Pharmacokinetics and toxicity of the antitumour agentN-[2-(dimethylamino)ethyl]acridine-4-carboxamide after i.v. administration in the mouse

Summary The pharmacokinetics, tissue distribution and toxicity of the antitumour agentN-[2-(dimethylamino)ethyl]acridine-4-carboxamide(AC) were studied after i.v. administration to mice. Over the dose range of 9–121 mol/kg (3–40 mg/kg), AC displayed linear kinetics with the following model-independent parameters: clearance (C), 21.0±1.9 l h^–1 kg^–1; steady-state volume of distribution (V_ss), 11.8±1.4 l/kg; and mean residence time (MRT), 0.56±0.02 h. The plasma concentration-time profiles for AC fitted a two-compartment model with the following parameters:C _c, 19.4±2.3 l h^–1 kg^–1; V_c, 7.08±1.06 l/kg;t _1/2 13.1±3.5 min; andt _1/2Z, 1.60±0.65 h. AC displayed moderately high binding in healthy mouse plasma, giving a free fraction of 15.9%–25.3% over the drug concentration range of 1–561 M. After the i.v. administration of 30 mol/kg [³H]-AC, high radioactivity concentrations were observed in all tissues (especially the brain and kidney), showing a hight _1/2c value (37–59 h). At 2 min (first blood collection), the AC concentration as measured by high-performance liquid chromatography (HPLC) comprised 61% of the plasma radioactivity concentration (expressed as AC equivalents/l). By 48 h, 73% of the dose had been eliminated, with 26% and 47% of the delivered drug being excreted by the urinary and faecal routes, respectively; <1% of the total dose was excreted as unchanged AC in the urine. At least five distinct radiochemical peaks were distinguishable by HPLC analysis of plasma extracts, with some similar peaks appearing in urine. The 121-mol/kg dose was well tolerated by mice, with sedation being the only obvious side effect and no significant alterations in blood biochemistry or haematological parameters being recorded. After receiving a dose of 152 mol/kg, all mice experienced clonic seizures for 2 min (with one death occuring) followed by a period of sedation that lasted for up to 2h. No leucopenia occurred, but some mild anaemia was noted. There was no significant change in blood biochemistry. A further 20% increase in the i.v. dose (to 182 mol/kg) resulted in mortality, with death occurring within 2 min of AC administration.Supported by the Auckland Medical Research Foundation and the Cancer Society of New Zealand     

Pharmacological attempts to improve the bioavailability of oral etoposide

Etoposide demonstrates incomplete and variable bioavailability after oral dosing, which may be due to its concentration and pH-dependent stability in artificial gastric and intestinal fluids. The use of agents that may influence etoposide stability and, thereby, bioavailability, was investigated in a number of clinical studies. Drugs that influence the rate of gastric emptying, while modulating the time of drug absorption, did not significantly alter the etoposide area under the concentration-time curve (AUC) or bioavailability. Specifically, metoclopramide had little effect on the etoposide absorption profile and did not significantly alter the AUC (AUC with etoposide alone, 68.4±20.3 g ml^–1 h, versus 74.3±25.9 g ml^–1 h with metoclopramide), suggesting that in most patients the drug is already emptied rapidly from the stomach. In contrast, propantheline produced a dramatic effect on etoposide absorption, delaying the time of maximal concentrationt _max from 1.1 to 3.5 h (P<0.01), but again without a significant improvement in drug AUC or bioavailability across the 24-h study period (AUC with etoposide alone 78.3±19.1 g ml^–1 h, versus 88.1±23.6 g ml^–1 h with propantheline). The effect of these drugs on the absorption of oral paracetamol, a drug included in the study as a marker of gastric emptying, was exactly the same as that found for etoposide, with no change in AUC being observed after metoclopramide or propantheline administration but a significant delay int _max being seen on co-administration with etoposide and propantheline. The co-administration of ethanol or bile salts (agents that significantly improved the stability of etoposide in artificial intestinal fluid) with oral etoposide similarly had no effect on improving the etoposide AUC or reducing the variability in AUC, suggesting that drug stability in vivo was not affected by these agents. In the third study the co-administration of cimetidine had no effect on the pharmacokinetics of oral or i.v. etoposide, despite the previous observation that etoposide stability was markedly improved at pH 3–5 as compared with pH 1 in artificial gastric fluid. This series of studies, designed to investigate factors that improved etoposide stability in laboratory studies, failed to demonstrate any potentially useful improvement in AUC or bioavailability in the clinical setting.     

