Zovirin

Uses

Zovirin is used for the treatment of chronic hepatitis C (CHC) virus infection in combination with other antiviral drugs in patients with compensated liver disease not previously treated with interferon alpha and in adult CHC patients coinfected with HIV. Zovirin should not be used alone.

Zovirin is also used to associated treatment for these conditions: Chronic Hepatitis C Virus (HCV) Infection, Severe Respiratory Syncytial Virus Infection

How Zovirin works

Zovirin is reported to have several mechanism of actions that lead to inhibition of viral RNA and protein synthesis. After activation by adenosine kinase to ribavirin mono-, di-, and triphosphate metabolites. Zovirin triphosphate (RTP) is the predominant metabolite which directly inhibits viral mRNA polymerase by binding to the nucleotide binding site of the enzyme. This prevents the binding of the correct nucleotides, leading to a reduction in viral replication or to the production of defective virions . RTP also demonstrates an inhibitory action on viral mRNA guanylyltransferase and mRNA 2′-O-methyltransferase of dengue virus. Inhibition of these enzymes disrupts the posttranslational capping of the 5′ end of viral mRNA through ribavirin being incorporated at the 5′ end in place of guanosine and preventing the cap methylation step.

Inhibition of host inosine monophosphate dehydrogenase (IMPDH) and subsequent depletion of GTP pool is proposed to be another mechanism of action of ribavirin. IMPDH catalyzes the rate-limiting step where inosine 5′-monophosphate is converted to xanthine monophosphate during guanosine monophosphate (GMP) synthesis. GMP is later converted to guanosine triphoshpate (GTP). Zovirin monophosphate mimics inosine 5′-monophosphate and acts as a competitive inhibitor of IMPDH. Inhibited de novo synthesis of guanine nucleotides and decreased intracellular GTP pools leads to a decline in viral protein synthesis and limit replication of viral genomes .

Zovirin acts as a mutagen in the target virus to cause an 'error catastrophe' due to increased viral mutations. RTP pairs with cytidine triphosphate or uridine triphosphate with equal efficiency and to block HCV RNA elongation. It causes premature termination of nascent HCV RNA and increases mutagenesis by producing defective virions .

Zovirin also exerts an immunomodulatory action of the host to the virus by shifting a Th2 response in favor of a Th1 phenotype. Th2 response and production of type 2 cytokines such as IL-4, IL-5, and IL-10 stimulates the humoral response which enhances immunity toward the virus . Zovirin enhanced induction of interferon-related genes, including the interferon-α receptor, and down-regulation of genes involved in interferon inhibition, apoptosis, and hepatic stellate cell activation in vitro .

Dosage

Zovirin dosage

The recommended duration of treatment for patients previously untreated with interferon is 24 to 48 weeks. After 24 weeks of treatment virologic response should be assessed. Treatment discontinuation should be considered in any patient who has not achieved an HCV RNA below the limit of detection of the assay by 24 weeks. There are no safety and efficacy data on treatment for longer than 48 weeks in the previously untreated patient population. In patients who relapse following interferon therapy, the recommended duration of treatment is 24 weeks. There are no safety and efficacy data on treatment for longer than 24 weeks in the relapse patient populations.

Zovirin + Interferon:Genotype Zovirin Daily Interferon alpha-2a Duration or interferon alpha-2b.

• All <75 kg:(400+600) mg 3 MIU 3 times weekly 48 weeks Genotypes subcutaneously (Genotype1&4)
• >75 kg:(600+600) mg 24 weeks (Genotype2&3)

Zovirin + Peg-Interferon:

Genotype Zovirin Daily Peg-Interferon alpha-2a Duration or Peg-interferon alpha-2b:

• 1 & 4 < 75 kg: (400+600) mg 180 gm once weekly 48 weeks
• > 75 kg: (600+600) mg subcutaneously 2 & 3 (400+400) mg 24 weeks

Zovirin may be administered without regard to food, but should be administered in a consistent manner. Drink plenty of water while being treated with this medication; drinking water will decrease the risk of serious side effects.

Side Effects

The most common adverse reactions in adults receiving combination therapy are psychiatric and central nervous system effects, severe ocular disorder, dental and periodontal disorders & growth inhibition in children and adolescents that may be irreversible in some patients. The most common adverse reactions in pediatric subjects were similar to those seen in adults.

