Emtricitabine & Tenofovir
PrEP (Emtricitabine + Tenofovir) is an antiviral medication
PrEP can be used to prevent viral infections such as HIV (Human Immunodeficiency Virus).
PrEP works by preventing viruses from infecting a person's cells. We need to understand a little more about viruses themselves in order to understand how this works.
WHAT ARE viruses?
Viruses are submicroscopic infectious agents that can only replicate if they are inside a host cell. They consist of genetic material wrapped in a protein capsule. Scientists debate about whether they are living or non-living organisms.
EXAMPLES OF VIRUSES
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) - causes coronavirus disease 2019 (COVID-19)
Human immunodeficiency viruses (HIV) - causes HIV infections which over time develops into AIDS (acquired immunodeficiency syndrome)
Varicella-zoster virus - causes chickenpox and shingles
How do Antivirals work?
Recall that viruses are simple entities made of genetic material inside a protein capsid. Sometimes, this is surrounded by a protective membrane. Anti-viral medications cannot 'kill' viruses, as they are not alive. Antiviral medications generally focus on interrupting the process of replicating genetic material.
Genetic material in humans is DNA (deoxyribonucleic acid). It is converted by the cell into RNA (ribonucleic acid) inside the nucleus, and the RNA is transported into the cell membrane. Inside the cell membrane, the ribosome is involved in translating the information from the RNA molecule into proteins and other cell products.
DNA and RNA are made up of nucleotides that contain bases cytosine, thymine, adenine, guanine and uracil in long chains.
If the chain is incomplete, the instructions don't work properly. The anti-viral medication PrEP works by interrupting the formation of DNA strands.
Human immunodeficiency virus
HIV viruses contain two copies of single stranded RNA molecules. When they find their way into a host cell, a process called reverse transcription makes them into double stranded DNA. These DNA molecules can be read by the cell machinery of the host cell, and the host starts making more HIV viruses.
PrEP (Emtricitabine + Tenofovir)
Compare the structures of the two components of PrEP with the nucleotide base they mimic below.
Tenofovir
Tenofovir mimics the nucleotide adenosine.
It binds to proteins that adenosine would normally bind to, but prevents other nucleotides from being added. Thus the DNA strand can't be made any longer, and it will not function.
Tenofovir binds to a protein called reverse transcriptase and prevents it from working.
Reverse transcriptase is a protein which creates new DNA strands from RNA material. If the virus cannot create new DNA strands, it cannot replicate.
Adenosine
Adenosine is a nucleotide which is used by all living things in DNA and RNA molecules.
Emtricitabine
Emtricitabine mimics the nucleotide cytosine.
It binds to proteins that cytosine would normally bind to, but prevents other nucleotides from being added. Thus the DNA strand can't be made any longer, and it will not function.
Emtricitabine binds to a protein called reverse transcriptase and prevents it from working.
Reverse transcriptase is a protein which creates new DNA strands from RNA material. If the virus cannot create new DNA strands, it cannot replicate.
cytosine
Cytosine is a nucleotide which is used by all living things in DNA and RNA molecules.