Antiseptics and Disinfectants
Session 43: Antiseptics and Disinfectants
Total Session Time: 120 minutes
Pre-requisites
Students Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |5 minutes |Presentation |Introduction, Learning Tasks |
|2 | |Presentation |General Properties of Antiseptics |
| |15 minutes | |and Disinfectants |
|3 |50 minutes |Presentation |Chemical Agents Used as |
| | | |Antiseptics and Disinfectants |
|4 |20 minutes |Presentation |Factors affecting action of |
| | | |antiseptics and disinfectants |
|5 |20 minutes | |Criteria for selection of |
| | |Presentation |antiseptics and disinfectants |
|6 |5 minutes |Presentation |Key Points |
| 7|5 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing
STEP 2: General Properties of Antiseptics and Disinfectants (15 minutes)
Antiseptics
mucous membranes and wounds) to kill or inhibit the growth of
microorganisms
disinfectant
o Toxicity to microorganisms but not to human cells
depending on the tissues they contact
cells that they can be used directly on skin, mucous membranes or
wounds
o They must have adequate antimicrobial activity
o The must not be toxic or irritating for skin
o Antiseptics are mostly used to reduce the microbial population on
the skin before surgery or on the hands to help prevent spread of
infection by this route. Antiseptics are often lower
concentrations of the agents used for disinfection
o The treatment of skin infections
o Prevention of infections in cuts and wounds
o Cleaning the skin area of surgery from microorganisms
o Prophylaxis and treatment of infections in mucosal areas such as
mouth, nose and vagina that are open to environment
o As a scrub for surgeons and the medical personnel
Disinfectants
concentrations
o Effective at room temperature
o Non-corrosive and nontoxic
o Inexpensive
STEP 2: Chemical Agents Used as Antiseptics and Disinfectants (50
minutes)
o Alcohols
o Acids and Esters
o Aldehydes
o Biguanides
o Halogens
o Hydrogen peroxide and peroxygen compounds
o Phenols
o The aliphatic alcohols (ethanol and isopropanol) are used for
disinfection and antisepsis
o They are bactericidal against vegetative forms, including
Mycobacterium species, but are not sporicidal
o Cidal activity drops sharply below 50% concentration
o Alcohols have poor penetration of organic matter and their use is
therefore restricted to clean conditions
o They possess properties such as a cleansing action and volatility,
are able to achieve a rapid and large reduction in skin flora and
are widely used for skin preparation before injection or other
surgical procedures
o Ethanol (CH3CH2OH)
ethanol is ineffective
a 70% solution is usually employed for the disinfection of
skin, clean instruments or surfaces
against most viruses, including HIV
cosmetic products as a solvent and preservative
o Isopropyl alcohol (isopropanol, CH3. CHOH.CH3)
is also about twice as toxic
viruses, and should be considered a limited-spectrum virucide
alternative to ethanol for preoperative skin treatment and is
also employed as a preservative for cosmetics
o Many aldehydes have antimicrobial properties, including sporicidal
activity,
o Glutaraldehyde (CHO(CH2)3CHO)
‘chemosterilant’
rate of kill, most vegetative bacteria being killed within a
minute of exposure, although bacterial spores may require 3
hours or more.
which are highly reactive and their presence is an important
component of biocidal activity
poor due to polymerization
active
acidic 2% or greater aqueous solution, which is stable on
prolonged storage
suitable alkalizing agent to bring the pH of the solution to
its optimum for activity
the order of 2 weeks
available
sterilization of medical and surgical materials that cannot be
sterilized by other methods
cystoscopes and bronchoscopes may be decontaminated by
glutaraldehyde treatment
o These do not require activation
o They are not irritating to the eyes or nasal passages
o Have excellent stability over the pH range 3–9
o Formaldehyde (HCHO)
disinfection purposes
isolators, safety cabinets and rooms
steam (LTSF) for the sterilization of heat-sensitive items
carcinogenic if inhaled, thus its use must be carefully
controlled
polymer, paraformaldehyde, or a liquid, formalin, which is a
34–38% aqueous solution
liquid with potassium permanganate and water
for disinfecting surfaces
formaldehyde are too irritant for routine application to skin,
while poor penetration and a tendency to polymerize on
surfaces limit its use as a disinfectant for pharmaceutical
purposes
o Chlorhexidine and alexidine
o Chlorhexidine base is not readily soluble in water, therefore the
freely soluble salts, acetate, gluconate and hydrochloride are
used in formulation.
