Pharmacokinetic and toxicity scaling of the antitumor agents amsacrine and CI-921, a new analogue, in mice, rats, rabbits, dogs, and humans.

The aim was to investigate interspecies relationships between body weight (W) (kg) and various pharmacokinetic parameters for the anti-tumor agents amsacrine and its 4-methyl-5-(N-methylcarboxamide) analogue, CI-921, and examine which pharmacokinetic parameter, if any, might be used to predict the toxicity of these agents. Pharmacokinetic, plasma protein binding, and toxicity data were available for CI-921 in mice, rats, rabbits, dogs, and humans. For amsacrine, similar interspecies pharmacokinetic data were available but toxicity and protein-binding data were available for only 3 species. Significant linear relationships were obtained for CI-921 between log W and log Vss (liters) (r = 0.971, P = 0.006), and log W and log Cl (liters/h) (r = 0.911, P = 0.031) resulting in the allometric equations Vss = 1.22W0.68 and Cl = 0.91W0.51. For amsacrine these corresponding equations were Vss = 3.37W0.81 (r = 0.996, P less than 0.001), and Cl = 2.28W0.46 (r = 0.952, P = 0.012). When interspecies differences in plasma protein binding were taken into account, the allometric relationships improved and the exponents of the power equations increased. For CI-921 the allometric equations for the kinetic parameters calculated from plasma "free" concentrations were: Vssfu (liters) = 247W0.93 (r = 0.984, P = 0.002) and Clu (liters/h) = 186W0.76 (r = 0.961, P = 0.009). The dog was a noticeable outlier in the relationship between the log maximum tolerated dose (MTD) (mg/kg) of CI-921 and log W. Omission of the latter resulted in a highly significant allometric relationship, MTD = 23.6W-0.14 (r = -0.988, P = 0.012). For amsacrine there was no significant allometric relationship between MTD and W. CI-921s prolonged t1/2 in the dog and the dog's increased susceptibility to CI-921 toxicity suggested a relationship between MTD and t1/2 (h). A significant linear relationship was observed between in MTD and t1/2 (r = -0.994, P less than 0.001), from which the following equation was developed MTD = 47.5e-0.51t1/2 Combining the amsacrine toxicity data in the latter relationship yielded a similar equation MTD = 44.7e-0.51t1/2 (r = -0.933, P less than 0.0001). It was concluded that allometric equations may be developed for CI-921 and amsacrine from animal pharmacokinetic data which allow a reasonable prediction of Cl and Vss in patients, despite these agents being eliminated mainly by biotransformation. However, similar relationships between toxicity and body weight were susceptible to variation between individual species. Species differences in the toxicity of these agents were predictable from the t1/2. This study emphasized the importance of pharmacokinetic data in preclinical toxicity and efficacy testing of antitumor agents.

Development of a radioimmunoassay for the anthrapyrazole chemotherapy agent CI-937 and the pharmacokinetics of CI-937 in rats.

The anthracyclines daunorubicin and doxorubicin are cancer chemotherapy agents that complex DNA and are widely utilized clinically. Cumulative cardiotoxicity, however, limits their prolonged use. The novel anthrapyrazole agent, CI-937, which has shown exceptional in vivo anticancer activity and reduced cardiotoxicity in preclinical models has been developed at the Parke-Davis Pharmaceutical Research Division, Warner-Lambert Co. Due to an inability to extract CI-937 reproducibly from biological fluids, high-performance liquid chromatography is not a feasible analytical method. We developed a radioimmunoassay by conjugating CI-937 to porcine thyroglobulin to elicit rabbit antibody which was used with a radioiodinated derivative. The assay was validated for rat plasma using 50 microliters of sample with a resulting limit of quantitation of 100 pg/ml. By dilution of samples the assay can quantitate CI-937 levels up to 16 micrograms/ml. The antiserum is very specific as evidenced by cross-reactivities of less than 0.4% for structural analogues and less than 0.004% for any of the commonly used cancer chemotherapy agents. Analysis of plasma samples from rats treated with a single 5 mg/kg i.v. dose indicated that CI-937 is rapidly cleared from plasma and is extensively bound to tissues.

