Low Prevalence of Screen-Detected Colorectal Cancer in an Average-Risk Population: The New Normal.

Prior studies have reported the prevalence of colorectal cancer (CRC) in average-risk screening population ages 50-75 to be 0.7%-1.0%.1,2 However, no estimates from studies enrolling individuals undergoing screening colonoscopy have been reported. The experience of ongoing studies enrolling average-risk individuals is that the prevalence rates are substantially lower. A 2020 study from a community-based cohort undergoing CRC screening with fecal immunochemical testing followed by diagnostic colonoscopy reported a CRC prevalence rate of 1.46 per 1000, or 0.15%.3 The aim of our study is to report the screen-detected prevalence of CRC and advanced neoplasia in average-risk asymptomatic individuals from selected academic and community medical centers in the United States, Canada, and Germany and describe associated risk factors.

15-LOX-1: a novel molecular target of nonsteroidal anti-inflammatory drug-induced apoptosis in colorectal cancer cells.

BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) appear to act via induction of apoptosis-programmed cell death-as potential colorectal cancer chemopreventive agents. NSAIDs can alter the production of different metabolites of polyunsaturated fatty acids (linoleic and arachidonic acids) through effects on lipoxygenases (LOXs) and cyclooxygenases. 15-LOX-1 is the main enzyme for metabolizing colonic linoleic acid to 13-S-hydroxyoctadecadienoic acid (13-S-HODE), which induces apoptosis. In human colorectal cancers, the expression of this enzyme is reduced. NSAIDs can increase 15-LOX enzymatic activity in normal leukocytes, but their effects on 15-LOX in neoplastic cells have been unknown. We tested the hypothesis that NSAIDs induce apoptosis in colorectal cancer cells by increasing the protein expression and enzymatic activity of 15-LOX-1. METHODS: We assessed 15-LOX-1 protein expression and enzymatic activity, 13-S-HODE levels, and 15-LOX-1 inhibition in association with cellular growth inhibition and apoptosis induced by NSAIDs (primarily sulindac and NS-398) in two colorectal cancer cell lines (RKO and HT-29). All P values are two-sided. RESULTS: Sulindac and NS-398 progressively increased 15-LOX-1 protein expression in RKO cells (at 24, 48, and 72 hours) in association with subsequent growth inhibition and apoptosis. Increased 13-S-HODE levels and the formation of 15-hydroxyeicosatetraenoic acid on incubation of the cells with the substrate arachidonic acid confirmed the enzymatic activity of 15-LOX-1. Inhibition of 15-LOX-1 in RKO cells by treatment with caffeic acid blocked NS-398-induced 13-S-HODE production, cellular growth inhibition, and apoptosis (P =. 007, P<.0001, and P<.0001, respectively); growth inhibition and apoptosis were restored by adding exogenous 13-S-HODE (P<.0001 for each) but not its parent compound, linoleic acid (P = 1.0 for each). Similar results occurred with other NSAIDs and in HT-29 cells. CONCLUSIONS: These data identify 15-LOX-1 as a novel molecular target of NSAIDs for inducing apoptosis in colorectal carcinogenesis.

Suppression of human colorectal mucosal prostaglandins: determining the lowest effective aspirin dose.

