PH1.1-13 | General Pharmacology Foundations — Glossary

WHO definition: a response to a drug that is noxious and unintended, occurring at doses normally used for prophylaxis, diagnosis, or therapy; distinct from medication errors and overdose.

A consensus list of potentially inappropriate medications for use in older adults (≥65 years), developed by the American Geriatrics Society; identifies drugs whose risk-benefit balance is unfavourable in elderly patients.

The fraction of an administered drug dose that reaches the systemic circulation in active form; IV administration is defined as 100% bioavailability.

The fraction of an administered dose that reaches systemic circulation in active form; defined as 1.0 (100%) for intravenous administration.

A trademarked commercial name for a drug assigned by the manufacturer; bioequivalent to the generic formulation but typically more expensive.

A drug combination in which the two agents react chemically to neutralise each other's effect; e.g., protamine sulfate neutralising heparin.

A clinical scoring system classifying the severity of liver cirrhosis (A, B, C) using bilirubin, albumin, PT/INR, ascites, and encephalopathy; used to guide drug dosing in hepatic impairment.

The volume of plasma cleared of drug per unit time; total CL = hepatic CL + renal CL + other; primary determinant of steady-state concentration.

Formula to estimate creatinine clearance: CrCl = [(140 − age) × weight(kg)] / [72 × serum creatinine(mg/dL)] × 0.85 for females; essential for detecting reduced renal function in elderly patients with misleadingly normal creatinine.

A drug that competes with the agonist for the same receptor binding site; can be displaced by increasing agonist concentration; shifts dose-response curve rightward without reducing Emax.

Stopping the suspected drug and observing whether the adverse event resolves; positive dechallenge strengthens causal attribution.

An intramuscular formulation in oil or polymer microspheres that releases drug slowly over weeks to months; used for antipsychotics, contraceptives, and hormonal therapies.

Reduction in receptor number or responsiveness following prolonged agonist exposure; the pharmacological basis of drug tolerance.

The physical and chemical form in which an active pharmaceutical ingredient is prepared for administration, including excipients, coatings, and release mechanisms.

An inhaler device that delivers drug as a dry powder, activated by the patient's inspiratory airflow; propellant-free but requires a minimum inspiratory flow rate.

The drug concentration producing 50% of the maximal effect; a measure of potency — lower EC50 means higher potency.

The maximal effect achievable by a drug regardless of dose; a measure of efficacy (intrinsic activity at the receptor).

An acid-resistant polymer coating on a tablet that prevents dissolution in the stomach (pH 1–3) and releases drug in the alkaline intestine; used for acid-labile drugs and drugs that irritate gastric mucosa.

The cycle of biliary drug excretion into the intestine followed by intestinal reabsorption and hepatic recycling; prolongs the effective half-life of drugs subject to this cycle (e.g., estrogens, some NSAIDs).

Increased synthesis of CYP450 enzymes following exposure to an inducing agent (e.g., rifampicin), resulting in faster metabolism of substrate drugs and reduced plasma concentrations.

Competitive or non-competitive blockade of CYP450 enzyme activity, reducing metabolism of substrate drugs and increasing their plasma concentrations — potentially to toxic levels.

The integration of best available research evidence with clinical expertise and patient values to inform therapeutic decisions.

Classification of drug safety in pregnancy based on human and animal teratogenicity studies: Category A (safest) through Category X (contraindicated); Category D = evidence of risk but benefit may outweigh risk in serious situations.

Elimination kinetics where a constant fraction of drug is eliminated per unit time (proportional to concentration); produces exponential decay curve; applies to most drugs at therapeutic doses.

The transformation of a drug by hepatic CYP450 enzymes before it reaches systemic circulation; drugs absorbed from the gut travel via the portal vein to the liver first, where high-extraction drugs are substantially degraded.

A drug that binds a receptor and produces the maximal possible biological response (100% intrinsic efficacy); e.g., morphine at the mu-opioid receptor.

The internationally standardised, non-proprietary name assigned to a drug by the WHO — the name to be used on all prescriptions per NMC guidelines.

