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Alan Franciscus
HCV Advocate

Tuesday, January 29, 2013

FDA Hepatitis Update - Tyzeka (telbivudine) label revisions

On January 28, 2013, FDA approved revisions to the Tyzeka (telbivudine) label to include long-term safety and efficacy data for subjects previously enrolled in the original two year GLOB and NV02B-015 trials who continued telbivudine treatment for up to 208 weeks.

Tyzeka is an HBV nucleoside analogue reverse transcriptase inhibitor 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 major label changes are summarized below.

Section 6 Adverse Reactions

Results at 208 Weeks
After 104 weeks of blinded therapy in trials 007 GLOBE and NV-02B-015, 667 subjects received Tyzeka in an open-label extension trial, CLDT600A2303.  Of those initially randomized to Tyzeka therapy, 78% of subjects (530/680) from trial 007 GLOBE and 82% (137/167) of subjects from trial NV-02B-015 enrolled into the extension trial and continued Tyzeka treatment for up to 208 weeks. The long-term Tyzeka safety population in trial CLDT600A2303 consisted of 655 subjects, including 518 subjects from trial 007 GLOBE and 137 subjects from trial NV-02B-015.

The overall safety profile from the pooled analysis up to 104 and 208 weeks was similar. Grade 3/4 creatine kinase (CK) elevations occurred in 16% of subjects (104/655) treated with Tyzeka in trial CLDT600A2303. Most grade 3/4 CK elevations were asymptomatic (74% of subjects without any muscle related adverse reaction) and transient (98% of episodes lasted one or two visits (visit interval 2 - 12 weeks) and 87% of subjects had one or two episodes). Most grade 3/4 CK elevations (93%) resolved spontaneously or returned to baseline levels. Two cases of myopathy and two cases of myositis were reported in the 655 Tyzeka-treated subjects.

Among the cohort of 655 subjects continuing Tyzeka for up to 208 weeks in trial CLDT600A2303, including the subgroup of patients (n=223) with mild renal impairment (eGFR  60-90 mL per min) at baseline, mean estimated Glomerular filtration rate (GFR) assessed by MDRD did not decline.

Section 12.4 Microbiology: Antiviral Activity

Transient reductions in HIV-1 RNA have been seen in some patients after administration of telbivudine in the absence of antiretroviral therapy. The clinical significance of these reductions has not been determined. 

Trial CLDT600A2303: After 2 years of Tyzeka monotherapy in the 007 GLOBE trial, 77% (505/656) of subjects entered the open-label CLDT600A2303 extension trial to continue Tyzeka for up to 2 additional years, including 349 subjects who had undetectable levels of HBV DNA and 156 subjects who were viremic at entry. The rtM204I/V substitution was detectable in the virus from 83% (39/47) of the subjects losing viral suppression and having evaluable genotypic data. Of evaluable viremic subjects entering the extension, 25/33 (76%) developed rtM204I/V substitutions. Overall, 64 subjects developed genotypic resistance to Tyzeka with evidence of emerging rtM204I/V substitutions during the 2 years of Tyzeka treatment in this extension trial.

Subjects with higher baseline viral load had higher rates of genotypic resistance to Tyzeka, while subjects who achieved HBV DNA levels less than 300 copies per mL at Week 24 had lower rates of genotypic resistance to Tyzeka. The cumulative frequency of genotypic resistance (emergence of the rtM204I/V substitution) to Tyzeka in nucleos(t)ide treatment-naïve subjects was 7% and 22% at Weeks 52 and 104 of the controlled 007 GLOBE trial, and 30% and 35% at Weeks 156 and 208 of the open-label extension trial (CLDT600A2303), respectively (Table 5).

One-hundred-sixty-seven subjects (25% of those in the 007 GLOBE trial) were treated with Tyzeka according to current dosing recommendations [see Indications and Usage (1.1)]. Eighty-four percent (140/167) of these subjects qualified at 24 weeks for continued Tyzeka treatment (HBV DNA less than 300 copies per mL). Retrospective calculation of the cumulative rate of genotypic resistance to Tyzeka for this subgroup of subjects was 0%, 3%, 12%, and 16% at Weeks 52, 104, 156, and 208, respectively.
The complete revised label can be viewed at Drugs@FDA.

Tyzeka is a product of Novartis.
Richard Klein
Office of Special Health Issues
Food and Drug Administration
Kimberly Struble
Division of Antiviral Drug Products
Food and Drug Administration

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