Pharmacokinetic Modelling of 5-FU Production from Capecitabine—A Population Study in 40 Adult Patients with Metastatic Cancer

Aims: To model the biotransformation steps of 5-FU production from capecitabine and identify patient characteristics that may influence the drug disposition. Methods: Blood samples and demographic data were collected from two phase I studies in which adult patients received oral capecitabine for various malignancies. Capecitabine, 5′-deoxy-5-fluorocytidine (5′-DFCR), 5′-deoxy-5-fluorouridine (5′-DFUR) and 5-fluorouracile (5-FU) concentration-time data were analysed via a population approach using NONMEM. Results: Forty patients and 75 pharmacokinetic time-courses were available for analysis. Capecitabine pharmacokinetics was ascribed to a one compartment model from which 5′-DFCR, 5′-DFUR and 5-FU were sequentially produced. Capecitabine oral absorption was characterized by a rapid first order input (K_a=2.1 ± 0.3 hr⁻¹) with a lag time (0.28 ± 0.11 hr), but related inter-occasion (IOV) and inter-subject (ISV) variabilities for these parameters, 167% and 110%, indicated that this oral absorption was highly variable. The capecitabine CL (CL₁₀ = 218± 18 L/hr, ISV = 18%) and 5′-DFUR elimination rate constant (K₃₄ = 5.3 ± 2.0 hr⁻¹, ISV = 25%) were influenced by total bilirubin (BILT). The elimination rate constant of plasma 5-FU (K₄₀) was 66 ± 24 hr⁻¹ (ISV = 34%).The final pharmacokinetic model was validated using 2000 bootstrap runs and provided non-parametric statistics of the parameters (median, 2.5th and 97.5th percentiles). Conclusions: This study supported the possibility of modelling a complex sequential metabolic pathway which produces pharmacologicaly active compounds from a prodrug. Only BILT significantly influenced the pharmacokinetics but this effect was not considered as relevant for dosing adjustment.     

Pharmacokinetics of disopyramide in patients with imminent to moderate cardiac failure

Summary The parmacokinetics of disopyramide (DP) in 10 patients with imminent to moderate cardiac failure has been studied and compared with the results in normal volunteers. The biological half life of rapid distribution (T1/2 α) and of elimination (T1/2 β) were increased (11.1±4.4 min and 9.7±4.2 h, respectively). Total body clearance (Cl_t) was decreased (0.467±0.215 ml · min⁻¹ · kg⁻¹), and the volume of distribution (V_d) was slightly reduced (0.610±0.1361 · kg⁻¹), probably due to the lower cardiac index. After oral administration, the time to peak serum concentration was increased (139±89 min), and the mean peak serum concentration (2.4±0.8% dose · 1⁻¹) was also higher than reported in normal subjects. Comparison of the areas under the concentration versus time curves after intravenous and oral administration (AUC i. v. and AUC oral) showed that DP was almost completely absorbed, its bioavailability being 97.5±15.0%.     

Bayesian pharmacokinetic estimation of vinorelbine in non-small-cell lung cancer patients

Objective: To develop a population pharmacokinetics of vinorelbine in a population of non-small-cell lung cancer (NSCLC) patients using a Bayesian estimation in order to calculate for any further patient, individual pharmacokinetic parameters from few blood samples. Methods: Vinorelbine was given by a 15-min infusion (30 mg · m⁻²) to eight patients with NSCLC. Its serum concentration was determined by HPLC and its pharmacokinetics was described by a three-compartment open model with elimination from the central compartment. Volume of the central compartment (V₁) and rate constants (k₁₀, k₁₂, k₂₁, k₁₃, k₃₁) were selected as population pharmacokinetic parameters and computed by non-linear regression (two-step approach) from 14 to 18 concentration measurements per course. Subsequently, these parameters were used by the Bayesian estimator to calculate individual pharmacokinetics from only 2 or 3 measured concentrations. Results: The population mean values (CV%) of V₁, k₁₀, k₁₂, k₂₁, k₁₃, k₃₁, CL, t _1/2 were respectively 21 l (55%), 3.2 h⁻¹ (29%), 7.7 h⁻¹ (74%), 1.3 h⁻¹ (67%), 4.7 h⁻¹ (53%), 0.04 h⁻¹ (20%), 57 l · h⁻¹ (31%) and 43 h (36%). The comparison of results obtained from the Bayesian estimator and from the three-compartment model showed that CL and t _1/2 were well predicted (relative deviation: ±12 to 22%) by the Bayesian method using only two blood samples. Conclusion: We demonstrated that Bayesian estimation allows, at minimal cost and minimal disturbance for the patient, the determination of several vinorelbine pharmacokinetic parameters and therefore dose adaptation from as few as two drug concentrations, measured at 6 h and 24 h after infusion. Received: 4 July 1997 / Accepted in revised form: 15 November 1997     

