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Ch. 15 - Antimicrobial Drugs
Norman-McKay- Microbiology: Basic and Clinical Principles 2nd Edition
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619Not the one you use?Change textbook
All textbooksNorman-McKay 2nd EditionCh. 15 - Antimicrobial DrugsProblem 7
Chapter 15, Problem 7

Choose the true statement(s) about therapeutic index (TI). Select all that apply.
a. A drug with a high therapeutic index would be effective above the dose at which it is potentially toxic.
b. A narrow TI is preferable.
c. A drug for which the maximum safe dose is close to the minimum effective dose would have a high TI.
d. It is one measure of a drug’s general safety.
e. A drug that is not selectively toxic would most likely have a high TI.

Verified step by step guidance
1
Step 1: Understand the definition of Therapeutic Index (TI). TI is a ratio that compares the toxic dose of a drug to its effective dose, usually expressed as \(TI = \frac{TD_{50}}{ED_{50}}\), where \(TD_{50}\) is the dose that causes toxicity in 50% of the population, and \(ED_{50}\) is the dose that produces the desired effect in 50% of the population.
Step 2: Analyze statement (a): "A drug with a high therapeutic index would be effective above the dose at which it is potentially toxic." Since a high TI means the toxic dose is much higher than the effective dose, the drug is effective at doses well below toxic levels, so this statement is false.
Step 3: Analyze statement (b): "A narrow TI is preferable." A narrow TI means the effective dose and toxic dose are close, which increases risk; therefore, this statement is false because a wide TI is generally preferable for safety.
Step 4: Analyze statement (c): "A drug for which the maximum safe dose is close to the minimum effective dose would have a high TI." If the safe dose is close to the effective dose, the TI is low, so this statement is false.
Step 5: Analyze statements (d) and (e): Statement (d) says TI is a measure of a drug’s general safety, which is true because TI indicates the margin between effective and toxic doses. Statement (e) says a drug that is not selectively toxic would most likely have a high TI; lack of selective toxicity usually means higher toxicity to host cells, so TI would be low, making this statement false.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Therapeutic Index (TI)

The therapeutic index is a ratio that compares the toxic dose of a drug to its effective dose, indicating the drug's safety margin. A high TI means there is a large gap between effective and toxic doses, making the drug safer to use. Conversely, a low or narrow TI indicates a small safety margin, requiring careful dosing.

Selective Toxicity

Selective toxicity refers to a drug's ability to target harmful microbes or cells without damaging the host's cells. Drugs with high selective toxicity tend to have higher therapeutic indices because they affect pathogens specifically, reducing side effects and toxicity to the patient.
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Safety and Efficacy in Drug Dosing

Drug safety involves balancing efficacy and toxicity, where the maximum safe dose should be well above the minimum effective dose. Drugs with a narrow therapeutic index require precise dosing to avoid toxicity, while those with a wide index allow more flexibility and are generally considered safer.
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Related Practice
Textbook Question

Which of the following antimicrobial properties would be the most crucial to consider in developing a new antimicrobial?

a. Selective toxicity

b. Ease of administration

c. Lack of drug interactions

d. Long half-life

e. The drug’s capacity to be bactericidal

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Textbook Question

Assume a bacterium makes beta-lactamase. Could you still use a glycopeptide drug to treat an infection caused by this bacterium? Explain your reasoning.

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Textbook Question

A patient has an uncomplicated infection with a Gram-negative bacterium. He also has a history of penicillin allergy. Which drug is the best treatment option for this patient?

a. Ampicillin

b. A first-generation cephalosporin

c. A carbapenem

d. Isoniazid

e. Azithromycin

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Textbook Question

Which drug family would be the most effective to treat a patient diagnosed with a MRSA infection?

a. Penicillins

b. Third-generation cephalosporins

c. Carbapenems

d. Lincosamides

e. Aminoglycosides

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Textbook Question

The difference between a synthetic drug and a semisynthetic drug is that

a. the semisynthetic drug is a modified synthetic drug.

b. the synthetic drug is a modified natural drug.

c. the synthetic drug is a modified semisynthetic drug.

d. the semisynthetic drug is a modified natural drug.

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Textbook Question

What advantages might a semisynthetic antimicrobial drug have over an antibiotic?

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