Plasma C24:0- and C26:0-lysophosphatidylcholines are reliable biomarkers for the diagnosis of peroxisomal ß-oxidation disorders.

The gold-standard diagnostic test for peroxisomal disorders (PDs) is plasma concentration analysis of very long-chain fatty acids (VLCFAs). However, this method's time-consuming nature and limitations in cases which present normal VLCFA levels necessitates alternative approaches. The analysis of C26:0-lysophosphatydylcholine (C26:0-LPC) in dried blood spot samples by tandem-mass spectrometry (MS/MS) has successfully been implemented in certain newborn screening programs to diagnose X-linked adrenoleukodystrophy (ALD). However, the diagnostic potential of very long-chain LPCs concentrations in plasma remains poorly understood. This study sought to evaluate the diagnostic performance of C26:0-LPC and other very long-chain LPCs, comparing them to VLCFA analysis in plasma. The study, which included 330 individuals affected by a peroxisomal ß-oxidation deficiency and 407 control individuals, revealed that C26:0- and C24:0-LPC concentrations demonstrated the highest diagnostic accuracy (98.8% and 98.4%, respectively), outperforming VLCFA when C26:0/C22:0 and C24:0/C22:0 ratios were combined (98.1%). Combining C24:0- and C26:0-LPC gave the highest sensitivity (99.7%), with ALD females exhibiting notably higher sensitivity compared with the VLCFA ratio combination (98.7% vs. 93.5%, respectively). In contrast, C22:0-LPC exhibited suboptimal performance, primarily due to its low sensitivity (75%), but we identified a potential use to help distinguish between ALD and Zellweger spectrum disorders. In summary, MS/MS analysis of plasma C24:0- and C26:0-LPC concentrations represents a rapid and straightforward approach to diagnose PDs, demonstrating superior diagnostic accuracy, particularly in ALD females, compared with conventional VLCFA biomarkers. We strongly recommend integrating very-long chain LPC plasma analysis in the diagnostic evaluation of individuals suspected of having a PD.

Analysis of a second-tier test panel in dried blood spot samples using liquid chromatography-tandem mass spectrometry in Catalonia's newborn screening programme.

OBJECTIVES: Acylcarnitine and amino acid analyses of dried blood spot (DBS) samples using tandem mass spectrometry in newborn screening (NBS) programmes can generate false positive (FP) results. Therefore, implementation of second-tier tests (2TTs) using DBS samples has become increasingly important to avoid FPs. The most widely used 2TT metabolites include methylmalonic acid, 3-hydroxypropionic acid, methylcitric acid, and homocysteine. METHODS: We simultaneously measured 46 underivatised metabolites, including organic acids, acylglycine and acylcarnitine isomers, homocysteine, and orotic acid, in DBS samples using tandem mass spectrometry. To validate this method, we analysed samples from 147 healthy newborns, 160 patients with genetic disorders diagnosed via NBS, 20 patients with acquired vitamin B12 deficiency, 10 newborns receiving antibiotic treatment, and nine external quality control samples. RESULTS: The validation study revealed that 31 metabolites showed good analytical performance. Furthermore, this method detected key metabolites for all diseases associated with increased levels of the following acylcarnitines: C3, C4, C5, C4DC/C5OH, and C5DC. The sensitivity of this method to detect all diseases was 100 %, and the specificity was 74-99 %, except for glutaric aciduria type 1. This method can also be used to diagnose mitochondrial fatty acid ß-oxidation disorders (FAODs) and urea cycle defects (UCDs). CONCLUSIONS: We have described a 2TT panel of 31 metabolites in DBS samples based on an easy and rapid method without derivatisation. Its implementation allowed us to distinguish between different organic acidurias, some FAODs, and UCDs. This new strategy has increased the efficiency of our NBS programme by reducing FP and false negative results, second sample requests, and the time required for diagnosis.

Preparing Enteral Formulas for Adult Patients with Phenylketonuria: A Minor Necessity but Major Challenge-A Case Report.

