Systematic review of first-in-human and early phase clinical trials for surgically implantable biological mitral valve substitutes

BACKGROUND

The aim of this review was the creation of uniform protocols to carry out and disclose First-In-Human and preliminary clinical trials of biological mitral valve replacement. The need for consistent methodology in these early trials was highlighted by the observation of significant variability in the methods and protocols used across different research.

METHODS

An extensive search through six major databases was carried out to retrieve First-In-Human (FIH) clinical studies evaluating surgically implanted bio-prostheses in the mitral position.

RESULTS

Following the PRISMA guideline, a systematic search identified 2082 published articles until March 2023. After removing duplicates (189), 1862 citations were screened, resulting in 22 eligible studies with 3332 patients for analysis. The mitral valve prostheses in these studies ranged from 21 to 37 mm, with the 29 mm size being most prevalent. Patient numbers varied, with the FIH subgroup including 31 patients and the older subgroup including 163 patients. Average study durations differed: the older subgroup lasted 4.57 years, the FIH subgroup 2.85 years, and the early phase studies spanned 8.05 years on average.

CONCLUSION

FIH clinical report is essential to assess the significance of clinical data required for a "de novo" surgical implant. In addition, understanding the performance of the device, and recognizing the difficulties associated with the innovation constitute important lessons. These insights could be beneficial for the development of bioprosthetic heart valves and formulating a protocol for an FIH clinical trial.

Optimising seed processing techniques to improve germination and sowability of native grasses for ecological restoration

Grasslands across the globe are undergoing expansive degradation due to human impacts and climate change. If restoration of degraded native grassland is to be achieved at the scale now required, cost-effective means for seed-based establishment of grass species is crucial. However, grass seeds present numerous challenges associated with handling and germination performance that must be overcome to improve the efficiency of seeding. Previous research has demonstrated that complete removal of the palea and lemma (husk) maximises germination performance, hence we investigated the effects of complete husk removal on seed handling and germination of four temperate Australian grass species. Three techniques were tested to remove the husk - manual cleaning, flaming or acid digestion (the latter two followed by a manual cleaning step); these techniques were refined and adapted to the selected species, and germination responses were compared. The complete removal of the husk improved seed handling and sowability for all species. Germination was improved in Microlaena stipoides by 19% and in Rytidosperma geniculatum by 11%. Of the husk removal methods tested, flaming was detrimental to seed germination and fatal for one species (R. geniculatum). Compared to manual cleaning, sulphuric acid improved the overall efficacy of the cleaning procedure and increased germination speed (T50) in Austrostipa scabra, Chloris truncata and M. stipoides, and improved final germination in R. geniculatum by 13%. The seed processing methods developed and tested in the present study can be applied to grass species that present similar handling and germination performance impediments. These and other technological developments (seed coating and precision sowing) will facilitate more efficient grassland restoration at large scale.

Multifaceted quality improvement initiative to decrease pediatric asthma readmissions

BACKGROUND

Asthma is the most common chronic disease of childhood and a leading cause of hospitalization in children. A primary goal of asthma control is prevention of hospitalizations. A hospital admission is the single strongest predictor of future hospital admissions for asthma. The 30-day asthma readmission rate at our institution was significantly higher than that of other hospitals in the Children's Hospital Association. As a result, a multifaceted quality improvement project was undertaken with the goal of reducing the 30-day inpatient asthma readmission rate by 50% within two years.

METHODS

Analysis of our institution's readmission patterns, value stream mapping of asthma admission, discharge, and follow-up processes, literature review, and examination of comparable successful programs around the United States were all utilized to identify potential targets for intervention. Interventions were implemented in a stepwise manner, and included increasing inhaler availability after discharge, modifying asthma education strategies, and providing in-home post-discharge follow-up. The primary outcome was a running 12-month average 30-day inpatient readmission rate. Secondary outcomes included process measures for individual interventions.

RESULTS

From a peak of 7.98% in January 2013, a steady decline to 1.65% was observed by July 2014, which represented a 79.3% reduction in 30-day readmissions.

CONCLUSION

A significant decrease in hospital readmissions for pediatric asthma is possible, through comprehensive, multidisciplinary quality improvement that spans the continuum of care.

A Review of Apparatus for Investigating the Mechanical Properties of Soft Animal Tissue in Vitro

This paper contains a review of the systems developed for testing skeletal muscle in vitro and it demonstrates how many of the design features and performance figures obtained are similar even though a range of engineering techniques have been used. The main topic considered is the uniaxial testing of skeletal muscle but it is also shown, by example, that similar ideas have been incorporated into machines for the uniaxial and multi-axial testing of other soft tissues.

Familial Alzheimer's disease and inherited prion disease in the UK are poorly ascertained

AIMS

To ascertain the frequency and geographical distribution of patients diagnosed with known genetic causes of Alzheimer's disease (AD) and inherited prion disease (IPD) in the UK 2001-2005. By comparison with frequencies predicted from published population studies, to estimate the proportion of patients with these conditions who are being accurately diagnosed.

METHODS

All the positive diagnostic test results (from both genetic testing centres) were identified for mutations in presenilin-1 (PSEN1), presenilin-2 (PSEN2), amyloid precursor protein (APP) and prion protein genes (PRNP) for patients resident in the UK in a 5 year period. The variation in the incidence of mutation detection between UK regions was assessed with census population data. Published studies of the genetic epidemiology of familial early onset AD (EOAD) were reviewed to produce estimates of the number of patients in the UK that should be detected.

RESULTS

The rate of detection of EOAD and IPD varied very significantly and consistently between regions of the UK with low rates of detection in Northern and Western Britain (72% less detection in these regions compared with Central and Southeast Britain). The estimates from population studies further suggest a greater number of patients with EOAD than are diagnosed by genetic testing throughout the UK.

CONCLUSIONS

It is likely that patients with EOAD and IPD are not being recognised and referred for testing. With the prospect of meaningful disease modifying therapeutics for these diseases, this study highlights an issue of relevance to neurologists and those planning for provision of National Health Services.

Neonatal cochlear function: measurement after exposure to acoustic noise during in utero MR imaging

PURPOSE

To establish whether fetal exposure to the operating noise of 1.5-T magnetic resonance (MR) imaging is associated with cochlear injury and subsequent hearing loss in neonates.

