Nucleotide analogues : a. Purine nucleosides and nucleotides i. Acyclovir (Ocuvir, Zovirax, Cyclovir) ii. Ganciclovir (Ganguard) b. Pyrimidine nucleoside and nucleotide inhibitors iii. Idoxuridine (Antizona, Dendrid) iv. Methisazone (Marboran) d. Adamantane amines 1. Amantadine (Symmetrel) 2. Rimantadine Miscellaneous i. Ribavirin (Virazole)
Synthesis
Metabolism: The bioavailability of acyclovir is 15%–30 % and it is
metabolized to 9-carboxy-methoxymethyl guanine, which is inactive.
Properties and uses: Acyclovir is a white crystalline powder,
slightly soluble in water, soluble in dimethyl sulphoxide and in dilute mineral
acids and alkali hydroxides, and very slightly soluble in ethanol. It is a
purine nucleoside analogue, used as antiviral agent against herpes viruses.
Assay: Dissolve the sample in anhydrous acetic acid and titrate with
0.1 M perchloric acid. Determine the end point potentiometrically. Perform a
blank titration.
Dose: For herpes virus infections the administered dose for
immuno-suppressed patients is up to 10 mg/kg body weight every 8 h.
Dosage forms: Acyclovir cream B.P., Acyclovir eye ointment B.P., Acyclovir
intravenous infusion B.P., Acyclovir oral suspension B.P., Acyclovir tablets
B.P., Dispersible acyclovir tablets B.P.
Metabolism of Valacyclovir: The related analogue 6-deoxy acyclovir is a
prodrug form of acyclovir that is activated through metabolism by xanthine
oxidase.
Metabolism of Cidofovir: It is metabolized by phosphorylation and it
gives cidofovir diphosphate.
Metabolism of Famciclovir: It is a prodrug of penciclovir, which is formed in vivo by hydrolysis of acetyl groups and oxidation at the 6th position by the mixed function oxidase. Penciclovir and its metabolite penciclovir triphosphate posseses antiviral activity.
Metabolism of vidarabine: It is deaminated rapidly by adenosine deaminase enzyme,
which is present in the serum and the red blood cells. The enzyme converts
vidarabine to its principal metabolite, arabinosyl hypoxanthine, which has weak
antiviral activity.
Uses: It is used for the short-term treatment of herpes simplex and
chicken pox caused by varicella-zoster virus (VZV).
Synthesis
Properties and uses: Ganciclovir is a white powder, soluble in water
and it is used as an antiviral agent.
Dose: The recommended dose is 5 mg/kg 1 h for infusion every 12 h for
14 days.
Synthesis
Metabolism: It has a plasma half-life of 30 min and it is rapidly
metabolized in the blood to idoxuracil and uracil.
Properties and uses: Idoxuridine is a white crystalline powder,
slightly soluble in water and in alcohol. It dissolves in dilute solutions of
alkali hydroxides. It is a pyrimidine nucleoside analogue and used as an
antiviral agent against herpes virus .
Assay: Dissolve the sample in dimethylformamide and titrate with 0.1 M
tetrabutyl ammonium hydroxide. Determine the end point potentiometrically.
Dose: The administered dose topically as a ointment is 0.5%, 4–16
times a day or 0.1 ml of a 0.1% solution every 1 to 2 h into the conjunctiva.
Dosage forms: Idoxuridine eye drops B.P.
Synthesis
Dose: The recommended oral dose is 1.5–3.0 g twice daily for four
days. As a prophylactic against small pox, it should be administered before the
8th or 9th day of the 12-day incubation period.
Uses: Used in the treatment of viral infection.
Synthesis
Metabolism: Approximately, 90% of the drug is excreted unchanged by the
kidney, primarily through glomerular filtration and tubular secretion, and there
are no reports of metabolic products. Acidification of urine increases the rate
of amantadine excretion.
Properties and uses: Amantadine hydrochloride is a white crystalline
powder, soluble in water and in alcohol. Amantadine is used in the treatment of
Parkinson’s disease. It is effective against influenza type-A virus, para
influenza, and some RNA virus. It is also used as a dopamine receptor agonist.
Assay: Dissolve the sample in a mixture of 0.01 M hydrochloric acid and
alcohol (1:10) and titrate with 0.1 M sodium hydroxide. Determine the end point
potentiometrically.
Dose: The usual recommended dose is 100 mg twice daily. For children
1–9 years of age the administered dose is 4–9 mg/kg and 9–12 years of age 100
mg twice daily.
Dosage forms: Amantadine capsules I.P., B.P., Amantadine oral solution B.P.
Synthesis
Metabolism: Rimantadine is metabolized in the liver and approximately 20% is
excreted unchanged as hydroxylated compound.
Properties and uses: Rimantadine is a white to off-white crystals,
soluble in water. It is used for the prevention of infection caused by various
strains of influenza virus-A.
Dose: The recommended dose usually is 300 mg.
1-(3,4-Dihydroxy-5-(hydroxymethyl)-tetrahydrofuran-2-yl)-1H-1,2,4-triazole-3-carboxamide
Synthesis
Properties and uses: Ribavirin is a white crystalline powder, soluble
in water, slightly soluble in ethanol and in methylene chloride. It is used in
the treatment of influenza type-A and -B, hepatitis, genital herpes, and Lassa
fever.
Assay: It is assayed by adopting liquid chromatography technique.
Dose: For viral hepatitis, influenza, and herpes virus infections, the
recommended dose is up to 1g per day in divided doses.
Dosage forms: Ribavirin nebulizer solution B.P.
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