Compositions for inhibiting beta-lactamase

The invention provides pharmaceutical compositions comprising compounds of formula I and IV: ##STR1##

• wherein R₁-R₁₁ and A have any of the values defined in the specification, and their pharmaceutically acceptable salts. The pharmaceutical compositions are useful for inhibiting -lactamase enzymes, for enhancing the activity of -lactam antibiotics, and for treating -lactam resistant bacterial infections in a mammal.