Phase I pharmacokinetic and pharmacodynamic study of a new anthrapyrazole, CI-937 (DUP937).

We performed a phase I trial of CI-937 (DUP937), an anthrapyrazole, with the following objectives: (a) to determine the maximally tolerated dose in humans; (b) to define the toxicity spectrum of this agent; (c) to describe the pharmacokinetics of the drug; (d) to test a pharmacokinetics based hypothesis of dose escalation; and (e) to relate drug pharmacokinetics to pharmacodynamics. CI-937 was administered as a single bolus injection every 3-4 weeks at doses ranging from 3.6 to 25.2 mg/m2. Thirty-two patients and 57 courses were evaluable for toxicity. Pharmacokinetic analysis was performed in 30 patients on the first course using a sensitive and selective radioimmunoassay. The maximally tolerated dose in patients with no prior therapy was 25.2 mg/m2 and dose-limiting toxicity was neutropenia. Thrombocytopenia, nausea, vomiting, stomatitis, and alopecia were mild. A partial response was recorded in a patient with mesothelioma. The area under the curve increased linearly with dose, and total body clearance of CI-937 was independent of dose. The mean total body clearance was 107 +/- 55.8 ml/min/m2, mean steady state volume of distribution was 492 +/- 469 liters/m2, and terminal half-life was 3.78 +/- 2.86 days. The extended factors of 2 methods of pharmacologically guided dose escalation were intended for use but ultimately were equivalent to that of the modified Fibonacci dose escalation method. Dose and the area under the curve were significant predictors of a percentage change in WBC and neutrophil count in a univariate analysis. Only dose and baseline neutrophil count predicted a percentage change in WBCs in a multifactor analysis. Dose and prior chemotherapy predicted percentage change in neutrophil count in a multifactor analysis. We conclude that the dose-limiting toxicity of CI-937 is neutropenia and that the recommended phase II starting dose is 22 mg/m2.

Phase I studies with trimetrexate: clinical pharmacology, analytical methodology, and pharmacokinetics.

Twenty-two patients with advanced solid tumors were treated with a quinazoline folate antagonist, trimetrexate, to determine the toxicity spectrum, the maximal tolerated dose, and the pharmacokinetics of the drug. Negligible toxicity was seen with single doses of 10-70 mg/m2 given as a 1-h infusion. Single doses of 120 mg/m2 infused over 1 h caused moderate to grade 4 toxicity in five of nine patients treated. Two patients who had no toxicity at this level were escalated to a dose of 213 mg/m2 with mild to moderate toxicity. The primary dose-limiting toxicity was myelosuppression. Moderate transaminase elevations, rash, anorexia, nausea and vomiting, and mucositis were occasionally seen. Although there was variation in dose tolerance to this drug, with selected patients able to tolerate higher doses, we consider 120 mg/m2 every 2 weeks to be the maximal tolerated dose, and the recommended Phase II starting dose. Trimetrexate plasma concentration-time curves were best described as biphasic (N = 9) or triphasic (N = 5) in form. The half-life of the terminal elimination-phase was 16.4 h. The mean residence time was 17.8 h. The volume of distribution of the plasma compartment and the volume of distribution at steady-state were 0.17 and 0.62 liter/kg, respectively. Plasma clearance was 53 ml/min. Plasma concentrations as determined by dihydrofolate reductase enzyme inhibition assay and high-performance liquid chromatography were initially identical, but diverged at later times. Divergences were seen also in urinary recovery as determined by the two methods. Both results suggest the appearance of metabolite(s) of trimetrexate which can inhibit dihydrofolate reductase. Measurable objective solid tumor responses were not seen in this Phase I study, although three patients with colon cancer had stable disease lasting 18, 26, and 26 weeks, respectively.

Phase I clinical and pharmacokinetic study of trimetrexate using a daily x5 schedule.

