Nitroglycerin

Section 1.1

Midwives may independently prescribe, order and administer this drug.

Nitroglycerin is a vasodilator which relaxes uterine smooth muscle, as well as vascular, bronchial, biliary, gastrointestinal and ureteral muscles.

Indications and Clinical Use:

For the treatment of hypertonic uterine contractions with non-reassuring fetal status as an adjunct to intrauterine resuscitation. This drug is for emergency purposes only, and its use should be immediately followed by a physician consultation and transfer of care. If used in an out-of-hospital setting, immediate emergency transport to hospital is required.

Contraindications:

Nitrates should not be administered to those with known hypersensitivity or idiosyncratic reaction to organic nitrates, severe anemia, hemorrhage, hypotension, uncorrected hypovolemia or severe liver disease. Although unlikely to be encountered in the provision of midwifery care, nitroglycerin is also contraindicated with conditions of head trauma, cerebral hemorrhage, increased intracranial pressure, restrictive cardiomyopathy, constrictive pericarditis and pericardial tamponade.

Warnings and Precautions:

To date, the evidence for safety and efficacy remains inconclusive. The use of nitroglycerin in pre-term labour is currently under evaluation. This application of nitroglycerin is NOT approved for use by registered midwives.

Pregnancy:

Human data suggest low risk-1st trimester data is limited, caution due to risk of hypotension.

Lactation:

No human data, probably compatible or limited data – Category L4 – Possibly hazardous -There are currently no reports of nitroglycerin use in lactation, based on size of molecule it is expected to enter milk and could be a concern with prolonged use.

Adverse Reactions:

Include headache, which occurs in up to 50% of users at the beginning of therapy. Less than 1% of users may experience itching, wheezing, tracheobronchitis, hypotension, reflex tachycardia, palpitations or bradycardia. Syncope due to nitrate vasodilation, although rare, has been reported. Weakness, dizziness, apprehension, restlessness, nausea, vomiting, diarrhea, abdominal pain, arthralgia, muscle twitching, blurred vision, and upper and lower respiratory infections have also been reported. Overdose symptoms are primarily related to vasodilation: flushing, headache, nausea, dizziness, hypotension and tachychardia. Methemoglobinemia is also a rare adverse effect. Most of these can be obviated by discontinuing the drug. Treatment is symptomatic and supportive. The hemodynamic effect of nitrates is brief.

Dosage and Administration:

Nitroglycerin 50 mcg IV given over 2 to 3 minutes; may be repeated every 90 seconds to three minutes as needed to a maximum dose of 500 mcg over 15 minutes

  • Please note, preparations come in different strengths
  • Dilute 1 mL of 5 mg/mL nitroglycerin with 100 mL of normal saline to make a concentration of 50 mcg/mL. Should NOT be mixed with other medications;
  • Administer 50 mcg per dose into lowest port on IV tubing over 1-2 minutes.
  • Sublingual spray may be used however it is significantly less reliable: 0.4 mg, one to two metered doses can be administered sublingually. The bioavailability of this route is variable and is reported to be no more than 38%.
  • An IV should be established, regardless of the route of administration, to prevent hypotension.
  • Nitroglycerin binds to plastic; therefore the solution must be used within 30 minutes of preparation.

Uterine relaxation is achieved within 40-90 seconds and lasts for about 1 minute.

Onset of Action:

Sublingual spray: 1-3 minutes; IV: Immediate

Peak effect:

Sublingual spray: 4-10 minutes; IV: immediate

Half-life:

1-4 minutes

Elimination:

Excreted by the kidneys (as inactive metabolites)