PDPrabha Dwivedi

Prabha Dwivedi

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Previous Organizations / Institutes

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Prabha Dwivedi has a total of 127 co-authors. Here are the top co-authors by number of shared publications:


Latest Publications

  • Impact of enzymatic hydrolysis on the quantification of total urinary concentrations of chemical biomarkers

    by Prabha Dwivedi, Xiaoliu Zhou, Tolar G. Powell, Antonia M. Calafat, Xiaoyun Ye


  • Open Access

    Prevalence of substandard and falsified artemisinin-based combination antimalarial medicines on Bioko Island, Equatorial Guinea

    by Harparkash Kaur, Elizabeth Louise Allan, Ibrahim Mamadu, Zoe Hall, Michael D Green, Isabel Swamidos, Prabha Dwivedi, Maria Julia Culzoni, Facundo M Fernandez, Guillermo Garcia, et al.

    Introduction Poor-quality artemisinin-containing antimalarials (ACAs), including falsified and substandard formulations, pose serious health concerns in malaria endemic countries. They can harm patients, contribute to the rise in drug resistance and increase the public’s mistrust of health systems. Systematic assessment of drug quality is needed to gain knowledge on the prevalence of the problem, to provide Ministries of Health with evidence on which local regulators can take action. Methods We used three sampling approaches to purchase 677 ACAs from 278 outlets on Bioko Island, Equatorial Guinea as follows: convenience survey using mystery client (n=16 outlets, 31 samples), full island-wide survey using mystery client (n=174 outlets, 368 samples) and randomised survey using an overt sampling approach (n=88 outlets, 278 samples). The stated active pharmaceutical ingredients (SAPIs) were assessed using high-performance liquid chromatography and confirmed by mass spectrometry at three independent laboratories. Results Content analysis showed 91.0% of ACAs were of acceptable quality, 1.6% were substandard and 7.4% falsified. No degraded medicines were detected. The prevalence of medicines without the SAPIs was higher for ACAs purchased in the convenience survey compared with the estimates obtained using the full island-wide survey-mystery client and randomised-overt sampling approaches. Comparable results were obtained for full island survey-mystery client and randomised overt. However, the availability of purchased artesunate monotherapies differed substantially according to the sampling approach used (convenience, 45.2%; full island-wide survey-mystery client, 32.6%; random-overt sampling approach, 21.9%). Of concern is that 37.1% (n=62) of these were falsified. Conclusion Falsified ACAs were found on Bioko Island, with the prevalence ranging between 6.1% and 16.1%, depending on the sampling method used. These findings underscore the vital need for national authorities to track the scale of ineffective medicines that jeopardise treatment of life-threatening diseases and value of a representative sampling approach to obtain/measure the true prevalence of poor-quality medicines.


  • Urinary Concentrations of the Antibacterial Agent Triclocarban in United States Residents: 2013–2014 National Health and Nutrition Examination Survey

    by Xiaoyun Ye, Lee-Yang Wong, Prabha Dwivedi, Xiaoliu Zhou, Tao Jia, Antonia M. Calafat

    Triclocarban is widely used as an antibacterial agent in personal care products, and the potential for human exposure exists. We present here the first nationally representative assessment of exposure to triclocarban among Americans ≥6 years of age who participated in the 2013–2014 National Health and Nutrition Examination Survey. We detected triclocarban at concentrations above 0.1 μg/L in 36.9% of 2686 urine samples examined. Triclocarban was detected more frequently in adolescents and adults than in children, and in non-Hispanic black compared to other ethnic groups. In univariate analysis, log-creatinine, sex, age, race, and body surface area (BSA) were significantly associated with the likelihood of having triclocarban concentrations above the 95th percentile. In multiple regression models, persons with BSA at or above the median (≥1.86 m2) were 2.43 times more likely than others, and non-Hispanic black and non-Hispanic white were 3.71 times and 2.23 times more likely than “all Hispanic,” respectively, to have urinary concentrations above the 95th percentile. We found no correlations between urinary concentrations of triclocarban and triclosan, another commonly used antibacterial agent. Observed differences among demographic groups examined may reflect differences in physiological factors (i.e., BSA) as well as use of personal care products containing triclocarban.


  • Microplasma Ionization of Volatile Organics for Improving Air/Water Monitoring Systems On-Board the International Space Station

    by Matthew C. Bernier, Rosana M. Alberici, Joel D. Keelor, Prabha Dwivedi, Stephen C. Zambrzycki, William T. Wallace, Daniel B. Gazda, Thomas F. Limero, Josh M. Symonds, Thomas M. Orlando, et al.

