Vol. 8, No. 3
Printed in Great Britain
Family Practice
©Oxford University Press 1991
Potential Drug Interactions in an
Ambulatory Geriatric Population
ANTHONY J. COSTA
Drug interactions are a common cause of iatrogenic
disease in geriatric patients. A number of studies have
documented risk factors for drug interactions,1"6 which
include female sex, advanced age, number of diagnoses, and number of medications. Computer programs now exist which allow one to analyse groups of
drugs for potential interactions7-'4 and, hopefully,
identification of potential drug interactions will allow
physicians to make appropriate changes and undertake
the surveillance necessary to avoid such complications.
notes from the year 1989. The medications taken by
the patient at the time of his/her last 1989 appointment
were used to evaluate potential drug interactions.
Non-prescription medications, as well as medications
prescribed by a doctor outside the Family Practice
METHODS
An audit was performed on the charts of 100 geriatric
patients seen in the Family Practice Center at Barberton Citizens Hospital. A computer printout was
obtained, listing all patients aged 60 and over who were
seen at the Family Practice Center during 1989.
Patients were listed in alphabetical order, and were
listed only once, regardless of the number of times they
had been seen during the year. Names were selected
randomly from this list by the head nurse. Patient identification number, age, sex, diagnoses, medications,
and allergies were obtained. Medications were
obtained from each chart by reviewing the medication
flow sheet, the prescription record, and the progress
Patient
characteristic
Director, Barberton Gtizens Hospital, Family Practice Residency
Program, 155 Fifth Street, N.E., Barberton, OH 44203, USA.
Taylor series 95% confidencce limits for RR.
TABLE 1 Relative risk with respect to patient characteristics
Potential
interactions
234
Yes
No
Relative risk
Sex
Male
Female
10
17
33
40
1.28 (0.65<RR<2.5)
Age
60-75
>75
23
4
62
11
0.99 (0.40<RR<2.45)
Diagnoses
0-2
>2
14
13
66
7
3.71 (2.09<RR<6.60)
Medications
0-3
>3
17
10
69
4
3.61 (2.11<RR<6.20)
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Costa, AJ. Potential drug interactions in an ambulatory geriatric population. Family Practice 1991; 8:
234-236.
Drug interactions are a common cause of iatrogenic disease in geriatric patients. Computer programs
now exist which allow one to analyse groups of drugs for potential interactions. In an audit of charts of
100 geriatric patients seen in the Family Practice Center at Barberton Citizens Hospital, a computer printout was obtained, listing all patients aged 60 years and over who were seen at the Center during 1989.
Names were selected randomly from this list by the head nurse and their charts were obtained for
review, generating information on patient identification number, age, sex, diagnoses, medications, and
allergies. The medications were analysed using the Hansten Drug Interaction Knowledge Base Program,
which identified 27 patients as being on a combination of medications which had one or more potential
drug interactions. A total of 37 potential drug interactions were identified in this group of 27 patients.
Relative risk ratios were determined using the computer program, 'Epi Info,' for sex (female versus
male), age (>75 vs. 60-75 years), number of diagnoses 53 vs. 0-2), and number of medications (2=4 vs.
0-3). The five medications, or groups of medications, which were most likely to be involved in potential
drug interactions were digoxin, (5-blockers, oestrogen, oral hypoglycaemic agents, and diuretics.
DRUG INTERACTIONS IN AN AMBULATORY GERIATRIC POPULATION
TABLE 2
235
Relative risk in relation to drugs administered
Potential interactions
Digoxin
+
—
Beta Blockers
+
—
+
-
Oral Hypoglycemics
+
—
Diuretics
+
-
1
72
Relative risk = 3.56
(2.13<RR<5.94)*
85
19
4
69
Relative risk = 3.09
(1.76<RR<5.43)*
7
2
3
70
Relative risk = 3.15
(1.80<RR<5.52)*
6
21
3
70
Relative risk = 2.89
(1.59<RR<5.24)*
12
15
20
53
Relative risk = 1.70
(0.90<RR<3.20)*
'Taylor Series 95% confidence limits for RR.
Center, were included in the analysis for potential drug
interactions if they had been recorded on the patient's
chart.
The medications were analysed using the Hansten
Drug Interaction Knowledge Base Program. This program, which was developed at the University of
Wyoming College of Human Medicine, has been
reviewed and validated,14 and is used extensively
throughout the United States.
RESULTS
The total group'included 57 women and 43 men, with a
mean age of 69.4 years, a mean number of diagnoses of
1.8, and a mean number of medications of 2.1.
Twenty-seven patients were identified as being on a
combination of medications which had one or more
potential drug interactions. The Hansten Program
classifies potential interactions as major, moderate, or
minor: of the 37 potential drug interactions identified,
one was classified as major, 21 were classified as moderate, and 15 were classified as minor.
The group identified with potential drug interactions
included 17 women and 10 men, with a mean age of
69.7 years, a mean number of diagnoses of 2.9, and a
mean number of medications of 3.7. The group without potential drug interactions included 40 women and
33 men, with a mean age of 69.3 years, a mean number
of diagnoses of 1.4, and a mean number of medications
of 1.5.
Relative risk ratios were determined using the computer program 'Epi Info' for sex (female vs. male), age
&75 vs. 60-75), number of diagnoses (>3 vs. 0-2), and
number of medications (^4 vs. 0-3) (Table 1).
The five medications, or groups of medications,
which were most likely to be involved in potential drug
interactions were digoxin, fi-blockers, oestrogen, oral
hypoglycaemic agents, and diuretics. The relative risk
ratios are shown in Table 2.
Although no actual drug interactions occurred in
this group of patients, there was no indication on chart
review that the physician was aware of the potential for
drug interactions in those cases identified. No specific
monitoring or dosage adjustment was apparent. Thus,
perhaps the most important risk factor for actual drug
interaction (i.e., being on medications which have the
potential to produce interactions) appeared to be unrecognized in this group of patients.
SUMMARY
Actual drug interactions are common in geriatric
patients and contribute significantly to the mortality
and morbidity of this group. It is important that physicians recognize drugs which have the potential for creating interactions when used together; this will allow
the dosage modifications and surveillance necessary to
prevent actual drug interactions from occurring. Physicians should be especially cautious of patients who fall
into identified high-risk groups (patients with three or
more chronic diagnoses, patients with four or more
chronic medications), as well as those patients who are
on high-risk medications (digoxin, fJ-blockers, oestrogen and oral hypoglycaemic agents).
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