Special Populations

Elderly: The pharmacokinetics of quinupristin and dalfopristin were studied in a population of elderly individuals (range 69 to 74 years). The pharmacokinetics of the drug products were not modified in these subjects.

Gender: The pharmacokinetics of quinupristin and dalfopristin are not modified by gender.

Renal Insufficiency: In patients with creatinine clearance 6-28 mL/min, the AUC of quinupristin and dalfopristin in combination with their major metabolites increased about 40% and 30%, respectively.

In patients undergoing Continuous Ambulatory Peritoneal Dialysis, dialysis clearance for quinupristin, dalfopristin and their metabolites is negligible. The plasma AUC of unchanged quinupristin and dalfopristin increased about 20% and 30%, respectively. The high molecular weight of both components of Synercid suggests that it is unlikely to be removed by hemodialysis.

Hepatic Insufficiency: In patients with hepatic dysfunction (Child-Pugh scores A and B), the terminal half-life of quinupristin and dalfopristin was not modified. However, the AUC of quinupristin and dalfopristin in combination with their major metabolites increased about 180% and 50%, respectively. (See DOSAGE AND ADMINISTRATION and PRECAUTIONS.)

Obesity (body mass index ³30): In obese patients the Cmax and AUC of quinupristin increased about 30% and those of dalfopristin about 40%.

Pediatric Patients: The pharmacokinetics of Synercid in patients less than 16 years of age have not been studied.

Microbiology

The streptogramin components of Synercid, quinupristin and dalfopristin, are present in a ratio of 30 parts quinupristin to 70 parts dalfopristin. These two components act synergistically so that Synercids microbiologic in vitro activity is greater than that of the components individually. Quinupristins and dalfopristins metabolites also contribute to the antimicrobial activity of Synercid. In vitro synergism of the major metabolites with the complementary parent compound has been demonstrated.

Synercid is bacteriostatic against Enterococcus faecium and bactericidal against strains of methicillin-susceptible and methicillin-resistant staphylococci.

The site of action of quinupristin and dalfopristin is the bacterial ribosome. Dalfopristin has been shown to inhibit the early phase of protein synthesis while quinupristin inhibits the late phase of protein synthesis.

In vitro combination testing of Synercid with aztreonam, cefotaxime, ciprofloxacin, and gentamicin against Enterobacteriaceae and Pseudomonas aeruginosa did not show antagonism.

In vitro combination testing of Synercid with prototype drugs of the following classes: aminoglycosides (gentamicin), b-lactams (cefepime, ampicillin, and amoxicillin), glycopeptides (vancomycin), quinolones (ciprofloxacin), tetracyclines (doxycycline) and also chloramphenicol against enterococci and staphylococci did not show antagonism.

The mode of action differs from that of other classes of antibacterial agents such as b-lactams, aminoglycosides, glycopeptides, quinolones, macrolides, lincosamides and tetracyclines. There is no cross resistance between Synercid and these agents when tested by the minimum inhibitory concentration (MIC) method.

In non-comparative studies, emerging resistance to Synercid during treatment of VREF infections occurred. Resistance to Synercid is associated with resistance to both components (i.e., quinupristin and dalfopristin).

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