BACKGROUND: A variety of studies have supported the finding that regular intake of aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory agents can affect colorectal cancer carcinogenesis. These agents inhibit the synthesis of prostaglandins. High levels of prostaglandins are observed in colon cancer tissues. PURPOSE: Experiments were planned to determine the lowest dose of aspirin that can markedly suppress the levels of mucosal prostaglandins E2 and F(2alpha) in colorectal mucosa and to determine whether a relationship exists between these levels and plasma levels of both acetylsalicylic acid and its metabolite, salicylic acid. METHODS: Healthy men and women aged 18 years or older participated in the study. The participants took a single, daily dose of aspirin (40.5, 81, 162, 324, or 648 mg) or a placebo for 14 days. Colorectal biopsy specimens were taken at baseline, 24 hours after the first dose of aspirin, and 24-30 hours and 72-78 hours after the last, i.e., fourteenth, daily dose of aspirin. The biopsy specimens were assayed for prostaglandins E2 and F(2alpha) by use of a competitive enzyme immunoassay. Plasma concentrations of acetylsalicylic acid and salicylic acid were determined by use of high-performance liquid chromatography. All P values are two-sided. RESULTS: A total of 65 subjects (10 receiving placebo, groups of 10 each receiving 40.5, 81, 162, or 324 mg of aspirin, and a group of 15 receiving 648 mg of aspirin) completed the protocol. One subject reported unacceptable drug-induced toxic effects and did not complete the protocol; other subjects reported acceptable side effects. The lowest dose to significantly suppress colorectal mucosal prostaglandin E2 concentrations from baseline at 24 hours after the first dose (by 22.6%; P = .002) and at 24-30 hours after the last dose (by 14.2%; P = .021) was 162 mg. At 72-78 hours after the last dose, there was significant suppression for subjects receiving 81 mg (by 23.7%; P = .008). The lowest dose to significantly suppress colorectal mucosal prostaglandin F(2alpha) concentrations from baseline at 24 hours after the first dose (by 18.3%; P = .032) was 324 mg. The lowest dose causing a marked reduction in the level of prostaglandin F(2alpha) at 24-30 hours (by 15.1%; P = .003) and 72-78 hours (by 23.0%; P = .0002) after the last dose was 40.5 mg. No detectable amounts of acetylsalicylic acid or salicylic acid were present in the plasma at any of the biopsy time points. CONCLUSIONS: The lowest doses of aspirin taken daily for 14 days to significantly suppress concentrations of colorectal mucosal prostaglandins E2 and F(2alpha) were 81 and 40.5 mg, respectively. The suppression occurred without detectable amounts of aspirin or salicylic acid in the plasma at the time points studied. On the basis of these observations, we recommend a single, daily dose of 81 mg of aspirin in future studies of this drug as a chemopreventive agent for colorectal cancer.

Uptake and intracellular distribution of doxorubicin metabolites in B-lymphocytes of chronic lymphocytic leukemia.

The toxicity of doxorubicin metabolites was evaluated on lymphocytes of B-cell chronic lymphocytic leukemia. Only doxorubicinol was found to be cytotoxic for these lymphocytes, whereas exposure to aglycones at concentrations as high as 5 microM for 1 h had no effect on the proliferative capacity of these cells. After exposure of cells to isomolar concentrations of doxorubicin or its metabolites, uptake/retention of doxorubicinol was 23% of doxorubicin, and uptake/retention of aglycones was 5 to 13% of doxorubicin. Seventy to 90% of doxorubicin and 60 to 90% of doxorubicinol taken up/retained by the cells were detected in the cell nuclear fraction, whereas only 20 to 40% of the aglycones were localized in the cell nucleus. Cytotoxicity of metabolites was generally related to the proportion of drug taken up/retained by the cells and localized to the nuclei. The low uptake and nuclear localization may be at least partially responsible for the lack of cytotoxicity of aglycones on B-lymphocytes from chronic lymphocytic leukemia.

Effect of allyl alcohol-induced sublethal hepatic damage upon doxorubicin metabolism and toxicity in the rabbit.

A model of hepatic dysfunction in vivo has been developed in rabbits to determine the effects of sublethal hepatocellular necrosis upon doxorubicin pharmacology. Eight New Zealand white rabbits were given 3 mg/kg doxorubicin i.v. Plasma doxorubicin and metabolite pharmacokinetics were determined and toxicity assessed by nadir complete blood counts. Hepatic function was assessed by the pulmonary excretion rate of 14CO2 from [14C]aminopyrine. Hepatocellular necrosis was produced by i.v. injection of 1.35 mg/kg of a 2% allyl alcohol solution. Doxorubicin administration and pharmacokinetics were repeated. Doxorubicin enhances the hepatotoxicity of allyl alcohol. Hepatocellular necrosis does not alter the plasma pharmacokinetics of doxorubicin but does increase the plasma exposure of doxorubicinol. Doxorubicin-induced myelosuppression is enhanced by allyl alcohol pretreatment. These data suggest that in circumstances of reduced hepatocellular volume or acute hepatocellular necrosis, a key plasma marker of doxorubicin-induced acute toxicity may be doxorubicinol.