MATERIALS AND METHODS

The study was performed with local research ethics committee approval and written informed parental consent. Neonatal hearing test results, including otoacoustic emission (OAE) data, were sought for all neonates delivered in Sheffield who had previously undergone in utero MR imaging between August 1999 and September 2007. The prevalence of hearing impairment in these neonates was determined, with corresponding 95% confidence intervals calculated by using the binomial exact method, and mean OAE measurements were compared with anonymized local audiometric reference data by using the t test.

RESULTS

One hundred three neonates who had undergone in utero MR imaging were identified; 96 of them had completed hearing screening assessment. Thirty-four of these babies were admitted to the neonatal intensive care unit (NICU), and one of them had bilateral hearing impairment. The prevalence of hearing impairment was 1% (one of 96; 95% confidence interval: 0.03%, 5.67%), which is in accordance with the prevalence expected, given the high proportion of babies in this study who had been in the NICU (ie, NICU graduates). In addition, for the well babies, there was no significant difference in mean OAE cochlear response compared with that for a reference data set of more than 16,000 OAE results. When NICU graduates were included in the comparison, a significant difference (P = .002) was found in one of four frequency bands used to analyze the cochlear response; however, this difference was small compared with the normal variation in OAE measurements.

CONCLUSION

The findings in this study provide some evidence that exposure of the fetus to 1.5-T MR imaging during the second and third trimesters of pregnancy is not associated with an increased risk of substantial neonatal hearing impairment.

Long-term trends in carpal tunnel syndrome

OBJECTIVE

To assess temporal trends in carpal tunnel syndrome (CTS) incidence, surgical treatment, and work-related lost time.

METHODS

Incident CTS and first-time carpal tunnel release among Olmsted County, Minnesota, residents were identified using the medical records linkage system of the Rochester Epidemiology Project; 80% of a sample were confirmed by medical record review. Work-related CTS was identified from the Minnesota Department of Labor and Industry.

RESULTS

Altogether, 10,069 Olmsted County residents were initially diagnosed with CTS in 1981-2005. Overall incidence (adjusted to the 2000 US population) was 491 and 258 per 100,000 person-years for women vs men (p < 0.0001) and 376 per 100,000 for both sexes combined. Adjusted annual rates increased from 258 per 100,000 in 1981-1985 to 424 in 2000-2005 (p < 0.0001). The average annual incidence of carpal tunnel release surgery was 109 per 100,000, while that for work-related CTS was 11 per 100,000. An increase in young, working-age individuals seeking medical attention for symptoms of less severe CTS in the early to mid-1980s was followed in the 1990s by an increasing incidence in elderly people.

CONCLUSIONS

The incidence of medically diagnosed carpal tunnel syndrome (CTS) accelerated in the 1980s. The cause of the increase is unclear, but it corresponds to an epidemic of CTS cases resulting in lost work days that began in the mid-1980s and lasted through the mid-1990s. The elderly present with more severe disease and are more likely to have carpal tunnel surgery, which may have significant health policy implications given the aging population.

Neutralizing antibodies to interferon beta: Assessment of their clinical and radiographic impact: An evidence report: Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology

The clinical and radiologic impact of developing neutralizing antibodies (NAbs) to interferon beta (IFNbeta) while on this therapy for multiple sclerosis (MS) is assessed. On the basis of Class II and III evidence, it is concluded that treatment of patients with MS with IFNbeta (Avonex, Betaseron, or Rebif) is associated with the production of NAbs (Level A). NAbs in the serum are probably associated with a reduction in the radiographic and clinical effectiveness of IFNbeta treatment (Level B). In addition, the rate of NAb production is probably less with IFNbeta-1a treatment than with IFNbeta-1b treatment, although the magnitude and persistence of this difference is difficult to determine (Level B). Finally, it is probable that there is a difference in seroprevalence due to variability in the dose of IFNbeta injected or in the frequency or route of its administration (Level B). Regardless of the explanation, it seems clear that IFNbeta-1a (as it is currently formulated for IM injection) is less immunogenic than the current IFNbeta preparations (either IFNbeta-1a or IFNbeta-1b) given multiple times per week subcutaneously (Level A). However, because NAbs disappear in some patients even with continued IFNbeta treatment (especially in patients with low titers), the persistence of this difference is difficult to determine (Level B). Although the finding of sustained high-titer NAbs (>100 to 200 NU/mL) is associated with a reduction in the therapeutic effects of IFNbeta on radiographic and clinical measures of MS disease activity, there is insufficient information on the utilization of NAb testing to provide specific recommendations regarding when to test, which test to use, how many tests are necessary, or which cutoff titer to apply (Level U).

An enteric-coated high-buffered pancrelipase reduces steatorrhea in patients with cystic fibrosis: a prospective, randomized study

OBJECTIVE

Enteric-coated (EC) high-buffered (2.5 mEq [2.5 mmol] bicarbonate per capsule) pancrelipase microsphere enzymes were compared to EC-nonbuffered pancreatic enzymes for efficacy in reducing steatorrhea in patients with cystic fibrosis.

DESIGN

Prospective, randomized, controlled trial using a crossover design with each subject as his/her own control.

SUBJECTS/SETTING

Eighteen subjects with cystic fibrosis, who had pancreatic insufficiency and required large enzyme doses, were studied over two consecutive 7-day treatment periods.

INTERVENTION

Each 7-day period consisted of 3 days at home followed by 4 days in a general clinical research center for careful control of diets, enzyme lipase doses (given at approximately 50% of the subject's usual lipase dose), and carmine red-labeled stool collections for 72-hour fecal fat balance studies.

MAIN OUTCOME MEASURE

Fecal fat excretion.

STATISTICAL ANALYSES PERFORMED

Differences in fat excretion, when each subject received EC-high-buffered pancrelipase vs EC-nonbuffered enzymes, were compared using linear modeling.

RESULTS

Mean fat excretion decreased significantly in each subject during periods when given EC-high-buffered pancrelipase compared with periods when given EC-nonbuffered enzymes (fat excretion 18.2% vs 24.9% or fat absorption 81.8% vs 75.1%, respectively; P=0.01). Thirteen of 18 subjects (72%) excreted less fat when receiving EC-high-buffered pancrelipase whereas 10 (56%) decreased fat excretion by more than 5%, and five subjects did not respond.

CONCLUSIONS

EC-high-buffered pancrelipase decreased fat excretion, symbolizing improved fat absorption, when compared with EC-nonbuffered pancreatic enzymes given at equivalent, reduced (approximately 50% of usual) lipase doses in nourished subjects with cystic fibrosis and mild pulmonary disease.

