Beta-l-thymidine

Uses

Chronic Hepatitis B: Beta-l-thymidine is used 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 Beta-l-thymidine:

• 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, Beta-l-thymidine 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, Beta-l-thymidine 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
• Beta-l-thymidine has not been evaluated in patients co-infected with HIV, HCV or HDV.
• Beta-l-thymidine has not been evaluated in liver transplant recipients or in patients with decompensated liver disease.
• Beta-l-thymidine 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.
• The safety and efficacy of Beta-l-thymidine have not been evaluated in Black/African American or Hispanic patients

Beta-l-thymidine is also used to associated treatment for these conditions: Hepatitis B Chronic Infection

How Beta-l-thymidine works

Beta-l-thymidine 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. Beta-l-thymidine inhibits anticompliment or second-strand DNA.

Dosage

Beta-l-thymidine dosage

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 log10copies per mL and ALT should be greater than or equal to 2x ULN prior to treatment with Beta-l-thymidine.

For HBeAg-negative patients, HBV DNA should be less than 7 log10copies per mL prior to treatment with Beta-l-thymidine.

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

Side Effects

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.

Toxicity

There is no information on intentional overdose of telbivudine, but one subject experienced an unintentional and asymptomatic overdose. Healthy subjects who received telbivudine doses up to 1800 mg/day for 4 days had no increase in or unexpected adverse events. A maximum tolerated dose for telbivudine has not been determined.

Precaution

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.

Interaction

Altered plasma concentration with drugs that affect renal function (e.g. aminoglycosides, loop diuretics, platinum compounds, vancomycin, amphotericin B). May increase risk of myopathy with other drugs associated with myopathy (e.g. azole antifungals, ciclosporin, corticosteroids, erythromycin, fibrates, HMG-CoA reductase inhibitors, penicillamine, zidovudine).

Food Interaction

• Take with or without food. The absorption is unaffected by food.

Beta-l-thymidine Drug Interaction

Major: interferon alfa-2b, peginterferon alfa-2bModerate: lithiumUnknown: aspirin, aspirin, amoxicillin / clavulanate, sulfamethoxazole / trimethoprim, ubiquinone, copper gluconate, glucose, ethanol, glycerin, heparin, arginine, levocarnitine, cysteine, acetaminophen / hydrocodone, acetaminophen, omeprazole, tramadol

Beta-l-thymidine Disease Interaction

Major: myopathyModerate: hemodialysis, renal dysfunction

Elimination Route

Absorbed following oral administration. Beta-l-thymidine absorption and exposure were unaffected when a single 600–mg dose was administered with a high–fat (~55 g), high–calorie (~950 kcal) meal.

Half Life

Approximately 15 hours.

Clearance

• 7.6 +/- 2.9 L/h [Normal renal function (Clcr>80 mL/min)]
• 5.0 +/- 1.2 L/h [Mild renal function impairement (Clcr=50-80 mL/min)]
• 2.6 +/- 1.2 L/h [Moderate renal function impairement (Clcr=30-49 mL/min)]
• 0.7 +/- 0.4 L/h [Severe renal function impairement (Clcr<30 mL/min)]

Elimination Route

Beta-l-thymidine is eliminated primarily by urinary excretion of unchanged drug.

Pregnancy & Breastfeeding use

Pregnancy Category B. Beta-l-thymidine 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.

Contraindication

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

Storage Condition

Store Beta-l-thymidine Tablets and Oral Solution in the original bottle at room temperature (15° to 30°C)

Innovators Monograph

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