Further support for changes in chloroquine disposition and metabolism between a low and a high dose

Summary The kinetics of chloroquine and its major metabolite desethylchloroquine were studied in patients with rheumatoid disease after single oral doses of chloroquine phosphate corresponding to 150 and 300 mg chloroquine base. The findings strengthen the previous finding that the disposition of chloroquine involves rate limiting steps.     

Stereoselectivity in the disposition of chloroquine and desethylchloroquine in rabbits.

Stereoselective pharmacokinetic properties of chloroquine (CAS 54-05-7) and desethylchloroquine were investigated in rabbits by administration of the separate enantiomers according to a cross-over design. The terminal half-life was longer for (R)-chloroquine than for (S)-chloroquine. A striking difference was revealed in the concentrations of metabolites. The levels of (R)-desethylchloroquine were higher than those of (S)-desethylchloroquine, resulting in a statistically significant higher AUC for the (R)-metabolite than for the (S)-metabolite.     

The effect of chloroquine on paracetamol disposition and kinetics.

The effect of chloroquine on paracetamol kinetics and disposition was investigated in six healthy male Ghanaian volunteers. Chloroquine administration shortened the time taken to reach peak plasma paracetamol concentration (tmax) in five of the volunteers. Peak plasma paracetamol concentration (Cmax) was significantly increased by chloroquine administration. The area under the plasma paracetamol concentration-time curve was also significantly increased by chloroquine administration. There was, however, no effect of chloroquine on paracetamol metabolism.     

On the dose dependency of Cyclosporin a absorption and disposition in healthy volunteers

The pharmacokinetics of Cyclosporin A (CyA, Sandimmune^R) was studied in 12 healthy male volunteers after oral dosing of 350 mg, 700 mg, and 1400 mg as a drinking solution. Blood samples were collected over 96 hr and analyzed by high pressure liquid chromatography. Concentration data were evaluated with model-independent and model-based linear pharmacokinetic concepts. Individual CyA concentration-time profiles in whole blood were well described by a two-compartment open model with zero-order absorption for all three doses. Comparison of pharmacokinetic parameters across doses indicates that both absorption and disposition are dose-dependent. Nonlinear disposition is suggested by the significant increase of the terminal half-life from 8.9±4.9hr to 11.9±4.9hr (mean±SD) after a 350 mg and a 1400 mg dose, respectively. Changes in the metabolic activity of the liver with concentration might be responsible for this phenomenon. In addition, the modeling approach indicated that bioavailability decreases with increasing dose. Moreover, the dependence of the rate of CyA absorption (zero-order rate constant) versus dose was well described by a hyperbola. The limited solubility of the drug in the gastrointestinal tract might be responsible for this behavior. The lag time (0.2–0.8 hr) was independent of dose. This value is similar to the time of gastric emptying in fasting volunteers. The duration of absorption for 11 of 12 subjects was in the range 2.5–3.5 hr over all doses and agrees well with the small intestine transit time. Some subjects showed a marked secondary peak at one or two doses, which could be adequately fitted by a model with two successive zero-order inputs. This double-peak behavior was ascribed to the influence of the food on gastric emptying. Dose dependency of disposition and absorption counterbalance each other in the usual dose range. This leads to an almost proportional increase of area under the blood CyA concentration-time profile with increasing dose.Part of this work was presented at the Third European Congress of Biopharmaceutics and Pharmacokinetics, Freiburg i.Br., Germany, 1987.This work is part of the doctoral dissertation of Jean-Philippe Reymond.Partly supported by Contrat de prestation 84112 between INSERM and Sandoz.     

Single dose pharmacokinetic study of clobazam in normal volunteers and epileptic patients.

The pharmacokinetics of clobazam were studied in six healthy volunteers and six age and sex matched enzyme-induced epileptic patients. In the epileptic patients the area under the plasma concentration-time curve for clobazam was significantly smaller and the area under the plasma concentration-time curve for N-desmethylclobazam was significantly greater than in the healthy volunteers. Plasma N-desmethylclobazam concentrations were found to be much higher than those of clobazam in the epileptic patients, raising the possibility that the antiepileptic properties of clobazam are to be attributed more to its metabolite than the parent drug.     

Single dose pharmacokinetics and pharmacodynamics of oxazepam in normal and renal dysfunction rats.

