Biomedical subjects

Xavier Vidal

Publications and source records attributed to Xavier Vidal.

9 recordsLinked to original sources

PubMed2006

Generation of light in media with a random distribution of nonlinear domains.

We show that the second order nonlinear generation of light, a process that it is assumed to require highly ordered materials, is also possible in structures of randomly oriented nonlinear domains. We explain theoretically why in such disordered structures the efficiency of the nonlinear generation of light grows linearly with the number of domains. Moreover, a higher degree of disorder, obtained when the dispersion is made very large, has no negative effect for the nonlinear light generation. In such conditions, light generation is shown to be equally efficient for any average size of the domains and also to grow linearly with respect to the number of domains.

Journal Article↗

PubMed2005

Population-based drug-induced agranulocytosis.

BACKGROUND: Since the publication of a major international case-control study on the risk of agranulocytosis associated with the use of medicines in the 1980s, many new drugs have been introduced in therapeutics. METHODS: Seventeen units of hematology contribute to the case-control surveillance of agranulocytosis and aplastic anemia in Barcelona, Spain. After a follow-up of 78.73 million person-years, 177 community cases of agranulocytosis were compared with 586 sex-, age, and hospital-matched control subjects with regard to previous use of medicines. RESULTS: The annual incidence of community-acquired agranulocytosis was 3.46:1 million, and it increased with age. The fatality rate was 7.0%, and the mortality rate was 0.24:1 million. The drug most strongly associated with a risk of agranulocytosis was ticlopidine hydrochloride with an odds ratio (OR) of 103.23 (95% confidence interval [CI], 12.73-837.44), followed by calcium dobesilate (OR, 77.84 [95% CI, 4.50-1346.20]), antithyroid drugs (OR, 52.75 [95% CI, 5.82-478.03]), dipyrone (metamizole sodium and metamizole magnesium) (OR, 25.76 [95% CI, 8.39-179.12]), and spironolactone (OR, 19.97 [95% CI, 2.27-175.89]). Other drugs associated with a significant risk were pyrithyldione, cinepazide, aprindine hydrochloride, carbamazepine, sulfonamides, phenytoin and phenytoin sodium, beta-lactam antibiotics, erythromycin stearate and erythromycin ethylsuccinate, and diclofenac sodium. Individual attributable incidences for all these drugs, which collectively accounted for 68.6% of cases, were less than 1:1 million per year. CONCLUSIONS: Agranulocytosis is rare but serious. A few drugs account for two thirds of the cases. Our results also provide reassurance regarding the risk associated with a number of newly marketed drugs.

Adolescent↗

PubMed2005

Reliability of retrospective clinical data to evaluate the effectiveness of lumbar fusion in chronic low back pain.

STUDY DESIGN: Patients in whom a posterior spinal fusion instrumentation had been performed to treat low back pain were asked to recall their preoperative clinical status by retrospectively filling out the same 3 self-evaluation scales they had completed before surgery in a prospective fashion. OBJECTIVES: To evaluate the impact of recollection error and compare outcomes using retrospective versus prospective methodologies among a cohort of patients treated with posterior spinal fusion instrumentation. SUMMARY OF BACKGROUND DATA: Literature on spine surgery from 1990 to 2000 shows a greater increase in retrospective studies as compared to randomized controlled trials and other prospective studies. Cross-sectional studies evaluate therapeutic effectiveness by comparing the current condition with the recalled (retrospectively recorded) pretreatment condition. There are no studies analyzing the characteristics of recalled data in a cohort of patients with chronic low back pain treated with posterior spinal fusion instrumentation. METHODS: The preoperative clinical status of 58 patients, 33 women and 25 men, with a mean age of 48.3 years (22-84 years) was assessed prospectively with 3 self evaluation questionnaires and retrospectively at a mean of 37.5 months (2-58 months) after surgery using the same questionnaires. The Wilcoxon test was used to compare prospective and retrospective preoperative data and to compare prospective outcomes with outcomes determined from cross-sectional data. Agreement between prospective and retrospective measures was estimated with intraclass correlation coefficients for absolute agreement and consistency. RESULTS: Comparisons between prospective and recalled data showed significant differences, demonstrating a worse preoperative situation when using retrospective data. Assessment of treatment effectiveness showed that cross-sectional evaluation significantly improved the real surgical outcome. Both absolute agreement and consistency intraclass correlation coefficients showed poor agreement between prospective and cross-sectional data, revealing no systematic bias. Follow-up, age, and gender did not modify agreement and cross-sectional overestimation. CONCLUSIONS: Relying on a patient's recall of preoperative clinical status is not an accurate method to evaluate surgical outcome after posterior spinal fusion instrumentation. Cross-sectional studies may overestimate the effectiveness of surgery.

Adult↗

PubMed2005

Case-control study of regular analgesic and nonsteroidal anti-inflammatory use and end-stage renal disease.

