A nano- or micro-scale therapeutic agent is provided for use in the treatment of an infection of a human or animal. The agent includes micro- and/or nano-particle carriers loaded with at least one inert precursor chemical. The carriers encapsulate the precursor which after release from the carrier are activatable by the physiological milieu in situ at the site of the infection to form an antimicrobial agent. Preferably, the precursor chemical or chemicals form an oxidative biocide on release, which oxidative biocide is hydrogen peroxide. Advantageously, the precursor chemicals also include an acetyl donor that on release reacts with the hydrogen peroxide to produce a mixture of peracetic acid and hydrogen peroxide. The carrier is preferably in the form of micro- and/or nano-particles that have been manufactured using a thermally induced phase separation (TIPS) process, for example the carrier may be a biodegradable polymer such as poly(lactic-co-glycolic acid) (PLGA).
