ALEXID belongs to a new class of penicillins - the amidinopenicillins - with antibacterial properties fundamentally different from those of the previously known acyl-aminopenicillins. Pivmecillinam is the oral form of this new amidinopenicillin. ALEXID, has selective and powerful antibacterial activity against Gram-negative bacilli, especially against those responsible for urinary tract infections. The spectrum of ALEXID comprises of E. Coli, Klebsiella, Enterobacter, Proteus, Salmonella, Shigella, Yersinia and some strains of Serratia marcescens. The in-vitro activity of ALEXID against E. coli is approximately 40 times higher than that of ampicillin. Contrary to other penicillins, ALEXID is practically inactive against Gram-positive organisms, e.g. it is inactive against Pseudomonas aeruginosa. ALEXID is bactericidal. It acts by interfering with bacterial cell wall synthesis, but the site of action differs from that of other penicillins. Consequently, cross resistance between ALEXID and other beta-lactam antibiotics is rare. On the contrary. ampicillin-resistant strains may well prove sensitive to ALEXID, and synergistic antibacterial activity can be obtained from combinations of ALEXID and other beta-lactam antibiotics, such as penicillins and cephalosporins. Following oral administration, maximum serum concentrations are obtained in about one hour and therapeutically effective concentrations are maintained for 4-5 hours. Mean peak concentrations after oral doses of 200 mg. 400 mg and 800 mg are 3 µg/ml, 5 µg/ml and 8 µg/ml respectively. Absorption is not affected by simultaneous food intake.