Analysis of Antiplatelet Effect of Ticlopidine In Humans: Modeling Based on Irreversible Inhibition of Platelet Precursors in Bone Marrow

The relationship between plasma concentration of ticlopidine and its inhibitory effect on platelet aggregation in human was analyzed using a pharmacokinetic/pharmacodynamic (PK/PD) model. The data of plasma concentration and inhibitory effect on platelet aggregation were taken from the literature. A two-compartment open model was fitted to plasma ticlopidine concentrations. Assuming that ticlopidine acts on platelet precursors in the bone marrow, the apparent reaction rate constant of ticlopidine and platelet precursors (K), apparent transformation rate constant of platelet precursors (k_r) and apparent elimination rate constant of platelets (k _e ) were estimated. The estimated values ± S.D. were 1.01 ± 1.08 ml g ^–1 hr^–1 for K, 0.265 ± 0.259 hr^–1 for k_r and 0.0747 ± 0.0112 hr ^–1 for k _e . The antiaggregation effects of ticlopidine on platelets after administration of 100, 200, and 300 mg (bid for 8 days) were simulated using the PD parameters of K, k_r, and k_e. While the antiaggregation effect reached steady state within 3–4 days without dose dependency of the interval, the maximum effect increased with dose. Furthermore, changing the elimination rate constant of ticlopidine from the central compartment in the model significantly changed the duration of inhibitory effect of ticlopidine on platelet aggregation. Therefore, the reported long duration of antiplatelet effect after discontinuation of ticlopidine, which is believed to be irreversible binding to the platelet, might have been partially caused by the delayed plasma elimination after a long therapy of ticlopidine. On the other hand, the mean life-span of platelets in the blood estimated by 1/k_e after administration of ticlopidine was 14 hr, far below the life-span of platelets in the blood. For a more detailed analysis of the antiplatelet effect of ticlopidine, the possible contribution of reversible binding of the drug to glycoprotein IIb/IIIa should be considered in future PK/PD models.     

Pharmacokinetics of propylene glycol after rectal administration

Propylene glycol is an excipient of various pharmaceutical preparations. The pharmacokinetics after rectal administration are studied, followed by a consideration on local and systemic side-effects for a solution of paracetamol in a mixture of propylene glycol and water. After administration of 8.64 g propylene glycol to 10 adults and 173 mg/kg body weight to 4 children, peak concentrations (C_max) of 119 mg/l and 171 mg/l respectively were reached (t_max) after 1.5 hr and 1.0 hr. The average terminal half-lives (t_1/2) in adults and children were respectively 2.8 hr and 2.6 hr, total body clearance (Cl/F) 0.20 l/hr^* kg and 0.21 l/hr^*kg and apparent volume of distribution (V_D/F) 0.79 l/kg and 0.77 l/kg.     

Sustained Increase in the Oral Bioavailability of Loperamide after a Single Oral Dose of HM30181, a P‐glycoprotein Inhibitor,in Healthy Male Participants

HM30181 is a new P‐glycoprotein (P‐gp) inhibitor. This study was conducted to investigate the effect of HM30181 and its duration of action on P‐gp inhibition using loperamide as a probe drug. An open‐label, five‐period, fixed‐sequence, cross‐over study was conducted in 25 healthy Korean participants, who received a single oral dose of loperamide at 16 mg in five periods lasting for 17 days. In period II, participants also randomly received a single oral dose of HM30181 at 1, 5, 10, 15 mg simultaneously with loperamide. Serial pharmacokinetic blood samples were obtained up to 72 and 336 hr after loperamide and HM30181 administration, respectively. A mixed‐effects analysis was performed to compare the area under the plasma concentration versus time curve from time 0 to 72 hr (AUC_0–72 hr) between periods and HM30181 dose groups. Tolerability was also assessed. The AUC_0–72 hr of repeatedly administered loperamide was significantly increased 1.18–1.62 times for up to 14 days after a single oral administration of HM30181, particularly at doses ≥10 mg although the between‐group difference failed to reach statistical significance. Plasma HM30181 was not detected in many participants including none at any sampling points beyond 48 hr after administration. Most adverse events (AEs) were mild to moderate and resolved spontaneously. The oral bioavailability of loperamide was significantly enhanced by a single oral administration of HM30181, which was sustained for up to 14 days. HM30181 was well tolerated in this selected population.     

