- Drug: Drug is any substance or product that is used or is intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient.Drugs thus can be classified according to this definition into four basic types:
- Modify physiological system, e.g. vaccines modifying immune system
- Explore physiological system, e.g. radioiodine dyes to exclude pathology
- Modify pathological system, e.g. diuretic to reverse edema
- Explore pathological system, e.g. radioactive dyes to confirm pathology.
- Pharmacokinetics: It is defined as movement of the drug in and alteration of the drug by the body; including absorption, binding/localization/storage, biotransformation and excretion of the drug.
- Pharmacodynamics: It is defined as the study of the biochemical and physiological effects of drugs and their mechanisms of action at organ system/subcellular/macromolecular levels.
- Chemotherapy: It is defined as the treatment of systemic infections or malignancy with specific drugs that have selective toxicity for the infecting organism or malignant cell respectively, with no or minimal effects on the host cell.Another classification of drugs may be:
- Pharmacodynamics agents—designed to have pharmacodynamics effects in the recipient
- Chemotherapeutic agents—inhibit or kill parasite/malignant cell with minimal pharmacodynamics effect to the recipient (however, there is no drug that has zero systemic effect).
- Essential medicines: They are defined as those drugs that satisfy the priority healthcare needs of the population. They are selected with due regard to public health relevance, evidence on efficacy and safety and comparative cost effectiveness.No. of essential drugs in National List of Essential Medicines of India:
- 2011 : 348
- 2015 : 376 (106 drugs added and 70 deleted from 2011 list)
- Orphan drugs: These are drugs or biological products for diagnosis or treatment or prevention of a rare disease or condition, or a more common disease (endemic only in resource poor countries) for which there is reasonable expectation that the cost of developing and marketing it will be recovered from the sales of that drug, e.g.:
- Sodium nitrite—used with sodium thiosulfate to treat cyanide poisoning
- Fomepizole—treat methanol and ethylene glycol poisoning
- Bioavailability: Defined as the rate and extent of absorption of a drug from a dosage form which is measure of the fraction of administered dose of the drug that reaches the systemic circulation in unchanged form.
- 100% bioavailability is attained in intravenous route.Exception: Chloramphenicol succinate; about 70% because renal excretion of ester before hydrolysis.
- Nearly 100% oral bioavailability is attained in levofloxacin.
- Apparent volume of distribution: Presuming that the body behaves as a single homogeneous compartment, the apparent volume of distribution is defined as the volume that would accommodate all the drug in the body; if the concentration throughout was the same as plasma.
- Biotransformation: Defined as the chemical alteration of blood in the body.Isoniazid undergoes phase II followed by phase I reaction.
- Clearance: It is defined as the theoretical volume of plasma from which the drug is completely removed in unit time.
- Phenytoin/tolbutamide/theophylline/warfarin initially show zero order but then follow 1st order kinetics
- Ethyl alcohol follows zero order kinetics.
- Plasma half-life: It is the time taken for the plasma concentration of the drug to be reduced to half from its original value
- Biological effect of peak effect half-life: The time in which pharmacological effect of a drug or its active metabolites is reduced to half
- Elimination half-life: The time in which the total amount of the drug in the body after equilibrium is attained (in plasma, fat, muscle, etc.) is reduced to half
- Hit and run drugs: Drugs whose peak effect half-life > elimination half-life, e.g. proton pump inhibitors, monoamine oxidase inhibitors.
- Loading dose: This is a single or few quickly repeated doses given in the beginning to attain target concentration rapidly.
- Maintenance dose: This dose is one that is to be repeated at specific intervals after the attainment of target steady state plasma concentration so as to maintain the same by balancing elimination.
- Receptor: It is defined as a macromolecule or binding site located on the surface or inside the effector cell that serves to recognize the signal molecule or drug and initiate the response to it, but itself has no other functions.Silent receptor: These bind to drugs but show no pharmacological response, e.g. plasma proteins.
- Agonist: An agent which activates a receptor to produce an effect similar to that of the physiological signal molecule. (Affinity is present and intrinsic activity = +1) (e.g. adrenaline at alpha adrenergic receptor, histamine at H1 receptor, etc.).
- Antagonist: An agent which prevents the action of an agonist on a receptor or the subsequent response, but does not have any effect of its own (affinity is present and intrinsic activity = 0) (propranolol at beta-adrenergic receptors).
