Non-linear absorption pharmacokinetics of amoxicillin: consequences for dosing regimens and clinical breakpoints

Amoxicillin Administration Regimen and Resistance Mechanisms of Staphylococcus aureus Established in Tissue Cage Infection Model

Staphylococcus aureus is a zoonotic pathogen that causes various life-threatening diseases. The mechanisms of action of amoxicillin against S. aureus are unclear. Here, we established a rabbit tissue cage infection model to evaluate the relationship between the pharmacokinetic/pharmacodynamic (PK/PD) parameters of amoxicillin and selective enrichment of resistant strains of S. aureus and to elucidate the evolution of its resistance to amoxicillin. S. aureus was injected into the tissue cages at 10¹⁰ colony forming units (CFU)/mL. We injected different intramuscular concentrations of amoxicillin at doses of 5, 10, 20, and 30 mg/kg body weight once a day for 5 days and 5, 10, 20, and 30 mg/kg body weight twice a day for 2.5 days. Differences in gene expression between two differentially resistant strains and a sensitive strain were evaluated using Illumina sequencing followed by COG and KEGG analysis. RT-qPCR was carried out to validate the difference in protein translation levels. Our results demonstrated that the emergence of resistant bacteria was dose dependent within a given time interval. In the same dosage group, the appearance of resistant bacteria increased with time. The resistant bacteria showed cumulative growth, and the level of resistance increased over time. The resistant bacteria were completely inhibited when the cumulative percentage of time over a 24-h period that the drug concentration exceeded the mutant prevention concentration (MPC) (%T > MPC) was ≥52%. We also found that mecA and femX in S. aureus played a leading role in the development of resistance to amoxicillin. In conclusion, it provide references for optimizing amoxicillin regimens to treat infections caused by S. aureus.

Reduced bioavailability of oral amoxicillin tablets compared to suspensions in Roux-en-Y gastric bypass bariatric subjects

AIMS

To evaluate the relative bioavailability of oral amoxicillin (AMX) tablets in comparison to AMX suspension in Roux-en-Y gastric bypass bariatric subjects.

METHODS

A randomized, double-blind, cross-over study was performed on the bioavailability of oral AMX tablets and suspension in Roux-en-Y gastric bypass subjects operated at least 3 months previously . Doses of 875 mg of the AMX tablet or 800 mg of the AMX suspension were given to all the subjects, allowing a washout of 7 days between the periods. Blood samples were collected at 0, 0.25, 0.5, 1, 1.5, 2, 4, 6 and 8 hours after drug administration and the AMX levels were quantified by liquid chromatography coupled with triple quadrupole tandem mass spectrometry. The pharmacokinetic parameters were calculated by noncompartmental analysis, normalized to an 875 mg dose and the bioavailability of the AMX from the tablets was compared to that from the suspension formulation.

RESULTS

Twenty subjects aged 42.65 ± 7.21 years and with a body mass index of 29.88 ± 4.36 kg/m² were enrolled in the study. The maximum AMX plasma concentration of the tablets and the suspension (normalized to 875 mg) were 7.42 ± 2.99 mg/L and 8.73 ± 3.26 mg/L (90% confidence interval of 70.71-99.11), and the total area under the curve from time zero to infinity were 23.10 ± 7.41 mg.h/L and 27.59 ± 8.32 mg.h/L (90% confidence interval of 71.25-97.32), respectively.

CONCLUSION

The tablets presented a lower bioavailability than the suspension formulation and the total absorbed amount of AMX in these subjects was lower in comparison to the standard AMX absorption rates in nonbariatric subjects, regardless of the formulation.

A rapid, simple and sensitive liquid chromatography tandem mass spectrometry assay to determine amoxicillin concentrations in biological matrix of little volume

To assess pharmacokinetics of amoxicillin (AMX) in mice, limitations such as a small sampling volume and low drug concentrations have to be addressed. Similar challenges are faced in a clinical framework, e.g. for therapeutic drug monitoring in neonates or small-scale in vitro investigations. An assay enabling quantification of small sample volumes but still at very low concentrations covering a broad concentration range is thus needed. A simple, rapid and highly sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and successfully validated for quantification of AMX in mouse serum according to European Medicines Agency guidelines. Sample preparation enabled the use of only 10 μL of serum, which is 5-fold less than comparable assays and allows to reduce the number of mice used in pharmacokinetic studies. After protein precipitation with 40 μL chilled methanol and dilution of the supernatant with water, the sample was injected into the LC system on a Poroshell 120 Phenyl Hexyl column (2.1 × 100 mm, 2.7 μm). Chromatographic separation was achieved using a gradient method consisting of acetonitrile and ultra-pure water, both with 0.1% (V/V) formic acid. Positive electrospray ionisation in multiple reaction monitoring mode was used for detection and quantification of AMX. Application to murine study samples demonstrated the reliability of the developed method being accurate and precise with a quantification range from 0.01 to 10 μg/mL. The assay is easily transferable due to a simple sample preparation and confirmed stability of AMX under various applied conditions.