Feedback modeling of non-esterified fatty acids in rats after nicotinic acid infusions

A feedback model was developed to describe the tolerance and oscillatory rebound seen in non-esterified fatty acid (NEFA) plasma concentrations following intravenous infusions of nicotinic acid (NiAc) to male Sprague-Dawley rats. NiAc was administered as an intravenous infusion over 30 min (0, 1, 5 or 20 μmol kg⁻¹ of body weight) or over 300 min (0, 5, 10 or 51 μmol kg⁻¹ of body weight), to healthy rats (n = 63), and serial arterial blood samples were taken for measurement of NiAc and NEFA plasma concentrations. Data were analyzed using nonlinear mixed effects modeling (NONMEM). The disposition of NiAc was described by a two-compartment model with endogenous turnover rate and two parallel capacity-limited elimination processes. The plasma concentration of NiAc was driving NEFA (R) turnover via an inhibitory drug-mechanism function acting on the formation of NEFA. The NEFA turnover was described by a feedback model with a moderator distributed over a series of transit compartments, where the first compartment (M ₁) inhibited the formation of R and the last compartment (M _N ) stimulated the loss of R. All processes regulating plasma NEFA concentrations were assumed to be captured by the moderator function. The potency, IC ₅₀, of NiAc was 45 nmol L⁻¹, the fractional turnover rate k _out was 0.41 L mmol⁻¹ min⁻¹ and the turnover rate of moderator k _tol was 0.027 min⁻¹. A lower physiological limit of NEFA was modeled as a NiAc-independent release (k _cap ) of NEFA into plasma and was estimated to 0.032 mmol L⁻¹ min⁻¹. This model can be used to provide information about factors that determine the time-course of NEFA response following different modes, rates and routes of administration of NiAc. The proposed model may also serve as a preclinical tool for analyzing and simulating drug-induced changes in plasma NEFA concentrations after treatment with NiAc or NiAc analogues.     

Receptor-mediated methylprednisolone pharmacodynamics in rats: Steroid-induced receptor down-regulation

Several approaches to receptor down-regulation were examined to extend previous receptor/ genemediated pharmacokinetic/dynamic models of corticosteroids. Down-regulation of the glucocorticoid receptor was considered as an instantaneous event or as a gradual steroid-receptor-mediated process. Concentrations of plasma methylprednisolone, free hepatic cytosolic receptors, and the activity of hepatic tyrosine aminotransferase (TAT) enzyme were measured for 16 hr following administration of 0, 10, and 50 mg/kg methylprednisolone sodium succinate to 93 adrenalectomized rats. Receptor down-regulation was best described by a fractional decrement in the rate of return of free cytosolic glucocorticoid receptor. Predicted values for free receptor, bound receptor, nuclear bound receptor, and transfer compartments were in accord with the expected rank order values based on the high and low steroid doses. Model parameter estimates were independent of dose and described the rapid depletion of free cytosolic receptor, latephase return of cytosolic receptor to a new baseline level that was 20–40% lower than control, and the TAT induction/dissipation pattern following steroid dosing. The microscopic association and dissociation constants describing the steroidreceptor interaction were 0.23 L/nmole per hr (k_on and 4.74 hr^–1 (k_off) for methylprednisolone compared to previously obtained values of 0.20 L/nmole per hr and 15.7 hr^–1 for the related steroid prednisolone. The time course of TAT induction was similar to that observed previously for prednisolone. Efficiency of TAT induction was more closely related to steroid receptor occupancy than plasma methylprednisolone concentrations due to receptor saturability and receptor recycling.Supported in part by Grant No. 24211 from the National Institutes of General Medical Sciences, NIH, and by a Fellowship from the American Foundation for Pharmaceutical Education for D.H.     

