Modeling Approach To Characterize Intraocular Doripenem Pharmacokinetics after Intravenous Administration to Rabbits, with Tentative Extrapolation to Humans

ABSTRACTThe aim of this study was to determine the penetration of doripenem administered intravenously into the rabbit aqueous and vitreous humors. Nineteen New Zealand White rabbits received a 20-mg dose of doripenem intravenously over 60 min. Specimens of aqueous humor, vitreous humor, and blood were obtained 30 min (n= 5), 1 h (n= 5), 2 h (n= 5), and 3 h (n= 4) after the beginning of the infusion and analyzed by high-performance liquid chromatography (HPLC). A pharmacokinetic (PK) model was developed to fit the experimental data. Doripenem concentrations in aqueous humor were lower than those in plasma ultrafiltrates at all sampling times, with an average aqueous humor-to-plasma ultrafiltrate area under the concentration-time curve ratio estimated as 8.3%. A pharmacokinetic model with peripheral elimination described the data adequately and was tentatively used to predict concentration-versus-time profiles and pharmacokinetic-pharmacodynamic (PK-PD) target attainment in patients under various dosing regimens. In conclusion, systematically administered doripenem does not seem to be a promising approach for the treatment of intraocular infections, especially since it could not be detected in the vitreous humor. However, this study has provided an opportunity to develop a new PK modeling approach to characterize the intraocular distribution of doripenem administered intravenously to rabbits, with tentative extrapolation to humans.

Biochemistry of Pro-B-Type Natriuretic Peptide-Derived Peptides: The Endocrine Heart Revisited

Background: Since the discovery of cardiac hormones almost 25 years ago, a vast amount of clinical research has identified the cardiac natriuretic peptides and their precursors as markers of heart failure. It even seems likely that the pro-B-type natriuretic peptide (proBNP)-derived peptides in plasma may become the most frequently measured peptides in the daily diagnosis and control of therapy. In contrast, the biochemistry of the peptides has received less attention. Methods: Published data available on the National Library of Medicine (NLM) were used as the basis for the review. Outcome: This review shows that the present understanding of the biochemistry of peptides is far from complete. In particular, cellular synthesis, including posttranslational precursor maturation, is poorly understood. Moreover, elimination of the precursor fragments is unknown. Elucidation of the molecular heterogeneity of proBNP products will therefore contribute to the understanding of the endocrine heart and may also have important diagnostic consequences. Above all, the different proBNP-derived peptides may not always be equal markers of the same pathophysiologic processes. A different metabolism and peripheral elimination may also impose new and peptide-specific limitations for diagnostic use. Conclusions: It is necessary to focus more on the biology of the proBNP-derived peptides. In turn, new insight into the biochemistry could pave the way for more sensitive and disease-specific assays in the clinical setting.

Cyclosporin A markedly enhances superantigen-induced peripheral T cell deletion and inhibits anergy induction.

Cyclosporin A (CsA) is a well-known immunosuppressive agent that modulates immune tolerance in many ways. CsA can give rise to a state of long-term nonimmunosuppressed transplantation tolerance, but it can also aggravate autoimmune diseases, and provoke specific forms of autoimmunity. These effects, which are often paradoxical, remain largely unexplained. In this study, we investigated the effects of CsA on superantigen (superAg)-reactive peripheral T cells. The intravenous injection of either staphylococcal enterotoxin B (SEB), or Mls-1a cells into Mls-1b recipients, causes long-term in vitro nonresponsiveness (anergy) and partial elimination of the peripheral T cell receptor (TCR) V beta 8+/CD4+ and -V beta 6+/CD4+ T cell subsets, respectively. We report that CsA markedly enhances the peripheral elimination of SEB- and Mls-1a-reactive T cells such that up to 90% of the targeted CD4+/V beta subpopulations are deleted. The degree of deletion depends on the dose and the schedule of CsA administration, and the number of superAg injections. In situations where the extent of deletion is only moderate, we find that the remaining superAg-reactive T cells fail to develop anergy, unlike the T cells of control superAg-immunized mice. Higher doses of CsA are required to enhance T cell deletion (greater than or equal to 25 mg/kg/d, i.p.) than to impair anergy induction (greater than or equal to 6.25 mg/kg/d, i.p.). In view of these results, it appears that the degree of tolerance in CsA/superAg-treated mice depends on the balance between these opposing effects, i.e., enhancement of peripheral elimination versus the abrogation of anergy. The possibility of enhancing or preventing immune tolerance with a drug may have important clinical implications.