Plasma and cerebrospinal fluid pharmacokinetics of 9-aminocamptothecin (9-AC), irinotecan (CPT-11), and SN-38 in nonhuman primates

Purpose: The plasma and cerebrospinal fluid (CSF) pharmacokinetics of the camptothecin analogs, 9-aminocamptothecin (9-AC) and irinotecan, were studied in a nonhuman primate model to determine their CSF penetration. Methods: 9-AC, 0.2 mg/kg (4 mg/m²) or 0.5 mg/kg (10 mg/m²), was infused intravenously over 15 min and irinotecan, 4.8 mg/kg (96 mg/m²) or 11.6 mg/kg (225 mg/m²), was infused over 30 min. Plasma and CSF samples were obtained at frequent intervals over 24 h. Lactone and total drug forms of 9-AC, irinotecan, and the active metabolite of irinotecan, SN-38, were quantified by reverse-phase HPLC. Results: 9-AC lactone had a clearance (CL) of 2.1 ± 0.9 l/kg per h, a volume of distribution at steady state (Vd_ss) of 1.6 ± 0.7 l/kg and a half-life (t_1/2) of 3.2 ± 0.8 h. The lactone form of 9-AC accounted for 26 ± 7% of the total drug in plasma. The CSF penetration of 9-AC lactone was limited. CSF 9-AC lactone concentration peaked 30 to 45 min after the dose at 11 to 21 nM (0.5 mg/kg dose), and the ratio of the areas under the CSF and plasma concentration-time curves (AUC^CSF: AUC^P) was only 3.5 ± 2.1%. For irinotecan, the CL was 3.4 ± 0.4 l/kg per h, the Vd_ss was 7.1 ± 1.3 l/kg, and the t_1/2 was 4.9 ± 2.2 h. Plasma AUCs of the lactone form of SN-38 were only 2.0% to 2.4% of the AUCs of irinotecan lactone. The lactone form of irinotecan accounted for 26 ± 5% of the total drug in plasma, and the lactone form of SN-38 accounted for 55 ± 6% of the total SN-38 in plasma. The AUC^CSF: AUC^P ratio for irinotecan lactone was 14 ± 3%. SN-38 lactone and carboxylate could not be measured (<1.0 nM ) in CSF. The AUC^CSF: AUC^P ratio for SN-38 lactone was estimated to be ≤ 8%. Conclusion: Despite their structural similarity, the CSF penetration of 9-AC and SN-38 is substantially less than that of topotecan which we previously found to have an AUC^CSF: AUC^P ratio of 32%. Received: 15 July 1997 / Accepted: 8 October 1997     

The plasma pharmacokinetics and cerebrospinal fluid penetration of the thymidylate synthase inhibitor raltitrexed (TomudexTM) in a nonhuman primate model

Purpose: Raltitrexed (Tomudex™), ZD1694) is a novel quinazoline folate analog that selectively inhibits thymidylate synthase. Intracellularly, raltitrexed is polyglutamated to its active form which can be retained in cells for prolonged periods. The pharmacokinetics of raltitrexed in plasma and cerebrospinal fluid (CSF) were studied in a nonhuman primate model. Methods: Animals received 3 mg/m² (n= 1), 6 mg/m² (n= 3), or 10 mg/m² (n= 3) i.v. over 15 min, and frequent plasma samples were obtained over 48 h. CSF samples were drawn from an indwelling 4th ventricular Ommaya reservoir over 48 h. Plasma and CSF raltitrexed concentrations were measured with a novel, sensitive enzyme inhibition assay with a lower limit of quantification of 0.005 μM. A three-compartment pharmacokinetic model was fitted to the raltitrexed plasma concentration-time data. Results: The plasma concentration-time profile of raltitrexed was triexponential with a rapid initial decline and a prolonged terminal elimination phase (t_1/2 > 24 h), which was related to retention of raltitrexed in a deep tissue compartment. At the peak approximately 30% of the administered dose was in the deep tissue compartment, and 24 h after the dosing >20% of the administered dose remained in the body with >99% in the deep tissue compartment. The mean peak (end of infusion) plasma concentrations after the 3, 6, and 10 mg/m² doses were 1.5, 2.4 and 4.8 μM, respectively. The clearance of raltitrexed ranged from 110 to 165 ml/min per m², and the steady-state volume of distribution exceeded 200 l/m². The CSF penetration of raltitrexed was limited (0.6 to 2.0%) and drug could only be detected in the CSF following a 10 mg/m² dose. Conclusions: The elimination of raltitrexed is triexponential with a prolonged terminal elimination phase. The pharmacokinetic profile is consistent with extensive polyglutamation and intracellular retention of ralitrexed. The three-compartment model presented here may be useful for the analysis of the pharmacokinetics of raltitrexed in humans. Received: 11 January 1999 / Accepted: 10 May 1999     

