Doi:10.1016/j.pec.2007.03.024

Patient Education and Counseling 67 (2007) 293–300 To err is human: Patient misinterpretations of prescription Michael S. Wolf ,Terry C. Davis William Shrank David N. Rapp ,, Pat F. Bass , Ulla M. Connor Marla Clayman , Ruth M. Parker a Health Literacy and Learning Program, Institute for Healthcare Studies, Northwestern University, United States b Center for Communication and Medicine, Division of General Internal Medicine, Northwestern University, United States c Louisiana State University Health Sciences Center at Shreveport, United States d Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, United States e School of Education and Social Policy, Northwestern University, United States f Department of Psychology, Northwestern University, United States g Indiana Center for Intercultural Communication, Indiana University-Purdue University at Indianapolis, United States h Emory University School of Medicine, United States Received 23 February 2007; received in revised form 28 March 2007; accepted 30 March 2007 Objective: To examine the nature and cause of patients’ misunderstanding common dosage instructions on prescription drug container labels.
Methods: In-person cognitive interviews including a literacy assessment were conducted among 395 patients at one of three primary care clinics inShreveport, Louisiana, Jackson, Michigan and Chicago, Illinois. Patients were asked to read and demonstrate understanding of dosage instructionsfor five common prescription medications. Correct understanding was determined by a panel of blinded physician raters reviewing patient verbatimresponses. Qualitative methods were employed to code incorrect responses and generate themes regarding causes for misunderstanding.
Results: Rates of misunderstanding for the five dosage instructions ranged from 8 to 33%. Patients with low literacy had higher rates ofmisunderstanding compared to those with marginal or adequate literacy (63% versus 51% versus 38%, p < 0.001). The 374 (19%) incorrectresponses were qualitatively reviewed. Six themes were derived to describe the common causes for misunderstanding: label language, complexityof instructions, implicit versus explicit dosage intervals, presence of distractors, label familiarity, and attentiveness to label instructions.
Conclusion: Misunderstanding dosage instructions on prescription drug labels is common. While limited literacy is associated with misunder-standing, the instructions themselves are awkwardly phrased, vague, and unnecessarily difficult.
Practice implications: Prescription drug labels should use explicit dosing intervals, clear and simple language, within a patient-friendly labelformat. Health literacy and cognitive factors research should be consulted.
# 2007 Published by Elsevier Ireland Ltd.
Keywords: Prescription; Drug; Medication; Dosage; Instructions; Warnings; Misunderstanding; Health literacy prescription drug labeling were specifically cited as a leadingroot cause of a large proportion of outpatient medication errors According to the Institute of Medicine (IOM) 2006 report, and adverse events, as patients may unintentionally misuse a Preventing Medication Error, more than one third of the 1.5 prescribed medicine due to improper understanding of million adverse drug events that occur in the United States each instructions. The prescription container label, in particular, year happen in outpatient settings . Problems with is often the sole, tangible source of specific dosage/usageinstructions given to and repeatedly used by the patient.
Despite their potential value, problems are clearly evident with * Corresponding author at: Health Literacy and Learning Program, Institute container labels Dosage instructions on the label can for Healthcare Studies and Division of General Internal Medicine, North- vary, as they are dependent on what the prescribing physician western University, 676 N. St. Clair Street, Suite 200, Chicago, IL 60611, writes, as well as how the pharmacist interprets them .
United States. Tel.: +1 312 695 0459; fax: +1 312 695 4307.
With little guidance available to providers, instructions 0738-3991/$ – see front matter # 2007 Published by Elsevier Ireland Ltd.
