Reading Medication Labels

Before you can calculate any dosage, you need to read the medication label accurately. The label tells you what you have — the drug name, strength, concentration, route, and form. Every dosage calculation starts here, and misreading a label is one of the most common sources of medication errors.

Parts of a Medication Label

Every medication label, whether on a bottle, vial, or blister pack, contains these critical pieces of information:

Note: Some look-alike/sound-alike generic names use mixed-case “Tall Man Lettering” (e.g., DOBUTamine, predniSONE) as an ISMP/FDA safety practice to prevent medication errors.

Identifying “What You Have” — The Supply on Hand

In dosage calculations, the label provides two key values that form the supply on hand:

$\text{Supply on Hand} = \frac{\text{Dosage Strength (Drug Amount)}}{\text{Unit or Volume (Quantity)}}$

For tablets and capsules, the supply on hand is straightforward — the strength per single unit:

• Label reads “Furosemide 40 mg” → You have 40 mg per 1 tablet
• Label reads “Amoxicillin 500 mg capsules” → You have 500 mg per 1 capsule

For liquid medications, the supply on hand is a concentration:

• Label reads “Amoxicillin 250 mg/5 mL” → You have 250 mg per 5 mL
• Label reads “Acetaminophen 160 mg/5 mL” → You have 160 mg per 5 mL

For injectable medications, the label shows concentration per mL:

• Label reads “Heparin 5,000 units/mL” → You have 5,000 units per 1 mL
• Label reads “Morphine sulfate 10 mg/mL” → You have 10 mg per 1 mL

Worked Examples

Example 1: Tablet Label

A medication label reads: Lisinopril 10 mg tablets, 90 tablets, PO

The physician orders Lisinopril 20 mg PO daily.

From this label you know:

• Drug: Lisinopril (generic)
• Supply on hand: 10 mg per tablet
• Route: PO (by mouth)
• What you need: 20 mg

You would give $\frac{20 \text{ mg}}{10 \text{ mg/tablet}} = 2$ tablets.

Example 2: Liquid Label

A medication label reads: Amoxicillin Oral Suspension 400 mg/5 mL, 100 mL bottle

The provider orders Amoxicillin 600 mg PO TID.

From this label you know:

• Drug: Amoxicillin (oral suspension)
• Concentration: 400 mg per 5 mL
• Total volume in bottle: 100 mL
• What you need: 600 mg per dose

Volume to administer: $\frac{600 \text{ mg}}{400 \text{ mg}} \times 5 \text{ mL} = 7.5 \text{ mL}$

Example 3: Injectable Label

A medication label reads: Furosemide Injection 10 mg/mL, 4 mL vial

The order reads Furosemide 30 mg IV STAT.

From this label you know:

• Drug: Furosemide (injection)
• Concentration: 10 mg per mL
• Total vial volume: 4 mL (so total drug in vial = 40 mg)
• What you need: 30 mg

Volume to draw up: $\frac{30 \text{ mg}}{10 \text{ mg/mL}} = 3 \text{ mL}$

The 4 mL vial contains enough (40 mg total) for this 30 mg dose.

Common Label Formats at a Glance

Practice Problems

Test your understanding with these problems. Click to reveal each answer.

Common Mistakes to Avoid

1. Confusing generic and brand names. Always verify you have the correct drug. Metformin is Glucophage. Furosemide is Lasix. Know both names.
2. Ignoring the “per” in concentrations. A label reading “250 mg/5 mL” means 250 mg in every 5 mL — not 250 mg in the entire bottle. Misreading this leads to massive dosing errors.
3. Not checking the route. A drug may come in PO and IV forms at different concentrations. Giving an IV concentration by mouth (or vice versa) can be dangerous.
4. Overlooking expiration dates. Expired medications may have reduced potency or altered chemical composition. Always check before administering.
5. Assuming one vial equals one dose. Multi-dose vials contain more drug than a single dose. Always calculate the exact volume needed.

Key Takeaways

• Every dosage calculation begins with correctly reading the medication label
• The supply on hand is the drug amount per unit (tablet) or per volume (mL) — it is the denominator in your dosage formula
• Tablets and capsules list strength per unit; liquids and injectables list a concentration (mg per mL or mg per stated volume)
• Always verify the drug name, strength, route, and expiration before administering
• When in doubt, compare the generic name on the label to the generic name on the medication order

Math for Nurses