Phase I dose escalation pharmacokinetics of O-(chloroacetylcarbamoyl) fumagillol (TNP-470) and its metabolites in AIDS patients with Kaposi's sarcoma

The pharmacokinetics of TNP-470 and its major metabolites were investigated in AIDS patients enrolled in a phase I dose escalation trial for the treatment of Kaposi's sarcoma. The patients received TNP-470 by 1-h intravenous infusion in dose cohorts of 10, 20, 30, 40, 50 and 70 mg/m². The parent drug and metabolites, MII and MIV, were measured by high-performance liquid chromatography/mass spectrometry (HPLC/MS) in plasma samples collected during and out to 168 h after the beginning of the infusion. Both metabolites were detected in all patients' plasma, while the parent drug was undetectable at time-points as early as 5 min after the end of infusion for some patients. A large interpatient variability of pharmacokinetic parameters among the dosing cohorts was observed for TNP-470, with a mean (±SD) plasma elimination half-life (t_1/2) of 0.06 ± 0.04 h, plasma clearance (CL) of 1487 ± 1216 l/h and an area under the concentration versus time curve (AUC) of 49.9 ± 35.8 ng/ml · h. Time to maximum plasma concentration (Tmax) typically occurred before the end of the infusion. The predominant plasma metabolite was MII with a t_1/2 of 1.21 ± 0.43 h, AUC of 1226 ± 2303 l/h and a Tmax occurring between 5 and 15 min after infusion. The reported active metabolite MIV had a t_1/2 of 0.24 ± 0.13 h, AUC of 24.9 ± 32.6 ng/ml · h and a Tmax occurring between the midpoint of the infusion and 15 min after infusion. The parent drug was undetectable by HPLC/MS/MS in urine samples collected and pooled between 0–6 and 6–24 h from the beginning of drug administration. Metabolite MIV was present in the 0–6-h urine pool of two patients enrolled in the highest dosing cohorts, equivalent to 0.4% of the administered dose. Metabolite MII was present in all 0–6-h samples analyzed and represented 1.12 ± 0.9% of the administered dose. Renal clearance (CL_R) for MII was 140 ± 70 ml/h. Received: 16 September 1999 / Accepted: 5 April 2000     

Pharmacokinetics and pharmacodynamics of MX2 hydrochloride in patients with advanced malignant disease

The purpose of the present study was to investigate the pharmacokinetics and pharmacodynamics of the new morpholino anthracycline drug MX2. A total of 27 patients with advanced cancer participated in a dose-escalation study in the first cycle of treatment with drug given i.v. at doses of 10–50 mg/m² (total dose 16.8–107.5 mg). The mean total systemic plasma clearance (CL) of MX2 was 2.98 ± 1.68 l/min, the mean volume of distribution at steady state was 1460 ± 749 l and mean elimination half-life was 10.8 ± 5.1 h. The area under the plasma concentration-time curve (AUC) of MX2 was linearly related to the dose per kilogram and the dose per body surface area (r ² = 0.43, P < 0.01 and r ² = 0.44, P < 0.01, respectively). CL did not correlate with total body weight, lean body mass or body surface area. The mean elimination half-lives of the metabolites M1, M2, M3 and M4 were 11.8 ± 5.0, 21.9 ± 11.8, 19.0 ± 11.3 and 12.3 ± 6.3 h, respectively. The fractional E _max model produced a much better fit to the relative nadir neutrophil count versus dose data (r ² = 0.42) than to the relative nadir neutrophil count versus AUC or peak concentration (C _max) data (r ² = 0.15 and 0.09, respectively). There seemed to be a threshold dose of about 65 mg of MX2 at or above which a large proportion of patients had a nadir neutrophil count of less than 0.5 × 10⁹/l. This study shows that the pharmacokinetics of MX2 are similar to those of other anthracyclines. With other anthracyclines the degree of myelosuppression seems to depend more on the AUC and C _max than on the delivered dose; however, with MX2 the degree of myelosuppression depends more on the dose given than on drug exposure expressed as the AUC or C _max. Received: 18 February 1996 / Accepted: 20 December 1996     

The pharmacokinetics of epirubicin and docetaxel in combination in rats

Purpose: The aim of the present study was to investigate possible pharmacokinetic interactions between epirubicin (EPI) and docetaxel (DTX) in rats. Methods: Male Sprague Dawley rats (n = 36) were used in the study. They received either DTX (5 mg/kg, n = 9), EPI (3.5 mg/kg, n = 13), or a combination (5 mg/kg + 3.5 mg/kg, n = 14), administered as intravenous bolus doses. Blood samples were collected at various time-points between 3 min and 45 h after dose administration. DTX and EPI plasma concentrations were determined by HPLC analysis. Pharmacokinetic evaluation was carried out using the NONMEM program. Results: A three-compartment model best described the concentration-time profiles for EPI. Clearance (CL), intercompartmental clearances (Q2 and Q3), central (V1) and peripheral (V2 and V3) volumes of distribution were estimated as 3.57 l/h per kg, 5.01 l/h per kg, 12.48 l/h per kg, 0.805 l/kg, 3.67 l/kg and 158 l/kg, respectively. A two-compartment model was sufficient to describe the DTX data. CL, intercompartmental clearance (Q), V1 and V2 for DTX were estimated as 7.3 l/h per kg, 4.6 l/h per kg, 0.69 l/kg and 2.6 l/kg, respectively. No significant change in the disposition of either drug was found when they were administered in combination compared to when they were given singly. Conclusion: Concurrent treatment with EPI and DTX does not appear to cause any changes in the pharmacokinetics of the drugs in rats. Received: 3 December 1998 / Accepted: 7 April 1999     

