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Drug interaction dilemmas
Citation
Peterson, GM, Drug interaction dilemmas, Journal of Pharmacy Practice and Research, 41, (1) pp. 7-12. ISSN 1445-937X (2011) [Letter or Note in Journal]
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Abstract
Drug interactions represent a dilemma when reviewing
patients’ medications. Clinicians either become paralysed
with fear or indifferently dismiss the relevance of any
possible drug interactions that they may encounter.
The ageing population, increasing complexity of
medication regimens used in ambulatory patients and a
fragmented health system with multiple prescribers
managing each patient make the occurrence of serious
drug interactions more likely.1-3 A recent issue of Nature
Medicine reported that as the use of multiple medications
increases (e.g. 1 in 10 Americans are now on 5 or more
medications, nearly twice the rate as in 2000), so does the
risk that these medicines may interact in unpredictable
ways that may not be quickly detected or that they are
co-prescribed without regard for potential interactions.4
Examples include the use of selective serotonin reuptake
inhibitors with either codeine or tamoxifen, when there is
evidence that some selective serotonin reuptake
inhibitors can inhibit the metabolism of codeine to
morphine via CYP2D6 and reduce the analgesic effect of
codeine, and similarly block tamoxifen’s conversion to
one of its active metabolites (endoxifen). Interestingly,
and illustrating the drug interaction conundrum, reference
to standard monographs, such as Stockley’s Drug
Interactions, indicates doubt over the clinical significance
of both these interactions.
The importance of drug interactions in terms of
incidence, clinical significance and cost to society is
difficult to assess.5 An estimated 1 in 200 hospitalised
patients have a serious adverse drug event caused by
drug interactions, 1 in 10 000 hospital deaths may be
attributed to drug interactions, and up to 20% of adverse
drug events needing hospitalisation are caused by drug
interactions.6-8 It has been suggested that 2% of
hospitalised cancer patients have a drug interaction as
their cause of admission.9,10
A large Canadian study reported that the risk of
hospitalisation for people over 65 years substantially
increased when exposed to a drug interaction.11 The
authors concluded that: ‘Many hospital admissions of
elderly patients for drug toxicity occur after administration
of a drug known to cause drug-drug interactions. Many
of these interactions could have been avoided’.11
Around 13% of preventable prescribing errors
detected in ambulatory patients were due to drug
interactions.12 In a study of 1601 elderly outpatients living
in six European countries, 46% of patients had at least
one clinically significant drug interaction, and 10% of
these interactions were of high severity.13 The link
between adverse effects and an underlying drug
interaction is probably under-recognised and frequently
attributed to comorbidities. Health professionals may not
suspect that an elderly patient’s new symptoms are due
to an underlying drug interaction.3
Conversely, drug interactions can be beneficial and
intentional, such as combining antihypertensives to
achieve a potentiated effect, and the clinical significance
of some interactions has been markedly overstated, e.g.
plasma protein binding displacement interactions.4,14
There is also significant inter-patient variability in
response to drug interactions, so that an interaction might
manifest clinically with adverse outcomes in one patient
and have no consequences in another.
Roughead et al. recently studied the prevalence of
hazardous drug interactions in the elderly Australian
veteran population.15 Using data from the Department of
Veterans’ Affairs pharmacy claims database, they
determined that 1.5% of the study population (n = 287
074) were dispensed potentially hazardous interacting
drug pairs during a 3-month period. When limited to
patients dispensed verapamil, methotrexate, amiodarone,
lithium, warfarin, cyclosporin or itraconazole, potentially
hazardous interactions occurred at a rate higher than 5%.
What does this mean? How could this occur? Either
the drug interactions are not being detected, are ignored,
or the combination of drugs is being managed and the
patients monitored to ensure that there are no adverse
clinical ramifications. It is unlikely that drug interactions
are routinely undetected. Statutory requirements
necessitate that Australian community pharmacies use
software systems that can identify potential drug
interactions, and alert the pharmacist to intervene before
dispensing the interacting drugs. In an area with a lot of
unknowns, there are several aspects relating to drug
interactions that are clear.
Item Details
Item Type: | Letter or Note in Journal |
---|---|
Research Division: | Biomedical and Clinical Sciences |
Research Group: | Pharmacology and pharmaceutical sciences |
Research Field: | Clinical pharmacy and pharmacy practice |
Objective Division: | Health |
Objective Group: | Public health (excl. specific population health) |
Objective Field: | Public health (excl. specific population health) not elsewhere classified |
UTAS Author: | Peterson, GM (Professor Gregory Peterson) |
ID Code: | 69348 |
Year Published: | 2011 |
Deposited By: | Pharmacy |
Deposited On: | 2011-04-19 |
Last Modified: | 2011-04-19 |
Downloads: | 9 View Download Statistics |
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