The Impact of Aqueous Solubility and Dose on the Pharmacokinetic Profiles of Resveratrol

Purpose  This study aimed at the investigation of the impact of aqueous solubility and dose manipulation on the pharmacokinetics of resveratrol. Methods  Water soluble intravenous and oral formulations of resveratrol were prepared with hydroxypropyl-β-cyclodextrin (HP-β-CD) and randomly methylated-β-cyclodextrin (RM-β-CD), respectively. Sodium salt and suspension of resveratrol in carboxymethyl cellulose (CMC) were used as the reference intravenous and oral formulations, respectively. The pharmacokinetics of resveratrol was assessed in Sprague–Dawley rats. Plasma resveratrol concentrations were measured by high performance liquid chromatography (HPLC). Results  Both HP-β-CD and RM-β-CD enhanced the aqueous solubility of resveratrol. After intravenous administration, rapid elimination of resveratrol was observed at all tested doses (5, 10, and 25 mg kg⁻¹) regardless of formulation types; with non-linear elimination occurring at the dose of 25 mg kg⁻¹. RM-β-CD significantly increased the maximal plasma concentration of orally administered resveratrol, but, it did not increase the oral bioavailability in comparison with the CMC suspension. Furthermore, the oral bioavailability remained unchanged among all tested doses (15, 25, and 50 mg kg⁻¹). Conclusions  Aqueous solubility barrier might affect the speed but not the extent of resveratrol absorption. Further, dose manipulation (up to 50 mg kg⁻¹) did not have a significant impact on the oral bioavailability of resveratrol. An erratum to this article can be found at     

3H羟基斑蝥胺的药物代谢动力学研究

将氚标记的羟基斑蝥胺在大鼠体内研究了药物代谢动力学。所得血药浓度-时间数据依一定程序在709电子计算机上拟合曲线,并计算有关参数。结果表明,静脉注射后符合二房室开放型模型,其药代动力学参数为:t1/2α0.067hr,t1/2β2.208hr,V_d(面积)1.237l/kg,V₁0.264l/kg,K_el1.470 hr^-1,清除率0.388l/hr/kg。灌胃后可以单室开放型模型描述,其药代动力学参数为:K_α2.990hr^-1,K_el0.257hr^-1,V_d1.603l/kg,t1/22.693hr,t_max0.90hr,C_max0.745μg/ml,F94.15%。尚将本药以静脉和灌胃两种途径给药后直接观察在大鼠体内的组织分布和在尿粪胆汁中的排泄,结果表明本药分布广,主要经肾排泄,且排泄较快,与药代动力学分析结果相一致。     

Enantioselective pharmacokinetics of tramadol in CYP2D6 extensive and poor metabolizers

Objective To describe in detail the intravenous, single oral and multiple oral dose enantioselective pharmacokinetics of tramadol in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs).Methods Eight EMs and eight PMs conducted three phases as an open-label cross-over trial with different formulations; 150 mg single oral tramadol hydrochloride, 50 mg single oral tramadol hydrochloride every 8 h for 48 h (steady state), 100 mg intravenous tramadol hydrochloride. Urine and plasma concentrations of (+/−)-tramadol and (+/−)-M1 were determined for 48 h after administration.Results In all three phases, there were significant differences between EMs and PMs in AUC and t_1/2 of (+)-tramadol (P≤0.0015), (−)-tramadol (P≤0.0062), (+)-M1 (P≤0.0198) and (−)-M1 (P≤0.0370), and significant differences in C_max of (+)-M1 (P<0.0001) and (−)-M1 (P≤0.0010). In Phase A and C, significant differences in t_max were seen for (+)-M1 (P≤0.0200). There were no statistical differences between the absolute bioavailability of tramadol in EMs and PMs. The urinary recoveries of (+)-tramadol, (−)-tramadol, (+)-M1 and (−)-M1 were statistically significantly different in EMs and PMs (P<0.05). Median antimodes of the urinary metabolic ratios of (+)-tramadol / (+)-M1 and (−)-M1 were 5.0 and 1.5, respectively, hereby clearly separating EMs and PMs in all three phases.Conclusion The impact of CYP2D6 phenotype on tramadol pharmacokinetics was similar after single oral, multiple oral and intravenous administration displaying significant pharmacokinetic differences between EMs and PMs of (+)-tramadol, (−)-tramadol, -(+)-M1 and (−)-M1. The O-demethylation of tramadol was catalysed stereospecific by CYP2D6 in the way that very little (+)-M1 was produced in PMs.     

