Distribution of [2-14C]merbarone in mice by autoradiography of whole-body cryosections.

The distribution of radiolabel in male mice was studied by autoradiography of whole-body cryosections at intervals during 24 h after i.v. injection (46.6 mg/kg) and during 4 h after oral administration (140 mg/kg) of [2-14C]merbarone. Following injection, radioactivity levels in the blood and highly vascular tissues declined to 8 h at which time only low levels were present in the systemic circulation. Only very low levels were seen in the brain and spinal cord at 0.5-3 min after dosing and levels were barely above background in autoradiograms obtained at 0.5-1 h. Radiolabel was concentrated in those regions which lack an effective blood-brain barrier particularly within the choroid plexuses. Radioactivity was rapidly taken up by the liver and kidneys and as the blood and body radioactivity levels decreased, these organs remained densely labeled. Significant biliary excretion had occurred by 30 min and the autoradiograms to 24 h showed radiolabeled compounds in the intestinal lumen. Between 1 and 8 h, the liver exhibited a stippled appearance as a result of labeling around branches of the portal vein due to enterohepatic recycling. The stippling was substantially diminished at 16 h. High levels of radioactivity were present in the kidney at 0.5-3 min after injection with both the kidney cortex and medulla initially densely labeled. At 4 h and thereafter, the radioactivity levels in the kidney were lower with most of the labeled compounds in the medulla. Accumulation in the liver and kidney was very low at 16-24 h after dosing and most of the merbarone dose had cleared from the body. Rapid absorption of merbarone occurred after oral administration with radiolabel first observed in the liver and kidney at 3-6 min after dosing. Peak levels in these organs and systemically were seen between 0.5 and 2 h. At 4 h, the radioactivity had largely cleared from the systemic circulation. The liver exhibited a stippled appearance soon after oral dosing similar to that observed following i.v. dosing affording evidence for enterohepatic recycling after i.v. administration. The relatively low systemic levels observed after oral dosing suggests that the liver binds much of the absorbed drug and its metabolites limiting the levels which reach the systemic circulation.

Intermediates of Krebs cycle correct the depression of the whole body oxygen consumption and lethal cooling in barbiturate poisoning in rat.

Rats poisoned with one LD50 of thiopental or amytal are shown to increase oxygen consumption when intraperitoneally given sucinate, malate, citrate, alpha-ketoglutarate, dimethylsuccinate or glutamate (the Krebs cycle intermediates or their precursors) but not when given glucose, pyruvate, acetate, benzoate or nicotinate (energy substrates of other metabolic stages etc). Survival was increased with succinate or malate from control groups, which ranged from 30-83% to 87-100%. These effects were unrelated to respiratory depression or hypoxia as judged by little or no effect of succinate on ventilation indices and by the lack of effect of oxygen administration. Body cooling of comatose rats at ambient temperature approximately 19 degrees C became slower with succinate, the rate of cooling correlated well with oxygen consumption decrease. Succinate had no potency to modify oxygen consumption and body temperature in intact rats. A condition for antidote effect of the Krebs intermediate was sufficiently high dosage (5 mmol/kg), further dose increase made no odds. Repeated dosing of succinate had more marked protective effect, than a single one, to oxygen consumption and tended to promote the attenuation of lethal effect of barbiturates. These data suggest that suppression of whole body oxygen consumption with barbiturate overdose could be an important contributor to both body cooling and mortality. Intermediates of Krebs cycle, not only succinate, may have a pronounced therapeutic effect under the proper treatment regimen. Availability of Krebs cycle intermediates may be a limiting factor for the whole body oxygen consumption in barbiturate coma, its role in brain needs further elucidation.

A phase II trial of merbarone (NSC 336628) in the treatment of recurrent epithelial ovarian carcinoma. A Gynecologic Oncology Group Study.

