'Under pressure': The role of therapeutic drug monitoring in the treatment of hypertension.

Antihypertensive drugs do not qualify as optimal candidates for therapeutic drug monitoring (TDM), given their obvious physiological effect, the absence of a clear relationship between drug concentrations and pharmacodynamic outcomes and their wide therapeutic range. However, since non-adherence is a major challenge in hypertension management, using drug concentrations can be of value to identify non-adherence as a first step towards better blood pressure control. In this article we discuss the key challenges associated with measuring and interpreting antihypertensive drug concentrations that are important when TDM is used to improve non-adherence. Additionally, we elaborate on the role of TDM in optimizing antihypertensive drug treatment besides addressing non-adherence by highlighting its value in specific patient groups with altered pharmacokinetic parameters such as female vs. male or elderly patients.

Developing practical recommendations for drug-disease interactions in patients with hypertension.

Background: Hypertension, a significant risk factor for cardiovascular diseases, demands proactive management as cardiovascular diseases remain the leading cause of death worldwide. Reducing systolic and diastolic blood pressure levels below recommended reference values of <140/90 mmHg can lead to a significant reduction of the risk of CVD and all-cause mortality. However, treatment of hypertension can be difficult and the presence of comorbidities could further complicate this treatment. Drugs used to manage these comorbidities may inadvertently have an impact on blood pressure, resulting in a phenomenon known as drug-disease interaction. This study aims to assess the safety of medication that can affect blood pressure in patients with hypertension and provide practical recommendations for healthcare professionals. Methods: For the development of recommendations for the drug-disease interaction (DDSI) hypertension, a six-step plan that combined literature selection and multidisciplinary expert opinion was used. The process involved (1) defining the scope of the DDSI and selecting relevant drugs, (2) collecting evidence, (3) data-extraction, (4) reaching of expert consensus, (5) publication and implementation of the recommendations in healthcare systems and (6) updating the information. Results: An increase of 10 mmHg in systolic blood pressure and 5 mmHg in diastolic blood pressure was defined as clinically relevant. Corticosteroids, danazol, and yohimbine caused a clinically relevant DDSI with hypertension. Several other drugs with warnings for hypertension in the official product information were assessed to have no clinically relevant DDSI due to minor influence or lack of data on blood pressure. Drugs with evidence for a relevant change in blood pressure which are prescribed under close monitoring of blood pressure according to clinical guidelines, were deemed to be not clinically relevant for signalling. Conclusion: This study provides specific recommendations that can be implemented directly in clinical practice, for example, in clinical decision support systems, potentially resulting in safer drug use in patients with hypertension and better healthcare by reducing alert fatigue. Future research should focus on evaluating the effectiveness of implementation strategies and their impact on reducing unsafe use of medication in patients with hypertension.

Quality-of-life and beliefs about medication in relation to a therapy adherence intervention in resistant hypertension: the Resistant HYpertension: MEasure to ReaCh Targets trial.

OBJECTIVE: To assess the impact of personalized feedback on therapy adherence testing results on quality of life and beliefs about medication in patients with resistant hypertension, as well as to identify patient-oriented predictors of therapy adherence. METHODS: This study was a prespecified post hoc analysis of the multicenter randomized controlled trial Resistant HYpertension: MEasure to ReaCh Targets (RHYME-RCT). Patients were randomized to a personalized feedback conversation on measured antihypertensive drug levels additional to standard-of-care, or standard-of-care only. The primary outcomes consisted of EuroQol EQ-5D-5L and Beliefs about Medicine Questionnaire (BMQ) scores at 12 months. RESULTS: A total of 56 patients with median age 61.5 [25th-75th percentile: 55.8-69.3] years (21.4% women) were included. Mean blood pressure ±SD was 149.8/84.1 ±â€Š14.9/13.8 mmHg while being on a median of 5.6 [4.8-7.3] defined daily dosages (DDD) of antihypertensive drugs. At 12 months, no differences were observed in EQ-5D-5L index (0.81 [0.69-0.89] vs. 0.89 [0.73-1.00]; P = 0.18) and visual analogue scale score on general patient-perceived health (70 [60-80] vs. 70 [60-82]; P = 0.53) between the intervention-arm and the standard-of-care only-arm. Likewise, individual EQ-5D-5L domain scores and BMQ scores did not differ between both arms. Irrespective of the intervention, independent positive predictors of the percentage adherence were patient age, EQ-5D-5L index score, BMQ-specific necessity score and concern score, whereas the total number of drugs prescribed was a negative predictor. CONCLUSION: Within this prespecified subanalysis of the randomized RHYME-RCT trial, implementation of a personalized feedback conversation targeting therapy adherence did not improve health-related quality-of-life and beliefs about medication in patients with resistant hypertension.