Functional studies with a full-length P-glycoprotein cDNA encoded by the Hamster pgp1 gene

We defined the pharmacokinetics of paclitaxel after i. v., i. p., p. o., and s. c. administration of 22.5 mg/kg to CD₂F₁ mice. Additional mice were studied after i. v. bolus dosing at 11.25 mg/kg or 3-h continuous i.v. infusions delivered at 43.24 g kg^–1 min^–1. Plasma was sampled between 5 min and 40 h after dosing. Brains, hearts, lungs, livers, kidneys, skeletal muscles, and, where applicable, testicles were sampled after i.v. dosing at 22.5 mg/kg. Liquid-liquid extraction followed by isocratic high-performance liquid chromatography (HPLC) with UV detection was used to determine paclitaxel concentrations in plasma and tissues. After i.v. administration to male mice, paclitaxel clearance (CL_tb) was 3.25 ml min^–1 kg^–1 and the terminal half-life (t _1/2) was 69 min. After i.v. administration to female mice, paclitaxel CL_tb was 4.54 ml min^–1 kg^–1 and the terminalt1/2 was 43 min. The bioavailability of paclitaxel was 10%, 0, and 0 after i.p., p.o., and s.c. administration, respectively. Paclitaxel bioavailability after i.p. administration was the same when the drug was delivered in a small volume to mimic the delivery method used to evaluate in vivo antitumor efficacy or when it was delivered in a large volume to simulate clinical protocols using i.p. regional therapy. Paclitaxel was not detected in the plasma of mice after i.p. delivery of the drug as a suspension in Klucel: Tween 80. Pharmacokinetic parameters were similar after i.v. delivery of paclitaxel at 22.5 and 11.25 mg/kg; however, the CL_tb calculated in these studies was much lower than that associated with 3-h continuous i.v. infusions. After i.v. administration, paclitaxel was distributed extensively to all tissues but the brain and testicle. These data are useful in interpreting preclinical efficacy studies of paclitaxel and predicting human pharmacokinetics through scaling techniques.This work was supported by contract NO1-CM27711 awarded by the National Cancer Institute, DHHS     

A limited sampling model for the pharmacokinetics of etoposide given orally

A limited sampling model of etoposide after oral administration to estimate the area under the plasma concentration-time curve from 0 to 24 h (AUC) by determination of the drug plasma levels at only two time points was developed by a multiple regression analysis on a training data set of 15 patients receiving oral doses ranging from 54 to 90 mg/m². The equation describing the model is AUC (g ml^–1 h)=5.183 (g ml^–1 h)+1.193 (h)×C_1h (g/ml)+8.439 (h)×C_4h (g/ml) (R ²=0.93,P=0.0001), whereC _1h andC _4h represent the plasma etoposide concentrations at 1 and 4 h, respectively. The model was validated prospectively on a test data set of 13 patients receiving oral doses ranging from 52 to 87 mg/m² and, additionally, on a data set of 7 patients receiving oral doses ranging between 176 and 200 mg/m², investigated in a previous study. Validation on both test data sets gave a relative mean predictive error of 0.1% and a relative root mean square error of 15.8% and 16.7%, respectively. The present study shows that it is possible to obtain a good estimate of the plasma AUC after oral administration of etoposide using a two-time-point sampling model. The model can be used to monitor the etoposide AUC in patients receiving chronic oral treatment.     

Intrahepatic and intravenous administration of adriamycin—A Comparative pharmacokinetic study in patients with malignant liver tumours

The pharmacokinetics of adriamycin in patients with malignant tumours of the liver were studied after peripheral intravenous treatment and after regional administration of the drug either by the arterial route or by the portal vein, with or without hepatic artery ligation. The plasma concentration of adriamycin after intravenous as well as after intrahepatic administration followed a three-compartment open model. The results in the present study confirm previous reports of a large inter-individual variation of the pharmacokinetics of adriamycin. After intravenous administration the individual variations in AUC/mg/m² andC _p,max/mg/m² (dose normalized area under plasma concentration time curve and dose normalized maximum plasma concentration, respectively) were more than 5-fold. The area under the plasma concentration time curve (AUC) was on the average 1.5 times higher after the peripheral intravenous administration than after intrahepatic administration. The reduction of maximum plasma concentration (C _p,max) of adriamycin after intrahepatic administration was even more pronounced than the reduction in AUC (mean valueC _p,max iv/C _p,max ihep=1.7). The plasma concentration of adriamycinol did not exceed 20 ng/ml. The AUC values of adriamycinol were 20% (median value) of the AUC values of adriamycin, indicating the importance of adriamycinol in the adriamycin therapy.     

Multiple-dose pharmacokinetics of epirubicin at four different dose levels: studies in patients with metastatic breast cancer

Summary Pharmacokinetic analysis of epirubicin and its metabolites epirubicinol and 7-deoxy-13-dihydro-epirubicinol aglycone during the first and the fourth courses of treatment was performed in 78 patients with metastatic breast cancer. The patients were treated every 3 weeks with epirubicin given as 10-min i.v. infusions at four different dose levels: 40, 60, 90 and 135 mg/m². In most cases (76 of 78 cases), plasma concentration-time curves fitted to a three-compartmental pharmacokinetic model. The terminal half-life of epirubicin was independent of dose and duration of treatment. Large interindividual differences were demonstrated (meant _1/2, 21.6±7.9 h; range, 10.6–69 h;n=110). In two subjects, extremely long half-lives and high serum bilirubin concentrations indicated impaired liver function. No correlation was found between the half-life and levels of liver alanine aminotransferase (ALAT) or serum creatinine. The metabolite epirubicinol appeared quickly after epirubicin administration and its half-lives were shorter than that of the parent compound (meant _1/2, 18.1±4.8 h; range, 8.2–38.4 h;n=105).Formation of the aglycone metabolite was delayed and the half-life of this metabolite was shorter than that of epirubicin (meant _1/2, 13±4.6 h; range, 2.7–29 h;n=104). The AUC of epirubicin and the total AUC (drug and metabolites) were linearly proportional to the dose, with the former value constituting two-thirds of the latter. A correlation was found between AUC and the plasma concentration of epirubicin at two time points (2 and 24 h after administration). The proposed model was AUC=9.44×c ₂+62.5×c ₂₄+157.7 (r=0.953).This work was supported by the Lundbeck Foundation, the Michaelsen Foundation and Farmitalia Carlo Erba Ltd.     