Investigation of bioavailability and pharmacokinetics of treosulfan capsules in patients with relapsed ovarian cancer

Purpose: Treosulfan (l-threitol-1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. In a pharmacologic study of the bioavailability of treosulfan in a capsule formulation, patients with relapsed ovarian carcinoma were treated with alternating doses of oral and intravenous (i.v.) treosulfan of 1.5 or 2.0 g daily for 5 to 8 days. Methods: A sensitive method for the determination of treosulfan in plasma and urine by reversed-phase high-performance liquid chromatography had previously been developed. Pharmacokinetic analyses of treosulfan were carried on plasma and urine samples from 20 i.v. courses and 20 courses of oral administration. Results: The bioavailability ratio (f) of oral to i.v. administration was calculated as 0.97 ± 0.18 (mean ± SD) using the values AUC_oral=82.1 ± 39.4 μg/ml h and AUC_i.v.=85.4 ± 30.3 μg/ml h. The peak plasma concentration c_max (29 ± 14 μg/ml vs 65 ± 23 μg/ml) was significantly (P < 0.01) higher after i.v. administration and the t_max after oral administration was 1.5 ± 0.34 h. The terminal half-life of treosulfan was about 1.8 h. The mean urinary excretion of the parent compound was about 15% of the administered total dose over 24 h (range 6–26%). Conclusions: The high and relatively constant bioavailability of treosulfan indicates that capsules provide a satisfactory noninvasive treatment alternative. A feasible and reliable oral treosulfan formulation could provide the basis for the development of long-term low-dose outpatient treatment of patients with malignant diseases. Received: 28 July 1999 / Accepted: 16 December 1999     

Clinical pharmacokinetics of the irinotecan metabolite 4-piperidinopiperidine and its possible clinical importance

Purpose: To investigate the clinical relevance of 4-piperidinopiperidine (4PP) in the activity of irinotecan (CPT-11), a high-performance liquid chromatography-turboionspray-tandem mass spectrometry assay for plasma 4PP was developed. Methods: Plasma samples were prepared for analysis following C18 solid-phase extraction. Chromatography was performed on a Waters Nova-Pak Phenyl column. Selected reaction monitoring with the mass transitions m/z 169.2 → 84.2 and 139.2 → 98.1 was used for the detection of 4PP and the internal standard (IS), 1-piperidineproprionitrile, respectively. Results: The assay was linear from 14.8 to 591.0 nM with absolute recoveries of 4PP (59.1 nM) and IS (143.7 nM) of 85.7% (n=10) and 86.7% (n=10), respectively. The accuracy and imprecision of the method (total) was ≥96.8% and ≤8.5% over the concentration range studied, respectively. 4PP was detectable in plasma following the administration of 125, 350, 500 mg/m² and 600 mg/m² CPT-11 to patients, with AUC_4PP correlated with the dose (r ²= 0.66). Plasma concentrations of 4PP declined slowly with a long terminal half-life (33.4 ± 17.1 h). Conclusions: Overall, the concentrations of 4PP in plasma were in the sub-micromolar range (<206.9 nM) and substantially lower than those capable of inducing apoptosis of cancer cells. Received: 29 March 1999 / Accepted: 19 July 1999     

Oral uracil and Ftorafur plus leucovorin: pharmacokinetics and toxicity in patients with metastatic cancer