Highly variable absorption of clavulanic acid during the day: a population pharmacokinetic analysis

Objectives

To calculate the clavulanic acid exposure of oral amoxicillin/clavulanic acid dosing regimens, to investigate variability using a population pharmacokinetic model and to explore target attainment using Monte Carlo simulations.

Methods

Two groups of healthy male volunteers received amoxicillin/clavulanic acid tablets at the start of a standard meal on two separate days 1 week apart. One group (n = 14) received 875/125 mg q12h and 500/125 mg q8h and the other group (n = 15) received 500/125 mg q12h and 250/125 mg q8h. In total, 1479 blood samples were collected until 8-12 h after administration. Concentrations were analysed using non-compartmental (WinNonLin) and population pharmacokinetic (NONMEM) methods.

Results

Median Cmax and AUC0-8 were 2.21 mg/L (0.21-4.35) and 4.99 mg·h/L (0.44-8.31), respectively. In 40/58 daily concentration-time profiles, Cmax and AUC0-8 of the morning dose were higher than with later doses. The final population model included a lag time (0.447 h), first-order absorption (3.99 h-1 at 8:00 h, between-subject variability 52.8%, between-occasion variability 48.5%), one distribution compartment (33.0 L, between-subject variability 23.9%) and first-order elimination (24.6 L/h, between-subject variability 26.7%). Bioavailability (fixed at 1 at 8:00 h, between-occasion variability 28.2%) and absorption rate decreased over the day. For 97.5% of the simulated population after 125 mg q12h or q8h, %fT > Ct at 0.5 mg/L was 8.33% (q12h) and 15.2% (q8h), %fT > Ct at 1 mg/L was 0% (q12h + q8h), and fAUC0-24 was 3.61 (q12h) and 5.56 (q8h)  mg·h/L.

Conclusions

Clavulanic acid absorption in healthy volunteers is highly variable. Bioavailability and absorption rate decrease over the day. The model developed here may serve to suggest clavulanic acid dosing regimens to optimize efficacy and prevent underdosing.

Population Pharmacokinetic Study of Amoxicillin-Treated Burn Patients Hospitalized at a Swiss Tertiary-Care Center

The objective of this study was to investigate the population pharmacokinetics (PK) of amoxicillin in ICU burn patients and the optimal dosage regimens. This was a prospective study involving 21 consecutive burn patients receiving amoxicillin. PK data were analyzed using nonlinear mixed-effects modeling. Monte-Carlo simulations assessed the influence of various amoxicillin dosage regimens with identified covariates on the probability to achieve a target (PTA) value of time during which free amoxicillin concentrations in plasma exceeded the MIC (fT>MIC). A two-compartment model best described the data. Creatinine clearance (CL_CR) and body weight (BW) influenced amoxicillin CL and central volume of distribution (V₁), respectively. The median CL_CR (Cockcroft-Gault formula) was high (128 ml/min), with 25% of patients having CL_CRs of >150 ml/min. The CL, V₁, and half-life (t_1/2) values at steady state for a patient with a CL_CR of 110 ml/min and BW of 70 kg were 13.6 liters/h, 9.7 liters, and 0.8 h, respectively. Simulations showed that a target fT>MIC of ≥50% was achieved (PTA > 90%) with standard amoxicillin dosage regimens (1 to 2 g every 6 to 8 h [q6-8h]) when the MIC was low (<1 mg/liter). However, increased dosages of up to 2 g/4 h were necessary in patients with augmented CL_Rs or higher MICs. Prolonging amoxicillin infusion from 30 min to 2 h had a favorable effect on target attainment. In conclusion, this population analysis shows an increased amoxicillin CL and substantial CL PK variability in burn patients compared to literature data with nonburn patients. Situations of augmented CL_CR and/or high bacterial MIC target values may require dosage increases and longer infusion durations. (This study has been registered at ClinicalTrials.gov under identifier NCT01965340.).

Clinical applications of population pharmacokinetic models of antibiotics: Challenges and perspectives

Because of increasing antimicrobial resistance and the shortage of new antibiotics, there is a growing need to optimize the use of old and new antibiotics. Modelling of the pharmacokinetic/pharmacodynamic (PK/PD) characteristics of antibiotics can support the optimization of dosing regimens. Antimicrobial efficacy is determined by susceptibility of the drug to the microorganism and exposure to the drug, which relies on the PK and the dose. Population PK models describe relationships between patients characteristics and drug exposure. This article highlights three clinical applications of these models applied to antibiotics: 1) dosing evaluation of old antibiotics, 2) setting clinical breakpoints and 3) dosing individualization using therapeutic drug monitoring (TDM). For each clinical application, challenges regarding interpretation are discussed. An important challenge is to improve the understanding of the interpretation of modelling results for good implementation of the dosing recommendations, clinical breakpoints and TDM advices. Therefore, also background information on PK/PD principles and approaches to analyse PK/PD data are provided.

