Free Antimicrobial Agents MCQs with Answers

• A. Destroyed by gastric acid
• B. Very active against sensitive gram positive cocci
• C. Used for treatment of meningococcal meningitis
• D. More concentrated in prostatic secretions and intraocular fluids

Explanation: Penicillin G is acid-labile, active against susceptible Gram-positive cocci, and used for meningococcal meningitis.

• A. Penicillin G
• B. Clindamycin
• C. Metronidazole
• D. Doxycycline

Explanation: Metronidazole can produce a disulfiram-like antabuse reaction with alcohol, causing flushing, nausea, vomiting and hypotension.

• A. H.pylori
• B. C.difficile
• C. K.pneumoniae
• D. Shigella

Explanation: Clostridioides difficile is the classic and most common important cause of antibiotic-associated diarrhoea, particularly after…

• A. Absolute alchohol
• B. Quaternary ammonium compound
• C. Sodium hypochlorite
• D. Iodine compound

Explanation: Sodium hypochlorite is used to disinfect blood spills because it effectively inactivates blood-borne pathogens when used at an appropriate…

• A. 50%
• B. 65%
• C. 70%
• D. 95%

Explanation: Ethanol is most effective as an antiseptic at about 70%, because water improves protein denaturation and allows better penetration into…

• A. Rifampicin
• B. Isoniazid
• C. Cefotaxime
• D. Aminoglycoside

Explanation: Isoniazid is mainly metabolized in the liver and usually does not require dosage reduction in renal failure.

• A. It is a topical antimicrobial
• B. It is a topical anesthestic
• C. Its ability to aid in blood coagulation
• D. All of the above

Explanation: Povidone-iodine releases iodine and acts as a broad-spectrum topical antimicrobial, which is useful for reducing oral microbial infection…

• A. Ethambutol
• B. Ethylene glycol
• C. Ciprofloxacin
• D. Tetracycline

Explanation: Ethambutol classically causes dose-related optic neuropathy, while ethylene glycol toxicity can produce severe visual injury and…

• A. They are fungistatic
• B. They are hepatotoxic
• C. Resistance to the drug is common
• D. They affect the metabolism of drugs such as cyclosporine necessitating an increasing in dosage

Explanation: Azoles inhibit fungal ergosterol synthesis and are usually fungistatic; hepatotoxicity and resistance are recognized problems.

• A. Doxycycline
• B. Demeclocyline
• C. Minocycline
• D. Tetracycline

Explanation: Ledermix paste contains demeclocycline together with a corticosteroid, triamcinolone.

• A. Prazequantal
• B. Metronidazole
• C. Niclosamide
• D. Pyrantel

Explanation: Praziquantel is an effective cestocidal drug used for cysticercosis. Metronidazole and pyrantel target other parasites, while niclosamide…

• A. Erythromycin
• B. Doxycycline
• C. Penicillin
• D. Streptomycin

Explanation: Erythromycin inhibits CYP3A4 and reduces terfenadine metabolism, increasing its concentration and prolonging the QT interval, which may…

• A. Local anesthetic property
• B. Local anesthetic and antiseptic action
• C. Antiseptic action
• D. Antibiotic action

Explanation: Chloroxylenol, the active antiseptic in products such as Dettol, damages microbial cell membranes and is used mainly for antisepsis.

• A. Indifference
• B. Synergy
• C. Antagonism
• D. Bacterial symbiosis

Explanation: Ampicillin damages the bacterial cell wall, allowing gentamicin to enter more readily and inhibit protein synthesis.

• A. Skin eruptions
• B. Angioneurotic edema
• C. Sialorrhea
• D. Serum imbalance
• E. Both A & B

Explanation: Drug allergy commonly produces skin eruptions and may cause angioneurotic edema from increased vascular permeability.

• A. Rifampicin causes hepatic enzyme induction and increase metabolism of OCP's
• B. Decreased absorption of OCP's
• C. Obstruction of fallopian tubes
• D. Increase excretion of OCP's

Explanation: Rifampicin strongly induces hepatic CYP450 enzymes, especially CYP3A4, which accelerates metabolism of oestrogen and progestin components…

• A. Tetracycline
• B. Sulphonamide
• C. Cephalosporin
• D. Lincemycin

Explanation: Cephalosporins are beta-lactam antibiotics structurally related to penicillins and share inhibition of bacterial cell-wall synthesis.

• A. Ampicillin
• B. Erythromycin
• C. Penicilling G
• D. Methicillin sodium

Explanation: Non-penicillinase-producing staphylococci remain susceptible to natural penicillins, so penicillin G is appropriate.

• A. Griseofulvin
• B. Amphotericin
• C. Fluconazole
• D. Sulfonates

Explanation: Fluconazole is well absorbed orally and reaches mucosal tissues, making it effective for both oropharyngeal and oesophageal candidiasis.

• A. Metronidazole
• B. Nystatin
• C. Tetracycline
• D. Sulphonamides

Explanation: Metronidazole is reduced inside susceptible organisms to reactive metabolites that damage DNA and cause strand breaks.