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Ridder A, O'Driscoll J, Khalil A, Thilaganathan B. Routine first-trimester pre-eclampsia screening and maternal left ventricular geometry. Ultrasound Obstet Gynecol 2024; 63:75-80. [PMID: 37448160 DOI: 10.1002/uog.26306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 06/26/2023] [Accepted: 06/27/2023] [Indexed: 07/15/2023]
Abstract
OBJECTIVE Pre-eclampsia (PE) is a pregnancy complication associated with premature cardiovascular disease morbidity and mortality (i.e. before 60 years of age or in the first year postpartum). PE is associated with adverse left ventricular (LV) remodeling in the peri- and postpartum periods, an independent risk factor for cardiovascular disease. This study aimed to compare LV geometry by LV mass (LVM) and LVM index (LVMI) between participants with a high vs low screening risk for preterm PE in the first trimester. METHODS This was a prospective cohort study of singleton pregnancies between 11 + 0 and 13 + 6 weeks' gestation that underwent screening for preterm PE as part of their routine first-trimester ultrasound assessment at a tertiary center in London, UK, from February 2019 until March 2020. Screening for preterm PE was performed using the Fetal Medicine Foundation algorithm. Participants with a screening risk of ≥ 1 in 50 for preterm PE were classified as high risk and those with a screening risk of ≤ 1 in 500 were classified as low risk. All participants underwent two-dimensional and M-mode transthoracic echocardiography. RESULTS A total of 128 participants in the first trimester of pregnancy were included in the analysis, with 57 (44.5%) participants screened as low risk and 71 (55.5%) participants as high risk for PE. The risk groups did not vary in maternal age and gestational age at assessment. Maternal body surface area and body mass index were significantly higher in the high-risk group (all P < 0.05). The high-risk participants were significantly more likely to be Afro-Caribbean, nulliparous and have a family history of hypertensive disease in pregnancy as well as other cardiovascular disease (all P < 0.05). In addition, mean arterial blood pressure (P < 0.001), mean heart rate (P < 0.001), median LVM (130.06 (interquartile range, 113.62-150.50) g vs 97.44 (81.68-114.16) g; P < 0.001) and mean LVMI (72.87 ± 12.2 g/m2 vs 57.54 ± 12.72 g/m2 ; P < 0.001) were significantly higher in the high-risk group. Consequently, those in the high-risk group were more likely to have abnormal LV geometry (37.1% vs 7.0%; P < 0.001). CONCLUSIONS Early echocardiographic assessment in participants at high risk of preterm PE may unmask clinically healthy individuals who are at increased risk for future cardiovascular disease. Adverse cardiac remodeling in the first trimester of pregnancy may be an indicator of decreased cardiovascular reserve and subsequent dysfunctional cardiovascular adaptation in pregnancy. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.
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Affiliation(s)
- A Ridder
- Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, University of London, London, UK
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK
| | - J O'Driscoll
- Department of Cardiology, St George's University Hospitals NHS Foundation Trust, University of London, London, UK
- School of Psychology and Life Sciences, Canterbury Christ Church University, Canterbury, UK
| | - A Khalil
- Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, University of London, London, UK
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK
| | - B Thilaganathan
- Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, University of London, London, UK
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK
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Giorgione V, Ridder A, Kalafat E, Khalil A, Thilaganathan B. Incidence of postpartum hypertension within 2 years of a pregnancy complicated by pre-eclampsia: a systematic review and meta-analysis. BJOG 2020; 128:495-503. [PMID: 32981216 DOI: 10.1111/1471-0528.16545] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/11/2020] [Indexed: 12/01/2022]
Abstract
BACKGROUND Women with a history of hypertensive disorders of pregnancy (HDP) are at increased long-term risk of cardiovascular disease. However, there has been increasing evidence on the same risks in the months following birth. OBJECTIVES This review aims to estimate the incidence of hypertension in the first 2 years after HDP. SEARCH STRATEGY MEDLINE, Embase and Cochrane databases were systematically searched in October 2019. SELECTION CRITERIA Observational studies comparing hypertension rate following HDP and normotensive pregnancies up to 2 years. DATA COLLECTION AND ANALYSIS A meta-analysis to calculate the odds ratio (OR) with a 95% confidence interval (CI) and a sub-group analysis excluding women with chronic hypertension were performed. MAIN RESULTS Hypertension was diagnosed within the first 2 years following pregnancy in 468/1646 (28.4%) and 584/6395 (9.1%) of the HDP and control groups, respectively (OR 6.28; 95% CI 4.18-9.43; I2 = 56%). The risk of hypertension in HDP group was significantly higher in the first 6 months following delivery (OR 18.33; 95% CI 1.35-249.48; I2 = 84%) than at 6-12 months (OR 4.36; 95% CI 2.81-6.76; I2 = 56%) or between 1-2 years postpartum (OR 7.24; 95% CI 4.44-11.80; I2 = 9%). A sub-group analysis demonstrated a similar increase in the risk of developing postpartum hypertension after HDP (OR 5.75; 95% CI 3.92-8.44; I2 = 49%) and pre-eclampsia (OR 6.83; 95% CI 4.25-10.96; I2 = 53%). CONCLUSIONS The augmented risk of hypertension after HDP is highest in the early postpartum period, suggesting that diagnosis and targeted interventions to improve maternal cardiovascular health may need to be commenced in the immediate postpartum period. TWEETABLE ABSTRACT The risk of hypertension within 2 years of birth is six-fold higher in women who experienced pre-eclampsia.