The clinical pharmacokinetics of N-5-dimethyl-9-[(2-methoxy-4-methyl-sulfonylamino)phenylamino]-4-acridinecarboxamide (CI-921) in a phase 1 trial

Summary The pharmacokinetics of CI-921 were studied after 65 infusions over a 20-fold dose range (13–270 mg/m² per day) in 16 patients during a phase 1 trial. CI-921 was given by a 15 min infusion on three consecutive days.Plasma samples were collected after the first and third infusions, and urine, at 6 h intervals throughout the 3 days. CI-921 concentrations were measured by an HPLC method. Maximum plasma concentrations ranged from 3–86 mol/l.The plasma concentration-time disposition curves were mainly biphasic over the 24-h postinfusion period. There was no significant difference by the paired t-test between the C_max, AUC,CL, V_ss, MRT, t_1/2, or t_1/2 calculated for the first and third infusions. The means (range) of model-independent pharmacokinetic parameters were: CL, 158 (94–290) ml/h per kg; V_ss, 319 (219–614) ml/kg; MRT, 2.1 (1.1–3.5) h; t_1/2, 0.5 (0.2–1.1) h; and t_1/2, 2.6 (1.1–5.0) h. There was a strong linear correlation between the dose and the AUC and C_max,suggesting linear kinetics over this dose range. A very small amount (<1%) of the total dose was excreted as unchanged CI-921 in the urine, mostly in the 12-h postinfusion period.     

Tumour profile ofN-[2-(dimethylamino)ethyl]acridine-4-carboxamide after intraperitoneal administration in the mouse

N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (AC) is an experimental antitumour agent that is being considered for phase I trials. After i.p. administration of 150 mg/kg [³H]-AC to tumour-bearing mice, AC was absorbed rapidly into the plasma and tissues such as the heart, liver, kidney and brain but more slowly into the s.c. tumour. The maximal AC concentration (86±36 mol/kg) in the tumour occurred at 35–60 min and was 3-fold the maximal plasma concentration, which occurred at 15 min. Although higher maximal concentrations were observed in other tissues, these concentrations fell rapidly in parallel with plasma concentrations. In contrast, AC concentrations in the tumour remained elevated, thet1/2 value (16.3 h) and mean residence time (MRT, 9.5 h) being prolonged in comparison with those in the plasma and other tissues (t1/2 range, 1.0–2.9 h; MRT, 1.2–1.4 h). AC concentrations were not detectable by our high-performance liquid chromatographic (HPLC) method (limit of detection, 0.02 mol/l) in the plasma or other tissues at 24 or 48 h after administration but were measurable in the tumour (1.6±0.8 and 0.6±0.3 mol/kg, respectively). Radioactivity concentrations in the plasma, tissues and tumour were very variable but were greater than the corresponding levels of unchanged parent AC. By 24 h, radioactivity concentrations in the plasma, tissues and tumour had fallen to similar levels with prolonged elimination profiles. Thus, the exposure of the s.c. implanted tumour to a threshold AC concentration for a prolonged time (>24 h) may partly explain the greater efficacy of AC against this tumour, whereas the shorter period of exposure of blood and other tissues may explain its low haematological toxicity.     

Evaluation of 9-dimethylaminomethyl-10-hydroxycamptothecin against xenografts derived from adult and childhood solid tumors

