Видарабин

Описание

Vidarabine (adenine arabinoside) is the stereoisomer of adenosine. This analog of a purine nucleoside exhibits selective activity against the herpes virus. The ribose residue is replaced with an arabinose residue. Like acyclovir, it turns into mono-, di-, and triphosphate in cells infected by a virus, thus inhibiting DNA polymerase, and correspondingly preventing DNA synthesis of the virus approximately 20–40 times more than in “host” cells. It is easily metabolized to a less active, yet nonetheless antiviral compound—arabinosylhypoxanthine. It has been successfully used for herpetic encephalitis, and for complicated shingles. It is used in the form of eye drops for herpetic keratoconjuctivitis. A synonym of this drug is Vira-A.

Химические свойства

Crystalline

Использование

Vidarabine, is an antiviral drug which is active against herpes simplex and varicella zoster viruses.

Показания

Vidarabine (adenine arabinoside, Vira-A) is an adenine nucleoside analogue containing arabinose in place of ribose. It is obtained from cultures of Streptomyces antibioticus and has activity against HSV-1, HSV-2, VZV, CMV, HBV, poxviruses, hepadnaviruses, rhabdoviruses, and certain RNA tumor viruses.

Общее описание

Chemically, vidarabine (Vira-A), is 9--D-arabinofuranosyladenine.The drug is the 2'epimer of natural adenosine.Introduced in 1960 as a candidate anticancer agent, vidarabinewas found to have broad-spectrum activity against DNAviruses.The drug is active against herpesviruses,poxviruses, rhabdoviruses, hepadnavirus, and some RNAtumor viruses. Vidarabine was marketed in the United Statesin 1977 as an alternative to idoxuridine for the treatment ofHSV keratitis and HSV encephalitis. Although the agent wasinitially prepared chemically, it is now obtained by fermentationwith strains of Streptomyces antibioticus.
The antiviral action of vidarabine is completely confinedto DNA viruses. Vidarabine inhibits viral DNA synthesis.Enzymes within the cell phosphorylate vidarabine to thetriphosphate, which competes with deoxyadenosine triphosphatefor viral DNA polymerase. Vidarabine triphosphate isalso incorporated into cellular and viral DNA, where it actsas a chain terminator. The triphosphate form of vidarabinealso inhibits a set of enzymes that are involved in methylationof uridine to thymidine: ribonucleoside reductase, RNApolyadenylase, and S-adenosylhomocysteine hydrolase.
At one time in the United States, intravenous vidarabinewas approved for use against HSV encephalitis, neonatalherpes, and herpes or varicella zoster in immunocompromisedpatients. Acyclovir has supplanted vidarabine as thedrug of choice in these cases.

Реакции воздуха и воды

Insoluble in water.

Профиль реактивности

Vidarabine is an aminoalcohol. Amines are chemical bases. They neutralize acids to form salts plus water. These acid-base reactions are exothermic. The amount of heat that is evolved per mole of amine in a neutralization is largely independent of the strength of the amine as a base. Amines may be incompatible with isocyanates, halogenated organics, peroxides, phenols (acidic), epoxides, anhydrides, and acid halides. Flammable gaseous hydrogen is generated by amines in combination with strong reducing agents, such as hydrides.

Пожароопасность

Flash point data for Vidarabine are not available; however Vidarabine is probably combustible.

Механизм действия

Vidarabine’s specific mechanism of action is not fully understood. Cellular enzymes convert this drug to a triphosphate that inhibits DNA polymerase activity. Vidarabine triphosphate competes with deoxyadenosine triphosphate (dATP) for access to DNA polymerase and also acts as a chain terminator. Although vidarabine is incorporated into host DNA to some extent, viral DNA polymerase is much more susceptible to inhibition by vidarabine. Vidarabine also inhibits ribonucleoside reductase and other enzymes. Resistance occurs as a result of DNA polymerase mutation.

Фармакокине?тика

Vidarabine is deaminated rapidly by adenosine deaminase, which is present in serum and red blood cells. The enzyme converts vidarabine to its principal metabolite, arabinosyl hypoxanthine (ara-HX), which has weak antiviral activity. The half-life of vidarabine is approximately 1 hour, whereas ara-HX has a half-life of 3.5 hours. The drug is detected mostly in the kidney, liver, and spleen, because 50% of it is recovered in the urine as ara-HX. Levels of vidarabine in CSF fluid are 50% of those in the plasma.

Клиническое использование

The principal use of vidarabine is in the treatment of HSV keratoconjunctivitis. It is also used to treat superficial keratitis in patients unresponsive or hypersensitive to topical idoxuridine.

Побочные эффекты

The most commonly observed side effects associated with vidarabine are lacrimation, burning, irritation, pain, and photophobia. Vidarabine has oncogenic and mutagenic potential; however, the risk of systemic effects is low because of its limited absorption. It should not be used in conjunction with ophthalmic corticosteroids, since these drugs increase the spread of HSV infection and may produce side effects such as increased intraocular pressure, glaucoma, and cataracts.

Профиль безопасности

Poison by ingestion and intravenous routes. Moderately toxic by intraperitoneal route. An experimental teratogen. Other experimental reproductive effects. Human systemic effects by intravenous route: central nervous system, blood, and other effects. A skin and eye irritant. Human mutation data reported. When heated to decomposition it emits toxic fumes of NOx.