The purpose of this work was to investigate the disposition characteristics and pharmacodynamics of a benzodiazepine, oxazepam, in renal dysfunction rats. For the in vivo experiment, normal and renal dysfunction rats were given 40 mg/kg of oxazepam as the bolus dose. A quantitative electroencephalographic (EEG) method was used as the surrogate measure of the pharmacological response. The oxazepam concentration in plasma and cerebrospinal fluid (CSF) was assayed by the HPLC method. The steady-state volume of distribution and clearance based on total and unbound plasma did not change in renal dysfunction rats. Amplitude changes in the EEG induced by oxazepam in normal and renal dysfunction rats were characterized by a log-concentration response model or sigmoidal Emax model. The pharmacodynamic parameters from these models were not altered in renal dysfunction. In in vitro binding studies for gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex, the oxazepam-induced effect was not potentiated by the plasma dialysate from renal dysfunction rats. Thus, it was suggested that the brain sensitivity to benzodiazepines was not altered in renal insufficiency.     

Prevention of chloroquine absorption by activated charcoal.

1. The ability of activated charcoal to prevent the absorption of chloroquine was investigated in healthy volunteers, and the effect of the charcoal-chloroquine ratio on the completeness of binding was studied in vitro. 2. After an overnight fast, six subjects ingested 500 mg of chloroquine phosphate with water, and another group of six subjects ingested 25 g of charcoal suspension within 5 min of chloroquine intake. The concentrations of chloroquine in plasma and whole blood were measured by high-performance liquid chromatography for 192 h. 3. Activated charcoal reduced the areas under the plasma and whole blood chloroquine concentration-time curves (AUC) from 0 to 192 h, the total AUCs, and the peak concentrations by 99% (P less than 0.001). 4. Chloroquine was very effectively bound by activated charcoal in vitro, even at low charcoal-chloroquine ratios. For example, at a ratio of 5:1, about 98% of chloroquine was bound. 5. Activated charcoal should be very effective in reducing the absorption of that fraction of chloroquine dose which is in the stomach at the time of charcoal administration. Because the acute toxicity of chloroquine is extremely high and death usually occurs within 1-3 h of overdosage, charcoal should be given as early as possible in suspected chloroquine intoxication.     

The disposition of chloroquine in healthy Nigerians after single intravenous and oral doses.

The pharmacokinetics of chloroquine after single oral (600 mg) and intravenous (2 mg kg-1) doses were studied in healthy black Nigerian students. The plasma concentrations of chloroquine and its desethylmetabolite were determined using a high performance liquid chromatography technique. Concentrations as low as 3 ng ml-1 were reproducibly determined. After i.v. dosage, the half-life ranged between 144 and 298 h; the total plasma clearance was between 282 and 1130 ml min-1 and the volume of distribution between 142 and 398 1 kg-1. Renal clearance was about 52% of plasma clearance. The estimated total urinary recovery of chloroquine and desethylchloroquine was 77% of the oral dose. There was no significant difference in the pharmacokinetics between the oral and the i.v. administration. The pharmacokinetic properties of chloroquine, in these black subjects did not differ from those previously demonstrated in Caucasians.     

Single dose absorption profiles and bioavailability of two different salbutamol tablets

In a single dose cross-over experiment in twelve healthy adults a comparison of the absorption profiles and the relative bioavailability was made between a new salbutamol containing tablet (preparation A = Salbutax) and a commercially available and accepted formulation as reference (preparation B), both containing 4 mg salbutamol. Salbutamol plasma concentrations were measured frequently during a period of 16 h post dosing. Maximum salbutamol plasma concentrations after intake of product A and product B on an empty stomach were reached after 2.3 +/- 0.9 (= mean +/- S.D.) and 2.4 +/- 1.1 h, respectively, and accounted for 14.3 +/- 2.5 and 12.8 +/- 2.6 micrograms X l-1, respectively. The differences were not found to be significant (p greater than 0.05). The areas under the plasma concentration-time curves (AUC0----16), as obtained after administration of tablet A and tablet B, accounted for 73.5 +/- 14.0 and 65.0 +/- 11.8 micrograms X l-1 X h, respectively, the difference being marginally significant (p = 0.05). This results in a relative bioavailability of 114.3 +/- 15.7% for the product A 4-mg tablets. It is concluded that both products can be considered as having comparable bioavailability.     

Stereoselective disposition of flurbiprofen in normal volunteers.