Chloramphenicol toxicity in neonates caused by immature hepatic UGT (glucuronidation) enzymes; accumulation of unconjugated chloramphenicol causes cardiovascular collapse, grey discolouration, and abdominal distension.

The time required for the plasma drug concentration to decrease by 50%; for first-order kinetics, t½ = 0.693 × Vd / CL; drug reaches steady state after 4–5 half-lives.

Drug administration into the subarachnoid space (cerebrospinal fluid), bypassing the blood-brain barrier; used for spinal anaesthesia and intrathecal chemotherapy.

A drug that binds a receptor and produces an effect opposite to that of an agonist by reducing constitutive receptor activity; distinct from an antagonist, which has zero intrinsic activity.

A pressurised canister that delivers a fixed drug dose as an aerosol using a propellant; requires coordination of actuation and inhalation, overcome by a spacer device.

The ratio of drug concentration in breast milk to plasma; a ratio > 1 indicates concentration in milk exceeds plasma; determines infant drug exposure during breastfeeding.

A standardised 10-question scoring instrument for ADR causality assessment; scores ≥9 = definite, 5–8 = probable, 1–4 = possible, ≤0 = doubtful ADR.

The number of patients who must be treated before one additional harm event occurs; a higher NNH indicates greater safety.

The number of patients who must be treated with a drug to prevent one additional bad outcome; NNT = 1 / Absolute Risk Reduction.

The critical developmental period (approximately weeks 3–8 post-fertilisation) during which major organ systems form; drug exposure during this window carries highest risk of major structural malformations.

Any route of drug administration that bypasses the gastrointestinal tract; includes intravenous, intramuscular, subcutaneous, intradermal, and intrathecal routes.

A drug that binds a receptor with high affinity but produces a submaximal response even at full receptor occupancy (intrinsic efficacy < 1); e.g., buprenorphine at the mu-opioid receptor.

The principle that only the non-ionised form of a drug diffuses across membranes; ionisation state depends on pKa and local pH (Henderson-Hasselbalch equation); predicts drug distribution across pH compartments.

A drug interaction occurring outside the body when two drugs are physically mixed (same syringe or infusion bag) and react chemically — causing precipitation, degradation, or inactivation before administration.

A drug interaction in which two drugs produce additive, synergistic, or antagonistic effects at the receptor or physiological level, without altering each other's plasma concentrations.

The branch of pharmacology that describes what a drug does to the body — receptor binding, mechanism of action, dose-response relationships, and therapeutic versus toxic effects.

The study of drugs derived from natural sources, including plants, fungi, marine organisms, and minerals.

A drug interaction in which one drug alters the absorption, distribution, metabolism, or excretion of another, changing its plasma concentration without directly affecting receptor-level pharmacodynamics.

The branch of pharmacology that describes what the body does to a drug — absorption, distribution, metabolism, and excretion (ADME).

A drug combination in which two drugs produce opposing effects by acting at the same receptor or pharmacological pathway; e.g., naloxone reversing morphine at the mu-opioid receptor.

The science of drugs, encompassing their sources, chemistry, mechanisms of action, therapeutic uses, and toxicity.

The clinical application of drugs to treat, prevent, or diagnose disease, integrating PK and PD to guide prescribing decisions.

WHO-defined science and activities related to the detection, assessment, understanding, and prevention of adverse drug effects and other drug-related problems.

India's national pharmacovigilance system, established by CDSCO in 2010, coordinated by the Indian Pharmacopoeia Commission (IPC) as the National Coordination Centre; uses Vigiflow to submit reports to the WHO VigiBase.

Functionalisation reactions (oxidation, reduction, hydrolysis) mediated primarily by CYP450 enzymes; add or expose polar functional groups on drug molecules; products may be active, inactive, or toxic.

Conjugation reactions (glucuronidation, sulfation, acetylation, methylation) that attach large polar groups to drugs or Phase I metabolites; products are almost always inactive and water-soluble.

A drug combination in which two drugs produce opposing effects through entirely different receptor systems; e.g., adrenaline counteracting histamine in anaphylaxis.