BACKGROUND: Patients with recurrent epithelial ovarian carcinoma who progress through a cisplatin-based regimen or recur less than 6 months after discontinuing cisplatin, have limited therapeutic options. The Gynecologic Oncology Group conducted a Phase II trial of merbarone in this patient population. METHODS: Twenty-seven patients with recurrent epithelial ovarian carcinoma who had previously received one prior cisplatin-based regimen were scheduled to receive 1000 mg/m2 of merbarone by continuous intravenous infusion through a central line each day for five days every four weeks. RESULTS: Of the 27 patients entered, one was ineligible because of wrong primary, and two never received the drug, leaving 24 patients evaluable for toxicity. Twenty of 24 were evaluable for response. The regimen was well tolerated with only one episode each of GOG grade 3 leukopenia (4%) or grade 4 granulocytopenia (4%). There was one episode (4%) of GOG grade 3 gastrointestinal toxicity. Prior to increasing the infusate concentration to 4 mg/ml, there was one episode (4%) of altered mental status which, in retrospect, may have been secondary to iatrogenic hyponatremia. There were two partial responses (10%) (95% confidence interval 1.2-31.7%). CONCLUSIONS: Merbarone exhibited minimal activity at this schedule in this pretreated group of patients with epithelial ovarian carcinoma.

Phase II trial of merbarone in pancreatic carcinoma. A Southwest Oncology Group study.

Twenty-nine patients with advanced pancreatic adenocarcinoma were treated with merbarone, utilizing a daily intravenous schedule for 5 days. Only two partial responses of short duration were observed. The major toxicities were renal, with an increase in creatinine or proteinuria in 17 patients, and mild to moderate nausea and vomiting seen in 22 patients. Merbarone in this dose and schedule has minimal activity in pancreatic cancer.

Effects of preparing and ligand-binding methods of small unilamellar liposomes on their blood elimination and tissue distribution in rats.

The effects of two methods of preparing small unilamellar vesicles (SUV) (detergent removal or sonication) on their in vivo elimination and tissue distribution was investigated in rats. The SUV prepared by either method had the same size distribution and lipid composition (egg yolk phosphatidylcholine/cholesterol/dipalmitoyl phosphatidylethanolamine or palmitic acid = 20/10/0.3, molar ratio). Three types of SUV made by either method were prepared. These contained one of three different surface ligand-binding functional groups (N-hydroxysuccinimide ester of palmitic acid, NHSP; glutaraldehyde-phosphatidylethanolamine, GA-PE; N-[4-(p-maleimidophenyl)butyryl]phosphatidylethanolamine, MPB-PE). SUV prepared by detergent removal were eliminated slowly from the circulation, and exhibited a low liver uptake and little leakage of [3H]inulin. There was no significant difference in elimination of the NHSP-SUV, GA-SUV or MPB-SUV prepared by detergent removal and their tissue distribution was similar. In contrast, the sonicated SUV were eliminated from the circulation much more rapidly mainly by liver uptake. The leakage of [3H]inulin from sonicated SUV into urine was relatively large. When sonicated control-SUV were prepared in the presence of the antioxidant, alpha-tocopherol (alpha-T-SUV), which reduces lipid peroxidation during sonication, the alpha-T-SUV were eliminated slowly with only a low liver uptake. Our results indicate that the rapid elimination and greater liver uptake of sonicated SUV is partly due to lipid peroxidation during preparation. These findings have relevance to the use of liposomes as a drug delivery system.

Phase II trial of merbarone in soft tissue sarcoma. A Southwest Oncology Group study.

Thirty-seven patients with advanced soft tissue sarcoma were treated with merbarone utilizing a daily intravenous schedule for five days. Only one partial response was observed in the thirty-three evaluable patients. The major toxicities were renal, with elevation of creatinine and/or proteinuria, and gastrointestinal, with mild to moderate nausea and vomiting. Merbarone in this dose and schedule has minimal activity in soft tissue sarcoma.

Phase II evaluation of merbarone in renal cell carcinoma.

The Southwest Oncology Group (SWOG) studied the response rate and toxicity of merbarone (1,000 mg/m2 IV continuous infusion days 1-5, q 21 days) in patients with advanced metastatic renal cell carcinoma. Among 36 eligible patients, there was one partial response for a response rate of 3% (95% C.I. 0.1-15%). There were no mixed responses. There were no treatment related deaths or adverse drug reactions. Significant anemia, diarrhea, and hypercalcemia were observed. Mild to moderate degrees of malaise/fatigue/lethargy, dizziness/vertigo, hyperglycemia, creatinine increase, nausea, vomiting, weight loss, pedal edema, dyspnea, and granulocytopenia were noted. Merbarone does not have significant activity as a single agent in advanced renal cell carcinoma.