BACKGROUND: Studies on the association between the long-term use of aspirin and other analgesic and nonsteroidal anti-inflammatory drugs (NSAIDs) and end-stage renal disease (ESRD) have given conflicting results. In order to examine this association, a case-control study with incident cases of ESRD was carried out. METHODS: The cases were all patients entering the local dialysis program because of ESRD in the study area between June 1, 1995 and November 30, 1997. They were classified according to the underlying disease, which had presumably led them to ESRD. Controls were patients admitted to the same hospitals from where the cases arose, also matched by age and sex. Odds ratios were calculated using a conditional logistic model, including potential confounding factors, both for the whole study population and for the various underlying diseases. RESULTS: Five hundred and eighty-three cases and 1190 controls were included in the analysis. Long-term use of any analgesic was associated with an overall odds ratio of 1.22 (95% CI, 0.89-1.66). For specific groups of drugs, the risks were 1.56 (1.05-2.30) for aspirin, 1.03 (0.60-1.76) for pyrazolones, 0.80 (0.39-1.63) for paracetamol, and 0.94 (0.57-1.56) for nonaspirin NSAIDs. The risk of ESRD associated with aspirin was related to the cumulated dose and duration of use, and it was particularly high among the subset of patients with vascular nephropathy as underlying disease [2.35 (1.17-4.72)]. CONCLUSION: Our data indicate that long-term use of nonaspirin analgesic drugs and NSAIDs is not associated with an increased risk of ESRD. However, the chronic use of aspirin may increase the risk of ESRD.

Adult↗

PubMed2004

Agranulocytosis associated with dipyrone (metamizol).

OBJECTIVES: Reported estimates of the risk of agranulocytosis associated with metamizol have varied by several orders of magnitude. We assessed this association in a large database for the surveillance of blood dyscrasias. METHODS: Since 1980, all laboratory units of haematology in a defined area (3.3-4.1x10(6) inhabitants) contribute to the ascertainment of all cases of agranulocytosis meeting strict diagnostic criteria. These cases of patients with agranulocytosis and sex-, age-, hospital- and date-matched controls were interviewed using a structured questionnaire about previous drug exposures, and relative risks were calculated for several categories of exposure to metamizol. RESULTS: After a total follow-up of 78.73x10(6) person-years, 273 community cases of agranulocytosis had been found--of which 96 were excluded for various reasons and 177 were included in the case-control analysis--and were compared with 586 matched controls. Thirty cases of agranulocytosis (16.9%) and nine controls (1.5%) had been exposed to metamizol during the week before the index day. The adjusted relative risk was 25.8 [95% confidence interval (CI), 8.4-79.1], and the attributable incidence was 0.56 (0.4-0.8) cases per million inhabitants and per year. The risk disappeared after more than 10 days since the last dose of metamizol, and it increased with duration of use. Those with agranulocytosis exposed to metamizol had taken the drug for longer periods than the exposed controls. Compared with the cases recently reported from Sweden, the duration of use of metamizol by our exposed cases was substantially shorter, and the use of concomitant medications potentially causing agranulocytosis was lower. DISCUSSION: In our milieu, agranulocytosis attributable to metamizol is rare. Geographical disparities in its risk estimate can be partly explained by differences in its patterns of use, in terms of dose, duration and concomitant medications.

Adverse Drug Reaction Reporting Systems↗

PubMed2004

Upper gastrointestinal bleeding associated with the use of NSAIDs: newer versus older agents.

AIM: The relative gastrointestinal toxicity of NSAIDs in normal clinical practice is unknown. The aim of this study was to estimate the risk of upper gastrointestinal bleeding associated with NSAIDs and analgesics, with special emphasis on those agents that have been introduced in recent years. DESIGN: Multicentre case-control study. PATIENTS: All incident community cases of upper gastrointestinal bleeding from a gastric or duodenal lesion in patients aged >18 years of age (4309 cases). After secondary exclusions, 2813 cases and 7193 matched controls were included in the analysis. SETTING: Eighteen hospitals in Spain and Italy with a total study experience of 10,734,897 person-years. MAIN OUTCOME MEASURE: Odds ratios of upper gastrointestinal bleeding for each drug, with adjustment for potential confounders. For each individual drug the reference category was defined as those not exposed to the drug. RESULTS: The incidence of upper gastrointestinal bleeding was 401.4 per million inhabitants aged >18 years. Thirty-eight percent of cases were attributable to NSAIDs. Individual risks for each NSAID were dose dependent. Ketorolac was associated with the highest risk estimate (24.7; 95% CI 8.0, 77.0). For newer NSAIDs, the risks were as follows: aceclofenac 1.4 (95% CI 0.6, 3.3), celecoxib 0.3 (95% CI 0.03, 4.1), dexketoprofen 4.9 (95% CI 1.7, 13.9), meloxicam 5.7 (95% CI 2.2, 15.0), nimesulide 3.2 (95% CI 1.9, 5.6) and rofecoxib 7.2 (95% CI 2.3, 23.0). The risk was significantly increased in patients with a history of peptic ulcer and/or upper gastrointestinal bleeding, and in those taking antiplatelet drugs. CONCLUSIONS: NSAID-induced upper gastrointestinal bleeding is a common cause of hospital admission. Apart from the patient's history of peptic ulcer, its risk depends on the particular drug and its dose, and on concomitant treatments. Our results do not confirm that greater selectivity for COX-2 confers less risk of upper gastrointestinal bleeding.

