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STALEVO (LEVODOPA WITH CARBIDOPA AND ENTACAPONE) TABLETS: PHARMACOKINETICS
The pharmacokinetics of Stalevo (Levodopa/Carbidopa/Entacapone) tablets have been studied in healthy subjects (age 45-75 years old). Overall, following administration of corresponding doses of levodopa, carbidopa and entacapone as Stalevo or as carbidopa/levodopa product plus Comtan (entacapone) tablets, the mean plasma concentrations of levodopa, carbidopa, and entacapone are comparable.
Absorption and Distribution
Both levodopa and entacapone are rapidly absorbed and eliminated, and their distribution volume is moderately small. Carbidopa is absorbed and eliminated slightly more slowly compared with levodopa and entacapone. There are substantial inter- and intra-individual variations in the absorption of levodopa, carbidopa and entacapone, particularly concerning its Cmax.
The food-effect on the Stalevo tablet has not been evaluated.
Since levodopa competes with certain amino acids for transport across the gut wall, the absorption of levodopa may be impaired in some patients on a high protein diet. Meals rich in large neutral amino acids may delay and reduce the absorption of levodopa.
Levodopa is bound to plasma protein only to a minor extent (about 10%-30%).
Following administration of Stalevo as a single dose to healthy male and female subjects, the peak concentration of carbidopa was reached within 2.5 to 3.4 hours on average. The mean Cmax ranged from about 40 to 225 ng/mL and the mean AUC from 170 to 1200 ng xh/mL, with different Stalevo strengths providing 12.5 mg, 25 mg, 37.5 mg or 50 mg of carbidopa.
Carbidopa is approximately 36% bound to plasma protein.
Following administration of Stalevo as a single dose to healthy male and female subjects, the peak concentration of entacapone in plasma was reached within 0.8 to 1.2 hours on average. The mean Cmax of entacapone was about 1200 to 1500 ng/mL and the AUC 1250 to 1750 ngxh/mL after administration of different Stalevo strengths all providing 200 mg of entacapone.
The plasma protein binding of entacapone is 98% over the concentration range of 0.4-50 mcg/mL. Entacapone binds mainly to serum albumin.
Metabolism and Elimination
The elimination half-life of levodopa, the active moiety of antiparkinsonian activity, was 1.7 hours (range 1.1-3.2 hours).
Levodopa is extensively metabolized to various metabolites. Two major pathways are decarboxylation by dopa decarboxylase (DDC) and O-methylation by catechol-O-methyltransferase (COMT).
The elimination half-life of carbidopa was on average 1.6 to 2 hours (range 0.7-4.0 hours).
Carbidopa is metabolized to two main metabolites (alpha-methyl-3-methoxy-4hydroxyphenylpropionic acid and alpha-methyl-3,4-dihydroxyphenylpropionic acid). These 2 metabolites are primarily eliminated in the urine unchanged or as glucuronide conjugates. Unchanged carbidopa accounts for 30% of the total urinary excretion.
The elimination half-life of entacapone was on average 0.8 to 1 hour (0.3-4.5 hours).
Entacapone is almost completely metabolized prior to excretion with only a very small amount (0.2% of dose) found unchanged in urine. The main metabolic pathway is isomerization to the cis-isomer, the only active metabolite. Entacapone and the cis-isomer are eliminated in the urine as glucuronide conjugates. The glucuronides account for 95% of all urinary metabolites (70% as parent and 25% as cis-isomer glucuronides). The glucuronide conjugate of the cis-isomer is inactive. After oral administration of a 14C-labeled dose of entacapone, 10% of labeled parent and metabolite is excreted in urine and 90% in feces.
Due to short elimination half-lives, no true accumulation of levodopa or entacapone occurs when they are administered repeatedly.
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Stalevo prescribing information
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