M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 commonly found on prescription drug labels may not always be clearly stated. In prior studies, half of adults inoutpatient primary care settings misunderstood one or more The methods and quantitative findings from this research primary and auxiliary prescription instructions and warnings study that detail the relationship between patient literacy and they encountered Patients with limited literacy skills misunderstanding prescription label instructions have been and those managing multiple medication regimens made more Improving prescription drug container label instructions is both a matter of health literacy and patient safety . This isespecially true since other sources of patient medication Subjects were adult patients who attended one of three information are insufficient. Prior studies have found that outpatient primary care clinics serving low-income community physicians and pharmacists frequently miss opportunities to populations in Shreveport, Louisiana, Jackson, Michigan and adequately counsel patients on newly prescribed medicines Chicago, Illinois. Recruitment took place over consecutive Other supplementary sources, such as consumer summers beginning July 2003. Patients were eligible if they medication information sheets and FDA-approved medication were 18 or older, and ineligible if the clinic nurse or study guides that may be dispensed with a prescribed medicine are research assistant identified a patient as having one or more of too complex and written at a reading grade level too high for the the following conditions: (1) blindness or severely impaired majority of patients to comprehend . As a result, these vision not correctable with eyeglasses; (2) deafness or hearing materials are not read Patients’ ability to decipher the problems uncorrectable with a hearing aid; (3) too ill to brief text instructions on the container label itself takes on participate; (4) non-English speaking. Institutional Review greater importance to ensure proper use.
Boards at each location approved the study.
A total of 458 patients were approached in the order they 1.1. Sources of comprehension failure: a conceptual model arrived at the clinics and prior to the medical encounter. Twelvepatients refused participation 26 were deemed ineligible, and The ability to read and understand prescription label 25 had incomplete information, leaving 395 patients participat- instructions may appear to be a simple task, yet van den ing in the study. A response rate was determined following Broek & Kremer describe various sources of failure in American Association for Public Opinion Research (AAPOR) comprehension that are particularly applicable for the standards; 92% of approached eligible patients participated in abbreviated text on container labels These include readers’ cognitive characteristics, constraints on the readingsituation, and the nature of the presented health information.
2.2. Structured interview and literacy assessment The influence of the latter set of factors is particularlyapplicable to the truncated text on container labels, and may A structured, cognitive interview protocol was developed to include text complexity, formatting and organizational issues.
assess understanding of different label dosage instructions Failure may also occur if instructions are not explicit, or if placed on five common prescription medications. This process purpose is not evident, such as providing an indication for use has been widely used by the research team, among others on the bottle label itself (i.e. ‘‘take for diabetes’’), which is not These included two antibiotics (amoxicillin (for part of routine practice for either physicians to add to the script pediatric use) and trimethoprim), an expectorant (guaifenesin), or pharmacists to include on the dispensed container label. The an anti-hypertensive, channel blocking agent (felodipine), and a presence of distracting information may limit comprehension diuretic (furosemide). A trained research assistant (RA) at each of the pertinent dosage/usage instructions and auxiliary site administered the interview to consenting patients that warnings that patients need to understand in order to safely included self-report of sociodemographic information (age, use a medicine. This might include the more prominently gender, race/ethnicity, education) source of payment for displayed pharmacy logo, phone number, serial number and medications, and number of prescription medications currently drug code, and other provider-directed content on the label.
taken daily. Actual prescription pill bottle containers withlabels were then shown to patients, one at a time, for review.
Once patients provided their interpretation on all of the labels,the RA administered a brief literacy assessment, ending the The purpose of this study was to investigate how patients approached and interpreted prescription drug label instructions,and to document the nature of misunderstanding that may 2.2.1. Understanding of medication primary container contribute to the high prevalence of medication error. We took a health literacy perspective towards the problem of misunder- To assess patient understanding of prescription medication standing prescription medication instructions. From this view, instructions included on the container primary labels, the RA it was hypothesized that misunderstanding would be the result asked ‘‘how would you take this medicine?’’ This question was of both patient literacy limitations and the ambiguity and often followed by one to two short probes (i.e. ‘‘anything inherent difficulty of label instructions themselves.
else?’’, ‘‘exactly how would you take the pills [medicine]?’’) to M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 initiate more detailed description of administration. The RA documented the verbatim response on a separate form.
Responses to the instructions for the five medications Mixed methods were used. Chi-square tests were calculated (N = 1,975) were then independently rated correct or incorrect to examine bivariate associations between health literacy by three general internal medicine attending physicians from (adequate, marginal, low), sociodemographic variables (age, three different academic medical centers. Each physician rater gender, race, education, number of medications currently was blinded to all patient information and was trained to follow taken), and understanding (yes or no) primary label instructions stringent coding guidelines agreed upon previously by the and attendance (yes or no) to the auxiliary warning instructions.
research team. Correct scores were to be given only if patient Quantitative analyses were conducted using Stata 9.0 (College responses included all aspects of the label’s instruction, including dosage, timing, and if applicable, duration.
