Tenofovir


Generic Medicine Info
Indications and Dosage
Oral
Chronic hepatitis B, HIV infection
Adult: 300 mg once daily.
Renal Impairment
Haemodialysis patients: 300 mg once every 7 days or after a cumulative total of 12 hr of dialysis.
CrCl (mL/min) Dosage
10-29 300 mg 72-96 hrly.
30-49 300 mg 48 hrly.
Administration
May be taken with or without food. Take consistently either always w/ or always w/o food.
Contraindications
Hypersensitivity. Lactation.
Special Precautions
Patient w/ hepatomegaly or other risk factors for liver disease. Renal impairment. Pregnancy.
Adverse Reactions
GI events (e.g. anorexia, abdominal pain and distention, diarrhoea, dyspepsia, flatulence, nausea, vomiting), asthenia, dizziness, fatigue, headache, rash, hypophosphatemia, raised liver enzymes, hepatitis, renal effects (e.g. nephritis, nephrogenic diabetes insipidus, proximal renal tubulopathy, renal failure), bone pain, osteomalacia, muscle weakness, myopathy. Rarely, raised serum amylase levels, pancreatitis, rhabdomyolysis.
Potentially Fatal: Lactic acidosis, severe hepatomegaly w/ steatosis.
Patient Counseling Information
This drug may cause dizziness, if affected, do not drive or operate machinery.
MonitoringParameters
Monitor renal function and serum phosphate concentrations before start of therapy, 4 wkly during the 1st wk, and then 3 mthly; hepatic function for several mth following discontinuation. Determine HIV status in all hepatitis B virus (HBV) infected patients prior to treatment.
Drug Interactions
Decreased plasma concentrations of atazanavir and increased plasma concentration of tenofovir when given concomitantly. Increased plasma concentration w/ ritonavir-boosted lopinavir. Tenofovir increases the plasma concentrations of didanosine. Increased risk of nephrotoxicity w/ drugs that reduce renal function (e.g. cidofovir, aciclovir, valaciclovir, aminoglycosides, high-dose or multiple NSAIDs). Decreased therapeutic effect w/ adefovir.
Food Interaction
Fatty meals may increase bioavailability of tenofovir.
Action
Description: Tenofovir disoproxil fumarate (TDF), an acyclic nucleoside phosphonate diester analog of adenosine monophosphate, is hydrolysed to tenofovir and subsequently phosphorylated by cellular enzymes to form tenofovir diphosphate, an obligate chain terminator. It interferes w/ DNA synthesis of HIV through competitive inhibition of reverse transcriptase and incorporation into viral DNA. It also inhibits hepatitis B virus polymerase, resulting in inhibition of viral replication.
Pharmacokinetics:
Absorption: Rapidly absorbed from the GI tract. Increased bioavailability when taken w/ a high fat meal. Bioavailability: Approx 25%. Time to peak plasma concentration: 1-2 hr.
Distribution: Widely distributed into body tissues, particularly the kidneys and liver. Volume of distribution: 1.2-1.3 L/kg. Plasma protein binding: <1%.
Metabolism: Tenofovir disoproxil fumarate is rapidly converted to tenofovir via hydrolysis, and subsequently, to the active form tenofovir diphosphate via phosphorylation by cellular enzymes.
Excretion: Via urine by active tubular secretion and glomerular filtration. Terminal elimination half-life: 12-18 hr.
Chemical Structure

Chemical Structure Image
Tenofovir

Source: National Center for Biotechnology Information. PubChem Database. Tenofovir, CID=464205, https://pubchem.ncbi.nlm.nih.gov/compound/Tenofovir (accessed on Jan. 22, 2020)

Storage
Store at 25°C.
MIMS Class
ATC Classification
J05AF07 - tenofovir disoproxil ; Belongs to the class of nucleoside and nucleotide reverse transcriptase inhibitors. Used in the systemic treatment of viral infections.
References
Anon. Tenofovir. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 10/09/2015.

Buckingham R (ed). Tenofovir. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 10/09/2015.

McEvoy GK, Snow EK, Miller J et al (eds). Tenofovir Disoproxil Fumarate. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 10/09/2015.

Viread Access Tablet, Coated (Gilead Sciences, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 10/09/2015.

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