Kinetics of cocaine distribution, elimination, and chronotropic effects

The pharmacokinetics of cocaine were studied in five subjects with histories of drug abuse who were otherwise healthy. A two-compartment system was used to model the distribution kinetics of the drug. The steady-state volume of distribution averaged 131.8 L or 1.96 L/kg, elimination clearance was 2.10 L/min, and the t 1/2 was 48 minutes. Cocaine concentrations in a hypothetic biophase were estimated to correlate the chronotropic effects of this drug with its pharmacokinetics. The experimentally determined kinetic parameters indicate that the peak chronotropic effect would occur 7.3 minutes after intravenous bolus injection of cocaine, and that biophase cocaine concentrations would initially accelerate the heart rate by 0.3 bpm for each 1 ng/ml. The kinetic analysis also demonstrated that the chronotropic effects of cocaine decline more rapidly than either plasma levels or biophase concentrations. This progressive attenuation in intensity of the chronotropic effect of a given biophase cocaine concentration could be modeled as a first-order process and is compatible with either the intervention of homeostatic reflex mechanisms or the phenomenon of acute tolerance.     

Cocaine esterase: interactions with cocaine and immune responses in mice

Cocaine esterase (CocE) is the most efficient protein catalyst for the hydrolysis of cocaine characterized to date. The aim of this study was to investigate the in vivo potency of CocE in blocking cocaine-induced toxicity in the mouse and to assess CocE's potential immunogenicity. Cocaine toxicity was quantified by measuring the occurrence of convulsions and lethality. Intravenous administration of CocE (0.1-1 mg) 1 min before cocaine administration produced dose-dependent rightward shifts of the dose-response curve for cocaine toxicity. More important, i.v. CocE (0.1-1 mg), given 1 min after the occurrence of cocaine-induced convulsions, shortened the recovery time after the convulsions and saved the mice from subsequent death. Effects of repeated exposures to CocE were evaluated by measuring anti-CocE antibody titers and the protective effects of i.v. CocE (0.32 mg) against toxicity elicited by i.p. cocaine (320 mg/kg) (i.e., 0-17% occurrence of convulsions and lethality). CocE retained its potency against cocaine toxicity in mice after a single prior CocE exposure (0.1-1 mg), and these mice did not show an immune response. CocE retained similar effectiveness in mice after three prior CocE exposures (0.1-1 mg/week for 3 weeks), although these mice displayed 10-fold higher antibody titers. CocE partially lost effectiveness (i.e., 33-50% occurrence of convulsions and lethality) in mice with four prior exposures to CocE (0.1-1 mg/2 week for four times), and these mice displayed approximately 100-fold higher antibody titers. These results suggest that CocE produces robust protection and reversal of cocaine toxicity, indicating CocE's therapeutic potential for acute cocaine toxicity. Repeated CocE exposures may increase its immunogenicity and partially reduce its protective ability.     

Repeated administration of a mutant cocaine esterase: effects on plasma cocaine levels, cocaine-induced cardiovascular activity, and immune responses in rhesus monkeys

Previous studies have demonstrated the capacity of a long-acting mutant form of a naturally occurring bacterial double mutant cocaine esterase (DM CocE) to antagonize the reinforcing, discriminative, convulsant, and lethal effects of cocaine in rodents and reverse the increases in mean arterial pressure (MAP) and heart rate (HR) produced by cocaine in rhesus monkeys. This study was aimed at characterizing the immunologic responses to repeated dosing with DM CocE and determining whether the development of anti-CocE antibodies altered the capacity of DM CocE to reduce plasma cocaine levels and ameliorate the cardiovascular effects of cocaine in rhesus monkeys. Under control conditions, intravenous administration of cocaine (3 mg/kg) resulted in a rapid increase in the plasma concentration of cocaine (n = 2) and long-lasting increases in MAP and HR (n = 3). Administration of DM CocE (0.32 mg/kg i.v.) 10 min after cocaine resulted in a rapid hydrolysis of cocaine with plasma levels below detection limits within 5 to 8 min. Elevations in MAP and HR were significantly reduced within 25 and 50 min of DM CocE administration, respectively. Although slight (10-fold) increases in anti-CocE antibodies were observed after the fourth administration of DM CocE, these antibodies did not alter the capacity of DM CocE to reduce plasma cocaine levels or ameliorate cocaine's cardiovascular effects. Anti-CocE titers were transient and generally dissipated within 8 weeks. Together, these results suggest that highly efficient cocaine esterases, such as DM CocE, may provide a novel and effective therapeutic for the treatment of acute cocaine intoxication in humans.     

