Protease Inhibitors (PIs) are a class of medications used to prevent infections by viruses, including HIV.

When HIV infects a CD4 cell (helper T-cell), it copies its genetic information and inserts it into the DNA of the CD4, or host, cell. As a result, the infected cell makes copies of the virus’s DNA and proteins. Protease is an enzyme that cleaves long protein chains into smaller sections, which are later assembled to create a functional virus. PIs block this action so that HIV continues to replicate, but cannot mature and infect other cells.

Over time, as HIV continues to make copies of itself, PIs may lose their effectiveness if the virus develops resistance to drugs. In HIV replication, each copy of the virus is slightly different than the last. Drugs become ineffective if the protease enzymes of newer copies develop resistance to the PI used.

To avoid drug resistance, PIs are usually taken in combination with two other anti-HIV drugs. This type of treatment method is known as Highly Active Anti-Retroviral Therapy (HAART).

Currently, some of the approved Protease Inhibitor drugs include:

• Aptivus (tipranavir)
• Crixivan (indinavir)
• Invirase (saquinavir mesylate)
• Kaletra (lopinavir/ritonavir)
• Lexiva (fosamprenavir)
• Norvir (ritonavir)
• Prezista (darunavir)
• Reyataz (atazanavir)
• Viracept (nelfinavir)

Side-effects of PIs include nausea and diarrhea. More serious side effects involve increased triglyceride and cholesterol levels (types of fatty substances), as well as elevated blood sugar levels which can lead to diabetes. PIs often change the way fat is distributed in the body, leading to weight gain in the stomach area, but weight loss around the face.