Inter- and intrapatient variability in etoposide kinetics with oral and intravenous drug administration

The objective of this study was to accurately determine the within- and between-patient variability in etoposide pharmacokinetics for i.v. and p.o. administered drug. Inter-and intrapatient variability in systemic etoposide exposure was measured following i.v. and p.o. drug administration using stable isotope dilution methodology. Seven patients received 50 mg of etoposide by both p.o. and i.v. routes of administration on three separate occasions 1 month apart. Etoposide plasma concentrations following p.o. and i.v. drug administration were quantitated by liquid chromatography-mass spectrometry for each route of administration. The area under the plasma etoposide concentration versus time curve, plasma etoposide clearance, and etoposide plasma half-life were calculated for each dose of drug. Kinetic measurements following i.v. and p.o. drug administration were compared. The within-patient variation in the areas under the plasma etoposide concentration versus time curves following i.v. drug administration was minimal [coefficient of variation (CV) = 9.3%]. Within-patient variability was increased 2.4-fold with oral drug administration (intrapatient CV = 22.2%). Between-patient variability was roughly three times as great as within-patient variability (interpatient i.v. CV = 28.4%; interpatient p.o. CV = 58.3%). Mean etoposide bioavailability at a dose of 50 mg was 64.6%, again with greater interpatient than intrapatient variability (34.8 versus 22.6%). Greater variation in drug toxicity is expected with p.o. compared with i.v. etoposide use. Administration of repeated doses of etoposide to the same patient should produce less variation in toxicity than between-patient dosing.

Paclitaxel, UFT, and calcium folinate in metastatic breast cancer

This is a phase I dose-escalation study of uracil and tegafur (in a molar ratio of 4:1 [UFT]) administered in combination with calcium folinate and paclitaxel in metastatic breast cancer. This trial was initiated to 1) determine the maximum tolerated dose and dose-limiting toxicities of UFT plus calcium folinate (Orzel) administered three times per day for 21 days in combination with paclitaxel; and 2) define the appropriate dose for phase II testing. Thus far, 14 patients have been accrued to three dose levels. Two patients developed dose-limiting toxicities at dose level 3. One patient experienced grade 3 hypotension. A second patient experienced grade 3 vomiting, grade 4 diarrhea, and severe hand-foot syndrome. Two partial responses and one complete response have been observed. Early trends suggest that this regimen is active in metastatic breast cancer and is well tolerated. Completion of this study is anticipated in 1999.

A pilot study of protracted low dose cisplatin and etoposide with concurrent thoracic radiotherapy in unresectable stage III nonsmall cell lung cancer

PURPOSE

A Phase II study to evaluate the response rate and toxicity of daily protracted cisplatin and etoposide with concurrent chest irradiation in patients with locally advanced, unresectable nonsmall cell lung cancer (NSCLC).

METHODS AND MATERIALS

Twenty-one patients with histologically confirmed locally advanced inoperable NSCLC (Stage IIIA or IIIB) were entered on study. Radiotherapy consisted of 50.4 Gy in 1.8 Gy fractions followed by a 10 Gy boost in 2 Gy fractions. Chemotherapy included the following: Cisplatin was given at 5 mg/m2 i.v. Monday-Friday before RT weeks 1-6. Etoposide was given at 25 mg/m2 i.v. M-F weeks 1, 2, 5, and 6, with 50 mg/m2 p.o. daily on the same weekends. Because of severe myelosuppression in the first two patients, etoposide only was subsequently changed to 20 mg/m2 i.v. M-F weeks 1, 2, 5, and 6.

RESULTS

Twenty patients were eligible and evaluable. The overall response rate was 65% (95% confidence interval 41-85%). The median progression-free survival was 43 weeks. The median overall survival was 50.2 weeks with a 1-year survival rate of 45%. Five patients (25%) developed severe radiation pneumonitis, leading to early closure of the study.

CONCLUSIONS

Combining daily protracted cisplatin and etoposide with concurrent thoracic irradiation in patients with locally advanced unresectable NSCLC yields a high overall response rate and a median survival that is at least comparable to other combined modality trials. However, future studies using protracted radiosensitizing chemotherapy should be approached cautiously in light of the high incidence of severe radiation pneumonitis encountered in this trial.