Antihypertensive drug concentration measurement combined with personalized feedback in resistant hypertension: a randomized controlled trial.

BACKGROUND: Adherence to antihypertensive drugs (AHDs) is crucial for controlling blood pressure (BP). We aimed to determine the effectiveness of measuring AHD concentrations using a dried blood spot (DBS) sampling method to identify nonadherence, combined with personalized feedback, in reducing resistant hypertension. METHODS: We conducted a multicenter, randomized, controlled trial (RHYME-RCT, ICTRP NTR6914) in patients with established resistant hypertension. Patients were randomized to receive either an intervention with standard of care (SoC) or SoC alone. SoC consisted of BP measurement and DBS sampling at baseline, 3 months (t3), 6 months (t6), and 12 months (t12); AHD concentrations were measured but not reported in this arm. In the intervention arm, results on AHD concentrations were discussed during a personalized feedback conversation at baseline and t3. Study endpoints included the proportion of patients with RH and AHD adherence at t12. RESULTS: Forty-nine patients were randomized to receive the intervention+SoC, and 51 were randomized to receive SoC alone. The proportion of adherent patients improved from 70.0 to 92.5% in the intervention+SoC arm ( P  = 0.008, n  = 40) and remained the same in the SoC arm (71.4%, n  = 42). The difference in adherence between the arms was statistically significant ( P  = 0.014). The prevalence of resistant hypertension decreased to 75.0% in the intervention+SoC arm ( P  < 0.001, n  = 40) and 59.5% in the SoC arm ( P  < 0.001, n  = 42) at t12; the difference between the arms was statistically nonsignificant ( P  = 0.14). CONCLUSION: Personalized feedback conversations based on DBS-derived AHD concentrations improved AHD adherence but did not reduce the prevalence of RH.

The impact of a summative national prescribing assessment and curriculum type on the development of the prescribing competence of junior doctors.

PURPOSE: The primary aim of this study was to investigate the effect of including the Dutch National Pharmacotherapy Assessment (DNPA) in the medical curriculum on the level and development of prescribing knowledge and skills of junior doctors. The secondary aim was to evaluate the relationship between the curriculum type and the prescribing competence of junior doctors. METHODS: We re-analysed the data of a longitudinal study conducted in 2016 involving recently graduated junior doctors from 11 medical schools across the Netherlands and Belgium. Participants completed three assessments during the first year after graduation (around graduation (+ / - 4 weeks), and 6 months, and 1 year after graduation), each of which contained 35 multiple choice questions (MCQs) assessing knowledge and three clinical case scenarios assessing skills. Only one medical school used the DNPA in its medical curriculum; the other medical schools used conventional means to assess prescribing knowledge and skills. Five medical schools were classified as providing solely theoretical clinical pharmacology and therapeutics (CPT) education; the others provided both theoretical and practical CPT education (mixed curriculum). RESULTS: Of the 1584 invited junior doctors, 556 (35.1%) participated, 326 (58.6%) completed the MCQs and 325 (58.5%) the clinical case scenarios in all three assessments. Junior doctors whose medical curriculum included the DNPA had higher knowledge scores than other junior doctors (76.7% [SD 12.5] vs. 67.8% [SD 12.6], 81.8% [SD 11.1] vs. 76.1% [SD 11.1], 77.0% [12.1] vs. 70.6% [SD 14.0], p < 0.05 for all three assessments, respectively). There was no difference in skills scores at the moment of graduation (p = 0.110), but after 6 and 12 months junior doctors whose medical curriculum included the DNPA had higher skills scores (both p < 0.001). Junior doctors educated with a mixed curriculum had significantly higher scores for both knowledge and skills than did junior doctors educated with a theoretical curriculum (p < 0.05 in all assessments). CONCLUSION: Our findings suggest that the inclusion of the knowledge focused DNPA in the medical curriculum improves the prescribing knowledge, but not the skills, of junior doctors at the moment of graduation. However, after 6 and 12 months, both the knowledge and skills were higher in the junior doctors whose medical curriculum included the DNPA. A curriculum that provides both theoretical and practical education seems to improve both prescribing knowledge and skills relative to a solely theoretical curriculum.

