Adverse Drug Reactions and Pharmacovigilance for NEET PG Pharmacology: Types A–F, Pharmacogenetics, PvPI, WHO-UMC Causality, Special Populations

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🎯 Exam priority: High. Expect a one-liner on an ADR type, a genetic reaction (slow acetylator, G6PD, HLA-B*1502, succinylcholine apnoea), a PvPI reporting fact, or a WHO-UMC causality category from a short case.

CBME mapping: PH 1.10 (geriatric, paediatric and special situations), PH 1.11 (ADRs and their types), PH 1.12 (pharmacovigilance and ADR reporting) and PH 1.13 (drug interactions).

What Counts as an ADR

• An adverse drug reaction is an unintended effect of a medicine that is undesirable, unpleasant or harmful. Every medicine can cause one. "Side effect" is an imprecise term.

• A reaction is serious if it causes death, is life-threatening, causes or prolongs hospitalisation, causes disability, or causes a congenital anomaly.

• Severity is graded mild, moderate, severe or lethal.

• Allergic (hypersensitivity) reactions are not dose-related and need prior exposure; they usually do not happen the first time a drug is ever taken.

• Higher risk: older adults, children, renal or hepatic impairment, genetic variants (for example, the variant behind abacavir hypersensitivity), and polypharmacy. Fatal ADRs occur mainly after age 75.

The Six Types: A to F

Type A reactions are a particular problem with drugs that have a narrow therapeutic index, such as bleeding with oral anticoagulants.

Pharmacogenetic Reactions

Drug elimination rates vary up to 40-fold between people, mostly because of genes and age.

Pharmacovigilance in India (PvPI)

• The Pharmacovigilance Programme of India was approved by MoHFW in July 2010. Its National Coordination Centre is the Indian Pharmacopoeia Commission, Ghaziabad, a WHO Collaborating Centre for pharmacovigilance since 30 October 2017.

• What to report (form version 1.4): all suspected ADRs, non-serious or serious, known or unknown, frequent or rare, to medicines, vaccines and herbal products. Every serious ADR must be reported.

• Who reports: any healthcare professional — clinicians, dentists, pharmacists, nurses.

• Where: the nearest ADR Monitoring Centre (AMC), or directly to the NCC; or by the toll-free helpline 1800-180-3024.

• Then: the AMC does the causality assessment on the WHO-UMC scale and forwards the report to the NCC through the ADR database.

• The patient's identity is confidential, and a report has no legal implication for the reporter. Serious adverse events after immunization can also be reported on the AEFI form.

Is the Drug to Blame? WHO-UMC Causality

• Dechallenge = stopping the drug and watching the response; rechallenge = giving it again. Rechallenge can prove the link, but is not done after a serious allergic reaction.

• If the drug is essential despite an allergy, desensitization may be used, such as penicillin for syphilis in a pregnant woman who is allergic to penicillin.

Older Adults

• Kidney: after 40, GFR falls by an average of 8 mL/min/1.73 m² per decade, yet serum creatinine often stays normal because muscle mass is lower — so estimate clearance rather than trust creatinine.

• Liver: phase I metabolism is more likely to be prolonged; phase II (conjugation) is largely unaffected, so phase II drugs may be preferred. First-pass metabolism falls about 1% a year after 40.

• Body composition: more fat raises the volume of distribution of lipophilic drugs such as diazepam (longer half-life); less body water lowers it for water-soluble drugs such as digoxin and aminoglycosides (higher levels).

• Higher stomach pH reduces calcium carbonate absorption; calcium citrate absorbs better.

• Hospital admissions from adverse drug effects are 4 to 7 times more common than in younger patients. The Beers Criteria flag risky drug-disease combinations, and a prescribing cascade is when a drug's adverse effect is mistaken for a new disease and treated with another drug.

Children and Pregnancy

• Neonates: less stomach acid raises the bioavailability of acid-labile penicillin and lowers that of weakly acidic phenobarbital. Thin skin increases transdermal absorption. Albumin is low until about 10–12 months, so free drug is higher.

• Many drugs (phenytoin, barbiturates, analgesics, cardiac glycosides) have half-lives 2 to 3 times longer in neonates. Younger children need higher per-kg doses of water-soluble drugs because more of their body weight is water.

• Pregnancy labelling: the US Pregnancy and Lactation Labeling Rule (published 4 December 2014, effective 30 June 2015) removed the letter categories A, B, C, D and X. Labels now give a risk summary, the supporting data and advice for counselling, plus information on pregnancy testing, contraception and infertility for males and females of reproductive potential. Older questions may still use the letters.

Traps the Examiner Sets

• Type A = augmented and dose-related; Type B = bizarre and not dose-related. Allergy is Type B.

• Pill failure with rifampin is Type F (failure), not Type B.

• Slow acetylators get isoniazid neuropathy and hydralazine lupus; fast acetylators need more isoniazid.

• Post-succinylcholine apnoea = pseudocholinesterase deficiency, not malignant hyperthermia.