Tactile information transfer: a comparison of two stimulation sites

Two experiments on the discrimination of time-varying tactile stimuli were performed, with comparison of stimulus delivery to the distal pad of the right index finger and to the right wrist (palmar surface). Subjects were required to perceive differences in short sequences of computer-generated stimulus elements (experiment 1) or differences in short tactile stimuli derived from a speech signal (experiment 2). The pulse-train stimuli were distinguished by differences in frequency (i.e., pulse repetition rate) and amplitude, and by the presence/absence of gaps (approximately 100-ms duration). Stimulation levels were 10 dB higher at the wrist than at the fingertip, to compensate for the lower vibration sensitivity at the wrist. Results indicate similar gap detection at wrist and fingertip and similar perception of frequency differences. However, perception of amplitude differences was found to be better at the wrist than at the fingertip. Maximum information transfer rates for the stimuli in experiment 1 were estimated at 7 bits s(-1) at the wrist and 5 bits s(-1) at the fingertip.

Syncope associated with pain as the presenting feature of neck malignancy: failure of cardiac pacemaker to prevent attacks in two cases

Two patients are described in whom syncope was the presenting clinical feature of an undiagnosed neck malignancy. Both patients also had attacks associated with paroxysms of severe neck pain. Neither patient responded to cardiac pacing.

Optic chiasm enhancement associated with giant aneurysm and yttrium treated pituitary adenoma

A patient with a history of pituitary tumour treated with yttrium 29 years before presented with an asymmetrical chiasmal neuropathy. Magnetic resonance imaging showed a partially thrombosed giant aneurysm of the right internal carotid artery, with enhancement of the chiasm and right optic tract adjacent to the aneurysm. It was thought that, in addition to the effects of compression, a peri-aneurysmal inflammatory reaction had developed, causing breakdown of the blood-brain barrier and consequent inflammatory changes in the optic chiasm. High dose steroid treatment led to significant improvement in vision within two weeks. Steroids may have a role in the acute preservation of vision in similar cases, as well as in cases of deterioration following coiling or embolisation of aneurysms where thrombosis within the aneurysm has been induced.

Monitoring hydrate formation and dissociation in sandstone and bulk with magnetic resonance imaging

Magnetic resonance imaging (MRI) has been shown to be a very effective tool for monitoring the formation and dissociation of hydrates because of the large intensity contrast between the images of the liquid components and the solid hydrate. Tetrahydrofuran/water hydrate was used because the two liquid components are miscible and form hydrate at ambient pressure. These properties made this feasibility study proceed much faster than using methane/water, which requires high pressure to form the hydrate. The formation and dissociation was monitored first in a THF/water-saturated Berea sandstone plug and second in the bulk. In both cases it appeared that nucleation was needed to begin the formation process, i.e., the presence of surfaces in the sandstone and shaking of the bulk solution. Dissociation appeared to be dominated by the rate of thermal energy transfer. The dissociation temperature of hydrate formed in the sandstone plug was not significantly different from the dissociation temperature in bulk.

Practice parameter: Immunotherapy for Guillain-Barre syndrome: Report of the Quality Standards Subcommittee of the American Academy of Neurology

OBJECTIVE

To provide an evidence-based statement to guide physicians in the management of Guillain-Barré syndrome (GBS).

METHODS

Literature search and derivation of evidence-based statements concerning the use of immunotherapy were performed.

RESULTS

Treatment with plasma exchange (PE) or IV immunoglobulin (IVIg) hastens recovery from GBS. Combining the two treatments is not beneficial. Steroid treatment given alone is not beneficial.

RECOMMENDATIONS

1) PE is recommended for nonambulant adult patients with GBS who seek treatment within 4 weeks of the onset of neuropathic symptoms. PE should also be considered for ambulant patients examined within 2 weeks of the onset of neuropathic symptoms; 2) IVIg is recommended for nonambulant adult patients with GBS within 2 or possibly 4 weeks of the onset of neuropathic symptoms. The effects of PE and IVIg are equivalent; 3) Corticosteroids are not recommended for the management of GBS; 4) Sequential treatment with PE followed by IVIg, or immunoabsorption followed by IVIg is not recommended for patients with GBS; and 5) PE and IVIg are treatment options for children with severe GBS.

The frequency of carpal tunnel syndrome in computer users at a medical facility

A survey was done of employees who were identified as frequent computer users. Although 29.6% of the employees reported hand paresthesias, only 27 employees (10.5%) met clinical criteria for carpal tunnel syndrome, and in 9 (3.5%) the syndrome was confirmed by nerve conduction studies. Affected and unaffected employees had similar occupations, years using a computer, and time using the computer during the day. The frequency of carpal tunnel syndrome in computer users is similar to that in the general population.

Practice parameter: early detection of dementia: mild cognitive impairment (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology

OBJECTIVE

The goal of this project was to determine whether screening different groups of elderly individuals in a general or specialty practice would be beneficial in detecting dementia.

BACKGROUND

Epidemiologic studies of aging and dementia have demonstrated that the use of research criteria for the classification of dementia has yielded three groups of subjects: those who are demented, those who are not demented, and a third group of individuals who cannot be classified as normal or demented but who are cognitively (usually memory) impaired.

METHODS

The authors conducted computerized literature searches and generated a set of abstracts based on text and index words selected to reflect the key issues to be addressed. Articles were abstracted to determine whether there were sufficient data to recommend the screening of asymptomatic individuals. Other research studies were evaluated to determine whether there was value in identifying individuals who were memory-impaired beyond what one would expect for age but who were not demented. Finally, screening instruments and evaluation techniques for the identification of cognitive impairment were reviewed.

RESULTS

There were insufficient data to make any recommendations regarding cognitive screening of asymptomatic individuals. Persons with memory impairment who were not demented were characterized in the literature as having mild cognitive impairment. These subjects were at increased risk for developing dementia or AD when compared with similarly aged individuals in the general population.

RECOMMENDATIONS

There were sufficient data to recommend the evaluation and clinical monitoring of persons with mild cognitive impairment due to their increased risk for developing dementia (Guideline). Screening instruments, e.g., Mini-Mental State Examination, were found to be useful to the clinician for assessing the degree of cognitive impairment (Guideline), as were neuropsychologic batteries (Guideline), brief focused cognitive instruments (Option), and certain structured informant interviews (Option). Increasing attention is being paid to persons with mild cognitive impairment for whom treatment options are being evaluated that may alter the rate of progression to dementia.

