Rifampin enhances cytochrome P450 (CYP) 2B6-mediated efavirenz 8-hydroxylation in healthy volunteers.

The effect of rifampin on the in vivo metabolism of the antiretroviral drug efavirenz was evaluated in healthy volunteers. In a cross-over placebo control trial, healthy subjects (n = 20) were administered a single 600 mg oral dose of efavirenz after pretreatment with placebo or rifampin (600 mg/day for 10 days). Plasma and urine concentrations of efavirenz, 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz were measured by LC-MS/MS. Compared to placebo treatment, rifampin increased the oral clearance (by ∼2.5-fold) and decreased maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC0-∞) of efavirenz (by ∼1.6- and ∼2.5-fold respectively) (p < 0.001). Rifampin treatment substantially increased the Cmax and AUC0-12h of 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz, metabolic ratio (AUC0-72h of metabolites to AUC0-72h efavirenz) and the amount of metabolites excreted in urine (Ae0-12hr) (all, p < 0.01). Female subjects had longer elimination half-life (1.6-2.2-fold) and larger weight-adjusted distribution volume (1.6-1.9-fold) of efavirenz than male subjects (p < 0.05) in placebo and rifampin treated groups respectively. In conclusion, rifampin enhances CYP2B6-mediated efavirenz 8-hydroxylation in vivo. The metabolism of a single oral dose of efavirenz may be a suitable in vivo marker of CYP2B6 activity to evaluate induction drug interactions involving this enzyme.

Predictors of aromatase inhibitor discontinuation as a result of treatment-emergent symptoms in early-stage breast cancer.

PURPOSE: Aromatase inhibitors (AIs) are effective for treatment of hormone receptor-positive breast cancer, but adherence and persistence with therapy are poor. Predictors of treatment discontinuation are not clearly defined. It is unknown whether patients with intolerable toxicity from one AI are able to tolerate another. PATIENTS AND METHODS: Women with early-stage breast cancer initiating AI therapy were enrolled onto a multicenter, prospective, open-label randomized trial of exemestane versus letrozole. Patients completed symptom questionnaires at baseline and serially during therapy. Patients who developed AI-associated intolerable symptoms and discontinued treatment were given the option to switch to the other study AI after a 2- to 8-week washout period. RESULTS: Of the 503 enrolled women, 32.4% discontinued initial AI therapy within 2 years because of adverse effects; 24.3% discontinued specifically because of musculoskeletal symptoms. Median time to treatment discontinuation as a result of any symptom was 6.1 months (range, 0.1 to 21.2 months) and was significantly shorter in patients randomly assigned to exemestane (hazard ratio [HR], 1.5; 95% CI, 1.1 to 2.1; P = .02). Younger age and taxane-based chemotherapy were associated with higher likelihood of treatment discontinuation (HR, 1.4; 95% CI, 1.02 to 1.9; P = .04; and HR, 1.9; 95% CI, 1.00 to 3.6; P = .048, respectively). Of the 83 patients who chose to switch to the second AI, 38.6% continued the alternate AI for a median of 13.7 months. CONCLUSION: Premature discontinuation of initial AI therapy as a result of symptoms is common, although more than one third of patients may be able to tolerate a different AI medication. Additional research is needed to identify predictive tools and interventions for AI-associated treatment-emergent symptoms.

Comparison of subjective and objective hot flash measures over time among breast cancer survivors initiating aromatase inhibitor therapy.