o Chlorhexidine exhibits the greatest antibacterial activity at pH
7–8 where it exists exclusively as a dication
o Activity is reduced by;
formation of insoluble salts
chloride, citrate and phosphate with due attention being
paid to the presence of hard water
purposes
o Chlorhexidine has widespread use, in particular as an antiseptic
o It has significant antibacterial activity, although Gram-negative
bacteria are less sensitive than Gram-positive organisms
whereas a 1:50000 dilution prevents growth of P. aeruginosa.
o Chlorhexidine is ineffective at ambient temperatures against
bacterial spores and M. tuberculosis
o Has limited antifungal activity
o Chlorhexidine is well tolerated and nontoxic when applied to skin
or mucous membranes and is an important preoperative antiseptic
o Chlorine
are commercially available e.g. liquid chlorine
compressing and cooling gaseous chlorine
chlorine whereas the word ‘chlorine’ is normally used to
signify a mixture of OCl-, Cl2, HOCl and other active chlorine
compounds in aqueous solution
of parts per million (ppm) or percentage of available chlorine
(avCl)
o Hypochlorites
the chlorine disinfectants, being readily available,
inexpensive and compatible with most anionic and cationic
surface-active agents
microorganisms including fungi and viruses
acid-fast bacilli and bacterial spores
can become unstable
frequently as the sodium or potassium salts of hypochlorous
acid (HOCl)
and its potent antimicrobial activity is dependent on pH as
shown:
(hypochlorite ion)
of the order of 100:1. By lowering the pH of hypochlorite
solutions the antimicrobial activity increases to an optimum
at about pH 5; however, this is concurrent with a decrease in
stability of the solutions
above equation) in order to maintain a high pH during storage
for stability
sufficiently for activity on dilution to use-strength
a daily basis
o Chloroform (CHCl3)
pharmaceuticals since the last century, although more recently
it has had limitations placed on its use
volatilization from products resulting in the possibility of
microbial growth
o Iodine
(on extended exposure), mycobacteria, fungi and viruses are
all susceptible
iodide ions are required for aqueous solutions such as Aqueous
Iodine Solution, BP 1988 (Lugol’s Solution) containing 5%
iodine in 10% potassium iodide solution
potassium iodide (2.5%) solution to give Weak Iodine Solution,
BP 1988 (Iodine Tincture)
chlorine on temperature and pH, although alkaline pH should be
avoided
matter
staining of skin and fabrics coupled with possible sensitizing
of skin and mucous membranes
o Iodophors
povidone iodine
antimicrobial activity
the complex formed between iodine and the carrier molecule
o Hydrogen peroxide and peracetic acid are high level disinfectants
due to their production of the highly reactive hydroxyl radical
o They have the added advantage that their decomposition products
are nontoxic and biodegradable
o The germicidal properties of hydrogen peroxide (H2O2) have been
known for more than a century
o It is active against protozoans e.g. acanthamoeba
o Concentrations of 3–6% are effective for general disinfection
purposes
o At high concentrations (up to 35%) and increased temperature
hydrogen peroxide is sporicidal
o Use has been made of this in vapour phase hydrogen peroxide
decontamination of equipment and enclosed spaces
o Peracetic acid (CH3COOOH) is the peroxide of acetic acid and is a
more potent biocide than hydrogen peroxide, with excellent rapid
biocidal activity against bacteria, including mycobacteria, fungi
viruses and spores
o It can be used in both the liquid and vapour phases and is active
in the presence of organic matter
o It is finding increasing use at concentrations of 0.2–0.35% as a
chemosterilant of medical equipment such as flexible endoscopes
o Its disadvantages are that
system)
o The combination of hydrogen peroxide and peracetic acid is
synergistic and is marketed as a cold sterilant for dialysis
machines
o Phenols are widely used as disinfectants and preservatives
o They have good antimicrobial activity and are rapidly bactericidal
but generally are not sporicidal
o Their activity is markedly diminished by dilution and is also
reduced by organic matter
o They are more active at acid pH
o The main disadvantages of phenols are their caustic effect on skin
