August 2000 · Vol. 49, No. 8
OBSERVATIONS FROM PRACTICE
Liquid Medication Dosing ErrorsFrederick S. Mosch, MD
SUBMITTED, REVISED, MARCH 7, 2000.
FROM THE DEPARTMENT OF FAMILY MEDICINE, REGIONS HOSPITAL, ST. PAUL (D.J.M.) AND THE INTERNAL MEDICINE RESIDENCY PROGRAM, UNIVERSITY OF MINNESOTA MEDICAL SCHOOL, MINNEAPOLIS (F.S.M.). PRESENTED AT THE MINNESOTA ACADEMY OF FAMILY PHYSICIANS RESEARCH FORUM, BROOKLYN PARK, MINNESOTA, ON APRIL 17, 1999. REPRINT REQUESTS SHOULD BE SENT TO DIANE MADLON-KAY, MD, DEPARTMENT OF FAMILY MEDICINE, REGIONS HOSPITAL, 640 JACKSON STREET, ST. PAUL, MN 55101-2595. E-MAIL: email@example.com.
BACKGROUND: Our goal was to examine the following issues relevant to the use of liquid medications: (1) which liquid medication dosing devices are commonly owned and used; (2) the ability of potential patients to accurately measure liquids using 3 different dosing devices; (3) their ability to correctly interpret a variety of dosing instructions; and (4) their ability to correctly interpret a pediatric dosing chart.
METHODS: One hundred thirty volunteers from the waiting areas of 3 primary care clinics in the St. Paul, Minnesota, area were interviewed. Participants were shown 7 liquid dosing devices and were asked which they had in their homes and which they had ever used. The participants were tested and scored on their ability to measure liquid medicines and interpret dosing instructions accurately. The total performance score was determined, with a maximum obtainable score of 11.
RESULTS: A household teaspoon was the device most frequently used for measuring liquid medication. Women and participants with more education had higher total performance scores. Common errors included misinterpreting instructions, confusing teaspoons and tablespoons on a medicine cup, and misreading a dosage chart when weight and age were discordant.
CONCLUSIONS: Clinicians need to be aware that many people continue to use inaccurate devices for measuring liquid medication, such as household spoons. They should encourage the use of more accurate devices, particularly the oral dosing syringe. Clinicians should always consider the possibility of a medication dosing error when faced with an apparent treatment failure.
syringes. (J Fam Pract 2000; 49:741-744)
Nearly 25 years ago, the American Academy of Pediatrics (AAP) Committee on Drugs described the inaccuracies of administering liquid medication by household spoons.1 The Committee recommended that physicians advise their community pharmacies to stock appropriate liquid administration devices and insist on the use of such devices when prescribing liquid medications. The committee recommended the use of the oral dosing syringe, which was described as novel and innovative. Since then, a variety of liquid medication dosing devices have been developed and have become widely available, each of which ha sits advantages and disadvantages.2
Limited information is available about the current use of liquid medicine dosing devices in this country. In a 1975 study3 when the oral dosing syringe was still new, 75% of patients used a household teaspoon or kitchen measuring spoon when dosing liquid medication. In a 1989 study from Israel,4 80% of the children were given medications by a household teaspoon. The purpose of our study was to examine the following issues concerning the use of liquid medications: (1) which of the many liquid medication dosing devices are commonly owned and used by families; (2) the ability of potential patients to accurately measure liquids using 3 different dosing devices; (3) their ability to correctly interpret a variety of dosing instructions; and (4) their ability to correctly interpret a pediatric dosing chart.
Our study was approved by the institutional review board of Ramsey (now Regions) Hospital in St. Paul, Minnesota. In the summer of 1996, one of the investigators (F.S.M.) interviewed a convenience sample of people in the waiting areas of 3 clinics in the St. Paul, Minnesota, area: Ramsey Clinic Maplewood, a small private multispecialty clinic serving a predominately white middle-class suburban population; Ramsey Family Physicians, a residency clinic serving primarily a white lower-socioeconomic population; and West Side Clinic, a community clinic serving mostly Hmong and Hispanic patients. These clinics were chosen to obtain subjects with a variety of socioeconomic and ethnic backgrounds. The interview consisted of several parts. Participants were shown the following liquid dosing devices: cylindrical spoon, medicine cup, oral dosing syringe, oral dropper, andby dispenser. In addition, they were shown a household teaspoon and a measuring spoon ([Figure]). They were asked which of the dosing devices they had in their homes and which they had ever used for dispensing liquid medications. Demographic information was also obtained.
The participants were also tested and scored on their ability to measure liquid medicines and interpret dosing instructions accurately. A total performance score was determined by adding the scores from the following activities, with a maximum obtainable score of 11. The investigator observed the subjects measuring 3 doses of medicine using a cylindrical spoon, medicine cup, and an oral dosing syringe and noted the accuracy of the measurement. The subjects received a score of 0 or 1 if the measurement was done incorrectly or correctly, respectively, for each of the 3 devices. Then the subjects were asked to indicate on a chart what times they would take medicine if it was prescribed every 6 hours, 4 times daily, and 3 times daily. The subjects received a score of 0, 1, or 2 for each of these 3 charts. The score of 0 was given if both the number of doses and the timing were incorrect, a 1 if either the number of doses or the timing was correct, and a 2 if both were correct. Finally, subjects were shown a pediatric dosing chart that had dosing listed by both age and weight and contained a note that dosing by weight is more accurate. Subjects were asked to indicate the correct dose for 2 children. In one example the child’s age and weight matched on the chart, and in the other the age and weight were discordant. A score of 1 was given for each correct reading of the dosing chart.
