Relevance of various animal models of human infections to establish therapeutic equivalence of a generic product of piperacillin/tazobactam

Clinical and economic impact of generic versus brand name meropenem use in an intensive care unit in Colombia

Background

Recent studies suggest that sustained use of generic antibiotics may be associated with clinical failure and emergence of antibacterial resistance. The present study was designed to determine the clinical outcome between the use of generic meropenem (GM) and brand-name meropenem (BNM). Additionally, this study evaluated the economic impact of GM and BNM to determine if the former represents a cost-effective alternative to the latter.

Methods

Patients treated between January 2011 and May 2014 received GM while patients treated between June 2014 and March 2017 received BNM. Mortality was compared between groups. Total infection cost was defined by the cost of antimicrobial consumption, length of stay, and laboratory and imaging exams until infection resolution.

Findings

A total of 168 patients were included; survival rate for the 68 patients treated with GM was 38% compared to 59% in the patients treated with BNM. Multivariate analysis showed that the variables most strongly-associated with mortality were cardiovascular disease (OR 18.18, 95% CI 1.25–262.3, p = 0.033) and treatment with generic meropenem (OR 18.45, 95% CI 1.45–232.32, p = 0.024). On the other hand, total infection cost did not show a significant difference between groups (BNM $10,771 vs. GM $11,343; p = 0.91).

Interpretation

The present study suggests that patients treated with GM have a risk of death 18 times higher compared to those treated with BNM. Furthermore, economic analysis shows that GM is not more cost effective than BNM.

Summary

More studies measuring clinical outcomes are needed to confirm the clinical equivalence of brand-name versus generic antibiotics, not only for meropenem but also for other molecules.

Nontherapeutic equivalence of a generic product of imipenem-cilastatin is caused more by chemical instability of the active pharmaceutical ingredient (imipenem) than by its substandard amount of cilastatin

Background

We demonstrated therapeutic nonequivalence of “bioequivalent” generics for meropenem, but there is no data with generics of other carbapenems.

Methods

One generic product of imipenem-cilastatin was compared with the innovator in terms of in vitro susceptibility testing, pharmaceutical equivalence, pharmacokinetic (PK) and pharmacodynamic (PD) equivalence in the neutropenic mouse thigh, lung and brain infection models. Both pharmaceutical forms were then subjected to analytical chemistry assays (LC/MS).

Results and conclusion

The generic product had 30% lower concentration of cilastatin compared with the innovator of imipenem-cilastatin. Regarding the active pharmaceutical ingredient (imipenem), we found no differences in MIC, MBC, concentration or potency or AUC, confirming equivalence in terms of in vitro activity. However, the generic failed therapeutic equivalence in all three animal models. Its E_max against S. aureus in the thigh model was consistently lower, killing from 0.1 to 7.3 million less microorganisms per gram in 24 hours than the innovator (P = 0.003). Against K. pneumoniae in the lung model, the generic exhibited a conspicuous Eagle effect fitting a Gaussian equation instead of the expected sigmoid curve of the Hill model. In the brain infection model with P. aeruginosa, the generic failed when bacterial growth was >4 log₁₀ CFU/g in 24 hours, but not if it was less than 2.5 log₁₀ CFU/g. These large differences in the PD profile cannot be explained by the lower concentration of cilastatin, and rather suggested a failure attributable to the imipenem constituent of the generic product. Analytical chemistry assays confirmed that, besides having 30% less cilastatin, the generic imipenem was more acidic, less stable, and exhibited four different degradation masses that were absent in the innovator.

Results of the effectiveness of two piperacillin-tazobactam molecules in the real world

OBJECTIVE

The objective was to determine the effectiveness of two piperacillin-tazobactam molecules in terms of all-cause mortality, mortality by infection, and hospital stay.

METHODS

A cohort study was performed involving patients treated with piperacillin-tazobactam at a clinic in Colombia. The patients were divided into those who received the innovator piperacillin-tazobactam (from July to December 2014) and those who received the generic piperacillin-tazobactam (from January to June 2015). Socio-demographic, clinical (all-cause mortality, death by infection, days of hospitalization), microbiological, pharmacological, and comorbidity variables were evaluated. Multivariate analyses were performed.

