Veterinary syndromic surveillance using swine production data for farm health management and early disease detection.

The use of syndromic surveillance (SyS) has grown in animal health since the 2010s, but the use of production data has been underexplored due to methodological and practical challenges. This paper aimed to tackle some of those challenges by developing a SyS system using production data routinely collected in pig breeding farms. Health-related indicators were created from the recorded data, and two different time-series types emerged: the weekly counts of events traditionally used in SyS; and continuous time-series, where every new event is a new observation, and grouping by time-unit is not applied. Exponentially Weighted Moving Average (EWMA) and Shewhart control charts were used for temporal aberration detection, using three detection limits to create a "severity" score. The system performance was evaluated using simulated outbreaks of porcine respiratory and reproduction syndrome (PRRS) as a disease introduction scenario. The system proved capable of providing early detection of unexpected trends, serving as a useful health and management decision support tool for farmers. Further research is needed to combine results of monitoring multiple parallel time-series into an overall assessment of the risk of reproduction failure.

A diagnostic real-time PCR assay for the rapid identification of the tomato-potato psyllid, Bactericera cockerelli (Sulc, 1909) and development of a psyllid barcoding database.

The accurate and rapid identification of insect pests is an important step in the prevention and control of outbreaks in areas that are otherwise pest free. The potato-tomato psyllid Bactericera cockerelli (Sulc, 1909) is the main vector of 'Candidatus Liberibacter solanacearum' on potato and tomato crops in North America and New Zealand; and is considered a threat for introduction in Europe and other pest-free regions. This study describes the design and validation of the first species-specific TaqMan probe-based real-time PCR assay, targeting the ITS2 gene region of B. cockerelli. The assay detected B. cockerelli genomic DNA from adults, immatures, and eggs, with 100% accuracy. This assay also detected DNA from cloned plasmids containing the ITS2 region of B. cockerelli with 100% accuracy. The assay showed 0% false positives when tested on genomic and cloned DNA from 73 other psyllid species collected from across Europe, New Zealand, Mexico and the USA. This included 8 other species in the Bactericera genus and the main vectors of 'Candidatus Liberibacter solanacearum' worldwide. The limit of detection for this assay at optimum conditions was 0.000001ng DNA (~200 copies) of ITS2 DNA which equates to around a 1:10000 dilution of DNA from one single adult specimen. This assay is the first real-time PCR based method for accurate, robust, sensitive and specific identification of B. cockerelli from all life stages. It can be used as a surveillance and monitoring tool to further study this important crop pest and to aid the prevention of outbreaks, or to prevent their spread after establishment in new areas.

Seasonal Abundance of Psyllid Species on Carrots and Potato Crops in Spain.

Psyllids (Hemiptera: Psylloidea) can transmit the phloem restricted bacterium 'Candidatus Liberibacter solanacearum' (Lso). In Europe, Lso causes severe losses to carrot and represents a threat to the potato industry. A rising concern is Lso transmission from carrot to potato and within potato, and this has driven the need for monitoring populations of psyllid species which could serve as vectors on both crops. This would provide a fundamental understanding of the epidemiology of Lso. Different sampling methods were used to survey populations of psyllid species in commercial carrot and potato fields in central and eastern mainland Spain from 2015 to 2017. Two psyllid species, Bactericera trigonica and Bactericera nigricornis were found on carrot and potato crops. In carrot fields the most abundant species was B. trigonica (occurring from crop emergence to harvest); whereas in potato crops the most abundant psyllid species was B. nigricornis. Depending on field location, the maximum psyllid populations occurred between June and October. Since B. nigricornis was found on both carrot and potato and is the only psyllid species able to feed and reproduce on both these crops in Europe, there is the potential risk of Lso transmission from carrot to potato.

Application of multiblock modelling to identify key drivers for antimicrobial use in pig production in four European countries.

Antimicrobial use in pig farming is influenced by a range of risk factors, including herd characteristics, biosecurity level, farm performance, occurrence of clinical signs and vaccination scheme, as well as farmers' attitudes and habits towards antimicrobial use. So far, the effect of these risk factors has been explored separately. Using an innovative method called multiblock partial least-squares regression, this study aimed to investigate, in a sample of 207 farrow-to-finish farms from Belgium, France, Germany and Sweden, the relative importance of the six above mentioned categories or 'blocks' of risk factors for antimicrobial use in pig production. Four country separate models were developed; they showed that all six blocks provided useful contribution to explaining antimicrobial use in at least one country. The occurrence of clinical signs, especially of respiratory and nervous diseases in fatteners, was one of the largest contributing blocks in all four countries, whereas the effect of the other blocks differed between countries. In terms of risk management, it suggests that a holistic and country-specific mitigation strategy is likely to be more effective. However, further research is needed to validate our findings in larger and more representative samples, as well as in other countries.