For qualitative analyses, a grounded theory approach was Inter-rater reliability was high (k = 0.85). The 147 responses used to explore the basis for patients’ misunderstanding of (7.4%) that received discordant ratings between the three each of the five dosage instructions using their documented reviewers were sent to an expert panel that included three primary verbatim responses . Grounded theory is a systematic care physicians and two health literacy experts for further review.
method for generating theoretical statements from case Each panel member, also blinded to patient information, studies. Based on our qualitative, cognitive interviews, independently reviewed and coded responses as correct or grounded theory guides the inductive process of organizing incorrect. For 76.2 % (n = 112) of the 147 responses, consensus content derived from patient responses. Patient misunder- was achieved among the five-member panel. A majority rule was standings were first reviewed by investigators (MSW, TCD, imposed for the remaining responses (n = 35).
RMP) and classified using both selective and in vivo codingschemes . Data were then reduced by one of the lead 2.2.2. Attendance to auxiliary (secondary) warning label investigators (MSW) through detailed a priori coding to classify the reason for error in understanding (label language, Attentiveness to the auxiliary or ‘‘secondary’’ warning label complexity, explicitness of instruction, presence of distracters, on the pill bottles by patients was also investigated. These and label familiarity). These predetermined codes were based labels provide supplementary instructions supporting the safe on previous studies and the conceptual model of sources of administration of the medications, such as ‘‘take with food’’ or comprehension failure . The reduced data was confirmed ‘‘do not chew or crush, swallow whole.’’ RAs were instructed based on the a priori coding scheme, and in vivo codes were during the interview to document (yes or no) whether patients allowed to develop based on emergent themes in responses.
either attempted to interpret the auxiliary label along with the Agreement among investigators was sought prior to classifying primary label, or physically turned the bottle to inspect the patient responses with any new themes. Open coding color stickers on which these warning messages are placed.
techniques were used . Qualitative analyses weresupported by NVivo 7 software (QSR International; Doncaster, 2.2.3. Reading versus demonstrating instructions Patients were further tested on their functional under- standing of the primary label instruction for guaifenesin (‘‘take two tablets by mouth twice daily’’). They were asked todemonstrate how many pills were to be taken on a daily basis.
After patients answered the first question, ‘‘how would you takethis medicine?’’ they were asked, ‘‘show me how many pills describes the study sample in detail, stratified by you would take [of this medicine] in one day’’. The container literacy. The mean age was 45 years (S.D. = 14; range 19–85 was filled with candy pills for patients to dispense and count out years). Fifty-seven percent of patients were recruited from the correct amount. Responses were coded as correct if their Shreveport, Louisiana, 25% from Jackson, Michigan, and 18% answer was ‘‘four’’, and incorrect if any other response was from Chicago, Illinois. Two-thirds (68%) were female, approximately half of patients were African American (47%)and half white (48%), and 28% reported less than a high school level of education attainment. Patient literacy was limited; 19% Patient literacy was assessed using the Rapid Estimate of were reading at or below a sixth grade level (low literacy) and Adult Literacy in Medicine (REALM), a reading recognition 29% were reading at the seventh to eighth grade level (marginal test comprised of 66 health-related words . The REALM is the most commonly used test of patient literacy in medical Patients were taking an average of three prescription settings . In healthcare studies where patients need only be medications, and 23% lacked insurance to cover these categorized as low (scores 0–44), marginal (scores 45–60) or prescribed drugs. The physician was the most likely source adequate (scores 61–66) readers, the information provided by of medication information for patients (71%). Low literacy was the REALM is generally sufficient. The REALM is highly associated with older age ( p < 0.001), African American correlated with standardized reading tests and the Test of race ( p < 0.001), and less education ( p < 0.001); differences Functional Health Literacy in Adults (TOFHLA) .
were also noted by site ( p < 0.002). No significant differences M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 Table 1Sample characteristics stratified by literacy level Source of support for understanding prescription medication instructions (%) Number of medications taken daily, mean (S.D.) Misunderstanding 1 or more dosage instructions (%) were reported between literacy, gender, source of payment for versus 80%, p < 0.001). No statistically significant associations medications, or number of prescription medications taken daily.
were noted by number of medications or age.
