MPSC 2026 Prelims Paper-I · Question 67 of 100

Correct — option (2), 'Only (b) is correct'. The drug, printed here as 'Chloroamphenicol' and standardly spelt chloramphenicol, is the textbook example of a broad spectrum antibiotic. Antibiotics are graded by how wide a range of organisms they act against. A broad spectrum antibiotic kills or inhibits a wide range of both Gram-positive and Gram-negative bacteria; a narrow spectrum antibiotic is effective mainly against one of those two groups; a limited spectrum antibiotic is effective against a single organism or a single disease. Chloramphenicol, first isolated in 1947, sits squarely in the first class. It is rapidly absorbed from the gastro-intestinal tract, so it can be given by mouth, and it has been used against typhoid, dysentery, acute fever, certain urinary infections, meningitis and pneumonia — a list of unrelated conditions caused by unrelated organisms, which is itself the evidence of a broad spectrum. There is a structural shortcut worth seeing here too. The four statements are mutually exclusive descriptions of one substance: a drug cannot be both narrow spectrum and broad spectrum, nor both broad and limited, nor an antibiotic and an antiseptic. Any option asserting two of them at once is therefore self-defeating before the pharmacology is even considered, which disposes of options (1) and (3) in a single stroke and leaves the paper asking one plain question — antibiotic or antiseptic.

• (1)Only (a) and (d) are correct — This option fails twice over. First, it is internally impossible: it claims the same drug is a narrow spectrum antibiotic and an antiseptic drug, two categories that cannot both hold of one substance. Second, both of its limbs are wrong on the facts. Chloramphenicol is broad spectrum, not narrow — penicillin G is the standard example of a narrow spectrum antibiotic, effective mainly against Gram-positive organisms. And it is not an antiseptic: antiseptics are applied to living surfaces such as wounds, cuts and diseased skin, whereas chloramphenicol is a systemic antibiotic absorbed from the gut and carried in the blood.
• (3)Only (b) and (c) are correct — The trap here is that limb (b) is right, so a candidate who checks only the first thing he recognises will stop and mark it. But limb (c) contradicts limb (b). 'Limited spectrum' is a real category in the classification — it describes an antibiotic effective against a single organism or a single disease — and precisely because it is real, it is the opposite end of the same scale from 'broad spectrum'. A drug active against typhoid, dysentery, meningitis, pneumonia and urinary infections is by definition not limited to one organism. The lesson is that a partly-correct option is worth nothing; every limb of a compound option must survive.
• (4)Only (d) is correct — This makes chloramphenicol an antiseptic, which confuses two different classes of antimicrobial. Antiseptics are applied to living tissue and are chosen for not damaging it — dettol, which is a mixture of chloroxylenol and terpineol; tincture of iodine; iodoform; boric acid in dilute solution as an eye wash. Disinfectants act on inanimate surfaces such as floors, drains and instruments, and the same chemical can serve as either depending on concentration: a 0.2 per cent solution of phenol is an antiseptic while a 1 per cent solution is a disinfectant. Antibiotics are a separate class again — substances produced by micro-organisms, or made in part by synthesis, which act inside the body at low concentration to stop other micro-organisms growing.

Medicines that act against micro-organisms are sorted by where they are used and how widely they act. Antibiotics work within the body: they are substances produced wholly or partly by micro-organisms which, in low concentration, inhibit the growth of or destroy other micro-organisms by interfering with their metabolic processes. Antiseptics and disinfectants work on surfaces: antiseptics on living tissue, disinfectants on inanimate objects. Within antibiotics, the spectrum classification is the one examiners test. Broad spectrum drugs hit a wide range of Gram-positive and Gram-negative bacteria and include chloramphenicol, tetracycline, ampicillin, amoxycillin, ofloxacin and vancomycin. Narrow spectrum drugs act mainly on one of the two groups, penicillin G being the classical case. Limited spectrum drugs are effective against a single organism or disease. A second, independent classification splits antibiotics into bactericidal, which kill the organism, and bacteriostatic, which merely stop it multiplying and leave the killing to the body's own defences.

