Comparative cerebrospinal fluid diffusion of imipenem and meropenem in rats

5-Fluorouracil exacerbates cefepime-induced convulsions in pentylenetetrazol-kindled mice

OBJECTIVE

The antibiotics cefepime and meropenem are recommended for the treatment of neutropenia. However, cefepime has been found to be associated with both peripheral and central adverse events such as renal impairment and seizures, respectively. Previous studies showed that cefepime exacerbated convulsions in corneal kindled mouse models of epilepsy. However, its involvement in chemotherapy-induced side effects is unknown.

METHODS

In this study, we examined the convulsive potential of cefepime (500 mg/kg) and meropenem (500 mg/kg) in pentylenetetrazol (PTZ)-kindled mice using an electroconvulsive shock test with low-intensity stimulus currents. Then, the effects of 5-fluorouracil (5-FU, 200 and 400 mg/kg, i.p.) treatment, a model of chemotherapy-induced side effects, were investigated in the PTZ-kindled mouse model.

RESULTS

In fully PTZ-kindled mice, intravenous administration of cefepime (500 mg/kg) or meropenem (500 mg/kg) did not elicit any convulsions in the electroconvulsive shock test with low-intensity stimulus currents. In the PTZ-kindled mice treated with 5-FU (200 mg/kg), intravenous administration of cefepime (500 mg/kg) exacerbated the convulsions that occurred within 1 min in the electroconvulsive shock test, and the mice subsequently developed convulsive status epilepticus. However, intravenous administration of meropenem (500 mg/kg) did not produce such effects.

CONCLUSION

These findings suggest that the combination of 5-FU and cefepime exacerbates early-onset convulsive seizures and elicits delayed-onset convulsive status epilepticus. Additionally, 5-FU treatment increases the risk of induction of neurotoxic side effects by cefepime.

Even apparently insignificant chemical deviations among bioequivalent generic antibiotics can lead to therapeutic nonequivalence: the case of meropenem

Several studies with animal models have demonstrated that bioequivalence of generic products of antibiotics like vancomycin, as currently defined, do not guarantee therapeutic equivalence. However, the amounts and characteristics of impurities and degradation products in these formulations do not violate the requirements of the U.S. Pharmacopeia (USP). Here, we provide experimental data with three generic products of meropenem that help in understanding how these apparently insignificant chemical differences affect the in vivo efficacy. Meropenem generics were compared with the innovator in vitro by microbiological assay, susceptibility testing, and liquid chromatography/mass spectrometry (LC/MS) analysis and in vivo with the neutropenic guinea pig soleus infection model (Pseudomonas aeruginosa) and the neutropenic mouse thigh (P. aeruginosa), brain (P. aeruginosa), and lung (Klebisella pneumoniae) infection models, adding the dihydropeptidase I (DHP-I) inhibitor cilastatin in different proportions to the carbapenem. We found that the concentration and potency of the active pharmaceutical ingredient, in vitro susceptibility testing, and mouse pharmacokinetics were identical for all products; however, two generics differed significantly from the innovator in the guinea pig and mouse models, while the third generic was therapeutically equivalent under all conditions. Trisodium adducts in a bioequivalent generic made it more susceptible to DHP-I hydrolysis and less stable at room temperature, explaining its therapeutic nonequivalence. We conclude that the therapeutic nonequivalence of generic products of meropenem is due to greater susceptibility to DHP-I hydrolysis. These failing generics are compliant with USP requirements and would remain undetectable under current regulations.

[Presumptive bacterial meningitis in adults: initial antimicrobial therapy]

CSF sterilization should be obtained very rapidly to reduce both mortality and morbidity due to bacterial meningitis. Thus, antibiotic treatment should be adapted to the suspected bacterium and administered as early as possible at high dosage with - if necessary - a loading dose and continuous perfusion. The rates of abnormal susceptibility to penicillin of Streptococcus pneumoniae, Neisseria meningitis and Haemophilus influenzae are 37%, 30% and 12% respectively. Thus, ceftriaxone or cefotaxim must be used as empirical treatment. Listeria monocytogenes remains fully susceptible to aminopenicillin, so, the combination aminopenicillin and aminoglycoside is the first-line treatment. Antibiotic resistance, allergy or contra-indications, are in fact rare but in these cases, antibiotic combinations are often needed. The latter are more or less complex and clinically validated; they include molecules such as vancomycine, fosfomycin, fluoroquinolone or linezolid.

