From the Guidelines
Morphine does have vasodilator effects, which can lead to decreased peripheral vascular resistance and reduced blood pressure. The most recent and highest quality study, 1, suggests that morphine causes venodilation and produces modest reductions in heart rate and systolic blood pressure, which can be beneficial in patients with non-ST-elevation acute coronary syndromes (NSTE-ACS). Some key points to consider when using morphine for its vasodilator effects include:
- Morphine should be administered with caution in patients with hypotension or those who have received a phosphodiesterase inhibitor
- Typical intravenous doses of 1-5 mg may be used, repeated every 5-30 minutes as needed to relieve symptoms and maintain patient comfort
- The use of morphine should not preclude the use of other anti-ischemic therapies with proven benefits
- Clinicians should be cautious when administering morphine to hemodynamically unstable patients or those with hypovolemia, as the vasodilatory effects could worsen hypotension. Overall, the vasodilator effects of morphine can be beneficial in certain clinical scenarios, but its use should be carefully considered and monitored.
From the FDA Drug Label
Effects of the Cardiovascular System In therapeutic doses, morphine does not usually exert major effects on the cardiovascular system. Morphine produces peripheral vasodilation which may result in orthostatic hypotension and fainting.
Morphine has vasodilator effects, which can lead to orthostatic hypotension and fainting. This is due to the peripheral vasodilation caused by morphine. 2
From the Research
Morphine's Vasodilator Effects
- Morphine has been shown to induce peripheral venous and arteriolar dilation in human subjects, as evidenced by a significant decrease in venous tone and an increase in forearm blood flow 3.
- The vasodilator effects of morphine are thought to be mediated by a reflex reduction in sympathetic alpha adrenergic tone, rather than a direct peripheral alpha adrenergic blocking effect 3.
- In patients with acute pulmonary edema, morphine has been shown to induce venodilation, which may contribute to its therapeutic effects in this condition 4.
- Morphine has also been shown to cause arteriolar vasodilation in healthy subjects, with a dose-dependent increase in forearm blood flow 5.
- The mechanisms of morphine's vasodilator effects are complex and may involve the release of histamine and nitric oxide, as well as the modulation of opioid receptors 5.
Clinical Implications
- The vasodilator effects of morphine may be beneficial in certain clinical situations, such as in the treatment of acute pulmonary edema or in the management of hypertension 4, 6.
- However, the hypotensive effects of morphine may also be a concern in certain patients, such as those with hypovolemia or shock 7.
- The use of morphine in patients with hypertension may require careful consideration of the potential effects on blood pressure and cardiovascular function 6.