[5] Mecillinam is active against most pathogenic Gram-negative bacteria, except Pseudomonas aeruginosa and some species of Proteus.

[6] Several studies have also found it to be as effective as other antibiotics for treating Staphylococcus saprophyticus infection, though it is Gram-positive, possibly because mecillinam reaches very high concentrations in urine.

[1] Worldwide resistance to mecillinam in bacteria causing urinary tract infection has remained very low since its introduction; a 2003 study conducted in 16 European countries and Canada found resistance to range from 1.2% (Escherichia coli) to 5.2% (Proteus mirabilis).

[7] Another large study conducted in Europe and Brazil obtained similar results — 95.9% of E. coli strains, for instance, were sensitive to mecillinam.

[2] Its most common side effects are rash and gastrointestinal upset, including nausea and vomiting.