Early virologic failure in HIV-1 infected subjects on didanosine/tenofovir/efavirenz: 12-week results from a randomized trial.
OBJECTIVE
To compare the safety and efficacy of two once-daily antiretroviral regimens containing lamivudine (3TC) or tenofovir disoproxil fumarate (TDF), each administered with didanosine (ddI) and efavirenz (EFV) as initial therapy to HIV-1-infected subjects.


METHODS
Single centre, randomized (1: 1), open-label study in antiretroviral-naive, HIV-infected adults. Subjects commenced either 3TC/ddI/EFV (3TC group) or TDF/ddI/EFV (TDF group). Safety, Medication Event Monitoring System (MEMScap) and plasma EFV concentration monitoring was performed over the study period. Comparisons between groups were assessed using chi test and linear regression analysis was used to assess the relationship between EFV concentrations and virological response.


RESULTS
Seventy-seven subjects were enrolled prior to recruitment being suspended, 36 to the 3TC group and 41 to the TDF group. Intention-to-treat analysis in which last observation carried forward (LOCF) found the mean viral log10 load [95% confidence interval (CI)] at weeks 4 and 12 to be 2.67 (2.47-2.87) and 1.83 (1.74-1.92) for the 3TC group and 2.75 (2.45-3.05) and 2.28 (1.96-2.6) for the TDF group (P = 0.013). Emergence of resistance occurred in five of 41 (12.2%) subjects in the TDF group up to week 12 compared with none of 36 in the 3TC group, (P < 0.05); these five subjects shared similar baseline characteristics (CD4+ cell counts < 200 x 10 cells/l and HIV-1 RNA > 100,000 copies/ml). Despite MEMScap monitoring showing > 99% adherence in all subjects, among the five failures, three had low EFV concentrations.


CONCLUSIONS
TDF/ddI/EFV as initial therapy appears to have diminished efficacy in subjects with CD4 < 200 x 10 cells/l and viral load > 100,000 copies/ml. Treatment failure with resistance was not attributable to baseline resistance, efavirenz exposure or poor adherence.
Chelsea and Westminster Hospital, London, UK. desmond.maitland@btinternet.com
Desmond
D
Maitland
Graeme
G
Moyle
James
J
Hand
Sundhiya
S
Mandalia
Marta
M
Boffito
Mark
M
Nelson
Brian
B
Gazzard
D000225:Adenine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D000328:Adult; D000480:Alkynes; D019380:Anti-HIV Agents / Q000008:administration & dosage*; D048588:Benzoxazines; D003521:Cyclopropanes; D016049:Didanosine / Q000008:administration & dosage*; D004338:Drug Combinations; D005260:Female; D015658:HIV Infections / Q000188:drug therapy*; D015497:HIV-1; D006801:Humans; D008297:Male; D008875:Middle Aged; D063065:Organophosphonates / Q000008:administration & dosage*; D010078:Oxazines / Q000008:administration & dosage*; D000068698:Tenofovir; D017211:Treatment Failure
D000480:Alkynes; D019380:Anti-HIV Agents; D048588:Benzoxazines; D003521:Cyclopropanes; D004338:Drug Combinations; D063065:Organophosphonates; D010078:Oxazines; D000068698:Tenofovir; D000225:Adenine; C098320:efavirenz; D016049:Didanosine