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Levodopa Carbidopa; Uses, Dosage, Side Effects, Interactions

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

Fast or irregular heartbeat
appetite loss
changes in nails
constipation
fatigue
fever
Back pain
dizziness
headache
increased cough
Acid or sour stomach
decreased appetite
Agitation
chest congestion
chest pain
cold sweats
confusion
decreased sexual ability or desire
stomach or abdominal cramps, gas, or pain
trouble sleeping

Less common

bleeding gums
blood in the urine or stools
chest pain
diarrhea
Burning, crawling, itching, numbness, prickling, “pins and needles“, or tingling feelings
difficulty in moving
muscle stiffness
redness of the face, neck, arms and occasionally, upper chest
lack or loss of strength
muscle spasm
difficult or labored breathing
dry mouth
headache
irritability
lack or loss of strength
loose stools
loss of interest or pleasure
muscle stiffness
night sweats
passing gas
stomach discomfort, upset, or pain
swollen joints
trouble concentrating
increased blood pressure

Drug Interactions of Levodopa-Carbidopa

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

antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
“azole” antifungal medications (e.g., fluconazole, ketoconazole)
calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
cyclosporine
diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
domperidone
macrolide antibiotics (e.g., azithromycin, clarithromycin, erythromycin)

selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine,paroxetine, sertraline)
serotonin antagonists (anti-emetic medications; e.g., granisetron, ondansetron)
serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., desvenlafaxine,duloxetine,venlafaxine)
thiazide diuretics (water pills; e.g., hydrochlorothiazide, indapamide, metolazone)
tramadol
tricyclic antidepressants (e.g., amitriptyline, clomipramine, trimipramine)

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.