Measuring Medicine: Milligrams, Moles, and More Quiz

Answer: As a percentage

Lidocaine comes in a variety of dosage forms, including injectable, topical jelly, and oral / topical viscous solution. Common strengths are 1%, 2% and 4%. One percent lidocaine means that there is one gram of lidocaine in one hundred total milliliters of liquid solution.

In addition to being a very useful topical anesthetic, lidocaine is also a cardiac antiarrhythmic - it can restore normal heart rhythm when injected intravenously during a cardiac emergency.

Answer: Enoxaparin

Enoxaparin (brand name: Lovenox) is a low molecular weight heparin measured in milligrams. Since dosage is based on the patient's weight, a variety of strengths are offered in color-coded prefilled syringes, ranging from the light blue 30mg syringes, through the dark blue 150mg.

Answer: Vitamin D

Vitamins A and E are also measured in units. Common strengths of cholecalciferol (a variety of vitamin D) are 200 and 400 units. Vitamin D is often added to products containing calcium, as the two work together to promote bone strength.

Vitamins C and K are measured in milligrams, and cyanocobalamin's (vitamin B12's) strength is usually expressed in micrograms. (A microgram is one thousandth of a milligram, or one millionth of a gram - just a little bit goes a long way!)

So what is a unit? It can be thought of in terms of activity level - exactly how much of an effect the drug has in the body. This is determined by laboratory data.

Answer: Potassium chloride

If you're not a chemist, converting from mEq to mg and back can be tricky. Actually, I'm not a chemist myself, so I won't try to explain. I will say that the strengths of "elemental" drugs are often expressed in mEq. Examples are calcium gluconate, sodium chloride, and sodium bicarbonate (although this last is often expressed as a percentage - 8.4% sodium bicarbonate is often referred to as "normal bicarb").

I've also seen the strength of sodium phosphate and potassium phosphate expressed in millimoles. Molarity is another of those chemistry concepts that I have yet to master.

Answer: As a ratio

A common strength of epinephrine is 1:10000 (meaning 1 part epinephrine in 10000 total parts of solution.) Do you remember the old days of the tv series "ER"? It seems like someone was always screaming that the trauma patient they were treating needed "another amp of epi!"

Answer: Grain

Occasionaly in the pharmacy, one still sees references to apothecary or avoirdupois measurements. Amber prescription vials come in various dram sizes, and bottles for liquids may bear the fluid ounce symbol f℥. Armour thyroid and phenobarbital are two other drugs that may be measured in grains.

Despite these remnants of a fading pharmaceutical tradition, metric measurements (grams, liters, and meters) should now always be listed first on labels, and are the primary units used in measurement, dosage, and calculation.

Answer: Weight-in-volume

When I first saw "0.15% w/v fluoride ion" on a tube of toothpaste, I wondered what w/v meant. My burning curiosity threatened to consume me, but I only learned the answer years later when I began studying pharmacy technology. Other variants are w/w (weight-in-weight) and v/v (volume-in-volume).

Answer: Yes

One milligram contains 1000 micrograms (mcg), so to convert: 3.2 * 1000 = 3200. So yes, this is correct. Some packaging (I suppose in order to avoid using a decimal point) states the drug's strength in mcg ("mikes," for those who like to sound cool). For example, 200 mcg instead of 0.2 mg or 125 mcg rather than 0.125 mg. People who handle drugs should read labels carefully and double-check to see if the strength stated on the package really is equivalent to the strength they are looking for.

Notice the use of the "tall-man" letters in DOBUTamine. This is a safety feature designed to distinguish look-alike/sound-alike drugs. (DOBUTamine can easily be confused with DOPamine. Another tricky example is prednisONE and prednisoLONE.)

Answer: True

Concentration refers to the amount of active ingredient per volume of solution. Often, drug manufacturers label their packages first with the total amount of active in ingredient and the total amount of solution, followed by a "reduced" or "simplified" concentration. Here are two examples of how strengths might be described:

Ondansetron 4mg/2ml
(2mg/ml)

Metoprolol tartrate 5mg/5ml
(1mg/ml)

Answer: 20

#20 tablets at 40mg each = 800mg of drug. 800 total mg of drug in 400 total ml of solution reduces to 40mg of drug in every 20ml of solution, which is what we were looking for.

The hospital where I work used quite a bit of this particular suspension. As it was stable for only 14 days in the refrigerator, we made 1 - 2 liters every two weeks. This was a LOT of tablets to crush! We also drew it into 20ml oral syringes, each of which we labelled. I was not a bit sorry when this labor-intensive process disappeared. A committee decided to switch to a different drug that is available as a very convenient, generic, unit-dosed powder for suspension. Nurses on the floor can mix the powder with water and give the resulting peach-flavored (read: very bitter, only slightly masked by huge amounts of artificial flavoring - yes, we sampled it) drink to the patient.