Initial clinical (phase I) trial of TLC D-99 (doxorubicin encapsulated in liposomes).

A liposome-encapsulated form of doxorubicin (TLC D-99), which was shown in preclinical toxicology to be less toxic to the gastrointestinal tract and myocardium than free doxorubicin, was administered by constant infusion (1.00-1.80 h) to 38 patients in single doses of 20, 30, 45, 60, 75, and 90 mg/m2 every 3 weeks and daily for 3 days at doses of 20, 25, and 30 mg/m2/day. The dose-limiting toxicity was leucopenia: the maximum tolerated doses were one at 90 mg/m2 and three at 25 mg/m2/day. Nausea, vomiting, and stomatitis were minimal or absent at each dose; alopecia was minor. Fever and chills were noted at most of the doses, and malaise was seen in some patients, especially at the higher doses. No hepatic, renal, or other organ toxicities were observed. Clinical cardiac toxicity was not observed in any patient; however, the cumulative doxorubicin dose was greater than 400 mg/m2 in only one patient. There was large variation among patients in estimated pharmacokinetic parameters and profiles. Higher plasma levels and dose intensities were achieved with TLC D-99 than were predicted for free doxorubicin. Liposome-encapsulated doxorubicin was well tolerated and produced less nausea, vomiting, and stomatitis than would be expected with free doxorubicin administered at equally myelosuppressive doses.

Adherence to oral tamoxifen: a comparison of patient self-report, pill counts, and microelectronic monitoring.

PURPOSE: Recent innovations allow the integration of microelectronics into drug packaging, providing a continuous record of the interactions of the patient with the drug package. We hypothesized that adherence to oral tamoxifen, as measured by a pressure-activated microelectronic monitoring device, would be significantly discrepant from traditional measures of patient adherence, ie, patient self-report (SR) and pill counts (PCs). PATIENTS AND METHODS: Twenty-six patients receiving oral tamoxifen therapy were assessed by patient SR, PCs, and Medication Event Monitoring System (MEMS; Aprex Corp, Fremont, CA) microelectronic monitoring. A microprocessor in the MEMS cap recorded each opening as a presumptive dose, listing the date, time, and duration of opening for later retrieval on a microcomputer. Patients were not informed that their adherence was to be monitored electronically or that PCs would be performed. RESULTS: A total of 2,102 days (70.1 months) of tamoxifen therapy were monitored; patients were monitored for a mean of 2.92 months of tamoxifen therapy. SR adherence to oral tamoxifen was significantly higher than that suggested by either PCs (SR missed doses only v PC, P = .008) or MEMS adherence monitoring (SR missed doses only v MEMS missed doses only, P = .005; SR dosing-interval errors only v MEMS dosing-interval errors only, P < .0001; SR all dosing errors v MEMS all dosing errors, P < .0005). PC data also suggested significantly higher adherence rates than MEMS monitoring. CONCLUSION: Microelectronic adherence monitoring provides both confirmatory and complimentary data regarding adherence behavior, while also allowing for the evaluation of patterns of nonadherence. Patient SRs and PCs likely overestimate the degree to which patients adhere to their tamoxifen regimen.

Antiemetic effect of oral versus intravenous metoclopramide in patients receiving cisplatin: a randomized, double-blind trial.

