Nigeria has become the third country to halt clinical trials of the antiretroviral (ARV) drug tenofovir as a prophylactic against HIV after the US-based supervisor of the trials found that proper standards were not being observed. "Regrettably, the tenofovir study in Nigeria will not be continuing because FHI has determined that the study team is not at this point able to comply with all of the standards that have been established for conducting this study," Family Health International (FHI) said in a statement earlier this month.