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.
Famvir (SmithKline Beecham)
250 mg film coated tablets
Indication: herpes zoster
Patients who present within 72 hours of developing herpes zoster can be treated with acyclovir tablets 5 times daily. Prescribers now have the option of treating adults with famciclovir tablets 3 times daily.
Famciclovir is rapidly absorbed from the gut, but absorption is delayed by food. The drug is quickly converted to penciclovir. This is converted to penciclovirtriphosphate in infected cells and, subsequently, viral DNA synthesis is inhibited. Excretion is by the kidneys, but no unchanged famciclovir is found in the urine. The interval between doses should be increased in patients with renal impairment. The half life of penciclovir is approximately 2 hours.
For the treatment of shingles, the efficacy of famciclovir is probably similar to that of acyclovir. However, the efficacy of famciclovir in ophthalmic herpeszoster and chicken pox has not been studied, and the drug is less efficacious in patients less than 50 years old. If treatment is started early enough, patients taking famciclovir will heal sooner than patients taking placebo. The duration of postherpetic neuralgia may also be reduced.
The adverse effects of famciclovir include headache and nausea. These effects are also associated with acyclovir, so at present the only advantage of famciclovir over acyclovir appears to be that it has to be taken less often.