Biliary elimination of cefotiam, an experimental and clinical study

Five isolated rabbit livers were in vitro perfused over a 3-hour period. After addition of 10 mg of cefotiam to the circulating blood, a biliary peak concentration of 76.2 +/- 14.2 micrograms/ml (mean +/- SEM) was reached between the 90th and 120th min; 3.1 +/- 0.4% of the dose given was excreted in the bile during the 3-hour period. In 10 recently cholecystectomized patients provided with a T-tube drain, 1 g of cefotiam was given intravenously. A biliary peak concentration of 340 +/- 81 micrograms/ml was observed 2 h later. 1.8 +/- 0.7% of the administered dose was recovered in the bile during the 12-hour period. In 5 clinically normal subjects given intravenously 1 g of cefotiam, 0.5 +/- 0.2% of the administered dose was found in the duodenal fluid aspirated over a 4-hour period. Cefotiam concentrations measured in choledochal and gallbladder bile collected simultaneously during operation 1 h after intravenous administration of 1 g of the drug to 10 patients were 502 +/- 102 micrograms/ml and 143 +/- 39 micrograms/ml, respectively; they exceeded significantly the concentration determined in the serum sampled at the same time (17.9 +/- 2.6 micrograms/ml). The biliary parameters of cefotiam were compared with those of 14 other beta-lactam antibiotics previously studied by the same procedure. The results of the present study are consistent with a possible beneficial effect of cefotiam in the treatment of biliary tract infections.     

Evaluation of the blood-brain barrier transport,population pharmacokinetics,and brain distribution of benztropine analogs and cocaine using in vitro and in vivo techniques

The N-substituted 3alpha-[bis(4'-fluorophenyl)methoxy]tropanes (AHN 2-003, AHN 1-055, AHN 2-005, and JHW 007) bind with high affinity to the dopamine transporter and inhibit dopamine uptake more potently than cocaine, but they demonstrate behavioral profiles in animal models of psychostimulant abuse that are unlike that of cocaine. The objective of this study was to characterize the in vitro permeability, brain distribution, and pharmacokinetics of the benztropine (BZT) analogs. Transport studies of cocaine and the BZT analogs (10-4 M) were conducted across bovine brain microvessel endothelial cells. Male Sprague-Dawley rats (approximately 300 g) were administered BZT analogs (10 mg/kg) or cocaine (5 mg/kg) via the tail vein. Blood and brain samples were collected over 36 h and assayed using UV-high-performance liquid chromatography. Transport of both AHN 1-055 (2.15 x 10-4 cm/s) and JHW 007 (2.83 x 10-4 cm/s) was higher (p < 0.05) than that of cocaine (1.63 x 10-4 cm/s). The volume of distribution (12.3-30.5 l/kg) of the analogs was significantly higher than cocaine (0.9 l/kg). The BZT analogs displayed a > or =8-fold higher elimination half-life (4.12-16.49 h) compared with cocaine (0.49 h). The brain-to-plasma partition coefficients were at least two-fold higher for the BZTs versus cocaine, except for AHN 2-003. The BZT analogs are highly permeable across the blood-brain barrier and possess a pharmacokinetic profile different from that of cocaine. These characteristics, in addition to their distinctive behavioral profiles, suggest that the BZT analogs may be promising candidates for the treatment of cocaine abuse.     

Biliary elimination of mezlocillin: an experimental and clinical study

The biliary elimination of mezlocillin, a new semisynthetic penicillin of the acyl-ureido-penicillin group, was investigated in vitro in rabbit liver preparations and in vivo in humans. Experimentally, mezlocillin recovery in the bile during perfusion of isolted rabbit liver (3 h; n = 5) averaged 20.3% of the administrered dose (10 mg). The mean peak concentration in the bile (758 +/- 129.3 micrograms/ml) was reached between 0.5 and 1 h. Biliary clearance was 169 ml/h. In healthy subjects (n = 5), the concentrations of antibiotic measured in the duodenal fluid during a period of 4 h after intravenous administration of 5 g of mezlocillin ranged between 440 and 637 micrograms/ml. In 10 cholecystectomized patients provided with a T-tube, intramuscular injection of 1 g of mezlocillin resulted in a biliary peak concentration of 295.7 +/- 58.1 micrograms/ml. Mean total amount of antibiotic eliminated in the bile over 12 h corresponded to 2.6% of the administered dose. Assays performed during surgery after intravenous administration of 2 g of mezlocillin (n = 10) showed antibiotic activity of 895 +/- 196 micrograms/ml in the common duct bile and 402 +/- 133 micrograms/ml in the gallbladder bile. These data were compared with the values determined for 11 other beta-lactamines studied under identical conditions.     

