Indinavir Increases Midazolam N-Glucuronidation in Humans: Identification of an Alternate CYP3A Inhibitor Using an In Vitro to In Vivo Approach.

Midazolam is a widely used index substrate for assessing effects of xenobiotics on CYP3A activity. A previous study involving human hepatocytes showed the primary route of midazolam metabolism, 1'-hydroxylation, shifted to N-glucuronidation in the presence of the CYP3A inhibitor ketoconazole, which may lead to an overprediction of the magnitude of a xenobiotic-midazolam interaction. Because ketoconazole is no longer recommended as a clinical CYP3A inhibitor, indinavir was selected as an alternate CYP3A inhibitor to evaluate the contribution of the N-glucuronidation pathway to midazolam metabolism. The effects of indinavir on midazolam 1'-hydroxylation and N-glucuronidation were first characterized in human-derived in vitro systems. Compared with vehicle, indinavir (10 µM) inhibited midazolam 1'-hydroxylation by recombinant CYP3A4, human liver microsomes, and high-CYP3A activity cryopreserved human hepatocytes by ≥70%; the IC50 obtained with hepatocytes (2.7 µM) was within reported human unbound indinavir Cmax (≤5 µM). Midazolam N-glucuronidation in hepatocytes increased in the presence of indinavir in both a concentration-dependent (1-33 µM) and time-dependent (0-4 hours) manner (by up to 2.5-fold), prompting assessment in human volunteers (n = 8). As predicted by these in vitro data, indinavir was a strong inhibitor of the 1'-hydroxylation pathway, decreasing the 1'-hydroxymidazolam/midazolam area under the plasma concentration versus time curve (AUC)0-12h ratio by 80%. Although not statistically significant, the midazolam N-glucuronide/midazolam AUC0-12h ratio increased by 40%, suggesting a shift to the N-glucuronidation pathway. The amount of midazolam N-glucuronide recovered in urine increased 4-fold but remained <10% of the oral midazolam dose (2.5 mg). A powered clinical study would clarify whether N-glucuronidation should be considered when assessing the magnitude of a xenobiotic-midazolam interaction.

Assessment of a candidate marker constituent predictive of a dietary substance-drug interaction: case study with grapefruit juice and CYP3A4 drug substrates.

Dietary substances, including herbal products and citrus juices, can perpetrate interactions with conventional medications. Regulatory guidances for dietary substance-drug interaction assessment are lacking. This deficiency is due in part to challenges unique to dietary substances, a lack of requisite human-derived data, and limited jurisdiction. An in vitro-in vivo extrapolation (IVIVE) approach to help address some of these hurdles was evaluated using the exemplar dietary substance grapefruit juice (GFJ), the candidate marker constituent 6',7'-dihydroxybergamottin (DHB), and the purported victim drug loperamide. First, the GFJ-loperamide interaction was assessed in 16 healthy volunteers. Loperamide (16 mg) was administered with 240 ml of water or GFJ; plasma was collected from 0 to 72 hours. Relative to water, GFJ increased the geometric mean loperamide area under the plasma concentration-time curve (AUC) significantly (1.7-fold). Second, the mechanism-based inhibition kinetics for DHB were recovered using human intestinal microsomes and the index CYP3A4 reaction, loperamide N-desmethylation (KI [concentration needed to achieve one-half kinact], 5.0 ± 0.9 µM; kinact [maximum inactivation rate constant], 0.38 ± 0.02 minute(-1)). These parameters were incorporated into a mechanistic static model, which predicted a 1.6-fold increase in loperamide AUC. Third, the successful IVIVE prompted further application to 15 previously reported GFJ-drug interaction studies selected according to predefined criteria. Twelve of the interactions were predicted to within the 25% predefined criterion. Results suggest that DHB could be used to predict the CYP3A4-mediated effect of GFJ. This time- and cost-effective IVIVE approach could be applied to other dietary substance-drug interactions to help prioritize new and existing drugs for more advanced (dynamic) modeling and simulation and clinical assessment.

A modified grapefruit juice eliminates two compound classes as major mediators of the grapefruit juice-fexofenadine interaction: an in vitro-in vivo "connect".

The grapefruit juice (GFJ)-fexofenadine interaction involves inhibition of intestinal organic anion transporting polypeptide (OATP)-mediated uptake. Only naringin has been shown clinically to inhibit intestinal OATP; other constituents have not been evaluated. The effects of a modified GFJ devoid of furanocoumarins (~99%) and polymethoxyflavones (~90%) on fexofenadine disposition were compared to effects of the original juice. Extracts of both juices inhibited estrone 3-sulfate and fexofenadine uptake by similar extents in OATP-transfected cells (~50% and ~25%, respectively). Healthy volunteers (n = 18) were administered fexofenadine (120 mg) with water, GFJ, or modified GFJ (240 mL) by randomized, three-way crossover design. Compared to water, both juices decreased fexofenadine geometric mean AUC and C(max) by ~25% (P ≤ .008 and P ≤ .011, respectively), with no effect on terminal half-life (P = .11). Similar effects by both juices on fexofenadine pharmacokinetics indicate furanocoumarins and polymethoxyflavones are not major mediators of the GFJ-fexofenadine interaction.

