A new in-vitro kinetic model to study the pharmacodynamics of antifungal agents: inhibition of the fungicidal activity of amphotericin B against Candida albicans by voriconazole.

The aim of this study was to develop and validate a new in-vitro kinetic model for the combination of two drugs with different half-lives, and to use this model for the study of the pharmacodynamic effects of amphotericin B and voriconazole, alone or in combination, against a strain of Candida albicans. Bolus doses of voriconazole and amphotericin B were administered to a starting inoculum of C. albicans. Antifungal-containing medium was eliminated and replaced by fresh medium using a peristaltic pump, with the flow-rate adjusted to obtain the desired half-life of the drug with the shorter half-life. A computer-controlled dosing pump compensated for the agent with the longer half-life. Voriconazole and amphotericin B half-lives were set to 6 and 24 h, respectively. Pharmacokinetic parameters were close to target values when both single doses and sequential doses were simulated. Voriconazole and amphotericin B administered alone demonstrated fungistatic and fungicidal activity, respectively. Simultaneous administration resulted in fungicidal activity, whereas pre-exposure of C. albicans to voriconazole, followed by amphotericin at 8 and 32 h, resulted in fungistatic activity similar to that observed with voriconazole alone. Using this model, which allowed a combination of antifungal agents with different half-lives, it was possible to demonstrate an antagonistic effect of voriconazole on the fungicidal activity of amphotericin B. The characteristics and clinical relevance of this interaction require further investigation.

Low utilisation of unactivated protein C in a patient with meningococcal septic shock and disseminated intravascular coagulation.

BACKGROUND: Activated protein C has recently been shown in a multicentre trial to significantly reduce mortality in patients with septic shock. There are also some case reports and minor studies demonstrating promising results with the unactivated form of protein C. However, in children with severe meningococcal infection, skin biopsies have demonstrated low expression of endothelial thrombomodulin and protein C receptors, suggesting low protein C activation capacity in severe meningococcal sepsis. METHODS: A patient with meningococcal septic shock was treated with two doses of the unactivated form of protein C, the first during intense activation of the coagulation system and the second during a phase of low grade or no activation. Repeated plasma samples were analysed for protein C concentration, which made it possible to compare pharmacokinetics and half-lives of the two administrations. A shorter half-life during intense coagulation was expected if there was an activation and consumption of the protein C administered. RESULTS: The calculated half-lives of protein C during intense and low grade activation were 32 h and 19 h, respectively, a magnitude similar to that reported in protein C-deficient patients without infection. CONCLUSION: The result indicates that whole body utilisation of the unactivated protein C was low. Endothelial impairment of protein C activation does not seem to be restricted to the skin vessels only.