    Low molecular weight polar organics are commonly observed in spacecraft environments. Increasing concentrations of one or more of these contaminants can negatively impact Environmental Control and ...


  • Open Access

    Quality of Antimalarials at the Epicenter of Antimalarial Drug Resistance: Results from an Overt and Mystery Client Survey in Cambodia

    by Shunmay Yeung, Harriet L. S. Lawford, Patricia Tabernero, Chea Nguon, Albert van Wyk, Naiela Malik, Mikhael DeSousa, Ouk Rada, Mam Boravann, Prabha Dwivedi, et al.

    Widespread availability of monotherapies and falsified antimalarials is thought to have contributed to the historical development of multidrug-resistant malaria in Cambodia. This study aimed to document the quality of artemisinin-containing antimalarials (ACAs) and to compare two methods of collecting antimalarials from drug outlets: through open surveyors and mystery clients (MCs). Few oral artemisinin-based monotherapies and no suspected falsified medicines were found. All 291 samples contained the stated active pharmaceutical ingredient (API) of which 69% were considered good quality by chemical analysis. Overall, medicine quality did not differ by collection method, although open surveyors were less likely to obtain oral artemisinin-based monotherapies than MCs. The results are an encouraging indication of the positive impact of the country's efforts to tackle falsified antimalarials and artemisinin-based monotherapies. However, poor-quality medicines remain an ongoing challenge that demands sustained political will and investment of human and financial resources.


  • Open Access

    A Repeat Random Survey of the Prevalence of Falsified and Substandard Antimalarials in the Lao PDR: A Change for the Better

    by Patricia Tabernero, Mayfong Mayxay, María Julia Culzoni, Prabha Dwivedi, Isabel Swamidoss, Elizabeth Louise Allan, Maniphone Khanthavong, Chindaphone Phonlavong, Chantala Vilayhong, Sengchanh Yeuchaixiong, et al.

    In 2003, a stratified random sample survey was conducted in the Lao People's Democratic Republic (Laos) to study the availability and quality of antimalarials in the private sector. In 2012, this survey was repeated to allow a statistically valid analysis of change through time. The counterfeit detection device 3 (CD-3) was used to assess packaging quality in the field and HPLC and mass spectroscopy analysis chemical analysis performed. The availability of oral artesunate monotherapies had significantly decreased from 22.9% (22) of 96 outlets in southern Laos in 2003 to 4.8% (7) of 144 outlets in 2012 (P < 0.0001). All the samples collected in the 2012 survey contained the correct active pharmaceutical ingredients (APIs) in contrast to the 21 (84%) falsified artesunate samples found in the 2003 survey. Although none of the medicines found in 2012 survey had evidence for falsification, 25.4% (37) of the samples were outside the 90–110% pharmacopeial limits of the label claim, suggesting that they were substandard or degraded. Results obtained from this survey show that patients are still exposed to poorly manufactured drugs or to ineffective medicines such as chloroquine. The quality of artemisinin-based combination therapies (ACTs) used in Laos needs to be monitored, since falsified ACTs would have devastating consequences in public health.


  • Open Access

    Quality of Artemisinin-Based Combination Formulations for Malaria Treatment: Prevalence and Risk Factors for Poor Quality Medicines in Public Facilities and Private Sector Drug Outlets in Enugu, Nigeria

    by Harparkash Kaur, Elizabeth Louise Allan, Ibrahim Mamadu, Zoe Hall, Ogochukwu Ibe, Mohamed El Sherbiny, Albert van Wyk, Shunmay Yeung, Isabel Swamidoss, Michael D. Green, et al.

    Artemisinin-based combination therapies are recommended by the World Health Organisation (WHO) as first-line treatment for Plasmodium falciparum malaria, yet medication must be of good quality for efficacious treatment. A recent meta-analysis reported 35% (796/2,296) of antimalarial drug samples from 21 Sub-Saharan African countries, purchased from outlets predominantly using convenience sampling, failed chemical content analysis. We used three sampling strategies to purchase artemisinin-containing antimalarials (ACAs) in Enugu metropolis, Nigeria, and compared the resulting quality estimates. ACAs were purchased using three sampling approaches - convenience, mystery clients and overt, within a defined area and sampling frame in Enugu metropolis. The active pharmaceutical ingredients were assessed using high-performance liquid chromatography and confirmed by mass spectrometry at three independent laboratories. Results were expressed as percentage of APIs stated on the packaging and used to categorise each sample as acceptable quality, substandard, degraded, or falsified. Content analysis of 3024 samples purchased from 421 outlets using convenience (n=200), mystery (n=1,919) and overt (n=905) approaches, showed overall 90.8% ACAs to be of acceptable quality, 6.8% substandard, 1.3% degraded and 1.2% falsified. Convenience sampling yielded a significantly higher prevalence of poor quality ACAs, but was not evident by the mystery and overt sampling strategies both of which yielded results that were comparable between each other. Artesunate (n=135; 4 falsified) and dihydroartemisinin (n=14) monotherapy tablets, not recommended by WHO, were also identified. Randomised sampling identified fewer falsified ACAs than previously reported by convenience approaches. Our findings emphasise the need for specific consideration to be given to sampling frame and sampling approach if representative information on drug quality is to be obtained.