1. The concentrations of the R- and S-enantiomers of flurbiprofen and its metabolites were measured in plasma and urine following the oral administration of 50 mg racemic flurbiprofen to six normal volunteers. 2. The AUC and half-life of the R-enantiomer were significantly lower than the corresponding S-enantiomer values reflecting the greater clearance of R-flurbiprofen (20.42 +/- 4.71 vs 16.12 +/- 3.60 ml min-1). 3. Ex vivo protein binding studies indicated that the percent unbound of R-flurbiprofen was (not significantly) greater than that of the S-enantiomer (0.055 +/- 0.008 vs 0.049 +/- 0.009) and the corresponding unbound clearances did not show enantioselectivity. 4. Both enantiomers were cleared primarily by metabolism to an acylglucuronide and 4'-hydroxyflurbiprofen. There was significant enantioselectivity (R greater than S) in the formation clearances of these metabolites which remained when unbound metabolite formation clearances were considered. 5. In conclusion, the disposition of the enantiomers of flurbiprofen exhibits enantioselectivity at the level of protein binding and metabolite formation.     

药物的肠吸收与处置研究进展

对近几年药物肠吸收与处置方面的研究进展进行了综述。包括:特定部位吸收、代谢的认识和利用,与药物首过效应有关的肠壁外泌及代谢作用的介绍,促进药物肠道吸收的方法及常用研究模型的比较。     

Antipyrine absorption and disposition in the elderly

Twelve young (24-41 years) and 11 elderly (62-77 years) volunteer subjects received a single 1.0-gram dose of antipyrine on three occasions: intravenously, orally in the fasting state and orally following a standard breakfast. Plasma antipyrine concentrations were determined for 24 h after each dose. Compared to young males, elderly men had significantly prolonged elimination half-life (17 vs. 11 h, p less than 0.025) and reduced clearance (32 vs. 54 ml/min, p less than 0.06). However, elderly and young women did not differ in half-life (12 vs. 11 h) or clearance (37 vs. 44 ml/min). After oral dosage in the fasting state, young and elderly groups (regardless of gender) did not differ in peak plasma antipyrine concentration (Cmax) or time of peak concentration (Tmax). Absolute bioavailability was not significantly less than 100% and was not related to age. Postprandial oral dosage of antipyrine caused reduced Cmax and prolonged Tmax in all groups, but absolute bioavailability was not significantly less than 100%. Again, there were no age-related differences. Although aging may lead to reduced clearance of antipyrine among men, there is no evidence that old age is associated with impairment of the rate or extent of antipyrine absorption from the gastrointestinal tract.     

Single dose and multiple dose studies of itraconazole nanoparticles.

The objective of this study was to determine and compare the lung and serum concentrations in mice following oral and pulmonary dosing of amorphous nanoparticulate itraconazole (ITZ) compositions as well as the Sporanox oral solution (itraconazole/Janssen). Second, the steady state partitioning of ITZ in lung tissue and circulatory compartments following repeated oral and pulmonary dosing was determined. The pulmonary formulation (ITZ-pulmonary) consisted of ITZ, polysorbate 80, and poloxamer 407 in a 1:0.75:0.75 ratio and the oral formulation (ITZ-oral) consisted of ITZ, PEG 8000, poloxamer 188, and sorbitan monooleate 80 in a 1:1:2:1 ratio. Mice were dosed every 12 h by nebulization with ITZ-pulmonary, or by oral gavage with ITZ-oral or Sporanox oral solution (n = 12 per study arm). ITZ-pulmonary achieved significantly greater (>10-fold) lung tissue concentrations compared to the Sporanox oral solution and ITZ-oral. There were no statistical differences between the two oral formulations. ITZ-pulmonary achieved significantly greater lung levels per unit serum concentration compared to the orally dosed ITZ compositions. High and sustained lung tissue concentrations were achieved via inhalation of an amorphous nanoparticulate ITZ-pulmonary composition while maintaining serum levels which are above the minimum lethal concentration (MLC) of Aspergillus fumigatus.     

