Action And Clinical Pharmacology: The principal pharmacological action of nitroglycerin is relaxation of vascular smooth muscle and consequent dilation of both peripheral arteries and veins, with more prominent effects on the latter. Dilation of the post-capillary vessels, including large veins, promotes peripheral pooling of blood and decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure (preload). Arteriolar relaxation reduces systemic vascular resistance and arterial pressure (afterload). Dilation of the coronary arteries also occurs. The relative importance of preload reduction, afterload reduction, and coronary dilation remains undefined.
When Minitran is applied to the skin, nitroglycerin is absorbed continuously through the skin into the systemic circulation. Thus, the active drug reaches target sites before inactivation by the liver. Nitroglycerin is rapidly metabolized, principally by a liver reductase, to form glycerol nitrate metabolites and inorganic nitrate. Two active major metabolites, 1,2- and 1,3-dinitroglycerols, the products of hydrolysis, appear to be less potent than nitroglycerin as vasodilators but have longer plasma half-lives. The dinitrates are further metabolized to mononitrates (biologically inactive with respect to cardiovascular effects) and ultimately to glycerol and carbon dioxide. There is extensive first-pass deactivation by the liver following gastrointestinal absorption.
In healthy volunteers, steady-state plasma concentrations of nitroglycerin were reached within 2 hours after application of the patch and were maintained at the same level for the duration of the study (24 hours). Upon removal of the patch, plasma concentrations decline rapidly.
Dosing regimens for most chronically used drugs are designed to provide plasma concentrations that are continuously greater than a minimally effective concentration. This strategy is probably inappropriate for organic nitrates. Some controlled clinical trials using exercise tolerance testing have shown maintenance of effectiveness when patches are worn continuously. The large majority of such controlled trials, however, has shown the development of tolerance (i.e., complete loss of effect as measured by exercise testing) within the first day. Tolerance has occurred even when doses greater than 4 mg/hr were delivered continuously. This dose is far in excess of the effective dose of 0.2 to 0.6 mg/hour delivered intermittently.
Efficacy of organic nitrates is restored after a period of absence of nitrates from the body. Drug-free intervals of 10 to 12 hours are known to be sufficient to restore response. Several studies have demonstrated that when nitroglycerin is administered according to an intermittent regimen, doses of nitroglycerin 0.4 to 0.8 mg/hour (20 to 40 cm have increased exercise capacity for up to 8 hours, with a trend of increased exercise capacity to 12 hours. The results of one controlled clinical trial suggests that the intermittent use of nitrates may be associated with decreased exercise tolerance during the last part of the nitrate-free interval, in comparison to placebo. The clinical relevance of this observation is unknown.
In another clinical trial, there was an increase in nocturnal angina attacks during the drug-free period in some patients treated with nitroglycerin as compared to placebo; therefore, the possibility of increased frequency of severity of angina during the nitrate-free interval should be considered. However, in one controlled clinical study, involving 291 patients with angina, involving exercise tolerance testing at 4 hours duration post-dosing. Minitran did not demonstrate any significant evidence of vascular tolerance or rebound angina attacks during long-term intermittent treatment.
Indications And Clinical Uses: Used intermittently (see Pharmacology) for the prevention of anginal attacks in patients with stable angina pectoris associated with coronary artery disease. It can be used in conjunction with other antianginal agents such as beta-blockers and/or calcium antagonists.
Minitran is not intended for the immediate relief of acute attacks of angina pectoris. Sublingual nitroglycerin preparations should be used for this purpose.
Contra-Indications: Known hypersensitivity to nitroglycerin or other nitrates or nitrites. Known or suspected hypersensitivity to components of the patch. Acute circulatory failure associated with marked hypotension (shock and states of collapse). Postural hypotension. Myocardial insufficiency due to obstruction (e.g., in the presence of aortic or mitral stenosis or constrictive pericarditis). Increased intracranial pressure. Increased intraocular pressure. Severe anemia.
Manufacturers’ Warnings In Clinical States: The benefits and safety of transdermal nitroglycerin in patients with acute myocardial infarction or congestive heart failure have not been established. If one elects to use Minitran in these conditions, careful clinical or hemodynamic monitoring must be used to avoid the hazards of hypotension and tachycardia.
Minitran must be removed before cardioversion or DC defibrillation is attempted, as well as before applying diathermy treatment, since it may be associated with damage to the paddles and burns to the patient.
Precautions: Headaches or symptoms of hypotension, such as weakness or dizziness, particularly when arising suddenly from a recumbent position, may occur. A reduction in dose or discontinuation of treatment may be necessary.
Caution should be exercised when using nitroglycerin in patients prone to, or who might be affected by hypotension. The drug therefore should be used with caution in patients who may have volume depletion from diuretic therapy or in patients who have low systolic blood pressure (e.g., below 90 mmHg). Paradoxical bradycardia and increased angina pectoris may accompany nitroglycerin-induced hypotension.
Nitrate therapy may aggravate the angina caused by hypertrophic cardiomyopathy.
