Fosdevirine

The World Health Organization has estimated that as many as 10% of the population worldwide may at some point experience at least one seizure. The percentage with active epilepsy is from 0.4% to 1%. From 40% to 65% of patients with HIV infection have been estimated to have some neurological involvement; the percentage reaches as high as 70% to 80% when post-mortem assessments are included. Estimates of the percentage of HIV-infected patients with seizure occurrence have varied widely, with one review finding a range from 2% to 20%. The highest percentage in this range was reported at a center that exclusively treated patients with neurological involvement, in India where HIV clade C subtype is predominant. Query of another neurology department's database determined that of the HIV-infected patients treated at the center, all of whom were referred for neurological symptoms, 6.1% experienced seizures. Underlying neurologic diseases in these patients included HIV-associated encephalopathy, progressive multifocal leukoencephalopathy, and toxoplasmosis. In a Spanish population, 3% of HIV-infected patients over a one-year study period were found to have new-onset seizures, which were attributed to drug toxicity in 47%, intracranial lesions in 35%, and metabolic derangements in 12%.
Drug-discontinuation studies, magnetic resonance imaging studies, and animal studies have produced recent evidence that some antiretroviral therapies may have neurotoxic effects, warranting further research. Individuals who are treated with highly active antiretroviral therapy are at risk for immune reconstitution inflammatory syndrome (IRIS), in which immune recovery triggers clinical deterioration as the newly invigorated immune system reacts to pathogens that either represent ongoing opportunistic infection or were previously successfully controlled. In a population initiating combination antiretroviral therapy between 1999 and 2007, 0.9% developed neurological manifestations of IRIS. Seizures may occur as part of a neurological IRIS syndrome, such as encephalitis and toxoplasmosis.
Two randomized, Phase 2b dose-finding studies were conducted in HIV-1 infected adults to compare GSK2248761 100 mg and 200 mg given once daily as part of an antiretroviral treatment regimen. One of the studies (SGN113399) was in subjects with prior exposure to antiretroviral therapy where GSK2248761 100 mg and 200 mg once daily were compared to determine the best dose in this population. A contemporary control arm receiving etravirine 200 mg twice daily was also included, and all arms included a twice-daily background therapy consisting of darunavir/ritonavir 600 mg/100 mg plus raltegravir 400 mg. The other study (SGN113404) was in treatment-naïve subjects, comparing GSK2248761 100 mg and 200 mg once daily to determine the best dose in this population. A contemporary control arm receiving efavirenz 600 mg once daily was also included, and all arms were given background therapy selected by investigators from either once-daily abacavir/lamivudine 600 mg/300 mg or tenofovir/emtricitabine 300 mg/200 mg. Of a planned total population in both studies of 300 subjects, 35 were enrolled before the studies were terminated because of the occurrence of seizures in five subjects. All of the subjects who experienced seizures were enrolled into SGN113399, four randomized to receive 200 mg GSK2248761 and one randomized to receive 100 mg GSK2248761. There were no seizures in the subjects receiving GSK2248761 in study SGN113404. At the time of study termination, subjects had been enrolled and received GSK2248761 at 19 sites in four countries: France, Romania, United States, and Germany. Although potential contributory conditions have been identified in some cases, definitive causative factors for the seizure occurrence have not been established.
The purpose of this study is to follow subjects who previously received GSK2248761 while enrolled in the Phase 2b studies, which were halted due to unexpected seizures. The study will collect data on all subjects and will be used to monitor for additional seizures as well as collect additional clinical data on all subjects.

This is a single-center, open-label, three-period, fixed-sequence cross over study in healthy adult subjects. A total of approximately 16 healthy subjects will be enrolled to provide data from 12 evaluable subjects. Subjects will have a screening visit within 30 days prior to the first dose of study drug, three treatment periods, and a follow-up visit 7-14 days after the last dose of study drug. There will be a washout period between Period 1 and Period 2 but no washout between Period 2 and Period 3. Day 1 of Period 3 will be the day after Day 5 of Period 2.