February 2016
clinical initiatives, research and current updates in treatment
Elastomeric infusion devices in cancer treatment: a brief guide Thomas Wong, River City Pharmacy, Icon Cancer Care In the day-hospital setting, when intravenous chemotherapy is given as a continuous infusion, the use of an ambulatory infusion device is indispensable. This article will explore the rationale of why chemotherapy is given as a continuous infusion, ambulatory infusion devices in general and will then focus on elastomeric devices: how they work, their advantages, disadvantages and then some tips and troubleshooting.
Why is chemotherapy given as a continuous infusion? Chemotherapy is given as a continuous infusion in an attempt to increase anti-tumour activity and also to reduce its toxicity.1 Administering by continuous infusion: ¬ ¬ Increases the exposure of cancer cells to chemotherapy agents with a short half-life e.g. cytarabine 1 ¬¬ Increases the likelihood of exposure to cancer cells when they are in the specific targeted phase for cellcycle specific chemotherapy agents e.g. cytarabine is S-phase specific
¬¬ Increases the duration of exposure to cancer cells results in increased effectiveness of some chemotherapy agents e.g. methotrexate ¬¬ Reduces acute toxicities e.g. fluorouracil and mucositis and neutropenia 1 ¬ ¬ Enables more dose intense schedules to be given e.g. fluorouracil Ambulatory infusion devices enable patients requiring continuous infusion chemotherapy to be treated on an outpatient basis. Without these devices, more frequent and longer hospital admissions would be required, reducing patient quality of life and increasing costs for the health system.1
Ambulatory infusion devices There are many different ambulatory infusion devices available on the market. Broadly speaking ambulatory infusion devices can be divided into battery-driven pumps (e.g. CADD pumps) and self-driven pumps (e.g. elastomeric devices). The most common elastomeric devices are the Baxter range and these are called Infusors and Folfusors (see figure 1).
Figure 1: Baxter Folfusor device
How do elastomeric devices work? With an elastomeric device, the drug is held in a stretchable balloon reservoir and the elastic wall of the balloon creates the pressure which drives drug delivery (see figure 2).2 The flow rate is determined by a flow restrictor that is located at the end of the tubing. The flow restrictor is a piece of tubing with a smaller bore (diameter) than the tubing. The smaller bore increases the pressure gradient and thereby slows the rate of flow of drug out the tubing.3
Factors which affect the flow rate of elastomeric devices There are a number of factors that can affect the flow rate of elastomeric devices, making it faster or slower, and these include: ¬¬ Height; if the device is lower than the flow restrictor, the flow rate will decrease, and conversely will increase if the device is above the flow restrictor ¬¬ Initial filling volume; if the device is under filled (<80%) the flow rate will increase and will decrease if filled close to its maximum allowed volume Continued on page 2