Early mandated social distancing is a strong predictor of reduction in peak daily new COVID-19 cases.

OBJECTIVES: Mandated social distancing has been applied globally to reduce the spread of coronavirus disease 2019 (COVID-19). However, the beneficial effects of this community-based intervention have not been proven or quantified for the COVID-19 pandemic. STUDY DESIGN: This is a regional population-level observational study. METHODS: Using publicly available data, we examined the effect of timing of mandated social distancing on the rate of COVID-19 cases in 119 geographic regions, derived from 41 states within the United States and 78 other countries. The highest number of new COVID-19 cases per day recorded within a geographic unit was the primary outcome. The total number of COVID-19 cases in regions where case numbers had reached the tail end of the outbreak was an exploratory outcome. RESULTS: We found that the highest number of new COVID-19 cases per day per million persons was significantly associated with the total number of COVID-19 cases per million persons on the day before mandated social distancing (ß = 0.66, P < 0.0001). These findings suggest that if mandated social distancing is not initiated until the number of existing COVID-19 cases has doubled, the eventual peak would result in 58% more COVID-19 cases per day. Subgroup analysis on those regions where the highest number of new COVID-19 cases per day has peaked showed increase in ß values to 0.85 (P < 0.0001). The total number of cases during the outbreak in a region was strongly predicted by the total number of COVID-19 cases on the day before mandated social distancing (ß = 0.97, P < 0.0001). CONCLUSIONS: Initiating mandated social distancing when the numbers of COVID-19 cases are low within a region significantly reduces the number of new daily COVID-19 cases and perhaps also reduces the total number of cases in the region.

Next generation secondary electron detector with energy analysis capability for SEM.

We report the working of a novel detector design based on a Bessel Box (BB) electron energy analyser in a scanning electron microscope (SEM). We demonstrate the application of our detector for elemental identification through Auger electron detection in an SEM environment and its potential as a complementary technique to energy dispersive X-ray (EDX) spectroscopy. We also demonstrate energy-filtered secondary electron imaging of a copper-on-silicon sample using an electron pass energy of 12 eV. LAY DESCRIPTION: Advancements in the field of the Scanning Electron Microscopy have been one of the major nanotechnology enablers. A Scanning Electron Microscope (SEM) generates a magnified image of the sample by bombarding it with an electron beam and detecting the electrons that scatter off the surface along with the electrons that are generated in the sample. Conventional detectors such as the Everhart-Thornley detector (ET) or through-the-lens (TTL) detectors, either offer little to no energy analysis (ET) or limited energy filtering capability (e.g the low-pass energy filter in TTL). This information is crucial to interpret the image of the sample under study. What is needed is a smart and compact detector that can detect electrons and furnish energy inside the SEM chamber. Here, we report a novel secondary electron (SE) detector design with energy analysis capability for use in scanning electron microscopes. The detector is based on the design of a Bessel Box (BB) energy analyser. We have designed and experimentally tested it in an SEM environment. The band-pass filter action of the detector enables the BB to be operated at a selected energy and allows a narrow window of energies to be detected for generating energy-filtered images.

Fc-Silent Anti-CD154 Domain Antibody Effectively Prevents Nonhuman Primate Renal Allograft Rejection.

The advent of costimulation blockade provides the prospect for targeted therapy with improved graft survival in transplant patients. Perhaps the most effective costimulation blockade in experimental models is the use of reagents to block the CD40/CD154 pathway. Unfortunately, successful clinical translation of anti-CD154 therapy has not been achieved. In an attempt to develop an agent that is as effective as previous CD154 blocking antibodies but lacks the risk of thromboembolism, we evaluated the efficacy and safety of a novel anti-human CD154 domain antibody (dAb, BMS-986004). The anti-CD154 dAb effectively blocked CD40-CD154 interactions but lacked crystallizable fragment (Fc) binding activity and resultant platelet activation. In a nonhuman primate kidney transplant model, anti-CD154 dAb was safe and efficacious, significantly prolonging allograft survival without evidence of thromboembolism (Median survival time 103 days). The combination of anti-CD154 dAb and conventional immunosuppression synergized to effectively control allograft rejection (Median survival time 397 days). Furthermore, anti-CD154 dAb treatment increased the frequency of CD4+ CD25+ Foxp3+ regulatory T cells. This study demonstrates that the use of a novel anti-CD154 dAb that lacks Fc binding activity is safe without evidence of thromboembolism and is equally as potent as previous anti-CD154 agents at prolonging renal allograft survival in a nonhuman primate preclinical model.