In a study of the antiemetic effectiveness of high-dose oral metoclopramide, 66 previously untreated patients receiving 60 mg/m2 cisplatin were entered into a double-blind randomized trial. Patients were stratified according to age and tumor type, then randomized to receive either oral or intravenous (IV) high-dose metoclopramide. Patients were evaluated for antiemetic protection, toxicity, affect (anxiety, hostility, and depression), and autonomic arousal (pulse rate and blood pressure) at three-hour intervals on the day of their chemotherapy. Metoclopramide serum levels were measured by high-performance liquid chromatography. Results indicated no significant differences between the oral and IV groups on any measurement of antiemetic protection, affect, or autonomic arousal. There were also no significant differences in side effects except for frequency of stools; patients who received oral metoclopramide had significantly more stools than patients who received IV metoclopramide. The mean (+/- SD) serum metoclopramide level at four hours achieved orally was 1,171 +/- 660 ng/mL; the mean (+/- SD) level achieved IV was 1,030 +/- 392 ng/mL (P = .498). We conclude that high-dose oral and IV regimens of metoclopramide as administered in this study have equivalent antiemetic efficacy in previously untreated patients receiving 60 mg/m2 cisplatin.

Effect of sublethal liver injury on doxorubicin metabolism.

Centrilobular hepatocyte contribution to doxorubicin (DOX) metabolism and myelotoxicity was probed with bromobenzene (BRB), a known centrilobular hepatotoxin. New Zealand White rabbits were given DOX, 3 mg/kg i.v. After 4 weeks, the rabbits were pretreated i. p. with 2.6 ml/kg 40% solution of BRB in corn oil followed 72 h later with a 3-mg/kg dose of DOX. Pharmacokinetics of DOX after BRB pretreatment was mildly changed from control. Significantly increased plasma concentrations of doxorubicinol and its aglycone product, 7-deoxydoxorubicinol aglycone, were detected. Treatment with BRB alone was not lethal; however, in three of seven rabbits, the combination of DOX and BRB was. The mortality appeared to be related to myelosuppression. We conclude that toxin-induced hepato-cellular necrosis causes increased DOX-induced myelotoxicity. Following BRB pretreatment, the relatively small pharmacokinetic changes of parent compound concentrations as compared with greater changes in plasma pharmacokinetics of its alcohol metabolites suggest systemic changes in drug metabolism and distribution in the setting of hepatic disease may be the cause of increased toxicity.

Chemoprevention: general perspective.

Chemoprevention is the use of natural or synthetic compounds to block, reverse, or prevent the development of invasive cancers. Cellular carcinogenesis forms the biologic basis for the identification of chemopreventives, assessment of their activity, and ultimately the success or failure of a chemopreventive. Chemopreventive agents undergo multistep evaluations to assess efficacy that are similar in concept but vastly different in practice to standard ablative oncologic therapeutics. In vitro assessments of potential anticarcinogenesis efficacy include measurements of an agent's antioxidant activity, induction of phase II metabolizing enzymes and effects upon cellular proliferation and apoptotic control pathways. In vivo efficacy is assessed primarily in rodent models of carcinogenesis that are specific for a given organ target. The role of genetically modified animal models in the in vivo assessment of chemoprevention agents remains unclear. Clinical assessment of chemopreventive agent efficacy consists of a multistep process of identification of an optimal chemopreventive agent (phase 1), demonstration of efficacy in humans through the modulation of reversal of a tissue, biochemical, and molecular surrogates for neoplastic transformation and invasion (phase 2) and cancer risk reduction in large cohort trials (phase 3). Opportunities and future needs include the development of reliable, predictive in vivo models of carcinogenesis, careful exploration of the preventive pharmacology of therapeutic agents being used for non-cancer prevention indications, and the incorporation of genetic risk cohorts to define cancer chemopreventive efficacy.

Colonic mucosal prostaglandin E2 and cyclooxygenase expression before and after low aspirin doses in subjects at high risk or at normal risk for colorectal cancer.

