Treatment of life-threatening multiresistant staphylococcal and enterococcal infections in patients with end-stage renal failure with quinupristin/dalfopristin: preliminary report

Expression of an additional cathelicidin antimicrobial peptide protects against bacterial skin infection

Cathelicidin antimicrobial peptides are effectors of innate immune defense in mammals. Humans and mice have only one cathelicidin gene, whereas domesticated mammals such as the pig, cow, and horse have multiple cathelicidin genes. We hypothesized that the evolution of multiple cathelicidin genes provides these animals with enhanced resistance to infection. To test this, we investigated the effects of the addition of cathelicidins by combining synthetic cathelicidin peptides in vitro, by producing human keratinocytes that overexpress cathelicidins in culture, or by producing transgenic mice that constitutively overexpress cathelicidins in vivo. The porcine cathelicidin peptide PR-39 acted additively with human cathelicidin LL-37 to kill group A Streptococcus (GAS). Lentiviral delivery of PR-39 enhanced killing of GAS by human keratinocytes. Finally, transgenic mice expressing PR-39 under the influence of a K14 promoter showed increased resistance to GAS skin infection (50% smaller necrotic ulcers and 60% fewer surviving bacteria). Similarly constructed transgenic mice designed to overexpress their native cathelicidin did not show increased resistance. These findings demonstrate that targeted gene transfer of a xenobiotic cathelicidin confers resistance against infection and suggests the benefit of duplication and divergence in the evolution of antimicrobial peptides.

Clinical pharmacokinetics of quinupristin/dalfopristin

Quinupristin/dalfopristin is a streptogramin antibacterial with a wide spectrum of Gram-positive antibacterial activity. The drug has minimal oral absorption and is administered intravenously as a fixed 30 : 70 ratio of quinupristin to dalfopristin. A linear relationship has been observed between the dose administered and maximum plasma concentrations. Single-dose administration of 7.5 mg/kg produced a maximal plasma concentration of 2.3-2.7 mg/L for quinupristin and 6.1-8.2 mg/L for dalfopristin. The area under the concentration-time curve (AUC) obtained with the same dose was 2.7-3.3 and 6.5-7.7 mg. h/L for quinupristin and dalfopristin, respectively. Repeated administration results in 13-21% increases in maximum plasma concentrations and 21-26% increases in AUC for both quinupristin and dalfopristin. Quinupristin and dalfopristin exhibit steady-state volumes of distribution of 0.46-0.54 and 0.24-0.30 L/kg, respectively. Quinupristin exhibits higher protein binding (55-78%) than dalfopristin (11-26%), though both entities distribute well into tissues. Concentrations exceeding those in blood have been reported for the kidney, liver, spleen, salivary glands and white blood cells of primates. Extravascular penetration, as measured in blister fluid, is 40-80%. Both quinupristin and dalfopristin are extensively metabolised via nonenzymatic reactions. Quinupristin is conjugated to form two active compounds, a cysteine moiety and a glutathione moiety. Dalfopristin is hydrolysed to the active metabolite pristinamycin IIA. The metabolites exert antibacterial activity similar to that of the parent compounds. Quinupristin/dalfopristin is excreted primarily in the faeces (75-77%), with lesser renal excretion (15-19%). The elimination half-lives of quinupristin and dalfopristin are similar, and are 0.7-1.3 hours after single doses. The metabolites have slightly longer half-lives, ranging from 1.2 to 1.8 hours. With repeated doses, plasma clearance of quinupristin and dalfopristin is reduced by approximately 20% compared with single doses, resulting in clearances of 0.7-0.8 L/h/kg. Saturable protein binding has been hypothesised as a causative mechanism. Quinupristin/dalfopristin is an inhibitor of cytochrome P450 3A4, resulting in multiple drug interactions. Ciclosporin AUC increased by 5-222% when coadministered with quinupristin/dalfopristin. Careful monitoring of patients receiving drugs that are substrates of cytochrome P450 3A4 is suggested.Quinupristin/dalfopristin is administered at 7.5 mg/kg every 8-12 hours, depending upon the severity of infection. The pharmacodynamic parameter linked with antibacterial activity for quinupristin/dalfopristin appears to be the ratio of AUC to the minimal inhibitory concentration. The additional activity of a prolonged post-antibiotic effect may also be important for efficacy.

Newer antibiotics for the treatment of respiratory tract infections

PURPOSE OF REVIEW

In this review, we highlight some of the developments achieved over the past 2 years in the field of novel antimicrobial compounds.

RECENT FINDINGS

Modification of existing compound classes to create more powerful compounds capable of overcoming pathogen resistance and the introduction of completely new classes of antibiotics and inhibitors of new bacterial targets or inhibitors of genes relating to virulence or pathogenesis are the strategies more commonly employed in pharmacologic research. Ketolides, oxazolidinones, streptogramins, glycylcyclines, and peptide deformylase inhibitors are among the most promising classes of antibiotics. Recently, several lines of research have documented that it is effective to target the infection process rather than killing bacteria. This is important because it is likely that such a therapeutic strategy could ablate infection without inducing resistance.

SUMMARY

Emergence of resistance to the antibiotics currently employed in clinical practice is a continual stimulus for further research aimed at identifying novel antimicrobial compounds. These drugs will perhaps effectively fight against bacteria that now are scarcely controlled by the traditional antimicrobial agents. Health care personnel must appreciate that only judicious use of antimicrobial drugs will prevent the further uncontrolled spread of bacterial resistance. Implementation of reference guidelines would probably be an effective way to limit antibiotic misuse.