Terbutaline vs Nitroglycerin: Pharmacokinetics and Clinical Use
Fundamental Pharmacologic Distinction
Terbutaline is a beta-2 adrenergic agonist used for bronchodilation and uterine relaxation, while nitroglycerin is a nitrate vasodilator used for cardiac ischemia, heart failure, and hypertensive emergencies—these are entirely different drug classes with distinct mechanisms, pharmacokinetics, and clinical applications. 1
Mechanism of Action
Nitroglycerin
- Acts as an endothelium-independent vasodilator that dilates both venous capacitance vessels (predominantly) and arterial vessels, reducing myocardial oxygen demand and enhancing oxygen delivery 1
- Dilates epicardial coronary arteries and promotes collateral flow to ischemic regions 1
- Venodilation decreases preload, which reduces left ventricular filling pressure—critical for acute pulmonary edema 2
Terbutaline
- Stimulates beta-2 adrenergic receptors, causing smooth muscle relaxation in bronchi and uterine tissue 1
- Provides more effective tocolysis with less impact on maternal blood pressure compared to nitroglycerin 3
Pharmacokinetic Profiles
Nitroglycerin
- Onset of action: 1-5 minutes intravenously 4
- Duration of action: 3-5 minutes intravenously 4
- Dosing: Initial IV dose 5-10 mcg/min, titrate by 5-10 mcg/min every 3-5 minutes, maximum 200 mcg/min 4, 2
- Critical limitation: Rapid tolerance develops within 24-48 hours with continuous use, requiring dose escalation 5
- Absorption issues: Significant interaction with PVC tubing—initial dosing should be 10-20 mcg/min if using standard PVC tubing 5
Terbutaline
- Onset of action: Rapid (minutes) when given subcutaneously 6
- Duration of action: Substantially longer than epinephrine—8 to 12 times longer duration than nitroglycerin for similar effects 7
- Dosing: 0.25 mg subcutaneously for tocolysis; 250 mcg IV for acute intrapartum fetal resuscitation 3, 8
Clinical Applications: When to Use Each
Nitroglycerin Indications
- Acute coronary syndrome with hypertension: IV nitroglycerin for ongoing ischemic symptoms not relieved by sublingual doses 1
- Acute cardiogenic pulmonary edema: High-dose IV nitroglycerin (combined with low-dose furosemide) reduces intubation rates and myocardial infarction 4, 1
- Hypertensive emergency with cardiac involvement: Only when accompanied by acute pulmonary edema or acute coronary syndrome—NOT for isolated severe hypertension 5
- Alternative for uterine relaxation: Can be used for placental removal, though terbutaline is more effective 1
Terbutaline Indications
- Acute bronchospasm: At least as effective as epinephrine for reversible bronchospasm in stable asthmatics 6
- External cephalic version: Significantly higher success rate (55% vs 23%) compared to nitroglycerin 8
- Acute intrapartum fetal resuscitation: Provides more effective tocolysis with lower median contraction frequency (2.9 vs 4 per 10 minutes) and reduced tachysystole (1.8% vs 18.9%) compared to nitroglycerin 3
Hemodynamic Effects: Critical Differences
Nitroglycerin
- Blood pressure: Causes significant decrease in mean arterial pressure (81 to 76 mm Hg) 3
- Contraindicated if systolic BP <90 mmHg: Vasodilators compromise organ perfusion below this threshold 5
- Target BP reduction: Only 20-25% reduction in mean arterial pressure in first hour to avoid organ hypoperfusion 5, 2
- Monitoring requirement: Continuous BP monitoring with arterial line recommended for borderline pressures 5
Terbutaline
- Blood pressure: Minimal impact on maternal blood pressure (82 to 81 mm Hg, not significant) 3
- Heart rate: Increases maternal heart rate and causes palpitations (17.2% incidence vs 0% with nitroglycerin) 8
- Cardiovascular safety: No cardiovascular side effects of significance noted in stable asthmatics 6
Critical Safety Considerations
Nitroglycerin Contraindications
- Absolute contraindications: Systolic BP <90 mmHg, phosphodiesterase inhibitor use within 24 hours (sildenafil) or 48 hours (tadalafil), right ventricular infarction, severe aortic stenosis, volume depletion 1, 2
- Adverse effects: Headache (frequent), hypotension (particularly with abrupt administration), reflex tachycardia 4, 5
- Drug interaction: Avoid with sodium nitroprusside in acute MI—nitroprusside decreases regional blood flow and increases myocardial damage 4
Terbutaline Contraindications
- Relative contraindications: History of 2nd or 3rd degree AV block, systolic heart failure, asthma (for beta-blockers, not terbutaline), bradycardia 4
- Adverse effects: Palpitations, increased heart rate, tremor 8
Comparative Efficacy in Obstetric Use
For external cephalic version, terbutaline is superior to nitroglycerin with a success rate of 55% vs 23% (P = 0.01). 8
- For acute intrapartum fetal resuscitation, both agents have similar success rates (terbutaline 71.9% vs nitroglycerin 64.2%, P = 0.38), but terbutaline provides more effective uterine relaxation 3
- Terbutaline reduces contraction frequency more effectively (2.9 vs 4 per 10 minutes, P < 0.002) and reduces tachysystole (1.8% vs 18.9%, P = 0.003) 3
When NOT to Use Nitroglycerin
- Isolated hypertensive emergency without cardiac involvement: Use nicardipine or labetalol instead 5
- Hypertensive urgency: Use oral agents (captopril, labetalol, or extended-release nifedipine) 5
- Eclampsia/preeclampsia: Use hydralazine, labetalol, or nicardipine 5
- Acute renal failure: Use clevidipine, fenoldopam, or nicardipine 5