Oral Dosage Practice Questions with Answers

Mastering oral dosage calculations is a fundamental skill for nursing students and healthcare professionals to ensure patient safety and therapeutic efficacy. Whether you are preparing for the NCLEX or working on a busy hospital floor, the ability to convert unit measurements and calculate the correct number of tablets or milliliters is critical to preventing medication errors. This guide provides a comprehensive overview of the formulas used in medication administration, followed by detailed practice problems to sharpen your clinical reasoning.

Concept Explanation

Oral dosage refers to the calculation of medication administered by mouth, typically in the form of tablets, capsules, or liquid solutions, based on a specific healthcare provider order and the concentration available on hand. To perform these calculations accurately, clinicians most often use the "Desired over Have" formula or dimensional analysis. The basic formula is represented as:

$$\ \frac{D}{H} \ \times Q = X$$

Where:

• D (Desired): The dose prescribed by the physician (e.g., 500 mg).
• H (Have): The dosage strength available on the medication label (e.g., 250 mg).
• Q (Quantity): The unit of form the drug comes in (e.g., 1 tablet or 5 mL).
• X (Amount to give): The final calculated amount to administer to the patient.

Before applying the formula, it is essential to ensure that the units of measurement for the Desired dose and the Have dose match. If they do not, a conversion must be performed first (e.g., converting grams to milligrams). Understanding NCLEX pharmacology practice questions involves recognizing these conversion factors, such as $1 \ \text{ gram} = 1,000 \ \text{ mg}$ and $1 \ \text{ mg} = 1,000 \ \text{ mcg}$. For pediatric or weight-based dosing, the process often includes an extra step of multiplying the dose per kilogram by the patient's weight in kilograms. You can explore more about specific medications in our NCLEX medication practice questions guide.

Solved Examples

1. Example 1: Tablet Calculation

   A physician orders 0.5 g of a medication. The pharmacy provides 250 mg tablets. How many tablets should the nurse administer?

   1. Convert grams to milligrams: $0.5 \ \text{ g} \ \times 1,000 = 500 \ \text{ mg}$.
   2. Identify variables: $D = 500 \ \text{ mg}$, $H = 250 \ \text{ mg}$, $Q = 1 \ \text{ tablet}$.
   3. Apply formula: $$\ \frac{500 \ \text{ mg}}{250 \ \text{ mg}} \ \times 1 \ \text{ tablet} = 2 \ \text{ tablets}$$
   4. Answer: 2 tablets.
2. Example 2: Liquid Medication Calculation

   The order is for Furosemide 30 mg PO. The bottle is labeled 10 mg/mL. How many mL will the nurse administer?

   1. Identify variables: $D = 30 \ \text{ mg}$, $H = 10 \ \text{ mg}$, $Q = 1 \ \text{ mL}$.
   2. Apply formula: $$\ \frac{30 \ \text{ mg}}{10 \ \text{ mg}} \ \times 1 \ \text{ mL} = 3 \ \text{ mL}$$
   3. Answer: 3 mL.
3. Example 3: Weight-Based Dosage

   A child weighing 20 kg is prescribed a medication at 5 mg/kg. The medication is available as 50 mg/5 mL. How many mL should be given?

   1. Calculate the total desired dose: $20 \ \text{ kg} \ \times 5 \ \text{ mg/kg} = 100 \ \text{ mg}$.
   2. Identify variables: $D = 100 \ \text{ mg}$, $H = 50 \ \text{ mg}$, $Q = 5 \ \text{ mL}$.
   3. Apply formula: $$\ \frac{100 \ \text{ mg}}{50 \ \text{ mg}} \ \times 5 \ \text{ mL} = 10 \ \text{ mL}$$
   4. Answer: 10 mL.

Practice Questions

1. The healthcare provider orders Amoxicillin 500 mg PO every 8 hours. The pharmacy supplies Amoxicillin oral suspension 250 mg/5 mL. How many mL should the nurse administer per dose?

2. A patient is prescribed 0.125 mg of Digoxin daily. The medication is available in 250 mcg tablets. How many tablets will the nurse give?

3. The order reads: Potassium Chloride 40 mEq PO. The available concentration is 20 mEq per 15 mL. How many mL will the nurse prepare?

4. A physician orders Warfarin 7.5 mg PO. The pharmacy sends 5 mg scored tablets. How many tablets should the patient receive?

5. The order is for Phenytoin 0.2 g PO twice daily. The available capsules are 100 mg each. How many capsules will the nurse administer per dose?

6. A patient is to receive 600 mg of Ibuprofen. The available liquid is 100 mg per 5 mL. How many teaspoons (tsp) should the nurse instruct the patient to take? (Note: $1 \ \text{ tsp} = 5 \ \text{ mL}$).

7. The order is for Sertraline 150 mg PO. The medication is available in 100 mg tablets. How many tablets are required for this dose?

8. A child weighing 44 lbs is prescribed a medication at 10 mg/kg/day divided into two doses. How many mg will the child receive per dose?

9. The prescription is for Cephalexin 0.5 g PO four times a day. The supply is 250 mg capsules. How many capsules will the patient take in a 24-hour period?

