Overview
Levodopa/Carbidopa is the most effective and commonly prescribed medication for managing the symptoms of Parkinson’s disease. Levodopa is converted into dopamine in the brain to replenish depleted stores, while carbidopa prevents the premature breakdown of levodopa outside the brain, reducing side effects and increasing efficacy.

Mechanism of Action
Parkinson’s disease is characterized by a depletion of dopamine in the striatum of the brain. Levodopa, a metabolic precursor of dopamine, crosses the blood-brain barrier and is converted into dopamine, restoring neurotransmitter levels. Carbidopa is a peripheral dopa decarboxylase inhibitor that does not cross the blood-brain barrier. It prevents the peripheral conversion of levodopa to dopamine, allowing more levodopa to reach the brain and significantly reducing peripheral side effects like nausea.

Dosage and Administration
The dosage must be carefully individualized and titrated for each patient. It is usually started at a low dose and gradually increased. It should ideally be taken on an empty stomach, about 30 minutes before or 1-2 hours after meals, as dietary proteins can interfere with its absorption.

Side Effects
Common side effects include nausea, vomiting, dizziness, and orthostatic hypotension. Long-term use is frequently associated with motor complications, such as dyskinesias (involuntary movements) and “wearing-off” effects (fluctuations in symptom control). Hallucinations and confusion may also occur, particularly in older patients.

Contraindications
It is contraindicated in patients with narrow-angle glaucoma or a known hypersensitivity to either component. It should not be used concurrently with non-selective monoamine oxidase (MAO) inhibitors due to the risk of hypertensive crisis.

Pregnancy and Lactation
It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Levodopa may inhibit lactation, and it is not recommended for nursing mothers.