Pegfilgrastim (pegylated filgrastim)

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.

Neulasta (Amgen)
syringes containing 6 mg/0.6 mL
Approved indication: neutropenia
Australian Medicines Handbook section 14.2.1

Granulocyte colony stimulating factor (G-CSF) promotes the production of neutrophils. Recombinant forms of G-CSF (filgrastim, lenograstim) can be used to treat neutropenia and are useful for patients receiving aggressive chemotherapy (see 'Granulocytecolony stimulating factor (G-CSF)' Aust Prescr 1994;17:96-9).

Recombinant G-CSF has to be given as a daily injection or infusion until the patient recovers. The half-life of filgrastim is approximately three hours, however the addition of a polyethylene glycol molecule extends this to 15-80hours. This enables patients to be treated with only one subcutaneous dose in each cycle of chemotherapy.

The prolonged half-life of pegylated filgrastim (pegfilgrastim) is brought about by reduced renal clearance. As pegfilgrastim clearance also involves it binding to receptors on neutrophils, clearance will increase as the patient recovers from neutropenia.

A single dose of pegfilgrastim has been compared with daily filgrastim in310 patients receiving chemotherapy for breast cancer. There were no significant differences in the duration and severity of the neutropenia. Febrile neutropenia developed in 9% of the patients given pegfilgrastim and 18% of those given filgrastim.1

The adverse effects of pegfilgrastim are similar to those of filgrastim. More than one in four patients will develop bone pain and this can be severe enough for some patients to need opioid analgesia. Serious adverse effects of filgrastim such as splenic rupture, adult respiratory distress syndrome and an aphylaxis have not yet been reported with pegfilgrastim.

Pegfilgrastim will probably not be significantly cheaper than filgrastim, but its less frequent administration makes it more convenient to use.