An anti-CD154 domain antibody prolongs graft survival and induces Foxp3(+) iTreg in the absence and presence of CTLA-4 Ig.

The use of monoclonal antibodies targeting the CD154 molecule remains one of the most effective means of promoting graft tolerance in animal models, but thromboembolic complications during early clinical trials have precluded their use in humans. Furthermore, the role of Fc-mediated deletion of CD154-expressing cells in the observed efficacy of these reagents remains controversial. Therefore, determining the requirements for anti-CD154-induced tolerance will instruct the development of safer but equally efficacious treatments. To investigate the mechanisms of action of anti-CD154 therapy, two alternative means of targeting the CD40-CD154 pathway were used: a nonagonistic anti-CD40 antibody and an Fc-silent anti-CD154 domain antibody. We compared these therapies to an Fc-intact anti-CD154 antibody in both a fully allogeneic model and a surrogate minor antigen model in which the fate of alloreactive cells could be tracked. Results indicated that anti-CD40 mAbs as well as Fc-silent anti-CD154 domain antibodies were equivalent to Fc-intact anti-CD154 mAbs in their ability to inhibit alloreactive T cell expansion, attenuate cytokine production of antigen-specific T cells and promote the conversion of Foxp3(+) iTreg. Importantly, iTreg conversion observed with Fc-silent anti-CD154 domain antibodies was preserved in the presence of CTLA4-Ig, suggesting that this therapy is a promising candidate for translation to clinical use.

Role of simvastatin in prevention of vasospasm and improving functional outcome after aneurysmal sub-arachnoid hemorrhage: a prospective, randomized, double-blind, placebo-controlled pilot trial.

BACKGROUND: Vasospasm plays a major role in the morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). The preliminary studies suggest that statins protect against cerebral vasospasm. OBJECTIVE: The aim of the study was to determine the role of simvastatin in preventing clinical vasospasm and improving functional outcome in patients with aSAH. METHODS: All patients with aSAH admitted within 96 h of ictus were randomized to receive either Simvastatin or placebo - 80 mg/day for 14 days. Thirty eight patients were recruited in the study- 19 received Simvastatin and 19 placebo. All the patients underwent surgical clipping of the aneurysm. The primary outcome of the study was the development of clinical cerebral vasospasm. The secondary outcomes included Glasgow Outcome Score (GOS), Modified Rankin Scale (MRS) and Barthel Index Score (MBI) at follow-up at 1, 3 and 6 months. RESULTS: 16% of the patients in the simvastatin group had high Middle Cerebral Artery velocities (> 160 cm/sec) on transcranial Doppler on one or more than one day during the study duration as compared to 26% of the patients in the placebo group (p = 0.70). Neurological deterioration occurred in 26% and 42% of the patients in simvastatin group versus placebo group, respectively (p = 0.31). There was an improvement in the functional outcome in the simvastatin group at 1, 3 or 6 months in the follow-up; however, this difference was not statistically significant. CONCLUSIONS: There was benefit of simvastatin in terms of reduction in clinical vasospasm, mortality or improved functional outcome, however, this was not statistically significant.

Monitored gradual occlusion of the internal carotid artery followed by ligation for giant internal carotid artery aneurysms.