Trimetrexate (TMQ; NSC 352122) is a potent inhibitor of dihydrofolate reductase with good activity against murine i.p.-implanted B16 melanoma and colon 26 tumors. Preclinical antineoplastic activity, demonstrated schedule dependency, and data suggesting effectiveness against methotrexate-resistant cells prompted a Phase I clinical and pharmacokinetic study of trimetrexate using an i.v. daily x5 schedule. Forty-three good performance status patients were treated with 12 dose levels using daily doses varying from 0.5 to 15 mg/m2/d. Plasma and urine samples were obtained for pharmacokinetic analysis using a high-performance liquid chromatographic method. Myelosuppression was dose limiting and 15 mg/m2/d x5 was the maximum tolerated dose. White blood cell (WBC) and platelet toxicity were noted at doses of 1.6 mg/m2 and above. Median WBC and platelet nadirs occurred on approximately Days 11-12 with recovery by Days 15-18. Nonhematological toxicity included mucositis, nausea and vomiting, stomatitis, diarrhea, and rash. Evidence for antitumor activity was seen in seven patients. Trimetrexate elimination from plasma could be represented as either a bi- or triexponential process. Terminal elimination half-lives were in the range of 5-14 h in patients represented by a triexponential model. Approximately 10-20% of the dose administered was excreted in urine over a 24-h period. The recommended starting dose for patients in Phase II trials using the d x5 i.v. schedule is 8.0 mg/m2/d repeated every 21 days. Dose escalations may be possible depending on the extent of prior therapy and individual tolerance of the drug.

A phase I and pharmacologic evaluation of the DNA intercalator CI-958 in patients with advanced solid tumors.

5-[(2-Aminoethyl)amino]-2-[2-(diethylamino)ethyl]-2H-[1]benzothiopyra no[4,3,2-cd]-indazol-8-ol trihydrochloride (CI-958) is the most active member of a new class of DNA intercalating compounds, the benzothiopyranoindazoles. Because of its broad spectrum and high degree of activity as well as a favorable toxicity profile in preclinical models, CI-958 was chosen for further development. The Phase I study described here was undertaken to determine the toxicity profile, maximum tolerated dose, and pharmacokinetics of CI-958 given as an i.v. infusion every 21 days. Adult patients with advanced refractory solid tumors who had adequate renal, hepatic, and hematological function, life expectancy, and performance status were eligible for this study. Written informed consent was obtained from all patients. Patients received a 1- or 2-h infusion of CI-958 at 21-day intervals. The starting dose was 5.2 mg/m2, and at least three patients were evaluated at each dose level before proceeding to a new dose level. A pharmacokinetically guided dose escalation design was used until reaching a predetermined target area under the plasma concentration versus time curve (AUC), after which a modified Fibonacci scheme was used. Forty-four patients (21 men and 23 women; median age, 59 years) received 162 courses of CI-958. Neutropenia and hepatorenal toxicity were the dose-limiting toxicities, which defined the maximum tolerated dose of CI-958 to be 875 mg/m2 when given as a 2-h infusion every 21 days. There were no tumor responses. Two patients had stable disease for >250 days. The recommended Phase II dose is 560 mg/m2 for patients with significant prior chemotherapy and 700 mg/m2 for patients with minimal prior chemotherapy. Pharmacokinetic analysis of plasma and urine concentration-time data from each patient was performed. At the recommended Phase II dose of 700 mg/m2, mean CI-958 clearance was 370 ml/min/m2, mean AUC was 33800 ng-h/ml, and mean terminal half-life (t1/2) was 15.5 days. The clearance was similar at all doses, and plasma CI-958 AUC increased proportionally with dose, consistent with linear pharmacokinetics. The percentage reduction in absolute neutrophil count from baseline was well predicted by AUC using a simple Emax model. The pharmacokinetically guided dose escalation saved five to six dose levels in reaching the maximum tolerated dose compared with a standard dose escalation scheme. This may represent the most successful application to date of this dose escalation technique.

Relationship between concentration and anticoagulant effect of heparin in plasma of normal subjects: magnitude and predictability of interindividual differences.