• PvPI: any healthcare professional can report; causality is assessed at the AMC using WHO-UMC.

• "Rechallenge not required" belongs to probable; "rechallenge satisfactory, if necessary" to certain.

• Normal creatinine in an 80-year-old does not mean normal renal function.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 A B C D E F = Augmented, Bizarre, Chronic, Delayed, End of use, Failure — the six ADR types in order

• 🧠 Slow and Sick — slow acetylators get isoniazid neuritis and hydralazine lupus

• 🧠 Sux stuck = Pseudo low — prolonged succinylcholine apnoea = pseudocholinesterase deficiency

• 🧠 Carba-B-1502 — carbamazepine SJS with HLA-B*1502

• 🧠 Certain needs a Comeback, Probable needs none — rechallenge: satisfactory if necessary (certain); not required (probable)

• 🧠 Old fat holds Diazepam, old dry raises Digoxin — more fat → bigger Vd for diazepam; less water → higher digoxin levels

Rapid-Revision Cards

• ADR

  Unintended, undesirable or harmful effect of a medicine.

• Serious ADR

  Death, life-threatening, hospitalisation, disability, congenital anomaly.

• Type A

  Augmented: dose-related, predictable (hypotension with antihypertensives).

• Type B

  Bizarre: not dose-related (allergy, SJS, malignant hyperthermia).

• Type C

  Chronic: cumulative dose (steroid adrenal suppression).

• Type D

  Delayed: teratogenesis, carcinogenesis.

• Type E

  End of use: withdrawal (opioids).

• Type F

  Failure: pill failure with rifampin.

• Slow acetylators

  INH neuritis; hydralazine/procainamide lupus.

• G6PD deficiency

  Haemolysis with primaquine, chloroquine.

• Succinylcholine apnoea

  Pseudocholinesterase deficiency.

• HLA-B*1502

  Carbamazepine SJS.

• CYP2C19 variants

  Clopidogrel less active.

• TPMT test

  Before azathioprine / 6-MP.

• PvPI

  Approved July 2010; NCC at IPC Ghaziabad.

• PvPI helpline

  1800-180-3024 (toll free).

• Who reports to PvPI

  Any healthcare professional.

• Causality under PvPI

  At the AMC, WHO-UMC scale.

• WHO-UMC certain

  Plausible timing, no other cause, rechallenge satisfactory if needed.

• WHO-UMC probable

  Unlikely other cause; rechallenge not required.

• WHO-UMC possible

  Could also be disease or other drugs.

• GFR after 40

  Falls about 8 mL/min/1.73 m² per decade.

• Older adults and phase II

  Conjugation largely unaffected by age.

• Pregnancy letters A–X

  Removed from US labels by the 2015 PLLR.

Sources

Facts in this article were checked against these documents.

• MSD Manual Professional Edition: Adverse Drug Reactions; Pharmacogenetics — Merck & Co. (MSD Manuals), 2025 (link)

• MSD Manual Professional Edition: Drug-Related Problems in Older Adults; Pharmacokinetics in Older Adults; Pharmacokinetics in Children — Merck & Co. (MSD Manuals), 2025 (link)

• Suspected Adverse Drug Reaction Reporting Form for Healthcare Professionals, Version 1.4 — Indian Pharmacopoeia Commission (NCC-PvPI), MoHFW, current (link)

• Pharmacovigilance Programme of India — National Coordination Centre — Indian Pharmacopoeia Commission, accessed November 2026

• Causality Assessment: WHO-UMC Causality Categories for ADR Reporting (training page reproducing the WHO-UMC system table) — National TB Elimination Programme, MoHFW, accessed November 2026 (link)

• Requirements for Pregnancy and Lactation Labeling — final rule (79 FR 72064) — US Food and Drug Administration, Federal Register, 2014 (link)

• Competency Based Undergraduate Curriculum, Pharmacology (PH 1.10–1.13) — National Medical Commission, 2024

Test Yourself: Practice Questions

Twenty-five questions in NEET PG style, including clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. Hypotension after starting an antihypertensive is which type of adverse drug reaction?

• (a) Type C (chronic)

• (b) Type A (augmented)

• (c) Type B (bizarre)

• (d) Type F (failure)

Q2. Malignant hyperthermia during general anaesthesia is classified as

• (a) Type B (idiosyncratic)

• (b) Type D (delayed)

• (c) Type A (augmented)

• (d) Type E (withdrawal)

Q3. Adrenal suppression after long-term corticosteroid therapy is a

• (a) Type F reaction

• (b) Type B reaction

• (c) Type E reaction

• (d) Type C (chronic) reaction

Q4. Oral contraceptive failure in a woman taking rifampin is which ADR type?

• (a) Type A (augmented)

• (b) Type D (delayed)

• (c) Type B (bizarre)

• (d) Type F (failure)

Q5. Teratogenesis is an example of which ADR type?

• (a) Type E (withdrawal)

• (b) Type A (augmented)

• (c) Type D (delayed)

• (d) Type C (chronic)

Q6. Which feature is typical of an allergic (hypersensitivity) drug reaction?