UNLABELLED: Development of potential cancer chemopreventive drugs involves the systematic evaluation of these drugs in preliminary Phase I and II studies in human beings to identify the optimal drug dose, drug toxicity, and surrogate end point biomarker modulation. OBJECTIVES: We tested the hypothesis that aspirin, at a single, once-daily 81-mg dose, will reduce colonic mucosal concentration of prostaglandin estradiol (E2) in individuals at high risk for colorectal cancer development similar to our prior observations in a young normal-risk population. METHODS: Aspirin was administered at a dose of 81 mg once daily for 28 days in a cohort of 92 matched high-risk and normal-risk colorectal cancer subjects. Prostaglandin E2 and cyclooxygenase expression were assayed from distal sigmoid biopsies from all of the subjects before and after treatment. RESULTS: The mean prostaglandin E2 for normal-risk subjects before aspirin treatment was 11.3 +/- 1.7 pg/microg (mean +/- SE) tissue protein and after aspirin treatment was 4.9 +/- 0.91 pg/microg tissue protein (P < 0.0001). In high-risk subjects, mean pretreatment prostaglandin E2 was 14.4 +/- 1.7 pg/microg tissue protein and after aspirin treatment was 4.7 +/- 0.70 pg/microg tissue protein (P < 0.0001). Aspirin treatment did not alter cyclooxygenase-1 protein expression. CONCLUSIONS: Aspirin treatment at a dose of 81 mg reduces colorectal mucosal prostaglandin E2 concentration after 28 daily doses. Risk for colorectal carcinoma did not modify colorectal mucosal baseline or post-aspirin prostaglandin E2, or cyclooxygenase expression. Colorectal mucosal prostaglandin concentration may be used as a "drug-effect surrogate biomarker," that is, a surrogate to assess sufficient delivery and tissue effect of a chemopreventive agent.

Relationship between cigarette smoking and Alzheimer's disease in a population-based case-control study.

We investigated whether cigarette smoking is negatively associated with Alzheimer's disease (AD) in a population-based, frequency-matched, case-control study of 152 AD patients and 180 controls. Ever having smoked was associated with lower risk of AD (adjusted odds ratio = 0.61; 95% confidence interval: 0.37-0.99). Additional multivariate analyses demonstrated that education and history of hypertension modified this association. The direction of the modification was for higher education level and history of hypertension to further reduce the risk. The "dose-response" pattern showed the greatest risk reduction among those who smoked least and suggests a biologic mechanism of a dose-dependent up-regulation of nicotinic (cholinergic) brain receptors. These data, although consistent with current opinion about pathophysiology of AD, do not suggest smoking should be used as a preventive strategy for AD.

Acute renal failure and renal tubular squamous metaplasia following treatment with streptozotocin.

Nephrotoxicity, in the form of transient proteinuria, azotemia, abnormalities of tubular function, and acute renal failure, is the major toxic condition following administration of streptozotocin. The renal morphologic and ultrastructural abnormalities associated with streptozotocin remain poorly defined. We describe a patient with metastatic islet cell tumor of the pancreas who was treated with 16 weekly courses of 1 g/m2 of streptozotocin without marked change in renal function. Following a six-week hiatus without change in renal function, a single course of 1 g/m2 of streptozotocin was administered and resulted in acute renal failure. Light microscopic examination of the kidneys showed irregularly dilated renal tubules lined by low cuboid epithelium. The cells were pleomorphic and showed some mitoses. Nuclei were irregular and variably hyperchromatic. Electron microscopic examination disclosed large aggregates of fine microfilaments in the proximal convoluted tubules and collecting ducts. Microfilament aggregates were both free in the cytoplasm and membrane bound. Microfilaments were proved to be tonofilaments by the demonstration of keratin within the epithelium, using the immunoperoxidase method. These data suggest that squamous metaplasia may be an important part of streptozotocin renal toxicity, and the suggestion is made that they may be an antecedent of neoplastic change.

Causes of death associated with Alzheimer disease: variation by level of cognitive impairment before death.

