Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Valtrex (Glaxo Wellcome)
500 mg tablets
Indication: herpes zoster
In 1994, the introduction of famciclovir offered a 3 times daily alternative to 5 times a day treatment with acyclovir. The manufacturers of acyclovir have now introduced their own 3 times a day treatment for shingles.
Although valaciclovir is considered to be a new chemical entity, it is anester of acyclovir. Following absorption, valaciclovir is rapidly converted to acyclovir. Less than 1% of a dose of valaciclovir is recovered unchanged in the urine; it is mainly eliminated as acyclovir and metabolites of acyclovir. As acyclovir is only partially absorbed from the gut, a higher plasma concentration of acyclovir can be obtained by giving valaciclovir.
Like acyclovir, valaciclovir is approved for the treatment of herpes zosterin immuno competent adults presenting within 72 hours of the rash, and also for ophthalmic zoster. The patients most likely to benefit from treatment are those over 50 years old. In these patients, treatment may shorten the duration of pain by a few days. The preventive effect of valaciclovir for post-herpeticneuralgia is unclear.
The most common adverse effects of treatment with valaciclovir are nausea and headache. Doses should be reduced in patients with renal impairment.
While valaciclovir adds to the choice of therapy, not all patients with herpeszoster require treatment with an antiviral drug.