A penicillin of the formula: <IMAGE> (i.e. 6-[D-2-(3-hydroxypyridazine-4-carbonamido)-2-(p-hydroxyphenyl)acetamid o]penicillanic acid), which is valuable as an antibacterial agent, a nutritional supplement in animal feeds and a therapeutic agent in poultry and mammals including man and is especially useful in the treatment of infectious diseases caused by Gram-positive and Gram-negative bacteria.