Purpose: To assess the pharmacokinetics of Ftorafur (tegafur, FT), 5-fluorouracil (5-FU), and uracil in 31 cancer patients who were enrolled in phase I studies of oral uracil and FT (UFT). The correlation between pharmacokinetic parameters and toxic effects of UFT was evaluated. Methods: Uracil and FT were orally administered in a 4:1 molar ratio at FT doses of 200–400 mg/m² per day. Patients also received leucovorin at 150 mg/day. Daily doses were divided into three doses and administered at 8-h intervals for 28 consecutive days. Plasma FT concentrations were measured by high-performance liquid chromatography, and plasma 5-FU and uracil concentrations were determined using gas chromatography-mass spectrometry. National Institutes of Health Common Toxicity Criteria were used for assessment of toxicity. Results: The concentrations of FT, 5-FU, and uracil showed wide interpatient variations. Maximum plasma concentrations (Cp_max) of all three compounds were achieved in 0.3 to 4.0 h. At the various study doses, the terminal half-life (t_1/2β) of FT ranged from 3.9 to 5.9 h, the area under the concentration-versus-time curve (AUC_0–6h) ranged from 16,220 to 52,446 (ng/ml)h, the total clearance (Cl_T) ranged from 100 to 175 ml/min, and the steady-state volume of distribution (Vd_ss) ranged from 18.3 to 28.7 l. The 5-FU generated from FT had an apparent distribution half-life (t_1/2α) and an apparent elimination half-life (t_1/2β) of 0.3–1.3 h and 4.9–7.0 h, respectively. The AUC_0–6h of 5-FU ranged from 120 to 325 (ng/ml)h. Uracil had a t_1/2α of 0.2–0.5 h and the level quickly returned to the endogenous level. The AUC_0–6h for uracil ranged from 605 to 3764 (ng/ml)h, the Cl_T ranged from 3225 to 7748 ml/min, and the Vd_ss ranged from 341 to 1354 l. The Cp_max and AUC_0–6h of both FT and uracil were significantly correlated with FT doses (P-values of 0.0244 and 0.0112) and with uracil doses (P-values of 0.0346 and 0.0083), respectively. In addition to interpatient variations, intrapatient variations were also observed in six patients who had pharmacology studies done on days 1 and 26 ± 2 at the same study dose. We found that the repeated treatment with UFT caused cumulative increases in the values of Cp_max, C_trough, and AUC_0–6h of FT and 5-FU. The major toxic effects observed were diarrhea and nausea and vomiting. The occurrence of these toxic effects correlated significantly with the Cp_max and AUC_0–6h of 5-FU. Conclusions: The pharmacology studies showed that FT and uracil were readily absorbed orally and that FT was rapidly converted to 5-FU. The preliminary findings suggest that determination of plasma levels of 5-FU after oral administration of UFT may help predict subsequent toxic effects. Received: 2 September 1999 / Accepted: 14 April 2000     

Modulation of the pharmacokinetics of the antitumour agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in mice by thalidomide

Background: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), an investigative drug currently in clinical trial, acts on tumour vasculature through the induction of cytokines. Coadministration of thalidomide, a modulator of cytokine production, potentiates the antitumour activity of DMXAA against the murine Colon 38 carcinoma in mice. We wished to determine whether alteration of the pharmacokinetics of DMXAA by thalidomide could provide an explanation for this potentiation. Results: Coadministration of thalidomide to Colon 38 tumour-bearing mice significantly (P < 0.05) increased the elimination half-life (t_1/2) of DMXAA in plasma (413 μmol/l), liver (132 μmol/l), and spleen (77 μmol/l), and significantly (P < 0.05) increased DMXAA concentrations in Colon 38 tumour tissue (0.25–4.5 h). l-Thalidomide had a greater effect on DMXAA elimination (P < 0.01) than did d-thalidomide or the racemate. Coadministration of thalidomide increased the area under the concentration-time curve (AUC) of DMXAA by 1.8-fold in plasma, liver and spleen, and by 3.0-fold in tumour. Bile from mice given thalidomide and DMXAA contained substantially lower amounts of the glucuronide metabolite of DMXAA (DMXAA-G) than did bile from mice given DMXAA alone. Conclusion: Glucuronidation is a major excretory pathway for DMXAA in the mouse. Thalidomide, probably as the l-form, decreases the rate of elimination of DMXAA from plasma, spleen, liver and tumour by altering the rate of glucuronidation. The reduction in the elimination of DMXAA by thalidomide may lead to a selective increase in exposure of tumour tissue to drug, providing a basis for its potentiation of antitumour activity. Received: 14 December 1999 / Accepted: 30 March 2000     

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     

Determination of flavopiridol (L86 8275; NSC 649890) in human plasma by reversed-phase liquid chromatography with electrochemical detection

