Contaminated dicloxacillin capsules as the source of an NDM-5/OXA-48-producing Enterobacter hormaechei ST79 outbreak, Denmark and Iceland, 2022 and 2023.

From October 2022 through January 2023, nine patients with NDM-5/OXA-48-carbapenemase-producing Enterobacter hormaechei ST79 were detected in Denmark and subsequently one patient in Iceland. There were no nosocomial links between patients, but they had all been treated with dicloxacillin capsules. An NDM-5/OXA-48-carbapenemase-producing E. hormaechei ST79, identical to patient isolates, was cultured from the surface of dicloxacillin capsules in Denmark, strongly implicating them as the source of the outbreak. Special attention is required to detect the outbreak strain in the microbiology laboratory.

The road to biologics in patients with hidradenitis suppurativa: a nationwide drug utilization study.

BACKGROUND: Prolonged systemic antibiotic treatment is often a part of management of hidradenitis suppurativa (HS). Although biologic therapies are now available, the patient's treatment journey leading to biologic therapy is unclear. OBJECTIVES: To examine treatment patterns and duration of systemic treatment use in patients with HS preceding biologic therapy. METHODS: We identified all patients with HS receiving treatment with biologics in the Danish National Patient Registry from 2010 to 2018 and extracted their entire prescription history of specific systemic treatments from the Danish National Prescription Registry since its inception in 1995. The patients' treatment journeys are graphically displayed through Sankey diagrams and box plots generated to show temporal distributions. Descriptive patient characteristics were presented as frequencies with percentages for categorical variables and as means with SDs or medians with interquartile ranges (IQRs) for continuous variables. RESULTS: A total of 225 patients with HS were included. Patients had most frequently been treated with penicillin (n = 214; 95·1%), dicloxacillin (n = 194; 86·2%), tetracycline (n = 145; 64·4%) and rifampicin/clindamycin (n = 111; 49·3%), as well as the retinoids isotretinoin and acitretin, and dapsone. Prior to biologic therapy, patients received a mean of 4·0 (SD 1·3) different systemic therapies, across a mean of 16·9 (SD 11·3) different treatment series. The mean time from first systemic therapy until biologic therapy was initiated was 15·3 (SD 5·1) years [8·2 (SD 5·9) years when excluding penicillin and dicloxacillin]. CONCLUSIONS: Patients with HS who receive biologic therapy have long preceding treatment histories with multiple drug classes and treatment series, many of which are supported by relatively weak evidence in HS. Delay in the initiation of biologic therapy may represent a missed opportunity to prevent disease progression. What is already known about this topic? The treatment journey leading to biologic therapy in patients with HS has not previously been investigated. What does this study add? Our data from 225 patients with HS illustrate that patients who receive biologic therapy have long preceding treatment histories with multiple drug classes and treatment series, many of which are supported by relatively weak evidence in HS.

Transfer of Dicloxacillin into Human Milk.

Background: Dicloxacillin is a beta-lactam antibiotic that is commonly used in the treatment of lactational mastitis in breastfeeding women. Although penicillins have long been considered safe for breastfeeding mothers and their infants, there is almost no data on the transfer of dicloxacillin into human breast milk despite the fact that it is commonly used for mastitis. Case Report: This study determined the drug concentration-time profile of dicloxacillin in milk samples collected from three lactating mothers consuming 500 mg dicloxacillin taken every 6 hours for treatment of mastitis. Milk levels were measured using liquid chromatography mass spectrometry. The maximum concentration of dicloxacillin in milk was 67.6 ng/mL. The relative infant dose (RID) was calculated to be 0.03%. This value is well below the theoretical level of concern of 10%. Discussion: The limited transfer of dicloxacillin into human milk is probably explained by the high plasma protein binding of dicloxacillin and its subsequent poor penetration into human milk. Conclusion: In this case series, the level of dicloxacillin in milk was found to be very low, and the RID to be only 0.03% of the maternal dose. Although the levels detected were low, dicloxacillin does transfer into breast milk. Caution should be exercised in infants with hypersensitivity to penicillins.

Acquired pyroglutamic acidosis due to long-term dicloxacillin and paracetamol use.

