Plerixafor

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Mozobil (Genzyme)
vials containing 20 mg/mL
Approved indications: lymphoma, multiple myeloma
Australian Medicines Handbook section 14.4

High-dose chemotherapy is used in the treatment of cancers such as non-Hodgkin's lymphoma and multiple myeloma. As this suppresses the bone marrow, the patient may be transfused with stem cells to improve survival. Autologous transplants use the patient's own previously collected stem cells. Normally there are not many stem cells in the peripheral blood, but they can be mobilised from bone marrow by colony stimulating factors such as granulocyte colony stimulating factor (G-CSF).

In some patients, G-CSF does not mobilise enough stem cells. By inhibiting a chemokine receptor, which has a role in holding cells within the bone marrow, plerixafor helps to release stem cells into the blood. Plerixafor was originally studied as a treatment for patients infected with HIV, but was found to cause an increase in white blood cells associated with stem cell mobilisation.

An open-label pilot study gave patients with multiple myeloma and non-Hodgkin's lymphoma different regimens of G-CSF and plerixafor. Most of the 40 patients who were given plerixafor had enough cells mobilised for transplantation.¹

A phase III trial randomised 298 patients with non-Hodgkin's lymphoma to receive G-CSF with or without plerixafor. G-CSF was given daily for up to eight days, with patients starting plerixafor or a placebo on the fourth day and continuing it for up to four days. The target was the collection of at least 5 x 10⁶ CD34+ cells per kg body weight within four days. This outcome was achieved by 59.3% of the 150 patients randomised to plerixafor, but by only 19.6% of those who added placebo. The response enabled 90% of the plerixafor group to have transplantation compared to 55.4% of the placebo group.²

Another study compared G-CSF with or without plerixafor in 302 patients with multiple myeloma. The target was the collection of 6 x 10⁶ CD34+ cells per kg within two days. This was achieved by 71.6% of the 148 patients randomised to receive plerixafor and 34.4% of the placebo group. Transplantation took place in 95.9% of the plerixafor group and 88.3% of the placebo group.³

The main trials did not give plerixafor alone. It is therefore only approved for use in combination with G-CSF.

There is a concern that plerixafor could mobilise tumour cells as well as stem cells. In a study of seven patients with multiple myeloma, G-CSF alone increased the frequency of tumour cells in five patients. Three patients given plerixafor after G-CSF had an increase in tumour cells in their peripheral blood, so plerixafor appears unlikely to have a significantly greater effect on tumour cell mobilisation.⁴

Plerixafor is given by subcutaneous injection and injection-site reactions are more common than with G-CSF alone. The drug is not metabolised and most of the dose is excreted in the urine. A reduced dose is given if the patient has moderate to severe renal impairment (creatinine clearance 20–50 mL/min). Patients complaining of upper abdominal or scapular pain should be investigated as animal studies show splenic enlargement. Some patients given plerixafor will have excess white cell production, while others will develop thrombocytopenia. Other adverse events which occur more frequently with G-CSF and plerixafor than with G-CSF alone include nausea, vomiting and diarrhoea.

While plerixafor increases the mobilisation of stem cells, it does not have much impact on the patients' survival. After a year, 88% of the patients with non-Hodgkin's lymphoma given plerixafor had survived compared with 87.2% of those given G-CSF alone.² In multiple myeloma, 95.3% of the plerixafor group had survived compared with 96.1% of the patients given G-CSF alone.³

manufacturer provided additional useful information

The Transparency Score () is explained in New drugs: transparency, Vol 37 No 1, Aust Prescr 2014;37:27.