Flucytosine Coupon: Antimycobacterials and Antifungals Quiz and Flashcards

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Questions and Answers

What is the mechanism of action of Isoniazid?

Inhibits assembly of mycolic acids into mycobacteria (correct)

Inhibits transcription

Inhibits bacterial DNA-dependent RNA polymerase

Inhibits bacterial mRNA synthesis

What is the most common adverse effect of Isoniazid?

Skin rash and drug fever

Gastrointestinal disturbances

Jaundice

Peripheral neuritis (correct)

Which bacterium is Rifampin specifically effective against?

Pseudomonas aeruginosa

Mycobacterium tuberculosis (correct)

Streptococcus pneumoniae

Escherichia coli

What is a key pharmacokinetic characteristic of Rifampin?

Induces hepatic microsomal enzymes Signup and view all the answers

Which antitubercular agent is hydrolyzed to its active compound?

Pyrazinamide Signup and view all the answers

What is the primary cause of fatal hepatitis associated with Isoniazid?

Toxic metabolite accumulation Signup and view all the answers

Why should doses of Isoniazid be reduced in chronic hepatic disease?

Risk of drug accumulation and toxicity Signup and view all the answers

What distinguishes Mycolic acids as unique compounds in mycobacteria?

Exclusive presence in mycobacterial cell walls Signup and view all the answers

Which drug is considered the most potent agent against Mycobacterium tuberculosis?

Isoniazid Signup and view all the answers

What is a key characteristic of Mycobacteria that influences the need for multi-drug therapy in tuberculosis treatment?

Common occurrence of resistance to a single drug Signup and view all the answers

Which drug is NOT listed as one of the first-line drugs for tuberculosis treatment?

Cycloserine Signup and view all the answers

What is one reason for continuing tuberculosis treatment well after the clinical symptoms disappear?

To ensure complete eradication of the bacteria Signup and view all the answers

Which drug is NOT mentioned as an antimycobacterial agent for tuberculosis?

Pyridoxine analog Signup and view all the answers

What is a common characteristic of Mycobacterium tuberculosis that makes multi-drug treatment crucial?

Frequent mutation to single drug therapy Signup and view all the answers

Which drug is NOT part of the group of antimycobacterial agents mentioned for tuberculosis?

Amphotericin B Signup and view all the answers

What is a key reason for using multi-drug treatment in tuberculosis even after the disappearance of clinical symptoms?

To prevent the development of resistant strains Signup and view all the answers

Which of the following is a common adverse effect of clofazimine?

All of the above Signup and view all the answers

What is the primary mechanism of action of amphotericin B?

Binds to ergosterol in the fungal membrane, disrupting membrane function Signup and view all the answers

Which of the following antifungal agents is considered the drug of choice for the treatment of most systemic mycoses?

Amphotericin B Signup and view all the answers

What is the primary route of administration for amphotericin B?

Intravenous Signup and view all the answers

Which of the following is a characteristic of systemic/subcutaneous mycotic infections?

They are life-threatening and difficult to treat Signup and view all the answers

What is the primary mechanism of action of clofazimine?

Inhibits bacterial DNA template function Signup and view all the answers

Which of the following is a characteristic of the antifungal spectrum of amphotericin B?

It is broad and effective against a wide range of fungal pathogens Signup and view all the answers

What is the primary reason for the increased incidence of mycoses in recent years?

Increased number of immunosuppressed patients Signup and view all the answers

What is the mechanism of action of Terbinafine (Lamisil)?

Inhibits squalene epoxidase Signup and view all the answers

Which antifungal is primarily used today for superficial mycotic infections?

Ketoconazole Signup and view all the answers

What is the primary clinical use of Nystatin (Bio-Statin)?

Oral treatment of oral thrush Signup and view all the answers

What is the common unintended effect of Ketoconazole (Nizoral, Extina)?

Increased hepatic enzymes Signup and view all the answers

Which antifungal agent is NOT given systemically due to toxicity concerns?

Miconazole Signup and view all the answers

What is the mode of excretion for Nystatin (Bio-Statin)?

Excreted in feces Signup and view all the answers

Which antifungal inhibits ergosterol synthesis and disrupts fungal membrane function?

Clotrimazole (Gyne-Lotrimin) Signup and view all the answers

'Inhibits squalene epoxidase' is associated with which antifungal agent?

Terbinafine (Lamisil) Signup and view all the answers

What is the primary mechanism of action of flucytosine (5-FC)?