An 85-year-old man with a background of transfusion-dependent chronic myelomonocytic leukaemia and chronic kidney disease stage III presented with symptomatic anaemia, acute kidney injury, sepsis and high anion gap metabolic acidosis (HAGMA). Initial treatment with intravenous antibiotics and blood transfusion was complicated by transfusion-associated circulatory overload, necessitating diuresis and non-invasive ventilation. Despite gradual clinical improvement, the patient's HAGMA persisted, and no cause was identified on urine testing or renal ultrasound. As the patient was on long-term dicloxacillin for infective endocarditis prophylaxis and regular paracetamol, pyroglutamic acidosis (PGA) (5-oxoproline acidosis) was considered. This was later confirmed with elevated serum levels, and the HAGMA resolved following cessation of these medications. Although considered an uncommon cause of HAGMA, PGA is likely also under-recognised, and to our knowledge, this may be the second reported case in the context of dicloxacillin.

Ischemic Stroke and Systemic Embolism in Warfarin Users With Atrial Fibrillation or Heart Valve Replacement Exposed to Dicloxacillin or Flucloxacillin.

The antibiotics dicloxacillin and flucloxacillin induce cytochrome P450-dependent metabolism of warfarin. We explored the influence of these drug-drug interactions on the clinical effectiveness of warfarin therapy due to atrial fibrillation or heart valve replacement. Using the population-based Danish registers, we performed a propensity-score matched cohort study including around 50,000 episodes of dicloxacillin/flucloxacillin matched to phenoxymethylpenicillin and to no antibiotic, respectively. We estimated hazard ratios (HRs) with 95% confidence intervals (CIs) by comparing 21-day (days 7-28) risks of ischemic stroke/systemic embolism (SE) following initiation of each exposure. When compared with phenoxymethylpenicillin, dicloxacillin/flucloxacillin was associated with an HR of ischemic stroke/SE of 2.09 (95% CI 1.51-2.90; strongest for dicloxacillin (HR 2.17; 95% CI 1.56-3.02)). Use of an untreated comparator strengthened the association (HR 2.84; 95% CI 1.97-4.09). Dicloxacillin should be used with caution in patients receiving warfarin. This may also apply to flucloxacillin; however, more data on the risks associated with flucloxacillin exposure during warfarin therapy are needed.

Effects of Dicloxacillin on Warfarin Dose in Patients With a Left Ventricular Assist Device.

Patients with a durable, continuous flow left ventricular assist device (CF-LVAD) require anticoagulation with warfarin to prevent thromboembolic events. Driveline infections (DLIs) are a common CF-LVAD complication. A common pathogen implicated in DLI is oxacillin-sensitive Staphylococcus aureus (OSSA), which is effectively treated by oral dicloxacillin. Previous published experiences have observed a significant drug interaction between dicloxacillin and warfarin resulting in decreased international normalized ratio (INR) and increased warfarin dosing requirements. We sought to analyze the effect of dicloxacillin on INR and warfarin dose when used for DLI in our CF-LVAD program. Five of 106 patients having received an CF-LVAD at our institution met the inclusion criteria for this case series. These patients required a mean 51.8% (standard deviation of 29.8%) weekly warfarin dose increase to restore INR to the therapeutic range after the addition of dicloxacillin. Three of the five patients subsequently had their dicloxacillin discontinued, with a mean decrease in weekly warfarin dose of 30.6% (standard deviation of 19.1%). In our experience, when coalesced with prior published reports, an empiric warfarin dose increase of 25% to 33% is reasonable upon initiation of dicloxacillin and an empiric warfarin dose reduction of 10% to 15% is recommended upon discontinuation of dicloxacillin. Close INR follow-up is warranted during and after dicloxacillin treatment.

Exploring anti-MRSA activity of chitosan-coated liposomal dicloxacillin.

One of the greatest disturbing global health problems is antibiotic-resistant bacterial infections, which have rendered numerous currently used antibiotics ineffective. Thus, the feasibility of chitosan-coated deformable liposomes (C-Lips) containing dicloxacillin (DLX) were evaluated for their efficacy against methicillin-resistant Staphylococcus aureus (MRSA) strains, which are resistant to beta lactam antibiotics. DLX-loaded liposomes (DLX-Lip) were prepared by a lipid film hydration method and then chitosan (CS) coated (C-DLX-Lip) by the electrostatic deposition method. Both DLX-Lips and C-DLX-Lips showed a particle size distribution with a nano-range and a narrow polydispersity index (PDI). After CS coating, the zeta potential was shifted from negative to positive value. The DLX entrapment efficiency (EE) and drug loading (DL) were 62% and 5.6% for C-DLX-Lips compared to 38% and 3.1% for DLX-Lip, respectively. The in vitro release profile of C-DLX-Lips possessed a slow release behavior. Moreover, the DLX-Lips and C-DLX-Lips demonstrated an enhanced anti-MRSA activity. These results revealed that DLX-Lips and C-DLX-Lips may serve as promising carriers for DLX to increase the efficacy against MRSA, which offers considerably clinical value for long-term use of DLX.

