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Introduction
1. Medications
1.1 Generic names and brand names
1.2 Classification of medications
1.3 Drug interactions and contraindications
1.4 Medications by organ system
1.5 Drug strengths, dose, and dosage forms
1.6 Routes of administration and special handling of drugs
1.7 Medication side effects, adverse effects and allergies
1.8 Indications of medications and dietary supplements
1.9 Drug stability
1.10 Narrow therapeutic index (NTI) medications
1.11 Pharmaceutical incompatibilities
1.12 Proper storage of medications
1.13 Vaccine types and schedules
2. Patient safety and quality assurance
3. Order entry and processing
4. Federal requirements
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1.10 Narrow therapeutic index (NTI) medications
Achievable PTCE
1. Medications
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Narrow therapeutic index (NTI) medications

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Therapeutic index (TI) or therapeutic ratio

The therapeutic index (TI) compares how much drug is needed to cause toxicity with how much is needed to produce the desired therapeutic effect.

It’s defined as:

TI = TD50/ED50,

where:

  • TD50 is the dose that produces toxicity in 50% of the population tested.
  • ED50 is the dose that produces the desired therapeutic effect in 50% of the population tested.

A higher TI generally means a safer drug, because there’s a wider gap between effective and toxic doses.

Some drugs have a narrow TI (also called NTI drugs or Narrow Therapeutic Range (NTR) drugs). With these drugs, the therapeutic and toxic doses are close together, so dosing and blood levels often need careful monitoring.

Common drugs with a narrow therapeutic index

  • Digoxin
  • Lithium
  • Phenytoin
  • Theophylline
  • Warfarin
  • Levothyroxine
  • Carbamazepine
  • Cyclosporine
  • Ethosuximide
  • Procainamide

Therapeutic index (TI)

  • Ratio of toxic dose (TD50) to effective dose (ED50): TI = TD50/ED50
  • Higher TI = safer drug (wider margin between effective and toxic doses)
  • Narrow TI (NTI/NTR) drugs require close monitoring

Common narrow therapeutic index drugs

  • Digoxin, lithium, phenytoin, theophylline, warfarin
  • Levothyroxine, carbamazepine, cyclosporine, ethosuximide, procainamide

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Narrow therapeutic index (NTI) medications

Therapeutic index (TI) or therapeutic ratio

The therapeutic index (TI) compares how much drug is needed to cause toxicity with how much is needed to produce the desired therapeutic effect.

It’s defined as:

TI = TD50/ED50,

where:

  • TD50 is the dose that produces toxicity in 50% of the population tested.
  • ED50 is the dose that produces the desired therapeutic effect in 50% of the population tested.

A higher TI generally means a safer drug, because there’s a wider gap between effective and toxic doses.

Some drugs have a narrow TI (also called NTI drugs or Narrow Therapeutic Range (NTR) drugs). With these drugs, the therapeutic and toxic doses are close together, so dosing and blood levels often need careful monitoring.

Common drugs with a narrow therapeutic index

  • Digoxin
  • Lithium
  • Phenytoin
  • Theophylline
  • Warfarin
  • Levothyroxine
  • Carbamazepine
  • Cyclosporine
  • Ethosuximide
  • Procainamide
Key points

Therapeutic index (TI)

  • Ratio of toxic dose (TD50) to effective dose (ED50): TI = TD50/ED50
  • Higher TI = safer drug (wider margin between effective and toxic doses)
  • Narrow TI (NTI/NTR) drugs require close monitoring

Common narrow therapeutic index drugs

  • Digoxin, lithium, phenytoin, theophylline, warfarin
  • Levothyroxine, carbamazepine, cyclosporine, ethosuximide, procainamide