ANarrow Therapeutic Index (NTI) drugis a medication in whichsmall differences in dose or blood concentrationcan lead to serioustoxicityorsubtherapeutic effects. These drugs requirecareful dosing and monitoringto avoid adverse effects or treatment failure.
Small Margin of Safety:The difference between theminimum effective concentration (MEC)and theminimum toxic concentration (MTC)is very narrow.
Requires Therapeutic Drug Monitoring (TDM):Blood levels of the drug must be regularly monitored to maintain efficacy while avoiding toxicity.
High Risk of Adverse Effects:Even minor dosage adjustments or variations in patient metabolism can cause toxicity.
Strict Pharmacokinetic and Pharmacodynamic Considerations:Factors likerenal and hepatic function, drug interactions, and patient weightsignificantly impact the drug’s effect.
Warfarin (Coumadin) → Risk of bleeding.
Digoxin → Risk of toxicity affecting the heart.
Phenytoin → Risk of severe neurological effects.
Levothyroxine → Risk of under- or over-treatment of thyroid disorders.
Theophylline → Risk of respiratory or cardiac toxicity.
Carbamazepine → Risk of serious neurological side effects.
A. Shorter window of guaranteed stability.→ Incorrect. NTI drugs do not necessarily have a shorter shelf-life or stability concerns compared to other drugs. Stability depends on formulation and storage conditions.
B. Incompatibility with therapeutic monitoring.→ Incorrect. NTI drugsrequiretherapeutic monitoring, not the opposite.
C. Synergistic effect on other medications.→ Incorrect. While NTI drugs can interact with other drugs, not all exhibit a synergistic effect (where combined drugs produce a greater effect than expected).
PTCB PTCE Exam Content Outline – Medication Safety and Quality Assurance(Monitoring NTI drugs).
FDA Narrow Therapeutic Index Drug List(Guidelines on NTI medications).
Lexicomp and Micromedex Drug Databases(Provide monitoring recommendations for NTI drugs).
USP <800> Hazardous Drugs and USP <797> Sterile Compounding Guidelines(Ensure safe handling and dispensing of NTI drugs).
Mosby’s Pharmacy Technician: Principles and Practice(NTI drug classification and monitoring).
Key Characteristics of NTI Drugs:Examples of NTI Drugs:Why the Other Answer Choices Are Incorrect:Pharmacy Technician References:
