Virofovir

Virofovir Uses, Dosage, Side Effects, Food Interaction and all others data.

Lamivudine is a synthetic nucleoside analogue. Lamivudine is phosphorylated intracellularly to lamivudine triphosphate. Incorporation of the monophosphate form into viral DNA occurs by hepatitis B virus (HBV) polymerase. As a result DNA chain is terminated. Lamivudine triphosphate also inhibits the RNA and DNA-dependent DNA polymerase activities of HIV-1 reverse transcriptase (RT). Lamivudine triphosphate is a very weak inhibitor of mammalian alpha, beta, and gamma-DNA polymerases.

Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) with activity against Human Immunodeficiency Virus Type 1 (HIV-1) and hepatitis B (HBV) to disrupt viral DNA synthesis. When phosphorylated, lamivudine can form active metabolites that compete for incorporation into viral DNA. Via DNA incorporation, lamivudine metabolites competitively inhibit the activity of the HIV reverse transcriptase enzyme and act as a chain terminator of DNA synthesis. Due to the lack of a 3'-OH group, incorporated nucleoside analogues prevent the formation of a 5' to 3' phosphodiester linkage that is essential for DNA chain elongation.

Tenofovir Disoproxil Fumarate, an acyclic nucleotide analogue of adenosine monophosphate, is a pro-drug of Tenofovir. It shows activity against hepatitis B virus polymerase and HIV reverse transcriptase after phosphorylation to the active diphosphate form. Tenofovir diphosphate inhibits viral polymerase (reverse transcriptase) by directly competing with the natural substrate deoxyribonucleotide and by causing DNA chain termination after its incorporation into viral DNA.

Tenofovir has been shown to be highly effective in patients that have never had an antiretroviral therapy and it seemed to have lower toxicity than other antivirals such as stavudine. In phase 3 clinical trials, tenofovir presented a similar efficacy than efavirenz in treatment-naive HIV patients. In hepatitis B infected patients, after one year of tenofovir treatment, the viral DNA levels were undetectable.

Virofovir
Uses
Dosage
Side Effect
Precautions
Interactions
Uses during Pregnancy
Uses during Breastfeeding
Accute Overdose
Food Interaction
Half Life
Volume of Distribution
Clearance
Interaction With other Medicine
Contradiction
Storage

Trade Name	Virofovir
Generic	Lamivudine + Tenofovir
Type	Tablet
Therapeutic Class
Manufacturer
Available Country	India
Last Updated:	September 19, 2023 at 7:00 am

Uses

Lamivudine is used for the treatment of chronic hepatitis B associated with evidence of hepatitis B viral replication and active liver inflammation.

This is used for the treatment of:

Chronic hepatitis B virus infection in adults
HIV infected adults in combination with other anti retroviral agents

Virofovir is also used to associated treatment for these conditions: Hepatitis B Chronic Infection, Human Immunodeficiency Virus (HIV) Infections

How Virofovir works

Lamivudine is a synthetic nucleoside analogue and is phosphorylated intracellularly to its active 5'-triphosphate metabolite, lamivudine triphosphate (L-TP). This nucleoside analogue is incorporated into viral DNA by HIV reverse transcriptase and HBV polymerase, resulting in DNA chain termination.

Once tenofovir is activated by a bi-phosphorylation it acts as an antiviral acyclic nucleoside phosphonate. It is a potent inhibitor of the viral reverse transcriptase with an inhibitory constant of approximately 0.022 micromolar.

Once activated, tenofovir acts with different mechanisms including the inhibition of viral polymerase causing chain termination and the inhibition of viral synthesis. All these activities are attained by its competition with deoxyadenosine 5'-triphosphate in the generation of new viral DNA. Once tenofovir is incorporated in the chain, it induces a chain termination which in order inhibits viral replication. The safety of tenofovir relies on its low affinity towards the cellular DNA polymerase including the mitochondrial DNA polymerase gamma.

Dosage

Virofovir dosage

The recommended oral dose of Lamivudine for the treatment of chronic hepatitis B in adults is 100 mg once daily.

The recommended dose of Tenofovir in chronic hepatitis B virus infection in adults 18 years of age and older with adequate renal function is 300 mg once daily with or without food.

Side Effects

Several serious adverse events reported with lamivudine (lactic acidosis and severe hepatomegaly with steatosis, post treatment exacerbations of hepatitis B, pancreatitis, and emergence of viral mutants associated with reduced drug susceptibility and diminished treatment response). Malaise, fatigue, fever, ENT infections, sore throat, nausea, vomiting, abdominal discomfort, pain, diarrhea, myalgia, arthralgia, headache, skin rashes may occur. Lactic acidosis and severe hepatomegaly with steatosis, have been reported.

The most common side effects are nausea, vomiting, diarrhea and flatulence.

Toxicity

The most common reported adverse reactions (incidence ≥15%) in adults were headache, nausea, malaise and fatigue, nasal signs and symptoms, diarrhea, and cough.

There haven't been reports regarding the LD50 of the parent compound nor the effects of an overdose. However, based on the reports with the derivative that most rapidly transforms into tenofovir, tenofovir disoproxil, it is recommended to monitor overdose patients. As well, it is widely known that tenofovir is efficiently removed by hemodialysis.

Administration of high doses of tenofovir has been reported to produce bone toxicity reported as osteomalacia and reduced bone mineral density and to produce some degree of renal toxicity.

To know more about the carcinogenicity and mutagenic potential of tenofovir, as well as the effect on fertility, please visit the drug entries for the derivatives tenofovir disoproxil and tenofovir alafenamide.

Precaution

Patients should be assessed before beginning treatment and during treatment with lamivudine by a physician experienced in the management of chronic hepatitis B.

Co-administration with other drugs: Tenofovir should not be administered concurrently with Emtricitabine & Tenofovir combination or Adefovir Dipivoxil.

Lactic Acidosis & Severe Hepatomegaly with Steatosis: Though the risk of occurrence of lactic acidosis is low for Tenofovir, treatment should be suspended in any patient who develops lactic acidosis or hepatotoxicity.

Exacerbation of hepatitis after discontinuation of treatment: Discontinuation of Tenofovirtherapy may be associated with severe acute exacerbation of hepatitis.

Interaction

Trimethoprim 160 mg / Sulfamethoxazole 800 mg once daily has been shown to increase lamivudine exposure (AUC). The effect of higher doses of trimethoprim /sulfamethoxazole on lamivudine pharmacokinetics has not been investigated.

Co-administration of Tenofovir with anti-retroviral, entecavir, lamivudine, methadone, oral contraceptives, ribavirin and tacrolimus did not result in significant drug interactions. The effects of co-administration of Tenofovir with other drugs that are renally eliminated or are known to affect renal function have not been evaluated.

Volume of Distribution

Apparent volume of distribution, IV administration = 1.3 ± 0.4 L/kg. Volume of distribution was independent of dose and did not correlate with body weight.

Accumulation of tenofovir in plasma is related to the presence of nephrotoxic effects. It is reported that tenofovir presents a volume of distribution of 0.813 L/kg.

Elimination Route

Lamivudine was rapidly absorbed after oral administration in HIV-infected patients. Absolute bioavailability in 12 adult patients was 86% ± 16% (mean ± SD) for the 150-mg tablet and 87% ± 13% for the oral solution. The peak serum lamivudine concentration (Cmax) was 1.5 ± 0.5 mcg/mL when an oral dose of 2 mg/kg twice a day was given to HIV-1 patients. When given with food, absorption is slower, compared to the fasted state.

Tenofovir as the active moiety presents a very low bioavailability when orally administered. Hence, the administration of this active agent is required to be under its two prodrug forms, tenofovir disoproxil and tenofovir alafenamide. This reduced absorption is suggested to be related to the presence of two negative charges among its structure. This negative charge limits its cellular penetration, and its passive diffusion across cellular membranes and intestinal mucosa hindering its availability for oral administration.

Intravenous tenofovir has been shown to produce a maximum plasma concentration of 2500 ng/ml with an AUC of 4800 ng.h/ml.

Half Life

5 to 7 hours (healthy or HBV-infected patients)

The reported half-life of tenofovir is of 32 hours.

Clearance

Renal clearance = 199.7 ± 56.9 mL/min [300 mg oral dose, healthy subjects]
Renal clearance = 280.4 ± 75.2 mL/min [single IV dose, HIV-1-infected patients]
Total clearance = 398.5 ± 69.1 mL/min [HIV-1-infected patients]

The clearance of tenofovir is highly dependent on the patient renal stage and hence the clearance rate in patients with renal impairment is reported to be of 134 ml/min while in patients with normal function the clearance rate can be of 210 ml/min.

Elimination Route

The majority of lamivudine is eliminated unchanged in urine by active organic cationic secretion. 5.2% ± 1.4% (mean ± SD) of the dose was excreted as the trans-sulfoxide metabolite in the urine. Lamivudine is excreted in human breast milk and into the milk of lactating rats.

Tenofovir is eliminated in the urine by tubular secretion and glomerular filtration. The elimination of this compound is driven by the activity of the human organic anion transporters 1 and 3 and its secretion is mainly ruled by the activity of the multidrug resistance-associated protein 4.

Pregnancy & Breastfeeding use

There is no adequate and well-controlled study in pregnant women. Lamivudine should be used during pregnancy only if the potential benefits outweigh the risks. Although it is not known if lamivudine is excreted in human milk, there is the potential for adverse effects from lamivudine in nursing infants. Mothers should be instructed not to breast feed if they are receiving lamivudine.

Pregnancy: Pregnancy category B. It should be used during pregnancy only if clearly needed.

Lactation: It is not known whether it is excreted in human milk. Mothers should be instructed not to breast feed if they are taking Tenofovir.

Contraindication

Lamivudine is contraindicated in patients hypersensitive to any of the components of the product.

Tenofovir is contraindicated in patients with known hypersensitivity to Tenofovir or any component of the product.

Special Warning

It is recommended that doses of Lamivudine should be adjusted in accordance with renal function. Dosage adjustment of Lamivudine in accordance with creatinine clearance is as follows:

CrCl 50 ml/min: 100 mg once daily
CrCl 30-49 ml/min: 100 mg first dose, then 50 mg once daily
CrCl 15-29 ml/min: 100 mg first dose, then 25 mg once daily
CrCl 5-14 ml/min: 35 mg first dose, then 15 mg once daily
CrCl <5 ml/min: 35 mg first dose, then 10 mg once daily

Use in children: Safety and efficacy of lamivudine for the treatment of chronic hepatitis B in children have not been established.

Pediatric use: Safety and effectiveness of Tenofovir in pediatric patients below the age of 18 years have not been established.Geriatrics use: Clinical studies of Tenofovir did not include sufficient numbers of subjects aged 65 years and over to determine whether they respond differently from younger subjects. But care should be taken in dose selection, and it may be useful to monitor renal function.Renal Impairment: Haemodialysis patients: 300 mg once every 7 days or after a cumulative total of 12 hr of dialysis.

CrCl (10-29 mL/min): 300 mg 72-96 hrly.
CrCl (30-49 mL/min): 300 mg 48 hrly.

Hepatic impairment

: No dose adjustment is required in patients with hepatic impairment.