We calculated descriptive statistics and frequency distributions for all variables. Chi-square analyses were used for categorical comparisons. Grouped t tests and analysis of variance techniques were used to assess the effect of categorical predictors and demographics on total score. Pearson correlations were calculated to assess relationships among continuous variables.
Of the 130 participants, 105 were women. The participants had a mean age of 40 years, a mean education level of 12.5 years, and a mean of 1.1 children in the household. Sixty-eight percent of the subjects were white, 19% Hispanic, 11% African American, and 2% Asian. English was the second language for 13% of the participants.
The liquid dosing devices available in the participants’ homes and the devices they used are shown in the [Table]. The one most frequently used (73%) for measuring liquid medication was a household teaspoon.
Ninety-two percent of the participants measured the correct dose when using the oral dosing syringe. Only 85% of the participants measured the correct dose of 1 tablespoon when using a medicine cup. The most frequent error (70%) occurred when the participants mistakenly measured 1 teaspoon instead of 1 tablespoon. Although 92% of the subjects ultimately measured the correct dose using the cylindrical spoon, many subjects spilled the liquid and required several attempts before measuring the correct dose.
Eighty-nine percent of participants noted the correct number of doses and time between doses when asked to indicate the times that they would take a medicine if they were instructed to take it 4 times daily and 3 times daily. Only 38% of the participants correctly indicated this information when they were instructed to take a medication every 6 hours. Participants commonly misinterpreted this instruction as meaning every 6 hours while awake, and indicated 3 rather than 4 doses.
The pediatric dosing chart was correctly interpreted by 87% of the participants for both case scenarios. Twelve percent of those surveyed gave the incorrect dose when the age and weight of the child were discordant, choosing the dose based on the child’s age rather than weight.
The participants’ mean total performance score was 9.5. Women scored significantly better than men. (9.7 vs 8.7, P <.05). Total performance score was significantly correlated with the participants’ education level (Pearson correlation=0.177, P <.05), but not with age or the number of children in the household. Total performance score did not differ significantly by the participants’ native language or ethnic group.
In 1975 the AAP Committee on Drugs denounced the use of household teaspoons for administering liquid medications.1 The volume of household teaspoons can range from 2 to 10 mL. Also, the same spoon when used by different persons may deliver from 3 to 7 mL. Therefore, even household measuring spoons are problematic. Participants in this study used a household teaspoon for measuring liquid medications more often than any other dosing device.
Oral dosing devices such as oral dosing syringes, oral droppers, cylindrical spoons, and medication cups are preferred over the traditional household teaspoon or measuring spoon, because they are more accurate. The advantages and disadvantages of the different devices have been described elsewhere.2 The cylindrical spoon has been described as having an increased potential for easy spillage before and during administration of medication.2 Participants in our study had problems with spillage with this device.
Study participants’ measurements were less accurate when using a measuring cup than when using a cylindrical spoon or oral dosing syringe, primarily because of confusion between the cup’s markings for tablespoons and teaspoons. A survey of poison control centers found 3 major causes of dosing errors using dispensing cups: (1) confusion of tablespoons for teaspoons; (2) the assumption that the entire cup was the unit of measure; and (3) the misinterpretation that 1 cupful was the recommended dose.5 After receiving reports of inappropriately marked plastic dosing cups, the Food and Drug Administration began a public education campaign in 1994 to increase health professional and consumer awareness of misdosing hazards with liquid medicines.6
The oral dosing syringe is felt to be the best device for delivery of liquid medication.2 Its advantages include accuracy, convenience, availability in various sizes, and relatively low expense. The syringe permits the user to direct the delivery of the medication to the back and side of the mouth of an infant or small child, thus minimizing spillage. It also reduces the risk of possible gagging and aspiration of medication. Only a third of this study’s participants had an oral dosing syringe in their home.
It is alarming that the majority of participants misinterpreted instructions to take a medicine every 6 hours, so that they would take only 3 rather than 4 doses of medicine in a day. This problem of misinterpreting dosing frequency appears to be relatively unrecognized, although it could be an important cause of apparent treatment failures. Studies of medication errors typically focus on mistakes that cause clinical symptoms. In a study of 1108 medication errors in pediatrics reported to poison control centers in France, none involved underdosage errors.7
Most participants were able to correctly interpret a pediatric dosing chart, although some errors were noted when the age and weight were discordant. In a previous study, only 40% of caretakers were able to state a correct dose of acetaminophen for their child when given the child’s weight and all package labeling.8 Parents often fail to revise medication doses as a child grows older and gains weight and therefore tend to underdose.4,8,9 Although less serious than overdosing in terms of morbidity, underdosing of acetaminophen may lead to ineffective treatment of fever and unnecessary visits to the clinic or emergency department.
It is not surprising that women and participants with higher education levels had higher total performance scores. In previous studies of liquid medication, the majority of the caretakers giving medication to children were mothers.3,8-10 Women are therefore more likely to have experience administering liquid medication than men. Fortunately, parental education has been shown to be very effective in eliminating medication dosing errors.10 In a recent study by McMahon and colleagues of 90 English-speaking and Spanish-speaking families, 100% of them dosed medication correctly when given instructions and a syringe with a line marked at the prescribed dose.
The recommendation for the use of the oral dosing syringe made by the AAP almost 25 years ago is just as relevant today. On the basis of our study results, we make the following additional recommendations to clinicians: (1) when possible, indicate the dosing interval by the number of doses in a day, rather than by the number of hours between doses; and (2) always consider the possibility of a medication dosing error when faced with an apparent treatment failure.
Our study was funded by a grant from the American Academy of Family Physicians Foundation and the Minnesota Academy of Family Physicians Foundation.
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