Hi there!

Welcome back to the RelayEd Tech Toolkit.

Last week, we practiced using medication concentrations as conversion factors to move between milligrams and milliliters.

This week, we’ll build on that skill by learning another way medication concentrations may be written: percent strength.

Today’s Theme: Percent means “per 100.”

Whenever you see a medication labeled:

1%

don’t think of the percentage as just a number to memorize.

Instead, think:

Percent strength tells you how much active ingredient is present in every 100 units of the finished product.

The units depend on the dosage form:

• 1% w/v means 1 g in every 100 mL
• 1% w/w means 1 g in every 100 g
• 1% v/v means 1 mL in every 100 mL

Once you identify what the percentage represents, you can use it as a conversion factor.

---

Calculation Corner: Percent Strength

Setup 1: Find grams in a liquid

A solution is labeled:

Dextrose 5% w/v

How many grams of dextrose are contained in 500 mL?

Step 1: Translate the percentage.

A 5% w/v solution contains:

5 g in every 100 mL

Step 2: Identify the finish line.

The question asks for grams, so arrange the concentration to cancel milliliters and leave grams.

Step 3: Set it up.

Entire Chain

500 mL × (5 g ÷ 100 mL) = 25 g

Answer: 25 g

Setup 2: Find milligrams per milliliter

A liquid medication is labeled:

2% w/v

What is the concentration in mg/mL?

Step 1: Translate the percentage.

A 2% w/v solution contains:

2 g in every 100 mL

Step 2: Convert grams to milligrams and divide by the volume.

2 g/100 mL × 1,000 mg/1 g = 20 mg/mL

Answer: 20 mg/mL

Setup 3: Find grams in a topical product

Hydrocortisone cream is labeled:

2.5% w/w

How many grams of hydrocortisone are contained in 60 g of cream?

Step 1: Translate the percentage.

A 2.5% w/w product contains:

2.5 g in every 100 g of product

Step 2: Identify the finish line.

The question asks for grams of hydrocortisone.

Step 3: Set it up.

Entire Chain

60 g cream × (2.5 g hydrocortisone ÷ 100 g cream) = 1.5 g hydrocortisone

Answer: 1.5 g of hydrocortisone

---

Try It Yourself

First, translate the percentage:

1% w/v = 1 g per 100 mL

Then convert grams to milligrams and set up the calculation:

20 mL × (1 g ÷ 100 mL) × (1,000 mg ÷ 1 g) = 200 mg

Answer: 200 mg

---

Test-Taking Tip: Start with "Per 100"

Whenever you see a percent strength, start by writing it as an amount per 100.

For example:

1% w/v = 1 g/100 mL

2.5% w/w = 2.5 g/100 g

0.5% v/v = 0.5 mL/100 mL

Then arrange the relationship so the units you already have cancel and the units you need remain.

Before selecting your answer, ask yourself:

• Did I correctly identify whether the product is w/v, w/w, or v/v?
• Did I begin with an amount per 100?
• Do my units cancel correctly?
• Did I convert grams to milligrams when needed?
• Does my final unit match what the question asked for?

PTCE Test Strategy

Percent-strength problems often become easier when you stop treating the percentage as a separate formula.

Instead, translate the percentage into a conversion factor.

Two common mistakes are:

• Forgetting that percent means “per 100”
• Forgetting to convert grams to milligrams

Shortcut: To convert % w/v to mg/mL, multiply the number in front of the percent sign by 10.

For example:

0.5% w/v = 5 mg/mL

1% w/v = 10 mg/mL

2% w/v = 20 mg/mL

The shortcut works because:

1 g/100 mL = 1,000 mg/100 mL = 10 mg/mL

Always confirm that the product is expressed as % w/v before using this shortcut.

---

Top 200 Drug Spotlight: Hydrocortisone

Generic: Hydrocortisone

Brand: Cortizone-10 and various store-brand products

Class: Topical corticosteroid

Common uses: Relief of itching, redness, and inflammation associated with certain skin conditions

Common dosage forms:

• Cream
• Ointment
• Lotion

Common topical strengths:

• 0.5%
• 1%
• 2.5%

Common local effects may include:

• Burning
• Itching
• Irritation
• Dryness
• Redness

Skin thinning or atrophy may occur, particularly with prolonged or inappropriate use.

Pearl:

Hydrocortisone products may have the same medication name but different:

• Strengths
• Dosage forms
• Directions
• Prescription statuses
• Intended application sites

Always verify the complete product description.

Safety Check:

Before processing or selecting a hydrocortisone product, check:

• Correct strength
• Correct dosage form
• Intended application site
• Appropriate quantity and directions
• Whether the product is prescription or over the counter
• Patient age
• Duplicate topical corticosteroid therapy
• Warnings involving the eyes, broken skin, infection, or prolonged use
• Whether the directions include an occlusive dressing, which may increase medication absorption

Bring unusual directions, prolonged use, application to a sensitive area, signs of infection, duplicate therapy, or other concerns to the pharmacist for review.

---

One-Minute Knowledge Check

1. A solution is labeled 4% w/v. How many grams of medication are present in 250 mL?

A. 4 g
B. 8 g
C. 10 g
D. 16 g

2. A medication is labeled 0.5% w/v. What is the concentration in mg/mL?

A. 0.5 mg/mL
B. 5 mg/mL
C. 50 mg/mL
D. 500 mg/mL

3. A 30 g tube contains hydrocortisone 2.5% w/w. How many grams of hydrocortisone are in the tube?

A. 0.075 g
B. 0.25 g
C. 0.75 g
D. 7.5 g

(Answers below.)

---

From the Marketplace

Preparing for the PTCE and want to see where you stand?

This week’s featured resource is the PTCB Practice Exams digital download, which includes two full pharmacy technician practice tests designed to help you identify weak areas, review key concepts, and build confidence before exam day.

The resource includes:

✅ 2 full practice exams
✅ 50 questions per exam
✅ 100 total questions
✅ One easy-to-intermediate exam
✅ One advanced exam
✅ Detailed answer key
✅ Explanations for every question
✅ Instant PDF digital download

Topics include:

💊 Top 200 drugs and drug classes
💊 Patient safety and quality assurance
💊 Federal pharmacy law
💊 DEA schedules and forms
💊 Pharmacy calculations
💊 Days-supply and insulin calculations
💊 Prescription processing
💊 Sig codes and abbreviations
💊 Inventory management
💊 Medication safety
💊 Brand and generic medications

The two-exam format makes it easy to begin with a more approachable review and then challenge yourself with a more advanced set.

Use the answer explanations to do more than check your score. Review why each answer is correct, note the topics you missed, and use those weak areas to guide your next study session.

Explore PTCE Practice Exams

Liz Fredrickson, PharmD, BCPS Founder, RelayEd liz@relayedllc.com

RelayEd provides independent educational resources and is not affiliated with or endorsed by PTCB. Always verify medication information using current product labeling, course materials, and workplace policies.