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7.4 Tissue-type Plasminogen Activator (t-PA)

Intravenous administration of nitroglycerin decreases the thrombolytic effect of tissue-type plasminogen activator (t-PA). Plasma levels of t-PA are reduced when coadministered with nitroglycerin. Therefore, caution should be observed in patients receiving RECTIV during t-PA therapy.

7.5 Heparin

Although an interaction has been reported between intravenous heparin and intravenous nitroglycerin (resulting in a decrease in the anticoagulant effect of heparin), the data are not consistent. If patients are to receive intravenous heparin and RECTIV concurrently, the anticoagulation status of the patient must be checked.

7.6 Ergotamine

Oral administration of nitroglycerin markedly decreases the first-pass metabolism of dihydroergotamine and consequently increases its oral bioavailability. Ergotamine is known to precipitate angina pectoris. Therefore the possibility of ergotism in patients receiving RECTIV should be considered.

7.7 Alcohol

The vasodilating effects of nitroglycerin have been shown to be additive to the effects observed with alcohol.

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Pregnancy Category C

Animal reproduction and teratogenicity studies have not been conducted with RECTIV. Nitroglycerin was not teratogenic when administered by topical or dietary route. There are no adequate and well-controlled studies in pregnant women. RECTIV should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Teratology studies in rats and rabbits were conducted with topically applied nitroglycerin ointment at doses up to 80 mg/kg/day and 240 mg/kg/day, respectively. No toxic effects on dams or fetuses were seen at any dose tested.

A teratogenicity study was conducted in rats with nitroglycerin administered in the diet at levels up to 1% content (approximately 430 mg/kg/day) on days 6 to 15 of gestation. In offspring of the high-dose group, an increased but not statistically significant incidence of diaphragmatic hernias was noted together with decreased hyoid bone ossification. The latter finding probably reflects delayed development, thus indicating no clear evidence of a potential teratogenic effect of nitroglycerin.

8.3 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 RECTIV is administered to a nursing woman.

8.4 Pediatric Use

The safety and effectiveness of RECTIV in pediatric patients under 18 years of age have not been established.

8.5 Geriatric Use

Clinical studies of RECTIV did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Clinical data from the published literature indicate that the elderly demonstrate increased sensitivity to nitrates, which may be therapeutic but also manifest by more frequent or severe hypotension and related dizziness or fainting. Increased sensitivity may reflect the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

10 OVERDOSAGE

Nitroglycerin toxicity is generally mild. The estimated adult oral lethal dose of nitroglycerin is 200 mg to 1,200 mg. Infants may be more susceptible to toxicity from nitroglycerin. Consultation with a poison center should be considered.

Laboratory determinations of serum levels of nitroglycerin and its metabolites are not widely available, and such determinations have, in any event, no established role in the management of nitroglycerin overdose.

No data are available to suggest physiological maneuvers (e.g., maneuvers to change the pH of the urine) that might accelerate elimination of nitroglycerin and its active metabolites. Similarly, it is not known which if any of these substances can usefully be removed from the body by hemodialysis.

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 not recommended.

In patients with renal disease or congestive heart failure, therapy resulting in central volume expansion is not without hazard. Treatment of RECTIV overdose in these patients may be subtle and difficult, and invasive monitoring may be required.

Methemoglobinemia

Methemoglobinemia has been rarely reported with organic nitrates. The diagnosis should be suspected in patients who exhibit signs of impaired oxygen delivery despite 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.

11 DESCRIPTION

Nitroglycerin is 1,2,3,-propanetriol trinitrate, an organic nitrate whose structural formula is as follows:

  • CH2 -ONO2
  • |
  • CH-ONO2
  • |
  • CH2 -ONO2

and whose molecular weight is 227.09. RECTIV (nitroglycerin) Ointment 0.4% contains 0.4% nitroglycerin w/w (4 mg nitroglycerin/1 g ointment), propylene glycol, lanolin, sorbitan sesquioleate, paraffin wax, and white petrolatum. RECTIV (nitroglycerin) Ointment 0.4% is available in tubes with a one-inch dosing line on the carton allowing the measurement of approximately 375 mg of nitroglycerin ointment 0.4% (1.5 mg nitroglycerin) for application.

12 CLINICAL PHARMACOLOGY

12.1 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. This leads to dephosphorylation of myosin light chains, which regulates the contractile state in smooth muscle and results in vasodilatation.

12.2 Pharmacodynamics

The principal pharmacological action of nitroglycerin is relaxation of vascular smooth muscle. Intra-anal application of nitroglycerin reduces sphincter tone and resting intra-anal pressure.

12.3 Pharmacokinetics

Absorption: In six healthy subjects, the average absolute bioavailability of nitroglycerin applied to the anal canal as a 0.2% w/w ointment was approximately 50% of the 0.75 mg nitroglycerin dose.

Distribution: The volume of distribution of nitroglycerin following intravenous administration is about 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: Nitroglycerin is metabolized by a liver reductase enzyme 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, the two major metabolites, 1,2- and 1,3- dinitroglycerols are found in plasma. The contribution of metabolites to the relaxation of the internal anal sphincter is unknown. The dinitrates are further metabolized to nonvasoactive mononitrates and ultimately to glycerol and carbon dioxide.

Elimination: Metabolism is the primary route of drug elimination. Nitroglycerin plasma concentrations decrease rapidly with a mean elimination half-life of two to three minutes. Half-life values range from 1.5 to 7.5 minutes. Clearance (13.6 L/min) greatly exceeds hepatic blood flow.

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