Antibiotics for Gram Positive Meningitis,Bhakti Patel M4 Medical Therapeutics,Case (adapted from ID consult 8/2006),62 yo woman with history of Hep C presenting with GBS cervical osteomyelitis refractory to initial medical management. She required a C5-7 anterior corpectomy with posterior C4-C7 spinal fusion, which was unfortunately complicated by a persistent dural leak, requiring surgical exploration with placement of a lumbar drain for repair. Post-operatively, CSF cultures grew E. Faecium sensitive to vancomycin. Despite prolonged treatment with vancomycin CSF cultures continued to grow E. faecium and the patients neurological status worsened. What would be your next step in the management of this patient?,Choosing the Right Antibiotic Pharmacokinetics of Antibiotics in CSF,Blood Brain Barrier Cerebral capillary endothelial cells have tight junctions instead of fenestrations; Consequently only water, most ions, and lipids pass freely. Glucose and other nutrients are transported via surface enzymes and transport molecules expressed by the endothelium. Pharmacokinetics The concentration of antibiotics in CSF depends on the balance between drug penetration and elimination through the blood brain barrier.,Choosing the Right Antibiotic Crossing the Blood Brain Barrier,Factors Influencing antibiotic concentrations in CSF,(CID 1998;27:1117-29),Choosing the Right Antibiotic Pharmacodynamics of Antibiotics in CSF,Pharmacodynamics: concerned with the time course of antimicrobial activity at the site of infection The CSF has poor immune response because there are very low concentrations of pathogen-specific antibodies and complement factors even during meninigitis. Therefore antibiotics should have rapid bactericidal activity for successful treatment (J Antimicrobial Chemo. 1993; 31, Suppl D, 61-70) Concentration-dependent killing: efficacy depends on high peak concentrations and prolonged recovery period after drug levels fall below MIC. The recovery period is characterized by postantibiotic effect, in which there is delayed regrowth of bacteria after exposure and removal of an antibiotic (examples:Aminoglycosides/Fluoroquinolones) Time-dependent killing: efficacy depends on the time their concentration exceeds the MIC (TMIC) (examples: Beta-lactams, macrolides, clindamycin) Inf Dis North Am. 1999 Sep; 13(3):595-618,Choosing the Right Antibiotic Microorganism susceptibility-Current Practice Guidelines,ClD 2004;39:1267-84,Gram Positive Organisms,Beta-Lactams,CNS penetration: Beta lactams penetrate the intact BBB poorly However in the presence of inflammation penicillins can achieve levels greater than 10x the minimal bactericidal concentration MBC90 for gram positive pathogens (Inf Dis N Am. 1999; 13 (3): 595-611) Pharmacodynamics Exhibits time-dependent bactericidal activity,Vancomycin,The emergence of penicillin and cephalosporin resistant strains of S. pneumo has resulted in increased use of Vancomycin for treatment of bacterial meningitisCNS Penetration: 10% of serum concentration Pharmacodynamics: Studies in rabbits suggest that maximal bacterial killing rate (BKR) is achieved when vancomycin levels are 5-10x the Minimal Bactericidal Concentration (MBC) CID 1998;27:1117-29,Vancomycin: Concerns about CNS Penetration,Given that CNS penetration by hydrophilic antibiotics like Vancomycin and Beta-lactams are dependent on meningeal inflammation, concomitant use with high dose steroids may reduce vancomycins penetration into the CSF Pharmacodynamics of Vancomycin for treatment of experimental Penicillin-, and Cephalosporin-resistant pneumococcal meningitis (Antimicrobial agents and Chemo, Apr 1999;43: 876-81) Experiment design: Using Rabbit meningitis model, animals were given either 20 or 40mg/kg doses of vancomycin (4 and 2 times a day respectively for a total 80mg/kg/daily dose), with and without steroids to determine the penetration of vancomycin in CSF. Results: In the non-steroid group, for both treatment groups (20, 40mg/kg doses) the CNS penetration was 20.1%. Mean concentration of vancomycin at 24-36hr of therapy was lower than levels achieved in the first 12hours consistent with decreasing antibiotic penetration with waning meningeal inflammation. In the steroid groups, the CNS penetration was decreased to 14.3% (P=0.035). The rate of bacterial clearance during the first 6 hours in the 20mg/kg group + steroids group was significantly lowered. However in the 40mg/kg group, the rate of clearing bacteria was similar to the animals not receiving steroids for the first 6hours. Conclusions: In the setting of adjuvant corticosteroid therapy, larger doses of vancomycin (40mg/kg BID) may be needed to achieve and maintain therapeutic concentrations in the CSF Clinical Implications: Clinical guidelines suggest that vancomycin should be given at total daily doses of 30-45mg/kg. This study suggests a larger total daily dose similar to that used in the pediatric population can overcome the CNS penetration impairment caused by concomitant steroid use.,