CNS Penetration of Drugs

Key Physicochemical Determinants

The blood-brain barrier (BBB) and blood-CSF barrier function as selective gatekeepers that restrict drug entry through multiple mechanisms, including tight junctions, lack of fenestrations, active efflux transporters, and metabolic enzymes at the barrier 1
Active efflux transporters (P-glycoprotein/MDR1, MRP4, BCRP) actively pump drugs out of the CNS, and drugs that are not substrates for these pumps are more likely to achieve therapeutic CNS concentrations 2, 3

Inflammation significantly increases drug penetration by disrupting BBB integrity, with beta-lactam antibiotics achieving 2-5 fold higher CSF concentrations with inflamed meninges 4
Vancomycin CSF penetration increases from 1% (uninflamed) to 5% (inflamed meninges), but concentrations remain unpredictable and often subtherapeutic even with inflammation 4

Linezolid achieves 66% CSF penetration with concentrations of 7-10 μg/mL, making it a suitable option for CNS infections 4
Ceftazidime-avibactam achieves CSF/serum ratios of 0.35-0.59 for ceftazidime and 0.51-0.57 for avibactam, indicating moderate CNS penetration 6
Trimethoprim-sulfamethoxazole achieves 13-53% CSF penetration for TMP and 17-63% for SMX, making it a less reliable option for CNS infections 4

Therapeutic drug monitoring of both blood and CSF is strongly recommended for CNS infections, with target CSF concentrations above the MIC of the isolated pathogen 7
High CNS drug concentrations carry seizure risk, particularly with beta-lactams, and dose adjustment is mandatory in renal impairment to prevent neurotoxicity 7
Efflux transporter interactions significantly impact CNS drug delivery, and pharmacological modulation of individual transporters may enhance CNS drug levels 2, 3

Surgical intervention improves outcomes when feasible, with drainage of focal abscesses and removal of infected foreign bodies (shunts, devices) recommended whenever possible 4, 6, 7