PH1.11-13 | PH1.11-13 | Adverse Drug Reactions, Pharmacovigilance and Drug Interactions — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Adverse drug reactions (ADRs) are unintended, noxious drug effects at normal therapeutic doses. The A–E classification: Type A (augmented — dose-dependent, most common, manage by dose reduction); Type B (bizarre/idiosyncratic — dose-independent, rare but severe, manage by withdrawal + never rechallenge for severe reactions); Type C (cumulative); Type D (delayed — teratogenicity, carcinogenicity); Type E (end-of-use/withdrawal).

Causality assessment: WHO-UMC (Certain/Probable/Possible/Unlikely); Naranjo Algorithm (10-item scored instrument; ≥9 = definite, 5–8 = probable, 1–4 = possible, ≤0 = doubtful). Both use temporal relationship, pharmacological plausibility, dechallenge, and rechallenge.

Pharmacovigilance: WHO-defined discipline for ADR detection, assessment, and prevention. India: PvPI operated by IPC (NCC), AMC network, CDSCO reporting form, Vigiflow database. Every clinician must report suspected ADRs — certainty is not required.

Drug interactions: (1) Pharmacokinetic — enzyme induction (rifampicin → ↓ warfarin/OCP levels), inhibition (erythromycin/clarithromycin → ↑ simvastatin), absorption chelation (antacids + fluoroquinolones), protein binding displacement. (2) Pharmacodynamic — additive (combination antihypertensives), synergistic hazardous (alcohol + BZD), pharmacological antagonism (naloxone + morphine). (3) Pharmaceutical — mixing incompatible drugs in same infusion (aminoglycosides + beta-lactams). Management: anticipate via drug history → identify → classify → avoid/adjust/monitor/document.

REFLECT

Think about a patient encounter — real or from a case study — where a drug reaction or drug interaction was identified or missed. Was a causality assessment performed? Was the event reported to a pharmacovigilance system? What would the complete stepwise ADR management process have looked like for that case? Write two or three sentences applying the WHO-UMC or Naranjo framework to that situation.