Mixed amoebicdes

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Chapter: Medicinal Chemistry : Antiamoebic Agents

1. Metronidazole (Flagyl, Metrogyl) 2. Tinidazole (Fasigyn) 3. Ornidazole (Ornida, Dazolic, Onidaz) 4. Nitazoxanide 5. Nimorazole (Nitroimidazole)


Antiamoebic Agents - Synthesis and Drug Profile

Mixed amoebicdes

 

1. Metronidazole (Flagyl, Metrogyl)


Synthesis


Mode of action: The reactive intermediate formed in the parasital reduction of the 5-nitro group of metronidazole covalently binds to the DNA of the parasite and triggers the lethal effects. Potential reactive intermediates include the nitroxide, nitroso, hydroxylamine, and amine.

Metabolism: In the liver, metabolism of metronidazole leads to two major metabolites, hydroxylation of the 2-methyl group to 2-hydroxymethyl metronidazole and oxidation to metronidazole acetic acid (MAA).


Properties and uses: Metronidazole is a white or yellowish crystalline powder, slightly soluble in water, acetone, alcohol, and methylene chloride. It is used in the treatment of intestinal and hepatic amoebiasis.

Assay: Dissolve the sample in anhydrous acetic acid and titrate with 0.1 M perchloric acid. Determine the end point potentiometrically.

Dose: For amoebiasis, the administered dose is 750 mg orally three times a day for 5–10 days. For trichomoniasis, the prescribed dose is 250 mg orally three times a day for 7 days. For giardiasis, the prescribed dose is 250 mg orally three times daily for 5–7 days.

Dosage forms: Metronidazole gel B.P., Metronidazole intravenous infusion B.P., Metronidazole suppositories B.P., Metronidazole tablets B.P.

 

2. Tinidazole (Fasigyn)


Mode of action: Tinidazole’s mechanism of action is similar to that of metronidazole. It is used in the treatment of intestinal and hepatic amoebiasis with a potential greater efficacy than metronidazole.

Metabolism: Tinidazole is metabolized by hydroxylation at the 2-methyl group and catalyzed by CYP3A4 to form inactive compound.

Synthesis


Properties and uses: Tinidazole is a white or pale yellow crystalline powder, practically insoluble in water, soluble in acetone and in methylene chloride, and sparingly soluble in methanol. Used as an antiprotozoal and antibacterial agent.

Assay: Dissolve the sample in anhydrous acetic acid and titrate with 0.1 M perchloric acid. Determine the end point potentiometrically.

Dose: For giardiasis, the administered dose is 2 mg as a single dose.

 

3. Ornidazole (Ornida, Dazolic, Onidaz)


Synthesis:


Properties and uses: It has a longer duration of action than metronidazole and used as an antiprotozoal.

Dose: The administered dose for amoebic dysentery in the case of adults is 1.5 g as a single daily dose for 3 days. Alternatively, for patients, whose weight is more than 60 kg, the dose is 1 g two times a day for  3 days. In the case of a child, the administered dose is 40 mg/kg daily. For amoebiasis, the recommended dose for adults is 5 g two times a day for 5–10 days. And in the case of a children, the dose is 25 mg/kg as a single daily dose for 5–10 days.

For giardiasis, in the case of adults, the dose is 1–1.5 g as a single daily dose for 1–2 days. In the case of a child, the dose is 30–40 mg/kg daily. In the case of trichomoniasis, the dose for adults is 1.5 g as a single daily dose or 0.5 g two times a day for 5 days. Treat sexual partners concomitantly. In the case of child, the dose is 25 mg/kg as a single dose. In the case of intravenous administration, during severe amoebic dysentery and amoebic liver abscess the prescribed dose for adults initially is 0.5–1 g infusion followed by 0.5 g every 12 h for 3–6 days. For a child, the dose is 20–30 mg/kg body weight daily.

 

4. Nitazoxanide


Synthesis


Mode of action: Nitazoxanide is a member of the 5-nitro heterocylces and is a prodrug forming a shortlived redox active intermediate. It appears to be more selective than metronidazole.

Uses: Used as an antiprotozoal agent.

 

5. Nimorazole (Nitroimidazole)


Synthesis


Properties and uses: It possesses antiamoebic activity, and hence, used against intestinal and hepatic amoebiasis.

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