Levodopa Carbidopa; Uses, Dosage, Side Effects, Interactions

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Levodopa is an amino acid precursor of dopamine with antiparkinsonian properties. Levodopa is a prodrug that is converted to dopamine by DOPA decarboxylase and can cross the blood-brain barrier. When in the brain, levodopa is decarboxylated to dopamine and stimulates the dopaminergic receptors, thereby compensating for the depleted supply of endogenous dopamine seen in Parkinson’s disease. To assure that adequate concentrations of levodopa reach the central nervous system, it is administered with carbidopa, a decarboxylase inhibitor that does not cross the blood-brain barrier, thereby diminishing the decarboxylation and inactivation of levodopa in peripheral tissues and increasing the delivery of dopamine to the CNS.

The naturally occurring form of dihydroxyphenylalanine and the immediate precursor of dopamine. Unlike dopamine itself, it can be taken orally and crosses the blood-brain barrier. It is rapidly taken up by dopaminergic neurons and converted to dopamine. It is used for the treatment of parkinsonian disorders and is usually given with agents that inhibit its conversion to dopamine outside of the central nervous system.

Mechanism of Action ofLevodopa-Carbidopa

Striatal dopamine levels in symptomatic Parkinson’s disease are decreased by 60 to 80%, striatal dopaminergic neurotransmission may be enhanced by exogenous supplementation of dopamine through administration of dopamine’s precursor, levodopa. A small percentage of each levodopa dose crosses the blood-brain barrier and is decarboxylated to dopamine. This newly formed dopamine then is available to stimulate dopaminergic receptors, thus compensating for the depleted supply of endogenous dopamine. However, L-DOPA is converted to dopamine in the periphery as well as in the CNS, so it is administered with a peripheral DDC (dopamine decarboxylase) inhibitor such as carbidopa, without which 90% is metabolized in the gut wall, and with a COMT inhibitor if possible; this prevents about a 5% loss. The form given therapeutically is, therefore, a prodrug which avoids decarboxylation in the stomach and periphery can cross the blood-brain barrier, and once in the brain is converted to the neurotransmitter dopamine by the enzyme aromatic-L-amino-acid decarboxylase.

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Indications of Levodopa-Carbidopa

  • Parkinson’s Disease
  • Restless Legs Syndrome
  • Periodic Limb Movement Disorder
  • Paralysis agitans
  • Parkinsonism
  • Postencephalitic parkinsonism
  • Restless Legs Syndrome
  • Advanced Motor fluctuations
  • For the treatment of idiopathic Parkinson’s disease (Paralysis Agitans), postencephalitic parkinsonism, symptomatic parkinsonism which may follow injury to the nervous system by carbon monoxide intoxication, and manganese intoxication.

Contra-Indications of Levodopa-Carbidopa

  • Malignant melanoma
  • Diabetes
  • Psychosis caused by a drug
  • A mental disorder with loss of normal personality & reality
  • Having thoughts of suicide
  • Signs or symptoms of neurosis
  • Depression
  • Wide-angle glaucoma
  • Closed angle glaucoma
  • Heart attack
  • Abnormal heart rhythm
  • Lung disease
  • Stomach ulcer
  • Ulcer of the duodenum
  • Ulcer from stomach acid
  • Liver problems
  • Bleeding of the stomach or intestines
  • Kidney disease with a reduction in kidney function
  • Seizures
  • Dyskinesia

Dosage of Levodopa-Carbidopa

    Parkinson’s disease
    For oral dosage form (tablets)
  • Adults and teenagers—At first, 250 milligrams (mg) two to four times a day. Your doctor may increase your dose if needed. However, the dose is usually not more than 8000 mg (8 grams) a day.
  • Children up to 12 years of age—Use and dose must be determined by your doctor.

For levodopa and carbidopa combination

For Parkinson’s disease

For oral tablet dosage form

  • Adults—At first, 1 tablet three or four times a day. Your doctor may need to change your dose, depending on how you respond to this combination of medicine.
  • Children and teenagers—Use and dose must be determined by your doctor

For an oral extended-release tablet dosage form

  • Adults—At first, 1 tablet two times a day. However, you may need to take more than this. Your doctor will decide the right dose for you, depending on your condition and the other medicines you may be taking for Parkinson’s disease.
  • Children and teenagers—Use and dose must be determined by your doctor.
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Side Effects of Levodopa-Carbidopa

The most common

More common

Less common

Drug Interactions of Levodopa-Carbidopa

Levo dopa-carbidopa may interact with following drugs, supplements & may decrease the efficacy of the drug

Pregnancy & Lactation

FDA Pregnancy Category C

Pregnancy

This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

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Lactation

Levodopa passes into breast milk. It is not known if carbidopa passes into breast milk. If you are a breastfeeding mother and are taking levodopa-carbidopa, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding. The safety and effectiveness of levodopa-carbidopa have not been established for use by people under 18 years of age.

References

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