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What is the half life for sinemet? How long should side effects continue?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Feb 23, 2021.

Official Answer

by Drugs.com

The half life of Sinemet immediate release is 90 minutes.

Sinemet is a combination medicine that contains levodopa and carbidopa. Levodopa is converted into dopamine in the brain and carbidopa inhibits an enzyme called decarboxylase, which breaks down levodopa before it gets to the brain. Carbidopa increases the half-life of levodopa from approximately 50 minutes to 90 minutes.

Sinemet is used to treat symptoms of Parkinson’s disease. The duration of effect of Sinemet is approximately three to four hours for immediate-release tablets. Depending on what the side effect is, it may last for the whole duration of effect. However, many people develop a tolerance to particular side effects, such as nausea, so these are usually not noticeable with regular dosing.

What is a half-life?

The half-life of a drug is an estimate of the time it takes for the concentration or amount in the body of that drug to be reduced by exactly one half (50%).

Sinemet contains two ingredients levodopa and carbidopa. Only levodopa is active, carbidopa just inhibits an enzyme called decarboxylase which exists naturally in our bodies which would convert levodopa into dopamine before it has a chance to reach the brain.

The half-life of Sinemet is 90 minutes but its effects will last for three to four hours (immediate release).

After four to five half-lives, 97% of a drug has cleared from the body, and the drug is no longer considered to be having an effect, although, for most drugs, actual noticeable effects would have worn off well before then. This means it will take approximately 450 minutes (7.5 hours) for one dose of Sinemet immediate release to be cleared from the body.

In reality, the half-life of Sinemet varies from person to person, and even sometimes within the same person. The half-life of Sinemet can be affected by dosage and several other factors including:

  • Formulation of Sinemet (eg controlled or immediate release)
  • Increased blood/brain barrier permeability (such as from infection)
  • Interacting medications
  • Pre-existing conditions
  • Regular dosing.

See our article Drug Half-life Explained for more general information about half-lives.

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