Collaboration Needed to Maximize Tamoxifen’s Benefit

May 2010, Vol 1, No 1

Barcelona—An effort to monitor and modify prescription drug use in breast cancer patients prescribed tamoxifen can help prevent the polypharmacy that lessens tamoxifen’s effectiveness.

Drugs including bupropion, fluoxetine, and paroxetine can inhibit the action of the CYP2D6 enzyme, which is crucial to the metabolism of tamoxifen for breast cancer. Sean Hopkins, BSc, RPEBC, a clinical pharmacy specialist in breast cancer at the Ottawa Hospital Regional Cancer Centre, Ottawa, Canada, described an effort at his institution to investigate how many patients taking hormonal therapy for breast cancer were also being prescribed CYP2D6 inhibitors. He presented his findings at EBCC7.

Mr Hopkins began by extracting drug claim data from the Ottawa Hospital Breast Cancer Disease Site Group clinical database, including any patients on tamoxifen, aromatase inhibitor (AI) therapy, or CYP2D6 inhibitors. Of 531 claims eligible for this analysis, 463 (87%) of these patients received 1 of the prescribed hormonal therapies while 68 (13%) were not on hormonal therapy but did receive the CYP2D6 medications. Seven patients (4.5%) receiving tamoxifen and 16 patients (5%) receiving an AI were concurrently on a strong CYP2D6 inhibitor. Moderate enzyme inhibitors were given to 1 patient (0.6%) on tamoxifen and 6 patients (1.9%) receiving an AI. Weak CYP2D6 inhibitors were given to 24 patients (16.5%) on tamoxifen and 40 patients (12.4%) on an AI.

Unlike a “straight” retrospective study, however, this one allowed intervention on the part of Mr Hopkins. He noted in a press release announcing the findings, “We have been able to take action as soon as we have discovered that a patient is taking interacting medication(s) by contacting the prescribing doctor in order to get them to switch to a different medication with no deleterious effect on tamoxifen metabolism.”

Communication Is Key

“We have known for a while that patients with a deficiency in CYP2D6 activity did not derive the full benefit from tamoxifen because they cannot metabolize it to endoxifen, its active metabolite,” said Mr Hopkins.

For these patients, having the knowledge to be able to plan effectively in advance is important, as it can take many weeks to wean patients off CYP2D6 inhibitors, and this may affect their breast cancer therapy. The findings reinforce the need for good communication between all healthcare providers in order to eliminate the risk of reducing the efficacy of prescribed therapy, Mr Hopkins indicated.

“Patients can receive care from many different healthcare professionals—oncologists, other specialists, family doctors, etc—and they can receive medications from multiple pharmacies,” he continued. “If there is insufficient information transfer between the individuals who care for a patient, the risks of drug interactions increase, and this can affect the quality and efficacy of care being given.”

In addition to communication, another means to better care could be greater openness among those providing and paying for care, Mr Hopkins said. “I believe that we need to have policies in place to require healthcare providers and their agencies, including private insurance companies, to provide better access to information for healthcare professionals involved in patient care. If these organizations try to protect their information in an unreasonable manner, it can seriously impact care and outcomes for patients.”

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