RESULTS

A total of 279 patients were included: 140 treated with the innovator piperacillin-tazobactam and 139 with the generic piperacillin-tazobactam. The median age was 63 years, and 56% of the patients were male. There was no statistically significant difference in death from all causes (22.9% vs. 14.4%, p=0.069), death by infection (7.9 vs. 10.8%, p=0.399), or hospital stay (18.1±16.2 vs. 15.7±11.6 days, p=0.178) between the innovator and generic piperacillin-tazobactam, respectively.

CONCLUSIONS

The generic piperacillin-tazobactam was equivalent to the innovator piperacillin-tazobactam with regards to all-cause mortality, mortality by infection, hospital stay, and safety, and at a lower cost, which may be useful for decision-makers in hospitals.

Enhanced sterilization and healing of cutaneous pseudomonas infection using 5-aminolevulinic acid as a photosensitizer with 410-nm LED light

BACKGROUND

Pseudomonas aeruginosa (PA) frequently develops antibiotic-resistant characteristics, which is clinically problematic. The main reason behind the rise of antibiotic-resistant PA is the extensive use of antibiotics. Therefore, a novel technique is needed to treat PA infections. Photodynamic therapy (PDT) is thought to have the potential to be a non-antibiotic treatment for infections. 5-Aminolevulinic acid (ALA), which works as a photosensitizer after being metabolized into protoporphyrin IX (PpIX) in the heme synthetic pathway, is used for PDT. Thus far, the in vivo effectiveness of PDT using ALA against PA is unknown.

OBJECTIVE

In this study, we investigated PDT using ALA both in vitro and in vivo.

METHODS AND RESULTS

Although PDT with ALA alone did not show a bactericidal effect on PA, PDT with both ALA and EDTA-2Na had a bactericidal effect in vitro. In in vivo experiments, wounds healed faster in PA-infected mice treated with PDT using both EDTA-2Na and ALA compared to non-PDT.

CONCLUSION

These results suggest that PDT with EDTA-2Na and ALA is a potential novel treatment option for PA-infected wounds.

In vivo pharmacodynamics of piperacillin/tazobactam: implications for antimicrobial efficacy and resistance suppression with innovator and generic products

Recent studies have shown that the pharmacodynamic (PD) index driving the efficacy of β-lactam/β-lactamase inhibitor combinations such as ceftazidime/avibactam and ceftolozane/tazobactam is the percentage of time the free inhibitor concentration is above a threshold (fT_>threshold). However, data with piperacillin/tazobactam (TZP) are scarce. Here we aimed to assess the relationship between fT_>threshold and TZP antibacterial efficacy by a population pharmacokinetic study in mice and dose-effect experiments in a neutropenic murine thigh infection model with two isogenic strains of Escherichia coli differentially expressing TEM-1 β-lactamase. We also explored the dynamics of resistance selection with the innovator and a non-equivalent generic, extrapolated the results to the clinic by Monte Carlo simulation of standard TZP doses, and estimated the economic impact of generic-selected resistance. The fT_>threshold index described well the efficacy of TZP versus E. coli, with threshold values from 0.5 mg/L to 2 mg/L and mean exposures of 42% for stasis and 56% for 1 log₁₀ kill. The non-equivalent generic required a longer exposure (fT_>threshold 33%) to suppress resistance compared with the innovator (fT_>threshold 22%), leading to a higher frequency of resistance selection in the clinical simulation (16% of patients with the generic vs. 1% with the innovator). Finally, we estimated that use of TZP generics in a scenario of 25% therapeutic non-equivalence would result in extra expenses approaching US$1 billion per year in the USA owing to selection of resistant micro-organisms, greatly offsetting the savings gained from generic substitution and further emphasising the need for demonstrated and not assumed therapeutic equivalence.

Impact on Bacterial Resistance of Therapeutically Nonequivalent Generics: The Case of Piperacillin-Tazobactam

Previous studies have demonstrated that pharmaceutical equivalence and pharmacokinetic equivalence of generic antibiotics are necessary but not sufficient conditions to guarantee therapeutic equivalence (better called pharmacodynamic equivalence). In addition, there is scientific evidence suggesting a direct link between pharmacodynamic nonequivalence of generic vancomycin and promotion of resistance in Staphylococcus aureus. To find out if even subtle deviations from the expected pharmacodynamic behavior with respect to the innovator could favor resistance, we studied a generic product of piperacillin-tazobactam characterized by pharmaceutical and pharmacokinetic equivalence but a faulty fit of Hill's Emax sigmoid model that could be interpreted as pharmacodynamic nonequivalence. We determined the impact in vivo of this generic product on the resistance of a mixed Escherichia coli population composed of ∼99% susceptible cells (ATCC 35218 strain) and a ∼1% isogenic resistant subpopulation that overproduces TEM-1 β-lactamase. After only 24 hours of treatment in the neutropenic murine thigh infection model, the generic amplified the resistant subpopulation up to 20-times compared with the innovator, following an inverted-U dose-response relationship. These findings highlight the critical role of therapeutic nonequivalence of generic antibiotics as a key factor contributing to the global problem of bacterial resistance.