OBJECTIVE: To demonstrate a technique of gradual monitored occlusion of the internal carotid artery (ICA) followed by ligation for giant aneurysms as an option for balloon test occlusion followed by permanent ligation of ICA. MATERIALS AND METHODS: Authors retrospectively analyzed 27 patients with giant and complex ICA aneurysms who underwent carotid artery ligation between January 2001 and December 2010. Clinical presentation included headache, vision loss and diplopia. There were 19 patients with cavernous aneurysm, 5 supraclinoid, 1 ophthalmic, 1 petrous segment and 1 cervical segment aneurysm located extracranially. All demonstrated good cross-circulation. Selverstone clamp was used for gradual occlusion of the ICA over 72 h under closed observation in the intensive care unit. RESULTS: Six patients developed hemiparesis in the postoperative period. Improvement occurred in one patient over two to three weeks while the remaining five patients had residual hemiparesis. One patient developed malignant MCA infarct for which decompressive craniectomy had to be done. There was no mortality in the present series. CONCLUSIONS: Gradual monitored occlusion and ICA ligation may be a simple, safe alternative procedure to clipping in surgically inaccessible and complex aneurysms, especially for surgeons with limited experience. Cross circulation study is an absolute requisite for carotid ligation.

Use of intravenous immune globulin in the ICU: a retrospective review of prescribing practices and patient outcomes.

RATIONALE: Intravenous immune globulin (IVIG) is a pooled human blood product. Much of IVIG use in Canada is prescribed for 'unlabelled' or 'off-label' indications. Due to costs, risk of use and limited supply, knowledge about the use of IVIG is important. We collected data regarding the usage of IVIG and outcomes of patients receiving IVIG in the intensive care units (ICUs) of two community and three academic hospitals. METHODS: We reviewed the charts of adult patients who received IVIG in the five ICUs over a 5-year period. Data collection included demographics, severity of illness, indication for and dose of IVIG, mortality and adverse effects. On the basis of a classification developed by Canadian Blood Services, the indications for IVIG were then classified as 'appropriate' or 'inappropriate'. RESULTS: One hundred and forty-five patients received IVIG in the ICU. In all, 19% of IVIG prescriptions were for 'appropriate' indications and 7% were 'inappropriate'. The remaining 74% were prescribed for indications with some evidence to support their use. Three indications accounted for 50% of all IVIG prescribed: Guillain-Barre syndrome (GBS), necrotising fasciitis (NF) and toxic epidermal necrolysis (TEN). Both the community and academic centres prescribed IVIG for similar indications. Adverse effects associated with IVIG administration included deep vein thrombosis/pulmonary embolism, fever and renal failure, although direct causation related to IVIG could not be established. The overall mortality rate was 55%. CONCLUSIONS: IVIG is used relatively infrequently in the critical care setting. The most common indications were GBS, TEN and NF. Mortality was high. There was no difference between community and academic ICUs.

Endoscopic third ventriculostomy: 5 years' experience at the All India Institute of Medical Sciences.

Endoscopic third ventriculostomy (ETV) is one of the efficacious surgical options available for obstructive hydrocephalus, and is preferable to a ventriculoperitoneal shunt in those eligible. We retrospectively studied 115 cases, who underwent ETV at our institute over the last 5 years. Thirty-eight patients were infants. Major indications for ETV were aqueductal stenosis (n = 60/115, 52.2%), Dandy-Walker malformation (15/115, 13%), associated arachnoid cyst (n = 13/115, 11.3%) and post-meningitic hydrocephalus (n = 12/115, 10.4%). Average duration of the follow-up was 10.6 months. Ninety-nine patients (86.1%) showed clinical improvement after surgery. Clinical improvement was seen in 27 out of 38 infants (71%) followed up. ETV is a highly effective tool in all age groups of patients for the management of hydrocephalus. Clinical features should be considered as indications of the success or failure of ventriculostomy in infants who have low-pressure hydrocephalus.

Early administration of thrombolysis can prevent myocardial necrosis: time is myocardium.

A case is presented in which a 66-year-old man received thrombolysis for an acute ST elevation myocardial infarction (STEMI) within 6 minutes of developing chest pain. An ECG performed 10 minutes after thrombolysis showed complete resolution of the ST segment elevation and showed no other abnormality. An echocardiogram showed normal left ventricular function and there was no detectable myocardial necrosis, as evidenced by two negative troponin assays. The case clearly reinforces the benefits of the rapid delivery of thrombolysis when appropriate for patients with STEMI. Clinicians need to be aware of the benefits of early thrombolysis as laid out in the national service framework. Evidence for the early administration of thrombolysis, data from the Myocardial Infarction National Audit Project and the future with regard to improving thrombolysis times are discussed.

