Table 2  A simple scheme to rank CSF-penetrating drugs or the CNS-penetration effectiveness (CPE) ranks, proposed by Letendre et al. (2008a). Rank based on the drug physicochemical characteristics, measured CSF concentrations and CNS efficacy data extracted from publicly available information.
Low  Intermediate  High
Tenofovir (PMPA)  Stavudine (d4T)  Zidovudine (AZT)
Didanosine (ddI)  Lamivudine (3TC)  Abacavir
Zalcitabine (ddC)  Emtricitabine (FTC)  Delavirdine
Nelfinavir  Efavirenz  Nevirapine
Ritonavir  Amprenavir
Saquinavir  Fosamprenavir
Enfuvirtide  Atazanavir
Indinavir