Nonvolumetric Glassware and Devices
Erlenmeyer Flasks, Beakers, and Prescription Bottles
Erlenmeyer flasks, beakers, and prescription bottles are not
volumetric devices and should NOT be used to measure liquids. "Graduation"
marks on such vessels are only approximations of liquid capacity. These
devices should only be used to mix or store solutions or other liquid preparations,
unless you first calibrate them to a known volume.
The Teaspoon and the problem concerning the actual volume of
liquid contained in a "teaspoonful" has existed for many years.
Despite various recommendations, the problem persists. Patients continue
to self-administer liquid doses from spoons which, in all probability,
are far from standard.
The U.S. Pharmacopoeia/National Formulary (USP/NF) recognizes the problem
and provides the following statement: "Agreement has not been reached
on a standard official teaspoonful, in spite of the need for such a standard
measure in connection with compounding and labeling liquid medicines. For
household purposes, an American Standard Teaspoon has been established
by the American Standards Association as containing 4.95 ± 0.24
ml. In view of the almost universal practice of employing teaspoons ordinarily
available in the household for the administration of medicine, the teaspoon
may be regarded as representing 5 ml." Household measures are, however,
far from standard. Teaspoons may be found with capacities ranging from
3 to 7 ml and the volume of liquid which may be held in a given teaspoon
varies with the viscosity and surface tension of the liquid. Thus, the
dosage becomes an almost unpredictable variable. Errors in dosage can be
- Writing and formulating all prescriptions using the metric system of
- Using the symbol for one fluid dram in the dosage instructions to represent
- Requesting physicians to designate on the prescription the number of
ml or mg desired in each dose.
- Dispensing a standard calibrated teaspoon, oral syringe, or other calibrated
measuring device with each prescription for an oral liquid where such a
dosage is used.