The present invention provides novel formulations of isobutyric acid (2R,3R,4R,5R)- 5-(4-amino-2-oxo-2H-pyrimidin-l-yl)-4-fluoro-2-isobutyryloxymethyl-4-methyl- tetrahydro-furan-3-yl ester) and hydroxypropylcellulose that provide high bulk density, low particle size better suited for improved compression and flow, good compression, and fast dissolution profiles.