OBJECTIVE: Hot flashes are valuable indicators of physiological condition and drug effect; however, subjective and objective measures do not always agree. No study has examined both subjective and objective hot flashes in women prescribed aromatase inhibitors. The study (1) compared subjective and objective hot flash measures, (2) examined changes in subjective and objective hot flashes over time, and (3) evaluated predictors of change in hot flashes in aromatase inhibitor-treated women. METHODS: Participants (n = 135) were enrolled in a randomized clinical trial comparing exemestane and letrozole for the treatment of breast cancer. Hot flashes were assessed before the start of the drug therapy and 1, 3, and 6 months later. Participants wore a sternal skin conductance monitor for 24 hours or longer at each time point. With each perceived hot flash, women pressed an event button and rated intensity and bother in a paper diary. RESULTS: Participants had a mean age of 60 years and were mainly white (92%). Across time points, monitor hot flashes were (1) significantly more frequent than diary and/or event button flashes (P < 0.05) and (2) moderately correlated with subjective measures (0.35 < r < 0.56). Monitor hot flashes did not significantly change over time with aromatase inhibitor therapy, whereas both diary and event button frequencies significantly varied but in dissimilar patterns (51% nonlinear). No consistent predictors of hot flashes across measures or time points were identified. CONCLUSIONS: Findings indicated dissimilarities between subjective and objective measures of hot flashes. Despite statistical significance, there was little clinically meaningful change in hot flashes after initiating aromatase inhibitor therapy.

Rapid identification of the hepatic cytochrome P450 2C19 activity using a novel and noninvasive [13C]pantoprazole breath test.

We tested the hypothesis that the stable isotope [(13)C]pantoprazole is O-demethylated by cytochrome P450 CYP2C19 and that the (13)CO(2) produced and exhaled in breath as a result can serve as a safe, rapid, and noninvasive phenotyping marker of CYP2C19 activity in vivo. Healthy volunteers who had been genotyped for the CYP2C19(*)2, CYP2C19(*)3, and CYP2C19(*)17 alleles were administered a single oral dose of [(13)C]pantoprazole sodium-sesquihydrate (100 mg) with 2.1 g of sodium bicarbonate. Exhaled (13)CO(2) and (12)CO(2) were measured by IR spectroscopy before (baseline) and 2.5 to 120 min after dosing. Ratios of (13)CO(2)/(12)CO(2) after [(13)C]pantoprazole relative to (13)CO(2)/(12)CO(2) at baseline were expressed as change over baseline (DOB). Maximal DOB, DOB(15) to DOB(120), and area under the DOB versus time curve (AUC(0-120) and AUC(0-infinity)) were significantly different among three genotype groups (CYP2C19(*)1/(*)1, n = 10; CYP2C19(*)1/(*)2 or CYP2C19(*)1/(*)3, n = 10; and CYP2C19(*)2/(*)2, n = 5) with predicted extensive metabolizers (EMs), intermediate metabolizers (IMs), and poor metabolizers (PMs) of CYP2C19, respectively (Kruskal-Wallis test, p < 0.01); linear regression analysis indicated a gene-dose effect relationship (r(2) ranged between 0.236 and 0.522; all p < 0.05). These breath test indices were significantly lower in PMs than IMs (p < 0.05) or EMs (p < 0.01) of CYP2C19. [(13)C]Pantoprazole plasma exposure showed significant inverse correlation with breath test indices in the respective subjects (Pearson r = -0.74; p = 0.038). These feasibility data suggest that the [(13)C]pantoprazole breath test is a reliable, rapid, and noninvasive probe of CYP2C19 and seems to be a useful tool to optimize drug therapy metabolized by CYP2C19.

Estrogen receptor genotypes influence hot flash prevalence and composite score before and after tamoxifen therapy.

PURPOSE: Hot flashes are common and frequently lead to drug discontinuation among women prescribed tamoxifen. We determined whether genetic polymorphisms in estrogen receptors (ESRs) alpha and beta (ESR1 and ESR2, respectively) are associated with tamoxifen-induced hot flashes. PATIENTS AND METHODS: We determined ESR1 PvuII and XbaI and ESR2-02 genotypes in 297 women who were initiating tamoxifen. One-week hot flash diaries were collected to calculate a hot flash score (frequency x severity) before and 1, 4, 8, and 12 months after starting tamoxifen. RESULTS: Approximately 80% of 297 participants reported hot flashes before or during the first year of tamoxifen. After 4 months of tamoxifen, premenopausal women who did not receive adjuvant chemotherapy had a four-fold increase in hot flash score (from 5.9 to 23.6; P = .003) compared with a 1.17-fold increase (from 19.6 to 23; P = .34) in those who received chemotherapy. In premenopausal women, increased number of ESR1 PvuII and XbaI CG alleles was associated with higher baseline hot flash scores compared with those who had other haplotypes (P = .0026). At 4 months, postmenopausal women with ESR1 PvuII CC and ESR2-02 GG genotypes had 4.6 times increases in hot flash scores than other postmenopausal women (56 v 12; P = .0007). Women who had the ESR2-02 AA genotype were significantly less likely to experience tamoxifen-induced hot flashes than women who carried at least one ESR-02 G allele (hazard ratio, 0.26; 95% CI, 0.10 to 0.63; P = .001). CONCLUSION: Knowledge of menopausal status, prior chemotherapy, and ESR genotype may help predict which women are most likely to suffer hot flashes during tamoxifen treatment.

