Development of a HPLC/MS/MS methodology for determining 3-O-methyldopa in human plasma and its application in a bioequivalence study

A simple, sensitive and specific HPLC/MS/MS methodology was developed and it was validated for determining 3-O-methyldopa, the major metabolite of dopamine, in human plasma. The separation was achieved on Atlantis T3 C18 analytical column (5 μm; 150 x 4.6 mm i.d.) using a mobile phase consisted of a solution of water and methanol (85:15, v/v) and containing formic acid 0.05 %. The extraction from the analyte and the internal standard sample was performed using a simple protein plasma precipitation with perchloric acid. The detection was conducted on a triple quadrupole tandem mass spectrometer with a positive multiple reaction monitoring mode (MRM). The monitored fragmentation transitions were m/z212.0  m/z 166.0 for 3-O-methyldopa and m/z 227.10  m/z 181.0 for carbidopa (internal standard).The calibration curves were linear in the range of 50–4000 ng/mL for 3-O-methyldopa. The methodology presented a good precision and accuracy in accordance to the criteria for biomedical analysis. And it was successfully applied to the bioequivalence study of two formulations levodopa + benserazide (200 + 50mg) in plasma samples from healthy human volunteers, following the ANVISA guidelines...

Does 3-O-Methyldopa(3-OMD) Inhibit the Binding of Levodopa to Plasma Protein / 대한정신약물학회지

OBJECTIVE: We determined the influence of 3-OMD in the protein binding of levodopa to estimate the effect of 3-OMD on the penetration of levodopa into brain. METHOD: P-glycoprotein in the brain may serve to limit drug penetration into the brain. Because it is not available as an experimental substance, but has similar binding properties with alpha 1 acid glycoprotein(AGP), we used AGP in this study. Additionally, we used blood plasma to see the affinity of plasma binding of levodopa. The final concentration of chemicals used in this study were 125, 250, 500, 1000, 2000, 4000 microgram/l for levodopa and 0, 1250, 5000, 10,000 microgram/l for 3-OMD, 1 mg/l for AGP. The free fraction of levodopa in blood plasma and AGP were separated by ultrafiltration method and determined by beta-counter, respectively. RESULTS: We found that levodopa did not bind with AGP, but only 22-24% from 125 microgram/l to 4000 microgram/l of it bound with blood plasma. The addition of 3-OMD to the blood plasma did not significantly change the binding of levodopa. CONCLUSIONS: We can conclude that 3-OMD does not influence the penetration of levodopa into brain. These small amount of the binding does not expect to influence to other drugs on the binding with plasma.