Molecular mechanisms of thioridazine resistance in Staphylococcus aureus.

Staphylococcus aureus has developed resistance towards the most commonly used anti-staphylococcal antibiotics. Therefore, there is an urgent need to find new treatment opportunities. A new approach relies on the use of helper compounds, which are able to potentiate the effect of antibiotics. A well-studied helper compound is thioridazine, which potentiates the effect of the ß-lactam antibiotic dicloxacillin against Methicillin-resistant Staphylococcus aureus (MRSA). In order to identify thioridazine's mechanism of action and how it potentiates the effect of dicloxacillin, we generated thioridazine resistant strains of MRSA USA300 by serial passage experiments. Selected strains were whole-genome sequenced to find mutations causing thioridazine resistance. Genes observed to be mutated were attempted deleted in MRSA USA300. The cls gene encoding a cardiolipin synthase important for synthesis of the membrane lipid cardiolipin was found to be mutated in thioridazine resistant strains. Deletion of this gene resulted in a two-fold increased Minimum inhibitory concentrations (MIC) value for thioridazine compared to the wild type and decreased susceptibility similar to the thioridazine resistant strains. Since cardiolipin likely plays a role in resistance towards thioridazine, it might also be important for the mechanism of action behind the potentiating effect of thioridazine. TDZ is known to intercalate into the membrane and we show here that TDZ can depolarize the plasma membrane. However, our results indicate that the membrane potential reducing effect of TDZ is independent of the resistance mechanism.

Use of Dicloxacillin and Risk of Pregnancy among Users of Oral Contraceptives.

The antibiotic dicloxacillin has been shown to induce drug-metabolizing CYP enzymes to a clinically relevant extent. In this study, we investigated whether the use of dicloxacillin confers an increased risk of unwanted pregnancy among oral contraceptive users. The study population comprised Danish women falling pregnant (1997-2015) during oral contraceptive use, defined as having filled a prescription for an oral contraceptive within 120 days both before and after the estimated date of conception. Data were analysed using a case-crossover approach. For each woman, we assessed the use of dicloxacillin preceding the date of conception and during 10 previous control periods and estimated the odds ratio for such unintended pregnancies associated with the use of dicloxacillin. Among 364 women using dicloxacillin prior to conception, 40 (11%) were exposed to dicloxacillin at the time of conception, yielding an odds ratio (OR) associating use of dicloxacillin to unintended pregnancy of 1.18 (95% CI 0.84-1.65). Supplementary and sensitivity analyses generally returned similar estimates, except for a slightly increased risk among users of progestogen-only oral contraceptives (OR 1.83, 95% CI 0.63-5.34). Analysis of other antibiotics as negative controls yielded results close to unity (ORs ranging from 0.83 to 1.13). In conclusion, our study found no evidence for an increased risk of oral contraceptive failure when using dicloxacillin. However, acknowledging study limitations, we suggest the use of supplementary barrier methods during treatment with dicloxacillin, until our findings are confirmed in further studies.

Chromatographic Methods for Quantitative Determination of Ampicillin, Dicloxacillin and Their Impurity 6-Aminopenicillanic Acid.

Two accurate, precise and sensitive high-performance thin layer chromatography (HPTLC) and high-performance liquid chromatography (HPLC) methods were developed for assay of ampicillin (AMP) and dicloxacillin (DX) in the presence of their impurity, 6-aminopenicillanic acid (APA). Method (A) is HPTLC method; using silica gel HPTLC F254 plates as a stationary phase with methanol: chloroform: acetic acid (1:9: 0.2, by volume) as a developing system. All the bands were scanned at 220 nm. Method (B) is reversed phase- HPLC which depended on isocratic elution using C18 column and mobile phase consisting of acetonitrile: water (60:40, v/v), pH adjusted to 4 with orthophosphoric acid, at a flow rate of 1 mL min-1 and ultraviolet detection at 240 nm. The proposed methods were validated as per ICH guidelines and their linearity was evident in the ranges of 0.5-2 µg band-1, 0.4-2 µg band-1 and 0.2-1.2 µg band-1 for method (A) and 5-40 µg mL-1, 5-40 µg mL-1 and 2-16 µg mL-1 for method (B) for AMP, DX and APA, respectively. The proposed methods were successfully used for assay of AMP and DX in pure form and in pharmaceutical formulation where no interference from the excipients was detected.