In industrial workers who have had long-term exposure to unknown (presumably high) doses of nitroglycerin, tolerance clearly occurs. There is moreover, physical dependence since chest pain, acute myocardial infarction, and even sudden death have occurred during temporary withdrawal of nitroglycerin from these workers. In clinical trials of angina patients, there are reports of anginal attacks being more easily provoked and of rebound in the hemodynamic effects soon after nitrate withdrawal. The importance of these observations to the routine clinical use of nitroglycerin has not been fully elucidated, but patients should be monitored closely for increased anginal symptoms during drug-free periods.
Caution should be exercised in patients with arterial hypoxemia due to anemia (see Contraindications), because in such patients the biotransformation of nitroglycerin is reduced. Similarly, caution is called for in patients with hypoxemia and a ventilation/perfusion imbalance due to lung disease or ischemic heart failure. Patients with angina pectoris, myocardial infarction, or cerebral ischemia frequently suffer from abnormalities of the small airways (especially alveolar hypoxia). Under these circumstances vasoconstriction occurs within the lung to shift perfusion from areas of alveolar hypoxia to better ventilated regions of the lung. As a potent vasodilator, nitroglycerin could reverse this protective vasoconstriction and thus result in increased perfusion to poorly ventilated areas, worsening of the ventilation/perfusion imbalance, and a further decrease in the arterial partial pressure of oxygen.
Tolerance to nitroglycerin with cross tolerance to other nitrates of nitrites may occur (see Pharmacology). Coadministration of other long-acting nitrates could jeopardize the integrity of the nitrate-free interval and therefore must be avoided. As tolerance to nitroglycerin patches develops, the effect of sublingual nitroglycerin on exercise tolerance, although still observable, is somewhat blunted.
Occupational Hazards: As patients may experience faintness and/or dizziness, reaction time when driving or operating machinery may be impaired, especially at the start of treatment.
Pregnancy: It is not known whether nitroglycerin can cause fetal harm when administered to pregnant women or can affect reproductive capacity. Therefore, use only if the potential benefit justifies the risk to the fetus.
Lactation: It is not known whether nitroglycerin is excreted in human milk. Benefits to the mother must be weighed against the risk to the infant.
Children: Safety and effectiveness of use in children have not been established.
Drug Interactions: Concomitant treatment with other vasodilators, calcium channel blockers, ACE inhibitors, beta-blockers, diuretics, antihypertensives, tricyclic antidepressants and major tranquilizers may potentiate the blood pressure lowering effect of Minitran. Dose adjustment may be necessary.
Alcohol may enhance sensitivity to the hypotensive effects of nitrates.
Marked symptomatic orthostatic hypotension has been reported when calcium channel blockers and organic nitrates were used in combination. Dosage adjustments of either class of agents may be necessary.
Concurrent administration of Minitran with dihydroergotamine may increase the bioavailability of dihydroergotamine. Special attention should be paid to this point in patients with coronary artery disease, because dihydroergotamine antagonizes the effect of nitroglycerin and may lead to coronary vasoconstriction.
The possibility that the ingestion of ASA and nonsteroidal anti-inflammatory drugs might diminish the therapeutic response to nitrates and nitroglycerin cannot be excluded.
Information for the Patient: Daily headaches sometimes accompany treatment with nitroglycerin. In patients who get these headaches, the headaches may be a marker of the activity of the drug. Patients should resist the temptation to avoid headaches by altering the schedule of their treatment with nitroglycerin, since loss of headache may be associated with simultaneous loss of antianginal efficacy.
Treatment with nitroglycerin may be associated with lightheadedness on standing, especially just after rising from a recumbent or seated position. This effect may be more frequent in patients who have also consumed alcohol.
After normal use, there is enough residual nitroglycerin in discarded patches that they are a potential hazard to children and pets.
A patient leaflet is supplied with the patches (see Blue Section – Information for the Patient).
Adverse Reactions: Headache, which may be severe, is the most commonly reported side effect. Headache may be recurrent with each daily dose, especially at high doses of nitroglycerin. Headaches may be treated with concomitant administration of mild analgesics. If such headaches are unresponsive to treatment, the nitroglycerin dosage should be reduced or the product discontinued. Transient episodes of lightheadedness, occasionally related to blood pressure changes, may also occur. Hypotension occurs infrequently, but in some patients it may be severe enough to warrant discontinuation of therapy.
Reddening of the skin, with or without a mild local itching or burning sensation, as well as allergic contact dermatitis may occasionally occur. Upon removal of the patch, any slight reddening of the skin will usually disappear within a few hours. The application site should be changed regularly to prevent local irritation.
Less frequently reported adverse reactions include dizziness, faintness, facial flushing and postural hypotension which may be associated with reflex tachycardia. Syncope, crescendo angina and rebound hypertension have been reported but are uncommon. Nausea and vomiting have been reported rarely.