Stereoselective pharmacokinetics of ketamine: R(-)-ketamine inhibits the elimination of S(+)-ketamine.

OBJECTIVE: We investigated the pharmacokinetics of ketamine with special regard to enantiomer-specific differences. METHODS: Ten healthy young male volunteers (mean age, 28 +/- 4 years; mean weight, 79 +/- 11 kg) received racemic ketamine and S(+)-ketamine in a randomized double-blind crossover study. Drugs were administered by a computer-controlled device. Two infusion cycles with linearly increasing targets [slope, 0.1 microg x ml(-1) x min(-1) for S(+)-ketamine and 0.2 microg x ml(-1) x min(-1) for racemic ketamine] were administered. Concentrations of the ketamine enantiomers were determined from arterial blood, and pharmacokinetic parameters were estimated with a 2- and 3-compartment model. RESULTS: The total doses needed to reach defined end points were 271 +/- 80 mg and 409 +/- 75 mg for S(+)-ketamine and racemic ketamine, respectively (P <.05). S(+)-ketamine showed a significantly higher clearance (26.3 +/- 3.5 ml x kg(-1) x min(-1)) compared with racemic ketamine (14.8 +/- 1.7 ml x kg(-1) x min(-1); P <.05) and R(-)-ketamine (13.8 +/- 1.3 ml x kg(-1) x min(-1); P <.05). Furthermore, the clearance of the S (+)-ketamine was smaller in the racemate (18.5 +/- 0.7 ml x kg(-1) x min(-1); P <.05) than for the pure isomer. CONCLUSIONS: These results demonstrate that R(-)-ketamine inhibits the elimination of S(+)-ketamine.     

In vivo study of acetylcholine esterase in basal forebrain, amygdala, and cortex in mild to moderate Alzheimer disease

It is currently unclear whether impairment of the cholinergic system is present in Alzheimer disease (AD) already at an early stage and to what extent it depends on degeneration of the nucleus basalis of Meynert (nbM). We examined acetylcholine esterase activity in vivo in the nbM, the amygdala, and cerebral neocortex. Measurements were performed in normal controls and in patients with mild to moderate AD with positron emission tomography (PET) and C-11-labeled N-methyl-4-piperidyl-acetate (MP4A) which is a specific substrate of AChE. AChE activity was reduced significantly in amygdala and cerebral cortex. In contrast, AChE activity and glucose metabolism appeared preserved or even increased in the nbM. The results support the concept that neocortical and amygdaloid functional changes of the cholinergic system are an early and leading event in AD, rather than the consequence of neurodegeneration of basal nuclei.     

In vitro characterization of poly(methyl-methaerylate) nanoparticles and correlation to their in vivo fate

The organ distribution of poly (methyl methacrylate) nanoparticles surface-modified by the adsorption of surfactants was related to the physicochemical propertics. The nanoparticles were modified by coating with poloxamer, poloxamine, Brij and polysorbate surfactants. They were characterized in terms of coating layer thickness, surface hydrophobicity (hydrophobic interaction chromatography) and interaction with serum components (zeta potential). The liver/spleen uptake of partictes coated with low molecular weight surfactants has been related to their hydrophobic coating layer interacting strongly with serum components. The protective effect of poloxamer 338 and poloxamine 908 could be explained by their ability to render the surfaces of the particles hydrophilic, which made a reduction of sérum opsonization possible. The in vitro characterization methods proved to be suitable to select surfactants with high potential to reduce the uptake of nanoparticles by liver and spleen macrophages. The affinity of particles to other sites in the body (bone marrow, lungs) could, however, not be explained using the above-mentioned in vitro characterization methods.     

The fate of inhaled drugs: the pharmacokinetics and pharmacodynamics of drugs administered by aerosol

Prior to a drug achieving its effects (ie, pharmacodynamics), there are numerous events within the body that determine its ultimate fate. The effects of the "body on the drug" has been referred to as pharmacokinetics-how the favorable lung-to-systemic effects predicted from this exercise translate into practice. Inhaled drugs have enjoyed the major feature of having "local" effects on the target organ of the lung. Broadly, lower doses can be used and adverse effects are often less than with oral or parenteral administration. Nevertheless, key features of respiratory drugs and their administration can impact their fate and ultimate utility. This review has provided some relevant examples of basic pharmacokinetics principles as related to inhaled products, with emphasis on those factors that help to partition lung-to-systemic effects.     

