Why levodopa can cause postural hypotension?

Levodopa can cause postural hypotension due to several mechanisms. Here are a few key factors:

Peripheral vasodilation: Levodopa increases the activity of the sympathetic nervous system, which can lead to peripheral vasodilation. This means that blood vessels in the body dilate, causing a drop in blood pressure. When standing up from a sitting or lying position, gravity pulls blood down into the legs, further reducing blood flow to the brain and causing dizziness or lightheadedness.

Impaired baroreflex function: The baroreflex is a physiological mechanism that helps regulate blood pressure by adjusting heart rate and blood vessel tone. Levodopa can interfere with the normal functioning of the baroreflex, making it less responsive to changes in blood pressure. This impaired baroreflex function can contribute to postural hypotension.

Interaction with antihypertensive medications: Many people with Parkinson's disease also take antihypertensive medications to manage their blood pressure. Levodopa can interact with some antihypertensive drugs, such as alpha-blockers and calcium channel blockers, potentially enhancing their blood pressure-lowering effects and increasing the risk of postural hypotension.

Dopamine metabolism: Levodopa is converted into dopamine in the body. Dopamine has various effects on the cardiovascular system, including increasing heart rate and contractility. However, dopamine can also cause peripheral vasodilation, which can contribute to postural hypotension.

Individual factors: The risk of postural hypotension with levodopa can vary among individuals. Factors such as age, overall health, and concomitant medications can influence a person's susceptibility to this side effect.

To manage postural hypotension caused by levodopa, healthcare providers may adjust the dosage or timing of levodopa, recommend dietary changes (such as increasing salt and fluid intake), advise on strategies for minimizing sudden changes in posture, and consider other medications to help manage blood pressure. Regular monitoring of blood pressure is important in individuals taking levodopa to ensure proper management and minimize the risk of adverse events.