Practice parameter: diagnosis of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology

OBJECTIVE

To update the 1994 practice parameter for the diagnosis of dementia in the elderly.

BACKGROUND

The AAN previously published a practice parameter on dementia in 1994. New research and clinical developments warrant an update of some aspects of diagnosis.

METHODS

Studies published in English from 1985 through 1999 were identified that addressed four questions: 1) Are the current criteria for the diagnosis of dementia reliable? 2) Are the current diagnostic criteria able to establish a diagnosis for the prevalent dementias in the elderly? 3) Do laboratory tests improve the accuracy of the clinical diagnosis of dementing illness? 4) What comorbidities should be evaluated in elderly patients undergoing an initial assessment for dementia?

RECOMMENDATIONS

Based on evidence in the literature, the following recommendations are made. 1) The DSM-III-R definition of dementia is reliable and should be used (Guideline). 2) The National Institute of Neurologic, Communicative Disorders and Stroke--AD and Related Disorders Association (NINCDS-ADRDA) or the Diagnostic and Statistical Manual, 3rd edition, revised (DSM-IIIR) diagnostic criteria for AD and clinical criteria for Creutzfeldt--Jakob disease (CJD) have sufficient reliability and validity and should be used (Guideline). Diagnostic criteria for vascular dementia, dementia with Lewy bodies, and frontotemporal dementia may be of use in clinical practice (Option) but have imperfect reliability and validity. 3) Structural neuroimaging with either a noncontrast CT or MR scan in the initial evaluation of patients with dementia is appropriate. Because of insufficient data on validity, no other imaging procedure is recommended (Guideline). There are currently no genetic markers recommended for routine diagnostic purposes (Guideline). The CSF 14-3-3 protein is useful for confirming or rejecting the diagnosis of CJD (Guideline). 4) Screening for depression, B(12) deficiency, and hypothyroidism should be performed (Guideline). Screening for syphilis in patients with dementia is not justified unless clinical suspicion for neurosyphilis is present (Guideline).

CONCLUSIONS

Diagnostic criteria for dementia have improved since the 1994 practice parameter. Further research is needed to improve clinical definitions of dementia and its subtypes, as well as to determine the utility of various instruments of neuroimaging, biomarkers, and genetic testing in increasing diagnostic accuracy.

Practice parameter: management of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology

OBJECTIVE

To define and investigate key issues in the management of dementia and to make literature-based treatment recommendations.

METHODS

The authors searched the literature for four clinical questions: 1) Does pharmacotherapy for cognitive symptoms improve outcomes in patients with dementia? 2) Does pharmacotherapy for noncognitive symptoms improve outcomes in patients with dementia? 3) Do educational interventions improve outcomes in patients and/or caregivers? 4) Do other nonpharmacologic interventions improve outcomes in patients and/or caregivers?

RESULTS

Cholinesterase inhibitors benefit patients with AD (Standard), although the average benefit appears small; vitamin E likely delays the time to clinical worsening (Guideline); selegiline, other antioxidants, anti-inflammatories, and estrogen require further study. Antipsychotics are effective for agitation or psychosis in patients with dementia where environmental manipulation fails (Standard), and antidepressants are effective in depressed patients with dementia (Guideline). Educational programs should be offered to family caregivers to improve caregiver satisfaction and to delay the time to nursing home placement (Guideline). Staff of long-term care facilities should also be educated about AD to minimize the unnecessary use of antipsychotic medications (Guideline). Behavior modification, scheduled toileting, and prompted voiding reduce urinary incontinence (Standard). Functional independence can be increased by graded assistance, skills practice, and positive reinforcement (Guideline).

Characterization of 2-[[4-[[2-(1H-tetrazol-5-ylmethyl)phenyl]methoxy]methyl]quinoline N-glucuronidation by in vitro and in vivo approaches

RG 12525 is a new chemical entity recently evaluated for the treatment of type II diabetes. Clinical studies have previously identified the tetrazole N2-glucuronide conjugate of RG 12525 as the predominant metabolite in plasma following oral administration of RG 12525. Species differences in RG 12525 glucuronidation were first investigated with incubations of RG 12525 with rat, monkey, and human hepatocytes. The results showed the N2-glucuronide to be the major metabolite in human and monkey samples, with only low levels observed for the rat. The formation of this glucuronide by human liver microsomes was subsequently characterized. RG 12525 N2-glucuronidation was found to have a pH optimum of 7.0 to 7.5 and demonstrated a high affinity with a K(m) range of 16.6 to 21.1 microM RG 12525 (n = 3). The rate of N2-glucuronide formation ranged from 2.5 to 15.4 nmol of RG 12525 N2-glucuronide formed/min/mg of protein ( approximately 6-fold) in the 21 samples assayed. The reaction was inhibited by known substrates for glucuronidation, with imipramine (62%), naringenin (44%), and scopoletin (38%) producing the largest degree of inhibition at equimolar concentrations of substrate and inhibitor. Of the eight expressed UDP-glucuronosyltransferase (UGT) forms assayed, UGT1A1 and 1A3 displayed the highest rate of RG 12525 N2-glucuronidation (0.109 and 0.125 nmol/min/mg, respectively). Finally, low levels of N2-glucuronidation of RG 12525 by human jejunum microsomes were demonstrated, suggesting that presystemic clearance via glucuronidation may constitute a barrier to bioavailability.

