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

Pharmacokinetic studies of various preparations of glyceryl trinitrate

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

Contrasting hemodynamic responses in severe heart failure: comparison of captopril and other vasodilator drugs

Four studies were conducted in 36 patients with severe chronic heart failure to compare the central hemodynamic effects of captopril (CPT) to other vasodilator agents. While CPT produced less marked increases in cardiac output than did hydralazine (n = 14), nitroprusside (n = 15), or prazosin (n = 7), it produced decreases in left ventricular filling pressures similar to nitroprusside and prazosin but more than hydralazine. CPT and isosorbide dinitrate (n = 11) produced similar decreases in systemic vascular resistance and left ventricular filling pressure. However, cardiac output increased less with CPT than with nitrates, because heart rate slowed during CPT therapy. In addition, mean right atrial pressure decreased less with CPT than with nitrates, because CPT had minimal effects on limb venous capacitance and pulmonary arteriolar resistance. Alterations in left ventricular pressure-volume relationships likely contributed to the marked decreases in left ventricular filling pressures seen with CPT. In conclusion, the central hemodynamic effects of CPT differ significantly from other vasodilator drugs used in the treatment of heart failure patients. These effects cannot be characterized simply in terms of "balanced" peripheral arterial and venous vasodilation; CPT exerts highly complex effects on peripheral vessels as well as having actions independent of its peripheral vasodilator effects.

Animal pharmacology of nitroglycerin

Nitroglycerin, first introduced over a hundred years ago, is now finding wider clinical applications. To a large degree, the renewed interest in the clinical pharmacologic usage of nitroglycerin is due to the availability of new formulations and drug delivery systems. The current review focuses on the physiological and pharmacological actions of nitroglycerin in mammals. Routes of nitroglycerin metabolism, biochemistry and absorption are discussed. The phenomenon of nitroglycerin tolerance is illustrated and related to specific quantitative alterations occurring at the cellular level. The cardiovascular effects of nitroglycerin are discussed in terms of its effects on coronary flow, the myocardium itself, and on the peripheral vasculature. The early speculation of Murrell (3) that nitroglycerin "would probably prove of service in the treatment of angina pectoris ... and other vascular disorders ..." has now been realized.

Oral isosorbide dinitrate in angina pectoris: comparison of duration of action an dose-response relation during acute and sustained therapy

The effects of different oral doses of isosorbide dinitrate administered acutely and four times daily during sustained therapy were studied in 12 patients with angina pectoris. After administration of 30, 60 and 120 mg of isosorbide dinitrate, the average plasma concentrations were higher and the area under the plasma concentration time curve was greater during sustained than during acute therapy (p less than 0.01). Reduction in standing systolic blood pressure was greater during acute than during sustained therapy (p less than 0.001). This reduction in systolic blood pressure was dose-related and persisted for 8 hours during acute therapy, but was not dose-related and was demonstrable for only 4 hours during sustained therapy. Compared with placebo therapy, exercise duration to the onset of angina and to the development of moderate angina increased significantly after each dose of isosorbide dinitrate for 8 hours during acute therapy but for only 2 hours during sustained therapy. During acute therapy, administration of a single dose of 15 or 30 mg of isosorbide dinitrate produced similar improvement in exercise tolerance as did a dose of 60 or 120 mg. During sustained therapy (15 mg four times daily), exercise tolerance increased to the same magnitude as with doses of 30, 60 or 120 mg four times daily. In most patients, near maximal improvement in exercise tolerance occurred after a dose of 15 or 30 mg four times daily. It is concluded that during sustained therapy with isosorbide dinitrate, partial tolerance to the antianginal and circulatory effects develops rapidly.

Hemodynamic characterization of tolerance to long-term hydralazine therapy in severe chronic heart failure

We performed hemodynamic studies in 11 patients with severe chronic heart failure whose symptoms had returned to their pretreatment status after 37 +/- 15 weeks (mean +/- S.E.M.) of therapy with the vasodilator hydralazine. The cardiac index increased from 1.85 to 3.47 liters per minute per square meter of body-surface area, and systemic vascular resistance decreased from 1748 to 754 dyn . sec. cm-5 (both p less than 0.01) during initial hydralazine administration but returned to pretreatment values on repeat evaluation; withdrawal of the drug produced no hemodynamic deterioration. Responsiveness to hydralazine could not be restored by doubling the oral dose or by intravenous administration; tolerance was associated with fluid retention in five patients but was not reversed by intensive diuresis. In contrast, the responses to nitroprusside evaluated before and after the development of hydralazine tolerance were unaltered; other oral vasodilators were still effective. We conclude that drug-specific tolerance may account for the lack of clinical improvement in some patients with severe heart failure who receive long-term treatment with hydralazine.