ICI 141,292 (epanolol) —pharmacokinetics after single and repeated oral administration in the elderly with moderate renal impairment

Summary The pharmacokinetics of ICI 141,292 (epanolol) were studied over 3 days after a single oral 200 mg dose and then over 24 h after 12 consecutive daily oral 200 mg doses in 16 elderly subjects (aged 65 to 94 years) with moderate renal impairment (mean creatinine clearance 33.2 ml · min⁻¹). There was wide inter-individual variability in peak plasma ICI 141,292 concentrations (C_max) but no significant difference was found between mean C_max after a single dose (44.3 ng. ml⁻¹) and after 12 doses (37.4 ng. ml⁻¹). The mean observed time to peak plasma ICI 141,292 concentration (t_max) after a single dose (1.61 h) did not differ significantly from that after 12 doses (1.75 h). On several occasions an analytically significant second peak in ICI 141,292 plasma concentration was observed. Following the peak(s), the plasma concentrations declined biphasically and a mean terminal phase plasma half-life (t11/2) of 28.3 (range 10.2–84.8) h was calculated after a single dose. The inter-individual variability in the area under the plasma concentration-time curve to 24 h AUC (0-24) was 54 fold but there was no significant difference between AUC (0-24) after a single dose (mean 226.0 rig·h·m1⁻¹) and AUC (0-24) after 12 consecutive doses of ICI 141,292 (mean 232.4 ng·h·ml⁻¹). The results show that consecutive daily administration of 12 oral doses of IC1 141,292 (200 mg) does not result in significant accumulation of drug in elderly subjects with moderate renal impairment.     

Pharmacokinetics and bioavailability of oral and intramuscular artemether

Objective: The pharmacokinetics and bioavailability of artemether and dihydroartemisinin were investigated in eight Thai males following the administration of single oral and intramuscular doses of artemether (300 mg) in a randomized two-way cross-over study. Results: Both oral and intramuscular artemether were well-tolerated. In most cases, artemether and dihydroartemisinin were detected in plasma after 30 min and declined to levels below the limit of detection within 18–24 h. Compared with intramuscular administration, oral administration of artemether resulted in a relatively rapid but incomplete absorption [C_max: 474 vs 540 ng · ml⁻¹; t _max: 2.0 vs 3.9 h; AUC: 2.17 vs 5.20 μg · h · ml⁻¹]. Geographic means of lag-time and absorption half-life (t _1/2a) of oral vs intramuscular artemether were 0.28 and 1.1 h vs 0.30 and 2 h, respectively. t _1/2z was significantly shortened after the oral dose [2.8 vs 6.9 h]. Mean oral bioavailability relative to intramuscular administration was 43.2%. The ratio of the AUCs of artemether to dihydroartemisinin was significantly lower after the oral than after the intramuscular dose (geometric mean: 0.29 vs 0.60). Received: 18 October 1996 / Accepted in revised form: 28 January 1997     

Unexpected effect of concomitantly administered curcumin on the pharmacokinetics of talinolol in healthy Chinese volunteers

Objective To investigate the effect of concomitantly administered curcumin on the pharmacokinetics of the β1 adrenoceptor blocker talinolol. Methods The study was conducted in a self-controlled, two-period experiment with a randomized, open-labeled design, using 12 healthy volunteers and a wash out period of 1 week between the administration of a single oral dose of 50 mg talinolol and the concomitant administration of curcumin (300 mg day⁻¹ for 6 days) and a single oral dose of 50 mg talinolol on the seventh day. Concentrations of talinolol were measured in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry. Non-compartmental analysis was used to characterize talinolol plasma concentration-time profiles, all pharmacokinetic parameters were calculated using DAS (ver. 2.0) software, and comparisons of mean values were analyzed by the Wilcoxon signed rank test. Differences were considered to be significant at p < 0.05 (two-sided test). Results The consumption of curcumin for 6 days reduced the area under the curve (AUC) from predose to infinity () of talinolol from 1860.0 ± 377.9 to 1246.0 ± 328.2 ng.h mL⁻¹, the highest observed concentration values (C_max) were significantly decreased from 147.8 ± 63.8 to 106.4 ± 39.9 ng mL⁻¹, and the CL/F was increased from 27.9 ± 5.5 to 43.1 ± 13.4 L.h⁻¹ (p < 0.05). There was no significant difference in sampling time for C_max (t_max) and elimination half-life (t_1/2) values between the two periods (p > 0.05). The interindividual variability in AUC_0–60 and C_max of talinolol was comparable in two study periods; the coefficient of variance (CV) of AUC_0–60 and C_max was 26 and 40% after curcumin versus 21 and 43% after talinolol alone, respectively. Conclusion We suggest that the reduced bioavailability of talinolol is most probably due to the low intraluminal curcumin concentration, or possibly due to the upregulation of further ATP-binding cassette transporters, such as MRP2, in different tissues.     