The topoisomerase I inhibitor 9-dimethylaminomethyl-10-hydroxycamptothecin (topotecan) was evaluated against a panel of xenografts comprising four lines of adult colon adenocarcinoma, three colon tumors derived from adolescents, six childhood rhabdomyosarcomas from previously untreated patients as well as sublines selected in vivo for resistance to vincristine and melphalan, and three lines of childhood osteogenic sarcoma. Efficacy was determined at maximal tolerated dose levels using intermittent i.p. administration [every 4 days for 4 doses (q4d×4)] or daily p.o. or i. p. administration 5 days per week for up to 20 courses. On a q4d×4 schedule, the maximum tolerated dose (MTD) was 12.5 mg/kg per administration, which caused marked weight loss and lethality in 5% of the tumor-bearing mice. This schedule caused significant growth inhibition (but no tumor regression) in advanced adult colon adenocarcinomas. The minimal treated/control (T/C) ratios were 0.49, 0.54, and 0.3 for three of the tumor lines and were achieved at 18–21 days after the initiation of treatment. In contrast, rhabdomyosarcomas were considerably more sensitive, with T/C ratios being <0.1 for three lines, whereas topotecan was less active against two other rhabdomyosarcoma xenografts (minimal T/C ratios, 0.17 and 0.14). As inhibitors of topoisomerase I have been demonstrated to have activity in the replication phase of the cell cycle (S-phase-specific), prolonged administration schedules were examined. Mice received topotecan 5 days per week for 3 weeks either by i.p. injection or by oral gavage (p.o.). In selected experiments, p.o. administration was continued for up to 20 weeks. Oral administration for 3 weeks (2 mg/kg per dose) resulted in complete regression of all six lines of rhabdomyosarcoma, with two lines demonstrating no regrowth during the period of observation (84 days). Similar results were obtained after i.p. administration, suggesting significant schedule dependency for these tumors. For colon tumors, the daily administration schedule (i.p. or p.o.) demonstrated some advantage over the intermittent schedule, resulting in partial regressions and significant inhibition of the growth of several colon adenocarcinoma lines. In rhabdomyosarcoma Rh 12 and VRC₅ colon adenocarcinoma, both of which demonstrated intermediate sensitivity to topotecan, and in osteosarcoma OS33, protracted p.o. administration for 13–20 weeks (1.0–1.5 mg/kg per dose given daily x 5 days) caused complete regression without regrowth in Rh12 and OS33 tumors and partial regression of all VRC₅ tumors. No toxicity was observed using this schedule of administration. Topotecan demonstrated significant activity against all three osteosarcoma xenografts examined, with optimal schedules causing complete regression in two lines. Topotecan demonstrated similar activity against KB 3-1 and KB 8-5 multidrug-resistant cells in culture, and the Rh 12/VCR an Rh 18/VCR xenografts selected for vincristine (VCR) resistance in vivo were as sensitive as their parental lines. However, Rh 28/L-PAM, selected for resistance to melphalan, was cross-resistant to topotecan. Plasma pharmacokinetics studies were carried out at the respective MTD for oral (2 mg/kg) or i.p. (1.75 mg/kg) administration. During oral administration the maximal plasma concentration (of the active lactone) was achieved at 0.25 h (C_max 41.7 ng/ml) and thet ₁/2 andt ₁/2 values were 0.55 and 2.8 h, respectively. Administration i.p. resulted in peak plasma levels of 523 ng/ml, witht ₁/2 andt ₁/2 elimination rates being 0.29 and 2.5 h, respectively. Although i.p. administration resulted in a 3-fold increase in AUC as compared with oral dosing, similar antitumor activity was observed against most xenograft lines. These results suggest that topotecan may have significant activity against several human cancers and that its efficacy may be schedule-dependent. Topotecan may have a particular role to play in the treatment of childhood solid tumors such as rhabdomyosarcoma and osteosarcoma.This work was supported in part by grants CA23099, CA21765 (CoRe) and by the American Lebanese Syrian Associated Charities (ALSAC)     

Pharmacokinetics of acridine-4-carboxamide in the rat,with extrapolation to humans

Summary The pharmacokinetics ofN-[2-(dimethylamino)ethyl]acridine-4-carboxamide (AC) were investigated in rats after i. v. administration of 18, 55 and 81 mol/kg [³H]-AC. The plasma concentration-time profiles of AC (as measured by high-performance liquid chromatography) typically exhibited biphasic elimination kinetics over the 8-h post-administration period. Over this dose range, AC's kinetics were first-order. The mean (±SD) model-independent pharmacokinetic parameters were; clearance (Cl), 5.3±1.1 1 h^–1 kg^–1; steady-state volume of distribution (Vss), 7.8±3.0 l/kg; mean residence time (MRT), 1.5±0.4 h; and terminal elimination half-life (t _1/2Z), 2.1±0.7 h (n=10). The radioactivity levels (expressed as AC equivalents) in plasma were 1.3 times the AC concentrations recorded at 2 min (the first time point) and remained relatively constant for 1–8 h after AC administration. By 6 h, plasma radioactivity concentrations were 20 times greater than AC levels. Taking into account the species differences in the unbound AC fraction in plasma (mouse, 16.3%; rat, 14.8%; human, 3.4%), allometric equations were developed from rat and mouse pharmacokinetic data that predicted a Cl value of 0.075 (range, 0.05–0.10; 95% confidence limits) 1 h^–1 kg^–1 and a V_ss value of 0.63 (range, 0.2–1.1) l/kg for total drug concentrations in humans.     

