• Narrow therapeutic index (NTI) drugs are defined as
those drugs where
.
small differences in dose or blood concentration may lead to dose and blood concentration dependent
, serious therapeutic failures or adverse drug reactions.
Is high therapeutic index Good or bad?
The larger the TI, the safer the drug is
. Conversely, a drug with a narrow TI has generally a steep concentration–response relationship for efficacy, toxicity or both so that there is a narrowly defined range between risk and benefit.
What is considered a safe therapeutic index?
| Term Meaning | TR Therapeutic Ratio |
|---|
How do you interpret therapeutic index?
- therapeutic index of a drug is the ratio of the dose that produces toxicity to the dose that produces a clinically desired or effective response.
- TD50 = the dose of drug that causes a toxic response in 50% of the population.
- ED50 = the dose of drug that is therapeutically effective in 50% of the population.
What is the therapeutic index and how is it used to guard against dangerous drugs?
The therapeutic index (TI)
estimates the margin of safety of a drug through the use of a ratio that measures the effective (therapeutic) dose (ED) and the lethal (toxic) dose (LD)
. The closer the ratio is to 1, the greater the danger of toxicity.
What will happen if the therapeutic index value is smaller?
If the TI is small (the difference between the two concentrations is very small),
the drug must be dosed carefully and the person receiving the drug should be monitored closely for any signs of drug toxicity
.
Why is the therapeutic index important?
The therapeutic index (TI) — which is typically considered as the
ratio of the highest exposure to the drug that results in no toxicity
to the exposure that produces the desired efficacy — is an important parameter in efforts to achieve this balance.
Which is the antidote for benzodiazepines?
Flumazenil
, a specific benzodiazepine antagonist, is useful in reversing the sedation and respiratory depression that often occur when benzodiazepines are administered to patients undergoing anesthesia or when patients have taken an intentional benzodiazepine overdose.
How do you calculate therapeutic index of a drug?
The therapeutic index formula
T 1 = 3 W a × 10 – 4
was derived from T
1
= LD
50
/ED
50
and ED
50
= L D 50 3 x W a × 10 – 4 . Findings have shown that, therapeutic index is a function of death reversal (s), safety factor (10
− 4
) and weight of animal (Wa).
What is the therapeutic range of a drug?
The therapeutic range of a drug is
the dosage range or blood plasma or serum concentration usually expected to achieve the desired therapeutic effect
.
Which drugs have a narrow therapeutic range?
Drugs with a narrow therapeutic index
4 We defined the following drugs to be NTI-drugs:
aminoglycosides, ciclosporin, carbamazepine, digoxin, digitoxin, flecainide, lithium, phenytoin, phenobarbital, rifampicin, theophylline and warfarin
.
What is the relationship between ED50 LD50 and therapeutic index?
Therapeutic index is defined as follows: LD50, or median lethal dose, is
the dose of drug that causes death in 50% of experimental animals
, and ED50, or median effective dose, is the dose that produces a specified effect (“response”) in 50% of the population under study.
What therapeutic drug monitoring means?
Therapeutic drug monitoring is
the measurement of specific drugs and/or their breakdown products (metabolites) at timed intervals to maintain a relatively constant concentration of the medication in the blood
.
What biological fluid is most used for drug measurement?
Plasma (P) and saliva (S)
are the main biological fluids used for drug monitoring.
What does it mean when a drug is 50% protein bound?
Answer: The percentage of drug NOT protein bound is the amount of drug that is free to work as expected. In this case, 50%
is unable to be effective
, because it is protein-bound. Protein binding has nothing to do with the destruction of protein, drug excretion, or protein in the diet.
How are drugs distributed?
Drug distribution is
the disbursement of an unmetabolized drug as it moves through the body’s blood and tissues
. The efficacy or toxicity of a drug depends on the distribution in specific tissues and in part explains the lack of correlation between plasma levels and the effects that are seen.
