Fig 1.
Determination of concentration and potency of the active pharmaceutical ingredient of a generic product and the innovator of imipenem-cilastatin by microbiological assay. There are 12 data-points per drug but the size of the error bar is smaller than each symbol (P = 0.728 by CFA).
Fig 2.
Quantitative assay by HPLC-UV for cilastatin concentration in a generic product and the innovator of imipenem; based on the chromatograms’ AUC for each product (right hand insets), the generic had a 30% lower concentration of the inhibitor with respect to the innovator.
Fig 3.
Chemical and physical stability.
Comparison of pH (A) and colorimetric changes (B) at room temperature (25°C) of a generic product and the innovator of imipenem-cilastatin during the first 24 hours after powder reconstitution.
Fig 4.
Comparison of a generic product and the innovator of imipenem-cilastatin immediately (A) and 24 hours after powder reconstitution standing at 4°C (B) and 25°C (C). There was no difference immediately after reconstitution in concentration or potency between innovator and generic. However, there were significant differences in potency after both products spent 24 hours at 4°C or 25°C because the generic was less stable than the innovator.
Fig 5.
Pharmacodynamics of One Generic and the innovator of imipenem-cilastatin against the wild-type strain S. aureus GRP-0057 in the neutropenic mouse thigh infection model.
The data shown in the graphs is pooled from 5 independent experiments comparing simultaneously both products, in which the generic was consistently less effective than the innovator.
Fig 6.
Pharmacodynamics (PD) of One Generic and the innovator of imipenem-cilastatin against the wild-type strain K. pneumoniae GRP-0107 in the neutropenic mouse lung infection model.
Opposite to the innovator, the generic product fitted a Gaussian instead of the Hill equation, displaying a well characterized Eagle effect. By definition, a generic with a different PD behavior is pharmaceutically nonequivalent (left panel). Increasing the dose above the limit of solubility did not affect the innovator, but deepened the Eagle effect of the generic, demonstrating that precipitation was not the cause of this aberrant PD pattern (right panel).
Fig 7.
Pharmacodynamics (PD) of One Generic and the innovator of imipenem-cilastatin against several strains of P. aeruginosa in the neutropenic mouse brain infection model.
There was no difference against P. aeruginosa GRP-0019, the strain with the lowest imipenem MIC (0.5 mg/L), as illustrated by the overlapping dose-effect curves (A). However, therapeutic nonequivalence was evident against the less susceptible strains P. aeruginosa ATCC 27853 (B) and P. aeruginosa GRP-0049 (C). As expected, the carbapenem-resistant P. aeruginosa GRP-0036 was untreatable in this model (not shown).
Fig 8.
LC/MS SCAN mode (range, m/z 100–1000) of the pharmaceutical forms of the generic product and the innovator of imipenem-cilastatin (Fresh Samples).
Left (generic) and right (innovator) panels show the spectrogram (up) and under it the centroids graphs describing the composition masses of each peak numbered. There were no differences in the analyte signal (peak 1 in both panels), i.e., the active pharmaceutical ingredient (m/z 300) is present in both products at the same concentration. However, the generic product exhibited different structural information in the full scan analysis, represented in peaks that expressed masses (peaks 2, 3, 4) absent in the innovator (which peaks 2, 3, 4, and 5 correspond to other masses). The peaks named 4 in the generic (left panel) and 5 in the innovator (right panel) have different abundance for the same concentration (250 mg/L).