Ketamine and xylazine combinations for short-term immobilization of wild variable flying foxes (Pteropus hypomelanus).

Collection of biological samples from pteropid bats requires chemical restraint of the bats to minimize risks to humans and stress to the bat. The effectiveness of an intravenous combination of ketamine and xylazine for short-term restraint of wild-caught variable flying foxes (Pteropus hypomelanus) in a field situation was evaluated. Eight adult male variable flying foxes were injected intravenously with 0.1 ml of ketamine and xylaxine containing 5 mg of ketamine and 1 mg of xylazine. The mean induction time was 80 +/- 20 sec, and mean immobilization time was 26 +/- 10 min. The ketamine-xylazine combination used in this study produced effective short-term immobilization of wild variable flying foxes for the collection of biological samples.

Neuronavigation in a developing country: a pilot study of efficacy and limitations in intracranial surgery.

CONTEXT: Neuronavigation provides a patient-specific, three-dimensional (3-D) anatomy for preoperative planning and intraoperative navigation. However, the initial and maintenance costs are quite prohibitive, especially in the Indian scenario. AIMS: To study the efficacy and limitations of neuronavigation, especially in the Indian scenario. SETTINGS AND DESIGN: A prospective nonrandomized study. MATERIALS AND METHODS: A total of 121 patients underwent intracranial surgery from 2002-2006, in which neuronavigation was used. In this, the initial part, we studied the efficacy and limitations of neuronavigation in the initial 37 patients. The efficacy of the image guidance was graded according to a point's scale in which points were awarded ranging from 0 to 3. Cranial image guided score (IGS) was calculated by the summation of grading during designing the flap/burr hole, delineation of the intraoperative anatomy, navigation and access to the lesion and resection / biopsy of the lesion or completion of the procedure. The scoring ranged from 0-12 and the utility of IGS in cranial neurosurgical procedures was calculated based on the total points for each surgery. RESULTS AND CONCLUSION: Cranial image guidance was useful in a variety of operative steps. Intraoperative approach and navigation was relatively easier with an increase in perception of safety. Limitations of IGS include learning curve, cost and the phenomenon of brain shift. Drawbacks of the study included that this was a subjective rather than a truly objective study and the relatively lesser number of patients. We hope to conduct a larger study with randomization but the question of ethical approval would be a primary concern.

Coagulase-negative staphylococci causing blood stream infection at an Indian tertiary care hospital: Prevalence, antimicrobial resistance and molecular characterisation.

INTRODUCTION: Recent years have seen a rise of coagulase-negative staphylococci (CoNS) from common contaminants to agents of nosocomial blood stream infections (BSI's). Molecular typing and establishing a correlation with antibiotic resistance is essential particularly in countries like India where genotyping studies for drug-resistant CoNS are sparse. METHODS: A prospective study was done over 18 months, wherein 42,693 blood samples were received, and 59 patients with BSI due to CoNS were evaluated. The isolates recovered were identified by a biochemical test panel and matrix-assisted laser desorption ionization - time of flight mass spectrometry followed by antimicrobial susceptibility testing by Kirby-Baur disc diffusion method and E-test strips. Staphylococcal chromosomal cassette mec (SCCmec) element was characterised by multiplex polymerase chain reaction for all methicillin-resistant (MR) isolates. RESULTS: The majority of CoNS isolated were constituted by Staphylococcus haemolyticus (47.5%) followed by Staphylococcus epidermidis (33.9%), Staphylococcus hominis (11.86%), Staphylococcus cohnii (5.08%) and Staphylococcus warneri (1.69%). Among all isolates 57.6% were MR with statistically significant higher resistance versus methicillin sensitive-CoNS. This difference was significant for erythromycin (76% vs. 44%, P = 0.011), rifampicin (50% vs. 12%,P= 0.002) and amikacin (26.5% vs. 4%, P = 0.023), ciprofloxacin (64.7% vs. 20%, P = 0.001) and cotrimoxazole (55.9% vs. 20%, P = 0.006). SCCmec type I was predominant (61.8%, P = 0.028) and exhibited multidrug resistance (76.2%). Coexistence of SCCmec type I and III was seen in 8.82% MR isolates. CONCLUSION: CoNS exhibit high antimicrobial resistance thereby limiting treatment options. The presence of new variants of SCCmec type in hospital-acquired CoNS may predict the antibiotic resistance pattern. This is the first evaluation of the molecular epidemiology of CoNS causing BSI from India and can serve as a guide in the formulation of hospital infection control and treatment guidelines.