Purpose: Flavopiridol is a flavone which inhibits several cyclin-dependent kinases, and exhibits potent growth-inhibitory activity against a number of human tumor cell lines both in vitro, and when grown as xenografts in mice. It is currently being evaluated in a phase I clinical trial at the National Cancer Institute. The objective of this project was to develop and validate an analytical method for the assay of flavopiridol in human plasma, with sufficient sensitivity to permit the plasma pharmacokinetics of flavopiridol to be studied during clinical trials. Methods: Flavopiridol was isolated from human plasma samples by extraction with t-butylmethyl ether following alkalinization with borate buffer (pH 8.0). The extract was evaporated, the residue was dissolved in mobile phase, and analyzed by reversed-phase high-pressure liquid chromatography. Chromatography was accomplished with a polymer-based C₁₈ column eluted with a mobile phase consisting of methanol-phosphate buffer, pH 11.0 (53:47 v/v). Electrochemical detection (ECD) was employed. Results: Flavopiridol was recovered from human plasma with an efficiency of 85–87%. Calibration curves were linear over the concentration range 10–500 nM (4.4–219 ng/ml). Plasma standard concentrations were measured with an accuracy and precision ranging from 3.2% to 10%. Regression analysis of flavopiridol concentrations of 15 clinical trial plasma samples ranging in concentration from approximately 50 to 4000 μM quantitated by both ECD and mass spectrometry showed close agreement. The equation of the regression line was y = 1.02x + 8 with a correlation coefficient of 0.969. Continuous infusion of flavopiridol in four patients for 72 h at a rate of 50 mg/m² per day, resulted in mean steady-state plasma concentrations of from 200 to 300 nM. Levels declined in a biexponential manner following termination of the infusion, falling to approximately 10 nM after 48 h. Conclusions: An analytical method for the assay of flavopiridol in human plasma was developed with sensitivity to at least 10 nM. The assay is accurate, precise and specific, and is suitable for determination of plasma flavopiridol concentrations for pharmacokinetic studies during clinical trials. Received: 2 September 1997 / Accepted: 15 January 1998     

Preclinical pharmacology and antitumour activity of the novel sequence-selective DNA minor-groove cross-linking agent DSB-120

 We examined the in vitro cytotoxicity, antitumour activity and preclinical pharmacokinetics of the novel sequence-selective, bifunctional alkylating agent DSB-120, a synthetic pyrrolo[1, 4][2, 1-c]benzodiazepine dimer. DSB-120 was shown to be a potent cytotoxic agent in vitro against a panel of human colon carcinomas [50% growth-inhibitory concentration (IC₅₀) 42±7.9 nM, mean±SE, n=7] and two rodent tumours (L1210 and ADJ/PC6). Antitumour activity was assessed in the bifunctional alkylating-agent-sensitive murine plasmacytoma ADJ/PC6 using a variety of administration protocols. The maximal antitumour eff- ects were observed following a single i.v. dose but the therapeutic index was only 2.6. DSB-120 was less effective when given i.p. either singly or by a daily+5 schedule. After a single i.v. dose at the maximum tolerated dose (MTD, 5 mg kg⁻¹) the plasma elimination was biphasic, with a short distribution phase (t _1/2α 4 min) being followed by a longer elimination phase (t _1/3β 38 min). Peak plasma concentrations were 25 μg ml⁻¹, the clearance was 1.3 ml g⁻¹ h⁻¹ and the AUC_0-∞ was 230 μg ml⁻¹ min. Concentrations of DSB-120 in ADJ/PC6 tumours were very low, showing a peak of 0.4 μg g⁻¹at 5 min. The steady-state tumour/plasma ratio was about 5% and the AUC was only 2.5% of that occurring in the plasma. DSB-120 appeared to be unstable in vivo, with only 1% of an administered dose being recovered unchanged in 24-h urine samples. Plasma protein binding was extensive at 96.6%. In conclusion, the poor antitumour activity of DSB-120 may be a consequence of low tumour selectivity and drug uptake as a result of high protein binding and/or extensive drug metabolism in vivo. Received: 5 November 1995/Accepted: 30 January 1996     

Plasma pharmacokinetics of N -[2-(dimethylamino)ethyl]acridine-4-carboxamide in a phase I trial

DACA {N-[2-(dimethylamino)ethyl]acridine-4-carboxamide} is an acridine derivative with high activity against solid tumours in mice and a dual mode of cytotoxic action involving topoisomerases I and II. The plasma pharmacokinetics of DACA were studied in 28 patients with solid tumours in a phase I trial. A single dose was given every 3 weeks, being escalated from a starting dose of 18 mg/m² (as the dihydrochloride trihydrate salt) to a maximal dose, limited by severe pain in the infusion arm, of 1000 mg/m². Drug was given by constant intravenous infusion with a target delivery period of 3 h. Blood samples were taken from the contralateral arm before, during and for up to 72 h after the infusion. DACA was separated from plasma by solid-phase extraction and was analysed by reversed-phase high-performance liquid chromatography (C18 column) using fluorescence detection. A two-compartment pharmacokinetic model provided the best fit for the concentration-time profiles obtained for most patients showing clearance of 1.00 ± 0.36 l h⁻¹ kg⁻¹, a volume of distribution of the central compartment of 0.72 ± 0.55 l/kg, an initial half-life of 0.28 ± 0.19 h and a terminal half-life of 2.04 ± 0.94 h. All pharmacokinetic parameters were independent of dose, indicating first-order kinetics. As DACA binds strongly to α₁-acid glycoprotein, plasma concentrations of this protein were determined and used to estimate free-drug fractions in plasma. Estimated values for the free fraction varied from 0.9% to 3.3% and were lower than those determined by equilibrium dialysis for mice and rats (15% and 16%, respectively). At the maximum tolerated dose (MTD) of 750 mg/m², the area under the drug concentration-time curve (AUC) was 46.2 ± 4.4 μM h, exceeding that obtained in mice treated at the MTD (23.4 μM h). On the other hand, the corresponding free-drug AUC was 0.92 ± 0.03 μM h, much lower than the corresponding value (3.5 μM h) determined for mice. These results suggest that free-drug rather than total drug concentrations are more appropriate for interspecies dose comparisons when significant differences exist in the free plasma fraction. Received: 27 August 1998 / Accepted: 10 December 1998     