10. The order is for Methadone 15 mg PO. The available concentration is 5 mg/5 mL. How many mL should be administered?

Answers & Explanations

1. Answer: 10 mL. Use the formula $\ \frac{500 \ \text{ mg}}{250 \ \text{ mg}} \ \times 5 \ \text{ mL} = 10 \ \text{ mL}$. The desired dose is 500 mg, the available is 250 mg, and the volume is 5 mL.
2. Answer: 0.5 tablets. First, convert 0.125 mg to mcg: $0.125 \ \times 1,000 = 125 \ \text{ mcg}$. Then apply the formula: $$\ \frac{125 \ \text{ mcg}}{250 \ \text{ mcg}} = 0.5 \ \text{ tablets}$$. For more practice on medications like Digoxin, see our NCLEX cardiovascular practice questions.
3. Answer: 30 mL. Apply the formula: $$\ \frac{40 \ \text{ mEq}}{20 \ \text{ mEq}} \ \times 15 \ \text{ mL} = 30 \ \text{ mL}$$.
4. Answer: 1.5 tablets. Using $D/H \ \times Q$: $$\ \frac{7.5 \ \text{ mg}}{5 \ \text{ mg}} \ \times 1 = 1.5 \ \text{ tablets}$$. Since the tablet is scored, it can be safely split.
5. Answer: 2 capsules. Convert 0.2 g to mg: $0.2 \ \times 1,000 = 200 \ \text{ mg}$. Then, $\ \frac{200 \ \text{ mg}}{100 \ \text{ mg}} = 2 \ \text{ capsules}$.
6. Answer: 6 tsp. First, find the mL: $\ \frac{600 \ \text{ mg}}{100 \ \text{ mg}} \ \times 5 \ \text{ mL} = 30 \ \text{ mL}$. Then convert mL to tsp: $30 \ \text{ mL} \div 5 \ \text{ mL/tsp} = 6 \ \text{ tsp}$.
7. Answer: 1.5 tablets. Apply the formula: $$\ \frac{150 \ \text{ mg}}{100 \ \text{ mg}} = 1.5 \ \text{ tablets}$$.
8. Answer: 100 mg. First, convert weight to kg: $44 \ \text{ lbs} \div 2.2 = 20 \ \text{ kg}$. Total daily dose: $20 \ \text{ kg} \ \times 10 \ \text{ mg/kg} = 200 \ \text{ mg/day}$. Divided into two doses: $200 \ \text{ mg} \div 2 = 100 \ \text{ mg/dose}$.
9. Answer: 8 capsules. Per dose: $0.5 \ \text{ g} = 500 \ \text{ mg}$. $\ \frac{500 \ \text{ mg}}{250 \ \text{ mg}} = 2 \ \text{ capsules per dose}$. Total per day (4 doses): $2 \ \times 4 = 8 \ \text{ capsules}$. Learn more about dosing for infections in our NCLEX antibiotic practice questions.
10. Answer: 15 mL. Apply the formula: $$\ \frac{15 \ \text{ mg}}{5 \ \text{ mg}} \ \times 5 \ \text{ mL} = 15 \ \text{ mL}$$.

1. A patient is ordered 1 gram of medication PO. The tablets are 500 mg each. How many tablets should be given?

• A1 tablet
• B2 tablets
• C3 tablets
• D4 tablets

Frequently Asked Questions

What is the "Desired over Have" formula?

The "Desired over Have" formula is a standard mathematical method used in nursing to calculate the correct amount of medication to administer by dividing the prescribed dose by the available dose and multiplying by the quantity or volume. This method is highly effective for both solid and liquid oral medications.

How do you convert grams to milligrams for oral dosage?

To convert grams to milligrams, you multiply the mass in grams by 1,000, as there are 1,000 milligrams in a single gram. This conversion is a necessary first step whenever the physician's order and the medication label use different metric prefixes. Detailed conversion tables can be found on sites like Khan Academy.

Can all oral tablets be crushed or split?

No, not all tablets can be crushed or split; specifically, enteric-coated, extended-release (ER), or sustained-release (SR) medications must be swallowed whole to maintain their intended absorption rate. Nurses should check the Institute for Safe Medication Practices (ISMP) list of "Do Not Crush" medications before altering any dosage form.

What is the importance of checking the expiration date on oral medications?

Checking the expiration date is vital because medications can lose their potency or undergo chemical changes over time, potentially becoming ineffective or harmful to the patient. Administering expired oral dosage forms is a violation of the "Rights of Medication Administration" and poses a significant safety risk.

How do you calculate a weight-based dose for a child?

Weight-based dosing involves first converting the patient's weight from pounds to kilograms (by dividing by 2.2), then multiplying the weight in kg by the ordered dose per unit of weight (e.g., mg/kg). For more complex scenarios involving multiple steps, using a AI Question Generator can help provide tailored practice problems.

What should a nurse do if a calculated dose seems unusually high or low?

If a calculation results in an unusual amount, such as more than three tablets or a very large volume of liquid, the nurse must re-calculate the dose and verify the order with the prescribing provider or a pharmacist. Clinical judgment is the final safeguard against mathematical errors in medication administration.