Somatostatin analogue phase I trials in neuroendocrine neoplasms

To further investigate the antineoplastic efficacy and safety of somatostatin analogues, 2 trials were performed. Octreotide, SMS 201-995 (Sandostatin), was escalated in doses ranging from 1,500 micrograms to 6,000 micrograms daily in 14 patients with carcinoid. Somatuline, (BIM 23014C, Angiopeptin, Lanreotide) was given in doses ranging from 2,250 micrograms to 9,000 micrograms daily to 13 neuroendocrine patients (6 carcinoid, 2 atypical carcinoid, 3 pancreatic islet cell and 2 small cell lung cancer patients). All patients successfully completed dose escalations without significant adverse effects and were evaluable for toxicity. The dose limiting side-effect of octreotide was the injection volume. No dose limiting adverse effects have been observed with somatuline. Carcinoid syndrome symptoms were better controlled with higher octreotide doses. Thirteen patients were evaluable for octreotide's antitumor efficacy with a partial response observed in 4 (31%), stable disease in 2 and progressive disease in 7 patients. Radiographic changes of increased tumor necrosis occurred in 5 patients and was independent of response. Somatuline resulted in a partial response in 4 patients (2 carcinoids, 1 gastrinoma and 1 small cell lung cancer) (31%), stable disease in 1 atypical carcinoid, and progressive disease in 8 (4 carcinoid, 1 atypical carcinoid, 2 islet cell and 1 multi-drug resistant small cell lung cancer). Six of the 8 carcinoid patients had radiographic changes of increased necrosis. Dose escalation of somatostatin analogues is well tolerated and may be associated with antitumor activity in some neuroendocrine neoplasms.

Chronic oral etoposide in the treatment of lung cancer

Etoposide is used commonly to treat both small cell lung cancer and non-small cell lung cancer. It is usually administered intravenously over 3 to 5 consecutive days, and usually given in combination with cisplatin. Preclinical cellular and clinical pharmacokinetic studies have demonstrated that etoposide is schedule-dependent and is optimally administered at low doses over prolonged periods of time. Recent early phase clinical trials have demonstrated that oral etoposide can be administered safely for 14 to 21 consecutive days. This schedule has demonstrated outstanding activity in patients with both recurrent and previously untreated small cell lung cancer. Activity against non-small cell lung cancer has also been reported; response rates are similar to those seen with the most active single agents used in the treatment of the disease. Chronic oral etoposide also has the advantages of outpatient convenience and tolerable side effects. This overview discusses the role of chronic oral etoposide in the management of small cell lung cancer and non-small cell lung cancer. The scientific rationale, results of early phase clinical trials, ongoing research, and future directions regarding the chronic administration of this important antineoplastic drug are also reviewed.

Metabolism and excretion of etoposide in isolated, perfused rat liver models

The clearance of etoposide and formation of etoposide glucuronide have been measured in an isolated, perfused rat liver model to evaluate the effect of impaired hepatic function on etoposide kinetics. Hepatocellular injury was produced by pretreatment of rats with allyl alcohol or carbon tetrachloride; ligation of the bile duct simulated obstructive biliary disease. Etoposide clearance (3.59 +/- 1.06 ml/min) was reduced by both carbon tetrachloride (2.07 +/- 0.64 ml/min; P = 0.05) and allyl alcohol treatment (2.14 +/- 0.62 ml/min; P = 0.05). Biliary obstruction also impaired etoposide clearance but to a lesser extent than hepatocellular injury (2.47 +/- 0.69 ml/min; P = 0.20 versus control). In both hepatocellular and obstructive models, direct biliary etoposide excretion decreased. The metabolic clearance of etoposide to its glucuronide declined by 36% in the hepatotoxin models but was not decreased by biliary obstruction. Following hepatic injury, there is a reduction in the metabolism and excretion of etoposide by the liver. This effect is most marked on biliary drug excretion. Obstructive biliary disease does not significantly alter etoposide glucuronidation. Since most cancer patients have increased bilirubin on the basis of obstructive disease, little or no etoposide dose alteration will be needed. However, in the patient with significant hepatocellular injury, impaired etoposide clearance will be more pronounced, and etoposide dose alterations may be needed.

Identification of etoposide glucuronide as a major metabolite of etoposide in the rat and rabbit

Isolated livers from male Sprague-Dawley rats were perfused at 20 ml/min for 3 h at 37 degrees C with 100 ml of an oxygenated, recirculating solution of 20% rat blood in Krebs bicarbonate buffer containing 20 micrograms/ml [3H]etoposide. Ninety % of administered radioactivity was eliminated in bile over a 3-h collection period. The clearance of etoposide was 3.56 ml/min indicating that, in the rat, it is not highly extracted. Its clearance is, therefore, independent of hepatic blood flow. Etoposide was both excreted into the bile and metabolized by the liver. Perfusate and bile samples analyzed by reverse-phase high-performance liquid chromatography techniques were found to contain three peaks of radioactivity. Positive and negative ion fast atom bombardment mass spectrometry identified the first two peaks as etoposide glucuronides and the third peak as parent drug. Following the i.v. administration of etoposide to rabbits, etoposide glucuronide was also identified in rabbit urine. The recovery of etoposide both from rabbit urine and rat bile was increased by preincubation with glucuronidase. However, the glucuronides were relatively resistant to the action of glucuronidase and showed varying sensitivity to the type of glucuronidase and the reaction conditions used. These studies document the presence of etoposide glucuronide as an etoposide metabolite in two mammalian species and suggest that previous clinical studies using beta-glucuronidase to quantitate glucuronide formation may have underestimated this metabolite due to its relative resistance to some glucuronidase preparations.