3.2. Prevalence and associations of misunderstanding 3.4. Nature of patient misunderstanding label dosage Overall, 46% of patients misunderstood one or more dosage The 374 (18.9%) total responses that were coded as incorrect instructions. The prevalence of misunderstanding among were qualitatively reviewed and coded using the pre-selected patients with adequate, marginal and low literacy was 38%,51%, and 63%, respectively ( p < 0.001). The rates ofmisunderstanding individual labels ranged from 8% for theinstructions on the label for Felodipine (‘‘Take one tablet bymouth once each day’’) to 33% for the instructions for Trime-thoprim (‘‘Take one tablet by mouth twice daily for 7 days’’;). Patients with low literacy were less able to understandinstructions compared to those with adequate literacy.
3.3. Reading versus demonstrating dosage instructions The ability to read dosage instructions did not always preclude the ability to demonstrate a functional understandingof prescription drug use (When asked how pills were tobe taken in a given day for the instruction, ‘‘Take two tablets bymouth twice daily’’, one third of patients were unable tocorrectly state ‘‘four pills’’. Rather, the most common incorrectanswer was ‘‘two pills’’. Patients with low literacy were lessable to state the correct number of pills taken daily compared to Fig. 1. Rates of correct understanding vs. Demonstration for the primary label those with marginal and adequate literacy (35% versus 63% instruction, ‘‘Take two tablets by mouth twice daily’’.
M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 Table 2Rates of understanding primary label instructions and attendance to auxiliary warnings, stratified by literacy level Take one teaspoonful by mouth three times daily Refrigerate, shake well, discard after [date] Take one tablet by mouth twice daily for 7 days You should avoid prolonged or excessive exposure to direct and/or artificial sunlight while taking this medication Medication should be taken with plenty of water Take one tablet in the morning and one at 5 p.m.
Do not take dairy products, antacids, or iron preparations a Included behavioral demonstration for Guaifenesin only.
coding scheme of likely causes for error in interpretation (n = 75), 79% of these patients could not recognize and (). One emergent cause, referred to as attentiveness to pronounce ‘‘antibiotic’’, 73% ‘‘orally’’, 70% ‘‘teaspoonful’’, label instructions, was included in addition to the predeter- 48% ‘‘medication’’, 45% ‘‘prescription’’, and 35% the word mined causes of label language, complexity of instructions, ‘‘dose’’. Poor word recognition may have contributed to implicit versus explicit dosage, presence of distracters, and patients misreading words on labels, such as ‘‘tablespoon’’ instead of ‘‘teaspoon’’. This accounted for 9% of errors(n = 34).
Interestingly, feedback documented by RAs from patient Certain common phrases used on medicine labels seemed interviews recommended the use of numeric symbols within the confusing and unfamiliar to patients within the context of the instruction rather than the written word equivalent (i.e. ‘‘2’’ instruction itself. Errors that appeared to be the result of label versus ‘‘two’’) for further reading ease.
language were most prevalent on the instruction, ‘‘Take twotablets by mouth twice daily’’. The repetitiveness between dosage (‘‘two’’) and frequency (‘‘twice’’) often led to the Instructions ranged in complexity, both with regards to the common interpretation ‘‘Take a pill twice a day’’, whereas calculation of the number of pills and times to be taken daily dosage would go ignored. This was confirmed in the follow-up (i.e. ‘‘Take one pill by mouth once each day’’ versus, ‘‘Take two demonstration task, ‘‘How many pills would you take in one tablets by mouth twice daily’’) and in the amount of content to day’’ with the common incorrect response of ‘‘two’’ (72% of be retained (dosage, frequency, and/or duration, as in ‘‘Take one tablet by mouth twice daily for seven days’’). Patients found Many terms commonly used on prescription labels had simpler dosing regimens to be easier to understand, while more exceptionally poor recognition rates by patients. Specifically, complex regimens had more errors in their interpretation among patients reading at the 6th grade level and below ). Eleven percent (n = 41) of incorrect responses Table 3Examples of the most common misunderstandings, by dosage instruction Take one teaspoonful by mouth three times daily Take three teaspoons daily; take three tablespoons every day; you should drink it three times a day Take one tablet by mouth twice daily for 7 days Take two pills a day; take it for 7 days; take one every day for a week; I’d take a pill everyday for 7 days Take it every 8 h; take it every day; take one every 12 h Take one tablet in the morning and one at 5 p.m.
