Clavulanic acid is a beta-lactamase inhibitor produced from Streptomyces clavuligerus, which when combined with certain beta-lactam antibiotics extends their activity against bacteria which owe their resistance to the production of beta-lacatamases. In combination with amoxycillin it extends the antibacterial activity of amoxycillin to include beta-lactamase-producing strains, which are otherwise resistant, as well as amoxycillin-resistant species such as Bacteroides fragilis. The addition of clavulanic acid to amoxycillin occasionally extends (but does not decrease) the susceptibility of amoxycillin-sensitive bacteria. Clavulanic acid is adequately absorbed after oral administration and its basic pharmacokinetic characteristics are similar to those of amoxycillin. Preliminary therapeutic trials suggest that amoxycillin plus clavulanic acid is effective in urinary tract infections caused by amoxycillin-resistant organisms and in lower respiratory tract infections unresponsive to previous routine antibiotic therapy, in hospitalised patients. It is generally well tolerated; nausea, vomiting, diarrhoea and skin rash being the most frequently reported adverse effects.