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Drug
Interactions in Primary Care Geriatrics -
Part two of a two-part
review
by
Anne Hume, Pharm.D.,FCCP, BCPS, Professor
of Pharmacy and Department Chair, URI
College of Pharmacy; Adjunct Professor of
Family Medicine, Brown University School
of Medicine; RIGEC Faculty
Member
In
last month's feature, Drug Interactions
in Primary Care Geriatrics, the case
of a 74 year old man with septic arthritis
and a deep venous thrombosis was
presented. In follow-up to the case, the
gentleman has subsequently been maintained
on a low molecular weight heparin as a
therapeutic INR had not been achieved
despite doses of warfarin 25mg daily. The
most likely cause for the failure to
achieve a therapeutic INR was the
concomitant use of rifampin as a potent
inducer of warfarin's hepatic
metabolism.
Drug
interactions remain a significant concern
in primary care geriatrics despite the
availability of different types of
computer screening programs. One recent
review has identified that
neuropsychological impairment,
hypotension, and acute renal failure are
the most common outcomes associated with
drug interactions in older persons. The
following table outlines common,
potentially important drug
interactions
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Common
Drug Interactions in
Geriatrics
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Pharmacokinetic
Interactions
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Primary
Drug
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Interacting
Drugs
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Warfarin
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Anti-infective
agents (eg. ciprofloxacin,
levofloxacin,
trimethoprim/sulfamethoxazole,
erythromycin/clarithromycin,
antifungal agents,
etc)
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Cisapride
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Antifungal
agents,
erythromycin/clarithromycin,
phenothiazines, etc.
|
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Amiodarone
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Warfarin,
digoxin
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Cimetidine
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Multiple
drugs, iron (decreased
absorption)
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Omeprazole
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Iron
(some of cimetidine's
interactions?)
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Quinolone
antibiotics
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Cations,
theophylline
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Phenytoin
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Multiple
drugs, low serum
albumin
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NSAIA
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Antihypertensive
agents such as diuretics,
beta-blockers, ACE inhibitors;
warfarin
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Pharmacodynamic
Interactions
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Multiple
anticholinergic agents prescribed
concomitantly
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Multiple
serotonergic drugs prescribed
concomitantly
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Multiple
drugs (& concomitant
conditions) that increase
potassium levels
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Concluding Tips:
At
every visit, review all medications that
the older person is taking, including
prescription, nonprescription, and natural
products in order to prevent drug
interactions and adverse drug
events.
A
great general website for drug
interactions is http://www.drug-interaction.com.
Also, www.drkoop.com
has a drug checker for prescription and
nonprescription products.
For
interactions involving grapefruit
interactions with prescriptions drugs:
www.powernetdesign.com/grapefruit
Finally,
for a varety of articles on drug
interactions, go to go to www.medscape.com.
Then, using the Search Medscape feature,
enter "drug interactions" and click "go."
For specific information about HIV
medications (which will become more
important), enter "HIV medications" in the
Search area.
Please
note: use of the Medscape site is free
of charge, but it does require you to
register in order to access all of the
articles and CME/CE
opportunities.
Clicking
on the links above will open a new window
in your browser at the selected web
site.
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