Monitoring antihypertensive drug concentrations to determine nonadherence in hypertensive patients with or without a kidney transplant.

BACKGROUND: Nonadherence to antihypertensive drugs (AHDs) is a major contributor to pseudo-resistant hypertension. The primary objective of this study was to determine the prevalence of nonadherence to AHDs among patients visiting the nephrology and vascular outpatient clinics. METHODS: Patients were eligible to participate in this prospective observational study if they used at least two AHDs that could be measured with a validated UHPLC-MS/MS method and had an office blood pressure at least 140 and/or at least 90 mmHg. For resistant hypertension, included patients had to use at least three AHDs including a diuretic or four AHDs. Adherence was assessed by measuring drug concentrations in blood. The complete absence of drug in blood was defined as nonadherence. A posthoc analysis was performed to determine the influence of a having a kidney transplant on the adherence rates. RESULTS: One hundred and forty-two patients were included of whom 66 patients fulfilled the definition of resistant hypertension. The overall adherence rate to AHDs was 78.2% ( n  = 111 patients), with the highest adherence rate for irbesartan (100%, n  = 9) and lowest adherence rate for bumetanide ( n  = 69%, n  = 13). In further analysis, only kidney transplantation could be identified as an important factor for adherence (adjusted odds ratio = 3.35; 95% confidence interval 1.23-9.09). A posthoc analysis showed that patients with a kidney transplant were more likely to be adherent to AHDs (non-KT cohort 64.0% vs. KT-cohort 85.7%, χ 2 (2) = 10.34, P  = 0.006). CONCLUSION: The adherence rate to AHDs in hypertensive patients was high (78.2%) and even higher after a kidney transplant (85.7%). Furthermore, patients after kidney transplant had a lower risk of being nonadherent to AHDs.

Do we become better prescribers after graduation: A 1-year international follow-up study among junior doctors.

AIM: The aim of this study was to investigate how the prescribing knowledge and skills of junior doctors in the Netherlands and Belgium develop in the year after graduation. We also analysed differences in knowledge and skills between surgical and nonsurgical junior doctors. METHODS: This international, multicentre (n = 11), longitudinal study analysed the learning curves of junior doctors working in various specialties via three validated assessments at about the time of graduation, and 6 months and 1 year after graduation. Each assessment contained 35 multiple choice questions (MCQs) on medication safety (passing grade ≥85%) and three clinical scenarios. RESULTS: In total, 556 junior doctors participated, 326 (58.6%) of whom completed the MCQs and 325 (58.5%) the clinical case scenarios of all three assessments. Mean prescribing knowledge was stable in the year after graduation, with 69% (SD 13) correctly answering questions at assessment 1 and 71% (SD 14) at assessment 3, whereas prescribing skills decreased: 63% of treatment plans were considered adequate at assessment 1 but only 40% at assessment 3 (P < .001). While nonsurgical doctors had similar learning curves for knowledge and skills as surgical doctors (P = .53 and P = .56 respectively), their overall level was higher at all three assessments (all P < .05). CONCLUSION: These results show that junior doctors' prescribing knowledge and skills did not improve while they were working in clinical practice. Moreover, their level was under the predefined passing grade. As this might adversely affect patient safety, educational interventions should be introduced to improve the prescribing competence of junior doctors.

Best Practices to Implement Dried Blood Spot Sampling for Therapeutic Drug Monitoring in Clinical Practice.

BACKGROUND: Sampling of blood at home to determine the concentration of drugs or other compounds can be effective in limiting hospital-based sampling. This could lower hospital visits and patient burden, improve the quality of life, and reduce health care costs. Dried blood spot (DBS) microsampling is often used for this purpose, wherein capillary blood, obtained by pricking the heel or finger, is used to measure different analytes. Although DBS has several advantages over venous blood sampling, it is not routinely implemented in clinical practice. To facilitate the bench to bedside transition, it is important to be aware of certain challenges that need to be considered and addressed. RESULTS: Here, important considerations regarding the implementation of DBS in clinical practice, the choice of patients, blood sampling, transport, and laboratory analysis are discussed. In addition, we share our experience and provide suggestions on how to deal with these problems in a clinical setting.

