40 Questions
What is the mechanism of action of Isoniazid?
Inhibits assembly of mycolic acids into mycobacteria
What is the most common adverse effect of Isoniazid?
Peripheral neuritis
Which bacterium is Rifampin specifically effective against?
Mycobacterium tuberculosis
What is a key pharmacokinetic characteristic of Rifampin?
Induces hepatic microsomal enzymes
Which antitubercular agent is hydrolyzed to its active compound?
Pyrazinamide
What is the primary cause of fatal hepatitis associated with Isoniazid?
Toxic metabolite accumulation
Why should doses of Isoniazid be reduced in chronic hepatic disease?
Risk of drug accumulation and toxicity
What distinguishes Mycolic acids as unique compounds in mycobacteria?
Exclusive presence in mycobacterial cell walls
Which drug is considered the most potent agent against Mycobacterium tuberculosis?
Isoniazid
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
Which drug is NOT listed as one of the first-line drugs for tuberculosis treatment?
Cycloserine
What is one reason for continuing tuberculosis treatment well after the clinical symptoms disappear?
To ensure complete eradication of the bacteria
Which drug is NOT mentioned as an antimycobacterial agent for tuberculosis?
Pyridoxine analog
What is a common characteristic of Mycobacterium tuberculosis that makes multi-drug treatment crucial?
Frequent mutation to single drug therapy
Which drug is NOT part of the group of antimycobacterial agents mentioned for tuberculosis?
Amphotericin B
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
Which of the following is a common adverse effect of clofazimine?
All of the above
What is the primary mechanism of action of amphotericin B?
Binds to ergosterol in the fungal membrane, disrupting membrane function
Which of the following antifungal agents is considered the drug of choice for the treatment of most systemic mycoses?
Amphotericin B
What is the primary route of administration for amphotericin B?
Intravenous
Which of the following is a characteristic of systemic/subcutaneous mycotic infections?
They are life-threatening and difficult to treat
What is the primary mechanism of action of clofazimine?
Inhibits bacterial DNA template function
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
What is the primary reason for the increased incidence of mycoses in recent years?
Increased number of immunosuppressed patients
What is the mechanism of action of Terbinafine (Lamisil)?
Inhibits squalene epoxidase
Which antifungal is primarily used today for superficial mycotic infections?
Ketoconazole
What is the primary clinical use of Nystatin (Bio-Statin)?
Oral treatment of oral thrush
What is the common unintended effect of Ketoconazole (Nizoral, Extina)?
Increased hepatic enzymes
Which antifungal agent is NOT given systemically due to toxicity concerns?
Miconazole
What is the mode of excretion for Nystatin (Bio-Statin)?
Excreted in feces
Which antifungal inhibits ergosterol synthesis and disrupts fungal membrane function?
Clotrimazole (Gyne-Lotrimin)
'Inhibits squalene epoxidase' is associated with which antifungal agent?
Terbinafine (Lamisil)
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.
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.
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.
Which of the following is a common toxic effect associated with flucytosine (5-FC) therapy?
Bone marrow suppression, leading to anemia, leukopenia, and thrombocytopenia.
What is the primary route of administration for flucytosine (5-FC)?
Oral administration
Which of the following fungal infections is flucytosine (5-FC) most commonly used to treat?
Cryptococcosis
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.
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.
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.
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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