Lavida

Lavida Mechanism of Action

carbidopa + levodopa

Manufacturer:

United Lab

Distributor:

Medichem
Full Prescribing Info
Action
Pharmacology: Pharmacodynamics: Levodopa, the metabolic precursor of dopamine, crosses the blood-brain barrier and is converted to dopamine in the basal ganglia. It is believed to act principally by increasing dopamine concentration in the brain. This is thought to be the mechanism whereby levodopa relieves symptoms of Parkinson's disease.
Carbidopa inhibits decarboxylation of peripheral levodopa, resulting to more levodopa available for transport to the brain. Carbidopa does not cross the blood-brain barrier and does not affect the metabolism of levodopa within the central nervous system (CNS). In doses that effectively inhibit peripheral decarboxylation of levodopa, carbidopa has little effect on the CNS, cardiovascular or gastrointestinal (GI) systems.
Levodopa + carbidopa improves overall therapeutic response compared with levodopa alone.
Pharmacokinetics: Levodopa is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the CNS. Thus, large doses of levodopa are required for adequate therapeutic effect.
Carbidopa reduces the amount of levodopa required to produce a given response by about 75%. When administered with levodopa, carbidopa increases both levodopa's plasma levels and half-life, and decreases plasma and urinary dopamine and homovanillic acid (HVA). Levodopa + carbidopa provides effective long lasting levodopa plasma levels at doses that are approximately 70% to 80% lower than those needed with levodopa alone.
The plasma-half-life of levodopa is about 50 minutes; it is increased to 1.5 hours when carbidopa and levodopa are administered together. At steady state, the bioavailability of carbidopa from levodopa + carbidopa is approximately 99% relative to the concomitant administration of levodopa and carbidopa.
Levodopa is widely distributed into most body tissues and the total volume of distribution is about 65% of body weight. There is considerable uptake of levodopa by the pancreas, liver, GI tract, salivary glands, kidneys, and skin. Levodopa is approximately 10% to 30% bound to plasma proteins. Carbidopa crosses the placenta and is distributed into milk.
Substantial amounts of levodopa are metabolized in the lumen of the stomach and intestines and on first pass through the liver. Most absorbed levodopa is decarboxylated to dopamine; more than 95% of the drug is decarboxylated peripherally by aromatic L-amino acid decarboxylase, a widely distributed enzyme. Small amounts of levodopa are metabolized to norepinephrine, epinephrine and 3-methoxytyramine. Dopamine is further metabolized to 3, 4- dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylacetic acid (HVA) and is excreted in urine. HVA, DOPAC and dopamine are the metabolites of levodopa present in cerebrospinal fluid (CSF). Carbidopa is not extensively metabolized; about 30% of an oral dose of carbidopa is excreted in urine unchanged within 24 hours.
When carbidopa and levodopa are administered concurrently, the urinary excretion of dopamine, DOPAC and HVA is substantially diminished, and the amount of unchanged levodopa excreted in urine has been reported to be increased by 6%.
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