Once we know how drugs act on enzymes and receptors, the next step is the families of drugs that treat illness directly: drugs that act on the nervous system, drugs that fight micro-organisms, and drugs that control fertility.
Neurologically active drugs
Tranquilizers (sedatives) act on the central nervous system and are used to treat stress, anxiety, mild and severe mental disease. Some, such as equanil, also help in hypertension. Barbiturates (e.g. veronal, luminal) are hypnotics that induce sleep; noradrenaline-related drugs and ones such as iproniazid and phenelzine act as antidepressants by keeping the mood-lifting neurotransmitter active.
Analgesics reduce pain without causing loss of consciousness. They are of two kinds:
- Non-narcotic (non-addictive) analgesics — aspirin and paracetamol. Besides relieving pain they reduce fever (antipyretic). Aspirin also prevents blood platelets from clumping, so a small daily dose is used to prevent heart attacks.
- Narcotic analgesics — morphine and its relatives (opioids, from the opium poppy). In medicinal doses they relieve severe pain (after surgery, in terminal cancer) and bring sleep, but they are habit-forming; abuse is harmful and can be fatal.
Antimicrobials
Antimicrobials kill or stop the growth of micro-organisms such as bacteria, fungi and viruses, or stop their harmful effect.
Antibiotics are substances produced (wholly or partly) by micro-organisms that, in low concentration, kill or inhibit other micro-organisms. Two ways of describing them:
- Bactericidal antibiotics kill the bacteria (e.g. penicillin, aminoglycosides, ofloxacin); bacteriostatic antibiotics inhibit growth (e.g. erythromycin, tetracycline, chloramphenicol).
- Broad-spectrum antibiotics act against many different bacteria (e.g. chloramphenicol, tetracycline); narrow-spectrum antibiotics act against only a few (e.g. penicillin G). Penicillin, discovered by Alexander Fleming, was the first antibiotic.
Antiseptics and disinfectants both kill or stop micro-organisms, but differ in where they are used. Antiseptics are applied to living tissue — skin, wounds, ulcers — without harming it (e.g. furacin, soframicine, tincture of iodine, the dyes used in skin ointments). Disinfectants are applied to non-living objects such as floors, drains and instruments and are too harsh for living tissue. The same chemical can be both, depending on concentration: a 0.2% solution of phenol acts as an antiseptic, while a 1% solution acts as a disinfectant. Dettol is a familiar antiseptic, a mixture of chloroxylenol and terpineol.
Antifertility drugs
Antifertility drugs control the population by preventing conception. They are oral contraceptives that contain synthetic versions of the female hormones oestrogen and progesterone. A common synthetic progesterone derivative is norethindrone, and a synthetic oestrogen is ethynylestradiol (novestrol). These hormones suppress ovulation, so the egg is not released.
What are tranquilizers? Name one and state a use.
Solution- Tranquilizers are neurologically active drugs that act on the central nervous system.
- They relieve stress, anxiety and mild to severe mental disease, and form a major part of sleeping pills.
- Example: equanil, which is also used to control hypertension.
Answer: Tranquilizers (e.g. equanil) act on the CNS to reduce stress and anxiety and are used to treat mental tension and hypertension.
Distinguish between narcotic and non-narcotic analgesics with examples.
Solution- Both reduce pain without loss of consciousness.
- Non-narcotic analgesics (e.g. aspirin, paracetamol) are non-addictive and also reduce fever; aspirin also thins the blood.
- Narcotic analgesics (e.g. morphine) relieve severe pain and bring sleep but are habit-forming and dangerous if abused.
Answer: Non-narcotic (aspirin, paracetamol) are non-addictive pain/fever relievers; narcotic (morphine) relieve severe pain but are addictive.
Differentiate bactericidal and bacteriostatic antibiotics, and broad- and narrow-spectrum antibiotics, with examples.
Solution- Bactericidal antibiotics kill bacteria (e.g. penicillin, ofloxacin); bacteriostatic antibiotics only inhibit their growth (e.g. erythromycin, tetracycline).
- Broad-spectrum antibiotics act against many kinds of bacteria (e.g. chloramphenicol, tetracycline).
- Narrow-spectrum antibiotics act against only a few (e.g. penicillin G).
Answer: Bactericidal kill (penicillin), bacteriostatic inhibit growth (erythromycin); broad-spectrum act on many bacteria (chloramphenicol), narrow-spectrum on few (penicillin G).
Differentiate between an antiseptic and a disinfectant. Give the phenol point.
Solution- Antiseptics are applied to living tissue (skin, wounds) and do not harm it; e.g. dettol, tincture of iodine.
- Disinfectants are applied to non-living objects (floors, instruments) and are too harsh for living tissue.
- The same chemical can be both: a 0.2% phenol solution is an antiseptic, while a 1% phenol solution is a disinfectant.
Answer: Antiseptics act on living tissue, disinfectants on non-living objects; 0.2% phenol is an antiseptic but 1% phenol is a disinfectant.
Why is a small daily dose of aspirin sometimes prescribed to heart patients?
Solution- Aspirin is a non-narcotic analgesic and antipyretic.
- Besides relieving pain and fever, it prevents blood platelets from clumping together.
- This anti-clotting action reduces the chance of clots blocking the heart's arteries, lowering the risk of a heart attack.
Answer: Aspirin prevents platelets from clumping, reducing blood clots, so a small daily dose lowers the risk of heart attacks.
What are antifertility drugs? Name the hormones they contain.
Solution- Antifertility drugs are oral contraceptives used to prevent conception and control population.
- They contain synthetic forms of the female sex hormones oestrogen and progesterone.
- Examples: norethindrone (a synthetic progesterone) and ethynylestradiol/novestrol (a synthetic oestrogen); they suppress ovulation.
Answer: Antifertility drugs are oral contraceptives containing synthetic oestrogen and progesterone (e.g. ethynylestradiol and norethindrone) that suppress ovulation.