and tissues and their systemic toxicity
o The more highly substituted phenols are less toxic and can be used
as preservatives and antiseptics
o They are less active than the simple phenolics, especially against
Gram-negative organisms
o To improve their poor aqueous solubility, phenolic disinfectants
are often formulated with soaps, synthetic detergents, and/or
solvents
o They include;
general purpose disinfectant, it is very irritating
and disinfectant
presence of organic matter
o Surface-active agents or surfactants are classified as anionic,
cationic, non-ionic or ampholytic according to the ionization of
the hydrophilic group in the molecule
o Within the various classes a range of detergent and disinfectant
activity is found
o The cationic agents used for their antimicrobial activity all fall
within the group known as the quaternary ammonium compounds (QACs)
o Benzalkonium chloride and cetrimide are employed extensively in
surgery, urology and gynaecology as aqueous and alcoholic
solutions and as creams
o The detergent properties of the QACs also provide a useful
activity, especially in hospitals, for general environmental
sanitation
|Activity: Take home Assignment (10 minutes) |
| |
|DIVIDE students in groups or individual. |
| |
|ASK the students to work on the following assignment |
| |
|Which of the agents described in this session are classified as high |
|level, intermediate level or low level disinfectants? |
| |
|ALLOCATE time for students to do the assignment and submit |
| |
|REFER students to recommended references |
STEP 3: Factors Affecting Action of Antiseptics and Disinfectants (20
minutes)
o The larger the number of contaminants the longer it takes to kill
them
o Microorganisms in areas difficulty to be accessed by chemical
agents are more difficulty to kill
o Spores are more resistant than vegetative forms of microorganisms
o Gram negative bacteria are more susceptible to alcohol than Gram
positive bacteria due high lipid content
o Organic matter e.g. serum, blood, pus, or fecal or lubricant
material may interfere with the antimicrobial activity of agents
used for antisepsis and disinfection e.g. Chlorine and iodine are
affected by organic matter
o Inorganic matter interferes with action of these agents on the
microorganisms
o Generally high concentration increases activity and shorten
duration of treatment
not effective as an antiseptic
o Temperature, pH, relative humidity, and water hardness
temperature increases, but some exceptions exist. Furthermore,
too great an increase in temperature causes the disinfectant
to degrade and weakens its germicidal activity and thus might
produce a potential health hazard
some disinfectants (e.g., glutaraldehyde, quaternary ammonium
compounds) but decreases the antimicrobial activity of others
(e.g., phenols, hypochlorites, and iodine). The pH influences
the antimicrobial activity by altering the disinfectant
molecule or the cell surface
influencing the activity of gaseous disinfectants/sterilants,
such as Ethylene oxide, chlorine dioxide, and formaldehyde
cations) reduces the rate of kill of certain disinfectants
because divalent cations (e.g., magnesium, calcium) in the
hard water interact with the disinfectant to form insoluble
precipitates
o Duration of exposure
appropriate minimum contact time
o Biofilm
production of thick masses of cells and extracellular
materials known as biofilm
to surfaces and cannot be easily removed
STEP 3: Criteria for Selection of Antiseptics and Disinfectants (20
minutes)
purpose depends on:
o Properties of the chemical agent including;
o Microbiological challenge
viruses etc.
o Intended application
o Environmental factors
activity of agent)
o Toxicity of the agent
o Cost
STEP 4: Key Points (5 minutes)
antiseptics
inanimate surfaces
disinfection process
factors including intended use, level of contamination and cost of the
chemical agent
STEP 5: Evaluation (5 minutes)
disinfection?
References
Hugo and Russell (2011), Pharmaceutical Microbiology 8th Edition, Willey-
Blackwel publications
Karen C. Carroll et al (2013); Jawetz, Melnick and Adelberg’s Medical
Microbiology 26th Ed. McGraw Hill Co. Inc.
Greenwood et al (2012); Medical Microbiology, 18th edition Churchill
Livingstone
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