The purposes of this investigation were to determine the magnitude of inter- and intraindividual variations in the relationship between heparin concentration and anticoagulant effect in normal adults, and to determine whether these variations are asociated with, and therefore predictable from, certain physiologic characteristics of individual subjects. Citrated plasma was obtained from 12 men and 5 women, 21 to 35 yr old. Heparin was added to the plasma to yield concentrations of 0.05 to 1.0 U/ml and the activated partial thromboplastin time (APTT) was determined. These studies were repeated once or twice over 65 days. Baseline APTT values (i.e., ATPP without added heparin) ranged from 25.6 to 36.2 sec and the hematocrit ranged from 39% to 50%. Both measures showed little intrasubject variation on the same day or on different days. There was an excellent linear relationship between In APTT and heparin concentration in the 0.05- to 0.8-U/ml range (r2 > 0.987 in all cases). The slope value for this relationship ranged from 1.51 to 3.88 ml/U and these interindividual differences were well reproducible on repeated testing. Women had lower hematocrits (p < 0.05) and higher slope values (p < 0.01) than men. Multiple linear regression analysis revealed a linear relationship between observed slope values and slope values calculated as a function of both hematocrit and baseline APTT. Age, weight, and the concentrations of various plasma proteins did not contribute significantly to the predictability of the slope. A multiple linear regression equation with hematocrit and baseline APtt as independent variables yielded a multiple correlation coefficient of 0.875 (p < 0.01). Thus, it may be possible to predict the APTT value produced by a given concentration of heparin in an individual subject from the subject's baseline APTT and hematocrit.

Relationship between concentration and anticoagulant effect of heparin in plasma of hospitalized patients: magnitude and predictability of interindividual differences.

The anticoagulant effect of heparin as reflected by the slope (S) of the relationship between heparin concentration and natural log of activated partial thromboplastin time (APTT) was determined in citrated plasma of 31 hospitalized, 21- to 80-yr-old patients (including many typical candidates for heparin therapy). Also determined were level of factors II, V, VII to XII, albumin, individual globulins, calcium, antithrombin III, fibrinogen, alpha-1-acid glycoprotein, alpha-1-antitrypsin, and alpha-2-macroglobulin and prothrombin time and hematocrit. Baseline APTT was 24.1 to 60.3 sec and S was 1.80 to 4.27 ml/u. S correlated with baseline APTT, hematocrit, total protein, functional antithrombin III, prothrombin time, beta-globulin, and factors II, VII, X, XI, and XII. A multiple linear regression equation with baseline APTT, total protein concentration, and factor XI as independent variables was "best" for predicting the S of these patients (r = 0.807, P less than 0.0001). A multiple linear regression equation with baseline APTT and hematocrit as independent variables, obtained in a previous study on healthy subjects, overpredicted the patients' S values. An equation with baseline APTT and gamma-globulins as independent variables yielded the best correlation predicted and actual S values for the combined group of patients and normal subjects (r = 0.715, P less than 0.0001). Our observations indicate that it may be possible to predict the heparin concentration-anticoagulant effect (APTT) relationship for individual patients before institution of heparin therapy.

Effect of pregnancy on the relationship between concentration and anticoagulant action of heparin.

The anticoagulant effect of heparin, as reflected by the slope of the relationship between heparin concentration and the logarithm of the activated partial thromboplastin time (APTT), was determined in citrated plasma of seven women in the third trimester of pregnancy and in 10 nonpregnant women of comparable age. Factors II, V, and VII to XII, albumin, individual globulins, antithrombin III, fibrinogen, alpha-1-acid glycoprotein, alpha-1-antitrypsin, alpha-2-macroglobulin, prothrombin time, and hematocrit were also determined. Baseline APTT (i.e., APTT without heparin) was 30.2 +/- 3.0 sec (mean +/- SD) in the pregnant women and 29.6 +/- 4.7 sec in the controls (NS). The heparin slope value was 1.68 +/- 0.46 ml/U in the pregnant women and 2.33 +/- 0.49 ml/U in the controls, showing that the anticoagulant effect of heparin is decreased in pregnancy. The prothrombin time was also decreased in pregnancy (19.1 +/- 0.8 vs 23.1 +/- 0.5 sec; P less than 0.01). Pregnancy was associated with a significant increase in the activity of factors VII, VIII, IX, and X and in the concentrations of fibrinogen, alpha-1-globulin, and alpha-1-antitrypsin. The plasma albumin concentration was decreased in the pregnant group. In both the pregnant and nonpregnant women (considered separately), the heparin slope value correlated negatively with factor XI activity (r = -0.85 and -0.71; P less than 0.05). Baseline APTT, which was consistently found to correlate with heparin slope value in previous reports on men and nonpregnant women, also showed such correlation in the nonpregnant group of the present study (r = 0.85; P less than 0.05) but not in the group of pregnant women (r = -0.54; NS). The relative heparin resistance in pregnancy in this investigation is consistent with clinical reports of increased heparin requirements during pregnancy.