Phenylketonuria (PKU) is the most frequent of the congenital errors of amino acid (AA) metabolism worldwide. It leads to the accumulation of the essential AA phenylalanine (Phe) and it is associated with severe neurological defects. The early diagnosis and treatment of this rare disease, achieved through newborn screening and low-Phe diet, has profoundly changed its clinical spectrum, resulting in normal cognitive development. We face the first generation of PKU patients perinatally diagnosed and treated who have reached adulthood, whose special needs must be addressed, including feeding through enteral nutrition (EN). However, recommendations regarding EN in PKU constitute a gap in the literature. Although protein substitutes for patients with PKU are offered in multiple forms (Phe-free L-amino acid or casein glycomacropeptide supplements), none of these commercial formulas ensures the whole provision of daily total energy and protein requirements, including a safe amount of Phe. Consequently, the combination of different products becomes necessary when artificial nutrition via tube feeding is required. Importantly, the composition of these specific formulas may result in physicochemical interactions when they are mixed with standard EN products, leading to enteral feeding tubes clogging, and also gastrointestinal concerns due to hyperosmolality. Herein, we present the first reported case of EN use in an adult patient with PKU, where the separate administration of protein substitutes and the other EN products avoided physicochemical interactions.

[Analysis of the implementation of a unified transportation system of the neonatal screening samples in Catalonia.] / Análisis de la implementación de un sistema de transporte unificado de las muestras de cribado neonatal en Cataluña.

The Neonatal Screening Program in Catalonia from its inception fifty years ago until today, has enabled the early diagnosis and treatment of more than 2,000 newborns. In the last decade, the Program has undergone various extensions regarding its panel of diseases and has improved its evaluation with the inclusion of quality indicators in all its stages. One of the pending subjects of the screening program has been the improvement of the quality indexes related to the sample's arrival time to the laboratory after their extraction. The extension of the territory, the dispersion of numerous maternal centers, as well as the diversity and heterogeneity of the sample transport systems, have been an obstacle to quality compliance of these indexes. With the aim of reducing the period of samples arrival to the laboratory and continue to move towards meeting the standards established by the Ministry of Health, in 2020 a unified sample transport system has been implemented for the entire Catalan territory. The times obtained during the first months with the new system, have shown a notable improvement in the results, achieving a reduction of 50% of the days between the extraction of the sample and its arrival at the laboratory.

El Programa de Cribado Neonatal (PCN) de Cataluña ha permitido el diagnóstico y tratamiento precoz de más de 2.000 recién nacidos desde su inicio hace cincuenta años hasta la actualidad. En la última década, el PCN ha experimentado diversas ampliaciones en cuanto a su panel de enfermedades y ha mejorado su evaluación con la inclusión de indicadores de calidad en todas sus etapas. Una de las asignaturas pendientes del programa de cribado ha sido la mejora de los indicadores relativos al tiempo de llegada de las muestras al laboratorio desde su extracción. La extensión territorial, la dispersión de los sesenta y seis centros maternales, así como la diversidad y heterogeneidad de los sistemas de transporte de muestras, han supuesto un obstáculo para el cumplimiento de la calidad de este indicador. Con el objetivo de reducir el período de llegada de las muestras al laboratorio y seguir avanzando en el cumplimiento de los estándares establecidos por el Ministerio de Sanidad, en 2020 se ha implementado un sistema de transporte de muestras unificado para todo el territorio catalán. Los tiempos obtenidos durante los primeros meses con el nuevo sistema muestran una mejora notable de los resultados, consiguiendo una reducción del 50% de los días transcurridos desde la extracción de la muestra hasta su llegada al laboratorio.

[Response of the Catalonia neonatal screening laboratory to the pandemic of SARS-CoV-2.] / Respuesta del Laboratorio de Cribado Neonatal de Cataluña ante la pandemia por SARS-CoV-2.

Faced with the prospect of a collapsed health system due to the COVID-19 pandemic, the professionals involved in the Neonatal Screening Programme (NSP) of Catalonia had to adapt to this situation in a flexible, forceful and efficient manner. The most important goals were to prevent the risk of infection in the professionals, in families and their newborns, as well as to ensure the same effectiveness for the early detection of the diseases included in our programme. To this end, the laboratory was reorganised by dividing the staff into groups and the spaces were redistributed. It was also necessary to modify several protocols and circuits, especially for the management of early discharges from maternity centres, and for the collection of the necessary second samples (from newborns with inconclusive results or for low quality samples). In general, a 36% reduction in the time of arrival of these second samples at the laboratory was achieved with respect to the previous circuit. In the specific case of cystic fibrosis detection, the implementation of a new strategy meant a 100% reduction in the request for second samples and a 70% reduction in the age of diagnosis of the newborn. After evaluating these changes, it can be concluded that in the face of the pandemic, the NSP of Catalonia showed determined leadership, aligning all its professionals, ensuring the continuity of the activity in the programme and generating new opportunities. The new processes and circuits implemented have been definitively consolidated, improving the efficiency of the programme.