Herd-specific interventions to reduce antimicrobial usage in pig production without jeopardising technical and economic performance.

Pig farmers are strongly encouraged to reduce their antimicrobial usage in order to reduce the risk of antimicrobial resistance. Herd-level intervention is needed to achieve national and European reduction targets. Alternative, especially preventive measures, have to be implemented to reduce the need for antimicrobial treatments. However, little is known about the feasibility, effectiveness and return on investment of such measures. The objective of this study was to assess, across four countries, the technical and economic impact of herd-specific interventions aiming at reducing antimicrobial usage in pig production while implementing alternative measures. An intervention study was conducted between February 2014 and August 2015 in 70 farrow-to-finish pig farms located in Belgium, France, Germany and Sweden. Herd-specific interventions were defined together with the farmer and the herd veterinarian. Farms were followed over one year and their antimicrobial usage and technical performance were compared with values from the year before intervention. Compliance with the intervention plan was also monitored. Changes in margin over feed cost and net farm profit were estimated in a subset of 33 Belgian and French farms with sufficient data, using deterministic and stochastic modeling. Following interventions, a substantial reduction in antimicrobial use was achieved without negative impact the overall farm technical performance. A median reduction of 47.0% of antimicrobial usage was achieved across four countries when expressed in terms of treatment incidence from birth to slaughter, corresponding to a 30.5% median reduction of antimicrobial expenditures. Farm compliance with intervention plans was high (median: 93%; min-max: 20; 100) and farms with higher compliance tended to achieve bigger reduction (ρ=-0.18, p=0.162). No association was found between achieved reduction and type or number of alternative measures implemented. Mortality in suckling piglets, weaners and fatteners, daily weight gain and feed conversion ratio did not significantly change over the course of the study, while the number of weaned piglets per sow per year slightly increased. The median change in net farm profit among Belgian and French farms was estimated to be €4.46 (Q25-Q75:-32.54; 80.50) and €1.23 (Q25-Q75:-32.55; 74.45) per sow per year using the detererministic and stochastic models, respectively. It was more influenced by a change in feed conversion ratio and daily weight gain than by a change in antimicrobial expenditures or intervention direct net cost. Therefore, costs of alternative measures should not be perceived as a barrier, but rather as an opportunity to optimise production practices for sustained productivity and improved animal health.

Higher perceived risk of antimicrobials is related to lower antimicrobial usage among pig farmers in four European countries.

The prudent use of antimicrobials (AMs) should be widened in pig farming to reduce the risk of AM resistance (AMR) in human and veterinary medicine. It is therefore important to understand pig farmers' motivators and the barriers to AM usage (AMU) on their farms. The authors investigated pig farmers' self-estimated levels of AMU, their perceived benefits and risks and the need for AMs in a cross-sectional survey in Belgium, France, Germany and Sweden. The authors also compared these perceptions between the four countries and related them to pig farmers' actual AMU. The results showed that farmers who used more AMs also estimated their own usage as higher. Farmers perceived many benefits but relatively few risks of AMU in pig farming. Some significant cross-country differences in farmers' perceptions were found, but they were relatively small. After controlling for country differences and farm differences, only perceived risks had a significant association with AMU. The authors therefore conclude that in order to promote prudent AMU, it seems most promising to focus on the structural differences in pig farming and veterinary medicine (e.g. legislation, role of the veterinarian) among countries. In addition, interventions which aim at reducing AMU should increase farmers' awareness of the risks of extensive AMU.

Quantitative and qualitative antimicrobial usage patterns in farrow-to-finish pig herds in Belgium, France, Germany and Sweden.

