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Influence of dosing regimen on adherence to antiretroviral therapy within PI and NNRTI regimens

Herrmann, S.E., McKinnon, E., John, M. and Mallal, S. (2007) Influence of dosing regimen on adherence to antiretroviral therapy within PI and NNRTI regimens. In: 4th International AIDS Conference on HIV Pathogenesis, Treatment and Prevention, 22 - 25 July, Sydney, Australia


Objectives: To determine whether medication adherence and HIV RNA viral load differed between patients grouped by treatment with PIs or NNRTIs on once daily (OD) vs twice daily (BD) antiretroviral therapy (ART).

Methods: Clinical information from the WA HIV Cohort is collated electronically. We previously validated a “medication score” calculated as percentage of prescribed tablets taken over the past 4 weeks. Scores are collated with clinical markers in the database and hard copy output allows visualisation of longitudinal treatment and adherence data. Data was collected on 415 patients on OD or BD regimens (2900 visits: mean visits/person=7; PI: 298/1380(22%) OD; NNRTI: 328/1520(22%) OD), from June 2003 to Dec 2006. Analyses of medication adherence (score of 100%) and viral suppression (<50 cps/ml) were undertaken by longitudinal logistic modeling to accommodate unbalanced follow-up.

Results: Complete adherence was reported at 75% of visits. In patients on PI-based therapies there was no significant difference in adherence in OD compared with BD regimens (OR=1.07, p=0.7). In contrast, for patients on NNRTI therapy adherence was significantly better amongst those on OD regimens (OR=2.96, p<0.0001). Viral suppression was observed at 80% of visits where patients had been on HAART for at least 6 mths. The strongest predictor of VL>50 was CD4 count <200 (p<0.0001). Amongst patients on a NNRTI-based regimen neither calendar time nor number of daily doses were associated with viral suppression (p>0.7). Amongst patients on PIs, suppression was reduced for OD dosing, particularly in earlier years (pre-2006: OR=1.85, p=0.04; 2006: OR=1.47, p=0.3).

Conclusions: Once daily dosing was correlated with improved adherence in patients on NNRTI regimens but not in those on PIs. Patient satisfaction with OD ART dosing may have resulted in greater adherence in the NNRTI group, however, in the PI group patient and prescribers’ preference may be for the extra ‘forgiveness’ that a twice daily regimen can provide.

Item Type: Conference Paper
Murdoch Affiliation(s): Centre for Clinical Immunology and Biomedical Statistics
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