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Therapeutic Drug Levels — NCLEX Cheat Sheet

Memorize narrow-window values

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👤 By the CinnaRN Clinical Content Team 🕐 Updated 2026-07-11 🏷️ Pharmacological Therapies 🔖 Free to read, print, and share

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Use this quick-reference guide to spot, treat, and prevent Therapeutic Drug Levels on the NCLEX. Keep it handy during review and on exam day!

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Cardiac

Key facts

Digoxin 0.5-2.0 ng/mL
Dig toxic >2.0; check K+

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Psych

Key facts

Lithium 0.6-1.2 mEq/L
Toxic >1.5 mEq/L

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Seizure

Key facts

Phenytoin (Dilantin) 10-20 mcg/mL
Toxic → nystagmus, ataxia

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Other

Key facts

Theophylline 10-20 mcg/mL
Vancomycin trough 10-20 mcg/mL
Acetaminophen <150 mcg/mL

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Quick Tip

A narrow therapeutic index means small changes in level can move from effective to toxic.

📖 Related Topics

Digoxin Toxicity Heparin Therapy Warfarin Therapy Acetaminophen Poisoning in Children

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