Tenofovir (Viread®) was invented by Antonín Holý from at the Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and patented in 1984, making this one of the earliest antiviral drugs. In collaboration with Gilead Sciences and the University of California, it was developed into its current form and was approved for use against HIV in 2001. It is now also being used for the Post-Exposure Prophylaxis of HIV.
Viread® is a defective nuclease that lacks the OH- group of the deoxyribose sugar. Because of this lack, when the Viread® particle is incorporated into the DNA strand, no other deoxyribose sugars can be added, terminating production. Viread® does not interact well with human DNA polymerases and so does not have a large effect on normal cell replication. It does interact with the viral reverse transcriptase that changes the viral RNA into DNA, preventing viral replication in the host cell.
The most common side effects with Viread® are gastrointestinal upsets such as loss of appetite, stomach ache, nausea, gas, cramping, diarrhoea and vomiting. Patients can also experience a skin rash, insomnia, headaches, dizziness and depression.
Like Emtriva® it can cause lactic acidosis so patients should be on the look out for sore muscles for no reason, fatigue, chills in the limbs and irregular heartbeat or trouble breathing. Lactic acidosis can be fatal if left untreated so it is important to seek urgent medical care should you start to exhibit these symptoms. Be aware this is a rare side effect.
Liver toxicity can occur so watch for jaundice, dark urine, light stools and fatigue. Viread® has also been linked to decreases in bone mineral density so it may be wise to speak to your doctor about supplements while taking Viread®.
People with pre-existing liver damage should be carefully monitored while taking Viread®, particularly those with viral hepatitis.
Lactic acidosis is more commonly seen in females, people who are overweight and those who have been taking HIV medication for an extended period of time.
Alcohol can exacerbate liver conditions so it is best to avoid heavy drinking while taking Viread®. The drug has been shown to increase symptoms of hepatitis for those suffering viral hepatitis B (HBV), though the drug itself has been approved for treatment of the HBV under controlled conditions. Be sure to inform your doctor if you have HBV so that the correct dose can be administered and liver function monitored. Patients with HBV have shown a significant increase in pathological symptoms following discontinuation of Viread® so should be monitored when coming off the course.
Those with a history of osteoporosis or other bone disorders should speak to their doctor before taking Viread®.
There is no evidence to say that Viread® is dangerous during pregnancy but insufficient data to claim it is safe. As a consequence, it should be given only in the utmost need to pregnant women. Viread® is transmitted through the breast milk, as is any live HIV virus and it is advised that those women on Viread® do not breastfeed.
Due to the method of clearance from the body via the kidneys it is advised that you avoid mixing Viread® with nephrotoxic (nephron=kidneys) drugs. Viread® has not been linked to kidney failure but it is still advised that kidney function is monitored. It is recommended for patients on didanosine that the didanosine is reduced or discontinued while as Viread® will increase didanosine bioavailability which can cause damage to the kidneys or pancreas.
Viread® should not be given along with HEPSERA.
Viread® is not the only drug to contain tenofovir and it is important to ensure the correct dose. Inform your doctor if you are taking any other anti-HIV medications to prevent overdosing. Often increasing the dose will not increase effectiveness against HIV but will exacerbate the side effects so it is important not to double up.
There is some evidence to show that Viread® bioavailability levels are boosted by the presence of Kaletra® in the patient’s system.
Viread® is one of the oldest anti-HIV drugs and as it acts on the DNA itself rather than a protein, resistance is rare though it does occur. It is listed on the World Health Organisations list of essential medicines for the treatment of HIV and has proved its worth in the fight to stem the tide of AIDS.
Recent studies show that Viread® may have a larger role to play than just as an anti-HIV drug. Patients with HBV have shown a reduction in viral load when taking Viread® and some have been shown to clear the HBV virus entirely from their system when taking Viread®. Despite this FDA has not approved Viread® for treatment of co-infection with HIV and HBV, concerned about the hepatotoxicity (hepato = liver) of Viread®. The situation is very different in Britain where Viread® is the first drug of choice for treating HIV and HBV co-infection.
The jury is still out on which approach is the correct one. This older of the HIV drugs may well give hope to those who are suffering a chronic HBV infection. Hepatitis C can now be cured in up to 80% of cases with correct administration of anti-virals. It may be that a solution to HBV is on the horizon.
For more information see:
WebMD – Viread
Gilead Sciences product information sheet – Viread