In vitro and in vivo profiles of ACH-702, an isothiazoloquinolone, against bacterial pathogens

ACH-702, a novel isothiazoloquinolone (ITQ), was assessed for antibacterial activity against a panel of Gram-positive and Gram-negative clinical isolates and found to possess broad-spectrum activity, especially against antibiotic-resistant Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA). For Gram-negative bacteria, ACH-702 showed exceptional potency against Haemophilus influenzae, Moraxella catarrhalis, and a Neisseria sp. but was less active against members of the Enterobacteriaceae. Good antibacterial activity was also evident against several anaerobes as well as Legionella pneumophila and Mycoplasma pneumoniae. Excellent bactericidal activity was observed for ACH-702 against several bacterial pathogens in time-kill assays, and postantibiotic effects (PAEs) of >1 h were evident with both laboratory and clinical strains of staphylococci at 10× MIC and similar in most cases to those observed for moxifloxacin at the same MIC multiple. In vivo efficacy was demonstrated against S. aureus with murine sepsis and thigh infection models, with decreases in the number of CFU/thigh equal to or greater than those observed after vancomycin treatment. Macromolecular synthesis assays showed specific dose-dependent inhibition of DNA replication in staphylococci, and biochemical analyses indicated potent dual inhibition of two essential DNA replication enzymes: DNA gyrase and topoisomerase IV. Additional biological data in support of an effective dual targeting mechanism of action include the following: low MIC values (≤0.25 μg/ml) against staphylococcal strains with single mutations in both gyrA and grlA (parC), retention of good antibacterial activity (MICs of ≤0.5 μg/ml) against staphylococcal strains with two mutations in both gyrA and grlA, and low frequencies for the selection of higher-level resistance (<10⁻¹⁰). These promising initial data support further study of isothiazoloquinolones as potential clinical candidates.     

In vivo efficacy and pharmacokinetics of voriconazole in an animal model of dermatophytosis

The standard treatment for tinea capitis caused by Microsporum species for many years has been oral griseofulvin, which is no longer universally marketed. Voriconazole has been demonstrated to inhibit growth of Microsporum canis in vitro. We evaluated the efficacy and tissue pharmacokinetics of oral voriconazole in a guinea pig model of dermatophytosis. Guinea pigs (n = 16) were inoculated with M. canis conidia on razed skin. Voriconazole was dosed orally at 20 mg/kg/day for 12 days (days 3 to 14). The guinea pigs were scored clinically (redness and lesion severity) and mycologically (microscopy and culture) until day 17. Voriconazole concentrations were measured day 14 in blood, skin biopsy specimens, and interstitial fluid obtained by microdialysis in selected animals. Clinically, the voriconazole-treated animals had significantly less redness and lower lesion scores than untreated animals from days 7 and 10, respectively (P < 0.05). Skin scrapings from seven of eight animals in the voriconazole-treated group were microscopy and culture negative in contrast to zero of eight animals from the untreated group at day 14. The colony counts per specimen were significantly higher in samples from untreated animals (mean colony count of 28) than in the voriconazole-treated animals (<1 in the voriconazole group [P < 0.0001]). The voriconazole concentration in microdialysate (unbound) ranged from 0.9 to 2.0 microg/ml and in the skin biopsy specimens total from 9.1 to 35.9 microg/g. In conclusion, orally administered voriconazole leads to skin concentrations greater than the necessary MICs for Microsporum and was shown to be highly efficacious in an animal model of dermatophytosis. Voriconazole may be a future alternative for treatment of tinea capitis in humans.     

Effect of human renal cationic transporter inhibition on the pharmacokinetics of varenicline, a new therapy for smoking cessation: an in vitro-in vivo study

Varenicline is predominantly eliminated unchanged in urine, and active tubular secretion partially contributes to its renal elimination. Transporter inhibition assays using human embryonic kidney 293 cells transfected with human renal transporters demonstrated that high concentrations of varenicline inhibited substrate uptake by hOCT2 (IC(50)=890 microM), with very weak or no measurable interactions with the other transporters hOAT1, hOAT3, hOCTN1, and hOCTN2. Varenicline was characterized as a moderate-affinity substrate for hOCT2 (K(m)=370 microM) and its hOCT2-mediated uptake was partially inhibited by cimetidine. Co-administration of cimetidine (1,200 mg/day) reduced the renal clearance of varenicline in 12 smokers, resulting in a 29.0% (90% CI: 21.5%-36.9%) increase in systemic exposure. This increase is not considered clinically relevant, as it should not give rise to safety concerns. Consequently, it can be reasonably expected that other inhibitors of hOCT2 would not cause greater renal interactions with varenicline than that seen with the efficient hOCT2 inhibitor cimetidine.     