Chloramphenicol has a place in the history of medicine out of proportion to its present use. Isolated in 1947 from a soil bacterium of the Streptomyces group, it was among the first antibiotics that could be given by mouth and that worked against a genuinely wide range of organisms, and it transformed the treatment of typhoid. Its use today is restricted, because it can cause serious suppression of the bone marrow, and safer drugs have replaced it for most purposes. That trajectory — a drug that changes medicine, then narrows to a reserve role as its harms and the organisms' resistance become clear — is the same story that now dominates the policy side of this topic. Indiscriminate use of broad spectrum antibiotics, incomplete courses, and their use in animal husbandry drive antimicrobial resistance, which is why prescription rules, hospital stewardship and the phrase 'complete the full course' now appear in general-studies papers as often as the chemistry does.

• Chloramphenicol is a broad spectrum antibiotic: it acts against a wide range of both Gram-positive and Gram-negative bacteria. Isolated in 1947, it is rapidly absorbed from the gastro-intestinal tract and so can be given orally.
• It has been used in typhoid, dysentery, acute fever, certain urinary infections, meningitis and pneumonia. Its use is restricted today because of the risk of serious bone-marrow toxicity, and safer drugs have displaced it for most indications.
• Spectrum classification: broad spectrum acts on a wide range of Gram-positive and Gram-negative bacteria (chloramphenicol, tetracycline, ampicillin, amoxycillin, vancomycin); narrow spectrum acts mainly on one group (penicillin G); limited spectrum acts on a single organism or disease.
• Antibiotics act inside the body at low concentration. Antiseptics are applied to living tissue — dettol (chloroxylenol with terpineol), tincture of iodine, iodoform, dilute boric acid as an eye wash. Disinfectants are applied to inanimate objects such as floors and instruments.
• The same chemical can be either antiseptic or disinfectant depending on strength: a 0.2 per cent solution of phenol acts as an antiseptic, a 1 per cent solution as a disinfectant. Concentration, not identity, decides.

• Stopping at the first correct limb of a compound option. Option (3) opens with the true statement and then adds a contradictory one; every limb must hold for the option to be marked.
• Treating 'limited spectrum' as an invented distractor. It is a genuine category in the classification — for drugs effective against a single organism or disease — which is exactly why it cannot also describe a broad spectrum drug.
• Confusing antibiotic with antiseptic because both fight microbes. The test is where the substance acts: an antibiotic works inside the body, an antiseptic on living tissue surfaces, a disinfectant on inanimate objects.

Three shapes recur. The classification question, as here — name a drug and ask for its class, with the spectrum categories as options. The example question, which runs the other way: which of the following is a broad spectrum antibiotic, or which is an antiseptic, with a mixed list. And the composition or use question, which asks what dettol is made of, what tincture of iodine is, or which antibiotic treats both tuberculosis and leprosy. A single table of drug, class, spectrum and one use answers all three, and the discriminating detail is almost always spectrum or site of action rather than chemistry. Note too the option architecture used here — statements that are mutually exclusive, offered in compound options — because recognising it lets you eliminate half the option set before you have recalled a single fact about the drug.

• practice — not a real PYQ

  Antiseptics and disinfectants differ principally in which one of the following respects?

  • (a)Antiseptics are applied to living tissues while disinfectants are applied to inanimate objects
  • (b)Antiseptics kill bacteria while disinfectants only inhibit their growth
  • (c)Antiseptics are natural products while disinfectants are synthetic
  • (d)Antiseptics act on viruses while disinfectants act on bacteria

  Answer(a) Antiseptics are applied to living tissues while disinfectants are applied to inanimate objects — the site of application is the distinction, not the chemistry. The same substance can serve as either depending on strength: a 0.2 per cent phenol solution is an antiseptic, a 1 per cent solution a disinfectant.

• practice — not a real PYQ

  Which one of the following is a narrow spectrum antibiotic, effective mainly against Gram-positive bacteria?

  • (a)Chloramphenicol
  • (b)Tetracycline
  • (c)Penicillin G
  • (d)Amoxycillin

  Answer(c) Penicillin G — the standard example of a narrow spectrum antibiotic. Chloramphenicol and tetracycline are broad spectrum, and amoxycillin is a semi-synthetic modification of penicillin developed precisely to widen its spectrum, so it too is broad spectrum.