Effect of acute marijuana on cardiovascular function and central nervous system pharmacokinetics of [(15)O]water: effect in occasional and chronic users.

The objective of this study was to evaluate the effect of the acute administration of marijuana (MJ) on cardiovascular (CV) function and CNS pharmacokinetics (PK) of [(15)O]water in occasional (O) versus chronic (C) MJ users. Each subject received four injections of [(15)O]water (one prior and three postsmoking) on two occasions in which they received active or placebo MJ. For each injection, measures of CV function and CNS PK [(15)O]water were made. Postsmoking, MJ influenced all measured CV and [(15)O]water PK parameters. C users reported significantly lower "highness" and smaller heart rate (HR) changes, which resulted in reduced rate pressure product (RPP) changes compared to O users, even though Delta(9)-tetrahydrocannabinol levels were higher, whereas changes in blood pressure (BP), arrival time, and [(15)O]water concentration were not significantly different between the groups. Significant CV changes resulted in changes in the whole-body distribution of cardiac output rather than changes in cerebral blood flow. Chronic MJ use produces tolerance to the HR increases induced by acute MJ smoking compared to changes observed in occasional users, without changing the effects on BP and [(15)O]water PK.

Contamination levels in blood samples drawn from the injection intravenous line.

PURPOSE: Securing two intravenous lines, one for injection and one for blood sampling, can be nearly impossible in compromised patients, therefore, a need exists to quantify the potential error when simplified techniques are employed. METHOD: Two venous catheters were placed. 2-deoxy-2-[18F]fluoro-glucose (FDG) was infused through one of the catheters. Venous blood samples were drawn from each line. Triplicate aliquots of plasma were analyzed in duplicate. RESULTS: Concentrations from the infusion line were 2.0% higher than the concentrations from the noninfusion line. The average error was 3.3%, 2.0%, and 0.7% higher for the first, second, and third samples, respectively. CONCLUSIONS: Blood sampling through the infusion catheter is a viable alternative to the placement of separate venous catheters. Sampling from the injection catheter, even with tubing flush and replacement, will potentially incur small (generally < 10%) over-estimations in concentration in initial samples. Subsequent sampling reduces the error to essentially zero by the third sample.

[15O]water pharmacokinetics: influence of age and gender in normal subjects.

PURPOSE: To compile a normal database for the characterization of global [15O]water pharmacokinetic behavior. PROCEDURES: The influences of age, gender, and body habitus on the pharmacokinetics of [15O]water were investigated in a series of normal subjects, N = 100 (50 males, 50 females, age = 19-79) who were participants in cognitive activation studies. Arterial blood was analyzed by autosampler and parametric images were constructed using a 40-second summed image and the autoradiographic model. RESULTS: Males and females were comparable with respect to age, number of injections administered, and dose (mCi) administered per injection but differed significantly with respect to height, weight, and normalized dose (mCi/kg). There were significant gender-based differences in the bolus arrival time, global cerebral blood flow (gCBF), area-under-the-curve (AUC), summed image concentration, and dose-normalized concentration but not dose-normalized AUC. Bolus arrival time, gCBF and dose-normalized AUC were significantly influenced by age. CONCLUSION: Age and gender are significant determinants of [15O]water pharmacokinetic behavior.