Limited sampling models for simultaneous estimation of the pharmacokinetics of irinotecan and its active metabolite SN-38

Irinotecan (CPT-11) is a novel topoisomerase I inhibitor with clinical activity in human malignancies. The objective of this study was to develop efficient limited sampling models (LSMs) to estimate simultaneously the area under the plasma concentration versus time curves (AUC) for both CPT-11 and its active metabolite SN-38. A total of 64 pharmacokinetic sets (24-h sampling) were obtained in phase I studies at doses ranging from 50 to 750 mg/m² (0.5-h i.v. infusion). The patients were randomly assigned to a training data set (n=32) and a test set (n=32). Multiple linear regression analyses were used to determine the optimal LSMs based on the correlation coefficient (r), bias (MPE%, percentage of mean prediction error), and precision (RMSE%, percentage of root mean squared prediction error). Of these LSMs, the ones including maximal concentrations of CPT-11 (0.5 h, the end of the i.v. infusion) and metabolite SN-38 ( 1 h) were favored along with predictive precision and clinical constraints. Several bivariate models including a 6-h time point as the last sampling time (or 7 h) were found to be highly predictive of either the CPT-11 AUC or the SN-38 AUC. The chosen sampling time points were the ones that allowed the best compromise between the accurate determination of either compound alone with the same sampling times. The simultaneously best prediction of both CPT-11 and SN-38 AUCs was obtained with sampling time points harvested at 0.5, 1, and 6 h (or 7 h). With these sampling time points a trivariate model was selected for the determination of CPT-11 AUC namely, CPT-11 AUC (ng h ml^–1)=0.820×C_0.5h+0.402×C_1h+15.47 ×C_6h+928, and a corresponding model was selected for the determination of metabolite AUC, i.e., SN-38 AUC (ng h ml^–1)=4.05×C_0.5h–0.81×C_1h+23.01×C_6h–69.78, whereC(t) is the concentration in nanograms per milliliter of either compound at a given timet. These models performed well with the test data sets for CPT-11 AUC (r=0.98, MPE%=–1.4, RMSE%=13.9) and for SN-38 AUC (r=0.95, MPE%=–6.5, RMSE%=37.7). In addition to the determination of AUCs (and hence clearance), these models also allow the determination of the maximal concentrations of both compounds, which might be needed for pharmacodynamics studies. Other bi- and trivariate models including other time points are also presented. These LSMs not only will facilitate ongoing and future clinical trials by significantly reducing the number of blood samples needed for pharmacokinetics studies but will hopefully contribute to a better knowledge of pharmacokinetic-pharmacodynamic relationships for both CPT-11 and its active metabolite SN-38.Abbreviations CPT-11 (7-Ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptothecin - SN-38 7-ethyl-10-hydroxy-camptothecin - AUC area under the plasma concentration versus time curve - MPE% percentage of mean prediction error (bias) - RMSE% percentage root mean squared prediction error (precision) - MRT mean residence time - Vdss volume of distribution at steady state - CL total body clearance     

Bendamustine pharmacokinetic profile and exposure–response relationships in patients with indolent non-Hodgkin’s lymphoma

Purpose

The pharmacokinetic profiles of bendamustine and active metabolites were defined in patients with rituximab-refractory, relapsed indolent B-cell non-Hodgkin’s lymphoma, and supported understanding of exposure–response relationships for efficacy and safety.

Methods

Bendamustine was administered as a 60-min 120 mg/m² intravenous infusion on days 1 and 2 of six 21-day cycles. Pharmacokinetic models were developed, with covariate assessment. Correlations between bendamustine exposure and responder status or occurrence of neutropenia, thrombocytopenia, fatigue, nausea, and vomiting were examined.

Results

Following a single dose of bendamustine HCl, concentrations declined in a triphasic manner, with rapid distribution, intermediate, and slow terminal phases. The intermediate t _1/2 (40 min) was considered the pharmacologically relevant (beta elimination) t _1/2 since the initial phases accounted for 99% of the AUC. Age, sex, mild/moderate renal, or mild liver impairment did not alter pharmacokinetics. Metabolite concentrations were low relative to parent. No correlation was observed between exposure and safety or efficacy measures because of the limited range of exposures after 120 mg/m² administration, except bendamustine C _max was a significant (P value = 0.013) predictor of the probability of nausea in patients, most of whom were pretreated with antiemetics.

Conclusions

The BSA-based dosing regimen for bendamustine achieved the targeted exposure and was associated with a high incidence of therapeutic response. Given the short t _1/2 and low concentrations of bendamustine observed by 12 h after dosing, the single-dose profile for bendamustine described by these analyses is expected to be representative of the multiple-dose profile. The occurrence of nausea was significantly related to bendamustine exposure, with the probability of nausea increasing as bendamustine C _max increases.     

A limited sampling strategy for estimation of the cladribine plasma area under the concentration versus time curve after intermittent i.v. infusion,s.c. injection,and oral administration