Adult↗

PubMed2003

Adverse effects of ACE inhibitors in patients with chronic heart failure and/or ventricular dysfunction : meta-analysis of randomised clinical trials.

BACKGROUND: The evidence-based benefit/risk evaluation of therapeutic interventions in randomised clinical trials should include both the assessment of the benefits and of the adverse outcomes. There is ample evidence that ACE inhibitors improve the symptoms and prognosis of chronic heart failure (CHF) and ventricular dysfunction. However, there is little systematic information on the tolerability and adverse effects associated with their use in these conditions. OBJECTIVE: To estimate the adverse events related to ACE inhibitor use in the treatment of CHF and ventricular dysfunction. DESIGN AND METHODS: Description of adverse events in reports of randomised clinical trials of ACE inhibitors in CHF or ventricular dysfunction was examined, and a meta-analysis was performed. Trials were included if they were placebo- or standard treatment-controlled, and if the treatment duration was at least 8 weeks. Relative risks and their 95% CIs were estimated with a random effects model. RESULTS: Only 22 (43%) of 51 original reports contained information on the number of withdrawals and their causes. Missing information from the remaining 29 trials was obtained from the authors. The weighted mean duration of treatment was 100.2 weeks. After excluding administrative reasons, heart failure, myocardial infarction and hypertension, the withdrawal rates attributed to adverse events were 13.8% and 9.4% for the ACE inhibitor and control groups, respectively (RR = 1.54 [95% CI 1.30-1.83]; weighted difference = 3.1 per 100 treated patients [95% CI 1.8-4.4]). Cough, hypotension, renal dysfunction, dizziness, hyperkalaemia, and impotence were all significantly more prevalent among patients treated with ACE inhibitors than among those in the control groups. CONCLUSIONS: Among patients with CHF or ventricular dysfunction enrolled in randomised clinical trials, treatment with an ACE inhibitor for an average of 2 years leads to an additional 3% of treatment withdrawals. In a significant proportion of the reports on these randomised clinical trials, information on adverse events leading to treatment withdrawal was inadequate. Proper evidence-based evaluation of the benefit/risk of therapeutic interventions needs a more systematic approach to reporting of adverse events experiences recorded in clinical trials.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2002

Prospective surveillance of acute serious liver disease unrelated to infectious, obstructive, or metabolic diseases: epidemiological and clinical features, and exposure to drugs.

BACKGROUND/AIMS: Acute serious liver disease which is unrelated to infectious, obstructive, or metabolic disease is uncommon. Many drugs have been implicated. Data on its epidemiology are scarce. We performed a population-based prospective study of acute serious liver disease in Catalonia (Spain). METHODS: A collaborating hospital network was set up. All patients with acute serious liver disease and negative viral hepatitis serological markers, without an obvious cause of liver disease, were included. RESULTS: The incidence of acute serious liver disease was 7.4 per 10(6) inhabitants per year (95% CI; 6.0-8.8), which increased with age. The incidence of hepatocellular acute serious liver disease (3.84 per 10(6) per year) was greater than that of cholestatic and mixed patterns. The case-fatality ratio was 11.9% and mortality 0.8 per million person-years. The risk of death was similar among patients with hepatocellular and cholestatic patterns. Non-steroidal antiinflammatory drugs, analgesics, and antibacterials were the most frequently used drugs. CONCLUSIONS: Acute serious liver disease which is unrelated to infectious, obstructive, or metabolic disease is rare. Its incidence increases with age. The prognosis of cholestatic acute serious liver disease does not significantly differ from that of the hepatocellular pattern. Non-steroidal antiinflammatory drugs, analgesics, and antibacterials were the most common drugs likely to be responsible for acute liver disease.

Acute Disease↗

PubMed2002

Case-population studies in pharmacoepidemiology.

The case-population approach aims at providing a risk estimate by comparing the incidence of the disease of interest among those exposed to the drug under study with the incidence among the non-exposed. For that purpose, the cases with the disease of interest have to be ascertained independently of the exposure status. Their rate and pattern of exposure have to be ascertained by interview with a structured questionnaire. Information on the patterns and the prevalence of drug consumption is needed in order to estimate the rate of exposure, and drug consumption statistics can be used to this end. In this paper, we review the main characteristics of studies using this approach or a similar one, and studies where series of cases exposed to the drug of interest were compared with drug consumption statistics. We looked at selected basic methodological requirements. Most of the studies reviewed suffer from incomplete case ascertainment, inaccurate definition of the disease of interest, incomplete information on exposures and other risk factors, and/or limited control of potential confounding, among other limitations. All the reviewed studies had several limitations regarding the estimation of the population at risk. The methods used in case-population studies should be clearly described, particularly with respect to the identification of the cases (numerator) and the estimation of the consumption prevalence (denominator). Case-population studies can give approximate risk estimates, but the method should be validated by comparing its results with those of case-control studies.

Case-Control Studies↗