Structure, recognition and adaptive binding in RNA aptamer complexes.

Novel features of RNA structure, recognition and discrimination have been recently elucidated through the solution structural characterization of RNA aptamers that bind cofactors, aminoglycoside antibiotics, amino acids and peptides with high affinity and specificity. This review presents the solution structures of RNA aptamer complexes with adenosine monophosphate, flavin mononucleotide, arginine/citrulline and tobramycin together with an example of hydrogen exchange measurements of the base-pair kinetics for the AMP-RNA aptamer complex. A comparative analysis of the structures of these RNA aptamer complexes yields the principles, patterns and diversity associated with RNA architecture, molecular recognition and adaptive binding associated with complex formation.

Molecular recognition in the FMN-RNA aptamer complex.

We report on a combined NMR-molecular dynamics calculation approach that has solved the solution structure of the complex of flavin mononucleotide (FMN) bound to the conserved internal loop segment of a 35 nucleotide RNA aptamer identified through in vitro selection. The FMN-RNA aptamer complex exhibits exceptionally well-resolved NMR spectra that have been assigned following application of two, three and four-dimensional heteronuclear NMR techniques on samples containing uniformly 13C, 15N-labeled RNA aptamer in the complex. The assignments were aided by a new through-bond NMR technique for assignment of guanine imino and adenine amino protons in RNA loop segments. The conserved internal loop zippers up through the formation of base-pair mismatches and a base-triple on complex formation with the isoalloxazine ring of FMN intercalating into the helix between a G.G mismatch and a G.U.A base-triple. The recognition specificity is associated with hydrogen bonding of the uracil like edge of the isoalloxazine ring of FMN to the Hoogsteen edge of an adenine at the intercalation site. There is significant overlap between the intercalated isoalloxazine ring and its adjacent base-triple platform in the complex. The remaining conserved residues in the internal loop participate in two G.A mismatches in the complex. The zippered-up internal loop and flanking stem regions form a continuous helix with a regular sugar-phosphate backbone except at a non-conserved adenine, which loops out of the helix to facilitate base-triple formation. Our solution structure of the FMN-RNA aptamer complex is to our knowledge the first structure of an RNA aptamer complex and outlines folding principles that are common to other RNA internal and hairpin loops, and molecular recognition principles common to model self-replication systems in chemical biology.

Solution conformation of the (+)-trans-anti-benzo[g]chrysene-dA adduct opposite dT in a DNA duplex.

The solution structure of the adduct derived from the covalent bonding of the fjord region (+)-(11S, 12R, 13R, 14S) stereoisomer of anti -11,12-dihydroxy-13,14-epoxy-11,12,13, 14-tetrahydrobenzo[g]chrysene, (+)- anti -B[g]CDE, to the exocyclic N(6)amino group of the adenine residue dA6, (designated (+)- trans-anti -(B[g]C)dA6), positioned opposite a thymine residue dT17 in the DNA sequence context d(C1-T2-C3-T4-C5-(B[g]C)A6-C7-T8-T9-C10-C11). d(G12-G13-A14-A15-G16-T17-G18-A19-G20++ +-A21-G22) (designated (B[g]C)dA. dT 11-mer duplex), has been studied using structural information derived from NMR data in combination with molecular dynamics (MD) calculations. The solution structure of the (+)- trans-anti -(B[g]C)dA.dT 11-mer duplex has been determined using an MD protocol where both interproton distance and dihedral angle restraints deduced from NOESY and COSY spectra are used during the refinement process, followed by additional relaxation matrix refinement to the observed NOESY intensities to account for spin diffusion effects. The results established that the covalently attached benzo[g]chrysene ring intercalates into the DNA helix directed towards the 5'-side of the modified strand and stacks predominantly with dT17 when intercalated between dC5.dG18 and (B[g]C)dA6.dT17 base-pairs. All base-pairs, including the modified (B[g]C)dA6.dT17 base-pair, are aligned through Watson-Crick pairing as in normal B -DNA. In addition, the potential strain associated with the highly sterically hindered fjord region of the aromatic portion of the benzo[g]chrysenyl ring is relieved through the adoption of a non-planar, propeller-like geometry within the chrysenyl ring system. This conformation shares common structural features with the related (+)- trans-anti -(B[c]Ph)dA adduct in the identical base sequence context, derived from the fjord region (+)-(1S,2R,3R,4S)-3, 4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene stereoisomer, in which intercalation is also observed towards the 5'-side of the modified dA6.dT17 base-pair.

