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Amprenavir "908" prodrug once & twice a day with Efavirenz.
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As you know amprenavir, as currently administerd, is 8 pills twice per day,
and has GI side effects. In order to address these limitations, GSK has
developed a new formulation of amprenavir called the "908" prodrug. It will
be taken 2 pills twice per day. 908 is being studied in once & twice daily
regimens in combination with a low dose of ritonavir, which enhances the
blood levels of 908. Clinical studies are taking place now.
GSK researchers reported (abstract 1737) at ICAAC on the effect of adding
efavirenz to the newly formulated amprenavir prodrug called "908" when used
in combination with RTV to boost 908 levels. Clinical studies are exploring
"908" as a once and twice daily PI regimen for treatment-naive and for
patients with PI-resistance. In a once daily regimen 1400 mg 908 + 200 mg RTV
is being studied. In this study, after 14 days of dual PI therapy (908+RTV
once daily), EFV 600 mg QD was added for an additional 14 days. We know from
previous studies that EFV can reduce APV Cmin by 40%. Similar results were
seen in this study. Results from this study show using only
200 mg of RTV with EFV+908 in a QD regimen reduced APV trough by about 35%.
But, when 300
mg of RTV was added 908 trough level was the same as without adding EFV. For
patients with PI
or APV resistance using 300 mg of RTV appears preferable when combining EFV
with 908 in a
QD regimen. In a BID regimen, 908 700mg + RTV 100mg BID is the currently
recommended dose, with or without EFV. It appears that an extra 100mg RTV is
only needed in the QD regimen.
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