Development and Validation of a Dried Blood Spot Assay Using UHPLC-MS/MS to Identify and Quantify 12 Antihypertensive Drugs and 4 Active Metabolites: Clinical Needs and Analytical Limitations.

PURPOSE: As nonadherence to antihypertensive drugs (AHDs) can increase the risk of cardiovascular events, hospitalization, and higher costs, there is a need for a reliable, objective, and easy method to assess nonadherence in patients. The dried blood spot (DBS) sampling method used to measure drug concentrations meets these requirements. For detecting nonadherence, identification is more important than quantification. Owing to their use in clinical practice, it is important to measure multiple AHDs with a single method. Therefore, we developed and validated a single DBS method for 17 commonly used AHDs and 4 active metabolites using ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). METHODS: Analytical validation of the DBS assay was performed in accordance with the guidelines on bioanalytical method validation of the European Medicines Agency and US Food and Drug Administration as well as the International Association of Therapeutic Drug Monitoring and Clinical Toxicology guidelines. RESULTS: We validated 12 of the 17 AHDs according to the European Medicines Agency and Food and Drug Administration requirements for bioanalytical method validation. Eleven AHDs were validated for both identification and quantification of drug concentrations, whereas nifedipine was only validated for identification. However, 5 of the 17 AHDs were excluded due to suboptimal validation results. Lercanidipine was excluded due to nonlinearity, and all 4 AHDs measured in the negative mode of UHPLC-MS/MS were not in accordance with one or more of the acceptance criteria and were therefore excluded. CONCLUSIONS: The described method accurately measured AHDs in DBS and can be used to determine nonadherence in patients. However, method validation revealed a challenging balance between analytical limitations and clinical needs when analyzing multiple drugs using the same method.

DiffErenCes in AntihypertenSive Drug Blood Levels in Patients with HypertensiON (DECISION): Protocol for a Prospective Observational Study Comparing Pharmacokinetics and Pharmacodynamics Between Young and Elderly Patients.

Adequate controlled blood pressure decreases the risk of cardiovascular events. However, the elderly are more vulnerable and thereby more prone to side effects of antihypertensive drugs. A lack of pharmacokinetic and pharmacodynamic (PK/PD) studies in older patients makes specific and tailored advices towards antihypertensive drug therapy difficult. The aim of our study, DiffErenCes In antihypertenSive drug levels In patients with hypertensiON (DECISION), is to fill in this PK/PD knowledge gap and move towards precision dosing. DECISION is a prospective observational PK/PD study set up to determine the difference in exposure to the antihypertensive drugs, losartan and perindopril, measured by drug levels in blood. The area under the curve (AUC; PK) and furthermore the association between the AUC and the effect on blood pressure (PD) will be compared between elderly and younger patients.

Sex Differences in Spironolactone and the Active Metabolite Canrenone Concentrations and Adherence.

We aim to investigate sex differences in blood concentrations of spironolactone and the active metabolite canrenone in resistant hypertension patients. Furthermore, sex differences in adherence for spironolactone and other antihypertensive drugs (AHDs) were studied. The patients in this post hoc study had all participated in a single-blind randomized controlled trial called RHYME-RCT (Dutch Trial Register, NL6736). Concentrations in blood of several AHDs were assessed in RHYME-RCT to investigate adherence to treatment. This allowed for a comparison of drug exposure to spironolactone and canrenone between males and females. In linear regression models, no statistically significant sex differences (N = 35) in spironolactone (B =-10.23, SE = 7.92, p = 0.206) or canrenone (B = 1.24, SE = 10.96, p = 0.911) concentrations after adjustment for dose and time between sampling and intake were found. Furthermore, no statistically significant differences in non-adherence to spironolactone were found between sexes (N = 54, male 15% vs. female 38%, p = 0.100), but non-adherence to spironolactone was associated with non-adherence to other AHDs (p ≤ 0.001). Spironolactone and canrenone concentrations were not different between males and females with resistant hypertension. Although not statistically significant, females were twice as likely to be non-adherent to spironolactone compared to males, and thereby also more likely to be non-adherent to other AHDs.

Comparison of automated office blood pressure measurement with 24-hour ambulatory blood pressure measurement.