Data on sales of antimicrobials using a standardised methodology have shown that there are vast differences between countries in amounts of antimicrobials sold for food-producing animals, but these data do not provide insight on how sales are distributed by species and age groups. The aim of this study was to compare herd level antimicrobial usage for pigs by age category, antimicrobial class and administration route for farrow-to-finish herds in four EU countries. A cross-sectional study was conducted among 227 farrow-to-finish pig herds with at least 100 sows and 500 finishing pigs in Belgium (n=47), France (n=60), Germany (n=60) and Sweden (n=60). Detailed information about the antimicrobial consumption for breeding and growing pigs was collected. Antimicrobial usage was quantified as active substance expressed as mg and then converted to treatment incidence (TI) based on Defined Daily Doses Animal per 1000 pig-days at risk. TIs varied between and within countries, herds and age groups. The Swedish herds had the lowest and the German herds the highest overall use. Most treatments were applied to weaned piglets except in the Swedish herds where treatments of suckling piglets were most frequent. Antimicrobials were most often applied through feed or water except in the Swedish herds where parenteral treatments were most frequent. Aminopenicillins was the antimicrobial class most commonly used. Use of third and fourth generation cephalosporins constituted 11% of use for the Belgian herds, which was higher compared to the other countries. There was a significant (p<0.01) association between the within-herd antimicrobial use across different age categories. This study has shown that there were large differences in antimicrobial use for pigs between countries, herds and age groups in farrow-to-finish herds of similar size when actual consumption data were compared. Collecting detailed usage data can be used to efficiently target high users in order to reduce antimicrobial consumption.

A Comparison of Pig Farmers' and Veterinarians' Perceptions and Intentions to Reduce Antimicrobial Usage in Six European Countries.

Antimicrobial (AM) resistance is an increasing problem in human and veterinary medicine. To manage this problem, the usage of AM should be reduced in pig farming, as well as in other areas. It is important to investigate the factors that influence both pig farmers' and veterinarians' intentions to reduce AM usage, which is a prerequisite for developing intervention measures. We conducted a mail survey among pig farmers (N = 1,294) and an online survey among veterinarians (N = 334) in Belgium, Denmark, France, Germany, Sweden and Switzerland. The farmers' survey assessed the perceived risks and benefits of and need for AM usage; the intention to reduce AM usage; farmers' efficacy (i.e. perception of their ability to reduce AM usage); support from their veterinarian; and the future reduction potential of AM usage. Additionally, self-reported reduction behaviours, the perceived farmers' barriers to reduce AM usage and relationships with farmers were assessed in the veterinarians' survey. The results showed that farmers and veterinarians had similar perceptions of the risks and benefits of AM usage. Veterinarians appeared to be more optimistic than pig farmers about reducing AM usage in pig farming. Farmers believed that their efficacy over AM reduction was relatively high. Farmers' intention to reduce AM usage and veterinarians' self-reported reduction behaviours were mainly associated with factors concerning the feasibility of reducing AM usage. To promote prudent AM usage, pig farmers should learn and experience how to reduce usage by applying alternative measures, whereas veterinarians should strengthen their advisory role and competencies to support and educate farmers.

The biosecurity status and its associations with production and management characteristics in farrow-to-finish pig herds.

Disease prevention through biosecurity measures is believed to be an important factor for improvement of the overall health status in animal production. This study aimed at assessing the levels of implementation of biosecurity measures in pig production in four European Union (EU) countries and to describe possible associations between the biosecurity level and farm and production characteristics. A cross-sectional study was conducted in 232 farrow-to-finish pig herds in Belgium, France, Germany and Sweden between December 2012 and December 2013. The biosecurity status in each of these herds was described and quantified by using the risk-based scoring tool Biocheck.UGentTM (www.biocheck.ugent.be). Production and management characteristics, obtained from the herd management system and by interviewing the farmer, were analysed for their association with the biosecurity level. A causal path was designed to study statistical associations. The results showed that there was substantial room for improvement in the biosecurity status on many pig farms. Significant differences (P<0.01) both in internal and external biosecurity levels were observed between countries. The external biosecurity status, combining all measures taken to prevent disease introduction into the herd, was highest in Germany and lowest in France. The internal biosecurity status, combining all measures taken to prevent within herd disease transmission, was highest in Sweden and lowest, with a large variation, in Belgium. External biosecurity scores were in general higher compared to internal biosecurity scores. The number of pathogens vaccinated against was significantly associated with internal biosecurity status, suggesting an overall more preventive approach towards the risk of disease transmission. A higher external biosecurity was associated with more weaned piglets per sow per year. Furthermore also the weaning age and the mortality till weaning were highly associated with the number of weaned piglets per sow per year. The negative association observed between the biosecurity level and the estimated frequency of treatment against certain clinical signs of disease as a proxy for disease incidence is consistent with the hypothesis that a higher biosecurity level results in healthier animals. These findings promote an improved biosecurity status at pig farms and are of relevance in the discussion on alternative ways to keep animals healthy with a reduced necessity of antimicrobials; Prevention is better than cure!