I would take it every day at 5 o’clock; take it at 5 p.m.
M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 omitted duration of use from the specified instruction. The Mistaking ‘‘teaspoon’’ for ‘‘tablespoon’’ was more common inclusion of duration on the label instruction also led to a loss of among patients with limited literacy, but one third of these other aspects of the instruction. For the label, ‘‘Take one tablet errors were made by patients with adequate literacy (n = 12).
by mouth twice daily for seven days’’, the second most commonerror made was an incorrect interpretation of dosing frequency (n = 34; i.e. ‘‘I’d take a pill every day for seven days’’).
3.4.3. Implicit versus explicit dosage intervals Patients were better able to interpret more explicit dose Although there may be a finite number of ways a physician frequencies as in ‘‘Take one tablet in the morning and one at 5 can prescribe a medicine, the same dose and frequency p.m.’’ (90%), compared with the more vague ‘‘Take two tablets schedule may be written in several different ways (i.e. every by mouth twice daily’’ (83%), and ‘‘Take one teaspoonful by 12 h, twice daily, in the morning and evening, 8 a.m. and 5 p.m., mouth three times daily’’ (73%). For the latter two instructions, etc.). This becomes especially problematic as many patients patients varied in their interpretation of ‘‘twice daily’’ and may have more than one healthcare provider prescribing ‘‘three times daily’’. For example, patients interpreted ‘‘twice medicine . The ability to follow instructions is crucial in daily’’ as both ‘‘every 8 h’’ and ‘‘every 12 h’’, and ‘‘three times ambulatory care, since the patient assumes the bulk of daily’’ ranged from ‘‘every 4 h’’ to ‘‘every 8 h’’.
responsibility for medication safety. Our present researchoffers timely evidence classifying the nature and causes of In 6% (n = 21) of the incorrect responses, patients had instructions that could potentially lead to errors and adverse difficulty navigating the label content itself and identifying the instructional content. Rather than describing the dosage of the Our prior studies have repeatedly shown that limited literacy medicine, responses detailed provider-directed content that significantly impairs one’s ability to read and demonstrate an surrounded and may have obscured the dosage instructions (i.e.
understanding of instructions and warnings found on com- stated combinations for the name of the drug, physician’s name, monly prescribed medicines While individual differ- refill and date). Patients turned the bottle to acknowledge ences in reading ability may be related to a greater risk for auxiliary warnings, as they were also recited along with the misunderstanding, problems are clearly evident with the label provider-directed content instead of the dose and frequency for itself, and the implicit nature and syntax of instructions.
use (i.e. ‘‘Take it with Food’’; ‘‘I would take them every day but Improving the reading ease of dosage instructions is therefore not with dairy products, antacids, or iron preparations’’; ‘‘I Many patients might presume the task of reviewing prescription drug labels to be overly simple. As a result, they may not allot adequate time to process and understand the Auxiliary instructions are often placed as stickers surround- information. This could explain why a majority of patients were ing or in back of the primary label. Very few patients were able to read back the instruction, while far fewer could familiar with these instructions. Less than 10% of patients demonstrate a proper understanding when probed further. An physically turned any of the bottles to examine these stickers earlier study by Morrell and colleagues found that older adults, (). Sixteen percent of patients attended to at least one who on average manage more medications than younger auxiliary instruction, and 2% made the action part of the routine patients, spent less time processing dosage instructions and inspection of the prescription bottle for all five medicines.
