The absorbance is the property of the chromophore  present in the molecule. The molecular formula for doxycycline hydrochloride hemiethanolate hemihydrate is (C22H24N2O8•HCl)2•C2H6O•H2O  and I don't see a significant chromophore in the hyclate part. So you can very well use the 273nm for absorbance  measurements.

Thank you. But should I be using any reference wavelength while measuring the absorbance values? How can I resolve the high values for blank clear plate itself?

I think this link is very useful, 

http://www.instanano.com/characterization/theoretical/concentration-calculation-from-uv-vis-absorbance/