Toxicity

Rivabirin and PEG-Interferon Alfa-2A dual therapy is associated with flu-like symptoms, depression, suicide, insomnia, irritability, relapse of drug abuse/overdose, hepatic decompensation in 2% of HIV co-infected patients and bacterial infections each occurring at a frequency of less than 1%. Zovirin-induced anemia is a dose-dependent adverse effect where reduced hemoglobin levels can be seen within the first 1-2 weeks in therapy. The mechanism of ribavirin-induced anemia has been shown to involve reductions in reticulocyte counts and erythrocyte Na-K pump activity, and increases in K-Cl cotransport, membrane bound IgG, and C3, and erythrocyte band 3 . Oral LD50 in rats is 2700 mg/kg. Intraperitoneal LD50 in mouse is 1300 mg/kg. Potential carcinogenic effects of ribavirin to humans cannot be yet excluded as it demonstrates mutagenic activity in the in vitro mouse lymphoma assay.

Precaution

Birth defects and fetal death with ribavirin: Do not use in pregnancy and for 6 months after treatment. Patients must have a negative pregnancy test prior to therapy, use at least 2 forms of contraception and undergo monthly pregnancy tests. For a male patient, it is very important for his female partner to avoid becoming pregnant during treatment and during the 7 months after treatment and do not have sex with a pregnant women.

Interaction

Nucleoside reverse transcriptase inhibitors or reduce dose or discontinue interferon, ribavirin or both with worsening toxicities

Azathioprine: Concomitant use of azathioprine with ribavirin has been reported to induce severe pancytopenia and may increase the risk of azathioprine-related myelotoxicity.

Food Interaction

• Avoid alcohol. Zovirin is used to treat chronic hepatitis C infection; ingesting alcohol may worsen this infection.
• Take with food. Taking ribavirin with a high-fat meal slows the absorption and increases the AUC and Cmax of ribavirin.

[Moderate] ADJUST DOSING INTERVAL: Food enhances the oral absorption and bioavailability of ribavirin.

Administration of a single oral dose of ribavirin following a high-fat meal delayed absorption (Tmax was doubled) but increased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) by up to 70% compared to administration in the fasting state.

MANAGEMENT: To ensure maximal oral absorption, ribavirin should be administered with or immediately after a meal.

Zovirin Disease Interaction

Major: anemia, mechanical ventilation, pulmonary deterioration, renal dysfunction

Volume of Distribution

Zovirin displays a large volume of distribution .

Elimination Route

Zovirin is reported to be rapidly and extensively absorbed following oral administration. The average time to reach Cmax was 2 hours after oral administration of 1200 mg ribavirin . The oral bioavailability is 64% following a single oral dose administration of 600mg ribavirin .

Half Life

The terminal half-life of ribavirin following administration of a single oral dose of 1200 mg is about 120 to 170 hours .

Clearance

The total apparent clearance rate after a single oral dose administration of 1200 mg ribavirin is 26L/h .

Elimination Route

The metabolites of ribavirin are renally excreted. After the oral administration of 600mg radiolabeled ribavirin, approximately 61% of the drug was detected in the urine and 12% was detected in the feces. 17% of administered dose was in unchanged form .

Pregnancy & Breastfeeding use

Pregnancy Category X. Zovirin produced significant embryocidal and/or teratogenic effects in all animal species in which adequate studies have been conducted. Malformations of the skull, palate, eye, jaw, limbs, skeleton and gastrointestinal tract were noted. The incidence and severity of teratogenic effects increased with escalation of the drug dose. Survival of fetuses and offspring was reduced.

Nursing Mothers: It is not known whether Zovirin is excreted in human milk. Because many drugs are excreted in human milk and to avoid any potential for serious adverse reactions in nursing infants from ribavirin, a decision should be made either to discontinue nursing or therapy with Zovirin, based on the importance of the therapy to the mother.

Contraindication

Women who are pregnant. Zovirin may cause fetal harm when administered to a pregnant woman. Zovirin is contraindicated in women who are or may become pregnant. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus. Patients with hemoglobinopathies (e.g., thalassemia major or sickle-cell anemia). In combination with didanosine. Reports of fatal hepatic failure, as well as peripheral neuropathy, pancreatitis and symptomatic hyperlactatemia/lactic acidosis have been reported in clinical trials.

Special Warning

Pediatric Use: Safety and effectiveness of Zovirin in combination with Peginterferon has not been established in pediatric patients below the age of 3 years.

Geriatric Use: The risk of toxic reactions to this drug may be greater in patients with impaired renal function. The dose of Zovirin should be reduced in patients with creatinine clearance less than or equal to 50 ml/min; and the dose of Interferon should be reduced in patients with creatinine clearance less than 30 ml/min.

Storage Condition

Keep out of the reach of children. Keep in a cool & dry place. Protect from light.

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