Polyhexamethylene biguanide (PHMB) / chlorhexidine (compounded)
Anti-infective · Rx (compounded)
Trade namesCompounded PHMB 0.02-0.08%, Chlorhexidine 0.02%
Drug classAnti-amoebic biguanide (compounded)
StrengthPHMB 0.02-0.08%; chlorhexidine 0.02%
AvailabilityRx (compounded)
Mechanism of actionCationic biguanides that disrupt the amoebic cell membrane and are cysticidal, active against both trophozoites and the resistant cyst form of Acanthamoeba.
Indication / reason for useAcanthamoeba keratitis, a devastating, often contact-lens-related infection (tap-water rinsing, swimming/showering in lenses, poor case hygiene).
Usual adult dosing1 drop q1h day and night for 3-7 days, then q1h while awake for weeks; prolonged taper over months, frequently as biguanide + diamidine (e.g. propamidine/hexamidine) dual therapy.
PreservativePreservative-free (compounded) , a preservative-free option exists
Contact lensesAbsolute contraindication to lens wear; central to prevention counselling for all lens patients.
Common / important adverse effectsSurface toxicity with prolonged use, limbitis, scleritis, keratopathy.
Contraindications & cautionsHypersensitivity.
Pregnancy / lactationLimited data; disease severity usually dictates treatment.
Practice notesSuspect in any contact-lens wearer with disproportionate pain, a ring infiltrate, radial keratoneuritis, or a 'herpes' keratitis not responding to antivirals, refer urgently for confocal microscopy and culture.
Chair-side reference only. Dosing, contraindications and pregnancy guidance here are not exhaustive. Confirm against the current prescribing information and the patient’s full history before prescribing or advising.