How telbivudine works
Telbivudine is a highly selective inhibitor of the hepatitis B virus (HBV). It prevents viral multiplication by interfering with DNA synthesis, specifically by blocking the virus’ DNA polymerase (the enzyme that is essential for DNA replication).
In addition to interfering with DNA synthesis, telbivudine is known to target misfolded superoxide dismutase (SOD1), a protein that is implicated in ALS.
About 10% to 20% of familial ALS and 1% to 2% of sporadic ALS cases are caused by a mutation in the SOD1 gene, which carries the instructions to make the SOD1 protein. This protein is responsible for clearing the highly reactive and unstable molecules called free radicals and prevents them from causing damage to the cells.
Although it is unclear how mutations in the SOD1 gene cause ALS, research in both animal models of ALS and humans have shown that they cause the SOD1 protein to fold incorrectly and form toxic aggregates inside cells.
It is known that zebrafish expressing the ALS-causing variant of the SOD1 gene exhibit ALS-like symptoms such as degeneration of motor neurons and functional problems such as swimming deficits. A study published in Neurobiology of Disease showed that in such zebrafish models, treatment with telbivudine alleviates motor neuron damage and improves swimming in a dose-dependent manner.
Telbivudine in clinical trials
The development process of telbivudine for the treatment of ALS is in its infancy, and no clinical studies have yet been conducted. However, several clinical trials testing telbivudine have validated its safety in humans.
In a Phase 3 clinical trial (NCT00057265), researchers found that most of the adverse events reported were mild and transient among 680 chronic hepatitis B patients, ages 16–70, receiving 600 mg of telbivudine once daily for 52 weeks. The most common adverse effects were nose and throat infections followed by fatigue and headache. Some serious side effects were also reported, the most common being elevated creatinine kinase levels that indicated heart or muscle injury. Myopathy (muscle pain and weakness) and liver failure were also noted.
A Phase 1 study (NCT00907894) investigated the safety of a single oral dose of telbivudine in children and adolescents with chronic hepatitis B infection. A total of 23 patients were included in the study. Of those, 15 were between 2 and 12, while eight were between 12 and 18. The adolescents received a daily dose of 600 mg of telbivudine, and the children received 15 mg or 25 mg per kg of their body weight, to a maximum dose of 600 mg. The patients were monitored for six days after the treatment, which was found to be well-tolerated by both study groups with mild adverse events reported in four patients. These included malaise, itchy skin, protein in the urine, and skin lesions.
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