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Affiliation(s)
- V Giorgione
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK
| | - A Ridder
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK
| | - E Kalafat
- Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, London, UK.,Department of Statistics, Faculty of Arts and Sciences, Middle East Technical University, Ankara, Turkey
| | - A Khalil
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK.,Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, London, UK
| | - B Thilaganathan
- Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University of London, London, UK.,Fetal Medicine Unit, St George's University Hospitals NHS Foundation Trust, London, UK
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Ridder A, Müller MLTM, Kotagal V, Frey KA, Albin RL, Bohnen NI. Impaired contrast sensitivity is associated with more severe cognitive impairment in Parkinson disease. Parkinsonism Relat Disord 2016; 34:15-19. [PMID: 27742131 DOI: 10.1016/j.parkreldis.2016.10.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 09/30/2016] [Accepted: 10/06/2016] [Indexed: 10/20/2022]
Abstract
OBJECTIVES Dopaminergic degeneration affects both nigrostriatal projection neurons and retinal amacrine cells in Parkinson disease (PD). Parkinsonian retinopathy is associated with impaired color discrimination and contrast sensitivity. Some prior studies described associations between color discrimination deficits and cognitive deficits in PD, suggesting that contrast discrimination deficits are due, at least in part, to cognitive deficits in PD. We investigated the relationship between cognitive deficits and impaired contrast sensitivity in PD. METHODS PD subjects, n = 43; 15F/28M; mean age 66.5 ± 8.2, Hoehn and Yahr stage 2.6 ± 0.6, and duration of disease of 6.2 ± 5.0 years underwent neuropsychological and Rabin contrast sensitivity testing. RESULTS Mean Rabin contrast sensitivity score was 1.34 ± 0.40. Bivariate analyses showed significant correlation between Rabin contrast sensitivity scores and global cognitive z-scores (R = 0.54, P = 0.0002). Cognitive domain Z-score post hoc analysis demonstrated most robust correlation between Rabin scores and executive functions (R = 0.49, P = 0.0009), followed by verbal learning (R = 0.44, P = 0.0028), visuospatial (R = 0.39, P = 0.001) and attention z-scores (R = 0.32, P = 0.036). CONCLUSIONS Impaired contrast sensitivity in PD is robustly associated with cognitive deficits, particularly executive function deficits. These results suggest that contrast sensitivity may be a useful biomarker for cognitive changes in PD and may have implications for driving safety evaluations in PD.
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Affiliation(s)
- A Ridder
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - M L T M Müller
- Department of Radiology, University of Michigan, Ann Arbor, MI, USA; University of Michigan, Morris K. Udall Center of Excellence for Parkinson's Disease Research, Ann Arbor, MI, USA
| | - V Kotagal
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA; Neurology Service and GRECC, VAAAHS, Ann Arbor, MI, USA
| | - K A Frey
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA; Department of Radiology, University of Michigan, Ann Arbor, MI, USA
| | - R L Albin
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA; University of Michigan, Morris K. Udall Center of Excellence for Parkinson's Disease Research, Ann Arbor, MI, USA; Neurology Service and GRECC, VAAAHS, Ann Arbor, MI, USA
| | - N I Bohnen
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA; Department of Radiology, University of Michigan, Ann Arbor, MI, USA; University of Michigan, Morris K. Udall Center of Excellence for Parkinson's Disease Research, Ann Arbor, MI, USA; Neurology Service and GRECC, VAAAHS, Ann Arbor, MI, USA.