Pharmacokinetics of oral O6-benzylguanine and evidence of interaction with oral ketoconazole in the rat

Purpose: O⁶-Benzylguanine (BG) is a modulator of the DNA repair protein, O⁶-alkylguanine-DNA alkyltransferase (AGT). BG is converted in mice, rats and humans to an equally active, yet longer-lived metabolite, O⁶-benzyl-8-oxoguanine (8-oxo-BG) by CYP1A2, CYP3A4 and aldehyde oxidase. Since intravenous BG is expected to enter phase I development with orally administered anticancer agents such as temozolomide, procarbazine or SarCNU, we determined the bioavailability of orally administered BG, as well as the effect of ketoconazole, a potent intestinal and hepatic CYP3A4 inhibitor, on the disposition of BG. Methods: Following intravenous or oral administration of BG in PEG-400/saline (40:60) to Sprague-Dawley rats, the pharmacokinetics of BG and 8-oxo-BG were determined. To determine the effect of CYP3A inhibition on disposition, oral BG was coadministered with ketoconazole. Results: The peak plasma concentration (C_max), time to C_max (t_max), and bioavailability (F) of oral BG were: 2.3 ± 0.9 μg/ml, 2.3 ± 0.6 h, and 65.5% respectively. The AUCs of BG and 8-oxo-BG were 13.1 ± 4.6 μg · h/ml and 1.7 ± 0.4 μg · h/ml after oral administration of BG. Coadministration with ketoconazole resulted in an increase in mean absorption time from 2.0 ± 0.3 h to 6.0 ± 0.9 h, a shift in t_max to 5 ± 3.3 h, a decrease in C_max to 0.96 ± 0.8 μg/ml, and a decrease in AUC_0-inf ratio of 8-oxo-BG:BG from about 0.12 to 0.04 (P < 0.05). The bioavailability of BG was not changed (65.5% vs 56.9%, P=0.78). Conclusions: The oral bioavailability of BG is high, warranting consideration of an oral formulation for clinical development. Coadministration of ketoconazole and BG resulted in delayed oral absorption and inhibition of conversion of BG to 8-oxo-BG in the rat model. Received: 12 July 1999 / Accepted: 11 February 2000     

Pharmacokinetic behavior of vincristine sulfate following administration of vincristine sulfate liposome injection

The pharmacokinetic behavior of vincristine sulfate (VINC) following administration of vincristine sulfate liposome injection (VSLI), 0.16 mg/ml, as an intravenous infusion over 60 min in 24 of 25 patients enrolled in a phase I clinical study of this drug is described. Plasma samples for determination of the pharmacokinetic behavior of VINC were collected during the infusion at 15, 30 and 60 min as well as at 2, 4, 8, 12, 48 and 72 h postinfusion. Total VINC concentration was determined using a validated high-performance liquid chromatographic (HPLC) assay. Patients receiving doses of 0.5 to 1.5 mg/m² VSLI did not provide useful pharmacokinetic data at late time-points owing to the limit of quantitation of the HPLC assay (28.6 ng/ml). Sufficient concentration-time data were available for seven of the patients receiving doses of VSLI from 2.0 to 2.8 mg/m² for compartmental modelling. A two-compartment open model (PCNONLIN Model 10) was the best fit for the observed VINC plasma data for these patients. The mean maximum observed concentration values were significantly greater for patients receiving VSLI at 2.8 mg/m² (2260 ± 212 ng/ml, n = 2) than for those receiving 2.0 mg/m² and 2.4 mg/m² (891 ± 671 ng/ml, n = 6; 679 ± 634 ng/ml, n = 6, respectively). No significant differences were observed in maximum concentration values between patients at 2.0 mg/m² and those at 2.4 mg/m². A trend towards higher parametric AUC (0 to ∞) values with increasing dose (on a milligram per meter squared basis) was observed but statistical significance was not reached. Comparison of the pharmacokinetic behavior of VSLI observed in this study with nonencapsulated VINC demonstrated that (1) the variability observed for VSLI pharmacokinetic parameters was similar to nonencapsulated VINC, (2) although variability in absolute concentration was observed␣between patients, the behavior of VSLI in individual patients followed a two- rather than a three-compartment open model, and (3) VINC plasma concentrations were significantly greater following administration of VSLI than described for nonencapsulated VINC. Overall, the results for patients treated with VSLI from 2.0 to 2.8 mg/m² suggest that this formulation protects VINC from the early phase of rapid elimination seen with nonencapsulated drug, resulting in significantly elevated VINC plasma concentrations over extended periods of time. Received: 19 November 1996 / Accepted: 25 July 1997     