Synthesis and in vitro Antioxidant Activity Study of Some Novel Substituted Piperazinyl Flavone Compounds.

BACKGROUND: A new series of 13 piperazinyl flavone derivatives has been synthesized and examined for their in vitro antiradical and antioxidant activities in response to the pharmacy industry's increasing demand for new non-toxic anti-inflammatory and anticancer drugs. METHOD: Their antioxidant activity was evaluated by the reactive oxygen species (ROS) scavenging assays, 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH•) and 2,2'-azino-bis(3- ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS+•) scavenging assays, and the ferric reducing antioxidant potency (TAC) method, and was compared to known positive controls, herbal infusions, and penicillins. Chemiluminescence, spectrophotometry, electron spin resonance (ESR) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) as the spin trap were the measurement techniques. RESULT: It was seen that synthesized compounds have a wide spectrum of antioxidant property. Some of the test compounds proved to be extremely efficient scavengers of H2O2 exhibiting, in some cases, EC50 of about 2 µM. The values of antioxidant status (TAS) were in the range of 49 ± 3.9 to 1283 ± 51.3 µM TE/g (TE = Trolox equivalent) and were lower than that of butylated hydroxytoluene (BHT) (1304 ± 43.2 µM TE/g) and green tea (1356 ± 40.0 µM TE/g), but for several synthesized compounds, they were higher than chamomille infusion and penicillins. Ferric reducing antioxidant powers (TAC) for the piperazinyl flavone derivatives were in the range 7 ± 0.5 to 104 ± 0.6 µM TE/g and were weaker than that of BHT (217 ± 5.3 µM TR/g ). CONCLUSION: Carboxylic or hydroxamic acid substituted piperazinyl flavones are potentially active as antioxidants, thus may be suggested as pharmacologically interesting ones.

Microdialysis as a tool to determine the local tissue concentration of dicloxacillin in man.

AIMS: The most common pathogen to cause postoperative infections in Denmark is Staphylococcus aureus. Despite using prophylactic antibiotics, infections are still seen. Whether the tissue concentration is above the minimal inhibitory concentration (MIC) for the pathogen is unknown. Thus, the concentration of dicloxacillin in muscle and adipose tissue was measured after intravenous administration, in healthy men. METHODS: MIC for dicloxacillin against S. aureus was determined using the broth macrodilution method. A microdialysis (MD) catheter was placed in the subcutaneous tissue of the abdomen and in the lateral vastus muscle of the thigh of six healthy male volunteers. They were given 2 g dicloxacillin intravenously. Samples from blood and MD fluid were collected. The unbound dicloxacillin was isolated from plasma. Samples were analysed with high performance liquid chromatography (HPLC). RESULTS: The maximum concentration was reached in muscle tissue after 0.5 h and in adipose tissue after 0.8 h. AUC0-6h for the dicloxacillin concentration in adipose tissue was significantly lower when compared to the unbound dicloxacillin concentration in plasma. The dicloxacillin concentration was above the MIC for sensitive S. aureus for a minimum of 2.3 h and a median of 4.1 h in muscle tissue and a minimum of 1.8 h and a median of 3.2 h in adipose tissue. CONCLUSIONS: The unbound dicloxacillin concentration in adipose and muscle tissue remained above the MIC for sensitive S. aureus, for a period sufficient for many orthopaedic procedures. Whether this is true in patients with compromised circulation remains to be investigated.

Dicloxacillin induces CYP2C19, CYP2C9 and CYP3A4 in vivo and in vitro.

AIM: The aim of this study was to study potential cytochrome P450 (CYP) induction by dicloxacillin. METHODS: We performed an open-label, randomized, two-phase, five-drug clinical pharmacokinetic cocktail crossover study in 12 healthy men with and without pretreatment with 1 g dicloxacillin three times daily for 10 days. Plasma and urine were collected over 24 h and the concentration of all five drugs and their primary metabolites was determined using a liquid chromatography coupled to triple quadrupole mass spectrometry method. Cryopreserved primary human hepatocytes were exposed to dicloxacillin for 48 h and changes in gene expression and the activity of CYP3A4, CYP2C9, CYP2B6 and CYP1A2 were investigated. The activation of nuclear receptors by dicloxacillin was assessed using luciferase assays. RESULTS: A total of 10 days of treatment with dicloxacillin resulted in a clinically and statistically significant reduction in the area under the plasma concentration-time curve from 0 to 24 h for omeprazole (CYP2C19) {geometric mean ratio [GMR] [95% confidence interval (CI)]: 0.33 [0.24, 0.45]}, tolbutamide (CYP2C9) [GMR (95% CI): 0.73 (0.65, 0.81)] and midazolam (CYP3A4) [GMR (95% CI): 0.54 (0.41, 0.72)]. Additionally, other relevant pharmacokinetic parameters were affected, indicating the induction of CYP2C- and CYP3A4-mediated metabolism by dicloxacillin. Investigations in primary hepatocytes showed a statistically significant dose-dependent increase in CYP expression and activity by dicloxacillin, caused by activation of the pregnane X receptor. CONCLUSIONS: Dicloxacillin is an inducer of CYP2C- and CYP3A-mediated drug metabolism, and we recommend caution when prescribing dicloxacillin to users of drugs with a narrow therapeutic window.