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Abrams P, Kelleher C, Staskin D, Kay R, Martan A, Mincik I, Newgreen D, Ridder A, Paireddy A, van Maanen R. Combination treatment with mirabegron and solifenacin in patients with overactive bladder: exploratory responder analyses of efficacy and evaluation of patient-reported outcomes from a randomized, double-blind, factorial, dose-ranging, Phase II study (SYMPHONY). World J Urol 2016; 35:827-838. [DOI: 10.1007/s00345-016-1908-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 07/23/2016] [Indexed: 11/25/2022] Open
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Martina R, Kay R, Maanen RV, Ridder A. The analysis of incontinence episodes and other count data in patients with overactive bladder by Poisson and negative binomial regression. Pharm Stat 2016; 15:379. [PMID: 27406877 DOI: 10.1002/pst.1752] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Heisen M, Baeten SA, Verheggen BG, Stoelzel M, Hakimi Z, Ridder A, van Maanen R, Stolk EA. Patient and physician preferences for oral pharmacotherapy for overactive bladder: two discrete choice experiments. Curr Med Res Opin 2016; 32:787-96. [PMID: 26789823 DOI: 10.1185/03007995.2016.1142959] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
OBJECTIVE We examined patient and treating physician (general practitioners, urologists, and [uro]gynecologists) preferences for oral pharmacotherapy (antimuscarinics and beta-3 adrenoceptor agonists) for overactive bladder to gain a deeper understanding of which attributes drive their treatment decision-making and to quantify to what extent. RESEARCH DESIGN AND METHODS Two separate discrete choice experiments were developed and validated using the input of patients and physicians. The patient experiment contained the following attributes: micturition frequency, incontinence, nocturia, urgency, dry mouth, constipation, increased heart rate, and increased blood pressure. The physician experiment contained two additional attributes: coping and atrial fibrillation. Both were fielded in five European countries. To allow for preference heterogeneity, utility functions were estimated using a mixed multinomial logit model. RESULTS A total of 442 patient and 318 physician responses were analyzed. Patients ranked the attributes based on their largest potential impact on treatment value as follows: incontinence, nocturia, risk of an increased heart rate, urgency, frequency, risk of increased blood pressure, risk of constipation, and risk of dry mouth; and physicians as follows: incontinence, urgency, nocturia, frequency, risk of dry mouth, coping, risk of increased heart rate, risk of increased blood pressure, risk of atrial fibrillation, and risk of constipation. CONCLUSION AND LIMITATIONS: In their valuations, physicians put more emphasis on increasing benefits, whereas patients put more emphasis on limiting risks of side effects. Another contrast that emerged was that patients' valuations of side effects were found to be fairly insensitive to the presented risk levels (with the exception of risk of dry mouth), whereas physicians' evaluated all side effects in a risk-level dependent manner. The obtained utility functions can be used to predict whether, to what extent, and for which reasons patients and physicians would choose one oral pharmacotherapy over another, as well as to advance shared decision-making.
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Affiliation(s)
- M Heisen
- a Pharmerit International , Rotterdam , The Netherlands
| | - S A Baeten
- a Pharmerit International , Rotterdam , The Netherlands
| | - B G Verheggen
- a Pharmerit International , Rotterdam , The Netherlands
| | - M Stoelzel
- b Astellas Pharma International , Leiden , The Netherlands
| | - Z Hakimi
- b Astellas Pharma International , Leiden , The Netherlands
| | - A Ridder
- b Astellas Pharma International , Leiden , The Netherlands
| | - R van Maanen
- b Astellas Pharma International , Leiden , The Netherlands
| | - E A Stolk
- c Institute for Medical Technology Assessment and Department of Health Policy and Management , Erasmus University Rotterdam , Rotterdam , The Netherlands
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de Greef-van der Sandt I, Newgreen D, Schaddelee M, Dorrepaal C, Martina R, Ridder A, van Maanen R. A quantitative benefit-risk assessment approach to improve decision making in drug development: Application of a multicriteria decision analysis model in the development of combination therapy for overactive bladder. Clin Pharmacol Ther 2015; 99:442-51. [PMID: 26422298 DOI: 10.1002/cpt.271] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Accepted: 09/24/2015] [Indexed: 01/22/2023]
Abstract
A multicriteria decision analysis (MCDA) approach was developed and used to estimate the benefit-risk of solifenacin and mirabegron and their combination in the treatment of overactive bladder (OAB). The objectives were 1) to develop an MCDA tool to compare drug effects in OAB quantitatively, 2) to establish transparency in the evaluation of the benefit-risk profile of various dose combinations, and 3) to quantify the added value of combination use compared to monotherapies. The MCDA model was developed using efficacy, safety, and tolerability attributes and the results of a phase II factorial design combination study were evaluated. Combinations of solifenacin 5 mg and mirabegron 25 mg and mirabegron 50 (5+25 and 5+50) scored the highest clinical utility and supported combination therapy development of solifenacin and mirabegron for phase III clinical development at these dose regimens. This case study underlines the benefit of using a quantitative approach in clinical drug development programs.