A clinical pharmacokinetics study of carzelesin given by short-term intravenous infusion in a phase I study

We investigated the pharmacokinetic behavior of carzelesin in 31 patients receiving this drug by 10-min intravenous infusion in a Phase I clinical trial, which was conducted at institutions in Nijmegen (institution 1) and Brussels (institution 2). The dose steps were 24, 48, 96, 130, 150, 170, 210, 250, and 300 μg/m². Carzelesin is a cyclopropylpyrroloindole prodrug that requires metabolic activation via U-76,073 to U-76,074. The lower limit of quantitation (LLQ) of the high-performance liquid chromatography (HPLC) method used in this study was 1 ng/ml for the parent drug and its metabolic products. Carzelesin was rapidly eliminated from plasma (elimination half-life 23 ± 9 min; mean value ± SD). At all dose levels, U-76,073 was found as early as in the first samples taken after the start of the infusion. However, the concentration of U-76,074 exceeded the LLQ for only short periods and only at the higher dose levels. Although the plasma levels of all three compounds were well above the respective IC₅₀ values obtained by in vitro clonogenic assays, they were much lower than those observed in a preclinical study in mice. There was a substantial discrepancy in the mean plasma clearance␣observed between patients from institution 1 (7.9 ± 2.1 l h⁻¹ m⁻²) and those from institution 2 (18.4 ± 13.6 l h⁻¹ m⁻²; P = 0.038), probably reflecting problems with drug administration in the latter institution. The results recorded for patients in institution 1 indicated that the AUC increased proportionately with increasing doses. There was a good correlation between the maximal plasma concentration and the AUC, enabling future monitoring of drug exposure from one timed blood sample. Urinary excretion of carzelesin was below 1% of the delivered dose. Received: 6 May 1997 / Accepted: 5 September 1997     

Lysophosphatidic acid (LPA)—a perspective marker in ovarian cancer

To compare plasma lysophosphatidic acid (LPA) levels in ovarian cancer patients in women with benign ovarian tumors and in women with no ovarian pathology. We correlated clinico-pathological parameters with plasma LPA levels. Capillary electrophoresis with indirect ultraviolet detection was used to analyze the plasma LPA levels of 159 patients (81 patients with ovarian cancer, 27 women without ovarian or uterine pathologies, and 51 patients with benign ovarian tumors) during a 5-year period. Patients with ovarian cancer had a significantly higher plasma LPA level (n = 81; median (med), 11.53 μmol/l; range, 1.78–43.21 μmol/l) compared with controls with no ovarian pathology (n = 27; med, 1.86 μmol/l; range, 0.94–9.73 μmol/l), and patients with benign ovarian tumor (n = 51; med, 6.17 μmol/l; range, 1.12–25.23 μmol/l; P < 0.001). We found that plasma LPA levels were associated with the International Federation of Gynecology and Obstetrics stage. The histological subtype and grade of ovarian cancer did not influence the plasma LPA levels in this study. The plasma LPA level can be a useful marker for ovarian cancer, particularly in the early stages of the disease.     

Plasma and CSF pharmacokinetics of ganciclovir in nonhuman primates

Purpose: The antiviral nucleoside analogue ganciclovir is a potent inhibitor of replication in herpes viruses and is effective against cytomegalovirus infections in immunocompromised patients. Ganciclovir is also used in cancer gene therapy studies that utilize the herpes simplex virus thymidine kinase gene (HSV-TK). The pharmacokinetics of ganciclovir in adults and children have been described previously but there are no detailed studies of the CNS pharmacology of ganciclovir. We studied the pharmacokinetics of ganciclovir in plasma and CSF in a nonhuman primate model that is highly predictive of the CSF penetration of drugs in humans. Methods: Ganciclovir, 10 mg/kg i.v., was administered over 30 min to three animals. Ganciclovir concentrations in plasma and CSF were measured using reverse-phase HPLC. Results: Peak plasma ganciclovir concentrations ranged from 18.3 to 20.0 μg/ml and the mean plasma AUC was 1075 ± 202 μg/ml · min. Disappearance of ganciclovir from the plasma was biexponential with a distribution half-life (t_1/2α) of 18 ± 7 min and an elimination half-life (t_1/2β) of 109 ± 7 min. Total body clearance (Cl_TB) was 9.4 ± 1.6 ml/min/kg. The mean CSF ganciclovir AUC was 168 ± 83 μg/ml · min and the mean peak CSF concentration was 0.7 ± 0.3 μg/ml. The ratio of the AUCs in CSF and plasma was 15.5 ± 7.1%. Conclusions: Ganciclovir penetrates into the CSF following i.v. administration. This finding will be useful in the design of gene therapy trials involving the HSV-TK gene followed by treatment with ganciclovir in CNS or leptomeningeal tumors. Received: 8 May 1998 / Accepted: 25 September 1998     

