Tenofovir

Description

Tenofovir is an analog of adenosine monophosphate that has antiviral activity. It is converted by cellular enzymes to tenofovir diphosphate, an obligate chain terminator that inhibits the activity of HIV reverse transcriptase and hepatitis B virus polymerase. Tenofovir diphosphate is a weak inhibitor of mammalian DNA polymerases α and β and mitochondrial DNA polymerase γ. For in vivo and cell culture use, tenofovir is supplied as a water soluble prodrug in the form of tenofovir disoproxil (fumarate) , which increases the intracellular diphosphorylated compound >1,000-fold above the level attained with unmodified tenofovir.

Chemical properties

White Crystalline Solid

The Uses of Tenofovir

Tenofovir is an acyclic phosphonate nucleotide analogue and reverse transcriptase inhibitor. It inhibits the activity of HIV reverse transcriptase through competing with the natural substrate deoxyadenosine 5’-triphosphate, causing the termination of DNA chain. It is used for the treatment of chronic heptatitis B as well as prevention and treatment of HIV/AIDS.

Definition

ChEBI: A member of the class of phosphonic acids that is methylphosphonic acid in which one of the methyl hydrogens is replaced by a [(2R)-1-(6-amino-9H-purin-9-yl)propan-2-yl]oxy group. An inhibitor of HIV-1 reverse transcriptase, the bis(isopropyloxycarbonyloxy ethyl) ester (disoproxil ester) prodrug is used as the fumaric acid salt in combination therapy for the treatment of HIV infection.

Indications

Tenofovir disoproxil fumarate (Viread) is a prodrug of tenofovir, a phosphorylated adenosine nucleoside analogue, and is the only available agent of its class. It is converted by cellular enzymes to tenofovir diphosphate, which competes with deoxyadenosine triphosphate (dATP) for access to reverse transcriptase and causes chain termination following its incorporation. Tenofovir was approved as part of a combination therapy for HIV in adults who failed treatment with other regimens; it appears to be effective against HIV strains that are resistant to NRTIs.

Acquired resistance

HIV variants with the K65R mutation and the K70E mutation in the reverse transcriptase demonstrate reduced susceptibility to tenofovir.

Pharmaceutical Applications

A nucleotide analog structurally similar to adefovir.
EC₅₀ values for HBV, assessed in the HepG2 2.2.15 cell line, ranged from 0.14 to 1.5 μm; the cytotoxic concentration exceeded 100 μm. A decline in HBV DNA levels below 10⁵ copies/mL at 48 weeks of therapy in 100% of patients receiving tenofovir compared with 44% on adefovir therapy has been reported. There are also case reports of patients with primary resistance to adefovir responding to tenofovir.
It is generally well tolerated in patients with chronic HBV; the most common side effects include nausea and gastrointestinal upset, headache, dizziness, fatigue and rash.

Biochem/physiol Actions

Tenofovir has a low oral bioavailability. Hence, it is available as a prodrug called tenofovir disoproxil fumarate. Once ingested, tenofovir disoproxil fumarate is hydrolyzed to tenofovir and phosphorylated. This is then incorporated into the viral DNA which leads to chain termination. Tenofovir is also effective against hepatitis B virus.

Clinical Use

Treatment of HIV infection in adults and children (in combination with other antiretroviral drugs)

Side Effects

Tenofovir is taken once daily and is generally well tolerated, perhaps because it produces less mitochondrial toxicity than the NRTIs. Nausea, vomiting, flatulence, and diarrhea occur in 10% or fewer patients. Resistance to tenofovir has been documented, and cross-resistance to NRTIs may occur.

storage

Store at -20°C