Absence of convulsive liability of doripenem, a new carbapenem antibiotic, in comparison with beta-lactam antibiotics

beta-Lactam antibiotics have been suggested to have some degree of convulsive activity and neurotoxicity in experimental animals as well as in clinical situations. We examined the convulsive activities of a new carbapenem antibiotic, (+)-(4R,5S,6S)-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-3-[[(3S,5S)-5-[(sulfamoylamino)methyl]-3-pyrrolidinyl]thio]-1-azabicyclo[3.2.0]hept-2-ene-2-carboxic acid monohydrate (doripenem) using several animals and compared them with beta-lactam antibiotics. In intravenous (IV) injection studies, imipenem/cilastatin, at 400/400mg/kg produced seizure discharges on electroencephalogram (EEG) accompanied with clonic convulsions in rats. Meropenem showed only wet dog shaking behavior at 200 and 400mg/kg. Doripenem caused no changes in the EEG and behavior in rats at 400mg/kg. Imipenem/cilastatin IV potentiated the pentylenetetrazol (PTZ)-induced convulsions in mice at 250/250 mg/kg, while meropenem, panipenem/betamipron, cefazolin or doripenem did not cause any marked effects at up to 500 mg/kg. In mouse intracerebroventricular (ICV) injection studies, imipenem, panipenem and cefazolin induced clonic convulsions in a dose-dependent manner in mice. Doripenem and meropenem did not induce convulsions at up to 100 microg/mouse. In dog ICV injection studies, imipenem produced generalized seizure discharge with clonic convulsions at 100 microg/dog. Meropenem also produced spikes or seizure discharges at 100, 300 and 1,000 microg/dog. However, doripenem had no effects on the EEG and behavior in dogs at any doses. In in vitro binding studies, imipenem, panipenem, cefazolin and meropenem inhibited [(3)H]muscimol binding to the GABA(A) receptor in mouse brain homogenates while doripenem did not cause any inhibition at up to 10mM. In addition, doripenem had no influence on the anti-convulsant actions of valproic acid in the PTZ- or bicuculine-induced convulsive model. These results clearly indicate that doripenem has no convulsive activity, suggesting that its neurotoxicity may be negligible in clinical use.

Ignoring pharmacokinetics may lead to isoboles misinterpretation: illustration with the norfloxacin-theophylline convulsant interaction in rats

PURPOSE

To investigate the norfloxacin-theophylline convulsant interaction in vivo, with an experimental approach distinguishing between pharmacodynamics and pharmacokinetics contributions to the observed effect.

METHODS

Male Sprague Dawley rats (n = 38) were infused each compound separately or in different combination ratios. Infusion was maintained until the onset of maximal seizures. Cerebrospinal fluid and plasma samples were collected for high performance liquid chromatography drug determination. The nature and intensity of the pharmacodynamics interaction between drugs was quantified with an isobolographic approach.

RESULTS

Isobolograms suggested a relatively marked antagonism between norfloxacin and theophylline at the cerebrospinal fluid (previously shown to be part of the biophase) and dose levels, but not at the plasma (free and total concentrations) levels. These apparent discrepancies could be explained by nonlinear distribution or/and distribution desequilibrium phenomenon.

CONCLUSIONS

These findings showed that the quantitative isobolographic approach is appropriate to assess the nature and intensity of the pharmacodynamic interaction between two drugs when data are collected within the biophase, but that data interpretation outside the biophase can be risky due to further pharmacokinetic complexities, in particular slow or/and nonlinear diffusion into the biophase.

Pharmacokinetic-pharmacodynamic modeling of the electroencephalogram effect of imipenem in healthy rats

A pharmacokinetic-pharmacodynamic (PK-PD) modeling approach was developed to investigate the epileptogenic activity of imipenem in rats. Initially, animals received an intravenous infusion of imipenem at a rate of 2.65 mg min(-1) for 30 min. Blood samples were collected for drug assay, and an electroencephalogram (EEG) was recorded during infusion and postinfusion. A dramatic delay was observed between concentrations of imipenem in serum and the EEG effect; this effect was accompanied by tremors and partial seizures. Indirect-effect models failed to describe these data, which were successfully fitted using an effect compartment model. The relationship between effect and concentration at the effect site was best described by a spline function. The elimination rate constant from the effect compartment was severalfold lower than that from the central compartment. The robustness of the model was then confirmed after administering the imipenem dose over 60 and 90 min. In conclusion, the successful PK-PD modeling of the imipenem EEG effect in rats constitutes a major improvement for better prediction of the epileptogenic risk associated with this antibiotic.