10th Anniversary Conference Of The British HIV Association [BHIVA] 15 – 17 April 2004, City Hall, Cardiff, UK

[AUTHOR(S):] S Taylor¹, S Allen², E Smit³, S Fidler⁴, S Gibbons⁵ S Drake¹, A Wade², P Cane³, J Fox⁴, DJ Back^5
1 Birmingham Heartlands Hospital, ² Coventry and Warwickshire Hospital, ³ Health Protection Agency, Birmingham Heartlands Hospital, ⁴ Imperial College London, ⁵ University of Liverpool, UK

BHIVA Conf 2004 Apr 15-17;10:O6

BACKGROUND: Current antiretroviral drugs differ in their relative plasma elimination half-lives (t_1/2). The reported EFV t_1/2 is 40–55 hours. Therefore, EFV concentrations may persist at therapeutic levels for greater than 1 week following discontinuation. If drugs with a shorter t_1/2 are stopped at the same time as EFV, patients will effectively be receiving monotherapy for a significant period of time.

METHODS: 10 HIV-1+ patients took part in a pharmacokinetic (PK) study. Blood was drawn at baseline (day 0) and at days 4, 7, 14 and 21 after stopping EFV. Plasma samples were analysed for EFV concentrations by high-performance liquid chromatography and T_1/2 determined by regression analysis. Viral RNA ± resistance testing was performed at each time point. A further 25 patients who stopped EFV after short-course antiretroviral therapy following seroconversion were assessed to obtain virological data on patients stopping EFV 7 days prior to nucleoside reverse transcriptase inhibitors (NRTIs). Resistance testing was performed before antiretroviral therapy and 4 weeks after stopping EFV.

RESULTS: Five patients had EFV T_1/2 within the expected range. However, five had EFV T_1/2 >100 hours (median 123, range 114-229). Four of these were black African women and three had therapeutic EFV >1000 ng/ml 2 weeks after stopping EFV. Of the 25 patients in the virological study only one had resistance 4 weeks after stopping treatment.

CONCLUSION: Virological data from persons fully suppressed at the time of stopping therapy suggest EFV can be stopped 7 days before other shorter-acting drugs. These extended PK data suggest the stop window should be increased to 2–3 weeks (or switch from EFV to cover this).

PRESENTING AUTHOR: S Taylor

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