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.
Valcyte (Roche)
450 mg film-coated tablets
Approved indication: cytomegalovirus retinitis
Australian Medicines Handbook section 5.3.1
Immunosuppressed patients, particularly those with AIDS, are at risk of cytomegalo virus infection. This can cause a retinitis which may result in blindness. Patients can be treated with ganciclovir, but as its oral bioavailability is low treatment has to begin with two or three weeks of intravenous therapy. Valganciclovir is a prodrug of ganciclovir which allows induction therapy to be given orally.
The bioavailability of valganciclovir is approximately 60%, but this can be increased by taking the drug with food. As valganciclovir is converted to ganciclovir in the gut wall and liver very little reaches the systemic circulation. Ganciclovir is mainly excreted in the urine, so the dose of valganciclovir should be reduced in patients with renal impairment.
A randomised trial studied the progression of newly diagnosed cytomegalo virus retinitis after four weeks of treatment. Seventy patients were treated with intravenous then oral ganciclovir and 71 patients took oral valganciclovir. The retinitis progressed in approximately 10% of each group. After four weeks all the patients took valganciclovir for maintenance. The retinitis progressed after a median time of 125 days in the patients induced with ganciclovir and 160 days in the valganciclovir group.1
As ganciclovir has many adverse effects it is not surprising that there are frequent adverse reactions in patients given valganciclovir. Diarrhoea, nausea and vomiting are common. As neutropenia occurs in 27% of patients and anaemia in 26%, frequent blood counts are indicated. Taking too much valganciclovir can cause fatal bone marrow suppression. It is therefore vital to remember that valganciclovir tablets should not be substituted, one for one, for ganciclovir capsules.
Patients with cytomegalovirus retinitis may prefer to begin their treatment with oral rather than intravenous therapy. As well as the convenience, valganciclovir avoids the morbidity associated with giving intravenous ganciclovir. However, the available information does not say if patients can be induced with valganciclovir then switched to ganciclovir for maintenance therapy.