A novel PBP3 substitution in Haemophilus influenzae confers reduced aminopenicillin susceptibility

BACKGROUND

Identification and characterization of non-typeable Haemophilus influenzae (NTHi) with reduced susceptibility to β-lactam antibiotics due to mutations in penicillin binding protein 3 (PBP3) is a clinical challenge. We analyzed a blood isolate, NTHi93-57485, that was categorized as aminopenicillin resistant but lacked key amino acid substitutions in PBP3 that have previously been associated with reduced aminopenicillin susceptibility. The significance of an alternative amino acid substitution (Y528H) in this isolate was examined.

RESULTS

Site-directed mutagenesis of a β-lactam susceptible H. influenzae (NTHi3655) was performed to introduce the Y528H substitution into wild-type ftsI (encoding for PBP3). Disc diffusion screening and broth microdilution determination of MICs for β-lactam agents were done with the NTHi3655-PBP3^Y528H mutant and were compared with the NTHi3655 wild-type as well as the original clinical isolate NTHi93-57485. Introduction of the Y528H substitution in NTHi3655 resulted in positive screening for β-lactam resistance. MICs for aminopenicillins were increased in the mutant compared to the wild-type. However, the mutant remained susceptible to aminopenicillins according to EUCAST clinical breakpoints (assuming intravenous treatment) and the introduction of Y528H alone did not increase the resistance to the same level as NTHi93-57485. None of the isolates had frame shift insertions in the acrR gene regulating the AcrAB efflux pump.

CONCLUSIONS

In parallel to the previously well-described PBP3-substitutions R517H and N526K, we demonstrate that Y528H confers reduced aminopenicillin susceptibility.

Two versus five days of antibiotics after appendectomy for complex acute appendicitis (APPIC): study protocol for a randomized controlled trial

BACKGROUND

Acute appendicitis is one of the most common indications for emergency surgery. In patients with a complex appendicitis, prolonged antibiotic prophylaxis is recommended after appendectomy. There is no consensus regarding the optimum duration of antibiotics. Guidelines propose 3 to 7 days of treatment, but shorter courses may be as effective in the prevention of infectious complications. At the same time, the global issue of increasing antimicrobial resistance urges for optimization of antibiotic strategies. The aim of this study is to determine whether a short course (48 h) of postoperative antibiotics is non-inferior to current standard practice of 5 days.

METHODS

Patients of 8 years and older undergoing appendectomy for acute complex appendicitis - defined as a gangrenous and/or perforated appendicitis or appendicitis in presence of an abscess - are eligible for inclusion. Immunocompromised or pregnant patients are excluded, as well as patients with a contraindication to the study antibiotics. In total, 1066 patients will be randomly allocated in a 1:1 ratio to the experimental treatment arm (48 h of postoperative intravenously administered (IV) antibiotics) or the control arm (5 days of postoperative IV antibiotics). After discharge from the hospital, patients participate in a productivity-cost-questionnaire at 4 weeks and a standardized telephone follow-up at 90 days after appendectomy. The primary outcome is a composite endpoint of infectious complications, including intra-abdominal abscess (IAA) and surgical site infection (SSI), and mortality within 90 days after appendectomy. Secondary outcomes include IAA, SSI, restart of antibiotics, length of hospital stay (LOS), reoperation, percutaneous drainage, readmission rate, and cost-effectiveness. The non-inferiority margin for the difference in the primary endpoint rate is set at 7.5% (one-sided test at ɑ 0.025). Both per-protocol and intention-to-treat analyses will be performed.

DISCUSSION

This trial will provide evidence on whether 48 h of postoperative antibiotics is non-inferior to a standard course of 5 days of antibiotics. If non-inferiority is established, longer intravenous administration following appendectomy for complex appendicitis can be abandoned, and guidelines need to be adjusted accordingly.

TRIAL REGISTRATION

Dutch Trial Register, NTR6128 . Registered on 20 December 2016.

Dramatic Increase of Amoxicillin-Induced Crystal Nephropathy Found in a Cohort Study of French Pharmacovigilance Centers

An increase in amoxicillin-induced crystal nephropathy (AICN) incidence has been recently suggested. The aims of this study were to investigate the trend of AICN incidence through Paris' regional centers of pharmacovigilance (Paris RCPVs) and better describe this rare adverse drug reaction. Forty-five AICN cases were identified between 1985 and 2016. All cases, except one, were reported since 2010. Amoxicillin (AMX) was administered intravenously (65 [interquartile range {IQR}, 43 to 110] mg/kg of body weight/day) in all patients, either for treating infection (n = 15) or as surgical prophylaxis (n = 30). Delay between AMX administration and AICN onset was 1 (IQR, 1 to 3) day; 30, 4, and 11 patients developed KDIGO stage 1, 2, and 3 acute kidney injury, respectively. Delay between AICN onset and kidney function recovery was 4 (IQR, 2 to 6) days. Precipitating factors were identified in only one-third of cases. Twelve patients required intensive care unit admission, and 8 needed renal replacement therapy. Neither chronic kidney disease nor death was observed. We confirmed the recent and dramatic increase of AICN in the Paris RCPVs since 2010. The absence of precipitating factors in the majority of cases and the onset of AICN in apparent routine indications, such as surgical prophylaxis, are alarming and justify a high vigilance from all AMX prescribers.