Ante la crisis de un sistema sanitario colapsado debido a la pandemia por la COVID-19, los profesionales implicados en el Programa de Cribado Neonatal (PCN) de Cataluña nos tuvimos que adaptar a dicha situación de forma ágil, contundente y eficiente. Los objetivos prioritarios fueron prevenir el riesgo de contagio tanto en los profesionales sanitarios como en las familias y sus recién nacidos, así como asegurar la misma eficacia para la detección precoz de las enfermedades incluidas en el PCN. Para ello, se reorganizó el laboratorio dividiendo en grupos al personal y se redistribuyeron los espacios. También fue necesario modificar varios protocolos y circuitos, en especial para la gestión de las altas precoces de los centros maternales y para la toma de las segundas muestras necesarias (de recién nacidos que presentaron resultados dudosos o por muestra inválida). En general, se consiguió una reducción del 36% del tiempo de llegada de estas segundas muestras al laboratorio respecto al circuito anterior. Para la detección de la fibrosis quística, la implementación de una nueva estrategia supuso una reducción del 100% en la solicitud de segundas muestras y del 70% en la edad de diagnóstico del recién nacido. Tras la evaluación de estos cambios, se puede concluir que ante la pandemia el PCN de Cataluña mostró un liderazgo decidido, alineando a todos sus profesionales, asegurando la continuidad de la actividad en el programa y generando nuevas oportunidades. Los nuevos procesos y circuitos de trabajo implantados han quedado definitivamente consolidados, mejorando la eficiencia del programa.

[First universal newborn screening program for severe combined immunodeficiency in Europe. Three-years' experience in Catalonia.] / Primer programa europeo de cribado neonatal para la inmunodeficiencia combinada grave: experiencia de tres años en Cataluña.

Severe combined immunodeficiency (SCID), the most severe form of T-cell immunodeficiency, can be screened at birth by quantifying T-cell receptor excision circles (TREC) in dried blood spot (DBS) samples. Early detection of this condition speeds up the establishment of appropriate treatment and increases the patient's life expectancy. Newborn screening for SCID started in January 2017 in Catalonia, the first Spanish and European region to universally include this testing. The results obtained in the first three years and a half of experience (January 2017 - June 2020) are shown here, using EnLite Neonatal TREC kit (Perkin Elmer) with 20 copies/µL as TREC detection cutoff. Of 222,857 newborns screened, 48 tested positive: three patients were diagnosed with SCID (incidence 1:74,285); 17 patients had clinically significant T-cell lymphopenia (non-SCID) with an incidence of 1 in 13,109 newborns; twenty two patients were considered false-positive cases because of an initially normal lymphocyte count with normalization of TREC between 3 and 6 months of life; one case had transient lymphopenia due to an initially low lymphocyte count with recovery in the following months; and five patients are still under study. The results obtained provide further evidence of the benefits of including this disease in newborn screening programs. Even longer follow-up could be necessary to define the exact incidence of SCID in Catalonia.

La inmunodeficiencia combinada grave (IDCG) es la forma más grave de inmunodeficiencia primaria, que afecta sobre todo a los linfocitos T, y puede ser detectada al nacer mediante la cuantificación de los círculos de escisión del receptor de linfocitos T (TREC) en una muestra de sangre impregnada en papel (DBS). La detección precoz de esta enfermedad permite establecer de forma temprana un tratamiento adecuado en el paciente, permitiendo así su curación. El cribado neonatal de IDCG comenzó en Cataluña en enero de 2017, siendo la primera región española y europea en incluirla oficial y universalmente en su programa. En el presente trabajo se presentan los resultados obtenidos durante los tres primeros años y medio de experiencia (enero 2017 ­ junio 2020) empleando el kit EnLite Neonatal TREC (Perkin Elmer), con un cutoff de detección de TREC de 20 copias/µL. De 222.857 recién nacidos analizados, cuarenta y ocho fueron detecciones positivas: tres casos de IDCG (incidencia de 1:74.285); diecisiete casos de linfopenia T no IDCG (incidencia de 1:13.109); veintidós casos falsos positivos (recuento de linfocitos inicialmente normal, con normalización de TREC entre los tres y seis meses de vida); un caso con linfopenia transitoria (con un recuento de linfocitos inicialmente bajo, que se normaliza en los meses siguientes); y cinco pacientes se encuentran todavía en estudio. Los resultados obtenidos aportan evidencias de los beneficios que supone incluir esta enfermedad en los programas de cribado neonatal. Podría ser necesario un seguimiento todavía más prolongado para acabar de definir la incidencia exacta de IDCG en Cataluña.