Percutaneous absorption and disposition of iodochlorhydroxyquin in dogs

The percutaneous absorption and disposition of iodochlorhydroxyquin (5-chloro-7-iodo-8-quinolinol; I) from a 3% cream were studied in five dogs over a 28-d topical treatment period. Plasma levels, determined by HPLC, were 0.275-0.525 microgram/mL. The steady-state elimination rate of total I in urine was 2.4-3.0 mg/d. The apparent elimination rate constant and half-life were 0.25 +/- 0.05 d-1 and 3.1 +/- 0.5 d, respectively. Greater than 50% of topically applied I was absorbed over 16 h. Occlusion of the skin without the drug indicated that the skin acted as a reservoir for the drug. Feces analysis for iodochlorhydroxyquin from one dog showed that 27.1 +/- 8.5 mg/d was eliminated via this route. Tissue levels of I 15 d after the 28-d topical treatment were 0.7 microgram/g of liver, 0.2 microgram/g of kidney, and 0.8 microgram/g of mesenteric fat. The apparent rate constants of plasma level decline after a 100-mg iv bolus dose of I were alpha = 3.9 h-1 and beta = 0.6 h-1. The urinary elimination after intravenous administration was biphasic. The rate constant for the slow elimination phase was 0.4 +/- 0.1 d-1, and the half-life was 2.0 +/- 0.5 d. The primary neurological symptoms observed during topical treatment were ataxia and hind limb paralysis. Microscopic examination revealed liver necrosis. A weight loss of 15.3 +/- 2.7% was also observed over the 28-d topical treatment period. The results indicate that significant percutaneous absorption of I occurs, and that chronic high-dose topical treatment may lead to toxicity.     

Percutaneous absorption and disposition of Tinopal EMS

A cotton-substantive, anionic, fluorescent whitening agent manufactured by several suppliers under various trade names e.g. Tinopal EMS, has been synthesized in radioactive form. Intubation of detergent or aqueous solution into rats resulted in little absorption from the intestinal tract as evidenced by low radioactivity in the urine and tissues. Most of the dose was excreted rapidly in the faeces. After parenteral administration to rats, the radioactivity was rapidly excreted in the faeces with small amounts remaining in tissues and organs. There was slight evidence of retention of radioactivity in the kidneys. Very small amounts of Tinopal EMS in detergent were absorbed through rat skin, but only when concentrations greater than those normally used by the consumer, together with occlusion of the skin were employed. Small amounts were absorbed through skin when applied in ethanol. It is concluded that the possibility of systemic toxic effects in man as a result of percutaneous absorption is remote.     

Correlation between inhibitory effect on platelet aggregation and disposition of sulfinpyrazone and its metabolites in rabbits. Part I: Single dose study

Simultaneous evaluation of inhibition of the sodium arachidonate-induced platelet aggregation and drug disposition was studied in rabbits receiving single doses of sulfinpyrazone (SO) and its sulfide metabolite (S). The metabolism of SO was found to be interconversible with that of S. Due to the parallelism of disposition profiles, the observed concentration-related inhibition not only strongly correlated with the much more potent sulfide, but also correlated with the p-OH-sulfide (OH-S) or with a summation of two substances. Exaggeration of inhibition at 24-30 h and rebound effect at 48 h were found after the substances were administered. There may exist a circadian rhythm of platelet aggregation.     

Mechanistic study on the intestinal absorption and disposition of baicalein.

The present study aims to investigate the mechanisms of intestinal absorption and disposition of flavonoid baicalein (B) in Caco-2 cell monolayer model, transporter overexpressing membrane, and cellular models. The bidirectional transport studies of B and its metabolite baicalein-7-glucuronide (BG) were conducted at various concentrations and in the absence or presence of the selected transporter inhibitors. To identify specific interactions of BG with ABC transporters, ABC transporter-ATPase assays were carried out on membrane vesicles prepared from Sf9 cells overexpressing human MDR1, MRP1, MRP2, MRP3 and MXR. To further confirm the interactions between BG and specific ABC transporters, inhibition of BG on the transport of substrates of specific transporters were evaluated using membrane vesicles overexpressing MRP1-3 and MXR, or K562MDR cells with overexpressing MDR1. The results showed that B could readily pass through Caco-2 cell monolayer, but with significant glucuronidation and sulfation. The extent of phase II metabolism of B during its transport was in dose-dependent manner. The intracellularly formed glucuronide and sulfate of B were efficiently extruded to both apical and basolateral sides of the Caco-2 monolayer, which were reduced in the presence of MRP inhibitors. Although BG was not permeable from apical to basolateral side, it exhibited significant efflux transport that was inhibited in the presence of MRPs inhibitors. Moreover, BG seemed to activate the ATPase activity of both MRP3 and MXR at a pharmacologically relevant concentration range.