 Cladribine is a newly developed antimetabolite with promising activity in lymphoproliferative disorders. Recent pharmacokinetics investigations have suggested that there is a relationship between its plasma area under the concentration versus time curve (AUC) and the degree of neutropenia posttreatment as well as the therapeutic outcome in hairy-cell leukemia. To enable a simple estimation of the plasma AUC, a limited sampling strategy was developed. Stepwise linear regression was used to determine which were the most important data points for estimation of the plasma AUC after 2-h i.v. infusion, s.c. injection (5 mg/m²), and oral administration (10 mg/m²) in 27 patients. The most important data points after i.v. infusion in 12 patients were 1, 4, and 24 h, in order of importance. The AUC could be estimated as 2.9081×C _1h ⁺5.1851×C _4h ⁺20.3265×C _24h .The accuracy and precision (mean value±SD for the determined/estimated AUC was 0.99±0.053) of the model could not be increased by the addition of more data points. A somewhat lower accuracy and precision (0.96± 0.089) was seen with the 2-, 4-, and 24-h data points. These were used to test the regression technique prospectively for the estimation of the AUC after i.v. administration in another set of 10 patients. The accuracy and precision of the estimation of the AUC was similar in this group (1.01±0.109). In all, 11 patients were treated orally (10 mg/m²) and 10 patients were treated by s.c. injection (5 mg/m²). The most important data points for estimation of the AUC were 2.5, 24, and 0.5 h after oral administration (AUC=0.8630×C _0.5 h+ 4.2337×C _2.5h ⁺45.4364×C _24h ) and 9, 1, and 16 h after s.c. injection (AUC=1.8821×C _1h +16.4256×C _9h ⁺ 25.4518×C _16h ). The accuracy and precision were 1.01±0.064 after oral dosing and 0.99±0.11 after s.c. injection. The derived mathematical models are reliable for estimation of the plasma AUC of cladribine after 2-h i.v. infusion, oral administration, and s.c. injection. Received: 8 October 1995/Accepted: 1 March 1996     

Effect of gastric pH on the relative oral bioavailability and pharmacokinetics of temozolomide

Purpose: Temozolomide is an imidazotetrazine alkylating agent which undergoes chemical conversion at physiological pH to the active species 5-(3-methyltriazene-1-yl)imidazole-4-carboxamide (MTIC) but is stable at acid pH. This study evaluated the effect of an increase in gastric pH, through the use of ranitidine, on the oral bioavailability and plasma pharmacokinetics of temozolomide and MTIC. Methods: Fifteen patients with advanced cancer were enrolled of which 12 were evaluable, all of whom had pharmacokinetic blood sampling. Each patient received temozolomide 150 mg m⁻² day⁻¹ for 5 days in cycle 1 and also received ranitidine 150 mg every 12 h either on days 1 and 2 or days 4 and 5. Gastric pH was monitored by the use of the Heidelberg capsule system. Results: Following the administration of ranitidine there was a rise in gastric pH by 1–2 pH units over the duration of the study period (pH range 2.2–5.2 without ranitidine and 3.5–6.0 with ranitidine). There was no difference in the pharmacokinetic parameters of temozolomide or MTIC with or without the concomitant administration of ranitidine. There was however, a lower C_max for temozolomide and MTIC for patients receiving ranitidine on day 1 and 2 versus day 4 and 5. Temozolomide was rapidly absorbed [time to maximum plasma concentration (t _max) 1.8 h] and eliminated [elimination half-life (t _1/2) 1.8 h] and MTIC followed a similar pattern with a t _max of 1.9 h and a t _1/2 of 1.9 h. Overall, the AUC of the MTIC represented about 2–4% of the AUC for temozolomide. Received: 15 December 1998 / Accepted: 16 March 1999     

Drug distribution and pharmacokinetic/pharmacodynamic relationship of paclitaxel and gemcitabine in patients with non-small-cell lung cancer

Background:Gemcitabine and paclitaxel are two of the mostactive agents in non-small-cell lung cancer (NSCLC), and pharmacologicinvestigation of the combination regimens including these drugs mayoffer a valuable opportunity in treatment optimization. The presentstudy investigates the pharmacokinetics and pharmacodynamics ofpaclitaxel and gemcitabine in chemotherapy-naive patients with advancedNSCLC within a phase I study. Patients and methods:Patients were given i.v. paclitaxel 100 mg/m² byone-hour infusion followed by gemcitabine 1500, 1750 and 2000mg/m² by 30-min administration. Plasma levels of paclitaxel,gemcitabine and its metabolite 2,2-difluorodeoxyuridine(dFdU) were determined by high-performance liquid chromatography (HPLC).Concentration-time curves were modeled by compartmental andnon-compartmental methods and pharmacokinetic/pharmacodynamic (PK/PD)relationships were fitted according to a sigmoid maximum effect(E_max) model. Results:Paclitaxelpharmacokinetics did not change as a result of dosage escalation ofgemcitabine from 1500 to 2000 mg/m². A nonproportionalincrease in gemcitabine peak plasma levels (C_max, from 18.56± 4.94 to 40.85 ± 14.85 µg/ml) and area under theplasma concentration-time curve (AUC, from 9.99 ± 2.75 to 25.01± 9.87 h·µg/ml) at 1500 and 2000mg/m², respectively, was observed, suggesting the occurrenceof saturation kinetics at higher doses. A significant relationshipbetween neutropenia and time of paclitaxel plasma levels 0.05µmol/l was observed, with a predicted time of 10.4 h to decreasecell count by 50%. A correlation was also observed betweenpercentage reduction of platelet count and gemcitabine C_max,with a predicted effective concentration to induce a 50% decreaseof 14.3 µg/ml. Conclusion:This study demonstratesthe lack of interaction between drugs, the nonproportionalpharmacokinetics of gemcitabine at higher doses and the E_maxrelationship of paclitaxel and gemcitabine with neutrophil and plateletcounts, respectively. In addition, gemcitabine 1500 mg/m² isthe recommended dosage in combination with paclitaxel 100mg/m² for future phase II studies, due to its predictablekinetic behaviour and less severe thrombocytopenia than expected.     