Increased effective vascular compliance and venous pooling of intravascular volume during sustained venodilation in conscious dogs

The hemodynamic effects of the long-acting antianginal drug molsidomine were studied in 8 chronically instrumented conscious dogs by measuring the partition of the intravascular volume and the effective compliance of the total vascular bed. The blood volume of the resting dogs was varied by +/- 4 ml/kg in a cycle of blood infusion, withdrawal and reinfusion within 12 minutes. Relating the observed alterations in mean right atrial pressure to the induced changes in intravascular volume, an effective compliance of 2.9 +/- 0.4 ml. mm Hg-1 . kg -1 (mean +/- SD) was found. Heart rate, total peripheral vascular resistance and the local capacity of the distal femoral vein did not change significantly during the cycle of volume alterations. Following 0.1 mg/kg molsidomine i.v., mean right atrial pressure was lowered by 1.6 mm Hg and mean left atrial pressure by 3.4 mm Hg; the effective compliance was elevated to 4.7 +/- 0.6 ml . mm Hg-1. kg -1 (p less than 0.001), and the central blood volume was lowered from 17.8 +/- 3.1 to 14.8 +/0 3.3 ml/kg (p less than 0.01), while the total blood volume remained constant. The decline in stroke volume and the reflexly induced increase in heart rate correlated with the control heart rate. Mean arterial pressure declined from 101 +/- 7 to 91 +/- 14 mm Hg (p less than 0.05) and total peripheral vascular resistance remained unaffected. It is concluded that molsidomine exerts exerts its hypotensive effect by dilation within the vascular low-pressure system and that this dilation can be described quantitatively in conscious animals by the analysis of the total effective vascular compliance.

Mechanisms and implications of vasodilator tolerance in the treatment of congestive heart failure

Vasodilators play an important role in the treatment of the patient with severe heart failure and increased systemic vascular resistance. However, there are both clinical data and theoretic reasons to anticipate that some degree of tolerance may develop during the long-term use of most agents. The cause of the increased vascular resistance of heart failure is not completely understood, but it appears to be related to a number of neuroendocrine, molecular and physical mechanisms including increased activity of the sympathetic nervous and renin-angiotensin systems, and increased vascular stiffness due to intra- and extracellular sodium and fluid accumulation. Not surprisingly, a lowering of systemic vascular resistance either by direct smooth muscle relaxers or by blockade of specific neuroendocrine systems may result in a number of compensatory responses at the neuroendocrine and/or molecular level. The over-all effectiveness of a particular vasodilator is the net sum of its direct pharmacologic action, and the neuroendocrine and molecular responses to the drug. The specific compensatory mechanisms activated depend on several factors including the type of vasodilator used, the dose employed, the baseline neuroendocrine status of the patient, the severity of heart failure and the functional integrity of various reflex systems. Although not directly applicable to patients with heart failure, much information derived from the use of these agents to treat patients with hypertension and angina pectoris suggests several potential mechanisms by which tolerance may develop to virtually all classes of vasodilators. The major types of vasodilators are discussed with regard to their potential mechanisms of tolerance. Finally, the evidence currently available from long-term studies is reviewed in order to assess the potential relevance of vasodilator tolerance to the clinical management of the patient with heart failure.

Kinetics of isosorbide dinitrate and relationships to pharmacological effects

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

Fate of isosorbide dinitrate and mononitrates in patients with renal failure

Isosorbide dinitrate 10 mg, isosorbide 5-mononitrate 5 mg and isosorbide 2-mononitrate 5 mg were administered orally to subjects with and without renal failure, and the plasma concentrations of isosorbide dinitrate and of both the mononitrates were measured. There was no striking difference in plasma concentration as a function of time between subjects with and without renal failure, except for a somewhat higher isosorbide 5-mononitrate concentration after administration of this metabolite to uraemic patients.