OBJECTIVE: To describe causes of death for patients with Alzheimer disease (AD) and other dementing illnesses enrolled in a population-based Alzheimer disease patient registry (ADPR) and to describe the variation in causes by the level of cognitive impairment before death in probable AD cases. SETTING: The ADPR enrolls and diagnoses newly recognized potential dementia cases occurring in a large, stable health maintenance organization. To date, 654 cases have been enrolled and followed annually to monitor cognitive decline and verify initial diagnosis. DESIGN: Longitudinal descriptive study. PATIENTS: ADPR enrollees who have died. MEASUREMENTS: Death certificates were obtained for all who died (total n = 104, probable AD = 55); reported causes of death were reviewed by a physician to determine the underlying cause. AD patients were categorized according to their Mini-Mental State Exam score (cognitive impairment) within 12 months of death as (a) mildly (21+), (b) moderately (15-20), or (c) severely (0-14) impaired, and underlying cause and all reported causes of death for each group were tabulated. MAIN RESULTS: Among probable AD patients, pneumonia and AD were most often recorded on death certificates when cognitive impairment within the year prior to death had reached the severe level; heart disease, stroke, and other common causes of death predominated in AD patients who were less cognitively impaired. CONCLUSIONS: When AD cases were followed from first diagnosis to death, the causes of death varied by level of cognitive impairment. Illnesses potentially amenable to treatment caused death at all levels of disease, but more so early in the course of AD. Cognitive impairment may make patients less able to recognize and report symptoms of medical problems, thereby complicating efforts to intervene.

Abdominopelvic computed tomography: evaluation in patients undergoing second-look laparotomy for ovarian carcinoma.

Preoperative abdominopelvic computed tomography results and operative findings were compared in 52 patients undergoing second-look laparotomy to confirm tumor status. Seventeen true-negative, 22 false-negative, and 13 true-positive scans were found. The sensitivity was 0.38, specificity was 1.0, and diagnostic accuracy was 0.58. Negative studies were associated with positive findings at laparotomy in 42% of all cases. Fourteen patients were identified who had computed tomography that would have enabled an attempt at the diagnosis of persistent cancer by computed tomography-directed needle aspiration or biopsy, thus avoiding laparotomy. Assuming 80% accuracy of needle aspiration, the cost of computed tomography in all 52 patients is considerably outweighed by the savings that could have been realized by eliminating the need for second-look surgery in these 11 women.

The effects of cimetidine upon the plasma pharmacokinetics of doxorubicin in rabbits.

Cimetidine is an H2 antagonist which inhibits cytochrome P-450 and reduces hepatic blood flow. To determine whether cimetidine interferes with the plasma pharmacokinetics of doxorubicin, we gave six female New Zealand rabbits doxorubicin 3 mg/kg, followed a month later by cimetidine 120 mg/kg every 12 h over 72 h and doxorubicin 3 mg/kg. Serial plasma specimens were obtained over 72 h and assayed for doxorubicin and its metabolites by high-performance liquid chromatography and fluorescence detection. Doxorubicin plasma pharmacokinetics were prolonged after cimetidine pretreatment [AUC 0.76 +/- 0.22 vs. 2.85 +/- 1.22 microM X h, no pretreatment vs pretreatment (p = 0.005), half-life = 11.7 +/- 6.55 vs 28.0 +/- 8.16 h (P = 0.0002), and clearance = 0.129 +/- 0.036 vs 0.036 +/- 0.011 l/min-1 kg-1 (P = 0.0007)]. No significant differences were found between the AUCs for doxorubicinol, 7-deoxy doxorubicinol aglycone, or two unidentified nonpolar metabolites in nonpretreatment and pretreatment studies. Cimetidine increases and prolongs the plasma exposure to doxorubicin in rabbits. Doxorubicin metabolism does not appear to be affected by cimetidine.

Augmentation of hepatic doxorubicin extraction with extracorporeal filtration avoids the dose-dependent, nonlinear increase in AUC observed with systemic administration.