Effect of cimetidine and ranitidine on the metabolism and toxicity of hexamethylmelamine

In a rat model, doses of 20-120 mg/kg of cimetidine prolonged in a dose-related manner the half-life of hexamethylmelamine by 29%-80%, while doses of 1-25 mg/kg of ranitidine did not. Administration of 120 mg/kg of cimetidine with a single 350-mg/kg dose of hexamethylmelamine increased toxicity from LD30 to LD75 (P = 0.005). When combined with 25 mg/kg of ranitidine, a statistically insignificant (P = 0.16) 15% increase in hexamethylmelamine toxicity was noted. These studies indicate that cimetidine but not ranitidine increases the toxicity of hexamethylmelamine through inhibition of microsomal metabolism.

Implications of hypercalcemia with respect to diagnosis and treatment of lung cancer

This study had two objectives. The first was to determine if hypercalcemia presents as an isolated finding in patients with lung cancer prior to the development of abnormalities on chest radiography. The second was to correlate the presence of hypercalcemia with survival after surgical therapy. A review of clinical material over a seven-year period yielded 67 patients with diagnoses of hypercalcemia and lung cancer. No patient presented with surgically curable lung cancer associated with hypercalcemia. A review of the literature disclosed only four cases in which a putative cure occurred in the presence of hypercalcemia. Review of the clinical material and the literature revealed no instance in which hypercalcemia per se led to the diagnosis of clinically occult lung cancer. Hypercalcemia was almost always associated with large tumor masses. Median survival after the discovery of hypercalcemia complicating carcinoma of the lung was one month.

Trimethoprim interferes with serum methotrexate assay by the competitive protein binding technique

Administration of Bactrim (a combination of trimethoprim and sulfamethoxazole) to a patient who also was receiving methotrexate caused a significant increase in apparent plasma methotrexate concentrations as determined by competitive protein binding assay with use of dihydrofolate reductase (EC 1.5.1.3) from Lactobacillus casei as the binding protein. This spurious increase was caused by trimethoprim in the patient's plasma. A plasma trimethoprim concentration of 0.1 mg/L inhibited binding of radiolabeled methotrexate to dihydrofolate reductase by 50%. In contrast, radioimmunoassay for methotrexate was not affected by concomitant administration of trimethoprim. The competitive protein binding assay for methotrexate should not be used in patients being treated with Bactrim or Septra (a similar combination). However, the L. casei competitive protein binding assay technique can be used to assay plasma trimethoprim concentrations with sensitivity to 0.02 mg of trimethoprim per liter.

Trimethoprim interferes with serum methotrexate assay by the competitive protein binding technique

Administration of Bactrim (a combination of trimethoprim and sulfamethoxazole) to a patient who also was receiving methotrexate caused a significant increase in apparent plasma methotrexate concentrations as determined by competitive protein binding assay with use of dihydrofolate reductase (EC 1.5.1.3) from Lactobacillus casei as the binding protein. This spurious increase was caused by trimethoprim in the patient's plasma. A plasma trimethoprim concentration of 0.1 mg/L inhibited binding of radiolabeled methotrexate to dihydrofolate reductase by 50%. In contrast, radioimmunoassay for methotrexate was not affected by concomitant administration of trimethoprim. The competitive protein binding assay for methotrexate should not be used in patients being treated with Bactrim or Septra (a similar combination). However, the L. casei competitive protein binding assay technique can be used to assay plasma trimethoprim concentrations with sensitivity to 0.02 mg of trimethoprim per liter.

Allopurinol kinetics

A spectrophotometric assay for measuring allopurinol and oxipurinol has been developed which can detect as little as 5 X 10(-8) M of each in serum and urine. With this assay, serum disappearance characteristics of intravenous and orally administered allopurinol have been investigated in man. Serum concentrations of both allopurinol and oxipurinol reach levels above 1 X 10(-5) M within minutes of intravenous administration and within 1 or 2 hr of oral administration of 300 mg allopurinol. Patients receiving 300 mg allopurinol daily show a mean serum concentration of 3 X 10(-5) M oxipurinol (range, 0.9 to 9 X 10(-5) M). Serum half-lives of allopurinol and oxipurinol were 39 +/- 11 min and 13.6 +/- 2.8 hr, respectively. Estimates of renal clearance were 13.6 and 18.9 ml/min for allopurinol and 23.2 and 30.6 ml/min for oxipurinol in 2 patients studied. The metabolic conversion of allopurinol to oxipurinol in man does not appear to be altered by long-term therapy with allopurinol, which suggests that this conversion takes place by way of an enzymatic reaction not strongly inhibited by either substrate or product. These results suggest the possibility of a nonxanthine oxidase enzymatic pathway for this conversion.