Perylene Toxicity in the Estuarine Environment of Ria de Aveiro (Portugal)

Perylene, a 5-ring polycyclic aromatic hydrocarbon is common in estuarine sediments and its toxicity in the benthic and planktonic compartments is not yet clarified. The objectives of this work were: (1) to follow the toxicity of high concentrations of perylene (110 mg l⁻¹) on benthic bacteria and macrofauna (amphipod Corophium multisetosum); (2) to determine the effects of a low load of perylene (2 μg l⁻¹) on the metabolism of suspended bacteriobenthos after 9-day exposure, mimicking the effects of tidal erosion; (3) to contrast the effects of this low perylene load on the particle-free bacterioplankton and on the suspended and particle-adhered bacteriobenthos. No impact was detected in bacterial abundance exposed to 110 mg perylene l⁻¹ for 9 days. This concentration of perylene evoked no acute effects in C. multisetosum but, chronic toxicity assays revealed statistically significant negative effects on survival, growth and number of pregnant females. The bacterioplankton and the suspended bacteriobenthos, exposed to 2 μg perylene l⁻¹ during 2 weeks, responded with altered profiles of activity when compared to the control suspension. These values ranged, respectively, for bacterial biomass production from 134 to 210 and from 24 to 184 μg C l⁻¹ h⁻¹, for aminopeptidase from 1824 to 11,127 and from 1464 to 15,488 nmol l⁻¹ h⁻¹, and for β-glucosidase from 87 to 400 and from 57 to 1278 nmol l⁻¹ h⁻¹. The rate of oxygen consumption in the perylene-exposed suspension (0.04–2.85 mmol O₂ kg⁻¹ dw sed h⁻¹) exhibited a clearly distinct profile in relation to the control (0.57–1.60 mmol O₂ kg⁻¹ dw sed h⁻¹). The overall reactivity of the bacteriobenthos to perylene was interpreted as the result of toxic pressure followed by evolution of a diverse bacterial community.     

Pharmacokinetics of Antimony in Patients Treated with Sodium Stibogluconate for Cutaneous Leishmaniasis

The pharmacokinetics of Sb was examined in 29 patients with cutaneous leishmaniasis following the intramuscular administration of a dose of sodium stibogluconate equivalent to 600 mg of Sb. Blood was sampled at different time intervals from each patient and Sb was measured in whole blood by electrothermal atomic absorption spectrophotometry after an appropriate dilution with Triton X-100. The 24-hr urine- was also collected and analyzed similarly. The blood concentration-time data conformed to the one-compartment open model with mean and (SEM) of the apparent first-order rate constants for absorption (k_a) and elimination (k_d) of 1.71 (0.15) and 0.391 (0.016) hr^–1, respectively. The maximum concentration of Sb achieved was 8.77 (0.39) mg/L and the peak time was 1.34 (0.09) hr. The total body clearance (TBC) and the volume of distribution (V_d) were 17.67 (1.38) L/hr and 45.7 (2.6) L, respectively, assuming a complete absorption. The fraction of dose of Sb excreted in the urine was 0.80 (0.07) and the renal clearance was 12.7 (1.16) L/hr. The frequency distribution pattern of the area-under-the-curve (AUC) appears to be bimodal and separates patients into those with low exposure to Sb (AUC = 11.7-29.04 mg.hr/L) (i.e., rapid eliminators) and those with high exposure to Sb (AUC = 31.5-49.1 mg.hr/ L) (i.e., slow eliminators). This may explain the variability observed in the response to treatment of leishmaniasis with sodium stibogluconate.     