Primer programa europeo de cribado neonatal para la inmunodeficiencia combinada grave: experiencia de tres años en Cataluña / First universal newborn screening program for severe combined immunodeficiency in Europe. Three-years' experience in Catalonia

La inmunodeficiencia combinada grave (IDCG) es la forma más grave de inmunodeficiencia primaria, que afecta sobre todo a los linfocitos T, y puede ser detectada al nacer mediante la cuantificación de los círculos de escisión del receptor de linfocitos T (TREC) en una muestra de sangre impregnada en papel (DBS). La detección precoz de esta enfermedad permite establecer de forma temprana un tratamiento adecuado en el paciente, permitiendo así su curación. El cribado neonatal de IDCG comenzó en Cataluña en enero de 2017, siendo la primera región española y europea en incluirla oficial y universalmente en su programa. En el presente trabajo se presentan los resultados obtenidos durante los tres primeros años y medio de experiencia (enero 2017 - junio 2020) empleando el kit EnLite Neonatal TREC (Perkin Elmer), con un cutoff de detección de TREC de 20 copias/miL. De 222.857 recién nacidos analizados, cuarenta y ocho fueron detecciones positivas: tres casos de IDCG (incidencia de 1:74.285); diecisiete casos de linfopenia T no IDCG (incidencia de 1:13.109); veintidós casos falsos positivos (recuento de linfocitos inicialmente normal, con normalización de TREC entre los tres y seis meses de vida); un caso con linfopenia transitoria (con un recuento de linfocitos inicialmente bajo, que se normaliza en los meses siguientes); y cinco pacientes se encuentran todavía en estudio. Los resultados obtenidos aportan evidencias de los beneficios que supone incluir esta enfermedad en los programas de cribado neonatal. Podría ser necesario un seguimiento todavía más prolongado para acabar de definir la incidencia exacta de IDCG en Cataluña

Severe combined immunodeficiency (SCID), the most severe form of T-cell immunodeficiency, can be screened at birth by quantifying T-cell receptor excision circles (TREC) in dried blood spot (DBS) samples. Early detection of this condition speeds up the establishment of appropriate treatment and increases the patient's life expectancy. Newborn screening for SCID started in January 2017 in Catalonia, the first Spanish and European region to universally include this testing. The results obtained in the first three years and a half of experience (January 2017 - June 2020) are shown here, using EnLite Neonatal TREC kit (Perkin Elmer) with 20 copies/miL as TREC detection cutoff. Of 222,857 newborns screened, 48 tested positive: three patients were diagnosed with SCID (incidence 1:74,285); 17 patients had clinically significant T-cell lymphopenia (non-SCID) with an incidence of 1 in 13,109 newborns; twenty two patients were considered false-positive cases because of an initially normal lymphocyte count with normalization of TREC between 3 and 6 months of life; one case had transient lymphopenia due to an initially low lymphocyte count with recovery in the following months; and five patients are still under study. The results obtained provide further evidence of the benefits of including this disease in newborn screening programs. Even longer follow-up could be necessary to define the exact incidence of SCID in Catalonia

Respuesta del laboratorio de cribado neonatal de Cataluña ante la pandemia por SARS-CoV-2 / Response of the Catalonia neonatal screening laboratory to the pandemic of SARS-CoV-2