Lack of correlation between in vitro inhibition of CYP3A-mediated metabolism by a PPAR-gamma agonist and its effect on the clinical pharmacokinetics of midazolam, an in vivo probe of CYP3A activity

RG 12525 (2-[[4-[[2-(1H-tetrazole-5-ylmethyl)phenyl]methoxy]phenoxy]methyl] quinolone) is a novel peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonist. In vitro microsomal inhibition assays indicated that RG 12525 is a potent inhibitor of CYP3A4, with a Ki value of 0.5 microM. With the conservative assumption that the total plasma concentration of drug was available to metabolic enzymes following RG 12525 oral administration, marked inhibition of CYP3A4 was expected to substantially reduce the systemic clearance of compounds metabolized by this enzyme. The possibility also existed for inhibition of intestinal and hepatic CYP3A4 by RG 12525 to reduce "first-pass" metabolism and increase absolute bioavailability of CYP3A4 substrates orally coadministered. Consequently, an in vivo drug-drug interaction study was performed to evaluate the effects of orally administered RG 12525 on in vivo CYP3A4 activity in healthy male subjects. The pharmacokinetics of oral midazolam, a probe for intestinal and hepatic CYP3A activity, was not influenced by either the low (100 mg qd for 4 days) or high (600 mg qd for4 days) RG 12525 dosing regimen despite the resulting total plasma concentrations of inhibitor that were well above in vitro Ki values. The point estimates and 90% confidence intervals for the ratios of mean midazolam AUC for subjects administered 100 mg RG 12525 (110.6; 98.7-124.1) and 600 mg RG 12525 (98.4; 84.4-114.7) versus midazolam alone were within 80% to 125%. To explain these results, factors that could limit the accuracy of in vitro models in predicting metabolic drug interactions, mainly the high degree of RG 12525 protein binding (> 99.9%), were considered. The lack of correlation between the in vitro inhibition of CYP3A4 by RG 12525 and the inconsequential effects of this compound on midazolam pharmacokinetics accentuate the need to recognize factors other than plasma drug concentrations and potency of in vitro enzyme inhibition when extrapolating in vitro data to predict in vivo drug-drug interactions.

Efficacy and safety of recombinant human nerve growth factor in patients with diabetic polyneuropathy: A randomized controlled trial. rhNGF Clinical Investigator Group

CONTEXT

Nerve growth factor is a neurotrophic factor that promotes the survival of small fiber sensory neurons and sympathetic neurons in the peripheral nervous system. Recombinant human nerve growth factor (rhNGF) has demonstrated efficacy as treatment for peripheral neuropathy in experimental models and phase 2 clinical trials.

OBJECTIVE

To evaluate the efficacy and safety of a 12-month regimen of rhNGF in patients with diabetic polyneuropathy.

DESIGN

Randomized, double-blind, placebo-controlled phase 3 trial conducted from July 1997 through May 1999.

SETTING

Eighty-four outpatient centers throughout the United States.

PATIENTS

A total of 1019 men and women aged 18 to 74 years with either type 1 or type 2 diabetes and a sensory polyneuropathy attributable to diabetes.

INTERVENTIONS

Patients were randomly assigned to receive either rhNGF, 0.1 microg/kg (n = 504), or placebo (n = 515) by subcutaneous injection 3 times per week for 48 weeks. Patients were assessed at baseline, 12 weeks, 24 weeks, and 48 weeks.

MAIN OUTCOME MEASURES

The primary outcome measure was a change in neuropathy between baseline and week 48, demonstrated by the Neuropathy Impairment Score for the Lower Limbs, compared between the 2 groups. Secondary outcome measures included quantitative sensory tests using the CASE IV System, the Neuropathy Symptom and Change questionnaire, the Patient Benefit Questionnaire (PBQ), and a global symptom assessment, as well as nerve conduction studies and occurrence of new plantar foot ulcers. Patients also were evaluated for presence of adverse events.

RESULTS

Among patients who received rhNGF, 418 (83%) completed the regimen compared with 461 (90%) who received placebo. Administration of rhNGF was safe, with few adverse events attributed to treatment apart from injection site pain/hyperalgesia and other pain syndromes. However, neither the primary end point (P =.25) nor most of the secondary end points demonstrated a significant benefit of rhNGF. Exceptions were the global symptom assessment (P =.03) and 2 of 32 comparisons within the PBQ, which showed a modest but significant benefit of rhNGF (P =.05 for severity of pain in the legs and P =.003 for 6-month symptoms in the feet and legs).

CONCLUSION

Unlike previous phase 2 trials, this phase 3 clinical trial failed to demonstrate a significant beneficial effect of rhNGF on diabetic polyneuropathy. JAMA. 2000;284:2215-2221.

Neurologic disorders masquerading as carpal tunnel syndrome: 12 cases of failed carpal tunnel release

We describe 12 patients with a diagnosis of carpal tunnel syndrome in whom carpal tunnel release was unsuccessful and another neurologic disorder was diagnosed subsequently. Final diagnoses included polyneuropathy, radiculopathy, motor neuron disease, spondylotic myelopathy, syringomyelia, and multiple sclerosis. Sources of error by the electromyographer and treating physician were identified. Care must be taken to avoid an inappropriate carpal tunnel operation when clinical or electrodiagnostic features are atypical.

Motor unit changes in sporadic idiopathic Parkinson's disease

We studied motor unit changes in 20 patients with Parkinson's disease (PD) and 20 age-matched control subjects to look for evidence of motorneuron degeneration in sporadic idiopathic PD. Patients and control subjects were screened by clinical criteria and nerve conduction studies to exclude those with peripheral neuropathic processes. Changes in motor unit morphology were investigated with subjective and computerized quantitative electromyography (QEMG) of the anterior tibialis (AT) and first dorsal interosseous. Multivariate comparisons showed a significant difference in the QEMG analysis for motor unit enlargement in patients with PD versus control subjects. Some of the univariate comparisons for both the subjective and QEMG analyses of the AT were also significant. These results demonstrate that motorneuron drop-out with reinnervation occurs in sporadic idiopathic PD. In summary, our findings provide evidence that clinically silent motorneuron disease occurs in typical cases of sporadic idiopathic PD, suggesting that it may be a normal part of the pathologic picture of PD. Any hypothesis concerning the pathogenic mechanism of PD would need to take into account such a finding.

Symptoms of 100 patients with electromyographically verified carpal tunnel syndrome

To determine the symptoms of carpal tunnel syndrome (CTS), screening evaluations were performed in 244 consecutive patients with sensory symptoms in the hand and unequivocal slowing of median nerve conduction at the wrist. This yielded 100 patients thought to have no explanation other than CTS for their upper limb complaints. These patients completed a hand symptom diagram (HSD) and questionnaire (HSQ) about their symptoms. CTS symptoms were most commonly reported in median and ulnar digits, followed by median digits only and a glove distribution. Unusual sensory patterns were reported by some patients. Based on the HSQ, paresthesias or pain proximal to the wrist occurred in 36.5% of hands. The usefulness of the HSD and HSQ for diagnosis was determined by asking three physicians, blinded to the diagnosis, to rate the likelihood of CTS in the patients with CTS and in 50 patients with other causes of upper extremity paresthesia. The sensitivities of the instruments ranged from 54.1% to 85.5%. Combining the HSD and HSQ ratings increased the range of sensitivities to 79.3% to 93.7%.