In vivo maternal-fetal pharmacokinetics of stavudine (2',3'-didehydro-3'-deoxythymidine) in pigtailed macaques (Macaca nemestrina).

To determine whether stavudine (2',3'-didehydro-3'-deoxythymidine) is actively transported in vivo across the placenta and to determine the extent of its transfer, stavudine was administered as an intravenous bolus to four near-term macaques (Macaca nemestrina) (5 mg/kg of body weight via the femoral vein) or to their fetuses (10 mg/kg via the carorid artery) at gestational age 134 +/- 5 days, with the administrations about 1 week apart. Antipyrine (a passive diffusion marker) was always coadministered (20 mg/kg) with stavudine. Samples of maternal and fetal plasma and amniotic fluid were collected at frequent intervals up to 240 min after the dose. In a separate experiment, three animals received stavudine for 30 h at a low rate of infusion (22 micrograms/min/kg via the femoral vein) to the dam or at a 10-fold-higher rate of infusion (220 micrograms/min/kg), separated by at least one week, in order to determine if the transplacental transfer of stavudine is saturable. Antipyrine (41.7 micrograms/min/kg) was coinfused with stavudine. Samples of maternal and fetal plasma and amniotic fluid were collected at regular intervals for up to 30 h. The concentrations of stavudine and antipyrine were determined by high-performance liquid chromatography. The transplacental maternal-fetal drug clearances were compared by the paired Student t test. The clearance associated with maternal-fetal transfer of the drug (CLdf) (0.54 +/- 0.08 ml/min/kg) was not significantly different (P > 0.05) from the clearance associated with fetal-maternal transfer of the drug, CLfd (0.66 +/- 0.11 ml/min/kg). Also, CLdf was not significantly different (P > 0.05) from CLfd when normalized with respect to the corresponding transplacental clearance of antipyrine (0.23 +/- 0.04 versus 0.36 +/- 0.25). The ratios of the steady-state plasma stavudine concentration in the fetus to that in the dam were 0.77 +/- 0.06 at the low stavudine infusion rate and 0.81 +/- 0.09 at the high stavudine infusion rate. The obtained data indicate that transfer of stavudine across the placenta is passive and constant over the dose range studied.     

Oral cocaine pharmacokinetics and pharmacodynamics in a cumulative-dose regimen: pharmacokinetic-pharmacodynamic modeling of concurrent operant and spontaneous behavior within an operant context

Despite wide use of cumulative-dosing procedures to evaluate dose-response relations, limited attention has been paid to investigating drug concentration-effect relations. We first characterized the pharmacokinetic (PK) parameters for i.v. (2 mg/kg) and oral cocaine (20 and 40 mg/kg) in rats. Cocaine's concentration-time profile for the escalating cumulative-dose regimen was simulated from PK parameters, dose size (1, 2, 7, 20, and 45 mg/kg by the oral route), and dosing interval (tau, 35 min) as well as validated from blood sampling at various time points. This concentration-time profile was integrated with pharmacodynamic (PD) profiles of differential reinforcement of low rate performance and spontaneous activity (large and small movements) under a differential reinforcement of low rate 45-s schedule. Effects on three behavioral measures were characterized by integrated PK-PD models using the sigmoid E(max) (for increases in shorter response rate or large movements) and inhibitory E(max) (for decreases in density of reinforcement) models. But for the intrinsic differences in baseline and efficacy values among the behavioral endpoints, one set of PD parameters (i.e., potency and Hill factors) predicted concentration-effect relations for the three behavioral indices across all five doses. Concurrent monitoring of operant and spontaneous activity behavior within an operant context provides a novel behavioral paradigm to investigate drug effects on spontaneous activity under conditions where a behavioral contingency exists. Additionally, a cumulative-dosing procedure is efficient for determining the entire dose-response relation and provides an ideal mode to study phenomena such as sensitization or tolerance by varying dose size and/or tau.