  • Electrothermal Vaporization Sample Introduction for Spaceflight Water Quality Monitoring via Gas Chromatography-Differential Mobility Spectrometry

    by William T. Wallace, Daniel B. Gazda, Thomas F. Limero, John M. Minton, Ariel V. Macatangay, Prabha Dwivedi, Facundo M. Fernández

    In the history of manned spaceflight, environmental monitoring has relied heavily on archival sampling. However, with the construction of the International Space Station (ISS) and the subsequent extension in mission duration up to one year, an enhanced, real-time method for environmental monitoring is necessary. The station air is currently monitored for trace volatile organic compounds (VOCs) using gas chromatography-differential mobility spectrometry (GC-DMS) via the Air Quality Monitor (AQM), while water is analyzed to measure total organic carbon and biocide concentrations using the Total Organic Carbon Analyzer (TOCA) and the Colorimetric Water Quality Monitoring Kit (CWQMK), respectively. As mission scenarios extend beyond low Earth orbit, a convergence in analytical instrumentation to analyze both air and water samples is highly desirable. Since the AQM currently provides quantitative, compound-specific information for air samples and many of the targets in air are also common to water, this platform is a logical starting point for developing a multimatrix monitor. Here, we report on the interfacing of an electrothermal vaporization (ETV) sample introduction unit with a ground-based AQM for monitoring target analytes in water. The results show that each of the compounds tested from water have similar GC-DMS parameters as the compounds tested in air. Moreover, the ETV enabled AQM detection of dimethlsilanediol (DMSD), a compound whose analysis had proven challenging using other sample introduction methods. Analysis of authentic ISS water samples using the ETV-AQM showed that DMSD could be successfully quantified, while the concentrations obtained for the other compounds also agreed well with laboratory results.


  • Open Access

    Desorption atmospheric pressure photoionization and direct analysis in real time coupled with travelling wave ion mobility mass spectrometry

    by Riikka‐Marjaana Räsänen, Prabha Dwivedi, Facundo M. Fernández, Tiina J. Kauppila

    RATIONALE: Ambient mass spectrometry (MS) is a tool for screening analytes directly from sample surfaces. However, background impurities may complicate the spectra and therefore fast separation techniques are needed. Here, we demonstrate the use of travelling wave ion mobility spectrometry in a comparative study of two ambient MS techniques. METHODS: Desorption atmospheric pressure photoionization (DAPPI) and direct analysis in real time (DART) were coupled with travelling wave ion mobility mass spectrometry (TWIM‐MS) for highly selective surface analysis. The ionization efficiencies of DAPPI and DART were compared. Test compounds were: bisphenol A, benzo[a]pyrene, ranitidine, cortisol and α‐tocopherol. DAPPI‐MS and DART‐TWIM‐MS were also applied to the analysis of chloroquine from dried blood spots, and α‐tocopherol from almond surface, and DAPPI‐TWIM‐MS was applied to analysis of pharmaceuticals and multivitamin tablets. RESULTS: DAPPI was approximately 100 times more sensitive than DART for bisphenol A and 10–20 times more sensitive for the other compounds. The limits of detection were between 30–290 and 330–8200 fmol for DAPPI and DART, respectively. Also, from the authentic samples, DAPPI ionized chloroquine and α‐tocopherol more efficiently than DART. The mobility separation enabled the detection of species with low signal intensities, e.g. thiamine and cholecalciferol, in the DAPPI‐TWIM‐MS analysis of multivitamin tablets. CONCLUSIONS: DAPPI ionized the studied compounds of interest more efficiently than DART. For both DAPPI and DART, the mobility separation prior to MS analysis reduced the amount of chemical noise in the mass spectrum and significantly increased the signal‐to‐noise ratio for the analytes. Copyright © 2014 John Wiley & Sons, Ltd.


  • Open Access

    Falsified medicines in Africa: all talk, no action

    by Paul N Newton, Patricia Tabernero, Prabha Dwivedi, María J Culzoni, María Eugenia Monge, Isabel Swamidoss, Dallas Mildenhall, Michael D Green, Richard Jähnke, Miguel dos Santos de Oliveira, et al.