The effect of varying extents of Fluosol-DA or normal saline haemodilution on the dose dependent kinetics of phenytoin in the rat

Effect of a Perfluorochemical Emulsion on the Rat Hepatic Mixed Function Oxidase System

The perfluorochemical components of synthetic oxygen transporting emulsions may persist in hepatic tissue. After a single 30% blood exchange with the perfluorochemical emulsion, Fluosol-DA 20%, the effects on the microsomal metabolism of 7-methoxycoumarin and 7-ethoxycoumarin were studied over a 9 week period. Fluosol-DA treated animals were compared with controls (sham) and hetastarch-treated controls. Changes in dealkylase activities were compared with induction by phenobarbitone and 3-methylcholanthrene. The liver to body weight ratio increased by 49% in Fluosol-DA-treated rats over the controls at 1 week and the microsomal protein was increased in the Fluosol-DA-treated rats after 4 and 9 weeks. Fluosol-DA treatment induced 7-methoxycoumarin demethylase with peak differences occurring at 1 week and a Vmax 75% greater than controls. Fluosol-DA was a more potent inducer of demethylase than phenobarbitone. In addition, 7-ethoxycoumarin de-ethylase was induced by Fluosol-DA with a peak induction at 4 weeks. The Vmax at 4 weeks in Fluosol-DA-treated rats was 122% greater than control. In this case, Fluosol-DA produced less induction in de-ethylase than 3-methylcholanthrene. These studies show that Fluosol-DA induces more than one form of cytochrome P450 and the effects resemble those of phenobarbitone more than those of 3-methylcholanthrene. Hetastarch, a plasma expander, did not affect liver weights, microsomal protein content, or the cytochrome P450 system.

Antiepileptic drug pharmacokinetics and neuropharmacokinetics in individual rats by repetitive withdrawal of blood and cerebrospinal fluid: phenytoin

The temporal pharmacokinetic (blood) and neuropharmacokinetic (cerebrospinal fluid, CSF) interrelationship of phenytoin was studied after acute and during chronic (up to 5 days) intraperitoneal administration of phenytoin (30, 50 or 100 mg/kg) using a new freely behaving rat model. After administration, phenytoin rapidly appeared in both serum (Tmax mean range 0.15-0.38 h) and CSF (Tmax mean range 0.9-1.4 h), suggesting ready penetration of the blood-brain barrier. However, transport across the blood-brain barrier may be rate limiting since whilst phenytoin concentrations rose dose dependently in serum, CSF concentrations did not. Further, the divergence between the blood and CSF compartments increased with chronic dosing. Cmax, AUC and t1/2 values for serum increased non-linearly, suggestive of accumulation kinetics. Based on these data, high initial phenytoin blood concentrations are essential if phenytoin entry into the brain is to be facilitated, and this may be important in studies of phenytoin in animal models of status epilepticus.

Acute effects of moderate Fluosol-DA hemodilution on hepatic microsomal and nonmicrosomal metabolism in rats

Fluosol has been shown to alter the disposition of several drugs immediately after its administration. Investigations in this laboratory established that the disposition of several drug markers requiring the hepatic microsomal cytochrome P-450 isoenzymes was time dependent for 72 hours. It was an additional purpose of the research to determine if the nonmicrosomal sulfation and acetylation pathways were also influenced by Fluosol hemodilution in a time dependent manner. Rats were moderately hemodiluted with Fluosol and received an intravenous dose of a drug marker 24, 48, or 72 hours after hemodilution. The formation clearance (ClF) of specific metabolites was used as the pharmacokinetic measure of a specific enzymatic activity. 3-Hydroxymethyl antipyrine ClF (phenobarbital inducible microsomal cytochrome P-450 isoenzymes) increased 300% only at 48 hours. Acetylsulfamethazine ClF (nonmicrosomal acetylation) increased 287% and 162% at 24 and 48 hours, respectively. Acetaminophen sulfate ClF (nonmicrosomal sulfation) decreased 30% only at 48 hours. Substantial evidence shows that cytochrome P-450 content is induced at 72 hours and remains induced for an unprecedented length of time by the PFCs in Fluosol. Therefore, it was unexpected that 3-hydroxymethyl antipyrine ClF was not increased at 72 hours. Several possible explanations are discussed for the unexpected findings.

Perfluorochemical erythrocyte substitutes: disposition and effects on drug distribution and elimination

As a result of their ability to transport oxygen, PFC emulsions are being investigated for possible use in a wide variety of conditions. The recent FDA approval of F-DA to diminish myocardial ischemia during angioplasty is the first marketing approval for such a product in the world. The many potential uses of such products may result in their common application in the future, especially as new and better products are developed. The elimination, distribution, and tissue retention of PFC emulsions as well as the physiological changes that occur upon their administration have been the subject of many investigations. The results indicate that these agents may influence the pharmacokinetic properties of other drugs by a wide variety of mechanisms. Several studies have shown significant, but not necessarily consistent, changes in drug elimination and distribution following PFC emulsion infusion. Changes appear dependent on the drug examined, emulsion utilized, degree of blood exchange, species utilized, and the controls chosen for comparison. Often, the changes are time dependent indicating the importance of conducting long-term studies. While PFC emulsions do not appear to alter renal elimination of drugs, several studies have demonstrated that these agents have the potential to induce drug metabolism from several days to possibly months after exposure. Observed changes in drug volumes of distribution, which are often time dependent, may be due to changes in normal drug transport throughout the circulation and/or changes in membrane permeability and cell transport mechanisms. Changes in drug transport may result from depletion of plasma proteins or increases in alpha 1-acid glycoprotein levels due to trauma or PFC emulsion effects. The binding of drugs by PFC emulsion droplets varies greatly and PFC emulsion components displace some plasma protein bound drugs. The wide variability in the results and conclusions of the pharmacokinetic studies conducted to date emphasize the importance of utilizing adequate controls to identify which alterations are PFC emulsion specific.