SN7 SHORT NOTE 5M

Classify antiseptics and disinfectants. Describe the important agents and the factors affecting their activity.

Pharmacology · 2nd Professional — Para-Clinical

Definition and Terminology

An antiseptic is applied to living tissue to reduce microbial numbers; a disinfectant is applied to inanimate objects; sterilisation destroys all microbial life including spores.

Classification and Agents

Class	Agents	Properties and uses
Alcohols	Ethanol 70%, isopropyl alcohol	Denature protein; rapid action; 70% is more effective than absolute alcohol, because water is needed for protein denaturation. Not sporicidal. Skin preparation and hand rub
Halogens — iodine	Povidone-iodine, tincture of iodine	Broad, including spores with prolonged contact; povidone-iodine releases iodine slowly and is less irritant; the standard for surgical skin preparation
Halogens — chlorine	Sodium hypochlorite (bleach), chlorine dioxide	Water treatment, surface disinfection, and sporicidal — hence its use against C. Difficile; inactivated by organic matter
Biguanide	Chlorhexidine	Good gram-positive and moderate gram-negative activity; substantive — it binds to skin and keratin and goes on acting for hours, which is why it is preferred for hand hygiene and central line insertion. Neurotoxic — must not contact the middle ear, meninges or eye
Aldehydes	Glutaraldehyde, formaldehyde	Sporicidal; used for endoscopes and instruments that cannot be autoclaved; irritant and sensitising, so ventilation and protection are needed
Oxidising agents	Hydrogen peroxide, potassium permanganate	Effervescence helps debride wounds; peracetic acid for instruments
Phenolics	Phenol, cresol, hexachlorophene	Environmental disinfection; hexachlorophene is neurotoxic in neonates
Quaternary ammonium (cationic)	Cetrimide, benzalkonium	Detergent and antiseptic; inactivated BY soap (anionic) and by organic matter
Metals	Silver sulphadiazine, silver nitrate	Burns; neonatal eye prophylaxis
Dyes	Gentian violet, acriflavine	Superficial fungal and bacterial infection

CLINICAL PEARL

Seventy per cent alcohol kills better than absolute alcohol, which surprises people. Denaturing a protein requires water; pure alcohol dehydrates the organism and coagulates a protective surface layer without penetrating. The presence of 30% water lets the alcohol enter and denature proteins throughout — a reminder that more concentrated is not automatically more effective.

Factors Affecting Activity

Concentration and contact time — most failures are from inadequate contact time rather than the wrong agent
Organic matter — blood, pus and faeces inactivate hypochlorite and quaternary ammonium compounds; surfaces must be cleaned before disinfection
PH and temperature; incompatibility — soap inactivates cationic agents
Nature of the organism — the order of resistance is prions > spores > mycobacteria > non-enveloped viruses > fungi > vegetative bacteria > enveloped viruses, which are the most easily killed

Applied Aspects

Hand hygiene is the single most effective infection control measure; alcohol rub is faster and more effective than soap for most organisms, and adherence is higher because it is quicker
But use soap and water for C. Difficile and when hands are visibly soiled, since alcohol does not remove spores
Chlorhexidine-alcohol is superior to povidone-iodine for surgical site and central line skin preparation, and must be allowed to dry before incision — both for efficacy and because it is flammable with diathermy
Never instil chlorhexidine into the ear with a perforated drum, or near the eye or meninges
Antiseptics do not substitute for sterilisation of surgical instruments; autoclaving remains the standard
Antiseptic solutions can themselves become contaminated — outbreaks of Pseudomonas and Burkholderia have been traced to diluted or reused antiseptic containers, which is a real hazard where cost drives dilution

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