Disinfectants and Antiseptics
Disinfection denotes the inactivation or
killing of pathogens (protozoa, bacteria,
fungi, viruses) in the human environ-
ment. This can be achieved by chemical
or physical means; the latter will not be
discussed here. Sterilization refers to
the killing of all germs, whether patho-
genic, dormant, or nonpathogenic. Anti-
sepsis refers to the reduction by chemi-
cal agents of germ numbers on skin and
mucosal surfaces.
Agents for chemical disinfection
ideally should cause rapid, complete,
and persistent inactivation of all germs,
but at the same time exhibit low toxic-
ity (systemic toxicity, tissue irritancy,
antigenicity) and be non-deleterious to
inanimate materials. These require-
ments call for chemical properties that
may exclude each other; therefore,
compromises guided by the intended
use have to be made.
Disinfectants come from various
chemical classes, including oxidants,
halogens or halogen-releasing agents,
alcohols, aldehydes, organic acids, phe-
nols, cationic surfactants (detergents)
and formerly also heavy metals. The ba-
sic mechanisms of action involve de-
naturation of proteins, inhibition of en-

tion; short, foaming action on contact
with blood and thus wound cleansing)
or with potassium permanganate
(0.0015% solution, slightly astringent),
as well as PVP iodine, chlorhexidine,
and biguanidines.
Hygienic and surgical hand disinfec-
tion: The former is required after a sus-
pected contamination, the latter before
surgical procedures. Alcohols, mixtures
of alcohols and phenols, cationic surfac-
tants, or acids are available for this pur-
pose. Admixture of other agents pro-
longs duration of action and reduces
flammability.
Disinfection of instruments: Instru-
ments that cannot be heat- or steam-
sterilized can be precleaned and then
disinfected with aldehydes and deter-
gents.
Surface (floor) disinfection employs
aldehydes combined with cationic sur-
factants and oxidants or, more rarely,
acidic or alkalizing agents.
Room disinfection: room air and
surfaces can be disinfected by spraying
or vaporizing of aldehydes, provided
that germs are freely accessible.
290 Disinfectants
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e. g., phenylphenol
eugenol
thymol
halogenated:
chlormethylphenol
7. Cationic
surfactants
Cationic soaps
e. g., benzalkonium
chlorhexidine
8. Heavy metal salts
Inanimate material: durable
against chemical + physical
measures
Inanimate matter:
sensitive to heat,
acids, oxidation etc.
Disinfection
of instruments
Skin disinfection
Disinfection of floors
or excrement
Disinfection
of mucous membranes
Wound disinfection
Phenols NaOCl
Cationic
surfactants
Phenols
Cationic surfactants

Ectoparasitic Infestations
Adverse hygienic conditions favor hu-
man infestation with multicellular or-
ganisms (referred to here as parasites).
Skin and hair are colonization sites for
arthropod ectoparasites, such as insects
(lice, fleas) and arachnids (mites).
Against these, insecticidal or arachnici-
dal agents, respectively, can be used.
Endoparasites invade the intestines or
even internal organs, and are mostly
members of the phyla of flatworms and
roundworms. They are combated with
anthelmintics.
Anthelmintics. As shown in the ta-
ble, the newer agents praziquantel and
mebendazole are adequate for the treat-
ment of diverse worm diseases. They
are generally well tolerated, as are the
other agents listed.
Insecticides. Whereas fleas can be
effectively dealt with by disinfection of
clothes and living quarters, lice and
mites require the topical application of
insecticides to the infested subject.
Chlorphenothane (DDT) kills in-
sects after absorption of a very small
amount, e.g., via foot contact with
sprayed surfaces (contact insecticide).
The cause of death is nervous system

tape worms (cestodes) praziquantel*
flukes (trematodes) e.g., Schistosoma praziquantel
species (bilharziasis)
Roundworms (nematodes)
pinworm (Enterobius vermicularis) mebendazole or pyrantel pamoate
whipworm (Trichuris trichiura) mebendazole
Ascaris lumbricoides mebendazole or pyrantel pamoate
Trichinella spiralis** mebendazole and thiabendazole
Strongyloides stercoralis thiabendazole
Hookworm (Necator americanus, and mebendazole or pyrantel pamoate
Ancylostoma duodenale) mebendazole or pyrantel pamoate
* not for ocular or spinal cord cysticercosis
** [thiabendazole: intestinal phase; mebendazole: tissue phase]
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Antiparasitic Agents 293
Flea
Damage to nervous system: convulsions, death
A. Endo- and ectoparasites: therapeutic agents
Tapeworms
e.g., beef
tapeworm
Louse
Round-
worms,
e.g.,
ascaris
Pinworm
Trichinella
larvae Scabies mite

of the infected erythrocytes releases the
merozoites and pyrogens. A fever attack
ensues and more erythrocytes are in-
fected. The generation period for the
next crop of merozoites determines the
interval between fever attacks. With
Plasmodium vivax and P. ovale, there can
be a parallel multiplication in the liver
(paraerythrocytic stage). Moreover,
some sporozoites may become dormant
in the liver as “hypnozoites” before en-
tering schizogony. When the sexual
forms (gametocytes) are ingested by a
feeding mosquito, they can initiate the
sexual reproductive stage of the cycle
that results in a new generation of
transmittable sporozoites.
Different antimalarials selectively
kill the parasite’s different developmen-
tal forms. The mechanism of action is
known for some of them: pyrimetha-
mine and dapsone inhibit dihydrofolate
reductase (p. 273), as does chlorguanide
(proguanil) via its active metabolite. The
sulfonamide sulfadoxine inhibits syn-
thesis of dihydrofolic acid (p. 272). Chlo-
roquine and quinine accumulate within
the acidic vacuoles of blood schizonts
and inhibit polymerization of heme, the
latter substance being toxic for the

methamine/sulfadoxine (or proguanil,
or doxycycline), the chloroquine ana-
logue amodiaquine, as well as quinine
or the better tolerated derivative meflo-
quine (blood-schizonticidal). Agents ac-
tive against blood schizonts do not pre-
vent the (symptom-free) hepatic infec-
tion, only the disease-causing infection
of erythrocytes (“suppression therapy”).
On return from an endemic malaria re-
gion, a 2 wk course of primaquine is ad-
equate for eradication of the late hepat-
ic stages (P. vivax and P. ovale).
Protection from mosquito bites
(net, skin-covering clothes, etc.) is a
very important prophylactic measure.
Antimalarial therapy employs the
same agents and is based on the same
principles. The blood-schizonticidal
halofantrine is reserved for therapy on-
ly. The pyrimethamine-sulfadoxine
combination may be used for initial self-
treatment.
Drug resistance is accelerating in
many endemic areas; malaria vaccines
may hold the greatest hope for control
of infection.
294 Antiparasitic Drugs
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Quinine
Proguanil
Pyrimethamine
Merozoites
Hypnozoite
Preerythrocytic cycle
1-4 weeks
Erythrocytic cycle
Blood
schizont
Erythrocyte
Only
Pl. vivax
Pl. ovale
Gametocytes
Sporozoites
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All rights reserved. Usage subject to terms and conditions of license.