Saccharide-RNA recognition in an aminoglycoside antibiotic-RNA aptamer complex.

BACKGROUND: Aminoglycoside antibiotics are known to target ribosomal, retroviral and catalytic RNAs with high affinity and specificity. Recently, in vitro selection experiments have identified RNA aptamers that bind to aminoglycoside antibiotics with nanomolar affinity and stringent specificity, allowing discrimination between closely related family members. There has, to date, been limited structural information on the molecular basis of such saccharide-RNA recognition. RESULTS: We describe a solution-structure determination of the tobramycin-RNA aptamer complex, obtained using NMR and molecular dynamics. The structure gives insight into the molecular features associated with saccharide-RNA recognition. Tobramycin adopts a defined alignment and binds to the RNA major groove centered about a stem-loop junction site. A portion of the bound tobramycin is encapsulated between the floor of the major groove and a looped-out cytosine residue that forms a flap over the binding site in the complex. CONCLUSIONS: The emergence of antibiotic-resistant pathogens and their impact on human health continues to be a major concern in the medical community. Rational modification of existing antibiotics aimed at improving their efficacy requires a molecular view of their receptor-binding sites. We have provided such a molecular view for a member of the aminoglycoside antibiotic family that targets RNA.

Duloxetine pharmacokinetics in cirrhotics compared with healthy subjects.

OBJECTIVE: To compare the pharmacokinetics of single-dose duloxetine in cirrhotic and healthy subjects. METHODS: An open-label inpatient study compared duloxetine pharmacokinetics in six subjects with moderate liver cirrhosis (Child-Pugh class B) to those in six healthy subjects. Subjects received a single 20 mg capsule of duloxetine following overnight fasting. Blood samples were collected up to 120 h post dose for determination of plasma concentrations of duloxetine and its major metabolites using a validated LC/MS/MS method. Plasma concentration-time data for duloxetine and its major metabolites were analyzed by noncompartmental methods. Specific pharmacokinetic parameters were assessed statistically using a mixed-effects model. RESULTS: Duloxetine apparent clearance was significantly lower (24 vs 160 l/h, p < 0.05) and AUC values were substantially higher (775 vs 268 ng x (h/ml) in cirrhotic compared to healthy subjects. The half-life of duloxetine was about three times longer (47.8 vs 13.5 h) in cirrhotic than in healthy subjects (p < 0.05). In contrast, there was no significant difference in Cmax or apparent volume of distribution between the two groups. The metabolites exhibited lower levels and longer half-lives in cirrhotic subjects compared to healthy subjects. The lower clearance and slower elimination of duloxetine in cirrhotic individuals is likely attributable to impaired duloxetine metabolism. CONCLUSIONS: The rate of duloxetine elimination is reduced for cirrhotic subjects, making dosage adjustments appropriate. Based on simulations, the duloxetine dose for at least an initial treatment period may need to be reduced and/or less frequently administered for patients with moderate cirrhosis.

Physiologically based and population PK modeling in optimizing drug development: A predict-learn-confirm analysis.