Perceptions of antimicrobial usage, antimicrobial resistance and policy measures to reduce antimicrobial usage in convenient samples of Belgian, French, German, Swedish and Swiss pig farmers.

We conducted a survey among convenient samples of pig farmers (N=281) in Belgium, France, Germany, Sweden and Switzerland. We identified some significant differences among the five investigated countries (independent variable) regarding farmers' antimicrobial usage compared to their own country and worries related to pig farming (dependent variables), but most of the differences were rather small. In general, farmers perceived their own antimicrobial usage to be lower than that of their peers in the same country and lower than or similar to that of farmers from other countries. This may be a consequence of our convenience sample, resulting in self-selection of highly motivated farmers. Farmers were significantly more worried about financial/legal issues than about antimicrobial resistance. They believed that a reduction in revenues for slaughter pigs treated with a large amount of antimicrobials would have the most impact on reduced antimicrobial usage in their country. Further, farmers who were more worried about antimicrobial resistance and who estimated their own antimicrobial usage as lower than their fellow countrymen, perceived more impact from policy measures on the reduction of antimicrobials. Our results indicated that the same policy measures can be applied to reduce antimicrobial usage in pig farming in all five countries. Moreover, it seems worthwhile to increase pig farmers' awareness of the threat of antimicrobial resistance and its relation to antimicrobial usage; not only because pig farmers appeared little worried about antimicrobial usage but also because it affected farmers' perception of policy measures to reduce antimicrobial usage. Our samples were not representative for the national pig farmer populations. Further research is therefore needed to examine to what extent our findings can be generalised to these populations and to farmers in other countries.

Effects of different antimicrobial treatments on serum acute phase responses and leucocyte counts in pigs after a primary and a secondary challenge infection with Actinobacillus pleuropneumoniae.

The susceptibility to an initial challenge and a re-challenge inoculation with Actinobacillus pleuropneumoniae was analysed in pigs that were treated with antimicrobials of different efficacies following the first exposure to A pleuropneumoniae. In brief, 30 nine-week-old specific pathogen-free pigs were allocated to five groups of six. After acclimatisation, four groups were inoculated with A pleuropneumoniae serotype 2. At the onset of clinical signs, three of the groups of pigs were treated with enrofloxacin, tetracycline or penicillin. A fourth group served as the inoculated control and the fifth group as a control group that had not been inoculated. On day 28, all five groups were re-challenged with the same strain of A pleuropneumoniae serotype 2 as had been used in the first inoculation. No treatments were carried out at this time. The acute phase responses and differential leucocyte counts were monitored in detail after both inoculations. Leucocytosis and acute phase responses in the forms of serum amyloid A, pig-major acute phase protein and haptoglobin were recorded in all of the inoculated groups after the onset of clinical signs following the first inoculation. A porcine mannan-binding lectin-A response was less evident in the pigs. Acute phase responses resembling those of the first inoculation were observed in the pigs that had not previously been inoculated and in the pigs treated with enrofloxacin. Acute phase responses were not recorded in the other three groups, where the pigs had seroconverted to A pleuropneumoniae serotype 2 following the first inoculation.

Disease patterns and immune responses in the offspring to sows with high or low antibody levels to Actinobacillus pleuropneumoniae serotype 2.

The serum antibody responses to Actinobacillus pleuropneumoniae and the secondary invader Pasteurella multocida were monitored from birth until slaughter in the offspring to sows with high or low levels of serum antibodies to A. pleuropneumoniae. Serum antibody concentrations to A. pleuropneumoniae were higher from birth to the age of 9 weeks in piglets delivered by high responding sows. In contrast, antibody levels to P. multocida were similar in both groups during this period. From the age of 20 and 15 weeks, antibody levels to A. pleuropneumoniae and P. multocida, respectively, were higher in the offspring to high responding sows. This implies that the offspring to sows with high levels of antibodies may be better protected during the first period of life because of a higher level of passively derived immunity. These piglets will also mount a higher antibody response when later infected, indicating a heritability of the humoral immune response.

