| Autor: |
Coutinho, Claude B., Spiegel, Herbert E., Kaplan, Stanley A., Yu, Margaret, Christian, Richard P., Carbone, John J., Symington, Julia, Cheripko, Joyce A., Lewis, Margaret, Tonchen, Alice, Crews, Theodore |
| Zdroj: |
Journal of Pharmaceutical Sciences; July 1971, Vol. 60 Issue: 7 p1014-1019, 6p |
| Abstrakt: |
The rate and extent of levodopa absorption and excretion following intravenous and oral administration of 2−14Clevodopa to acute and chronically treated dogs were investigated. Plasma levels of intact levodopa following the intravenous administration declined rapidly during the first 4-6 hr. The elimination-rate constant of intact levodopa from the plasma ranged between 0.73 and 0.99 hr.−1, which corresponds to a half-life of approximately 40-60 min. The elimination-rate constant of total plasma 14C ranged between 0.007 and 0.085 hr.−1, which corresponds to a half-life of 8-9 hr., indicating that the total 14C was eliminated at one-tenth the rate of intact levodopa. Peak plasma levels of intact levodopa and of total plasma 14C following oral administration were attained 25-30 min. after dosing. Approximately 70-75% of the intravenous and 57-70% of the oral radioactive doses were excreted in urine over a 72-hr. period. Levodopa and dopamine accounted for a very small percentage of the radioactivity in the urine. Approximately 3.0-7.0% of the intravenous or oral radioactive dose was excreted in the feces. The efficiency of absorption of total radioactivity was calculated to range between 83.0 and 92.0%. Analysis of the ratio of intact levodopa levels to total 14C levels indicated that only 22.0-30.0% of the administered dose reached the general circulation as intact levodopa, suggesting that the remainder of the absorbed dose, approximately 60.0%, is biotransformed in the gastrointestinal tract prior to absorption and/or in the liver during its "first passage" to the general circulation. |
| Databáze: |
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