Ante la crisis de un sistema sanitario colapsado debido a la pandemia por la COVID-19, los profesionales implicados en el Programa de Cribado Neonatal (PCN) de Cataluña nos tuvimos que adaptar a dicha situación de forma ágil, contundente y eficiente. Los objetivos prioritarios fueron prevenir el riesgo de contagio tanto en los profesionales sanitarios como en las familias y sus recién nacidos, así como asegurar la misma eficacia para la detección precoz de las enfermedades incluidas en el PCN. Para ello, se reorganizó el laboratorio dividiendo en grupos al personal y se redistribuyeron los espacios. También fue necesario modificar varios protocolos y circuitos, en especial para la gestión de las altas precoces de los centros maternales y para la toma de las segundas muestras necesarias (de recién nacidos que presentaron resultados dudosos o por muestra inválida). En general, se consiguió una reducción del 36% del tiempo de llegada de estas segundas muestras al laboratorio respecto al circuito anterior. Para la detección de la fibrosis quística, la implementación de una nueva estrategia supuso una reducción del 100% en la solicitud de segundas muestras y del 70% en la edad de diagnóstico del recién nacido. Tras la evaluación de estos cambios, se puede concluir que ante la pandemia el PCN de Cataluña mostró un liderazgo decidido, alineando a todos sus profesionales, asegurando la continuidad de la actividad en el programa y generando nuevas oportunidades. Los nuevos procesos y circuitos de trabajo implantados han quedado definitivamente consolidados, mejorando la eficiencia del programa

Faced with the prospect of a collapsed health system due to the COVID-19 pandemic, the professionals involved in the Neonatal Screening Programme (NSP) of Catalonia had to adapt to this situation in a flexible, forceful and efficient manner. The most important goals were to prevent the risk of infection in the professionals, in families and their newborns, as well as to ensure the same effectiveness for the early detection of the diseases included in our programme. To this end, the laboratory was reorganised by dividing the staff into groups and the spaces were redistributed. It was also necessary to modify several protocols and circuits, especially for the management of early discharges from maternity centres, and for the collection of the necessary second samples (from newborns with inconclusive results or for low quality samples). In general, a 36% reduction in the time of arrival of these second samples at the laboratory was achieved with respect to the previous circuit. In the specific case of cystic fibrosis detection, the implementation of a new strategy meant a 100% reduction in the request for second samples and a 70% reduction in the age of diagnosis of the newborn. After evaluating these changes, it can be concluded that in the face of the pandemic, the NSP of Catalonia showed determined leadership, aligning all its professionals, ensuring the continuity of the activity in the programme and generating new opportunities. The new processes and circuits implemented have been definitively consolidated, improving the efficiency of the programme

Criterios de extracción de muestra en situaciones especiales del cribado neonatal. Revisión / Criteria for specimen collection in special situations of newborn screening. Review

La espectrometría de masas en tándem (MS-MS) ha permitido ampliar el alcance del cribado neonatal. Eso hace más complicado determinar el momento más adecuado para la toma de muestra, sobre todo en recién nacidos prematuros y/o bajo peso y/o ingresados en unidades neonatales. El objetivo del presente estudio ha sido revisar las normas de toma de muestra de los distintos programas en estas situaciones, a nivel nacional e internacional. Se obtienen los datos a través de páginas web de salud pública, de plataformas de búsqueda o por contacto con los centros. Existe gran disparidad de criterios para la toma de una nueva muestra, incluso dentro de un mismo país. La limitación de información disponible, hizo imposible obtener resultados de muchos países, en particular de África, Asia o Latinoamérica. A pesar de que cada vez más estados se acogen a las recomendaciones del Clinical and Laboratory Standards Institute u otros organismos internacionales, el aumento del coste que implica, hace muy difícil conseguir la estandarización

The most significant breakthrough in the newborn screening (NBS) programs was the introduction of the tandem mass spectrometry (MS-MS) to the laboratory, which makes it possible to detect multiple disorders. However, it is difficult to choose the ideal time for the specimen collection, particularly in preterm, low birth weight, and sick newborns. The aim of this study was to revise the protocols, in national and international programs for specimen collection in these newborns. Data were collected from web pages of public health, internet searches, and contact with the laboratories. The results showed a great disparity in criteria for a new specimen collection, as well as among different centres within a country. It has been difficult to obtain this information from many countries in Africa, Asia, and Latin America. Although an increasing number of laboratories follow the recommendations of the Clinical and Laboratory Standards Institute or other international guidelines, the increased cost involved makes standardisation difficult

¿Podemos descartar infección congénita por citomegalovirus cuando la reacción en cadena de la polimerasa viral es negativa en la prueba del talón? / Can we rule out a congenital cytomegalovirus infection when the result of polymerase chain reaction in dried blood spots is negative?