Liposomal daunorubicin plasmatic and renal disposition in patients with acute leukemia

Liposomal formulations of anthracyclines have been developed to increase their delivery to solid tumors while reducing toxicity in normal tissues. DaunoXome (DNX, NeXstar) is a liposomal-encapsulated preparation of daunorubicin registered for treatment of Kaposi's sarcoma that during prior in vitro studies showed a toxicity to leukemic cells at least comparable to that of free daunorubicin. The aim of our study was to determine DNX pharmacokinetics in 11 poor-risk patients with acute leukemia treated with DNX 60 mg/m² IV on days 1, 3, and 5. Blood and urine samples were collected at appropriate intervals after each of the three DNX administrations. The total amount of daunorubicin (free and entrapped) (t-DNR) and of its metabolite daunorubicinol (DNRol) was assayed by HPLC. The main pharmacokinetic parameters (t_1/2α 4.54 ± 0.87 h; Vd_ss 2.88 ± 0.93 l/m²; Cl 0.47 ± 0.26 l/h/m²) showed that in patients with acute leukemia liposomal-entrapped daunorubicin pharmacokinetics greatly differed from that observed for the conventional formulation. In fact, DNX produced mean plasma AUC levels (t-DNR AUC_0–∞ 456.27 ± 182.64 μg/ml/h) about 100- to 200-fold greater than those reported for the free drug at comparable doses due to a very much lower total body clearance. Volume of distribution at steady state was 200- to 500-fold lower than for the free drug. Plasma AUC of DNRol (17.62 ± 7.13 μg/ml · h) was similar to or even greater than that observed with free daunorubicin for comparable doses. Cumulative urinary excretion showed that about 6% and 12% of the total dose of DNX administered was excreted in urine as daunorubicin and daunorubicinol, respectively. No major toxicity was encountered. Therefore, pharmacokinetic characteristics suggest that DNX may be more convenient than free daunorubicin in the treatment of acute leukemia. In fact, liposomal formulation may allow a reduction of daunorubicin captation in normal tissues, thus minimizing toxicity at least for the parent drug, and guarantee an unimpeded access to leukemic cells in the bloodstream and bone marrow, thus theoretically improving efficacy. Received: 17 March 2000 / Accepted: 25 May 2000     

Circadian rhythm of 5-fluorouracil population pharmacokinetics in patients with metastatic colorectal cancer

Purpose: The purpose of this work was to estimate the population pharmacokinetic parameters of 5-fluorouracil (5-FU) in patients with advanced colorectal cancer using circadian change kinetics. Methods: Eighty-five patients (32 females, 53 males) were enrolled onto this study. All patients received folinic acid (200 mg/m²) by intravenous infusion over 2 h followed by a 5-FU loading dose (400 mg/m²) and then continuous infusion (600 mg/m²) for 22 h. This whole regimen was repeated on day 2 and was given on a 14-day cycle. Plasma 5-FU determinations were performed by high-performance liquid chromatography with ultraviolet absorbance detection. Pharmacokinetic analyses were performed using the NONMEM computer program through the Visual-NM graphical interface. An open one-compartment pharmacokinetic model with zero-order input rate was used to describe the kinetics of 5-FU; moreover, circadian time-dependent changes in 5-FU concentrations were taken into account in the model. The circadian model was defined as the sum of two cyclic components; the amplitude of the first cyclic component (over 24 h) was about 30% of the average clearance and the amplitude of the second cyclic component (over 12 h) was about 50% of the amplitude of the first component. The acrophase (peak) times of the first and the second periodic component were 04 h 12 m and 00 h 25 m, respectively. The potential sources of variability on the population parameters (65 patients) were investigated using patient's sex, body area, age, body weight, height, liver enzymes and serum creatinine as covariables. Results: Only the estimated clearance circadian changes were different for the two sexes. The population parameter estimates of mean clearance (CL _mean ) and initial volume of distribution (V), were as follows: the male subgroup showed a CL _mean value twice larger (125 l/h) than the value observed in the female subgroup (65 l/h), and V = 21 l. A validation group of 20 additional patients was used to evaluate the predictive performances of the population parameters. The individual pharmacokinetic parameters were computed by means of a Bayesian fitting procedure. From the resulting individualized parameter values, concentrations of 5-FU in the plasma were calculated. To evaluate the performance of the Bayesian estimation, the experimental concentrations were compared with the predicted ones. Conclusion: In conclusion, a chronomodulated delivery schedule of 5-FU should be performed, using a perfusion rate inversely proportional to the circadian variations of clearance in order to maintain stable 5-FU plasma levels. Such a treatment schedule may result in increased effectiveness of the treatment and decreased occurrence of drug-associated side-effects. The present study develops a complete procedure to efficiently estimate 5-FU clearance in order to optimize dosage regimens in individual patients. Received: 21 September 1998 / Accepted: 20 January 1999