Prospective characterization of musculoskeletal symptoms in early stage breast cancer patients treated with aromatase inhibitors.

PURPOSE: Aromatase inhibitors (AIs) are increasingly used as adjuvant treatment of postmenopausal women with hormone receptor-positive breast cancer. AIs are commonly associated with musculoskeletal symptoms. The primary objective of this study was to describe the musculoskeletal symptoms that developed in the first 100 subjects enrolled who had at least 6 months follow-up. METHODS: Women with early stage hormone receptor-positive breast cancer were recruited into a multicenter randomized clinical trial to study the pharmacogenomics of two AIs, exemestane, and letrozole. Patients completed the Health Assessment Questionnaire (HAQ) and Visual Analog Scale (VAS) at baseline, 1, 3, 6, and 12 months to assess changes in function and pain, respectively. Patients were referred for evaluation by a rheumatologist if their HAQ and/or VAS scores exceeded a predefined threshold. RESULTS: Forty-four of 97 eligible patients (45.4%) met criteria for rheumatologic referral. Three patients were ineligible because of elevated baseline HAQ (2) and failure to initiate AI therapy (1). No baseline characteristics were significantly associated with referral. Median time to onset of symptoms was 1.6 months (range 0.4-10 months). Clinical and laboratory evaluation of patients evaluated by rheumatology suggested that the majority developed either non-inflammatory musculoskeletal symptoms or inflammation localized to tenosynovial structures. Thirteen patients discontinued AI therapy because of musculoskeletal toxicity after a median 6.1 months (range 2.2-13 months). CONCLUSIONS: Musculoskeletal side effects were common in AI-treated patients, resulting in therapy discontinuation in more than 10% of patients. There are no identifiable pre-therapy indicators of risk, and the etiology remains elusive.

Association of polymorphisms of angiogenesis genes with breast cancer.

BACKGROUND: Few studies have systematically explored a pathway approach: to test the association of multiple polymorphisms from multiple genes important to angiogenesis simultaneously with risk of breast cancer. We report our preliminary data evaluating the association of polymorphisms from seven genes known to influence angiogenesis with the likelihood of having breast cancer. METHODS: We recruited 715 controls and 520 subjects with breast cancer. Subjects provided a blood specimen and completed a questionnaire that included common breast cancer risk factors and breast cancer status. We evaluated candidate polymorphisms in the following genes: Hypoxia Inducible Factor-1 alpha (HIF1alpha), Vascular Endothelial Growth Factor (VEGF), VEGF Receptor 1 (VEGFR-1), VEGFR-2, endothelial Nitric Oxide Synthase (eNOS), Neuropilin-1 (NRP-1) and Neuropilin-2 (NRP-2). Testing for associations between each polymorphism and the presence or absence of breast cancer was performed. RESULTS: VEGF-2578 AA and -1498 CC genotypes were more common in cancer cases than controls (P = 0.06 and P = 0.04, respectively). These two genotypes remained significant predictors of breast cancer status after adjusting for non-genetic risk factors estimated by the Gail model (P = 0.03 and P = 0.03, respectively). When comparing women with invasive versus pre-invasive breast cancer, the eNOS-786 TT and eNOS 894 GG genotypes were associated with a greater likelihood of invasive disease and the eNOS 894 GG genotype was associated with a greater likelihood of having metastatic disease. CONCLUSION: There is an association of the VEGF-2578A and -1498C alleles with increased breast cancer risk. This association remains significant when adjusted for Gail score-related risk factors.

