In accordance with the present invention an orally active monosulfactam antibiotics having a crystalline structure and thereby improved stability are disclosed. The antibiotics comprise the dierythromycin (M(+)=erythromycin.H(+)) salt or the dicholine (M(+)=HOCH2CH2N(+)(CH3)3) salt of the acid (M(+)=H(+)) having the formula IMAGE that is, [3S(Z)]-2[[[1-(2-amino-4-thiazolyl)-2-[[2,2-dimethyl-4-oxo-1-(sulfooxy )-3-azetidinyl]-amino]-2-oxoethylidene]amino]oxy]acetic acid.
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