Sensitive, specific radioimmunoassay for quantifying pergolide in plasma.

Pergolide, a synthetic ergoline with potent dopaminergic activity, is used to treat Parkinson disease. The low plasma concentrations of pergolide achieved during therapy complicate the development of a method for its analysis. Because radioimmunoassay successfully measures other structurally related ergolines in physiological fluids, we undertook the development of a radioimmunoassay of pergolide. The detection limit of the radioimmunoassay is 21 ng/L with an optimal working range from 100 to 1000 ng/L. We maximized assay specificity by using a monoclonal antibody that displayed low cross-reactivity with pergolide sulfoxide, a major metabolite found in animals. The radioimmunoassay has performed acceptably for > 2 years during toxicology studies with rats and rhesus monkeys and in clinical studies involving patients with Parkinson disease. We consider the radioimmunoassay a valid method for quantifying therapeutic concentrations of pergolide in plasma.

Fluoxetine disposition and elimination in cirrhosis.

Fluoxetine is a specific and potent inhibitor of presynaptic serotonin reuptake and has been shown to be a clinically effective antidepressant. Elimination of the drug depends primarily on hepatic metabolism, with formation of a pharmacologically active demethylated product, norfluoxetine. The present study assesses for the first time the effect of chronic liver disease on these processes. Our data show that in stable alcoholic cirrhosis, the elimination of fluoxetine is significantly reduced. The mean t1/2 was 6.6 vs. 2.2 days and plasma clearance was 4.2 vs. 9.6 ml/min/kg for patients with cirrhosis vs. normal volunteers, respectively. In addition, the formation of norfluoxetine was decreased and its clearance was also reduced. Thus, at steady state both fluoxetine and norfluoxetine concentrations will be higher in patients with cirrhosis, unless the dosage is reduced. Conventional liver tests and indocyanine green clearance in cirrhosis did not correlate in a predictive manner with individual patients' elimination of fluoxetine.

Serum propoxyphene concentrations in a cohort of opiate addicts on long-term propoxyphene maintenance therapy. Evidence for drug tolerance in humans.

Propoxyphene, norpropoxyphene, and cyclic dinorpropoxyphene concentrations in the sera of eight opiate addicts were measured by gas chromatography. The addicts were enrolled in a propoxyphene maintenance program and had received 800-1600 mg of propoxyphene napsylate daily for 13-50 months. Serum propoxyphene and norpropoxyphene ranged from 127 to 1070 ng/mL and 814 to 2638 ng/mL, respectively, and their ratio ranged from 0.1 to 0.4. A roughly linear dose-to-serum-concentration relationship was found for serum propoxyphene and norpropoxyphene in the cohort. Cyclic dinorpropoxyphene was detected in three of the subjects' sera. Because tolerance to propoxyphene occurs, knowledge of prior drug exposure is necessary to determine whether an elevated propoxyphene or norpropoxyphene concentration is toxic to patients or decedents with apparent propoxyphene overdose. Serum norpropoxyphene concentration exceeds that of propoxyphene following chronic propoxyphene use. Measurable cyclic dinorpropoxyphene implies chronic propoxyphene use but its absence does not exclude chronic use.

The application of stable isotopes to studies of drug bioavailability and bioequivalence.

The increased availability of chemical intermediates and automated instrumentation has resulted in expanded use of stable isotopes for bioavailability and bioequivalence studies in recent years. Initially, stable isotopes were confined to the labeling of mass internal standard compounds for gas chromatography/mass spectrometry. More recently, their in vivo use has expanded and proved to be a powerful pharmacologic tool. The lack of toxicity of stable isotopes, particularly deuterium and carbon-13, make them ideally suited for human studies. The primary advantage of the isotopic methods is that the drug can be administered concomitantly either by two routes (e.g., parenteral and oral) or in two formulations (e.g., solution and solid dosage). Thus, a single set of blood samples serves to describe the time course of the routes or formulations being compared. The concomitant administration reduces variability inherent in dual administration, the single assay for both forms further reduces variation, and the method minimizes both drug exposure and discomfort to the subject. In addition to single-dose administration, in which two routes or dosage forms are compared, the technique is well suited to "pulse" administration, wherein the kinetics of a single dose, during multiple or chronic dosing regimens, can be compared with single-dose kinetics.

Pharmacokinetics and protein binding of cefamandole and its 1-methyl-1 H-tetrazole-5-thiol side chain in subjects with normal and impaired renal function.

