Nitroglycerin Tablet, USP
TABLE OF CONTENTS
Nitroglycerin, an organic nitrate, is a vasodilating agent. The chemical name for nitroglycerin is 1, 2, 3 propanetriol trinitrate and the chemical structure is:
Molecular weight: 227.09
Nitroglycerin is a stabilized sublingual compressed nitroglycerin tablet that contains 0.3 mg (1/200 grain), 0.4 mg (1/150 grain), or 0.6 mg (1/100 grain) nitroglycerin; as well as lactose monohydrate, NF; glyceryl monostearate, NF; pregelatinized starch, NF; calcium stearate, NF powder; and silicon dioxide, colloidal, NF.
|2. INDICATIONS AND USAGE|
Nitroglycerin is indicated for the acute relief of an attack or acute prophylaxis of angina pectoris due to coronary artery disease.
|3. DOSAGE AND ADMINISTRATION|
One tablet should be dissolved under the tongue or in the buccal pouch at the first sign of an acute anginal attack. The dose may be repeated approximately every 5 minutes, until relief is obtained. If the pain persists after a total of 3 tablets in a 15-minute period, prompt medical attention is recommended. Nitroglycerin may be used prophylactically 5 to 10 minutes prior to engaging in activities which might precipitate an acute attack.
During administration the patient should rest, preferably in the sitting position.
No dosage adjustment is required in patients with renal failure.
Allergic reactions to organic nitrates are extremely rare, but they do occur. Nitroglycerin is contraindicated in patients who are allergic to it.
Sublingual nitroglycerin therapy is contraindicated in patients with early myocardial infarction, severe anemia, increased intracranial pressure, and those with a known hypersensitivity to nitroglycerin.
Administration of nitroglycerin tablets, USP is contraindicated in patients who are using Viagra® since Viagra has been shown to potentiate the hypotensive effects of organic nitrates.
|5. MECHANISM OF ACTION|
Nitroglycerin forms free radical nitric oxide (NO) which activates guanylate cyclase, resulting in an increase of guanosine 3'5' monophosphate (cyclic GMP) in smooth muscle and other tissues. These events lead to dephosphorylation of myosin light chains, which regulate the contractile state in smooth muscle, and result in vasodilatation.
|6. USE IN SPECIFIC POPULATIONS|
6.1 Usage in Pregnancy
Pregnancy Category C
There are no adequate and well-controlled studies in pregnant women. Nitroglycerin should be given to a pregnant woman only if clearly needed.
6.2 Nursing Mothers
It is not known whether nitroglycerin is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when nitroglycerin is administered to a nursing woman.
6.3 Pediatric Use
Safety and effectiveness in pediatric patients have not been established.
6.4 Geriatric Use
Clinical studies of nitroglycerin did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
|7. WARNINGS AND PRECAUTIONS|
The benefits of sublingual nitroglycerin in patients with acute myocardial infarction or congestive heart failure have not been established. If one elects to use nitroglycerin in these conditions, careful clinical or hemodynamic monitoring must be used because of the possibility of hypotension and tachycardia.
General: Only the smallest dose required for effective relief of the acute anginal attack should be used. Excessive use may lead to the development of tolerance. Nitroglycerin tablets are intended for sublingual or buccal administration and should not be swallowed.
Severe hypotension, particularly with upright posture, may occur with small doses of nitroglycerin. This drug should therefore be used with caution in patients who may be volume-depleted or who, for whatever reason, are already hypotensive. Hypotension induced by nitroglycerin may be accompanied by paradoxical bradycardia and increased angina pectoris.
Nitrate therapy may aggravate the angina caused by hypertrophic cardiomyopathy.
As tolerance to other forms of nitroglycerin develops, the effects of sublingual nitroglycerin on exercise tolerance, although still observable, is blunted.
In industrial workers who have had long-term exposure to unknown (presumably high) doses of organic nitrates, tolerance rarely occurs. Chest pain, acute myocardial infraction, and even sudden death have occurred during temporary withdrawal of nitrates from these workers, demonstrating the existence of true physical dependence.
Several clinical trials of nitroglycerin patches or infusions in patients with angina pectoris have evaluated regimens which incorporated a 10 to 12 hour nitrate free interval. In some of these trials, an increase in the frequency of anginal attacks during the nitrate free interval was observed in a small number of patients. In one trial, patients had decreased exercise tolerance at the end of the nitrate interval. Hemodynamic rebound has been observed only rarely; on the other hand, few studies were so designed that rebound, if it had occurred, would have been detected.