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Affiliation(s)
| | - D Newgreen
- Astellas Pharma Europe, Leiden, The Netherlands
| | | | - C Dorrepaal
- Astellas Pharma Europe, Leiden, The Netherlands
| | - R Martina
- Astellas Pharma Europe, Leiden, The Netherlands
| | - A Ridder
- Astellas Pharma Europe, Leiden, The Netherlands
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Martina R, Kay R, van Maanen R, Ridder A. The analysis of incontinence episodes and other count data in patients with overactive bladder by Poisson and negative binomial regression. Pharm Stat 2014; 14:151-60. [DOI: 10.1002/pst.1664] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 10/20/2014] [Accepted: 10/30/2014] [Indexed: 11/11/2022]
Affiliation(s)
- R. Martina
- Department of Health Sciences; University of Leicester; Leicester UK
| | - R. Kay
- RK Statistics Ltd; Bakewell UK
| | | | - A. Ridder
- Astellas Pharma Europe BV; Leiden The Netherlands
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Van Dyke MV, Martyny JW, Marola J, Ramamoorthy P, Ridder A, Harbeck RJ, Rose CS. Efficacy of occupant-collected dust samples in the evaluation of residential allergen and fungal levels. J Occup Environ Hyg 2012; 9:14-24. [PMID: 22150472 DOI: 10.1080/15459624.2012.633069] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
This study evaluated the ability of a resident to evaluate their home for allergens and mold using a settled dust test kit compared with evaluation and collection of settled dust by an industrial hygienist. Forty-three home residents were provided with a kit containing written instructions and a vacuum cleaner attachment for collecting a settled dust sample. Within 2 weeks of receiving the occupant-collected sample, an industrial hygienist evaluated these homes, including a visual inspection, collection of settled dust, and collection of spore trap samples. Settled dust samples were analyzed for major dog, cat, dust mite, and cockroach allergens using immunoassay methods, and for mold spore equivalents using quantitative polymerase chain reaction methods for the 13 mold species or species groups comprising the American Relative Moldiness Index (ARMI). Allergen concentrations and ARMIs were compared between the resident- and industrial hygienist-collected samples. Linear regression between the two sets of samples showed strong correlations for dog allergen (r(2) = 0.92) and cat allergen (r(2) = 0.90). Correlations for dust mite (r(2) = 0.57) and cockroach allergens (r(2) = 0.22) were lower, likely due to most samples being near the limit of detection. ARMIs were highly correlated (r(2) = 0.68) and were in categorical (high, medium, or low) agreement for 76% of residences. These results show that residents can reliably follow directions and collect settled dust samples, providing an efficient method to remotely screen homes for elevated allergen levels and to identify homes with a potential mold or moisture problem that may need further evaluation.
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Affiliation(s)
- M V Van Dyke
- National Jewish Health, Denver, Colorado 80206, USA.