PURPOSE: Although 24-hour ambulatory blood pressure measurement (24-h ABPM) is the most important method to establish true hypertension, in clinical practice often repeated automated office blood pressure (AOBP) measurements are used because of convenience and lower costs. We aimed to assess the agreement rate between a 30 and 60 min AOBP and 24-h ABPM. MATERIALS AND METHODS: Patients with known hypertension (cohort 1) and patients visiting the neurology outpatient clinic after minor stroke or transient ischaemic attack (cohort 2) were selected. We performed AOBP for 30-60 min at 5-min intervals followed by 24-h ABPM and calculated average values of both measurements. Agreement between the two methods was studied with McNemar and Bland-Altman plots with a clinically relevant limit of agreement of ≤10 mm Hg difference in systolic BP. RESULTS: Our final cohort consisted of 135 patients from cohort 1 and 72 patients from cohort 2. We found relatively low agreement based on the clinical relevant cut-off value; 64.7% of the measurements were within the limits of agreement for 24-h systolic and 50.2% for 24-h diastolic. This was 61.4% for daytime systolic and 56.6% for daytime diastolic. In 73.5% of the patients, both methods led to the same diagnosis of either being hypertensive or non-hypertensive. This resulted in a significant difference between the methods to determine the diagnosis of hypertension (p < 0.0001). CONCLUSION: We conclude that 30-60 min AOBP measurements cannot replace a 24-h ABPM and propose to perform 24-h ABPM at least on a yearly basis to confirm AOBP measurements.

Introducing the importance and difficulties of a three-step approach to improve nonadherence to antihypertensive drugs: a case series.

Nonadherence to antihypertensive drugs is an important reason for not reaching blood pressure goals. A possible method to improve nonadherence involves three essential steps: identification of nonadherent patients (step 1), determination of underlying causes (step 2) and a personalized solution (step 3). We present three unique cases to show the importance and difficulties of this three-step approach. Patients participated in a randomized controlled trial to improve nonadherence to antihypertensive drugs (RHYME-RCT, Dutch Trial Register NL6736). Drug level measurements were used to identify nonadherence to antihypertensive drugs and communication on drug levels was supported by a tailored feedback tool in these patients. These cases showed that a three-step approach of identifying nonadherence and determination of the underlying cause, can lead to a personalized solution to improve therapy even when nonadherence was excluded. Open communication with patients remains an essential part when improving nonadherence.

An Accidental Repetitive 10-Fold Overdose of Sildenafil in a Young Infant with Pulmonary Hypertension.

Sildenafil is a selective phosphodiesterase type-5 inhibitor that is increasingly used to treat pulmonary hypertension (PH) in neonates. Only little is known about the relation between the dose of sildenafil, plasma concentrations, and the degree of toxicity. Here, we present a young infant with congenital diaphragmatic hernia and PH who received an unintentional 10-fold overdose of oral sildenafil for 6 consecutive days. This overdose, compared to the therapeutic dose, resulted in increased plasma concentrations of sildenafil from 42 to 521 mcg/L and desmethylsildenafil from 81 to 393 mcg/L. However, the high exposure only led to diarrhea, without any other serious adverse events. This case describes the mild symptoms upon an overdose with the role of therapeutic drug monitoring to monitor exposure in relation to symptoms and therewith support clinical decision-making.

Clinical Applicability of Monitoring Antihypertensive Drug Levels in Blood.

Dried blood spot (DBS) analysis is a novel analytical method for therapeutic drug monitoring to identify nonadherence to antihypertensive drugs. This study was conducted to evaluate the clinical applicability of measuring drug concentrations of 8 antihypertensive drugs, using DBS and venipuncture. Furthermore, this study aimed to provide more insight into the between-patient variability in drug concentrations. False-negative values from DBS compared with a venipuncture were determined to assess drug adherence. A generalized estimating equation was used to estimate the model parameters, including sex, dose, age, weight, and the time interval, between drug intake and sampling, on the Cplasma (drug concentration in plasma). No false-negative values were found when measuring nonadherence using DBS compared with venipuncture. A high variability in Cplasma between patients was observed, especially at peak concentrations with a fold change reaching from 2.3 to 35.2. The time of intake was significantly related to the height of the Cplasma in 7 of the 8 measured drugs with a P<0.05, but the influence of dose, weight, age, and sex on drug levels differed largely between the measured drugs. DBS is a reliable and convenient method to assess nonadherence to antihypertensive drugs in clinical practice. The Cplasma of the 8 antihypertensive drugs in this study show a large interindividual difference, and therefore, low plasma concentrations do not necessarily mean nonadherence. Nonadherence can only be confirmed if drug levels are undetectable, that is, values below the lower limit of detection.

