Figure 7

Representative HPLC chromatograms of methylnaltrexone and naltrexone in plasma samples. (A), a chromatogram of a standard plasma extract of methylnaltrexone (100.0 ng/mL) and naltrexone (50.0 ng/mL); (B), 92.5 ng/mL methylnaltrexone was detected after 3.0 mg/kg administration; (C), a gradually reduced methylnaltrexone level (4.7 ng/mL) was detected as time elapsed. At all measured time points, no naltrexone level was detected, as shown in (B) and (C). MNTX, methylnaltrexone; NTX, naltrexone.