Evaluation of merbarone (NSC 336628) in disseminated malignant melanoma. A Southwest Oncology Group study.

Merbarone, NSC 336628, is an investigational anticancer drug with activity against experimental animal tumors including melanoma. This paper presents results of a Phase II clinical study of merbarone in patients with biopsy proven stage IV malignant melanoma without prior chemotherapy and with no evidence of CNS involvement. Thirty-five patients with median age 58 (range 27-81), with performance status 0-2 were treated with merbarone 1000 mg/m2/day for five days by intravenous continuous infusion repeated every 3 weeks. All patients (21 males and 14 females) were evaluable for toxicity. Two patients were not evaluable for response having been removed from protocol treatment due to toxicity and received other treatment during the first course of chemotherapy. Among the evaluable patients there was one complete response in a supraclavicular lymph node lasting four months and one partial liver response lasting three months. The remaining thirty-one patients were non-responders. Of these one had a stable disease lasting 21 months. The overall objective response rate was 6% (2/35) with a 95% confidence interval of 1%-19%. Twenty-six of the 35 patients have died. The estimated median survival of the entire group was 9 months with a 95% confidence interval six to eleven months. Renal toxicity was dose-limiting and manifested as increasing serum creatinine (54% of patients), proteinuria (51%) and hematuria (9%). One patient experienced grade 4 creatinine increase, proteinuria and acute renal failure. Other toxicities included nausea (71%), vomiting (51%0, malaise (23%), weakness (20%), alopecia (17%), diarrhea (17), anorexia (14%) transaminase (SGOT, SGPT) increase (14%), constipation (14%), alkaline phosphatase or 5'nucleotidase increase (9%), and fever (9%). Hematologic toxicity (granulocytopenia, leukopenia, and anemia) was generally mild and infrequent (29%, only one patient had grade 4 granulocytopenia). Overall 9 patients (26%) had at least one grade 3 toxicity. We conclude that merbarone at this dose and schedule has detectable but minimal activity in the treatment of metastatic malignant melanoma and given the significant renal toxicity this schedule does not merit further evaluation in this disease.

A retrospective survey of anaesthesia in horses with colic.

The purpose of this survey was to identify complications occurring in horses with colic during anaesthesia and recovery from anaesthesia; and to determine any relationships between these complications and drugs used for induction or maintenance of anaesthesia. Two hundred and thirty nine horses were anaesthetised on a total of 250 occasions for colic surgery between January 1985 and May 1987. Of these, 189 recovered from 200 anaesthetic episodes. Most horses received xylazine and guaifenesin with either thiobarbiturate (68 per cent) or ketamine (24 per cent) and anaesthesia was maintained with either halothane (51 per cent), isoflurane (43 per cent), or first halothane then isoflurane (6 per cent). Sixty nine per cent also received an opioid. Hypotension or tachycardia were recorded in 15 and 13 per cent of anaesthesias, respectively. Arterial PO2 was less than 13.3 kPa in 17 per cent of 175 anaesthesias. None of these complications was associated with a specific anaesthetic agent. Hypertension was recorded in 11.5 per cent of anaesthesias and occurred more frequently during isoflurane anaesthesia (P < 0.05). The mean duration of anaesthesia was 126 mins (range, 50-270 mins), and was not different for horses receiving thiobarbiturate or ketamine, halothane or isoflurane. The time taken to stand after anaesthesia recorded on 149 occasions and was 63 +/- 24 mins (range, 15-135 mins). This was not different for the different anaesthetic agents. Horses that were excited or had difficulty standing up during recovery had a significantly longer duration of anaesthesia (165 +/- 51 mins) (P < 0.05) but no specific anaesthetic agent was involved. Of the 189 horses, 148 (75 per cent) survived and were discharged from the hospital. Horses that did not survive had a significantly increased prevalence of anaesthetic complications, and longer durations of anaesthesia.