Clinical Validation of a Dried Blood Spot Assay for 8 Antihypertensive Drugs and 4 Active Metabolites.

BACKGROUND: Drug nonadherence is one of the major challenges faced by resistant hypertension patients, and identification of this problem is needed for optimizing pharmacotherapy. Dried blood spot (DBS) sampling is a minimally invasive method designed to detect and determine the degree of nonadherence. In this study, a DBS method for qualifying 8 antihypertensive drugs (AHDs) and 4 active metabolites was developed and validated using ultra high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). METHOD: The DBS assay was validated analytically and clinically, in accordance with FDA requirements. Analytical validation was accomplished using UHPLC-MS/MS. For clinical validation, paired peak and trough levels of DBS and plasma samples were simultaneously collected and comparatively analyzed using Deming regression and Bland-Altman analyses. All concentrations below the set lower limit were excluded. Deming regression analysis was used to predict comparison bias between the collected plasma and DBS samples, with DBS concentrations corrected accordingly. RESULTS: The UHPLC-MS/MS method for simultaneously measuring 8 AHDs and their metabolites in DBS, was successfully validated. With Deming regression no bias was observed in N = 1; constant bias was seen in N = 6 and proportional bias in N = 11 of the AHDs and metabolites. After correction for bias, only one metabolite (canrenone) met the 20% acceptance limit for quantification, after Bland-Altman analyses. In addition, amlodipine, valsartan, and [enalaprilate] met the 25% acceptance limit. CONCLUSIONS: A novel DBS assay for simultaneously qualifying and quantifying 8 AHDs and their metabolites, has been successfully developed and validated. The DBS assay is therefore a suitable method to detect drug nonadherence. However, with the exception of canrenone, the interchangeable use of plasma and DBS sampling to interpret drug quantities should be avoided.

Drug nonadherence is a common but often overlooked cause of hypertensive urgency and emergency at the emergency department.

OBJECTIVES: Over 70% of patients who visit the emergency department with a hypertensive emergency or a hypertensive urgency have previously been diagnosed with hypertension. Drug nonadherence is assumed to play an important role in development of hypertensive urgency and hypertensive emergency, but exact numbers are lacking. We aimed to retrospectively compare characteristics of patients with hypertensive urgency and hypertensive emergency and to prospectively quantify the attribution of drug nonadherence. METHODS: We retrospectively analysed clinical data including information on nonadherence obtained by treating physicians of patients with SBP at least 180 mmHg and DBP at least 110 mmHg visiting the emergency department between 2012 and 2015. We prospectively studied drug adherence among patients admitted to the emergency department with severely elevated BP by measuring plasma drug levels using liquid chromatography tandem mass spectrometry from September 2016 to March 2017. RESULTS: Of the 1163 patients retrospectively analysed, 257 (22.0%) met the criteria for hypertensive urgency and 356 (30.6%) for hypertensive emergency. Mean SBP (SD) was 203 (19) mmHg and mean DBP 121 (12) mmHg. Mean age was 60.1 (14.6) years; 55.1% were men. In 6.3% of patients with hypertensive urgency or hypertensive emergency, nonadherence was recorded as an attributing factor. Of the 59 patients prospectively analysed, 18 (30.5%) were nonadherent for at least one of the prescribed antihypertensive drugs. CONCLUSION: Hypertensive urgency and hypertensive emergency are common health problems resulting in frequent emergency department admissions. Workup of patients with a hypertensive urgency or hypertensive emergency should include an assessment of drug adherence to optimize treatment strategy.

Effect of residual doxycycline concentrations on resistance selection and transfer in porcine commensal Escherichia coli.

