Telbivudine is a synthetic thymidine nucleoside analogue with activity against hepatitis B virus (HBV). Telbivudine is the unmodified β–L enantiomer of the naturally occurring nucleoside, thymidine. It undergoes phosphorylation via interaction with cellular kinases to form the active metabolite, telbivudine 5'-triphosphate.

Telbivudine 5'–triphosphate inhibits HBV DNA polymerase (reverse transcriptase) by competing with the natural substrate, thymidine 5'–triphosphate. This leads to the chain termination of DNA synthesis, thereby inhibiting viral replication. Incorporation of telbivudine 5'–triphosphate into viral DNA also causes DNA chain termination, resulting in inhibition of HBV replication. Telbivudine inhibits anticompliment or second-strand DNA.

Chronic Hepatitis B: Telbivudine is indicated for the treatment of chronic hepatitis B in adult patients with evidence of viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease. The following points should be considered when initiating therapy with Telbivudine:

• This indication is based on virologic, serologic, biochemical and histologic responses in nucleoside treatment naïve adult patients with HBeAg positive and HBeAg negative chronic hepatitis B with compensated liver disease 
• For HBeAg-positive patients, Telbivudine should only be initiated in patients with HBV DNA less than 9 log10 copies per mL and ALT greater than or equal to 2x Upper Limit of Normal (ULN) prior to treatment.
• For HBeAg-negative patients, Telbivudine should only be initiated in patients with HBV DNA less than 7 log10 copies per mL prior to treatment.
• On-treatment response should guide continued therapy 
• Telbivudine has not been evaluated in patients co-infected with HIV, HCV or HDV.
• Telbivudine has not been evaluated in liver transplant recipients or in patients with decompensated liver disease.
• Telbivudine has not been studied in well-controlled trials for the treatment of patients with established nucleoside analog reverse transcriptase inhibitor-resistant hepatitis B virus infection, but is expected to be cross-resistant to lamivudine.

Adults and Adolescents (16 years of age and older): Due to higher rates of resistance that may develop with longer term treatment among patients with incomplete viral suppression, treatment should only be initiated, if pre-treatment HBV DNA and ALT measurements are known, in the following patient populations-

For HBeAg-positive patients, HBV DNA should be less than 9 log10 copies per mL and ALT should be greater than or equal to 2x ULN prior to treatment with Telbivudine.

For HBeAg-negative patients, HBV DNA should be less than 7 log10 copies per mL prior to treatment with Telbivudine.

HBV DNA levels should be monitored at 24 weeks of treatment to assure complete viral suppression (HBV DNA less than 300 copies per mL). Alternate therapy should be initiated for patients who have detectable HBV DNA after 24 weeks of treatment. Optimal therapy should be guided by further resistance testing.

The recommended dose of Telbivudine for the treatment of chronic hepatitis B: 600 mg once daily, taken orally, with or without food. Telbivudine Oral Solution (30 mL) may be considered for patients who have difficulty with swallowing tablets.

Hypersensitivity. Combination of Telbivudine with pegylated interferon alfa-2a is contraindicated because of increased risk of peripheral neuropathy

Cough, dizziness, fatigue, GI effects (e.g. abdominal pain, diarrhoea, nausea, vomiting, dyspepsia), rash, arthralgia, myalgia, myopathy, malaise, back pain, nasopharyngitis, headache, flu or flu-like symptoms, insomnia; increased serum amylase, lipase, creatine phosphokinase, alanine aminotransferase levels; peripheral neuropathy, rhabdomyolysis.

Severe acute exacerbations of hepatitis B. Monitor hepatic function in discontinued therapy. Lactic acidosis, severe hepatomegaly with steatosis, myopathy, rhabdomyolysis, uncomplicated myalgia. Discontinue if myopathy is diagnosed. Increased risk of peripheral neuropathy when combined with pegylated interferon α-2a. Decompensated cirrhosis, renal impairment or on hemodialysis; liver transplant recipients or under immunosuppressant therapy. May impair the ability to drive or operate machinery. Pregnancy. Childn <16 yr. Elderly.

Pregnancy & Lactation

Pregnancy Category B. Telbivudine is not teratogenic and has shown no adverse effects in developing embryos and fetuses in preclinical studies. Studies in pregnant rats and rabbits showed that telbivudine crosses the placenta. Developmental toxicity studies revealed no evidence of harm to the fetus in rats and rabbits at doses up to 1000 mg per kg per day, providing exposure levels 6- and 37-times higher, respectively, than those observed with the 600 mg per day dose in humans.

There are no adequate and well-controlled trials of Tyzeka in pregnant women. Because animal reproductive toxicity studies are not always predictive of human response, Tyzeka should be used during pregnancy only if potential benefits outweigh the risks.