Responses of pigs to a re-challenge with Actinobacillus pleuropneumoniae after being treated with different antimicrobials following their initial exposure.

Four groups of six specific pathogen-free (SPF) pigs were inoculated intranasally with Actinobacillus pleuropneumoniae serotype 2 and treated with either enrofloxacin, tetracycline or penicillin at the onset of clinical disease, or left untreated. A fifth group was left uninoculated. The inoculated control and the penicillin-treated groups developed severe disease, but the groups treated with enrofloxacin and tetracycline recovered rapidly. All the inoculated pigs, except those treated with enrofloxacin developed serum antibodies to A pleuropneumoniae. On day 28, all five groups were challenged with A pleuropneumoniae without any subsequent treatment. The previously uninoculated control group and the enrofloxacin-treated group developed severe disease, but the three seropositive groups remained unaffected.

Antimicrobial susceptibility in Escherichia coli of human and avian origin--a comparison of wild-type distributions.

In the present study, the antimicrobial susceptibilities of 97 Escherichia coli isolates from birds, and 100 clinical isolates from blood cultures, were determined by disk diffusion. The wild-type distributions were defined by the normalized resistance interpretation method. It is shown that the avian and clinical inhibition zone diameter distributions of wild-type E. coli are indistinguishable.

Lameness in piglets. Abrasions in nursing piglets and transfer of protection towards infections with Streptococci from sow to offspring.

A group of 175 newborn piglets were monitored with respect to development of abrasions and lameness. Lameness was diagnosed in 10.9% of the piglets. About every second litter was affected and around 75% of these diagnoses took place during the first 3 weeks of life. Skin lesions were present already on day 3. They increased in magnitude until day 10 and thereafter declined. They were generally bilateral and most commonly observed as abrasions over the carpal joints. Hocks, face and tails were affected in a similar way, but at lower magnitudes. Sole bruising was observed in 87% of the piglets on the third day of life, and moderate to severe lesions dominated until day 10. Thereafter the incidence decreased, indicating healing with time. Still 39% of the piglets were affected at day 17. There was a significant positive correlation between skin lesions of carpus and hock within all examination days in selected piglets with known identity (n = 48). Between day 10 and 17 significant positive correlations were found within all examination sites with exception of abdomen and teats. The offspring of sows treated against mastitis expressed more abrasions then piglets delivered by healthy sows and the mortality during the first 17 days postpartum was significantly higher among piglets delivered by sows treated for mastitis. The level of serum antibodies to Streptococcus equisimilis in eight dams decreased during the last month of gestation and a declining maternal immunity to S. equisimilis was demonstrated in all piglets (n = 47) during the first 5 weeks of life. During the first 2 weeks of life somewhat lower median levels of serum antibodies were recorded among the piglets that were treated against arthritis (n = 8).

Mutation frequency and biological cost of antibiotic resistance in Helicobacter pylori.

Among the several factors that affect the appearance and spread of acquired antibiotic resistance, the mutation frequency and the biological cost of resistance are of special importance. Measurements of the mutation frequency to rifampicin resistance in Helicobacter pylori strains isolated from dyspeptic patients showed that approximately 1/4 of the isolates had higher mutation frequencies than Enterobacteriaceae mismatch-repair defective mutants. This high mutation frequency could explain why resistance is so frequently acquired during antibiotic treatment of H. pylori infections. Inactivation of the mutS gene had no substantial effect on the mutation frequency, suggesting that MutS-dependent mismatch repair is absent in this bacterium. Furthermore, clarithromycin resistance conferred a biological cost, as measured by a decreased competitive ability of the resistant mutants in mice. In clinical isolates this cost could be reduced, indicating that compensation is a clinically relevant phenomenon that could act to stabilize resistant bacteria in a population.

Comparative studies on neutralisation of primary HIV-1 isolates by human sera and rabbit anti-V3 peptide sera.