INTRODUCCIÓN: La determinación de la presencia de ADN de citomegalovirus (CMV) mediante técnicas de reacción en cadena de la polimerasa a tiempo real (rt-PCR) en la gota de sangre seca en el papel absorbente usado para la realización de la prueba de detección precoz neonatal ha sido validada para el diagnóstico retrospectivo de infección congénita por CMV (CMVc) en estudios realizados en otros países, pero no en el nuestro. El objetivo de este estudio es analizar el valor diagnóstico de esta técnica en nuestro centro. MÉTODOS: Estudio retrospectivo transversal observacional de todos los pacientes con diagnóstico confirmado de CMVc entre enero de 2007 y septiembre de 2012. Se ha determinado la presencia de ADN viral de CMV en las muestras de sangre seca de la prueba del talón de estos pacientes mediante rt-PCR. RESULTADOS: Se incluyeron 14 pacientes; 4/14 sintomáticos y 4/14 con secuelas. La detección de CMV por rt-PCR fue positiva únicamente en 7 de ellos. Se demostró una relación estadísticamente significativa entre la negatividad de la rt-PCR y cargas virales más bajas al nacimiento. CONCLUSIÓN: A pesar del pequeño tamaño muestral, nuestros datos ponen en evidencia la presencia de un número importante de falsos negativos en la detección de CMV por rt-PCR en este tipo de muestras en el diagnóstico de CMVc, especialmente en pacientes con cargas virales bajas al nacimiento

INTRODUCTION: The detection of cytomegalovirus (CMV) DNA by real time polymerase chain reaction (rt-PCR) in dried blood spots collected routinely for metabolic screening has been assessed for the retrospective diagnosis of congenital CMV (cCMV) infection in many studies, but not in Spain. The aim of this study is to analyze the diagnostic accuracy of this technique in our hospital. METHODS: A cross-sectional retrospective observational study was conducted including all patients born between January, 2007 and September, 2012 with confirmed cCMV infection. The assessment of CMV DNA was made by using rt-PCR in dried blood spots of these patients. RESULTS: Fourteen patients were included: 4/14 were symptomatic and 4/14 had sequelae. The detection of CMV DNA by rt-PCR was positive in only 7 patients. A statistically significant relationship between low viral load at birth and negative rt-PCR in dried blood spots was demonstrated. CONCLUSIONS: Despite the low number of patients included, our data highlight an important amount of false negative results in the DNA CMV detection by rt-PCR in these samples for the retrospective diagnosis of cCMV infection, especially in cases with low viral load at birth

[Can we rule out a congenital cytomegalovirus infection when the result of polymerase chain reaction in dried blood spots is negative?]. / ¿Podemos descartar infección congénita por citomegalovirus cuando la reacción en cadena de la polimerasa viral es negativa en la prueba del talón?

INTRODUCTION: The detection of cytomegalovirus (CMV) DNA by real time polymerase chain reaction (rt-PCR) in dried blood spots collected routinely for metabolic screening has been assessed for the retrospective diagnosis of congenital CMV (cCMV) infection in many studies, but not in Spain. The aim of this study is to analyze the diagnostic accuracy of this technique in our hospital. METHODS: A cross-sectional retrospective observational study was conducted including all patients born between January, 2007 and September, 2012 with confirmed cCMV infection. The assessment of CMV DNA was made by using rt-PCR in dried blood spots of these patients. RESULTS: Fourteen patients were included: 4/14 were symptomatic and 4/14 had sequelae. The detection of CMV DNA by rt-PCR was positive in only 7 patients. A statistically significant relationship between low viral load at birth and negative rt-PCR in dried blood spots was demonstrated. CONCLUSIONS: Despite the low number of patients included, our data highlight an important amount of false negative results in the DNA CMV detection by rt-PCR in these samples for the retrospective diagnosis of cCMV infection, especially in cases with low viral load at birth.

Determinación de linezolid en plasma mediante cromatografía líquida de alta resolución para la monitorización terapéutica en pacientes / Determination of linezolid in human plasma by high-performance liquid chromatography for therapeutic drug monitoring