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Chapple C, Yamaguchi O, Ridder A, Liehne J, Carl S, Mattiasson A, Aramburu M, Lucas M, Everaert K. CLINICAL PROOF OF CONCEPT STUDY (BLOSSOM) SHOWS NOVEL β3 ADRENOCEPTOR AGONIST YM178 IS EFFECTIVE AND WELL TOLERATED IN THE TREATMENT OF SYMPTOMS OF OVERACTIVE BLADDER. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/s1569-9056(08)60672-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Chapple CR, Rechberger T, Al-Shukri S, Meffan P, Everaert K, Huang M, Ridder A. Randomized, double-blind placebo- and tolterodine-controlled trial of the once-daily antimuscarinic agent solifenacin in patients with symptomatic overactive bladder. BJU Int 2004; 93:303-10. [PMID: 14764127 DOI: 10.1111/j.1464-410x.2004.04606.x] [Citation(s) in RCA: 244] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To assess in a phase 3a trial the efficacy of solifenacin succinate, a once-daily oral antimuscarinic agent in development at 5-mg and 10-mg dosage strengths, for the treatment of overactive bladder (OAB) (Yamanouchi Pharmaceutical Co. Ltd, Tokyo, Japan) compared with placebo in patients with symptoms of OAB, i.e. urgency, incontinence, and frequency, with additional objectives being to assess the safety and tolerability of solifenacin and to compare the efficacy and safety of solifenacin with tolterodine 2 mg twice daily. PATIENTS AND METHODS The study was an international, multicentre, randomized, double-blind, tolterodine- and placebo-controlled trial conducted at 98 centres. Adult patients with symptomatic OAB for > or = 3 months were eligible; after a single-blind 2-week placebo run-in period patients were randomized equally to a 12-week double-blind treatment with either tolterodine 2 mg twice daily, placebo, solifenacin 5 mg or 10 mg once daily. Efficacy variables included change from baseline in the mean number of urgency, incontinence and urge incontinence episodes, and change from baseline in voids/24 h and mean volume voided/void. RESULTS In all, 1281 patients were enrolled, 1081 randomized and 1077 treated; 1033 were evaluated for efficacy. Compared with placebo, the change from baseline (-1.41, -32.7%) in the mean number of urgency episodes per 24 h was statistically significantly lower with solifenacin 5 mg (-2.85, -51.9%) and 10 mg (-3.07, -54.7%; both P < 0.001), but not with tolterodine (-2.05, -37.9%; P = 0.0511). There was a statistically insignificant decrease in episodes of incontinence with tolterodine (-1.14; P = 0.1122) but a significant decrease in patients treated with solifenacin 5 (-1.42; P = 0.008) and 10 mg (-1.45; P = 0.0038). Compared with placebo (-1.20, -8.1%) the mean number of voids/24 h was significantly lower in patients receiving tolterodine (-1.88, -15%; P = 0.0145), solifenacin 5 (-2.19, -17%) and 10 mg (-2.61, -20%; both P < 0.001). The mean volume voided/void was also significantly higher with all three active treatments (P < 0.001). Solifenacin was well tolerated; compared with placebo (4.9%), dry mouth (the most common side-effect), mostly mild, was reported in 18.6% of patients receiving tolterodine, 14.0% receiving 5 mg and 21.3% receiving 10 mg solifenacin. CONCLUSION Solifenacin 5 and 10 mg once daily improved urgency and other symptoms of OAB, and was associated with an acceptable level of anticholinergic side-effects. Solifenacin demonstrated significantly favourable efficacy to side-effect ratio in treating symptomatic OAB.
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Affiliation(s)
- C R Chapple
- Department of Urology, Royal Hallamshire Hospital, Sheffield, UK.
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Abstract
Haloalkane dehalogenase converts haloalkanes to their corresponding alcohols. The 3D structure, reaction mechanism and kinetic mechanism have been studied. The steady state k(cat) with 1,2-dichloroethane and 1,2-dibromoethane is limited mainly by the rate of release of the halide ion from the buried active-site cavity. During catalysis, the halogen that is cleaved off (Cl alpha) from 1,2-dichloroethane interacts with Trp125 and the Cl beta interacts with Phe172. Both these residues have van der Waals contacts with Val226. To establish the effect of these interactions on catalysis, and in an attempt to change enzyme activity without directly mutating residues involved in catalysis, we mutated Val226 to Gly, Ala and Leu. The Val226Ala and Val226Leu mutants had a 2.5-fold higher catalytic rate for 1,2-dibromoethane than the wild-type enzyme. A pre-steady state kinetic analysis of the Val226Ala mutant enzyme showed that the increase in k(cat) could be attributed to an increase in the rate of a conformational change that precedes halide release, causing a faster overall rate of halide dissociation. The k(cat) for 1,2-dichloroethane conversion was not elevated, although the rate of chloride release was also faster than in the wild-type enzyme. This was caused by a 3-fold decrease in the rate of formation of the alkyl-enzyme intermediate for 1,2-dichloroethane. Val226 seems to contribute to leaving group (Cl alpha or Br alpha) stabilization via Trp125, and can influence halide release and substrate binding via an interaction with Phe172. These studies indicate that wild-type haloalkane dehalogenase is optimized for 1,2-dichloroethane, although 1,2-dibromoethane is a better substrate.
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Affiliation(s)
- J P Schanstra
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands
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