<chemical> (2s-(2 alpha,5 alpha,6 beta(s*)))-6-((amino(4-hydroxyphenyl)acetyl)amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylic acid. A broad-spectrum semisynthetic antibiotic similar to ampicillin except that its resistance to gastric acid permits higher serum levels with oral administration. Pharmacological action: penicillins.