The 1-methyl-1 H-tetrazole-5-thiol (MTT) side chain present on several new cephalosporins may be an important factor in coagulopathy observed during therapy with these antibiotics. To determine the plasma kinetics and protein binding of the side chain and to test the hypothesis that renal failure alters these parameters, we gave six normal volunteers and six anuric patients a single iv dose of 15 mg of cefamandole/kg. Plasma concentrations of cefamandole and free MTT were measured by high-performance liquid chromatography 14 times during the 48-hr period after the dose was given. A compartment-independent pharmacokinetic analysis showed that MTT was rapidly removed from the plasma of normal subjects, but that peak concentrations of MTT were nearly three times greater and persisted for 48 hr in patients with renal failure. Further, renal failure caused a significant MTT protein-binding defect. If a relation exists between hypoprothrombinemia and plasma concentrations of MTT side chain, patients with reduced renal function may be at increased risk for this adverse effect.

Fluoxetine: clinical pharmacology and physiologic disposition.

Fluoxetine (30 mg), administered for 7 days to normal volunteers, produced a 66% inhibition of tritiated serotonin uptake into platelets. Plasma concentrations of fluoxetine correlated positively with inhibition of serotonin uptake. Fluoxetine is well absorbed after oral administration in both the fed and fasted states and demonstrates dose proportionality. Fluoxetine disappears from plasma with a half-life of 1-3 days; its metabolite norfluoxetine has a plasma half-life of 7-15 days. After administration of 14C-fluoxetine, approximately 65% of the administered dose of radioactivity is recovered in urine and about 15% in feces. Fluoxetine, given as a single dose or in multiple doses over 8 days, did not produce significant effects on the plasma disappearance of warfarin, diazepam, tolbutamide, or chlorothiazide. Coadministration of fluoxetine and ethanol did not result in an increase from control values in the blood ethanol levels, nor did it produce significant changes in physiologic, psychometric, or psychomotor activity. Pharmacokinetics of fluoxetine in the elderly and normal volunteers appear to be similar. In addition, pharmacokinetic analyses in patients with varying degrees of renal impairment did not show significant differences from healthy subjects.

Stereoselective inversion of (R)-fenoprofen to (S)-fenoprofen in humans.

The concentrations of the (R)- and (S)-enantiomers of fenoprofen (alpha-methyl-3-phenoxy-benzeneacetic acid) were measured in plasma and urine of volunteers after oral administration of the (R,S)-racemate. In addition, urinary concentrations of the (R)- and (S)-4'-hydroxy metabolite of fenoprofen, the major metabolite, were measured. The (R)-enantiomer of fenoprofen was stereoselectively inverted to (S)-fenoprofen, which was the major isomeric form found in plasma and urine. A potency comparison of the enantiomers in vitro showed the (S)-isomer to be 35 times more active than the (R)-isomer in inhibiting the fatty acid cyclo-oxygenase pathway from human platelets. In vivo, the similar pharmacological potency of the two enantiomers previously observed in experimental animals may have been due to the rapid inversion of the (R)- to (S)-isomer.

Tracer microspheres as compliance markers in clinical research.

Tracer microspheres are small, ceramic-like particles (50 micron) containing one of several radionuclide markers. We have utilized them over a period of 9 years as quantitative fecal markers for recovery measurements in metabolic studies. The markers have been administered daily for up to 2 weeks, during which time the marker concentration per unit dry weight of feces remains fairly constant. Data on the markers and our experience with them are presented along with the concerns that must be addressed in considering them as compliance markers.

Fluoxetine kinetics and protein binding in normal and impaired renal function.

The effect of decreased renal function on the disposition and elimination of the nontricyclic antidepressant fluoxetine was examined in 25 adult male subjects after a single 40-mg oral dose. Blood samples for the measurement of fluoxetine and its active metabolite norfluoxetine were drawn 13 times in the first 48 hr after dosing and thrice weekly thereafter for 4 wk. All urine was collected in daily aliquots for 4 wk and was assayed for fluoxetine and norfluoxetine concentrations. The extent of fluoxetine binding to plasma protein was determined by equilibrium dialysis. Kinetic analyses were by noncompartmental methods. The drug and its metabolite were distributed over a large apparent volume and both were eliminated slowly. No correlations between the degree of renal dysfunction and the rate of elimination, volume of distribution, or protein binding were found. Plasma concentrations of fluoxetine and norfluoxetine were not significantly changed by hemodialysis.

Determination of clofilium, a new antifibrillatory agent, in plasma by gas chromatography--mass spectrometry.

A sensitive and selective method for the assay of the new quaternary amine antifibrillatory agent clofilium is described. Plasma samples were extracted with dichloromethane (98.5 +/- 0.2% recovery) and analyzed by gas chromatography--mass spectrometry operating in the electron-impact mode. The method involves a Hofmann elimination of an N-alkyl radical from clofilium and the internal standard in the presence of a strong nucleophile in the injector of the gas chromatograph. The resulting tertiary amines are chromatographed and detected by selective ion monitoring. The ratio of the clofilium base peak (m/z 224) to the internal standard peak (m/z 210) was linear relative to the plasma clofilium concentration over the range of 25-1000 ng/ml plasma.

