Equivalent single-dose pharmacokinetics of two different dosing methods of prolonged-release fulvestrant ('Faslodex') in postmenopausal women with advanced breast cancer

PURPOSE

To compare the pharmacokinetics of two different dosing methods of fulvestrant ('Faslodex'), an estrogen receptor antagonist with no known agonist activity, for the treatment of advanced breast cancer.

METHODS

Postmenopausal women with advanced breast cancer were randomly assigned to receive a single 5-ml intramuscular injection of 250 mg fulvestrant, or two 2.5-ml intramuscular injections with a total of 250 mg fulvestrant. Blood samples were taken for pharmacokinetic analysis up to 28 days after injection.

RESULTS

Plasma concentrations of fulvestrant were measurable up to 28 days after both dosing methods. The concentration-time profiles were relatively shallow, spanning an approximate threefold range from 3 h after dosing to Cmin measured on day 28. Peak plasma concentrations (Cmax) of fulvestrant occurred between 1 and 11 days after dosing, with mean Cmax values of 6.0 and 6.2 ng/ml following one 5-ml injection and two 2.5-ml injections, respectively. The plasma concentration-time profiles were very similar in terms of duration and concentration, and overall exposure to fulvestrant was similar in both dosing groups (the ratio of the AUC(0-28) of the single-injection group to that of the double-injection group was 1.01; 95% confidence interval 0.68-1.51).

CONCLUSION

This study found no evidence of any pharmacokinetic difference between one 5-ml injection and two 2.5-ml injections. The two methods can be used interchangeably, depending on which is more convenient in any particular clinical setting.

Immunohistochemical localization of the neural cannabinoid receptor in rat brain

The cannabinoid receptor family consists of two inhibitory G-protein-coupled receptors, CB1 and CB2. CB1 is distributed primarily in neural tissue, whereas CB2 is distributed predominantly in immune cells. The distribution of cannabinoid receptors in neural tissue has been demonstrated by using ligand binding autoradiography with CP55,940, a high-affinity cannabinoid receptor ligand, and in situ hybridization. However, the localization of CB1 within individual cells in the brain remains to be defined. In the present study, domain-specific polyclonal antibody to amino acids 83-98 of CB1 was used to define the expression of the neural cannabinoid receptor at the histochemical level. The use of CB1-specific antiserum is advantageous in view of recent reports that CB2 also is expressed in the brain and binds CP55,940. Thus, utilization of anti-CB1 antiserum would allow for the specific detection of CB1 protein expression. The regional staining pattern for CB1 in rat brain was consistent with that reported for CB1 using ligand binding autoradiography and in situ hybridization. Intense immunoreactivity was present in the hippocampal formation, the basal ganglia, and the molecular layer of the cerebellum. Moderate immunohistochemical staining was observed in the olfactory bulb, piriform cortex, cerebral cortex, and the granular layer of the cerebellum. In addition, immunoreactive staining was concentrated on afferent projections and dendritic processes of neuronal cells and was present within cell bodies and on cell surfaces. These data indicate that the anti-CB1 antibody is a sensitive probe for the unequivocal histological discrimination of CB1 protein expression.

Changes in red blood cell methotrexate pharmacology and their impact on outcome when cytarabine is infused with methotrexate in the treatment of acute lymphocytic leukemia in children: a pediatric oncology group study

Since it is unclear whether methotrexate and cytarabine are synergistic or antagonistic in the treatment of acute lymphoblastic leukemia, the Pediatric Oncology Group studied the prognostic significance of a potential interaction between these agents. RBC methotrexate concentrations were compared from 140 patients at lower risk of relapse randomized to two treatment groups: one receiving six methotrexate infusions with overlapping cytarabine; the other, six methotrexate infusions alone. Samples from 248 patients from all risk groups were studied to determine whether patients with extremely low RBC methotrexate concentrations had inferior outcomes. Among low-risk patients studied 3 weeks after the sixth infusion, median RBC methotrexate concentrations were 0.13 nmol/ml RBCs (n = 71) for the methotrexate-only group and 0.02 nmol/ml RBCs (n = 69) for the methotrexate/cytarabine-treated low-risk patients, P < 0.001 by the two-sided Wilcoxon test. For low- and high-risk patients receiving methotrexate/cytarabine infusions, event-free survival at 1 and 3 years after RBC sampling was 97 +/- 2% and 90 +/- 3% for patients with concentrations greater than the median, and 88 +/- 3% and 78 +/- 4% for those with concentrations at or below the median. Log rank comparisons of event-free survival in the first year and overall yielded P = 0.005 and P = 0.04, respectively. Cytarabine altered methotrexate pharmacology when the drugs were infused together. Patients whose levels were extremely low had an adverse prognosis. Although this study could not assess efficacy of the methotrexate/cytarabine combination, it appears that concurrent administration is not optimal.