Randomized controlled trial shows biofeedback to be superior to pelvic floor exercises for fecal incontinence.

PURPOSE: This study aimed to compare manometric biofeedback with pelvic floor exercises for the treatment of fecal incontinence in a randomized controlled trial controlling for nonspecific treatment effects. METHODS: After excluding patients who were adequately treated with medication, education, and behavioral strategies (21%), 108 patients (83 females; average age, 59.6 years) underwent either pelvic floor exercises alone (n = 63) or manometric biofeedback plus pelvic floor exercises (n = 45). Patients in both groups were taught behavioral strategies to avoid incontinence. RESULTS: At three-month follow-up, biofeedback patients had significantly greater reductions on the Fecal Incontinence Severity Index (P = 0.01) and fewer days with fecal incontinence (P = 0.083). Biofeedback training increased anal canal squeeze pressure more than pelvic floor exercises did (P = 0.014) and with less abdominal tension during squeeze (P = 0.001). Three months after training 76% of patients treated with biofeedback vs. 41% patients treated with pelvic floor exercises (chi-squared = 12.5, P < 0.001) reported adequate relief. Before treatment, the groups did not differ on demographic, physiologic, or psychologic variables, symptom severity, duration of illness, quality-of-life impact, or expectation of benefit. At 12-month follow-up, biofeedback patients continued to show significantly greater reduction in Fecal Incontinence Severity Index scores (F = 4.83, P = 0.03), and more patients continued to report adequate relief (chi-squared = 3.64, P = 0.056). CONCLUSION: This investigation provides definitive support for the efficacy of biofeedback. Biofeedback training resulted in greater reductions in fecal incontinence severity and days with fecal incontinence. Biofeedback was also more effective than pelvic floor exercises alone in producing adequate relief of fecal incontinence symptoms in patients for whom conservative medical management had failed.

Increased colonic pain sensitivity in irritable bowel syndrome is the result of an increased tendency to report pain rather than increased neurosensory sensitivity.

OBJECTIVE: The aim was to determine whether lower visceral pain thresholds in irritable bowel syndrome (IBS) primarily reflect physiological or psychological factors. METHODS: Firstly, 121 IBS patients and 28 controls underwent balloon distensions in the descending colon using the ascending methods of limits (AML) to assess pain and urge thresholds. Secondly, sensory decision theory analysis was used to separate physiological from psychological components of perception: neurosensory sensitivity (p(A)) was measured by the ability to discriminate between 30 mm Hg vs 34 mm Hg distensions; psychological influences were measured by the report criterion-that is, the overall tendency to report pain, indexed by the median intensity rating for all distensions, independent of intensity. Psychological symptoms were assessed using the Brief Symptom Inventory (BSI). RESULTS: IBS patients had lower AML pain thresholds (median: 28 mm Hg vs 40 mm Hg; p<0.001), but similar neurosensory sensitivity (median p(A): 0.5 vs 0.5; p = 0.69; 42.6% vs 42.9% were able to discriminate between the stimuli better than chance) and a greater tendency to report pain (median report criterion: 4.0 ("mild" pain) vs 5.2 ("weak" pain); p = 0.003). AML pain thresholds were not correlated with neurosensory sensitivity (r = -0.13; p = 0.14), but were strongly correlated with report criterion (r = 0.67; p<0.0001). Report criterion was inversely correlated with BSI somatisation (r = -0.26; p = 0.001) and BSI global score (r = -0.18; p = 0.035). Similar results were seen for the non-painful sensation of urgency. CONCLUSION: Increased colonic sensitivity in IBS is strongly influenced by a psychological tendency to report pain and urge rather than increased neurosensory sensitivity.

Randomized, controlled trial shows biofeedback to be superior to alternative treatments for patients with pelvic floor dyssynergia-type constipation.