Reversible binding of drug to plasma proteins (albumin, alpha-1 acid glycoprotein); bound drug is pharmacologically inactive and not filtered by the glomerulus; only the free fraction is active.

The concurrent use of five or more medications by a single patient; associated with increased risk of drug-drug interactions, adverse effects, and reduced adherence; especially prevalent in elderly patients.

A drug combination outcome where the combined effect is greater than the arithmetic sum of the individual effects; e.g., alcohol plus benzodiazepines on CNS/respiratory depression.

A pharmacologically inactive compound that is converted to an active drug by metabolism (e.g., enalapril → enalaprilat; codeine → morphine via CYP2D6).

An experimental study in which participants are randomly allocated to intervention or control groups to establish causal efficacy with minimised bias.

WHO (1985) framework requiring that patients receive drugs appropriate to their clinical needs, in correct doses, for adequate duration, at the lowest cost to themselves and the community.

Deliberately reintroducing the suspected drug after dechallenge to confirm causal attribution; provides strong causal evidence but is absolutely contraindicated for severe ADRs (anaphylaxis, SJS, agranulocytosis).

Indian drug schedule for prescription-only medicines; the prescription is retained by the pharmacist; covers most antibiotics, antihypertensives, and antidiabetics.

A more restrictive Indian drug schedule for broad-spectrum antibiotics and select drugs subject to pharmacist register-keeping; introduced as an antibiotic stewardship measure.

Indian drug schedule for narcotic and psychotropic substances requiring special triplicate prescriptions and strict regulatory control.

A valved holding chamber attached to an MDI that holds the drug cloud and allows inhalation at the patient's pace, removing the need for actuation-inhalation coordination.

The plateau plasma concentration reached after 4–5 half-lives of repeated dosing, when the rate of drug input equals the rate of elimination.

Administration by placing drug under the tongue; absorbed via sublingual veins directly into systemic circulation, bypassing first-pass metabolism; used for GTN, buprenorphine.

A formulation that releases drug gradually over 8–24 hours using a polymer matrix, osmotic pump, or layered coating; provides smoother plasma concentrations and reduced dosing frequency; must not be crushed.

The capacity of a drug or other agent to cause structural or functional abnormalities in the developing embryo or foetus; maximal risk during organogenesis (weeks 3–8 post-fertilisation).

TI = TD50 / ED50; the ratio of the dose producing toxicity in 50% of the population to the dose producing the desired effect in 50%. A narrow TI indicates a small margin between effective and toxic doses.

A skin-adherent formulation that delivers drug through the skin into the systemic circulation at a controlled rate, bypassing first-pass metabolism; examples include GTN, fentanyl, and oestrogen patches.

Augmented adverse drug reaction: dose-dependent, pharmacologically predictable, the most common type (~80%); manageable by dose reduction; e.g., bleeding with warfarin.

Bizarre/idiosyncratic adverse drug reaction: dose-independent, pharmacologically unpredictable, less common but typically more severe; often immune-mediated; requires drug withdrawal; e.g., anaphylaxis to penicillin, SJS with carbamazepine.

Increase in receptor number or sensitivity following prolonged antagonist exposure; the basis of rebound effects (e.g., tachycardia after abrupt beta-blocker withdrawal).

An apparent (not anatomical) volume calculated as Dose / initial plasma concentration; high Vd indicates extensive tissue binding; low Vd indicates drug remains in plasma.

Drug dosing expressed as mg per kg of body weight, used in paediatrics to account for variation in body size and organ function relative to adults; preferred over fixed adult doses for patients outside the standard adult weight range.

Standardised categories for classifying the probability that a drug caused an adverse event: Certain, Probable, Possible, Unlikely, Unclassifiable, Unassessable — based on temporal relationship, pharmacological plausibility, dechallenge, and rechallenge.

Elimination kinetics where a constant amount of drug is eliminated per unit time, regardless of concentration (enzyme saturation); applies to ethanol and phenytoin at high doses; small dose increases cause disproportionately large concentration rises.