Demonstration of Therapeutic Equivalence of Fluconazole Generic Products in the Neutropenic Mouse Model of Disseminated Candidiasis

Some generics of antibacterials fail therapeutic equivalence despite being pharmaceutical equivalents of their innovators, but data are scarce with antifungals. We used the neutropenic mice model of disseminated candidiasis to challenge the therapeutic equivalence of three generic products of fluconazole compared with the innovator in terms of concentration of the active pharmaceutical ingredient, analytical chemistry (liquid chromatography/mass spectrometry), in vitro susceptibility testing, single-dose serum pharmacokinetics in infected mice, and in vivo pharmacodynamics. Neutropenic, five week-old, murine pathogen free male mice of the strain Udea:ICR(CD-2) were injected in the tail vein with Candida albicans GRP-0144 (MIC = 0.25 mg/L) or Candida albicans CIB-19177 (MIC = 4 mg/L). Subcutaneous therapy with fluconazole (generics or innovator) and sterile saline (untreated controls) started 2 h after infection and ended 24 h later, with doses ranging from no effect to maximal effect (1 to 128 mg/kg per day) divided every 3 or 6 hours. The Hill’s model was fitted to the data by nonlinear regression, and results from each group compared by curve fitting analysis. All products were identical in terms of concentration, chromatographic and spectrographic profiles, MICs, mouse pharmacokinetics, and in vivo pharmacodynamic parameters. In conclusion, the generic products studied were pharmaceutically and therapeutically equivalent to the innovator of fluconazole.

Pharmacodynamics of nine generic products of amikacin compared with the innovator in the neutropenic mouse thigh infection model

Background

Previously, we validated the mouse thigh infection model to test the therapeutic equivalence of generic antibiotic products. Here, our aim was to compare the in vivo efficacy of amikacin products in clinical use in Colombia using this animal model.

Results

All except one generic product had the same in vitro potency, judging by the lack of differences on MIC and MBC compared with the innovator. However, eight of nine generic products failed in the neutropenic mouse thigh infection model to achieve the innovator’s maximum effect (E_max ≤ 5.65 for the generics vs. 6.58 log₁₀ CFU/g for the innovator) against Escherichia coli SIG-1, after subcutaneous treatment every 6 h with doses ranging from 1.5 to 3072 mg/kg per day.

Conclusion

As we demonstrated previously with other antibiotics such as vancomycin, gentamicin and oxacillin, the generic products of amikacin failed the in vivo efficacy testing. The therapeutic equivalence should be assessed in vivo before clinical approval of generic products.

A strain-independent method to induce progressive and lethal pneumococcal pneumonia in neutropenic mice

Background

Experimental models of pneumonia with penicillin non-susceptible Streptococcus pneumoniae (PNSSP) are hard to reproduce because the majority of strains with clinical relevance (like serotypes 6B, 9 V and 19 F) have low murine virulence. By optimization of culture and inoculum conditions of PNSSP (using porcine mucin), our aim was to develop a suitable, reliable and reproducible pneumonia mouse model for anti-infective pharmacology research.

Results

Seven PNSSP strains, including serotypes 6B, 9 V, 14 and 19 F were included. Strain INS-E611 displayed the highest murine virulence and was chosen to validate the lung model. Nose-instilled pneumococci grew between 2.1 and 2.5 log₁₀ CFU/g of lung in 24 hours when an optimized culture of bacterial cells was used, but animals were all alive and recovered of infection after 36 h. In contrast, inoculum supplementation with mucin led to 100% mortality related to a successful lung infection confirmed by histopathology. These findings were reproduced with all seven PNSSP strains in neutropenic mice. Immunocompetent animals cleared all strains spontaneously.

Conclusions

This pneumonia model produces a progressive and uniformly fatal lung infection with diverse serotypes of PNSSP independently of their intrinsic murine virulence.