PURPOSE: Regional therapy of primary or metastatic liver cancer with low hepatic extraction ratio drugs such as doxorubicin is constrained by development of systemic toxicity. To examine the effect of augmentation of hepatic drug extraction, a swine model of hepatic artery infusion (HAI) with minimally invasive hepatic venous isolation and hepatic venous drug extraction (HVDE) was developed to study the comparative pharmacokinetic profiles of regional and systemically administered doxorubicin. METHODS: Doxorubicin 0.5-9 mg/kg was administered to 31 pigs over 90 min either by HAI with simultaneous HVDE or by standard systemic vein infusion. Systemic artery and hepatic vein plasma samples were collected periodically (0 to 240 min) for determination of doxorubicin concentrations by high-performance liquid chromatography. Pharmacokinetic profiles were modeled with PCNONLIN 4.2. RESULTS: Concentration-time data were best described in all pigs by a two-compartment open model of elimination. Independent of the route of administration, AUC and Cmax values increased with dose. Mean systemic AUC and Cmax values were consistently lower with regional administration, with statistically significant decreases at the 0.5 and 3 mg/kg doses, whereas there was no relationship between hepatic vein parameters and route of administration. There was a linear relationship between mean systemic AUC values and dose in pigs receiving doxorubicin via HAI with HVDE, whereas mean systemic AUC values increased exponentially at doses of 5 mg/kg or above with systemic vein administration. CONCLUSIONS: Administration of doxorubicin by HAI with simultaneous HVDE significantly decreases systemic exposure in comparison with standard systemic vein drug infusion, and may protect against nonlinear increases in exposure at higher doses.

Improved high-performance liquid chromatography assay of doxorubicin: detection of circulating aglycones in human plasma and comparison with thin-layer chromatography.

We compared doxorubicin and metabolite pharmacokinetic data obtained from thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) assay of plasma samples from six patients who had been treated with doxorubicin. Duplicate 1-ml samples were extracted with chloroform: isopropanol (1:1) and assayed using a sensitive HPLC system incorporating a dual pump gradient with tetrahydrofuran as the mobile phase and fluorescence detection. Duplicate 1-ml samples from the same specimens were assayed using a modification of a previously described TLC assay. Areas under the curve for doxorubicin by HPLC (3.36 +/- 2.30 microM X h) and TLC (4.16 +/- 2.50 microM X h) were not significantly different (P = 0.5). Terminal half-life of doxorubicin by HPLC (28.0 +/- 6.98 h) and TLC (23.2 +/- 7.8) (P = 0.29) and the calculated total-body clearances by HPLC (0.55 +/- 0.29 l/min) and TLC (0.45 +/- 0.23) (P = 0.55) were not significantly different. Areas under the curve for doxorubicinol by HPLC (2.75 +/- 1.4 microM X h) and TLC (2.53 +/- 7.1 microM X h) (P = 0.73) showed no significant differences. HPLC detected a mixed 7-deoxydoxorubicinol aglycone-doxorubicin aglycone peak, 7-deoxydoxorubicin aglycone, and two nonpolar, unidentified metabolites. TLC detected the following aglycone metabolites: doxorubicin aglycone, doxorubicinol aglycone, 7-deoxydoxorubicinol aglycone, an unidentified polar metabolite, and several unidentified nonpolar metabolites. From these data we conclude that HPLC and TLC detect concentrations of doxorubicin and doxorubicinol from human plasma equally well to concentrations of 7.0 nM (4 pmol injected doxorubicin). Aglycones do circulate in human plasma at concentrations above the detection limits of both assays. Doxorubicinol aglycone, which is detected by TLC but not by HPLC, may be formed from artifactual breakdown of doxorubicinol during TLC development. Unidentified nonpolar compounds seen on HPLC and TLC may represent further doxorubicin metabolism than previously described.

The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin in rabbits.

