Advances in the macrolides and quinolones

Pharmacokinetic/pharmacodynamic modelling of roxithromycin for the inhibitory effect of tumour necrosis factor-alpha and interleukin-6 production in dogs

The objective of the present study was to determine and characterize the relationship between the plasma concentration of roxithromycin, and its inhibitory effect on cytokine production, in order to predict its possible clinical relevance. Six healthy beagle dogs received a single intravenous dose of 20-mg roxithromycin per kg body weight. Blood samples were obtained at different time points. The plasma was analysed with respect to roxithromycin, tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). The concentration-effect relationship was explored by modelling the data using two compartmental model and an indirect response model with an E(max) concentration-effect relationship. The estimated pharmacokinetic parameters (geometric mean) were as follows: V(c) = 2.59 l; k(10) = 0.08/h; k(12) = 0.26/h; k(21) = 0.40/h. The pharmacodynamic parameters (geometric mean) for the inhibitory effect on cytokine production induced by heat-killed Staphylococcus aureus (HKSA) were for TNF-alpha (k(in) = 1.42 microg/h; k(out) = 1.10 microg/h; EC(50) > 5.69 mg/l) and for IL-6 (k(in) = 2.31 microg/h; k(out) = 2.04 microg/h; EC(50) = 21.07 mg/l) production, respectively. The inhibitory effect of roxithromycin on production can be adequately described by the indirect response model with an E(max) concentration-effect relationship.

Quinolone Resistance: Older Concepts and Newer Developments

New quinolone compounds have been recommended for use in the treatment of respiratory tract infections, particularly pneumonia caused by multi drug-resistant Streptococcus pneumoniae. Of concern, however, is the recent emergence of pneumococcal isolates with reduced susceptibilities to both old and new quinolone compounds. This necessitates the employment of quinolone-use strategies aimed at restricting the emergence of resistance, to extend the effectiveness of this very important class of antibacterial agents. This article provides a comprehensive review of the recent discoveries in type II topoisomerase/quinolone structure-function relationships. It also addresses new insights into the mechanisms of quinolone resistance, the predicted trends in quinolone resistance, and possible strategies for quinolone use against S. pneumoniae.

The new antibiotics

It is easy to become overwhelmed by the amount of information available on the new antibiotics and difficult to keep abreast of the appropriate indications for each of them. For most patients with community-acquired infections, the first-line agent is usually not one of the newer agents, but a standard regimen, or at times, no antibiotic at all. The development of resistance is likely to parallel the extent to which these agents are prescribed. They should be used only when standard treatment fails, when compliance with treatment is a real and serious issue, or when the patient has a real allergic reaction to the standard regimen.