Nitrate tolerance as a result of sublingual nitroglycerin administration is probably possible, but only in patients who maintain high continuous nitrate levels for more than 10 or 12 hours daily. Such use of sublingual nitroglycerin would entail administration of scores of tablets daily and is not recommended.
The drug should be discontinued if blurring of vision or drying of the mouth occurs. Excessive dosage of nitroglycerin may produce severe headaches.
Information for Patients
Nitroglycerin is a sublingual tablet and should not be chewed, crushed, or swallowed.
If possible, patients should sit down when taking nitroglycerin tablets and should use caution when returning to a standing position. This eliminates the possibility of falling due to lightheadedness or dizziness.
One tablet should be dissolved under the tongue or in the buccal pouch at the first sign of an acute anginal attack. The dose may be repeated approximately every 5 minutes, until relief is obtained.
If chest pain persists after a total of 3 tablets in a 15-minute period, or the pain is different than is typically experienced, prompt medical attention is recommended.
Nitroglycerin may be used prophylactically 5 to 10 minutes prior to engaging in activities which might precipitate an acute attack.
Nitroglycerin may produce a burning or tingling sensation when administered sublingually; however, the ability to produce a burning or tingling sensation should not be considered a reliable method for determining the potency of the tablets.
Headaches can sometimes accompany treatment with nitroglycerin. In patients who get these headaches, the headaches may be a marker of the activity of the drug.
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.
Nitroglycerin should be kept in the original glass container and must be tightly capped after each use to prevent loss of tablet potency.
|8. ADVERSE REACTIONS|
Headache which may be severe and persistent may occur immediately after use. Vertigo, dizziness, weakness, palpitation, and other manifestations of postural hypotension may develop occasionally, particularly in erect, immobile patients. Marked sensitivity to the hypotensive effects of nitrates (manifested by nausea, vomiting, weakness, diaphoresis, pallor, and collapse) may occur at therapeutic doses. Syncope due to nitrate vasodilatation has been reported. Flushing, drug rash, and exfoliative dermatitis have been reported in patients receiving nitrate therapy.
HEMODYNAMIC EFFECTS: The effects of nitroglycerin overdose are generally the results of nitroglycerin’s capacity to induce vasodilatation, venous pooling, reduced cardiac output, and hypotension. These hemodynamic changes may have protean manifestations, including increased intracranial pressure, with any or all of persistent throbbing headache, confusion, and moderate fever; vertigo; palpitations; tachycardia; visual disturbances; nausea and vomiting (possibly with colic and even bloody diarrhea); syncope (especially in the upright posture); dyspnea, later followed by reduced ventilatory effort, diaphoresis, with the skin either flushed or cold and clammy; heart block and bradycardia; paralysis; coma; seizures; and death.
No specific antagonist to the vasodilator effects of nitroglycerin is known, and no intervention has been subject to controlled study as a therapy of nitroglycerin overdose.
Because the hypotension associated with nitroglycerin overdose is the result of venodilatation and arterial hypovolemia, prudent therapy in this situation should be directed toward increase in central fluid volume. Passive elevation of the patient’s legs may be sufficient, but intravenous infusion of normal saline or similar fluid may also be necessary.
The use of epinephrine or other arterial vasoconstrictors in this setting is likely to do more harm than good.
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: Methemoglobinemia has been rarely reported in association with organic nitrates. 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, intravenous administration of methylene blue, 1 to 2 mg/kg of body weight, may be required.
|10. DRUG INTERACTIONS|
Patients receiving antihypertensive drugs, beta-adrenergic blockers, or phenothiazines and nitrates should be observed for possible additive hypotensive effects. Marked orthostatic hypotension has been reported when calcium channel blockers and organic nitrates were used concomitantly.
Concomitant use of nitrates and alcohol may cause hypotension.
The vasodilatory and hemodynamic effects of nitroglycerin may be enhanced by concomitant administration of aspirin.
Intravenous administration of nitroglycerin decreases the thrombolytic effect of alteplase. Therefore, caution should be observed in patients receiving sublingual nitroglycerin during alteplase therapy.
Intravenous nitroglycerin reduces the anticoagulant effect of heparin and activated partial thromboplastin times (APTT) should be monitored in patients receiving heparin and intravenous nitroglycerin. It is not known if this effect occurs following single sublingual nitroglycerin doses.