The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin was studied in six female New Zealand white rabbits. Plasma pharmacokinetic data were first obtained from rabbits given 3 mg/kg doxorubicin. After 1 month, the same rabbits were treated with ranitidine, 2.5 mg/kg or 25 mg/kg, before and during doxorubicin administration. The plasma doxorubicin assays to determine pharmacokinetic parameters were repeated. Drug toxicity was evaluated using complete blood counts, and hepatic function was measured using a 14C-aminopyrine breath test. High-dose ranitidine increased the total exposure to doxorubicin (area under the curve of doxorubicin alone = 1.44 +/- 0.88 microM.h/ml vs 4.49 +/- 2.35 microM.hr/ml for doxorubicin given with high-dose ranitidine; P = 0.06). Low-dose ranitidine did not alter doxorubicin pharmacokinetics. Exposure to doxorubicinol was altered by either high-dose or low-dose ranitidine. 14C-Aminopyrine half-life was altered by a ranitidine dose of 25 mg/kg (aminopyrine half-life after placebo control = 97 +/- 6 min as against aminopyrine half-life after ranitidine = 121 +/- 7 min; mean +/- SEM; P less than 0.02). Low-dose ranitidine did not exacerbate doxorubicin-induced myelosuppression. High-dose ranitidine enhanced doxorubicin-induced erythroid suppression while sparing the myeloid series. At cytochrome P-450-inhibitory doses, ranitidine's effects upon doxorubicin plasma pharmacokinetics are similar to those previously seen with cimetidine. These changes did not appear to alter drug detoxification and are not related to microsomal inhibition of doxorubicin detoxification. Low doses of ranitidine do not alter doxorubicin plasma pharmacokinetics or toxicity in rabbits.

Effect of phenytoin on the pharmacokinetics of doxorubicin and doxorubicinol in the rabbit.

Doxorubicin is metabolized extensively to doxorubicinol by the ubiquitous aldoketoreductase enzymes. The extent of conversion to this alcohol metabolite is important since doxorubicinol may be the major contributor to cardiotoxicity. Aldoketoreductases are inhibited in vitro by phenytoin. The present study was conducted to examine the effect of phenytoin on doxorubicin pharmacokinetics. Doxorubicin single-dose pharmacokinetic studies were performed in 10 New Zealand White rabbits after pretreatment with phenytoin or phenytoin vehicle (control) infusions in crossover fashion with 4-6 weeks between studies. Infusions were commenced 16 h before and during the course of the doxorubicin pharmacokinetic studies. Phenytoin infusion was guided by plasma phenytoin estimation to maintain total plasma concentrations between 20 and 30 micrograms/ml. Following doxorubicin 5 mg/kg by i.v. bolus, blood samples were obtained at intervals over 32 h. Plasma doxorubicin and doxorubicinol concentrations were measured by HPLC. The mean plasma phenytoin concentrations ranged from 17.4 to 33.9 micrograms/ml. Phenytoin infusion did not alter doxorubicin pharmacokinetics. The elimination half-life and volume of distribution were almost identical to control. Clearance of doxorubicin during phenytoin administration (60.9 +/- 5.8 ml/min per kg, mean +/- SE) was similar to that during vehicle infusion (67.5 +/- 5.4 ml/min per kg). Phenytoin administration was associated with a significant decrease in doxorubicinol elimination half-life from 41.0 +/- 4.8 to 25.6 +/- 2.8 h. The area under the plasma concentration/time curve (AUC) for doxorubicinol decreased significantly from 666.8 +/- 100.4 to 491.5 +/- 65.7 n.h.ml-1. These data suggest that phenytoin at clinically relevant concentrations does not alter the conversion of doxorubicin to doxorubicinol in the rabbit. The reduction in the AUC for doxorubicinol caused by phenytoin appears to be due to an increased rate of doxorubicinol elimination. Phenytoin or similar agents may have the effect of modifying doxorubicinol plasma concentrations by induction of doxorubicinol metabolism rather than by inhibition of aldoketoreductase enzymes.