Anandamide inhibits macrophage-mediated killing of tumor necrosis factor-sensitive cells

Anandamide (arachidonoylethanolamide) was shown to inhibit macrophage-mediated killing of tumor necrosis factor-sensitive murine L929 fibroblasts. Scanning electron microscopy (SEM) demonstrated that L929 cells, co-cultured with Propionibacterium acnes (P. acnes)-activated peritoneal macrophages from mice treated with vehicle, were either disrupted or had surface abnormalities and numerous punctate lesions. In contrast, L929 cells co-cultured with macrophages from mice receiving P. acnes in concert with Anandamide (20 mg/kg-80 mg/kg) or the exogenous cannabinoid delta-9-tetrahydrocannabinol (THC; 80 mg/kg) did not exhibit ultrastructural abnormalities. Cytotoxicity assays were performed in parallel with SEM in order to determine whether ultrastructural observations correlated with target cell killing as measured by release of radiolabel from L929 target cells. P. acnes-activated macrophages from vehicle-treated mice elicited 41% specific release of radiolabel from [51Cr]-labeled L929 cells. In contrast, macrophages from animals treated with P. acnes and with 20, 40, or 80 mg/kg Anandamide exhibited 38%, 25%, or 28% specific release of radiolabel, respectively. Similarly, macrophages from animals treated with P. acnes and with 80 mg/kg THC exhibited 21% specific release of radiolabel. In vitro cytotoxicity studies using radiolabeled L929 target cells and conditioned medium from RAW264.7 murine macrophage-like cells allowed for determination of the time interval over which Anandamide exerted its inhibitory effect. Maximal inhibition of target cell killing occurred when conditioned medium was obtained from macrophages exposed to Anandamide for 1 hr prior to activation. In contrast, conditioned medium from THC-treated macrophages exerted its maximal inhibition of target cell killing when obtained from RAW264.7 cells pretreated for 24hr-48hr prior to activation. These results indicate that Anandamide and THC exert a similar inhibition of killing of TNF-sensitive target cells. However, the time interval over which these two substances elicit their suppressive effect differs.

The disposition and metabolic fate of 14C-meropenem in man

1. The metabolism and pharmacokinetics of 14C-meropenem were studied in five volunteers who received 0.5 g (40 microCi) of the radiolabelled drug by i.v. infusion. 2. The maximum concentration of drug in plasma was 27 +/- 2 micrograms/ml (70 microM) corresponding to 98% of plasma radioactivity at the end of a 30 min infusion. The elimination half-life for meropenem in plasma was 1 h and meropenem remained the major radioactive component up to 6 h, but represented a decreasing proportion of the plasma radioactivity with time. One metabolite (the ring-open lactam) accounted for most of the remaining plasma radioactivity. The maximum concentration of metabolite was 1 +/- 0.1 micrograms/ml and the concentration of total radioactivity decreased to 2% of the peak value by 8 h. 3. Over the 5 days of the study, urinary excretion of radioactivity accounted for 99 +/- 0.5% dose, most of which was recovered in the first 8 h. There was negligible excretion in faeces. 4. Structural confirmation of the drug-related components in urine was accomplished by h.p.l.c.-mass spectrometry. Meropenem accounted for 71 +/- 2% dose of 14C and the ring-open lactam metabolite for most of the remainder, no other metabolites were detected. 5. Meropenem was the major radioactive component in urine up to 8 h after dosing and is therefore remarkably stable to human renal dehydropeptidase (DHP-1) compared with other carbapenems in clinical use.

Red blood cell methotrexate and folate levels in children with acute lymphoblastic leukemia undergoing therapy: a Pediatric Oncology Group pilot study

We enrolled children with acute lymphoblastic leukemia (ALL) in a Pediatric Oncology Group (POG) pilot study to monitor erythrocyte (RBC) methotrexate (MTX) and folate (F) levels before and during treatment. The mean value for RBCF at diagnosis was 0.86 +/- 0.46 nmol/ml RBC in the 214 patients who achieved remission and 1.21 +/- 0.74 nmol/ml RBC in the 10 patients who did not (P = 0.020). Folate levels tended to increase during remission induction, but they dropped following an intensive consolidation with methotrexate to levels that were sustained throughout chemotherapy treatment. Methotrexate levels reached mean values of approximately 0.15 nmol/ml RBC at the end of an intensive methotrexate consolidation, then fell to levels that were sustained throughout maintenance therapy. There was a weak correlation between improved event-free survival and higher RBCMTX levels after consolidation, but no correlation was found between improved survival and the level of RBCMTX or RBCF during maintenance therapy. A larger study with more complete data is needed to determine whether RBCMTX or RBCF might be useful in predicting event-free survival in patients with ALL.

