# Situation: A 68-year-old woman with newly diagnosed primary hypothyroidism and stable angina is started on levothyroxine 25 mcg daily. She also takes calcium carbonate and ferrous sulfate, each once daily. She wakes at 05:30 and eats breakfast at 06:30, lunch at 12:00, and dinner at 18:00. The nurse plans her daily medication schedule. Which schedule is BEST?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630404  
> language: ko  
> subject: Nursing Practice IV — Care of Clients with Problems in Nutrition and Gastrointestinal, Metabolism and Endocrine, Perception and Coordination

## 문제

Situation: A 68-year-old woman with newly diagnosed primary hypothyroidism and stable angina is started on levothyroxine 25 mcg daily. She also takes calcium carbonate and ferrous sulfate, each once daily. She wakes at 05:30 and eats breakfast at 06:30, lunch at 12:00, and dinner at 18:00.

The nurse plans her daily medication schedule. Which schedule is BEST?

## 보기

1. Levothyroxine 05:45; calcium at 08:00; iron with dinner
2. Levothyroxine with breakfast; calcium and iron with dinner
3. Levothyroxine 05:45; calcium with lunch; iron with dinner **✔ 정답**
4. Levothyroxine 05:45; calcium and iron with breakfast at 06:30

**정답: 3**

## 해설

Levothyroxine is taken on an empty stomach with water 30–60 minutes before breakfast, and it is separated from calcium and iron by about 4 hours because both bind it and reduce absorption. Taking it at 05:45 with calcium at 12:00 and iron at 18:00 meets both rules and also keeps calcium and iron apart from each other.

## 심화 해설

The best schedule
Two rules govern her levothyroxine. Levothyroxine is taken on an empty stomach with water 30–60 minutes before breakfast, and it is separated from calcium and iron by about 4 hours, because both bind it and reduce absorption. Taking levothyroxine at 05:45, calcium with lunch at 12:00, and iron with dinner at 18:00 meets both rules and also keeps calcium and iron apart from each other.

Why absorption is so sensitive
Levothyroxine is absorbed in the small intestine, and its absorption is easily reduced by food, coffee, and certain minerals. Calcium carbonate and ferrous sulfate form insoluble complexes with levothyroxine in the gut, so less hormone enters the bloodstream. The effect is large enough to raise thyroid-stimulating hormone (TSH) and make the client appear under-treated. Consistency matters as much as timing: taking the tablet the same way every day keeps absorption predictable so that dose adjustments based on TSH are meaningful. Calcium can also reduce iron absorption, so spacing the two supplements apart is an added benefit of this schedule.

| Schedule | Empty stomach? | 4 h from calcium and iron? | Verdict |
| --- | --- | --- | --- |
| 05:45; calcium 08:00; iron dinner | Yes | No (calcium about 2 h later) | Inadequate |
| With breakfast; calcium and iron dinner | No | Yes | Absorption reduced and variable |
| 05:45; calcium lunch; iron dinner | Yes | Yes | Best |
| 05:45; calcium and iron at 06:30 | Yes | No (45 minutes) | Absorption falls |

Why the other schedules fail
Calcium at 08:00 is only about 2 hours after levothyroxine, short of the 4-hour separation. Taking levothyroxine with breakfast reduces and varies its absorption. Taking calcium and iron with breakfast at 06:30 leaves only 45 minutes after levothyroxine, so binding in the gut lowers the amount absorbed.

Teaching points
The nurse teaches her to take levothyroxine with a full glass of water on waking, wait before eating or drinking coffee, take calcium and iron at separate later meals, and keep the routine the same every day. She should not stop or change the dose without consulting the provider.

Exam takeaway
Key point Levothyroxine: empty stomach, 30–60 minutes before breakfast, and about 4 hours away from calcium, iron, and antacids. Pick the schedule that satisfies every rule at once.

## 임상 시나리오

Scheduling LevothyroxineEmpty stomach and four-hour spacing
Levothyroxine is taken with water 30–60 minutes before breakfast, on an empty stomach, at the same time each day.

Calcium and iron bind levothyroxine and reduce absorption, so they are taken about 4 hours later. Levothyroxine at 05:45, calcium at lunch, and iron at dinner meets all the rules.

CautionInconsistent timing makes absorption unpredictable and can lead to misleading TSH results and unnecessary dose changes.

## 핵심 개념

- **Levothyroxine** — Synthetic thyroxine (T4) used to replace thyroid hormone in hypothyroidism.
- **Drug binding interaction** — A reaction in the gut where one substance attaches to a drug and reduces its absorption.
- **Primary hypothyroidism** — Underactivity of the thyroid gland itself, causing low thyroid hormone and high TSH.
- **Calcium carbonate** — A calcium supplement that can bind levothyroxine and reduce its absorption.

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