DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

to be equivalent to 5 mL and a “tablespoon” equivalent
to 15 mL, but the actual volumes held by ordinary
household teaspoons and tablespoons are far too variable
to be used reliably for measurement of medications.
Prescribing oral medications in “drops” likewise can
cause problems when accuracy of dose is important,
unless the patient understands that only the calibrated
dropper (for drops or teaspoon measures) provided by
the manufacturer or pharmacist should be used to dispense
the medication. Thus, one possible dosage for a
pediatric iron product would be more accurately written
“15 milligrams (0.6 mL) three times daily” instead
of “one dropperful three times daily,” because a true
dropperful could result in iron overdose.
Abbreviations lead to dispensing errors (Teichman
and Caffee, 2002). A prescription intending every-otherday
dosing (qod) may be miswritten as “od” by the
physician for “other-day dosing”; the pharmacist may
interpret “od” as the abbreviation of the Latin for “right
eye.” Once-daily dosing at bedtime (qhs) may be misinterpreted
as “qhr” for “every hour.” The use of a slash
mark (/) to separate names and doses can result in the
incorrect drug or dose being dispensed; the slash mark
may be interpreted as a letter or number. When medications
are measured in units, or international units, the
abbreviation “U” or “I” must NOT be used, as it leads to
errors such as misinterpretation of “U” as 0 or 4, or “IU”
as 10 or 14. The word “unit” should be written as such.
Drug products available in the U.S. that are dosed in units
(e.g., corticotropin) or international unit measures are
“harmonized” by those responsible for drug standardization
to avoid errors in dosing (see “Drug Standards and
Classification”). Examples of confusion in the interpretation
of a physician order abound (Kohn, 2001) and are
considered further in “Errors in Drug Orders.” To avoid
errors, practitioners in the U.S. must write out the Rx
fully in English, and pharmacists must clarify their concerns
with prescribers, not patients.
Proper Patient Information
The patient’s name and address are needed on the prescription
order to ensure that the correct medication
goes to the proper patient and also for identification and
recordkeeping purposes. For medications whose dosage
involves a calculation, a patient’s pertinent factors, such
as weight, age, or body surface area, also should be
listed on the prescription. Prescribers should view this
effort as one that serves their goal of protecting their
patient from errors rather than a burden (safety first).
Prescribers often commit errors in dosage calculations
(Lesar et al., 1997) that can be prevented
(Kuperman et al., 2001; Conroy et al., 2007). When prescribing
a drug whose dosage involves a calculation
based on body weight or surface area, both the calculated
dose and the dosage formula used, such as “240 mg
every 8 hours (40 mg/kg/day),” should be included to
allow another healthcare professional to double-check
the prescribed dosage. Pharmacists always should recalculate
dosage equations when filling such prescriptions.
Medication orders in hospitals and some clinic settings,
such as those for antibiotics or anti-seizure medications
that are sometimes difficult to adequately dose (e.g.,
phenytoin), can specify the patient diagnosis and desired
drug and request dosing by the clinical pharmacist.
Proper Use of Prescription Pad
All prescriptions should be written in ink; this practice
is compulsory for schedule II prescriptions under the
U.S. Controlled Substances Act (CSA) of 1970,
because erasures on a prescription easily can lead to
dispensing errors or diversion of controlled substances.
Prescription pad blanks normally are imprinted
with a heading that gives the name of the physician and
the address and phone number of the practice site
(Figure AI–1). When using institutional blanks that do
not bear the physician’s information, the physician
always should print his or her name and phone number
on the face of the prescription to clearly identify the prescriber
and facilitate communication with other healthcare
professionals if questions arise. U.S. law requires
that prescriptions for controlled substances include the
name, address, and Drug Enforcement Administration
(DEA) registration number of the physician.
The date of the prescription is an important part of
the patient’s medical record, and it can assist the pharmacist
in recognizing potential problems. For example,
when an opioid is prescribed for pain due to an injury,
and the prescription is presented to a pharmacist
2 weeks after issuance, the drug may no longer be indicated.
Compliance behavior also can be estimated using
the dates when a prescription is filled and refilled. The
CSA requires that all orders for controlled substances
(Table AI–1) be dated as of, and signed on, the day
issued and prohibits filling or refilling orders for substances
in schedules III and IV >6 months after their
date of issuance. When writing the original prescription,
the physician should designate the number of
refills allowed. For maintenance medications without
abuse potential, it is reasonable to write for a 1-month
supply and to mark the prescription form for refills to
be dispensed over a period sufficient to supply the
patient until the next scheduled visit to the physician.
1881
APPENDIX I
PRINCIPLES OF PRESCRIPTION ORDER WRITING AND PATIENT COMPLIANCE