CYP2D6 genotype, antidepressant use, and tamoxifen metabolism during adjuvant breast cancer treatment.

BACKGROUND: The efficacy of tamoxifen therapy for the treatment of breast cancer varies widely among individuals. Plasma concentrations of the active tamoxifen metabolite endoxifen are associated with the cytochrome P450 (CYP) 2D6 genotype. We examined the effects of concomitant use of selective serotonin reuptake inhibitor antidepressants, which are CYP2D6 enzyme inhibitors commonly prescribed to treat hot flashes in women who take tamoxifen, and genotypes for genes that encode tamoxifen-metabolizing enzymes on plasma concentrations of tamoxifen and its metabolites. METHODS: Eighty patients with newly diagnosed with breast cancer who were beginning tamoxifen therapy (20 mg/day orally), 24 of whom were taking CYP2D6 inhibitors, were genotyped for common alleles of the CYP2D6, CYP2C9, CYP3A5, and sulfotransferase (SULT) 1A1 genes. Plasma concentrations of tamoxifen and its metabolites were measured after 1 and 4 months of tamoxifen therapy. Differences in plasma concentrations of tamoxifen and its metabolites between genotype groups were analyzed by the Wilcoxon rank sum test. All statistical tests were two-sided. RESULTS: Among all women, plasma endoxifen concentrations after 4 months of tamoxifen therapy were statistically significantly lower in subjects with a CYP2D6 homozygous variant genotype (20.0 nM, 95% confidence interval [CI] = 11.1 to 28.9 nM) or a heterozygous genotype (43.1 nM, 95% CI = 33.3 to 52.9 nM) than in those with a homozygous wild-type genotype (78.0 nM, 95%CI = 65.9 to 90.1 nM) (both P = .003). Among subjects who carried a homozygous wild-type genotype, the mean plasma endoxifen concentration for those who were using CYP2D6 inhibitors was 58% lower than that for those who were not (38.6 nM versus 91.4 nM, difference = -52.8 nM, 95% CI = -86.1 to -19.5 nM, P = .0025). The plasma endoxifen concentration was slightly reduced in women taking venlafaxine, a weak inhibitor of CYP2D6, whereas the plasma endoxifen concentration was reduced substantially in subjects who took paroxetine (a potent inhibitor of CYP2D6). Genetic variations of CYP2C9, CYP3A5, or SULT1A1 had no statistically significant associations with plasma concentrations of tamoxifen or its metabolites. CONCLUSION: Interactions between CYP2D6 polymorphisms and coadministered antidepressants and other drugs that are CYP2D6 inhibitors may be associated with altered tamoxifen activity.

Safety of propofol administered by registered nurses with gastroenterologist supervision in 2000 endoscopic cases.

OBJECTIVES: Propofol has certain advantages over benzodiazepines plus narcotics as sedation for endoscopy. In a few centers, propofol has reportedly been used in endoscopic procedures and administered by nurses supervised by gastroenterologists without attendance by anesthesiologists or nurse anesthetists. METHODS: As part of our continuous quality improvement program, we prospectively recorded the doses of propofol and adverse reactions to the drug in our initial 2000 cases. In all cases propofol was administered by nurses who were supervised by gastroenterologists, with no involvement by an anesthesia specialist. RESULTS: The 2000 cases included 2222 procedures. There were five episodes of oxygen desaturation to <85%, four of which seemed to be related to excessive administration of propofol and were treated by brief (< 1 min) periods of mask ventilation. No patient required endotracheal intubation or hospital admission, or suffered long-term sequelae from propofol administration. There were no perforations in 977 colonoscopies. CONCLUSIONS: Propofol can be given safely by appropriately trained nurses under supervision by endoscopists. Technology that allows immediate detection of apnea would likely further improve its safety.