Structure-function analysis of human cytochrome P-450 2B6 using a novel substrate, site-directed mutagenesis, and molecular modeling

The structural basis for functional differences between human cytochrome P-450 2B6 and rat 2B1 was investigated. An amino acid sequence alignment predicted the location of 2B6 substrate recognition site (SRS) residues. Ten residues within these SRSs unique to 2B6 compared with 2B1, 2B4, and 2B11 were chosen for mutagenesis. Two additional sites that differ between 2B6 and 2B1 and are known to have a role in 2B1 substrate specificity were also mutated. The 2B6 mutants were expressed in Spodoptera frugiperda cells and characterized using the 2B6-specific substrate RP 73401 [3-cyclopentyloxy-N-(3,5-dichloro-4-pyridyl)-4-methoxybenzamide], the 2B1-selective substrate androstenedione, and the common substrate 7-ethoxy-4-trifluoromethylcoumarin. Mutants F107I and L363V exhibited decreased RP 73401 hydroxylation but retained most of the wild-type level of 2B6 7-ethoxy-4-trifluoromethylcoumarin O-deethylase activity. In addition, SRS exchanges were studied in which the amino acid sequence of 2B6 SRSs was converted to the sequence of 2B1. Each of these constructs, having two to seven substitutions, expressed at levels similar to 2B6 but did not acquire significant androstenedione hydroxylase activity. Docking of RP 73401 into the active site of a 2B6 homology model suggested a direct interaction with residue L363 but not with F107. Findings from this study suggest that 1) residues F107 and L363 are necessary for 2B6 RP 73401 hydroxylase activity, 2) 2B6 is able to tolerate multiple SRS substitutions without compromising protein expression levels or protein stability, and 3) conferring androstenedione hydroxylase function to cytochrome P-450 2B6 is more complex than altering a single SRS.

Use of the steroid derivative RPR 106541 in combination with site-directed mutagenesis for enhanced cytochrome P-450 3A4 structure/function analysis

RPR 106541 (20R-16alpha,17alpha-[butylidenebis(oxy)]-6al pha, 9alpha-difluoro-11beta-hydroxy-17beta-(methylthio)androst a-4-en-3-one) is an airway-selective steroid developed for the treatment of asthma. Two metabolites produced by human liver microsomes were identified as R- and S-sulfoxide diastereomers based on liquid chromatography/mass spectrometry analysis, proton nuclear magnetic resonance, and cochromatography with standards. Sulfoxide formation was determined to be cytochrome P-450 (CYP) 3A4-dependent by correlation with CYP3A4-marker nifedipine oxidase activity, inhibition by cyclosporin A and troleandomycin, and inhibition of R- (70%) and S- (64%) sulfoxide formation by anti-3A antibody. Expressed CYP2C forms catalyzed RPR 106541 sulfoxidation; however, other phenotyping approaches failed to confirm the involvement of CYP2C forms in these reactions in human liver microsomes. Expressed CYP3A4 catalyzed the formation of the sulfoxide diastereomers in a 1:1 ratio, whereas CYP3A5 displayed stereoselectivity for formation of the S-diastereomer. The high rate of sulfoxidation by CYP3A4 and the blockage of oxidative metabolism at the electronically favored 6beta-position provided advantages for RPR 106541 over other substrates as an active site probe of CYP3A4. Therefore, oxidation of RPR 106541 by various CYP3A4 substrate recognition site (SRS) mutants was assessed. In SRS-4, A305V and F304A showed dramatically reduced rates of R-diastereomer formation (83 and 64% decreases, respectively), but S-diastereomer formation was affected to a lesser extent. A370V (SRS-5) showed decreased formation of the R-sulfoxide (52%) but increased formation of the S-diastereomer. In the SRS-2 region, the most dramatic change in sulfoxide ratios was observed for L210A. In conclusion, the structure of RPR 106541 imposes specific constraints on enzyme binding and activity and thus represents an improved CYP3A4 probe substrate.

Detection of very complex taste mixtures

Mixtures can often be tasted when all components are too weak to be tasted separately. Such mixtures are said to be integrative. Integration was demonstrated by mixing compounds in concentrations proportional to their separate detection thresholds and then measuring the detection threshold of the mixture as a whole by forced choice with plain water. Mixtures of 3, 6, 12 and 24 compounds were thus evaluated. With earlier data on 2-, 3- and 4-component mixtures, the results show that the concentration of any constituent compound goes down in approximate proportion to the number of compounds with which it is in mixture. This nearly complete integration describes mixtures of like-quality compounds, of unlike-quality compounds, and of both like- and unlike-quality compounds together. Integrative mixtures provide a model for the detection of the ultracomplex stimuli of everyday life, such as foods and drinking waters. Although the degree of integration may trail off slightly with mixtures of high complexity, the results proffer no limit on the number of compounds that can be at least partially integrated. In principle, integration permits detection of natural substances whose myriad components could all be far below threshold. The mechanism of taste integration is speculative, but the facts are congenial to the hypothesis of multiple parallel channels for the processing of intensity and quality.

Use of transient evoked otoacoustic emissions to detect and monitor cochlear damage caused by platinum-containing drugs

Transient evoked otoacoustic emissions (TEOAE) have been evaluated as a means of monitoring cochlear function in patients receiving the chemotherapeutic agents cisplatin and carboplatin (-cis-diammine, 1,1-cyclobutane dicarboxylate (2) -0,0-platinum). Patients receiving these drugs were monitored prospectively with pure tone audiometry (PTA), tympanometry and TEOAE. Data was collected on 22 subjects receiving cisplatin and nine subjects receiving carboplatin. Significant deterioration in both PTA thresholds and TEOAE energy levels (with no change in tympanometry) were detected in the cisplatin group. No significant deterioration in audiological parameters occurred in the carboplatin group. It is indicated that cisplatin has a significant ototoxic effect in the majority of patients, whereas any ototoxic effect of carboplatin was undetectable. Our findings were different from previous studies in that the measurable changes in TEOAE occurred later than changes in the pure tone audiogram for the cisplatin group.