Targeting intracellular Staphylococcus aureus to lower recurrence of orthopaedic infection.

Staphylococcus aureus is often found in orthopaedic infections and may be protected from commonly prescribed antibiotics by forming biofilms or growing intracellularly within osteoblasts. To investigate the effect of non-antibiotic compounds in conjunction with antibiotics to clear intracellular and biofilm forming S. aureus causing osteomyelitis. SAOS-2 osteoblast-like cell lines were infected with S. aureus BB1279. Antibiotics (vancomycin, VAN; and dicloxacillin, DICLOX), bacterial efflux pump inhibitors (piperine, PIP; carbonyl cyanide m-chlorophenyl hydrazone, CCCP), and bone morphogenetic protein (BMP-2) were evaluated individually and in combination to kill intracellular bacteria. We present direct evidence that after gentamicin killed extracellular planktonic bacteria and antibiotics had been stopped, seeding from the infected osteoblasts grew as biofilms. VAN was ineffective in treating the intracellular bacteria even at 10× MIC; however in presence of PIP or CCCP the intracellular S. aureus was significantly reduced. Bacterial efflux pump inhibitors (PIP and CCCP) were effective in enhancing permeability of antibiotics within the osteoblasts and facilitated killing of intracellular S. aureus. Confocal laser scanning microscopy (CLSM) showed increased uptake of propidium iodide within osteoblasts in presence of PIP and CCCP. BMP-2 had no effect on growth of S. aureus either alone or in combination with antibiotics. Combined application of antibiotics and natural agents could help in the treatment of osteoblast infected intracellular bacteria and biofilms associated with osteomyelitis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1086-1092, 2018.

Prevalence of dynapenic obesity and sarcopenic obesity and their associations with cardiovascular disease risk factors in peritoneal dialysis patients

BACKGROUND: Dynapenic obesity and sarcopenic obesity increase cardiovascular disease (CVD) and mortality in nonuremic patients. The present study was designed to determine the prevalence of dynapenic obesity and sarcopenic obesity and their associations with CVD risk factors in peritoneal dialysis (PD) patients. METHODS: All eligible PD patients in Tehran peritoneal dialysis centers were included in this cross-sectional study. Skeletal muscle mass and fat mass were assessed using bioelectrical impedance analysis. Muscle strength and physical performance were determined using hand grip strength and a 4-meter walk gait speed test, respectively. In addition, a 5-mL blood sample was obtained from each patient. RESULTS: The prevalence of dynapenic obesity and sarcopenic obesity were 11.4% and 3.8% in PD patients, respectively. Serum high-sensitive C-reactive protein (hs-CRP), soluble intercellular adhesion molecule type 1, triglyceride, total cholesterol, and low-density lipoprotein cholesterol were significantly higher in PD patients with dynapenic obesity than in dynapenic nonobese and nondynapenic nonobese patients. Similarly, serum concentrations of CVD risk factors in PD patients with sarcopenic obesity were higher than in nonsarcopenic nonobese patients, but these differences were statistically significant only for serum hs-CRP and triglyceride. In addition, muscle strength and skeletal muscle mass percentage were negatively associated with markers of inflammation and dyslipidemia, whereas body fat percentage was positively associated with these CVD risk factors. CONCLUSION: This study indicates that although the prevalence of dynapenic obesity and sarcopenic obesity are relatively low in PD patients, these disorders may be associated with CVD risk factors.

Determining optimal dosing regimen of oral administration of dicloxacillin using Monte Carlo simulation.