Multiple-dose pharmacokinetics, pharmacodynamics, and safety of atorvastatin, an inhibitor of HMG-CoA reductase, in healthy subjects.

This study examined the pharmacokinetics, pharmacodynamics, and safety of atorvastatin, an investigational inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, in 50 healthy subjects by means of a randomized, double-blind parallel-group design. Volunteers received rising single and multiple doses of 0.5 to 80 mg/day atorvastatin (40 subjects) or placebo (10 subjects). The drug was administered once or twice daily for 14 days. Atorvastatin was well tolerated by healthy subjects. The most common adverse events reported after atorvastatin-headache and nausea-occurred as frequently after placebo. Atorvastatin peak concentration and area under the plasma concentration-time curve (AUC) values increased more than proportionally with atorvastatin dose after both single and multiple drug doses. The extent of atorvastatin absorption (AUC) was similar after once- or twice-daily drug administration. Steady-state drug concentrations were achieved by the third day of drug dosing. Mean elimination half-life values ranged from 11 to 24 hours. Atorvastatin accumulation was approximately 1.5- and 3.0-fold after once- and twice-daily administration, respectively. Atorvastatin produced dose-related reductions in total cholesterol and low-density lipoprotein cholesterol that were similar after once- and twice-daily drug administration. Reductions in mean total cholesterol and low-density lipoprotein cholesterol values ranged from 13% and 22% (2.5 mg/day) to 45% and 58% (80 mg/day), respectively (p < or = 0.0013 in comparison with placebo and with baseline over this dose range). In summary, atorvastatin doses of up to 80 mg/day were well tolerated and had significant cholesterol-lowering effects.

Pharmacodynamic effects and pharmacokinetics of atorvastatin after administration to normocholesterolemic subjects in the morning and evening.

The pharmacodynamic effects and pharmacokinetics of atorvastatin, a potent investigational inhibitor of HMG-CoA reductase, were studied in 16 normolipidemic subjects after administration of 40 mg daily for 15 days in the morning or evening. Lipid and apolipoprotein parameters were determined, and plasma atorvastatin equivalent concentrations were measured according to a validated enzyme inhibition bioassay procedure. Atorvastatin was well tolerated by the participants. Overall, mean reductions of 34% in total cholesterol, 48% in low-density lipoprotein (LDL) cholesterol, 37% in very low density lipoprotein (VLDL) cholesterol, 25% in triglycerides, 6% in apolipoprotein A-I, and 34% in apolipoprotein B were observed. Changes in lipid and apolipoprotein values were similar after morning and evening administration of atorvastatin. In contrast, studies with other HMG-CoA reductase inhibitors have consistently shown that evening administration results in larger reductions in total and LDL cholesterol than does morning administration. Rate and extent of equivalent absorption of atorvastatin were lower during evening than morning administration. Mean elimination half-life values were similar, however, suggesting that there is no diurnal variation in disposition of this drug. Pharmacokinetic differences did not correlate with effects on serum lipids.

Effect of food on the bioavailability of atorvastatin, an HMG-CoA reductase inhibitor.

To determine whether atorvastatin, a new HMG-CoA reductase inhibitor, could be administered with food in Phase II and III clinical trials, a nonblind, randomized, two-way crossover study was conducted to assess the effect of food on rate and extent of atorvastatin absorption. Sixteen healthy volunteers received single 80-mg atorvastatin capsule doses on two occasions one week apart: once after an 8-hour overnight fast and once with a medium-fat breakfast. The single 80-mg atorvastatin capsule doses were well-tolerated. Mean maximum plasma atorvastatin equivalent concentration (Cmax) and area under the concentration-time curve (AUC) values with food were 47.9% and 12.7% lower, respectively, than without food. Mean time of maximum observed concentration (tmax) and elimination half-life (t1/2) values were 5.9 and 32.0 hours, respectively, with food and 2.6 and 35.7 hours, respectively, without food. A medium-fat breakfast decreased the rate of atorvastatin absorption significantly, but had little impact on extent of drug absorption. Changes in rate of atorvastatin absorption are not expected to have a clinically significant effect, as subsequent multiple-dose clinical studies have shown that dose but not plasma atorvastatin concentration profiles correlates with lipid-lowering effects.

