Always calculate the dose of medications yourself
Always calculate the dose of medications yourself: Excerpt from Avoiding Common Pediatric Errors
Author:
Michael S. Potter, Nickie Niforatos, MD,
Heidi Herrera, MD and Anthony Slonim, MD
What to Do - Take Action
Medication errors are a major patient safety problem for children and physicians have a role in their prevention.
Medical errors represent a major public health problem in the United
States, and medication errors represent an important subset with specific
challenges for providing safe care for children. Medication errors lead to
prolonged hospitalizations, unnecessary evaluations and treatments, and occasionally death. Pediatric patients are particularly vulnerable tothese errors
since dosages are prescribed based upon the child's weight or body surface
area (Fig. 61.1). Children also cannot intercept errors like adults can, and the
pharmacokinetics of certain drugs are age-dependent and require alterations
in prescribing (Fig. 61.1).
To combat these sources of prescribing error, physicians should always make a point of performing medication calculations themselves,
making use of computerized calculations and other decision support
tools, such as reference texts and ordering outlines, that help to provide appropriate reference material at the point of calculating and
prescribing.
Documentation of the formula used and the actual calculations is helpful, because calculation errors can be detected more effectively.
Wt: 13 kg
Allergies: none
Erythromycin 150 mg (12 mg/kg/dose) PO every 6 hours
In addition to recognizing calculation errors with this type of documentation, dosage errors can also be identified. Inthe example above, a therapeuticdoseoferythromycintotreatanacuteinfectionis50mg/kg/day;however,
the use of erythromycin as a prokinetic agent is dosed at 20 mg/kg/day. A
number of sources are available to help the physician confirm the dose of
a medication, including The Harriet Lane Handbook and personal digital
assistant (PDA) programs, such as Epocrates.
• Different and changing pharmacokinetic parameters between patients at various ages and stages
of maturational development.
• Need for calculation of individualized doses based on the patient's age, weight (mg/kg), body
surface area (mg/m2), and clinical condition.
• Lack of available dosage forms and concentrations appropriate for administration to neonates,
infants, and children. Frequently, dosage formulations are extemporaneously compounded and
lack stability, compatibility, or bioavailability data.
• Need of precise dose measurement and appropriate drug delivery systems.
• Lack of published information or Food and Drug Administration-approved labeling regarding
dosing, pharmacokinetics, safety, efficacy, and clinical use of drugs in the pediatric population.
Figure 61.1. Factors Placing Pediatric Patients at Increased Risk for Adverse
Drug Reactions (From Levine SR, Cohen MR, Blanchard NR, et al. Guidelines
for preventing medication errors in pediatrics. J Pediatr Pharmacol Ther. 2001;6:
426–442).
Many hospitals have initiated computerized provider order entry programs (CPOE) to help standardize medication prescribing. These systems
allow the medications to be ordered with a weight-based dose (i.e., mg/kg)
and also allow the program to perform the appropriate calculation. Although
thesesystemsprovideimportantsafetynets,particularlyinpreventingerrors
causedbydifficult-to-readpenmanship,theseprogramsarenotfoolproofand
require a number of precautions. If the CPOE system prompts the user with
common doses, the physician must select the appropriate dose for the desired effect. For example, in ordering ceftriaxone, there may be an automatic
prompt for 50 mg/kg intravenous (IV) daily; however, if treating a patient
for meningitis, the physician must recognize that the meningitic doses of the
antibiotic is 50 mg/kg/dose IV twice a day (BID).
Whether a physician is using a CPOE system or paper-and-pen prescriptions, a number of additional safety measures should be considered for
calculatingmedicationdoses.Aphysicianmustrecognizeiftheper-kilogram
dosage,whencalculated,exceedsthetotaldailydose.Adultmedicationdoses
have been calculated on the average ideal body weight of 60 to 75 kg. Generally, a pediatric patient weighing >60 kg is prescribed medications on
adult-dose regimens, rather than a per-kilogram regimen; however, almost
all medications have a recommended total daily dose, which may be reached
even in children weighing <60 kg. Toillustrate thispoint, considerthe treatment of meningitis in a 45-kg patient. The maximum dose of ceftriaxone is
4 g per 24 hours, so this child should be given the antibiotic according to the
total daily dose (2,000 mg BID) rather than the calculated dose (50 mg/kg
BID, which would be 2,250 mg BID).
The route of administration and the route of excretion also play significantrolesindeterminingmedicationdoses.Generallyspeaking,thebioavailability of a medication is greater when administered parenterally (i.e., IV)
thanenterally(i.e.,bymouth[PO]).Often,thedifferenceissmallandPO/IV
doses are the same; however, in cases where there is a significant difference in
bioavailability, the doses differ based on route of administration. For example, an initial dose of labetalol is 2 mg/kg/dose when given orally, but only
0.2 mg/kg/dose, when given intravenously, a 10-fold difference in dosage.
The route of excretion is most pertinent to patients with impaired renal or
hepatic function. In patients with renal failure, medications can be adjusted
by either increasing the interval of administration (i.e., from every 4 hours
to every 8 hours) or by decreasing the dose amount (i.e., from 4 mg/kg
to 2 mg/kg). Dose adjustments are less common in liver failure. Rather
than changing the drug dose, the drug choice is given greater attention to
preserve function; for example, using nonsteroidal anti-inflammatory drugs
rather than acetaminophen to pain or fever.
Drug form (tab vs. suspension) is also pertinent in medication orders.
In these instances, the conversion from drug dose (i.e., mg) to drug volume
(i.e., mL) must also be considered and calculated correctly. For example,
amoxicillin suspensions can be made in the following concentrations: 200
mg/5 mL or 400 mg/5 mL. A patient prescribed 400 mg of amoxicillin will
be instructed to take 10 mL of the first suspension but only 5 mL of the
second.
Many mistakes can be made in calculating doses in routine medication
orders. To minimize mistakes, the provider should always have access to a
drug reference guide, calculate doses themselves, and consider the treatment
strategy, including what is being treated and what is the therapeutic goal.
Suggested Readings
Kumm S. University of Kansas School of Nursing. Basic Drug Calculations Review. Available at:
http://classes.kumc.edu/son/nurs420/clinical/basic review.htm. Accessed July 27, 2007.
Levine SR, Cohen MR, Blanchard NR, et al. Guidelines for preventing medication errors in
pediatrics. J Pediatr Pharmacol Ther. 2001;6:426–442.
>
Book Source Details
- Book Title: Avoiding Common Pediatric Errors
- Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
- Year of Publication: 2008
- Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.
More About Drug Allergies
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- [ read ]
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Avoiding Common Pediatric Errors
Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD
Publisher: Lippincott Williams & Wilkins
Copyright: 2008
ISBN: 0-7817-7489-6
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