Drug Interactions between foscarbidopa / foslevodopa and telbivudine

MONITOR: Polyneuropathy has been reported during treatment with levodopa/carbidopa combinations, and concurrent use of other medications that are also associated with this adverse effect may potentiate the risk and/or severity of nerve damage. Polyneuropathy has most commonly been observed in patients receiving levodopa/carbidopa by continuous intestinal infusion, with a frequency of up to 5.8% in clinical trials. Cases were generally consistent with axonal polyneuropathy, manifested as sensory or sensorimotor neuropathies, with subacute or chronic onset. Reported symptoms primarily included numbness, tingling, decreased sensation, weakness, and pain in the legs, hands, feet, and extremities. Many of these patients had deficiencies in folic acid, vitamin B12 and vitamin B6 as well as elevated homocysteine levels. However, there was insufficient information to determine the potential role of vitamin deficiencies in the etiology of neuropathy associated with the treatment. It is also unknown whether there is a causal relationship between polyneuropathy and treatment with levodopa/carbidopa combinations.

MANAGEMENT: Before initiating treatment with enteral formulations of levodopa/carbidopa, the manufacturers recommend evaluating patients for history or signs of polyneuropathy and known risk factors such as diabetes mellitus, hypothyroidism, or concomitant use of other medications associated with polyneuropathy. For patients with preexisting polyneuropathy, the benefits of treatment should be carefully weighed against the potential risks, including the potential for impaired mobility. Plasma concentrations of vitamin B12, vitamin B6, homocysteine, methylmalonic acid, and folic acid should be obtained at baseline and at regular intervals during treatment. Patients who develop symptoms of peripheral neuropathy and low plasma concentrations of vitamin B6 and/or vitamin B12, or elevated homocysteine or methylmalonic acid concentrations, may benefit from vitamin supplementation. Physicians should carefully evaluate if a dose adjustment is warranted and assess the benefit versus risk of continued treatment.