The transport of anti-HIV drugs across blood–CNS interfaces: Summary of current knowledge and recommendations for further research

The advent of highly active antiretroviral therapy (HAART), which constitutes HIV protease inhibitors, nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and nucleotide reverse transcriptase inhibitors, has dramatically reduced the morbidity and mortality associated with human immunodeficiency virus (HIV) infection in resource-rich countries. However, this disease still kills several million people each year. Though the reason for therapeutic failure is multi-factorial, an important concern is the treatment and control of HIV within the central nervous system (CNS). Due to the restricted entry of anti-HIV drugs, the brain is thought to form a viral sanctuary site. This not only results in virological resistance, but also is often associated with the development of complications such as HIV-associated dementia. The CNS delivery of anti-HIV drugs is limited by the blood–brain and blood–CSF interfaces due to a combination of restricted paracellular movement, powerful metabolic enzymes and numerous transporters including members of the ATP binding cassette (ABC) and solute carrier (SLC) superfamilies. A better appreciation of the transporters present at the brain barriers will prove a valuable milestone in understanding the limited brain penetration of anti-HIV drugs in HIV and also aid the development of new anti-HIV drugs and drug combinations, with enhanced efficacy in the CNS. This review aims to summarise current knowledge on the transport of anti-HIV drugs across the blood–brain barrier and the choroid plexus, as well as provide recommendations for future research.