Targeted mutation of CCK2 receptor gene modifies the behavioural effects of diazepam in female mice

Rationale Evidence suggests that GABA and CCK have opposite roles in the regulation of anxiety. Objective The aim of the present work was to study diazepam-induced anxiolytic-like action and impairment of motor co-ordination, and the parameters of benzodiazepine receptors in mice lacking CCK₂ receptors. Methods The action of diazepam (0.5–3 mg/kg IP) was studied in the elevated plus-maze model of anxiety and rotarod test using mice lacking CCK₂ receptors. The parameters of benzodiazepine receptors were analysed using [³H]-flunitrazepam binding. Results In the plus-maze test, the exploratory activity of the homozygous (−/−) mice was significantly higher compared to their wild-type (+/+) littermates. However, the wild-type (+/+) mice displayed higher sensitivity to the anxiolytic-like action of diazepam. Even the lowest dose of diazepam (0.5 mg/kg) induced a significant increase of open arm entries in the wild-type (+/+) mice. A similar effect in the homozygous (−/−) mice was established after the administration of diazepam 1 mg/kg. The highest dose of diazepam (3 mg/kg) caused a prominent anxiolytic-like effect in the wild-type (+/+) mice, whereas in the homozygous (−/−) animals suppression of locomotor activity was evident. The performance of the homozygous (−/−) mice in the rotarod test did not differ from that of the wild-type (+/+) littermates. However, a difference between the wild-type (+/+) and homozygous (−/−) animals became evident after treatment with diazepam. Diazepam (0.5 and 3 mg/kg) induced significantly stronger impairment of motor co-ordination in the homozygous (−/−) mice compared to their wild-type (+/+) littermates. The density of benzodiazepine binding sites was increased in the cerebellum, but not in the cerebral cortex and hippocampus, of the homozygous (−/−) mice. Conclusions Female mice lacking CCK₂ receptors are less anxious than their wild-type (+/+) littermates. The reduced anxiety in homozygous (−/−) mice probably explains why the administration of a higher dose of diazepam is necessary to induce an anxiolytic-like action in these animals. The highest dose of diazepam (3 mg/kg) induced significantly stronger suppression of locomotor activity and impairment of motor co-ordination in the homozygous (−/−) mice compared to the wild-type (+/+) littermates. The increase in the action of diazepam is probably related to the elevated density of benzodiazepine receptors in the cerebellum of homozygous (−/−) mice. The present study seems to be in favour of increased tone of the GABAergic system in mice without CCK₂ receptors.     

Interindividual variability in catalytic activity and immunoreactivity of three major human liver cytochrome P450 isozymes

Objective: Interindividual variations in immunoreactivity and function of three major human drug metabolising P450 monooxygenases has been investigated in liver microsomes from 42 Caucasians (kidney donors or liver biopsies). Methods: Diclofenac 4′-hydroxylation, dextromethorphan O-demethylation and midazolam 1′-hydroxylation, measured by HPLC in incubates, were used as probes to determine CYP2C9, CYP2D6 and CYP3A4 function kinetics, respectively. Immunoquantification of the three isoforms was achieved by Western blotting, using rabbit polyclonal antibodies raised against human CYP2C9 and human CYP3A4, and mouse monoclonal antibody raised against human CYP2D6. Results: Diclofenac 4′-hydroxylation exhibited Michaelis-Menten kinetics with k_M= 3.4 μmol ⋅l⁻¹ and V_max = 45 nmole ⋅mg⁻¹P ⋅h⁻¹. Relative immunoreactivity of CYP2C9 was correlated with V_max and CL_int. Dextromethorphan O-demethylation in EM (extensive metabolisers) liver microsomes also showed Michaelis-Menten kinetics, with k_M = 4.4 μmol ⋅l⁻¹ and V_max = 5.0 nmol ⋅mg⁻¹P ⋅h⁻¹. Relative immunoreactivity of CYP2D6 was correlated with V_max and CL_int. Midazolam 1′-hydroxylation also exhibited Michaelis-Menten kinetics with k_M = 3.3 μmol ⋅l⁻¹ and V_max = 35 nmol ⋅mg⁻¹P ⋅h⁻¹. Relative immunoreactivity of CYP3A4 was correlated with V_max and CL_int. Immunoreactivity and function were correlated for each isozyme, but there was no cross correlation between isozymes. Conclusion: The velocity of metabolite formation (V_max) by the three major human drug metabolising P450 monooxygenases is correlated with their immunoreactivity in liver microsomes. Interindividual variation was much larger for V_max than k_M. Interindividual variability was more pronounced for CYP2D6, probably due to the presence of several different functional alleles in the population of extensive metabolisers. Received: 27 December 1995/Accepted in revised form: 29 March 1996     