Flucytosine is converted to 5-fluorouracil (5-FU) within fungal cells, which inhibits thymidylate synthase and disrupts fungal DNA and RNA synthesis. Signup and view all the answers

Which of the following is true about the distribution of flucytosine (5-FC)?

Flucytosine has a very narrow therapeutic index, with a small difference between the effective and toxic doses. Signup and view all the answers

How is flucytosine (5-FC) typically used in combination with other antifungal agents?

Flucytosine is used in combination with amphotericin B to treat cryptococcal meningitis and other systemic mycoses. Signup and view all the answers

Which of the following is a common toxic effect associated with flucytosine (5-FC) therapy?

Bone marrow suppression, leading to anemia, leukopenia, and thrombocytopenia. Signup and view all the answers

What is the primary route of administration for flucytosine (5-FC)?

Oral administration Signup and view all the answers

Which of the following fungal infections is flucytosine (5-FC) most commonly used to treat?

Cryptococcosis Signup and view all the answers

What is the primary mechanism of synergy between flucytosine (5-FC) and amphotericin B?

Amphotericin B and flucytosine have complementary mechanisms of action, targeting different aspects of fungal physiology. Signup and view all the answers

What is the therapeutic index (ratio of toxic to effective dose) for flucytosine (5-FC)?

The therapeutic index for flucytosine is approximately 1, indicating a narrow safety margin. Signup and view all the answers

Study Notes

Antimycobacterial Agents

Mycobacterium tuberculosis is always treated with a combination of antitubercular agents to prevent resistance.
Isoniazid:
- Inhibits the assembly of mycolic acids into mycobacteria.
- Selective against mycobacteria.
- Well-absorbed orally, metabolized in the liver, and distributed widely (crosses the blood-brain barrier).
- Adverse effects: dose-related peripheral neuritis, fatal hepatitis (more common in elderly, alcoholics, and patients on rifampin).
Rifampin:
- Inhibits bacterial DNA-dependent RNA polymerase.
- Bactericidal for intracellular and extracellular mycobacteria.
- Well-absorbed orally, metabolized in the liver, and distributed widely (crosses the blood-brain barrier).
- Adverse effects: hypersensitivity, GI symptoms, jaundice, and orange-red color in urine, feces, and other secretions.
- Induces hepatic microsomal enzymes, increasing metabolism of other drugs.

Pyrazinamide

Must be hydrolyzed to an active compound.
Used orally as an antimycobacterial agent.

Antifungal Agents

Increased incidence of mycoses due to immunosuppressed patients.
Systemic mycotic infections are life-threatening and difficult to treat.
Amphotericin B:
- Polyene macrolide antimicrobial.
- DOC for treatment of most systemic mycoses.
- Binds to ergosterol, disrupting fungal membrane function.
- Broad spectrum against various fungi, including Candida albicans and Aspergillus.
- Administered IV, distributes to infected keratinized tissue, and eliminated by the kidney.
- Unintended effects: allergic reactions, GI upset, headache, hepatotoxicity, and teratogenicity.
Terbinafine:
- Inhibits squalene epoxidase, leading to inhibition of ergosterol synthesis.
- Used to treat tinea infections (onychomycosis).
- Administered orally and topically, distributes to keratinized tissue, and metabolized in the liver.
- Unintended effects: GI upset, increased hepatic enzymes, and contraindicated in hepatic dysfunction.
Nystatin:
- Binds to ergosterol, disrupting fungal membrane function.
- Used to treat oral thrush and intestinal candidiasis.
- Poor oral absorption, excreted in feces.
- Unintended effects: GI upset.

Topical Antifungals

Ketoconazole:
- Inhibits ergosterol synthesis.
- Used to treat superficial mycotic infections (cutaneous candidiasis, tinea infections).
Miconazole, Clotrimazole, Terconazole, and Tioconazole:
- Inhibit ergosterol synthesis.
- Used topically to treat vaginal candidiasis, tinea infections, and other superficial mycotic infections.
- Not given systemically due to toxicity.

Systemic Antifungals

Flucytosine:
- Fluorinated pyrimidine antimetabolite.
- Employed synergistically with Amphotericin B.
- Converted to an antimetabolite within fungal cells, inhibiting thymidylate synthase and DNA and RNA synthesis.
- Used to treat meningitis due to Cryptococcus neoformans and candida infections.
- Well-absorbed orally, distributes to the CNS, and eliminated by the kidney.
- Unintended effects: bone marrow suppression, GI symptoms, and increased liver enzymes.

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Test your knowledge on the indications, contraindications, interactions, mechanisms of action, unintended effects, and drug resistance of antimycobacterial agents for tuberculosis and leprosy, as well as antifungal agents.

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