herpes symptoms : Antiviral Drugs For Herpes Treatment part2

Mechanism of action



Antiviral agents reduce viral replication by inhibiting viral DNA synthesis, needed to reproduce itself. This helps to keep the virus inactive.

Approved indications and uses



Acyclovir is indicated for:



treatment of initial episodes and the management of recurrent episodes of genital herpes


treatment of acute herpes zoster (shingles)


treatment of chickenpox (varicella)


Valacyclovir is indicated for:



treatment or suppression of genital herpes and for the suppression of recurrent genital herpes


reduction of transmission of genital herpes


treatment of herpes zoster


treatment of cold sores (herpes labialis)


Famciclovir is indicated for:



treatment or suppression of recurrent genital herpes


treatment of acute herpes zoster


Efficacy



Clinical studies have not found any significant differences in effectiveness among the three medications. All are quite safe, very rarely producing any side effects at all. For the treatment of first genital herpes infections, oral acyclovir or valacyclovir is preferable to famciclovir. The efficacy of famciclovir for initial episode genital herpes infection has not been established.

Intravenous acyclovir is used to treat serious flare-ups or outbreaks that effect internal organs.

Adverse reactions and side effects


All these agents are well tolerated and have excellent safety records. Possible side effects from oral agents include nausea, vomiting, headache, fatigue, tremor, and very rarely, seizures. They can effect the kidney, however, and people with kidney problems should use them with caution and at lower doses. Intravenous administration increases the risk for kidney problems and can cause blood clots at the injection site. In rare cases, it can cause central nervous system complications.

Pharmacokinetics


Acyclovir has poor bioavailability of about 20% and a short half-life, which necessitates frequent dosing. Acyclovir speeds healing of lesions and suppress viral shedding if taken within 24 hours of the first indication of a recurrent episode. Early treatment may even prevent the development of lesions in some patients.

Valacyclovir provides a unique mechanism of enhancing the oral bioavailability of the parent compound, acyclovir. Valacyclovir is a prodrug converted to acyclovir in the intestine and liver. It has better bioavailability (about 55%) and has a longer duration of action than acyclovir. Thus, valacyclovir requires less frequent dosing than acyclovir. Valacyclovir is most effective if taken within 24 hours of the first signs of an outbreak.

Famciclovir is a prodrug for the active metabolite penciclovir. Famciclovir is converted into its active compound within the infected cell by contact with an enzyme from the virus. It has high bioavailability of 77%. It remains active in the body longer than acyclovir (half the dose is still active after 10 to 20 hours) and, like valacyclovir, requires less frequent dosing (usually two or three times a day). It is most effective if taken within six hours of onset of symptoms.

Both Famciclovir and valacyclovir have greater oral bioavailability that acyclovir. Famciclovir and valacyclovir, which are better absorbed by the body, can be taken less often than acyclovir. The simpler dosing schedule of famciclovir and valacyclovir, allows patients more convenient dosing regimens with less interruption of their activities of daily living.

by Yury Bayarski