Introducción. Linezolid es un antibiótico sintético de un nuevo grupo, las oxazolidinonas, con espectro de actividad para grampositivos. Está indicado en infecciones de piel y tejidos blandos e infecciones nosocomiales adquiridas en la comunidad así como infecciones causadas por Staphylococcus aureus y Enterococus meticilin y vancomicin-resistentes, respectivamente. El objetivo de este trabajo es desarrollar y evaluar un método de cromatografía líquida de alta resolución (HPLC) para la monitorización de niveles plasmáticos de linezolid en muestras de pacientes. Material y métodos. Se utilizó como fase móvil una mezcla de acetonitrilo y agua con flujo isocrático de 1mL y una columna corta C18. La detección se realizó en un detector ultravioleta/visible a 254nm. El tratamiento de la muestra fue por precipitación de proteínas con ácido tricloroacético y posterior inyección del sobrenadante. Resultados. El método fue lineal y validado para un intervalo de 0,25 a 20mg/L. La precisión intra e interensayo (CV) fue inferior al 1% y 1,6%, respectivamente. La exactitud osciló entre -4,3% y 0,4%. La recuperación media fue superior al 82%. No se encontraron interferencias con otros fármacos habitualmente utilizados en la terapia combinada con linezolid. Tampoco se detectaron interferencias endógenas de la propia matriz biológica. Conclusiones. El método descrito para cuantificar linezolid en muestras de plasma es sensible, reproducible, específico, rápido y requiere poca muestra, por lo que le hace adecuado para la monitorización terapéutica (AU)

Introduction. Linezolid is a synthetic antibiotic of the group of the oxazolidinones with Gram positive spectrum of activity. It is indicated in skin and soft tissue infections, community-acquired nosocomial infections and infections caused by methicillin-resistant and vancomycin-resistant Staphylococcus aureus and Enterococcus, respectively. The aim of this work is to develop and evaluate a high pressure (HPLC) method for the monitoring of plasma levels of linezolid in patients samples. Materials and methods. The mobile phase consisted of a mixture of acetonitrile and water with a flow rate of 1mL/min and a short C18 column. An ultraviolet/visible detector at 254nm was used to detect the peaks. Sample treatment consisted of precipitation of plasma proteins with trichloroacetic acid and then injection of the supernatant. Results. The method was linear and validated from 0,25 to 20mg/L. The within-day and between-day coefficient of variation (CV) was less 1% and 1,6%, respectively. The accuracy varied between −4,3% and 0,4%. The average recovery was greater than 82%. No interferences were found with other drugs habitually used in the therapy combined with linezolid. Endogenous interferences of the biological matrix were not detected. Conclusions. The method described to quantify linezolid in plasma samples is sensitive, reproducible, specific, rapid and needs very little sample, which makes it suitable for therapeutic drug monitoring (AU)

Population pharmacokinetics of lopinavir/ritonavir (Kaletra) in HIV-infected patients.

BACKGROUND: A relationship between plasma concentrations and viral suppression in patients receiving lopinavir (LPV)/ritonavir (RTV) has been observed. Therefore, it is important to increase our knowledge about factors that determine interpatient variability in LPV pharmacokinetics (PK). METHODS: The study, designed to develop and validate population PK models for LPV and RTV, involved 263 ambulatory patients treated with 400/100 mg of LPV/RTV twice daily. A database of 1110 concentrations of LPV and RTV (647 from a single time-point and 463 from 73 full PK profiles) was available. Concentrations were determined at steady state using high-performance liquid chromatography with ultraviolet detection. PK analysis was performed with NONMEM software. Age, gender, height, total body weight, body mass index, RTV trough concentration (RTC), hepatitis C virus coinfection, total bilirubin, hospital of origin, formulation and concomitant administration of efavirenz (EFV), saquinavir (SQV), atazanavir (ATV), and tenofovir were analyzed as possible covariates influencing LPV/RTV kinetic behavior. RESULTS: Population models were developed with 954 drug plasma concentrations from 201 patients, and the validation was conducted in the remaining 62 patients (156 concentrations). A 1-compartment model with first-order absorption (including lag-time) and elimination best described the PK. Proportional error models for interindividual and residual variability were used. The final models for the drugs oral clearance (CL/F) were as follows: CL/F(LPV)(L/h)=0.216·BMI·0.81(RTC)·1.25(EFV)·0.84(ATV); CL/F(RTV)(L/h) = 8.00·1.34(SQV)·1.77(EFV)·1.35(ATV). The predictive performance of the final population PK models was tested using standardized mean prediction errors, showing values of 0.03 ± 0.74 and 0.05 ± 0.91 for LPV and RTV, and normalized prediction distribution error, confirming the suitability of both models. CONCLUSIONS: These validated models could be implemented in clinical PK software and applied to dose individualization using a Bayesian approach for both drugs.