beta-Hydroxybutyrate: a urinary marker of imipenem induced nephrotoxicity in the cynomolgus monkey detected by high field 1H NMR spectroscopy

The use of 1H NMR as a complement to conventional clinical chemistry and histopathology resulted in the detection of hitherto unsuspected changes in urine composition as a result of imipenem induced nephrotoxicity. Large quantities of beta-hydroxybutyrate, as well as other ketone bodies were detected, indicating a disruption of energy metabolism. beta-Hydroxybutyrate may provide a useful non-invasive marker for imipenem toxicity.

The disposition and metabolism of meropenem in laboratory animals and man

The disposition and metabolism of meropenem were studied in rats, dogs and cynomolgus monkeys following intravenous administration of [14C]-meropenem, and also in man following intravenous infusion of meropenem. Following intravenous administration to rats and dogs, radioactive material was very rapidly and widely distributed in the tissues, with highest levels detected in the kidney and other highly perfused organs. Concentrations in all tissues decreased rapidly with time. The plasma elimination half-life of meropenem was approximately 6 min in rats, 30 min in monkeys, 45 min in dogs and 1h in man. In all species 90-100% of the dose was excreted via the urine within 24 h. Analysis of the radioactive material in urine from animal studies showed that the major components were unchanged compound (36-43%) and a metabolite corresponding to a beta-lactam ring-opened form (34-51%). In man, approximately 65% of the dose was excreted in urine as unchanged meropenem and most of the remainder as the ring-opened metabolite. As part of the preclinical safety evaluation programme of meropenem, the distribution, metabolism and excretion of [14C]-meropenem were studied in the rat, dog and cynomolgus monkey after single intravenous administration at dose levels corresponding to the lower doses used in toxicity studies. In addition, the metabolism and pharmacokinetics of meropenem in human volunteers were studied.

The disposition and metabolism of the synthetic prostaglandin fluprostenol (ICI 81,008) in the horse

1. Following single intramuscular doses of [14C]fluprostenol (0.5--2.4 micrograms/kg) to three female horses and to three gelded male horses, radioactivity was present in the plasma within 5 min; peak concn. (0.32--1.30 ng/ml fluprostenol equiv.) occurred 5 to 90 min after injection. Radioactivity was still present in the plasma of the females after three days. About 88% of fluprostenol is bound to plasma proteins. 2. Radioactivity was present in the parotid saliva of the gelded male horses within 10 min. Peak concn. (45--91 pg/ml fluprostenol equiv.) occurred from 5 min to 1 h after injection. Saliva : plasma concn. ratios varied inversely with saliva flow rate and limiting ratios were 0.33 and 0.41 for the combined results of two experiments on each of two male horses; the calculated value is 0.46 Chromatography indicated that the majority of plasma and saliva radioactivity was [14C]fluprostenol. 3. Excretion of radioactivity in the urine was rapid and virtually complete 12 h after dosing. The total radioactivity excreted in urine by the female horses was 45% of the dose (96 h) and by the gelded male horses 53% (30 h). About 30% of the radioactivity present in the urines was unchanged fluprostenol. 4. Faecal excretion, which was substantially complete after 2 days, accounted for 32% of the radioactivity administered to the female horses. 5. Tissue conc. of radioactivity in the female horses at four days were below the limits of detection (90 pg/g), but 0.2--0.9% of the dose was detected at the site of injection.

The absorption and elimination of ICI 74,917 in man

1 The pharmacokinetics of ICI 74,917 were studied in both asthmatic patients and normal volunteers. 2 The tritiated compound was administered to the lungs by inhalation from an aerosol and a bronchoscope, and by intravenous, oral and buccal routes. Radioactivity was measured in plasma, urine, faeces, sputum and exhaled air. 3 After bronchoscopic administration 63% of the available dose was absorbed; after aerosol administration 8% was absorbed from the lung and more than 50% swallowed. 5 Intravenous studies indicated that the drug is excreted in the bile and urine in the ratio 2:1. 5 Minimal oral and no buccal absorption occurred. 6 There was no evidence of tritium exchange or drug metabolism. 7 The mean terminal half-life following administration by all route was 16.1 hours. However, the majority of the dose was rapidly excreted. 8 Aerosol administration is the method of choice for the clinical use of ICI 74,917.