A multimodal assessment of sensory thresholds in aging

Young and elderly subjects yielded forced-choice detection thresholds in each of seven sensory tasks: (1) taste of sodium chloride, (2) smell of butanol, (3) cooling, (4) low-frequency vibrotaction, (5) high-frequency vibrotaction, (6) low-frequency hearing, and (7) high-frequency hearing. Average scores across these tasks nearly perfectly separated the 22 elderly from the 15 young subjects. For individual modalities, however, separation between the groups varied from complete (high-frequency touch) to negligible (low-frequency hearing). Scores on the Boston Picture Naming Test and especially the Wechsler Logical Memory Test correlated strongly with average threshold score (Pearson r = .80) and moderately with scores on individual modalities. This sensory-cognitive link is not caused, as might be supposed, by diminishing age-related capacity to handle the detection task, because the very same task resulted in negligible age effect (low-frequency hearing) and large effect (high-frequency hearing) in the same subjects.

Temperature sensitivity of the body surface over the life span

Detection thresholds to warming and cooling were measured in 13 regions of the body in 60 adults aged between 18 and 88 years. From these thresholds were constructed maps of thermal sensitivity homologous to body maps of spatial acuity (in the older literature two-point discrimination), long known to the somatosensory scientist. Maps of cold and warm sensitivity for young, middle-aged and elderly adults, show how sensitivity changes with age in the various body regions. Three characteristics emerge, irrespective of age: (1) sensitivity varies approximately 100-fold over the body surface. The face, especially near the mouth, is exquisitely sensitive, the extremities, by comparison, poor, other regions, intermediate. (2) All body regions are more sensitive to cold than to warm. (3) The better a region is at detecting cold, the better it is at detecting warm. With age, thermal sensitivity declines. The greatest changes take place in the extremities, especially the foot, where thresholds often become too large to measure. Central regions give up their sensitivity with age more slowly, and even (as in the lips) inconsequentially. Similar age-related changes have also previously been shown to characterize spatial acuity.

The costs of early hearing screening in England and Wales

A survey was carried out in 10 centres in England and Wales to determine the costs of hearing screening in the first year of life. The screens that were studied were targeted neonatal, universal neonatal, and the health visitor distraction test (HVDT) or alternative surveillance. Valid data were available from five centres for targeted neonatal screening (TNS), three for universal neonatal screening (UNS), and nine for the HVDT, although only five of the HVDT screens had valid data for follow up costs. The neonatal costs were consistent across the centres surveyed, whereas those for the HVDT screen varied considerably. The mean service costs for TNS, UNS, and the HVDT at 1994 prices were 5052 Pounds, 13,881 Pounds, and 24,519 Pounds for a standardised district of 1000 live births. Three conclusions seem justified. Firstly, UNS need not be prohibitively expensive as it costs considerably less than HVDT screening. Secondly, TNS appears to be a relatively inexpensive way of improving the age of identification of a proportion of the congenitally hearing impaired. Thirdly, given the published yields for UNS and the HVDT, the results indicate that UNS offers the most cost effective overall approach with alternative systems in place to identify late onset permanent hearing losses.

Pancreatic enzyme supplementation in cystic fibrosis patients before and after fibrosing colonopathy

BACKGROUND

In 1994 we cared for nine cystic fibrosis patients with fibrosing colonopathy. To evaluate the relationship between fibrosing colonopathy and supplemental pancreatic enzymes we reviewed our dosing of enzymes prior to fibrosing colonopathy development and then evaluated the subsequent effect of drastically reducing pancreatic enzyme dose.

METHODS

We retrospectively reviewed pancreatic enzyme dosing for 267 cystic fibrosis patients with pancreatic insufficiency. The supplemental enzyme history of nine patients with fibrosing colonopathy was contrasted with the history of 258 nonaffected patients. The pancreatic enzyme doses of 75 patients taking at least 6,000 U lipase/kg/meal were systematically reduced to approximately 2,000 lipase units/kg/meal. We evaluated the effect of this dose reduction on change in height and weight z scores one year after achievement of stable enzyme dose.

RESULTS

In the year prior to diagnosis patients with fibrosing colonopathy took a significantly larger pancreatic enzyme dose, whether assessed by highest dose or cumulative dose, than did nonaffected patients. Similar results were observed after controlling for sex and age. All 75 patients on at least 6,000 U lipase/kg/meal were able to tolerate a significant reduction in dose while achieving clinically acceptable nutrient absorption, with no change over one year in height and weight z scores.

CONCLUSIONS

Our data demonstrate a strong relationship between very high doses of pancreatic enzyme supplementation and formation of fibrosing colonopathy. These very high doses do not appear to be needed for adequate nutrient absorption and growth.

AAEM minimonograph #26: the electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine

The electrodiagnosis of carpal tunnel syndrome (CTS) is reviewed, including discussions of old and new techniques of motor and sensory nerve conduction, anomalous innervation, and needle electrode examination. A variety of sensitive nerve conduction studies (NCSs) are available for the evaluation of a patient with suspected CTS. For any particular patient, the NCS method chosen by the clinical neurophysiologist may vary for a number of reasons, including the severity of the deficit and the presence of superimposed conditions.

AAEM minimonograph #26: the electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine

The electrodiagnosis of carpal tunnel syndrome (CTS) is reviewed, including discussions of old and new techniques of motor and sensory nerve conduction, anomalous innervation, and needle electrode examination. A variety of sensitive nerve conduction studies (NCSs) are available for the evaluation of a patient with suspected CTS. For any particular patient, the NCS method chosen by the clinical neurophysiologist may vary for a number of reasons, including the severity of the deficit and the presence of superimposed conditions.

Detection of very complex taste mixtures: generous integration across constituent compounds

Mixtures of compounds can often be tasted even when all of their components are too weak to be tasted separately. Such mixtures are said to be integrative. Integration was demonstrated by mixing compounds in concentrations proportional to their separate detection thresholds and then measuring the detection threshold of the mixture as a whole by forced choice with plain water. Mixtures of 3, 6, 12, and 24 compounds were thus evaluated. With earlier data on two-, three-, and four-component mixtures (Stevens, J. C. Detection of taste in mixture with other tastes: Issues of masking and aging. Chem. Senses 21:211-221; 1996.), the results show that the concentration of any constituent compound goes down in approximate proportion to the number of compounds with which it is in mixture. This nearly complete integration seems to describe mixtures of like-quality compounds, of unlike-quality compounds, and of both like- and unlike-quality compounds. Integrative mixtures of the sort studied here provide a model for the detection of the ultracomplex stimuli of everyday life, such as foods and drinking waters. Although the degree of integration may trail off slightly with mixtures of high complexity, the present result proffers no limit on the number of compounds that can be at least partially integrated. In principle, integration permits the detection of natural substances whose myriad components could all be far below threshold. The mechanism of taste integration is speculative, but the facts are congenial to the hypothesis of multiple parallel channels for the processing of intensity and quality.

