Anti-Amoebic Agents - Medicinal Chemistry



People living in the tropical countries with poor sanitizations from:

Infection due to microbe’s viz. Bacteria, fungi, protozoa virus and rickettisia.

Infection due to paralytic worms and insects.

Antiamoebic drugs:

Amoebiasis is the parasitic protozoal infection caused by entamoeba hysstolytica, with or without clinical manifestations.

This disease is due to poor hygienic condition and transmitted by faecal –oral route. Amoebae are present in the lumen or wall of the gut of human beings.

Classification of Antiamoebic drugs:

A) Chemical classification of Antiamoebic drugs:

Alkaloid:  -e.g. Emetine and Dihydro emetine.

Amaroids: – Quassin

Antibiotics: – Promomycine

Quinoline derivatives:

a) Halogenated hydroxy Quinoline :-diiodohydroxyquinoline (Iodoquinol) ,Iodochlorhyquinoline (clioquinol)

b) Amino Quinoline: chloroquine, amodiaquine.

Heterocyclic compound:

a) Furan derivatives: Diloxanide

b) Imidazole derivatives: Metronidazole.

Organometalic compound:  Acetarsol


B) On the basis of site of action they are grouped as follows:

Luminal amoebicides: e.g. Diloxinide furoate, Paromomycin Halogenated hydroquinolines.

Tissue or systemic amoebicides:-Emetine and its derivatives.

Mixed amoebicide:  Metronidazole.


Emetine is an alkaloid obtained from ipecacuhana.

It can be obtained by methylation of cephaeline; the other alkaloid is also present which can be prepared by synthetically.

It contains tetra hydro Quinoline heterocycle.

Physical properties of Emetine:

Emetine hydro chloride is a dihydro salt of emetine.

It is white or slightly yellow crystalline powder.

It is odourless.

It is tasteless.

It is soluble in water and alcohol. 

Emetine is levo rotetory

Chemical properties of Emetine:

It gives bright green colour when a mixture of molybdenum trioxide and sulphuric acid is sprinkled on it.

It contains two basic nitrogen atom .hence it form salt quite readily with two molecules of hydrochloric acid gives an emetine hydro chloride.

Stability and storage of Emetine:

It becomes faintly yellow on exposure to light .it is stored in tightly closed light resistant containers.

Uses of Emetine:

Intestinal Amoebiasis (amoebic dysentery)

Hepatic Amoebiasis (amoebic hepatitis)

Amoebic infection of lung, brain and other tissues

Pharmaceutical formulations: Emetine injection

Brand names: Stembin, Hemometina


Structure of Metronidazole:

Chemical names:  2-(2methyl, 5 nitro imidazole -1 Yl) ethanol. OR 1-(2-hydroxy ethyl), 2 methyl, 5 nitro imidazole.

Chemistry of Metronidazole: 

It is 5 nitro imidazole derivatives.

It contains 2-hydroxy ethyl group and methyl group at 1 and 2 position respectively.

Activation of either the group leads to inactivation.

Physical Properties of Metronidazole:

It is white or creamy white crystalline powder.

It having slightly odour.

It has bitter and saline test.

It is slightly soluble in water.

It is soluble in alcohol.

Chemical properties of Metronidazole:

When its solution in sulphuric acid is treated with picric acid, it gets precipitate as its Picrate which melts at 150 degree Celsius.

Nitro group of Metronidazole on reduction with Zn/HCl is converted in to amino group which undergo diazotiastion with HNO2 diazotised product on coupling with Beta Naphthol in NAOH gives orange red colour.

Pharmaceutical formulations: Metronidazole tablets, injection, suppositories.

Brand names: Flagyl, Metroquin, Metroquniol

Diloxanide furoate

Physical Properties of Diloxanide furoate:

It occurs white crystalline powder

It is odourless and tasteless

It is slightly soluble in water.

It is dissolved completely in chloroform.

Chemical properties of Diloxanide furoate:

When its solution in pyridine is treated with tetra butyl ammonium bromide, its enolic form reacts to form salt.

Stability and storage of Diloxanide furoate:

It is affected by light and hence it is stored in well closed light resistant containers.

Uses of Diloxanide furoate:

Amoebic dysentery,

Symptomic cyst-passer

Hepatic abscesses in conjugation with chloroquine or Metronidazole.

Pharmaceutical formulations: Diloxanide furoate tablets

Brand names: Entamizole, Flagyl-DF, Diloxyl


Physical Properties of Promomycine:

It is official as sulphate salt which occurs as creamy –white to light yellow powder.

It is odourless

It is hygroscopic in nature

It is very soluble in water

It is practically insoluble in alcohol and chloroform

Stability and storage of Promomycine:

It is hygroscopic and hence it stored in tightly closed containers

Uses of Promomycine:

It has antibacterial activity .hence it is used to suppress intestinal flora.

It has amoebicide activity and hence is used to treat intestinal amoebiasis (amoebic dysentery)

It is used to treat leishmaniasis (kala azar)

It is used to treat balantidiasis (diarrhea type symptoms due to balantadium coli).

It has also Anthelmentics activity (to treat tapeworm infection)

Pharmaceutical formulation: Promomycine sulphate tablet, Promomycine sulphate syrup. 

Brand names: Paramicina, Hamagen                      

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