Safety,tolerability and pharmacokinetics of multiple oral doses of AFN-1252 administered as immediate release (IR) tablets in healthy subjects

Background: AFN-1252 is a novel inhibitor of FabI, which is essential in Staphylococcus spp. This study evaluated the safety, tolerability and pharmacokinetics of multiple oral doses of AFN-1252 immediate-release tablets.

Methods: Part I evaluated AFN-1252 as a single 200 mg dose in fed versus fasted subjects. Part II evaluated 200, 300 and 400 mg doses of AFN-1252 administered once-daily for 10 days.

Results: Pharmacokinetics indicated good absorption with a median T_max of 2–3 hours, and a mean t_1/2 of 7–10 hours, for all doses. C_max and AUC responses were non-linear. A high-fat meal reduced AUC_0–t and C_max values by 62% and 48%, respectively, and delayed T_max by 2.5 hours. All adverse events, including possibly drug-related headache and nausea, were mild or moderate.

Conclusions: Multiple ascending doses of AFN-1252 were safe and well tolerated. AFN-1252 has potential for once- or twice-daily dosing in the treatment of staphylococcal infections.     

Pharmacology of intracellular cytosine-arabinoside-5′-triphosphate in malignant cells of pediatric patients with initial or relapsed leukemia and in normal lymphocytes

Purpose The prodrug cytosinearabinoside (ara-C) is widely used in the treatment of acute leukemias. The active drug is the intracellular metabolite cytosine-arabinoside-5′-triphosphate (ara-CTP). The purpose of the present study was to investigate the relation between sensitivity and pharmacokinetic parameters C _max, t _1/2 and AUC of ara-CTP. The obtained results were compared to previous studies. Experimental design C _max, t _1/2 and AUC of ara-CTP were assessed in leukemic cells of 17 pediatric patients with acute lymphoblastic leukemia (ALL) and in 6 lymphoblastic cell lines and compared with normal lymphocytes of 9 healthy donors by high pressure liquid chromatography (HPLC). The sensitivity of the cells against ara-C was determined by the MTT assay. Results The intracellular accumulation of ara-CTP was significantly lower in normal lymphocytes (C _max 47.7–60.9 pmol/10⁶ cells) compared to leukemic cell lines (C _max 11–1128 pmol/10⁶ cells) and leukemic cells of our patients (C _max 85.9–631 pmol/10⁶ cells). Similar results were found for the AUC. There was no significant difference between initial and relapsed leukemias in our small cohort. A correlation between sensitivity in terms of IC₅₀ values and the intracellular ara-CTP accumulation was observed in cell lines, but not in leukemic cells and normal lymphocytes from healthy donors. Conclusions Pharmacokinetic parameters varied tremendously in leukemic cells in contrast to normal lymphocytes without a difference in sensitivity. It is worthwhile to compare literature data to assess an optimal dosage of ara-C in pediatric patients.     

Bioavailability and pharmacokinetics of the cardioprotecting flavonoid 7-monohydroxyethylrutoside in mice

Purpose The pharmacokinetics and bioavailability of monoHER, a promising protector against doxorubicin-induced cardiotoxicity, were determined after different routes of administration.Methods Mice were treated with 500 mg.kg^–1 monoHER intraperitoneally (i.p.), subcutaneously (s.c.) or intravenously (i.v.) or with 1000 mg.kg^–1 orally. Heart tissue and plasma were collected 24 h after administration. In addition liver and kidney tissues were collected after s.c. administration. The levels of monoHER were measured by HPLC with electrochemical detection.Results After i.v. administration the AUC_{0–120 min} values of monoHER in plasma and heart tissue were 20.5±5.3 mol.min.ml^–1 and 4.9±1.3 mol.min.g^–1 wet tissue, respectively. After i.p. administration, a mean peak plasma concentration of about 130 M monoHER was maintained from 5 to 15 min after administration. The AUC_{0–120 min} values of monoHER were 6.1±1.1 mol.min.ml^–1 and 1.6±0.4 mol.min.g^–1 wet tissue in plasma and heart tissue, respectively. After s.c. administration, monoHER levels in plasma reached a maximum (about 230 M) between 10 and 20 min after administration. The AUC_{0–120 min} values of monoHER in plasma, heart, liver and kidney tissues were 8.0±0.6 mol.min.ml^–1, 2.0±0.1, 22.4±2.0 and 20.5±5.7 mol.min.g^–1, respectively. The i.p. and s.c. bioavailabilities were about 30% and 40%, respectively. After oral administration, monoHER could not be detected in plasma, indicating that monoHER had a very poor oral bioavailability.Conclusions MonoHER was amply taken up by the drug elimination organs liver and kidney and less by the target organ heart. Under cardioprotective conditions (500 mg/kg, i.p.), the C_max was 131 M and the AUC was 6.3 M.min. These values will be considered endpoints for the clinical phase I study of monoHER.     

