augmentation of cardiac function and improvement of myocardial cellular morphology.

Efficacy and safety of verapamil in patients with angina pectoris after 1 year of continuous, high-dose therapy

The long-term efficacy and safety of high-dose verapamil therapy (480 mg/day) was assessed in 26 patients with chronic stable angina pectoris during a 3-phase protocol: Phase 1--an initial, 6-week placebo-controlled, double-blind crossover assessment; Phase 2--an open label, 1-year follow-up; and Phase 3--a final drug withdrawal and rechallenge 10-week study. Three patients withdrew during Phase 2 (1 had hepatitis and 2 underwent coronary bypass surgery). Adverse effects during Phase 2 were mild, consisting of constipation (6 patients) and prolongation of the P-R interval (5 patients); however, no patient required alteration of the 480 mg/day dosage. At the end of Phase 2, 10 patients underwent the Phase 3 study, commencing with a 2-week period in which verapamil was either tapered gradually or abruptly discontinued. This was followed by an 8-week double-blind, placebo-controlled crossover rechallenge study with verapamil. The clinical and exercise responses to verapamil compared with placebo were similar during the Phase 3 protocol and the initial Phase 1 study (treadmill time increased by 55% and anginal attacks per week decreased by 63% during Phase 3, compared with a 28% increase and a 42% decrease, respectively, during Phase 1, p = not significant [NS]). Withdrawal of verapamil produced a similar return of anginal symptoms whether the drug was abruptly discontinued or its administration tapered. No patient had unstable angina pectoris or acute myocardial infarction. These investigations demonstrate that verapamil is safe and effective when evaluated after 1 year of continuous therapy using a dosage of 480 mg/day. There is no evidence of drug tachyphylaxis, nor does verapamil appear to cause an abrupt withdrawal syndrome in patients with chronic stable angina pectoris.