Pharmacokinetics of morphine and its surrogates II: methods of separation of stabilized heroin and its metabolites from hydrolyzing biological fluids and applications to protein binding and red blood cell partition studies.

The inhibition of the spontaneous hydrolysis of heroin in fresh dog plasma on blood (t1/2 = 8 min) is effected by 10 mg of sodium fluoride/ml (t1/2 = 40 min) and 35 microgram of tetraethyl pyrophosphate/ml (t1/2 = 415 min). Tetraethyl pyrophosphate is the inhibitor of choice and gives the same stability for heroin as in phosphate buffer. Aged plasma loses its enzymatic efficiency. Heroin in cerebrospinal fluid hydrolyzes at rates similar to those in buffer. Modified extraction procedures developed for enzyme-inhibited plasma at pH 4.5 have high extraction efficiencies (86--100%) and permit isolation of undergraded heroin from its metabolites. Separations of heroin and metabolites from enzyme-inhibited plasma were effected by described high-pressure liquid chromatographic systems and from TLC with elution of pertinent developed spots. Efficiencies of these TLC recoveries were 81 +/- 1% for heroin and 82 +/- 1% for morphine. Contrary to the literature, heroin has significant protein binding where 40% of that not bound to an ultrafiltration membrane is bound to dog plasma proteins. The apparent partition coefficient is 1.4 +/- 0.2 between red blood cells and plasma water, and it is 0.8 +/- 0.1 between red blood cells and dog plasma.