Tricyclic antidepressants (amitriptyline, desipramine, doxepin, others) and anticholinergic drugs may cause dry mouth and diminished salivary secretions. This may make dissolution of sublingual nitroglycerin difficult. Increasing salivation with chewing gum or artificial saliva products may prove useful in aiding dissolution of sublingual nitroglycerin.
Oral administration of nitroglycerin markedly decreases the first-pass metabolism of dihydroergotamine and subsequently increases its oral bioavailability. Ergotamine is known to precipitate angina pectoris. Therefore, patients receiving sublingual nitroglycerin should avoid ergotamine and related drugs or be monitored for symptoms of ergotism if this is not possible.
Administration of nitroglycerin is contraindicated in patients who are using Viagra (sildenafil citrate). Viagra has been shown to potentiate the hypotensive effects of organic nitrates.
A decrease in therapeutic effect of sublingual nitroglycerin may result from use of longacting nitrates.
Drug/Laboratory Test Interactions: Nitrates may interfere with the Zlatkis-Zak color reaction causing a false report of decreased serum cholesterol.
Absorption: Nitroglycerin is rapidly absorbed following sublingual administration of nitroglycerin tablets. Mean peak nitroglycerin plasma concentrations occur at a mean time of approximately 6 to 7 minutes postdose. Maximum plasma nitroglycerin concentrations (Cmax) and area under the plasma concentration-time curves (AUC) increase dose-proportionally following 0.3 to 0.6 mg nitroglycerin. The absolute bioavailability of nitroglycerin from nitroglycerin tablets is approximately 40% but tends to be variable due to factors influencing drug absorption such as sublingual hydration and mucosal metabolism.
Distribution: The volume of distribution (VArea) of nitroglycerin following intravenous administration is 3.3 L/kg. At plasma concentrations between 50 and 500 ng/mL, the binding of nitroglycerin to plasma proteins is approximately 60%, while that of 1,2- and 1,3-dinitroglycerin is 60% and 30%, respectively.
Metabolism: A liver reductase enzyme is of primary importance in the metabolism of nitroglycerin to glycerol di- and mononitrate metabolites and ultimately to glycerol and organic nitrate. Known sites of extrahepatic metabolism include red blood cells and vascular walls. In addition to nitroglycerin, 2 major metabolites 1,2- and 1,3-dinitroglycerin, are found in plasma. Mean peak 1,2- and 1,3-dinitroglycerin plasma concentrations occur at approximately 15 minutes postdose. The elimination half-life of 1,2- and 1,3-dinitroglycerin is 36 and 32 minutes, respectively. The 1,2- and 1,3-dinitroglycerin metabolites have been reported to possess approximately 2% and 10% of the pharmacological activity of nitroglycerin. Higher plasma concentrations of the dinitro metabolites, along with their nearly 10-fold longer elimination half-lives, may contribute significantly to the duration of pharmacologic effect. Glycerol mononitrate metabolites of nitroglycerin are biologically inactive.
Elimination: Nitroglycerin plasma concentrations decrease rapidly with a mean elimination half-life of 2 to 3 minutes. Half-life values range from 1.5 to 7.5 minutes. Clearance (13.6 L/min) greatly exceeds hepatic blood flow. Metabolism is the primary route of drug elimination.
|12. HOW SUPPLIED/STORAGE AND HANDLING|
1) How Available:
a) Brand name: NITROSTAT, by PFIZER PHARMS.
b) Generic drugs: None.
2) How Supplied:
Nitrostat is supplied as white, round, flat-faced tablets in 3 strengths (0.3 mg, 0.4 mg, and 0.6 mg) in bottles containing 100 tablets each, with color-coded labels, and in color-coded Patient Convenience Packages of 4 bottles of 25 tablets each.
0.3 mg (1/200 grain): Coded “N” on one side and “3” on the other.
N 0071-0417-24—Bottle of 100 tablets
0.4 mg (1/150 grain): Coded “N” on one side and “4” on the other.
N 0071-0418-13—Convenience Package
N 0071-0418-24—Bottle of 100 tablets
0.6 mg (1/100 grain): Coded “N” on one side and “6” on the other.
N 0071-0419-24—Bottle of 100 tablets
3) Storage: Store at Controlled Room Temperature 20°-25°C (68°-77°F) [see USP].