The effect of the menstrual cycle on the pharmacokinetics of caffeine in normal, healthy eumenorrheic females

  Objective: Hormonal fluctuations of estrogen and progesterone in eumenorrheic women may be capable of altering the pharmacokinetics of certain agents. The objective of this study was to determine the effect of the luteal, ovulatory and follicular phases of the menstrual cycle on the pharmacokinetics of caffeine, a low clearance, flow-independent drug. Methods: Subjects were ten healthy, non-smoking, eumenorrheic females who were not pregnant and had not used oral contraceptives for a minimum of 3 months prior to the study. Blood samples were collected during one menstrual cycle for the determination of estradiol and progesterone concentrations during the follicular (days 2–6 post-onset of menses), ovulatory (days 13–16 post-onset of menses) and luteal (days 22–26 post-onset of menses) phases. Caffeine was administered over a single menstrual cycle during the follicular, ovulatory and luteal phases. Each subject was administered a single oral dose of caffeine (300 mg) in 100 ml of lemonade during each phase of the menstrual cycle. A venous catheter was used to collect blood samples at pre-dose and at the following time points: 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10, 12 and 24 h. Plasma caffeine concentrations were determined using a validated ultraviolet high-performance liquid chromatography method. Results: There were no significant (P < 0.05) differences in the pharmacokinetic parameters of caffeine across the menstrual cycle phases. The average area under the plasma concentration–time curve (AUC_inf) was 93.01 mg l^−1.h and the absorption rate constant (k _a) was 2.88 h⁻¹ during the ovulatory phase, 83.0 mg l⁻¹ h and 2.06 h⁻¹, respectively, during the luteal phase and 84.7 mg l^−1.h and 1.84 h⁻¹, respectively, during the follicular phase. Conclusions: These findings suggest that the menstrual cycle does not significantly alter the pharmacokinetics of caffeine. Received: 16 November 1998 / Accepted in revised form: 19 April 1999     

Pharmacokinetics and pharmacodynamics of acetazolamide in patients with transient intraocular pressure elevation

Objective: To characterize the pharmacokinetics and pharmacodynamics of acetazolamide in patients with transient intraocular pressure (IOP) elevation and to provide individual patients with the optimal dosage regimen for this drug. Methods: We studied 17 patients with transient IOP elevation, who were given 62.5–500 mg acetazolamide orally as single or repetitive doses. Plasma acetazolamide concentration and IOP were measured at approximately 1, 3, 5, and 9 h after the last acetazolamide administration. Pharmacokinetics and pharmacodynamics were analyzed by nonlinear mixed-effect modeling using the program NONMEM. Results: The plasma concentration profile of acetazolamide was characterized by a one-compartment model with first-order absorption. The apparent oral clearance was related to the creatine clearance (CCR) which was estimated by the Cockcroft and Gault equation, as follows: 0.0468 · CCR l · h⁻¹. The estimated apparent oral volume of distribution, first-order absorption rate constant, and absorption lag time were 0.231 l · kg⁻¹, 0.821 · h⁻¹, and 0.497 h, respectively. IOP after oral acetazolamide administration was characterized by an E_max model. The maximal effect in lowering the IOP (E_max) was 7.2 mmHg, and the concentration corresponding to 50% of the maximal effect (EC₅₀) was 1.64 μg · ml⁻¹. As 70% of E_max was achieved at a plasma concentration of 4 μg · ml⁻¹, this concentration was considered satisfactory for lowering IOP. The recommended dosage was calculated so that the minimum plasma concentration at steady state exceeded this target concentration; 250 mg t.i.d., 125 mg t.i.d., 125 mg b.i.d., and 125 mg once daily for the patients with CCR values of 70, 50, 30, and 10 ml · min⁻¹, respectively. Conclusion: Measuring plasma concentrations of acetazolamide and subsequent pharmacokinetic and pharmacodynamic analyses are useful for estimating its concentration-dependent effectiveness in lowering the IOP in individual patients. The dosage regimen presented in this study is expected to improve the benefits of acetazolamide pharmacotherapy in most elderly patients with transient rises in IOP following intraocular surgery. Received: 10 April 1997 / Accepted in revised form: 21 October 1997