consequently made more errors in interpretation . Thesemistakes could lead to compromised health outcomes, such as 3.4.6. Attentiveness to label instructions under-treatment (i.e. taking two rather than four pills a day) or Several patients provided detailed responses that verbally possible harm (i.e. taking too much of a medicine or not ‘implemented’ the regimen (‘‘It’s an antibiotic, and I would take one pill in the morning when I wake, and another pill after The manner in which physicians write dosage instructions dinner—I would do that for a week’’). Even though tasks were requires patients to make inferences as to when to specifically not timed, many patients appeared to have responded quickly, implement the prescribed regimen (i.e. Take two tablets by and by doing so made simple mistakes. When answers were mouth twice daily; Take one teaspoon by mouth three times provided in haste, patients often skipped or omitted dosage daily). Our findings suggest that patients’ interpretations may information (‘‘Take two a day’’; ‘‘I’d take three pills daily’’).
widely vary when dosing intervals are presented in vague terms Patients with adequate literacy were more likely than as ‘‘twice daily’’ or ‘‘three times daily’’, which may stray from patients with low literacy to omit the duration of use for the the original intent of the prescribing physician. Park and instruction, ‘‘Take one tablet by mouth twice daily for seven colleagues suggest that making inferences is a complex days’’ (n = 41; 44% versus 18%, p < 0.001). They were equally cognitive process, and the elderly may have greater difficulty likely to make errors wherein dose and interval were inverted for the same instruction and for ‘‘Take one teaspoonful by Some misunderstandings appeared to be the result of mouth three times daily’’ (n = 60; 39% versus 43%, p = 0.65).
container label organization. The prescription labels were M.S. Wolf et al. / Patient Education and Counseling 67 (2007) 293–300 typical of the order in which most pharmacies present drug 4.4.1. Use explicit language when describing dose information, often emphasizing (by yellow highlight, large font, bold text) content that is irrelevant to the patient. The Three previous studies also found more explicit instruction inclusion of such distracting information may be particularly improved comprehension . This might help pace problematic for individuals with limited literacy, who face patients and allow them to direct necessary attention for greater reading difficulty in less familiar and technical contexts processing each component of dosage. For instance, the actual dose (number of pills to be taken at a time) could be separatedfrom the interval (times per day), as in the example ‘‘Take 2 tablets in the morning, and take 2 tablets in the evening.’’ We investigated patient understanding of prescription drug 4.4.2. Organize label in a way to minimize distracters label instructions, not whether a medication error occurred.
The label should be re-organized, separating distracting Patients’ actual prescription drug-taking behaviors were not elements that often comprise provider-directed content examined. Patients’ motivation, concentration and comprehen- (pharmacy logo, drug serial number, pharmacy address and sion might have been greater if they reported on their own phone number) away from dosage instructions. Auxiliary medicine. Similarly, we interviewed patients before their instructions might also be placed in a set location (i.e. backside medical encounter. It is also possible that the reason for the of label), instead of being stuck on in various locations, so medical visit altered patients’ concentration, although patients patients can have routine expectations of their location.
were offered the opportunity to refuse and anyone too acutelyill was not interviewed. We also did not conduct a chart review, and thereby could not identify if patients had actual experience Doak, Doak, and Root (1993) offer guidance as to how to with any of the study medications. Only patients who were make health information more suitable for patients with limited proficient in the English language were also included. This was literacy, such as dosage instructions and warning messages on due in part to criteria for using the Rapid Estimate of Adult auxiliary labels. The use of numbers rather than the text Literacy in Medicine (REALM) as our literacy assessment.
equivalent should be promoted for reading ease, and unclarified Further research should investigate the effect of cultural medical jargon (i.e. antibiotic) or awkward terms (i.e. twice) prescription drug label instructions.
We would like to thank Mary Bocchini, Katherine Davis, Prescription drug labels often are the only print source of and Silvia Skripkauskas for their assistance in implementing dosage instructions received by patients. Given the tangible nature of the prescription bottle, these label instructions may be Funding: Dr. Wolf is supported by a career development the ‘last line’ of informational support detailing how and when award through the Centers for Disease Control and Prevention a patient should administer a prescribed medicine. Yet many of the common phrases used to describe dosage instructions areinadequately written and contribute to misunderstanding.
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