Detection of a target taste in a complex masker

Detection thresholds for sodium chloride were compared in aqueous solution, in mixture with a sucrose masker, in mixture with a citric acid masker, and in mixture with both of these maskers together. Separately the two maskers raised the threshold of sodium chloride by three to four times, and together by over nine times, a result consistent with independence (additivity) of the two masking effects. To achieve comparable masking with either sucrose alone or with citric acid alone would require increasing their masking concentrations by about ten times. Hence multiple masking can be a far more efficient means of concealing a taste, whether an unpleasant one (e.g. the bitter taste of medicine) or a pleasant one (e.g. a salty or sweet condiment). Multiple masking has dietary and culinary significance, especially for middle aged and elderly persons concerned about salt intake, because their thresholds for NaCl, whether with or without maskers, are typically two or three times higher than those of youthful persons.

Human liver CYP2B6-catalyzed hydroxylation of RP 73401

RP 73401 is a potent inhibitor of cyclic nucleotide phosphodiesterase type IV. RP 73401 is metabolized by human liver microsomes almost exclusively by transhydroxylation of the cyclopentyl group to RPR 113406. Liquid chromatography/mass spectrometry/mass spectrometry analysis of plasma from patients given RP 73401 also revealed a molecular ion and fragmentation consistent with RPR 113406. Thus, the objective was to determine the oxidative enzyme(s) responsible for RP 73401 hydroxylation. Kinetic constants of RP 113406 formation ranged from 8 to 26 MM and 0.83 to 5.99 nmol/min/mg protein for K(m) and V(max), respectively (n = 3). Enzyme activity varied 23-fold among 15 human liver microsome samples and correlated with CYP2A6-catalyzed coumarin hydroxylase (r2 = 0.85, P < .01) and CYP2B6-catalyzed 7-ethoxytrifluoromethylcoumarin O-deethylase (r2 = 0.82, P < .01) activities. Chemical inhibition studies showed a 63% decrease in RP 73401 hydroxylation by 500 microM orphenadrine. Coumarin (10 microM), however, did not inhibit RP 73401 hydroxylation. Also, anti-CYP2B1 IgG produced 85% inhibition of RP 73401 hydroxylation, but only a negligible decline in coumarin hydroxylase activity. Of the 10 expressed P450 forms studied, only CYP2B6 catalyzed RP 73401 hydroxylation. Finally, expressed CYP2B6 showed a high affinity (K(m) = 22.5 microM) for RP 73401 hydroxylation, similar to the human liver microsome studies.

The effect of RPR 102341 on theophylline metabolism and phenacetin O-deethylase activity in human liver microsomes

PURPOSE

RPR 102341 is structurally similar to the fluoroquinolone class of antibiotics. Because some fluoroquinolones have been shown to inhibit theophylline metabolism, concomitant administration may increase plasma levels of theophylline resulting in serious adverse effects. The purpose of this study was to determine if RPR 102341 affects theophylline metabolism in vitro and, thus, predict whether a clinically significant drug interaction is likely to occur. In addition, the effect of RPR 102341 on phenacetin O-deethylase activity was determined to address the enzymatic basis of a potential drug interaction.

METHODS

The in vitro theophylline metabolism assay was conducted according to a modification of a published procedure. The phenacetin O-deethylase assay was conducted according to a modification of a published procedure.

RESULTS

The rate of conversion of theophylline to 3-methylxanthine in human liver microsomes in the presence of 100 microM and 500 microM RPR 102341 was 93.6 and 106 percent of the control reactions, respectively. The formation of 1-methylxanthine was 97.6 and 100 percent of the control, and 1.3-dimethyluric acid formation was 88.9 and 95.2 percent of control at 100 microM and 500 microM RPR 102341, respectively. In agreement, RPR 102341 caused no inhibition of human liver CYP1A2-catalyzed phenacetin O-deethylase activity. Finally, no inhibition was observed when RPR 102341 was incubated with human liver microsomes and an NADPH regenerating system prior to the addition of theophylline.

CONCLUSIONS

Based on these studies, RPR 102341 is not expected to cause significant drug interactions with theophylline.

Orphenadrine and methimazole inhibit multiple cytochrome P450 enzymes in human liver microsomes

The specificities of orphenadrine and methimazole on eight human liver P450 enzyme activities were evaluated by studying the extent of inhibition at different concentrations in two protocols: competitive inhibition and preincubation. In the competitive inhibition protocol, orphenadrine decreased CYP2B6 marker activity up to 45-57% in human liver microsomes and up to 80-97% in cell microsomes containing cDNA-expressed CYP2B6. Orphenadrine strongly decreased CYP2D6 marker activity by 80-90%. Orphenadrine also partially decreased the CYP1A2, CYP2A6, CYP3A4, and CYP2C19 marker activities. In the preincubation protocol, orphenadrine decreased the CYP2B6 activity in cDNA-expressed cell microsomes to completion. In human liver microsomes, orphenadrine strongly decreased the marker activities of CYP2B6, CYP2D6, as well as CYP2C9; and partially decreased the marker activities of CYP1A2, CYP2A6, CYP3A4, and CYP2C19. In the competitive inhibition protocol, methimazole had no effect on the marker activities of CYP2E1 and CYP2A6; slightly decreased CYP2D6 marker activity; partially decreased the marker activities of CYP2C19, CYP2C9, and CYP2B6; and dramatically decreased CYP3A4 marker activity. Methimazole decreased CYP1A2 marker activity at lower concentrations, but not at the highest concentration studied (1 mM). In the preincubation protocol, methimazole was shown to be a potent and nonspecific inhibitor of all the enzyme activities. Marker activities of CYP2C9, CYP2C19, and CYP3A4 were completely inhibited at relatively low concentrations. This study indicates orphenadrine cannot be used as a selective inhibitor of CYP2B6 in human liver microsomes and that methimazole is not a selective inhibitor of the flavin-containing monooxygenase in human liver microsomes.