Tolerance and pharmacokinetics of single-dose atorvastatin, a potent inhibitor of HMG-CoA reductase, in healthy subjects.

Tolerance and pharmacokinetics after single-dose administration of atorvastatin, an investigational inhibitor of HMG-CoA reductase, were examined in 22 healthy volunteers in a three-period, partially-blinded study. Participants received capsule and solution doses of atorvastatin (0.5 to 120 mg) and placebo at weekly intervals. Atorvastatin was well tolerated at doses as high as 80 mg. The adverse event profile was similar after administration of atorvastatin capsules and placebo. Atorvastatin solution was slightly less well tolerated. The most common side effect after administration of capsules and solution was headache, followed by sporadic reports of diarrhea, flatulence, and nausea. At the 120-mg solution dose, one participant experienced mild, transient restlessness, euphoria, and mental confusion that were considered to be dose-limiting side effects. Mean concentrations of atorvastatin, maximum concentration (Cmax), and area under the concentration-time curve from time 0 to the time of the last detectable concentration (AUCo-tldc) increased with increasing dose. Plasma elimination half-life (t1/2) ranged from 14.7 to 57.6 hours. The bioavailability of atorvastatin capsules was similar to that of solution. These results suggest that atorvastatin is well tolerated after single doses as high as 80 mg, and may require administration only once daily.

Effect of age and gender on pharmacokinetics of atorvastatin in humans.

Atorvastatin is a new 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor that reduces plasma cholesterol by inhibiting cholesterol synthesis and increasing cellular uptake of low density lipoproteins. The effects of age and gender on the pharmacokinetics of atorvastatin after administration of single 20-mg tablets of atorvastatin were studied in 16 young and 16 elderly volunteers (8 men and 8 women in each age group). Plasma equivalent concentrations of atorvastatin were quantitated by a validated enzyme inhibition bioassay. Atorvastatin was well tolerated by the participants. The equivalent maximum concentration (Cmax) of atorvastatin was 42.5% higher in elderly participants (age, 66-92 years) than in young participants (age, 19-35 years) and 17.6% higher in women than in men. In addition, mean area under the concentration-time curve (AUC0-infinity) and half-life (t1/2) were 27.3% greater and 36.2% longer, respectively, in elderly adults than in young adults and 11.3% lower and 19.9% shorter, respectively, in women than in men. Because the primary site of action for HMG-CoA reductase inhibitors is the liver and atorvastatin is subject to extensive first-pass hepatic metabolism, it is unclear whether these age- and gender-related differences in the pharmacokinetics of atorvastatin will be clinically important. Results of subsequent safety and efficacy trials should help clarify the clinical significance of these pharmacokinetic differences.

Clinical pharmacokinetics of 3-deazaguanine.

3-Deazaguanine (3DG), an antipurine antimetabolite, has recently completed a phase I clinical trial at this Institute. The drug was given on a daily x 5 schedule by i.v. infusion over 0.25-2.16 h. The pharmacokinetics of 3DG during 16 courses were studied in 12 patients at doses of 200-800 mg/m2. 3DG in plasma was measured by an isocratic reverse-phase high-performance liquid chromatographic (HPLC) procedure carried out on IBM phenyl columns at 40 degrees C using 10 mM phosphate buffer (pH 7) as the mobile phase and detection at 300 nm. Plasma decay of 3DG was biexponential in all patients. The AUC correlated linearly with dose at 200-600 mg/m2 but deviated from linearity at doses greater than 600 mg/m2. The drug was cleared rapidly from plasma; at doses of 200-600 mg/m2, the mean plasma clearance was 61.64 +/- 9.97 l/h and the mean terminal-phase elimination half-life was 1.6 +/- 0.6 h. The steady-state volume of distribution (98.9 +/- 29.1 l) and distribution coefficient (1.24 +/- 0.39 l/kg) indicated extensive tissue distribution for the drug. No statistically significant difference was observed between the pharmacokinetics of 3DG on day 1 and that on day 4 as evaluated in three patients for whom complete plasma data were available on both days.