Pig feed may contain various levels of antimicrobial residues due to cross-contamination. A previous study showed that a 3% carry-over level of doxycycline (DOX) in the feed results in porcine faecal concentrations of approximately 4 mg/L. The aim of this study was to determine the effect of residual DOX concentrations (1 and 4 mg/L) in vitro on selection of DOX-resistant porcine commensal Escherichia coli and transfer of their resistance plasmids. Three different DOX-resistant porcine commensal E. coli strains and their plasmids were characterised. These strains were each brought in competition with a susceptible strain in a medium containing 0, 1 and 4 mg/L DOX. Resistant bacteria, susceptible bacteria and transconjugants were enumerated after 24 h and 48 h. The tet(A)-carrying plasmids showed genetic backbones that are also present among human E. coli isolates. Ratios of resistant to susceptible bacteria were significantly higher at 1 and 4 mg/L DOX compared with the blank control, but there was no significant difference between 1 and 4 mg/L. Plasmid transfer frequencies were affected by 1 or 4 mg/L DOX in the medium for only one of the resistance plasmids. In conclusion, DOX concentrations of 1 and 4 mg/L can select for resistant E. coli in vitro. Further research is needed to determine the effect of these concentrations in the complex environment of the porcine intestinal microbiota.

Residues of chlortetracycline, doxycycline and sulfadiazine-trimethoprim in intestinal content and feces of pigs due to cross-contamination of feed.

BACKGROUND: Cross-contamination of feed with low concentrations of antimicrobials can occur at production, transport and/or farm level. Concerns are rising about possible effects of this contaminated feed on resistance selection in the intestinal microbiota. Therefore, an experiment with pigs was set up, in which intestinal and fecal concentrations of chlortetracycline (CTC), doxycycline (DOX) and sulfadiazine-trimethoprim (SDZ-TRIM) were determined after administration of feed containing a 3 % carry-over level of these antimicrobials. RESULTS: The poor oral bioavailability of tetracyclines resulted in rather high concentrations in cecal and colonic content and feces at steady-state conditions. A mean concentration of 10 mg/kg CTC and 4 mg/kg DOX in the feces was reached, which is higher than concentrations that were shown to cause resistance selection. On the other hand, lower mean levels of SDZ (0.7 mg/kg) and TRIM (< limit of detection of 0.016 mg/kg) were found in the feces, corresponding with the high oral bioavailability of SDZ and TRIM in pigs. CONCLUSIONS: The relation between the oral bioavailability and intestinal concentrations of the tested antimicrobials, may be of help in assessing the risks of cross-contaminated feed. However, future research is needed to confirm our results and to evaluate the effects of these detected concentrations on resistance selection in the intestinal microbiota of pigs.

Antimicrobial resistance and population structure of Staphylococcus aureus recovered from pigs farms.

Staphylococcus aureus is a burden in human and veterinary medicine. During the last decade, an increasing number of studies reported the presence of livestock-associated methicillin-resistant S. aureus (LA-MRSA) clonal complex (CC) 398 in pigs. During 2013, a survey was performed in pig farms (n=328) randomly selected over Belgium, to monitor the current epidemiological situation of LA-MRSA among asymptomatic pigs and compare with former data to determine possible evolutions. Per farm, nose swabs were taken from 20 animals and pooled. MRSA was detected in 215 farms. Most isolates belonged to CC398 (n=211), and the remaining were ST9/t337 (n=1), ST80/t044 (n=2) and ST239/t4150 (n=1). A large diversity (n=19) of spa-types was found in the CC398 isolates. More than 90% of the isolates were non-wild type (NWT) to tetracycline and trimethoprim. NWT isolates were also found for ciprofloxacin (61.1%), clindamycin (64.4%), erythromycin (57.8%), kanamycin (43.1%) and gentamicin (45.5%). Microarray analysis showed that most CC398 isolates carried genes encoding resistance to tetracycline [tet(M)], macrolide-lincosamide-streptogramin group [erm(B), erm(C), lnu(A), vga(A)], aminoglycosides (aacA-aphD,aa dD, aphA3, sat) and/or phenicols (fexA). One CC398 isolate carried the multi-resistance gene cfr. The non-CC398 isolates carried virulence genes, as the egc-like cluster. The ST80 strain carried the Panton-Valentine leukocidin gene and corresponded to the community-acquired (CA-)MRSA ST80-IV European clone. The MRSA prevalence among pigs in Belgium remains similar to previous studies but a larger diversity in spa-types has been detected in this study. The recovery of CA-MRSA from livestock indicates that one should remain vigilant to the evolution of LA-MRSA in pigs.