Dr John Campbell
Dr John Campbell
@campbellteaching·3.3M subscribers·3.1K videos

Applied Pharmacology 5, Theraputic Index

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March 23, 2017

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Therapeutic index is a measure of how safe a drug is, comparing the effective dose with the toxic dose.

Notes

The therapeutic index (TI) (also called therapeutic ratio) is a comparison of the dose of a drug that causes the therapeutic effect to the amount that causes toxicity. This describes the margin of safety, accounting for the effective dose, toxic dose and even potential lethal dose. The related terms therapeutic window or safety window refer to a range of doses which optimize between efficacy and toxicity. This is always where we aim to be.

High (wide) TI is good for good safety profile, drug has low toxicity

Low (narrow) TI is more risky (NTI drugs, narrow therapeutic index), drug more toxic

TD (toxic dose)

TI = -----

ED (effective dose)

TD50 (toxic dose)

TI = -----

ED50 (effective dose)

Lethal dose

Toxicity effects

Adverse response threshold

Therapeutic window / range

Duration of action

Sub therapeutic range

Desired response threshold

Eg, anticoagulants, hypotensives, hypoglycaemics, analgesics, diuretics,

Low (narrow) Therapeutic Index drugs

Digoxin 2:1

Paracetamol (acetaminophen) 7 gram fatal dose

Lithium – nephrotoxicity, ataxia, discordination

Warfarin -

Gentamycin – nephrotoxic, auditory nerve damage - ototoxicity

Vancomycin - nephro

Phenytoin, fast uncontrolled eye movements, dizzy confused, poor coordination, slured speech

Antidepressants, tricyclics

Insulin,

AZT,

High (wide) TI drugs

NSAIDs

Benzodiazepines

Most antibiotics

Furosemide

SSRIs

Does not include any synergistic effects, e.g. diazepam and alcohol or diazepam and morphine, aspirin and warfarin, pharmacokinetic, pharmacodynamics effects, eg. Furosemide and ACEIs (oprils)

Guests & Subjects Covered

Notes TheTherapeutic IndexInsulin AZT HighNSAIDs Benzodiazepines MostFurosemide SSRIs Does

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Applied Pharmacology 5, Theraputic Index · Dr John Campbell · Sentinel