Measurement of serum and tissue concentration of moxalactam using high pressure liquid chromatography.

We describe a sensitive high pressure liquid chromatographic (HPLC) procedure for the analysis of the new beta-lactam antibiotic moxalactam. Conditions are described for either measurement of total drug concentration or the concentration of the individual isomers. The proteins in a 1.0 ml plasma sample are denatured with isopropyl alcohol which is then extracted into a chloroform reagent, leaving the drug in the aqueous phase. An aliquot is then injected into a mu-bondapak phenyl column. A similar extraction procedure was employed for tissue homogenates. Linear regression analysis and comparison of the HPLC assay with the microbiological assay gave a correlation coefficient of 0.97. Analysis of tissue samples indicated that significant concentrations of moxalactam were obtained at the site of infection.

Hydrolysis of cefamandole nafate in dialysis patients.

The hydrolysis of cefamandole nafate was examined in vivo in five dialysis patients and five subjects with normal renal function. The plasma half-life of cefamandole was prolonged in the patients with renal failure compared with normal subjects (18.3 +/- 4.5 [standard deviation] versus 10.35 +/- 1.4 min, P less than 0.01). The pharmacokinetics of cefamandole nafate best fit two-compartment, open-model kinetics. We conclude that patients with severe renal failure are capable of hydrolyzing cefamandole nafate to cefamandole and formate at a rate sufficiently rapid so as not to allow an accumulation of cefamandole nafate. The difference in half-life may be related to urinary excretion of cefamandole nafate in normal individuals.

The effect of time of death on extravascular tissue/blood secobarbital concentration ratios in the rat.

Extravascular liver/blood and brain/blood ratios were found to be an average of 6% and 1% higher, respectively, in all experiments than total liver/blood and brain/blood ratios. This difference may be informative in establishing true tissue levels. There was a significant time effect (P less than 0.05) with the extravascular liver/blood ratios but not with the extravscular brain/blood ratios. Extravascular liver/blood ratios were slightly higher in phenobarbital-pretreated animals than in non-pretreated animals. Tissue secobarbital levels in pretreated and non-pretreated animals are not different at 1/4 or 1 h, even though pretreated animals received higher doses than non-pretreated animals. Tissue levels are significantly higher (P less than 0.01) in pretreated animals than in non-pretreated animals at 4 h. It is possible that, at this time period, the barbiturate-metabolizing enzymes have become saturated or exhausted.

The effect of crystal size on the bioavailability of benoxaprofen: studies utilizing deuterium labeled drug.

A study of the effect of crystal size on the bioavailability of benoxaprofen, 2-[4-chlorophenyl]-alpha-methyl-5-benzoxazoleacetic acid, in man is reported. The technique utilized comparison of either the plasma concentrations or urine levels, resulting from administration of deuterium labeled (2H7) drug in solution coadministered with a test capsule formulation. Drug concentrations were determined by gas chromatography, and the ratio of labeled to unlabeled drug was obtained by gas chromatography mass spectrometry. Measurements following coadministration of labeled and unlabeled drug in solution established the absence of an isotope effect due to the presence of deuterium. The dry formulations consisted of either a 3.17--100 micron fraction (mean = 18.5 microns) or a 32--1000 micron fraction (mean = 610 microns) formulated with starch powder. The results in three subjects indicate an almost complete availability (0.95--0.98) of the small crystals as measured by comparison of either area under the plasma level curves or urine excretion (0.94--0.97) of labeled versus unlabeled drug measured to 168 hours. The larger crystals exhibited a lower availability as shown by plasma levels (0.41--0.46) or urine recovery (0.39--0.43). A higher dose of the large crystal formulation resulted in decreased relative availability with a fourfold dose dropping availability to 0.22 in a single subject.

Pharmacology of cinoxacin in humans.

Cinoxacin was almost completely absorbed when given orally and was found to be approximately 60 to 70% protein bound. Peak serum concentrations were reached within 2 h, and detectable serum concentrations persisted up to 12 h after administration of 0.25-, 0.5-, and 1-g multiple oral doses. Although food delayed the absorption and caused a 30% reduction in mean peak serum concentrations, the overall 24-h urinary recovery was not significantly altered. Approximately 50 to 55% of the drug was excreted in the urine as unchanged drug. At 12 h, urine concentrations were still above the minimal inhibitory concentration for most common gram-negative urinary pathogens. Cinoxacin was well tolerated when administered to 23 volunteers from 10 to 28 days. Resistance among fecal isolates initially susceptible to cinoxacin was not observed in nine volunteers who were administered 0.5 g every 12 h for 4 to 28 days.