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The use of virtual inhibitory quotient (VIQ) in antiretroviral (ART) experienced patients taking amprenavir/lopinavir combinations
Conference presentation

The use of virtual inhibitory quotient (VIQ) in antiretroviral (ART) experienced patients taking amprenavir/lopinavir combinations

E. Phillips, A. Tseng, S. Walker, M. Loutfy, S. Walmsley, S. Tailor and P.R. Harrigan
9th Conference on Retroviruses and Opportunistic Infections (Seattle, U.S.A, 24/02/2002–28/02/2002)
2002
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Abstract

Background: There is increasing evidence to suggest that drug levels of protease inhibitors (Pis) correlate with virologic outcome. The appropriate application of VIQ (C min/(virtual phenotype [VP] fold change x protein corrected EC 50 for wildtype) has not been defined. VIQ may be a more useful measurement than drug levels alone in ART experienced patients since it incoporates VP as a measure of drug resistance. Methods: To explore relationships between VIQ and virologic outcome, we measured pre- and post-PI levels in 16 ART, PI-experienced patients who had been tolerating amprenavir/lopinavir/ritonavir combinations for at least 3 months (median = 5 months, median baseline viral load [VL] = 107,035 copies/mL). VIQs were calculated from the VPs of amprenavir and lopinavir prior to starting therapy (VIRCO, UK) and the measured C min of amprenavir and lopinavir, respectively. Results: 6/16 patients had a nondetectable VL (<50 copies/mL) at the time levels were measured while 10/16 had VL > 50 copies/mL. The median Cmins for amprenavir and lopinavir were 1085 ng/mL (219-1997 ng/mL) and 3272 ng/ml (1901-6553 ng/mL) respectively. For amprenavir the median VIQ was significantly higher in the group with VL < 50 copies/mL (VIQ = 2.58 [1-9.08]) vs those with VL > 50 copies/mL (VIQ = 0.62 [0.03-2.25]), p=0.013 (Mann Whitney U). For lopinavir there was a trend towards a higher median VIQ in the group with VL < 50 copies/mL (VIQ = 12.2 [2.73-112.7]) vs those with VL > 50 (VIQ = 1.82 [0.33-11.4]), p=0.076 (Mann Whitney U). 83% (5/6) of those with undetectable VLs (<50 copies/mL) had lopinavir VIQ > 15 and/or amprenavir VIQ > 1.3 vs only 2/10 (20%) of those with VL > 50 copies/mL (p=0.01, chi). Conclusions: For treatment experienced patients initiating amprenavir/lopinavir combinations, VIQ may be a potentially useful tool to identify those at risk for treatment failure with conventional dosing.

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