BACKGROUND: Dicloxacillin, a semisynthetic isoxazolyl penicillin, exhibits antimicrobial activity against a wide variety of Gram-positive bacteria, as well as stability against penicillinases and low level of toxicity. The objective of this study was to obtain optimal dosing regimen of oral administration of dicloxacillin by analyzing the pharmacokinetic (PK) index in healthy volunteers and in vitro antibacterial activity by using Monte Carlo simulation. MATERIALS AND METHODS: A total of 867 clinical isolates from community-onset infections were collected from 31 secondary hospitals in People's Republic of China. The minimum inhibitory concentration (MIC) values of dicloxacillin were determined by the agar dilution method. Based on the MICs and the PK parameters of different dosage regimens, Monte Carlo simulation was performed to simulate the PK/pharmacodynamic indices of 250 mg once-daily (qd), 500 mg qd, 1,000 mg qd, 2,000 mg qd, 250 mg every 6 hours (q6h), and 500 mg q6h, respectively. The probability of target attainment was estimated at each MIC value, and the cumulative fraction of response (CFR) was calculated to evaluate the efficacy of these regimens. RESULTS: Dicloxacillin showed poor antibacterial activity against Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae. Resistance to dicloxacillin was observed in 7.5% of coagulase-negative Staphylococcus (CNS) isolates and 9.2% of other Streptococcus isolates, whereas 1.5% of methicillin-sensitive Staphylococcus aureus (MSSA) was resistant to dicloxacillin. Multiple-dose regimens could obtain higher CFR than single-dose regimens against H. influenza and S. pneumoniae. However, all dosing regimens against MSSA achieved CFR ≥$90%. Meanwhile, dosing regimen of 2,000 mg qd, 250 mg q6h, and 500 mg q6h could achieve >90% of CFR for CNS. For other Streptococcus isolates, multiple-dose regimens achieved CFR ≥90%. CONCLUSION: Dicloxacillin has a significant antibacterial activity against MSSA, CNS, and other Streptococcus isolates. The simulation results suggest that dicloxacillin 250 mg q6h and 500 mg q6h dosing regimens may be recommended for clinical applications, especially for community-onset infections.

Combination of thioridazine and dicloxacillin as a possible treatment strategy of staphylococci.

We have previously shown that the phenothiazine, thioridazine, acts in synergy with the beta-lactam antibiotic, dicloxacillin, to kill methicillin-resistant Staphylococcus aureus. In this study, we investigated whether synergy by combining these two drugs could also be observed in vancomycin intermediate susceptible S. aureus (VISA) and methicillin-resistant Staphylococcus epidermidis (MRSE). Synergy was observed in three of four tested VISA strains, suggesting that the thickening of cell wall does not interfere with the effects of thioridazine. In S. epidermidis, no synergy was observed in all tested strains, suggesting that synergy by combining thioridazine and dicloxacillin is isolated to S. aureus species.

Systemic thioridazine in combination with dicloxacillin against early aortic graft infections caused by Staphylococcus aureus in a porcine model: In vivo results do not reproduce the in vitro synergistic activity.

INTRODUCTION: Conservative treatment solutions against aortic prosthetic vascular graft infection (APVGI) for inoperable patients are limited. The combination of antibiotics with antibacterial helper compounds, such as the neuroleptic drug thioridazine (TDZ), should be explored. AIM: To investigate the efficacy of conservative systemic treatment with dicloxacillin (DCX) in combination with TDZ (DCX+TDZ), compared to DCX alone, against early APVGI caused by methicillin-sensitive Staphylococcus aureus (MSSA) in a porcine model. METHODS: The synergism of DCX+TDZ against MSSA was initially assessed in vitro by viability assay. Thereafter, thirty-two pigs had polyester grafts implanted in the infrarenal aorta, followed by inoculation with 106 CFU of MSSA, and were randomly administered oral systemic treatment with either 1) DCX or 2) DCX+TDZ. Treatment was initiated one week postoperatively and continued for a further 21 days. Weight, temperature, and blood samples were collected at predefined intervals. By termination, bacterial quantities from the graft surface, graft material, and perigraft tissue were obtained. RESULTS: Despite in vitro synergism, the porcine experiment revealed no statistical differences for bacteriological endpoints between the two treatment groups, and none of the treatments eradicated the APVGI. Accordingly, the mixed model analyses of weight, temperature, and blood samples revealed no statistical differences. CONCLUSION: Conservative systemic treatment with DCX+TDZ did not reproduce in vitro results against APVGI caused by MSSA in this porcine model. However, unexpected severe adverse effects related to the planned dose of TDZ required a considerable reduction to the administered dose of TDZ, which may have compromised the results.