Physiologically based pharmacokinetic (PBPK) modeling and classical population pharmacokinetic (PK) model-based simulations are increasingly used to answer various drug development questions. In this study, we propose a methodology to optimize the development of drugs, primarily cleared by the kidney, using model-based approaches to determine the need for a dedicated renal impairment (RI) study. First, the impact of RI on drug exposure is simulated via PBPK modeling and then confirmed using classical population PK modeling of phase 2/3 data. This methodology was successfully evaluated and applied to an investigational agent, orteronel (nonsteroidal, reversible, selective 17,20-lyase inhibitor). A phase 1 RI study confirmed the accuracy of model-based predictions. Hence, for drugs eliminated primarily via renal clearance, this modeling approach can enable inclusion of patients with RI in phase 3 trials at appropriate doses, which may be an alternative to a dedicated RI study, or suggest that only a reduced-size study in severe RI may be sufficient.

Inhibition of CYP2D6 by quinidine and its effects on the metabolism of cilostazol.

OBJECTIVE: In vitro results are inconclusive as to whether cilostazol is metabolised by cytochrome P450 isoenzyme 2D6 (CYP2D6). The goals of this study were (1) to assure the dose of quinidine and timing relative to cilostazol used in this study were adequate to cause inhibition of CYP2D6, (2) to evaluate carryover effects of quinidine administration, and (3) to evaluate the effect of CYP2D6 deficiency and administration of quinidine (a CYP2D6 inhibitor) on the pharmacokinetics of a single 100 mg oral dose of cilostazol. DESIGN: This study was conducted as a single-centre, open-label, randomised sequence, 2-period, crossover pharmacokinetic trial. Water alone (treatment without quinidine) or two 200 mg oral doses of quinidine sulfate with water were administered 25 hours and 1 hour prior to a single 100 mg dose of cilostazol in period 1. Study participants were crossed over to opposite treatment in period 2. Metoprolol 25 mg, used as a positive control, was administered 1 hour after quinidine sulfate with water or using water alone to assess the magnitude of CYP2D6 inhibition by quinidine. STUDY PARTICIPANTS: 22 healthy nonsmoking Caucasian (14 male and 8 female) volunteers participated in the study. MAIN OUTCOME MEASURES: Serial blood and urine samples were collected at predose and after cilostazol administration to characterise cilostazol and its metabolite pharmacokinetics. Additional plasma samples were taken to assess the pharmacokinetics of quinidine. Urine samples were collected to measure metoprolol and hydroxymetoprolol. RESULTS: Administration of metoprolol with quinidine caused a significant (p < 0.001) decrease in the urinary 4-hydroxymetoprolol/metoprolol ratio compared with administration of metoprolol alone (42-fold decrease, 0.065 vs 2.707). Hence, quinidine effectively converted extensive metabolisers of CYP2D6 to poor metabolisers of CYP2D6. The 21-day washout period was adequate to have complete recovery from quinidine inhibition of CYP2D6. The analysis of variance demonstrated that the mean maximum plasma concentration (Cmax) for cilostazol, both adjusted and unadjusted for the free fraction, was higher in the control group than in the quinidine group (p = 0.023). However, the time to Cmax (p = 0.669), the area under the plasma concentration-time curve from time zero to infinity (AUC infinity; p = 0.133), and the apparent oral clearance (p = 0.135) were unchanged. The geometric mean ratios (90% confidence interval) comparing with quinidine (test) and without quinidine (reference) coadministration for Cmax and AUC infinity are 0.86 (0.77, 0.95) and 0.92 (0.84, 1.00), respectively. Similar patterns were observed for OPC-13015 and OPC-13213 with regard to Cmax, area under the plasma concentration-time curve from time zero to the last measurable concentration at time t, and AUC infinity (where determinable). The slight decrease in the systemic availability of cilostazol and its metabolites was thought to be a result of the increased gastrointestinal motility secondary to quinidine. CONCLUSIONS: Administration of quinidine sulfate 200 mg profoundly inhibited CYP2D6-mediated metabolism. The effects of quinidine inhibition of CYP2D6 metabolism were completely reversible during the 21-day washout period. Coadministration of quinidine with cilostazol had no substantial effect on cilostazol or its metabolites (OPC-13015 and OPC-13213). Hence, CYP2D6 does not have a significant contribution in the metabolic elimination of cilostazol.