Vidarabine originates from two nucleosides called spongouridine and spongothymidine which come from the sponge called Tethya crypta. It began being chemically synthesized in 1960. This led to the discovery of D-arabinose. It's administered topically as an ointment and is sold under the brand name Vira A. The chemical formula is C10H15N5O5.
It was the first analog nucleoside antiviral administered. It also was the first to be approved for treating herpes infections. Vidarabine has antineoplastic properties, and its main use is in treating viruses. Its antiviral properties were discovered and it is now used for that purpose. Vidarabine works by affecting how viruses reproduce. It's a nucleoside analog, so the virus uses that in the RNA synthesis. The telomeres are unable to properly reproduce and the virus dies as a result of the blocking action of the protein
In a three-step process, vidarabine prevents the replication and synthesis of DNA in viruses. Its half-life is 60 minutes and it has a solubility of .05%. Vidarabine was originally created at Stanford Research Institute.
It is no longer available as an intravenous medicine. It is possibly poisonous when ingested, and is used exclusively topically.
The method of action is not completely understood. It is known to affect how RNA in viruses is synthesized as well as the cells.
Vidarabine is reduced to arabinosylhypoxanthine. This is the principal metabolite. It has low solubility. Because of this, it can be only detected in the aqueous humor if the cornea has an epithelial defect. It easily crosses the placenta and blood-brain barrier. Most of it is excreted by the kidneys. In normal adults, the plasma half-life is 1.5 hours.
60% of vidarabine is excreted by the kidneys through urine as 9-β-D-arabinofuranosylhypoxanthine.
Currently, the main use is an ophthalmic ointment. Patients with symptoms will be analyzed by an eye doctor with a microscope before being prescribed the medication.
Every gram has 30 mg of vidarabine monohydrate. This is equal to 28.11 of vidarabine in an inert, serial, petrolatum base.
The physician diagnoses the condition and prescribes the medication upon examination. If there is a detected presence of typical geographic or dendritic lesions while examining using a slit-lamp, then the patient is diagnosed with keratitis.
IT is prescribed when the patient is not responsive to other medications, including topical idoxuridine. It is also an alternative when the patient has toxic or allergic reactions because of idoxurdine.
Different side effects have been reported in relation to the eye. One is ocular toxicity consisting of increased tearing and occasional hyperemia. Another effect to the eyes is increased tears, called lacrimation, or blurred vision which is common in medications such as that one.
Another side effect can be photophobia and increased sensitivity to light in patients. At the site of administration, there could be pain or irritation. Some patients report overall sensitivity or superficial punctate keratitis. Other vision effects include painful peripheral neuropathy.
In laboratory testings, increased tumors in livers were found in mice. This indicates that vidarabine is a possible carcinogen. Male mice showed more kidney neoplasia. Other lab studies showed rats had more intestinal, thyroid and testicular neoplasia. There was also an increase in thyroid adenoma in male and female rats.
Other reported side effects include hyphema, vascularization, uveitis, secondary glaucoma, corneal vascularization and trophic defects. Patients experience foreign body sensation and irritation. Another possible side effect is a rash. There are also occurrence of anemia or elevated transaminases.
Studies show that vidarabine increases the likelihood of cell mutation. When it is applied to human leukocytes, it affects how genes are expressed and it can cause chromosome breaks and gaps. This gene damage is possibly inheritable.
Vidarabine is a possible teratogen, and pregnant women are advised not to use it. Studies in animals show fetal abnormalities when it is used. It is not known whether or not it is expressed in breast milk, however, it is up to the mother to decide if she wants to stop breastfeeding.
Vidarabine is expelled through the gastrointestinal tract, and it could possibly cause GI toxicity. It can also cause acute neurotoxicities, weakness, thrombocytopenia or hypokalemia.
The ointment is prescribed topically. The patient is to administer about one-half inch of vidarabine to the eye area, specifically the lower part of the conjunctival sac five times a day every three hours. The patient is not to use the medication too many times a day. They are to be monitored for 7 days. If improvement isn't seen, or complete re-epithelialization has not happened after 21 days, then other methods should be used.
When a dose is missed, reapply as soon as remembered or wait until the next dose.
Usage should not exceed recommended treatment length. However, difficult or recurring cases may have a longer treatment period.
In superficial herpes simplex keratitis, using vidarabine and corticosteroid is not advised. It potentially could help severe infections, however, it also has the potential to spread. If this method is taken, then different side effects could happen including glaucoma, cataract formation or intraocular pressure. Other potential side effects are ocular edema or progression of a viral or bacterial infection.
When allopurinol and vidarabine are used together, side effects of anemia, tremors, pain, nausea and pruritus are seen in some patients.
Vidarabine and acyclovir both show uses for anti-herpetic activity. They have different mechanisms of action and work synergistically on the plaque formation.
Hallucinosis has been reported when patients use too much. It is only to be used under close supervision of an eye doctor.
Some patients with CNS infections with impaired renal functions might need a large volume of IV solution to solubilize vidarabine. Patients with impaired kidney or liver function should use vidarabine with caution, as well as patients prone to cerebral edema or fluid overload. In these cases, leukocyte and platelet counts, serum AST (SGOT) concentration, hematocrit and hemoglobin should be monitored.
There is no recommended safe dosage for children under the age of two. The use in geriatrics is not documented, however there are no contraindications for it.
If vidarabine is ingested, there is a possibility of burns or pain in the mouth, esophagus or gastrointestinal tract.
With chronic exposure, an individual might express hypersensitivity. This includes allergic reactions such as asthma with bronchospasm, wheezing or hypersensitivity dermatitis.
Because of the potential of producing abnormalities of the liver, kidneys and hematopoietic system, there would be a need for tests after long exposure. This includes but is not limited to urinalysis, complete blood count and kidney and liver function tests.
If there is evidence of respiratory depression or respiratory tract depression, then there is need to perform a chest x-ray, monitor arterial blood gases and perform tests on pulmonary functions.
Vidarabine, when it is consumed, is a potentially life-threatening poison. The remedy is activated charcoal, as well as dilution.
When it is heated to the point it decomposes, vidarabine emits nitrous oxides toxic fumes.
The debate on contact lenses is unsettled. However, in most cases wearing contact lenses would be corrosive, dangerous and unproductive for the treatment.
Proper disposal methods are to be discussed with environmental protection agencies.
Vidarabine is not effective against adenoviral ocular infections or RNA virus. It's also not effective against fungal, bacterial or chlamydial infections. It is not approved for adenoviruses or nonviral trophic ulcers.
Vidarabine is to be stored at temperatures less than 40 degrees Celcius. The preferable temperature is between 15 to 30 degrees. It should not be frozen.
As well as being used as a nucleoside antibiotic, Vidarabine has a variety of antiviral applications. It was researched as a potential cancer treatment and it was the first antiviral ever approved for used. The nucleoside was discovered in a sponge and is now created synthetically using a culture.
Vidarabine is used in a variety of eye conditions. These include keratoconjunctivitis, herpes simplex virus treatment and keratitis.
It acts by inhibiting the viruses DNA polymerase and inhibits virus-induced ribonucleotide reductase as well as other enzymes specific to viruses involved in DNA synthesis. This acts by preventing the DNA chain to lengthen. Intracellularly, it is phosphorylated to arabinosyl adenosine monophosphate or triphosphate. It might be given with other antibiotics like erythromycin, gentamicin, or chloramphenicol. Vidarabine is prescribed by an eye doctor following an examination. The patient follows the application schedule and uses it three times a day. If it is ingested it can be toxic or fatal. Because of this, care should be used to use the appropriate amount.