Symptoms And Treatment Of Overdose: Symptoms: Nitroglycerin overdose may result in severe hypotension, persistent throbbing headache, vertigo, palpitations, visual disturbances, flushing, and perspiring skin (later becoming cold and cyanotic), nausea and vomiting (possibly with colic and even bloody diarrhea), syncope (especially in the upright posture), methemoglobinemia with cyanosis, initial hyperpnea, dyspnea, and slow breathing, slow pulse (dicrotic and intermittent), heart block, and bradycardia, increased intracranial pressure with cerebral symptoms of fever, confusion and coma possibly followed by paralysis, clonic convulsions and death due to circulatory collapse.
Treatment: Keep the patient recumbent in a shock position and comfortably warm. Remove all nitroglycerin patches. Passive movement of the extremities may aid venous return. Administer oxygen and artificially ventilate if necessary. Epinephrine is ineffective in reversing the severe hypotensive events associated with overdose; it and related compounds are contraindicated in this situation.
I.V. infusion of normal saline or similar fluid may also be required to produce sufficient central volume expansion. However, in patients with renal disease or congestive heart failure, therapy resulting in central volume expansion is not without hazard. Treatment of nitroglycerin overdose in these patients may be subtle and difficult, and invasive monitoring may be required.
Methemoglobinemia: Case reports of clinically significant methemoglobinemia are rare at conventional doses of nitroglycerin. The formation of methemoglobin is dose-related, and in the case of genetic abnormalities of hemoglobin that favor methemoglobin formation, even conventional doses of organic nitrates can produce harmful concentrations of methemoglobin. Methemoglobin levels are available from most clinical laboratories. The diagnosis should be suspected in patients who exhibit signs of impaired oxygen delivery despite adequate cardiac output and adequate arterial pO2. Classically, methemoglobinemic blood is described as chocolate brown, without color change on exposure to air. If methemoglobinemia is present, i.v. administration of 1 to 2 mg/kg methylene blue 1% solution for injection may be required.
Dosage And Administration: Daily Dosage Schedule: The daily dosage schedule is based on intermittent therapy to prevent the development of tolerance to nitroglycerin. The optimal dose should be selected based upon the clinical response, side effects and the effects of therapy on blood pressure.
The suggested starting dose is between 0.2 and 0.4 mg/hour. Doses between 0.2 and 0.8 mg/hour have shown continued effectiveness for 12 hours daily for at least 1 month (the longest period of studies) of intermittent administration. Although the minimum nitrate-free interval has not been defined, data show that a nitrate-free interval of 10 to 12 hours is sufficient (see Pharmacology). Thus, an appropriate dosing schedule for nitroglycerin patches would include a daily patch-on period of 12 to 14 hours during waking hours and a patch-off period of 10 to 12 hours, usually overnight.
Prevention of Tolerance: Although some controlled clinical trials using exercise tolerance testing have shown maintenance of effectiveness when patches are worn continuously, the large majority of such controlled trials have shown the development of tolerance (i.e., complete loss of effect) within the first 24 hours after therapy was initiated. Dose adjustments even to levels much higher than generally used did not prevent the development of tolerance.
Tolerance can be prevented or attenuated by use of an intermittent dosage schedule. Although the minimum nitrate-free interval has not been defined, clinical trials have demonstrated that an appropriate dosing schedule for nitroglycerin patches would provide for a daily patch-on period of 12 to 14 hours and a daily patch-off period of 10 to 12 hours. The patch-free time should coincide with the period in which angina pectoris is least likely to occur (usually at night). Patients should be watched carefully for an increase of angina pectoris during the patch-free period. Adjustment of background medication may be required.
The dose of Minitran should be periodically reviewed in relation to continuing antianginal control.
Site of Application: Minitran should be applied to the chest, shoulders, upper arm or back and should not be applied to the distal extremities. The skin area should be free of hair in order to provide direct contact of the patch to the skin. If hair is likely to interfere with adhesion of the patch, the area may be lightly shaved. The skin area should be clean, dry and free of irritation or cuts. A different skin site should be used each time a new Minitran patch is applied. It may be necessary to apply more than one patch in order to achieve the optimal dose level. Following use, the patch should be discarded in a manner that prevents accidental application or ingestion by curious children or others.
Availability And Storage: The Minitran transdermal delivery system is a unit designed to provide continuous controlled release of nitroglycerin through intact skin. The rate of release of nitroglycerin is linearly dependent upon the area of the applied system; each cmof applied system delivers approximately 0.03 mg of nitroglycerin per hour. Thus, the 6.7, 13.3, and 20 cmsystems deliver approximately 0.2, 0.4, and 0.6 mg of nitroglycerin per hour, respectively.
The remainder of the nitroglycerin in each system serves as a reservoir and is not delivered in normal use. After 12 hours, for example, each system has delivered about 14% of its original content of nitroglycerin.
The Minitran transdermal delivery system contains nitroglycerin in a hypoallergenic, medical grade, acrylate-based polymer adhesive. Each patch is packaged in foil/polymer film laminate. Cartons of 30 and 100.
Store at controlled room temperature 15 to 30°C. Extremes of temperature and/or humidity should be avoided.
MINITRAN 3M Pharmaceuticals Nitroglycerin Antianginal