An open study to assess the safety,tolerance and pharmacokinetics of an intravenous infusion of granisetron given at 3 mg over 30 s in patients receiving chemotherapy for malignant disease

Granisetron is a highly potent and selective 5-hydroxytryptamine₃ (5-HT₃) receptor antagonist indicated for the prevention of cytotoxic-induced nausea and vomiting. Clinical trials have demonstrated granisetron to be effective and well tolerated at a standard dose of 40 g/kg or 3 mg given i.v. as a 5-min infusion. In this study, the efficacy and safety of granisetron given as a 30-s infusion was assessed. A total of 21 patients, scheduled to undergo chemotherapy, received a single 3-mg i.v. dose of granisetron over 30 s, completed at 1 h before chemotherapy administration. Patients were allowed two further i.v. doses of granisetron at 3 mg within the 24-h assessment period. Changes from baseline values in vital signs were analysed prior to granisetron administration and at 30 s as well as 1, 10, 15, 30 and 60 min after granisetron administration. Holter ECG recordings were taken for 6 h prior to and 1 h after administration. No significant change was found in vital signs at 30 s or 1 min after granisetron infusion. There was a small but statistically significant fall in diastolic blood pressure as compared with baseline and a non-significant trend in favour of a reduction in heart rate at 10 and 15 min. No ECG abnormality was recorded post-infusion that had not been present pre-infusion. None of these changes was considered to be clinically relevant. The treatment was well tolerated. The most frequenctly reported adverse events were constipation (n=6) and headache (n=5). Maximal plasma levels of granisetron were within the range of 44.57–410 ng/ml except in one patient. The median values recorded for peak concentration (C_max) and area under the curve (AUC) were 195 ng/ml and 71.2 ng h ml^–1, respectively. In conclusion, granisetron at 3 mg was shown to be safe and well tolerated when given as a 30-s i.v. infusion to patients receiving chemotherapy for malignant disease.     

Comparative pharmacokinetics of ifosfamide, 4-hydroxyifosfamide, chloroacetaldehyde, and 2- and 3-dechloroethylifosfamide in patients on fractionated intravenous ifosfamide therapy

The initial metabolism of the oxazaphosphorine cytostatic ifosfamide (IF) consists of two different pathways: ring oxidation at carbon-4 forms the cytostatically active metabolite 4-hydroxyifosfamide (4-OH-IF, activated ifosfamide), whereas side-chain oxidation with liberation of the presumably neurotoxic compound chloroacetaldehyde (CAA) that may also be responsible for IF-associated nephrotoxicity results in the formation of the cytostatically inactive metabolites 2-dechloroethylifosfamide (2-DCE-IF) and 3-dechloroethylifosfamide (3-DCE-IF). The pharmacokinetics of IF and its metabolites were investigated in 11 patients with bronchogenic carcinoma receiving IF on a 5-day divided-dose schedule (1.5 g/m² daily). Blood samples were drawn on days 1 and 5 for up to 24 h after the start of the IF infusion. IF, 2-DCE-IF, and 3-DCE-IF were simultaneously quantified by gas chromatography (GC) with an NIP flame-ionization detector (NPFID), CAA was determined by GC with an electron-capture detector (ECD), and the highly unstable compound 4-OH-IF was measured using a high-performance liquid chromatography (HPLC) assay with fluorometric detection of 7-OH-quinoline, which is formed by the condensation of 4-OH-IF-derived acrolein withm-aminophenol. As compared with the values obtained on day 1, on day 5 the terminal half-life and AUC values determined for IF were reduced by 30% (6.36 vs 4.06 h and 1781 vs 1204 nmol h ml^–1, respectively), whereas the maximal concentration (C_max) values were not affected significantly (199.1 vs 181.1 nmol ml^–1). This known phenomenon is explained by autoinduction of hepatic IF metabolism and was paralleled by increased metabolite levels. The mean C_max values determined for 4-OH-IF, CAA, 3-DCE-IF, and 2-DCE-IF (on day 1/on day 5) were 1.51/2.59, 2.69/4.85, 12.9/26.5, and 8.6/16.7 nmol ml^–1, respectively. The corresponding AUC values were 11.3/16.5, 30.3/34.3, 146/354, and 111/209 nmol h ml^–1, respectively. As calculated by intraindividual comparison, the mean C_max (day 5)C_max (day 1) ratios for 4-OH-IF, CAA, 3-DCE-IF, and 2-DCE-IF were 1.94^*, 2.05^*, 2.52^*, and 2.33^*, respectively; the corresponding AUC (day 5)AUC (day 1) ratios were 1.51^*, 1.29, 2.34^*, and 2.23^*, respectively (^* P<0.05). These data reveal that during fractionated-dose IF therapy the cancerotoxic effect of the drug increases. If the assumed role of CAA in IF-associated neurotoxicity and nephrotoxicity is a dose-dependent phenomenon, the probability of developing these side effects would also increase during prolonged IF application.Abbreviations IF ifosfamide - CAA chloroacetaldehyde - CP cyclophosphamide - 4-OH-IF 4-hydroxyifosfamide (activated ifosfamide) - 2-DCE-IF 2-dechloroethylifosfamide - 3-DCE-IF 3-dechloroethylifosfamide