Topic Seven: PHMB
PHMB, also known as the antimicrobial/antiseptic Polyhexamethylene biguanide, polyhexanide, is relatively new to the UK wound care market.
PHMB has been used for over 60 years in a wide range of applications, from swimming pool sanitisers to preservatives in cosmetics and contact lens solutions. In Europe, it has been available as a wound irrigation fluid for some time (Butcher, 2012).
PHMB is a heterodisperse mixture of polymers and is a synthetic compound structurally similar to naturally occurring antimicrobial peptides (AMPs). AMPs are important in innate immune responses and are produced by the majority of living organisms. They have a broad spectrum of activity against bacteria, viruses and fungi (Moore & Gray, 2007). AMPs are produced by many cells within the wound, such as keratinocytes and inflammatory neutrophils, where they are thought to play a role in the protection against infection (Sorensen et al., 2003).
Mode of Action
PHMB is a positively charged (cationic) polymer, which works against negatively charged microorganisms. The positively charged molecules bind to bacterial cell membranes, which breaks down the cell integrity and ultimately kills bacteria. This mode of action is quick, so microorganisms are unlikely to develop resistance to PHMB (King et al., 2017).
The structural similarities between AMPs and PHMB mean that PHMB can insert into bacterial cell membranes and kill bacteria in a similar way to AMPs (Moore & Gray, 2007). PHMB is thought to adhere to and disrupt target cell membranes, causing them to leak potassium ions and other cytosolic components (Davies et al., 1968; Broxton et al., 1984; Yasudak et al., 2003; Butcher, 2012).
PHMB may be used to reduce the wound bioburden. In vitro work indicates that following PHMB contact with Escherichia coli, there is a rapid attraction of PHMB towards the negatively charged bacterial cell surface, resulting in cell death (McDonnell & Russell, 1999; King et al., 2017).
PHMB has a broad spectrum of action against pathogens, including Gram-positive and Gram-negative bacteria, Staphylococcus aureus, Methicillin Resistant Staphylococcus aureus (MRSA), fungi, and biofilms (King et al., 2017).
Advantages of PHMB
- Excellent skin tolerance
- Non-toxic, non-irritant
- Hypoallergenic
- No known resistance
- Safe
PHMB has been incorporated into a variety of wound products with a choice of dressings available. This offers the health care professional an alternative method of using. PHMB Dressings include:
- Solutions and gels
- Adherent and non-adherent bacterial-barrier products
- Biocellulose PHMB-donating dressings
(Butcher, 2012)
Indications for use
Examples of wound types that can be considered for treatment with PHMB dressings include:
- Second-degree burns
- Post-surgical wounds
- Traumatic wounds
- Donor and recipient sites
- Leg ulcers
- Pressure ulcers
- Epidermolysis bullosa and scleroderma wounds
- Varying levels of exudate, dependent on the wound dressing, of critically colonised and infected wounds
(King et al., 2016)
PHMB has been shown to exhibit the following benefits:
- Improving healing rates by controlling infection
- Encouraging the formation of healthy granulation tissue
- Reducing wound-related pain
- Reducing infection-associated wound malodour
- Reducing slough and non-viable tissue from the wound
- Reducing periwound damage
(King et al., 2016)
Contraindications
Known sensitivity to PHMB.
Safety and efficacy of PHMB
PHMB is considered to be non-toxic and tolerated with no systemic uptake detected and no reported chronic health effects. Tests of compatibility for PHMB (which measure its antimicrobial activity in relation to its cytoxicity) have shown that PHMB results in less damage to healthy cells than other antimicrobial agents such as chlorhexidine and povidone iodine (Hubner & Kramer, 2010).
PHMB containing dressings have been shown to be active against biofilms (Lenselink & Andriessess, 2011).