IgG binding to V3 peptides and serum neutralising responses were studied in four HIV-1 infected individuals with progressive disease over a period of 31-70 months. The 18-20 mer peptides comprised residues 299-317 (numbering of HIV1 MN) in the N-terminal half of the V3 loop of the envelope glycoprotein gp120 and were derived from the sequences of autologous, as well as heterologous isolates. All four individuals studied lacked anti-V3 IgG binding to at least one autologous V3 sequence. V3 peptides to which autologous sera lacked binding IgG were all immunogenic in rabbits and induced antisera that were broadly cross-reactive by EIA and broadly cross-neutralising to primary HIV-1 isolates. This indicates that the peptides are immunogenic per se and that the respective human hosts have selective defects in recognising the corresponding V3 sequences. Despite the absence of antibody binding to autologous V3 peptides, the human sera had neutralising antibodies to autologous (three out of four cases), as well as heterologous isolates (all cases). Moreover, in vitro exposure of the patients' isolates to autologous neutralising serum or the homologous rabbit antiserum selected for variants with amino acid substitutions close to the crown of the V3 loop or in regions outside the sequence corresponding to peptides used for immunisation. The amino acid exchanges affected V3 positions known to be antigenic and which are also prone to change successively in infected persons. It is likely that neutralising antibodies recognise both linear and conformational epitopes in the V3 loop. Apparently, there are several, but restricted, numbers of ways for this structure to change its conformation and thereby give rise to neutralisation resistant viruses.

Transcriptional regulation and biological significance of the insulin like growth factor II gene.

The insulin like growth factors I and II are the most ubiquitous in the mammalian embryo. Moreover they play a pivotal role in the development and growth of tumours. The bioavailability of these growth factors is regulated on a transcriptional as well as on a posttranslational level. The expression of non-signalling receptors as well as binding proteins does further tune the local concentration of IGFs. This paper aims at reviewing how the transcription of the IGF genes is regulated. The biological significance of these control mechanisms will be discussed.

Critical dissolution tests of oral systems based on statistically designed experiments. II. In vitro optimization of screened variables on ER-coated spheres for the establishment of an in vitro/in vivo correlation.

The study was designed to optimize the effects of the screened in vitro dissolution variables agitation, temperature, osmolality, and polarity on the release of the neuroleptic compound remoxipride from extended release coated spheres. The variables were varied independently by means of a fractional factorial design. The in vitro tests were performed with the Basket method (USP). The polarity and the osmolality of the medium had significant effects on the dissolution rate of remoxipride. A statistical model was calculated based on the obtained dissolution in vitro. The model was then used to predict the in vitro conditions that most closely correlated with the dissolution rate of remoxipride in vivo, after administration of the formulation to 16 volunteers. The predicted in vitro conditions were experimentally verified, and an excellent association with the in vivo behavior of the formulation was found. Validation of the optimal in vitro conditions was performed on another batch of the formulation. The dissolution profile obtained showed a significant association with the corresponding dissolution profile in vivo. The use of statistically designed experiments in the development of critical dissolution tests for the establishment of in vitro/in vivo correlations seems to be a useful working approach, and supports further application to other oral solid systems.

Critical dissolution tests of oral systems based on statistically designed experiments. III. In vitro/in vivo correlation for multiple-unit capsules of paracetamol based on PLS modeling.

The main aims of the present study were to establish an in vitro/in vivo correlation for multiple-unit capsules of paracetamol by means of statistical prediction models and to investigate the effect of a number of in vitro variables on the discussion rate of paracetamol from the formulation. A fractional factorial screening design was used to investigate the effects of the variables agitation, pH, osmolality, viscosity, and the presence of bile salt on the dissolution rate of paracetamol. The effects were evaluated in two separate partial least-squares models, in which the responses were expressed as the cumulative percentage of paracetamol dissolved at specified time-points (model I) and as the shape (beta) and scale (eta) parameters according to the Weibull function (model II). It was concluded that agitation and viscosity had significant effects on the dissolution rate of paracetamol. Statistical models based on the responses from models I and II were then used to predict the in vitro conditions most closely correlated with the in vitro dissolution of paracetamol after administration of the formulation to 10 healthy volunteers. The predicted optimal in vitro conditions were similar for the two models and not too far from what is expected from the gastrointestinal tract. The experimental verification of the in vitro conditions showed that both models were equally good, and contributed to high degrees of correlation with the in vivo dissolution behavior of the formulation during 9 hr. The relationships obtained when plotting the percentage dissolved in vitro versus in vivo were y = 1.1x (r2 = 0.98) and y = 1.1x (r2 = 0.94) for models I and II, respectively. Based on these results, it is difficult to state a preference for one of the models. Finally, the use of statistical prediction models to develop critical in vitro tests is a successful approach in the establishment of associations between dissolution behavior in vitro and in vivo for oral extended-release systems.