A high-performance liquid chromatographic assay for CI-973, a new anticancer platinum diamine complex, in human plasma and urine ultrafiltrates.

CI-973 is a new platinum compound with antitumor properties that is currently undergoing phase II clinical trials. A high-performance liquid chromatographic (HPLC) assay was developed and validated for ultrafiltrates of human plasma and urine to support phase I clinical trials. Plasma ultrafiltrate (0.5 ml) was extracted using C18 solid-phase cartridges. Urine was diluted 10-fold and extracted first with SAX solid-phase cartridges and then with C18 cartridges. For both matrices, the eluate from the C18 cartridges was injected directly. A Whatman PAC 10 column (4.6 x 250 mm, 10-microns particle size) and ultraviolet detection at 205 nm were used for both analyses. The mobile-phase buffer was 0.05 M sodium perchlorate (pH 2.3). The mobile-phase acetonitrile:buffer ratio, column temperature, and flow rate were 89:11 (v/v), 40 degrees C, and 2.0 ml/min, respectively, for the plasma ultrafiltrate assay and 85:15 (v/v), 50 degrees C, and 1.0 ml/min, respectively, for the urine ultrafiltrate assay. Standard curves were linear from 0.25 to 500 micrograms/ml and from 1.0 to 250 micrograms/ml for the plasma and urine assays, respectively. The accuracy of the assay lay within 4.5% of the nominal values, and the precision was 6.2%; the recovery of CI-973 varied from 79.2% to 105%. CI-973 remains stable in plasma for at least 6 h, at room temperature, in ultrafiltrates of both matrices for at least 15 days at -72 degrees C, and in water for at least 6 months at -72 degrees C.

Pharmacometric analysis of the effect of furosemide on suramin pharmacokinetics.

STUDY OBJECTIVE: To characterize the effects of furosemide on the pharmacokinetics of suramin, a renally eliminated investigational antineoplastic agent. DESIGN: Retrospective population pharmacokinetic analysis. SETTING: Government biomedical research facility. PATIENTS: Twenty-six men with hormone-refractory prostate cancer and one with adrenocortical carcinoma. INTERVENTIONS: Patients received suramin by continuous or intermittent infusion with and without concomitant furosemide. MEASUREMENTS AND MAIN RESULTS: Optimum suramin regimens were achieved by adaptive feedback control, and pharmacokinetic data were collected both in the presence and absence of furosemide. Suramin concentrations were determined by high-performance liquid chromatography (coefficient of variation < 8%). Suramin concentrations were fit to a three-compartment linear model with six coefficients and two rate inputs, which allowed furosemide to affect suramin pharmacokinetics. Individual and population parameter estimates were determined using the iterative two-stage approach. Concomitant furosemide was associated with a median decrease in total body clearance of suramin by 36% (range 0-63%, p < 0.0001). No other parameter was significantly altered, and there was no trend for change in any pharmacokinetic value with time. Suramin plasma concentrations were simulated with and without prolonged furosemide therapy in 26 patients for 12 weeks. The average suramin concentration increased by greater than 33% in 12 patients; 2 patients had a greater than 67% increase in this extreme case model. CONCLUSION: Coadministration of furosemide with suramin can cause an increase in suramin concentrations; however, due to suramin's long half-life, its rate of accumulation is very slow. Nonetheless, in individuals receiving suramin by nonadaptive control, appropriate precautions should be taken when prolonged furosemide therapy is begun.

Distribution of [14C]suramin in tissues of male rats following a single intravenous dose.