• (a) It occurs only with overdose

• (b) It is not dose-related and needs prior exposure

• (c) It occurs on the very first ever dose in most patients

• (d) It is dose-related and predictable

Q7. Isoniazid peripheral neuritis is more likely in

• (a) fast acetylators

• (b) G6PD-deficient patients

• (c) people with pseudocholinesterase deficiency

• (d) slow acetylators

Q8. Drug-induced lupus with hydralazine is linked to

• (a) fast acetylation

• (b) HLA-B*1502

• (c) CYP2C19 variants

• (d) slow acetylation

Q9. Prolonged apnoea after a normal dose of succinylcholine suggests

• (a) G6PD deficiency

• (b) plasma pseudocholinesterase deficiency

• (c) malignant hyperthermia

• (d) slow acetylation

Q10. Before starting carbamazepine, testing for which marker reduces the risk of Stevens-Johnson syndrome?

• (a) G6PD

• (b) HLA-B*1502

• (c) TPMT

• (d) CYP2C19

Q11. Reduced antiplatelet effect of clopidogrel is associated with variants in

• (a) VKORC1

• (b) N-acetyltransferase

• (c) CYP2C19

• (d) CYP2D6

Q12. Primaquine can cause haemolytic anaemia in

• (a) G6PD deficiency

• (b) pseudocholinesterase deficiency

• (c) slow acetylators

• (d) HLA-B*1502 carriers

Q13. Under PvPI, who may report a suspected adverse drug reaction on the healthcare professional form?

• (a) Only the drug manufacturer

• (b) Any healthcare professional, including clinicians, dentists, pharmacists and nurses

• (c) Only the hospital pharmacist

• (d) Only the treating consultant

Q14. The National Coordination Centre of the Pharmacovigilance Programme of India is located at

• (a) the Indian Pharmacopoeia Commission, Ghaziabad

• (b) NCDC, Delhi

• (c) CDSCO headquarters, New Delhi

• (d) AIIMS, New Delhi

Q15. Which reactions should be reported under PvPI?

• (a) Only fatal reactions

• (b) All suspected ADRs — serious or non-serious, known or unknown — to medicines, vaccines and herbal products

• (c) Only reactions to newly approved drugs

• (d) Only serious and unknown reactions to allopathic drugs

Q16. Under PvPI, causality assessment of a submitted report is done

• (a) by the reporting doctor using the Naranjo scale

• (b) by the manufacturer

• (c) by the court

• (d) at the ADR Monitoring Centre using the WHO-UMC scale

Q17. A rash with a reasonable time link to a drug, unlikely to be due to disease or other drugs, improving on withdrawal, with no rechallenge, is

• (a) possible

• (b) unlikely

• (c) certain

• (d) probable / likely

Q18. In the WHO-UMC system, an event that could also be explained by disease or other drugs, with unclear withdrawal information, is

• (a) certain

• (b) probable

• (c) unassessable

• (d) possible

Q19. Why is serum creatinine misleading for drug dosing in an 80-year-old?

• (a) It is unaffected by GFR

• (b) It often stays normal despite reduced GFR because muscle mass is lower

• (c) It measures liver function

• (d) It rises falsely with age

Q20. In older adults, which drug's volume of distribution rises because body fat increases?

• (a) Diazepam

• (b) Lithium

• (c) Digoxin

• (d) Gentamicin

Q21. When a drug's adverse effect is mistaken for a new disease and treated with another drug, this is called

• (a) therapeutic duplication

• (b) a prescribing cascade

• (c) a Type F reaction

• (d) tachyphylaxis

Q22. The US Pregnancy and Lactation Labeling Rule (effective 2015)

• (a) banned all drugs in the first trimester

• (b) removed the pregnancy letter categories A, B, C, D and X

• (c) added category X

• (d) applies only to vaccines

Q23. Compared with adults, neonates have

• (a) lower transdermal absorption

• (b) shorter half-lives of phenytoin

• (c) higher bioavailability of acid-labile penicillin because of less gastric acid

• (d) higher albumin levels

Q24. An 84-year-old on digoxin becomes toxic at a dose that suited her at 60, although her serum creatinine is normal. Two age-related reasons are

• (a) less body water raising digoxin concentration, and a lower GFR hidden by low muscle mass

• (b) higher albumin and faster absorption

• (c) more body fat and faster metabolism

• (d) enzyme induction and more body water

Q25. A potent steroid cream is applied over large areas of a 3-week-old baby's skin. The particular risk is

• (a) no absorption at all

• (b) increased systemic absorption through thin neonatal skin

• (c) allergy only

• (d) rapid first-pass metabolism

Active Recall

From memory: define an ADR and a serious ADR; list types A to F with one example each; name five pharmacogenetic reactions and the drug involved; explain who reports to PvPI, where and how causality is assessed; give the WHO-UMC categories; and list the pharmacokinetic changes of old age.