PURPOSE: This study was designed to determine whether biofeedback is more effective than diazepam or placebo in a randomized, controlled trial for patients with pelvic floor dyssynergia-type constipation, and whether instrumented biofeedback is necessary for successful training. METHODS: A total of 117 patients participated in a four-week run-in (education and medical management). The 84 who remained constipated were randomized to biofeedback (n=30), diazepam (n=30), or placebo (n=24). All patients were trained to do pelvic floor muscle exercises to correct pelvic floor dyssynergia during six biweekly one-hour sessions, but only biofeedback patients received electromyography feedback. All other patients received pills one to two hours before attempting defecation. Diary data on cathartic use, straining, incomplete bowel movements, Bristol stool scores, and compliance with homework were reviewed biweekly. RESULTS: Before treatment, the groups did not differ on demographic (average age, 50 years; 85 percent females), physiologic or psychologic characteristics, severity of constipation, or expectation of benefit. Biofeedback was superior to diazepam by intention-to-treat analysis (70 vs. 23 percent reported adequate relief of constipation 3 months after treatment, chi-squared=13.1, P<0.001), and also superior to placebo (38 percent successful, chi-squared=5.7, P=0.017). Biofeedback patients had significantly more unassisted bowel movements at follow-up compared with placebo (P=0.005), with a trend favoring biofeedback over diazepam (P=0.067). Biofeedback patients reduced pelvic floor electromyography during straining significantly more than diazepam patients (P<0.001). CONCLUSIONS: This investigation provides definitive support for the efficacy of biofeedback for pelvic floor dyssynergia and shows that instrumented biofeedback is essential to successful treatment.

Medical management of fecal incontinence.

Diarrhea and constipation are known risk factors for fecal incontinence. This report reviews how to diagnose and medically treat patients with chronic diarrhea, chronic constipation with overflow incontinence, and incontinence resulting from rectal mucosal prolapse secondary to hemorrhoids. Antidiarrheal agents (including loperamide, diphenoxylate, and difenoxin) and the tricyclic antidepressant amitriptyline improve continence in patients with diarrhea-associated incontinence. Other antidiarrheal agents are under investigation. The mechanism is believed to be decreased intestinal motility and stool frequency resulting in more formed stools. Increases in anal canal resting pressure may also contribute to improvement in continence. Adverse effects are constipation from excessive use. In addition to antidiarrheal drugs, fiber supplements may improve incontinence associated with diarrhea. Transient, benign cases of constipation usually respond to increasing fluid intake and dietary fiber, improving mobility, or eliminating the concurrent use of constipating drugs. For mild to moderate constipation, bulking agents, laxatives, and stool softeners are used cautiously so as not to excessively loosen stools and exacerbate anal incontinence. Laxatives have been shown to improve continence, possibly through the mechanism of eliminating fecal impaction. Prolapsing hemorrhoids may partially obstruct defecation and cause soilage from the passage of fecal material, mucus, or blood. With endoscopic banding, a ligator is attached to an endoscope and a tight band is placed around the enlarged vein, causing the hemorrhoid to thrombose.

Biofeedback treatment of constipation: a critical review.

PURPOSE: This review was designed to 1) critically examine the research design used in investigations of biofeedback for pelvic floor dyssynergia, 2) compare the various biofeedback treatment protocols for pelvic floor dyssynergia-type constipation used in this research, 3) identify factors that influence treatment outcome, and 4) identify goals for future biofeedback research for pelvic floor dyssynergia. METHODS: A comprehensive review of both the pediatric and adult research from 1970 to 2002 on "biofeedback for constipation" was conducted using a Medline search in all languages. Only prospective studies including five or more subjects that described the treatment protocol were included. In addition, a meta-analysis of these studies was performed to compare the outcome of different biofeedback protocols for treating constipation. RESULTS: Thirty-eight studies were reviewed, and sample size, treatment protocol, outcome rates, number of sessions, and etiology are shown in a table. Ten studies using a parallel treatment design were reviewed in detail, including seven that randomized subjects to treatment groups. A meta-analysis (weighted by subjects) was performed to compare the results of two treatment protocols prevalent in the literature. The mean success rate of studies using pressure biofeedback (78 percent) was superior (P = 0.018) to the mean success rate for studies using electromyography biofeedback (70 percent). However, the mean success rates comparing studies using intra-anal electromyography sensors to studies using perianal electromyography sensors were 69 and 72 percent, respectively, indicating no advantages for one type of electromyography protocol over the other (P = 0.428). In addition to the varied protocols and instrumentation used, there also are inconsistencies in the literature regarding the severity and etiology of symptoms, patient selection criteria, and the definition of a successful outcome. Finally, no anatomic, physiologic, or demographic variables were identified that would assist in predicting successful outcome. Having significant psychological symptoms was identified as a factor that may influence treatment outcome, but this requires further study. CONCLUSION: Although most studies report positive results using biofeedback to treat constipation, quality research is lacking. Specific recommendations are made for future investigations to 1) improve experimental design, 2) clearly define outcome measures, 3) identify the etiology and severity of symptoms, 4) determine which treatment protocol and which component of treatment is most effective for different types of subjects, 5) systematically explore the role of psychopathology in this population, 6) use an adequate sample size that allows for meaningful analysis, and 7) include long-term follow-up data.