PURPOSE: Suramin has been shown to have efficacy in treatment of prostate cancer. In the present study we evaluated distribution of [14C]suramin in tissues over time following a single intravenous dose. METHODS: Male rats were given a single IV dose of 300 mg/kg [14C]suramin and sacrificed at 1 or 6 hours, or at 1, 7, 14, 28, 56, or 84 days postdose. Radioactivity remaining in tissues was measured by quantitative whole body autoradiography. RESULTS: At one hour highest tissue activity was found in blood vessel walls and caecum, followed by lung, blood, skin, preputial, thyroid, brown fat, heart, kidney, lymph nodes, liver, salivary, adrenal, Harder's and lacrimal glands, prostate, and spleen. Considerable activity was present in membranes surrounding muscle groups, bone and other organs. Relatively low activity was found in brain tissue although persistent concentration was evident in choroid plexus. High levels were present in bladder and caecum contents. Activity declined in blood but continued to increase in many tissues at later time points. Kidney reached maximum levels at 7 days postdose and retained concentration considerably higher than other tissues over the course of the study. Concentrations in tissues were persistent and considerable activity remained at 84 days postdose. Terminal elimination half life in tissues was prolonged, approximately 39 days in blood and 91 and 102 days in kidney and spleen, respectively. Uptake in prostate was highest in membranous structures separating secretory lobules. CONCLUSION: Suramin is widely distributed to tissues and appears to have particular affinity for boundary membranes surrounding organs and other structural tissue elements, possibly due to uptake by glycosaminoglycans. Antitumor activity may be related to inhibition of growth factors associated with these elements.

Pharmacokinetics of heparin V: in vivo and in vitro factors affecting the relationship between concentration and anticoagulant effect of heparin in rat plasma.

There are appreciable interindividual variations in rats of baseline activated partial thromboplastin time (APTT) and of the anticoagulant effect of heparin added to plasma (as reflected by the slope of the regression line describing the essentially linear relationship between ln APTT and heparin concentration). Determination of baseline APTT and slope value on two occasions, 7 days apart, in the same rats revealed that (unlike in humans) these characteristics were subject also to considerable intraindividual variation. To explore the possible reasons for the observed variability, the effect of citrate concentration (acid citrate solution is used as a blood anticoagulant in the collection of plasma), calcium concentration (in the recalcifying solution used to initiate coagulation), and plasma incubation time (for activating the coagulation system) was determined. All three variables had pronounced effects on the anticoagulant response to heparin. Since rat erythrocytes are almost totally impermeable to citrate, hematocrit is a determinant of plasma citrate concentration when acid citrate solution is added in constant proportion to rat blood. Accordingly, inter- and intraindividual differences in baseline APTT and slope values were measured in another experiment in which the citrate solution to plasma (rather than blood) volume ratio was held constant and blood samples were obtained 30 days apart to permit the return of hematocrit values to normal. Intraindividual variation of the coagulation characteristics was appreciably decreased under these conditions. There are important differences between rats and humans with respect to the effect of citrate concentration and plasma incubation time on baseline APTT and on the anticoagulant action of heparin, as well as with respect to the relationship between these two characteristics.

Pharmacokinetics of heparin VII: Effect of pregnancy on the relationship between concentration and anticoagulant action of heparin in rats.

The effect of pregnancy on the anticoagulant action of heparin was determined by comparing the slope of the relationship between the natural logarithm of the activated partial thromboplastin time (APTT) and heparin concentration (the heparin slope) in the plasma of pregnant and nonpregnant female inbred Lewis rats. Also determined were the prothrombin time, hematocrit, and the activities of coagulation factors II, VII, VIII, X, XI, and XII. The heparin slope was significantly decreased in pregnant rats at the 20th day of gestation but not in rats at the 10th day of gestation, indicative of a decreased anticoagulant action of heparin in late pregnancy. The hematocrit and prothrombin time were decreased, and the baseline APTT (i.e., the APTT without added heparin) as well as the activities of factors II, VII, and X were increased in pregnant rats at the 20th day of gestation. Both pregnant and nonpregnant animals showed a significant negative correlation between prothrombin time and factor II activity and a significant positive correlation between the activities of factors II and X. The effects of pregnancy in rats on heparin slope, prothrombin time, hematocrit, and factors VII, VIII, X, and XII are qualitatively the same as those in pregnant women in the third trimester. The increases in factor II activity and baseline APTT found in the rats were not observed in humans. Pregnant rats, like pregnant women, are relatively resistant to the anticoagulant action of heparin.