- Inverse agonist: An agent which activates a receptor to produce an effect in the opposite direction to that of the agonist (affinity present and intrinsic activity = –1 to 0) (DMCM on BZD receptor).
- Partial agonist: An agent which activates a receptor to produce submaximal effect, but antagonizes the action of a full agonist (affinity present and intrinsic activity = 0 to +1) (Dichloroisoproterenol on beta-adrenergic receptors).
- Ligand: Any molecule which attaches selectively to particular receptors or sites.
- Competitive or equilibrium type: Increased kM but Vmax is unchanged, e.g. Methotrexate on dihydrofolate reductase
- Fixed dose combination: A single formulation containing 2 or more drugs in a fixed dose ratio. NLEM India 2011 approves only 12 FDCs where as WHO approves 23 of them. Most widely used FDC is ORS.
- Placebo: This is an inert substance given in the garb of medicine which works by psychodynamics rather than pharmacodynamics means.Naloxone suppresses endorphins in brain and can antagonize psychodynamics effect too.
- Tolerance: It refers to the requirement of higher doses of a drug to produce a given response, e. g. sulfonylureas in type 2 DM.
- Cross tolerance: It is a development of tolerance to pharmacologically related drugs, e. g. alcoholics are relatively resistant to barbiturates and general anesthetics.
- Tachyphylaxis: It refers to rapid development of tolerance when doses of a drug repeated in quick succession result in marked reduction in response. For example, tyramine, ephedrine.
- Drug resistance: It refers to tolerance of microorganisms to inhibitory actions of anti-microbials, e.g. Staphylococcus to penicillin.
- Shelf life/life period of a drug: The period between date of manufacture and date of expiry.
- Expiry date: It is a date stamped on all medicines beyond which medicine actually does not lose its potency or become toxic but simply the quality of the medicine is not assured beyond it; and the manufacturer is not liable if any harm arises from the use of it.The degradation product of only one drug is toxic in man: tetracycline
- Adverse drug reaction: It is any noxious change which is suspected to be due to a drug, occurs at doses normally used in man, requires treatment or decrease in dose or indicated caution in the future use of the same drug.
- Type A: Augmented pharmacological effects—dose dependent and predictable, e.g. hypoglycemia caused by anti-diabetics like SUs.
- Type B: Bizarre or idiosyncratic—dose independent and unpredictable, e.g. allergic reaction to penicillins
- Type C: Chronic effects, e.g. peptic ulcer due to NSAIDs
- Type D: Delayed effects, e.g. phocomelia due to thalidomide
- Type E: End of treatment effect, e.g. morphine withdrawal
- Type F: Failure of therapy.
- Idiosyncrasy: It is genetically determined abnormal reactivity to a chemical, e. g. dose unrelated serious aplastic anemia in some individuals.
- Drug dependence: It is a state in which use of drugs for personal satisfaction is accorded a higher priority than other basic needs, often in the face of known risks to health. Types— psychological dependence, physical dependence, drug abuse, drug addiction and drug habituation.
- Teratogenicity: It refers to the capacity of a drug to cause fetal abnormalities when administered to the pregnant mother.
- Iatrogenicity: Induced inadvertently by a physician or surgeon or by medical treatment or diagnostic procedures.
|Risk category of drugs during pregnancy|
Adequate studies in pregnant women have failed to demonstrate a risk to the fetus
Inj. Mag. sulfate, thyroxine
Adequate human studies are lacking, but animal studies have failed to demonstrate a risk to the fetus
Adequate studies in pregnant women have failed to demonstrate a risk to the fetus, but animal studies have shown an adverse effect on the fetus
Penicillin V, amoxicillin, cefaclor, erythromycin, paracetamol, lignocaine
No adequate studies in pregnant women and animal studies are lacking or have shown and adverse effect on fetus, but potential benefit may warrant use of the drug in pregnant women despite potential risk
Morphine, codeine, atropine, corticosteroids, adrenaline, thiopentone, bupivacaine
There is evidence of human fetal risk, but the potential benefits from use of the drug may be acceptable despite the potential risk
Aspirin, phenytoin, carbamazepine, valproate, lorazepam
Studies in animals or humans have demonstrated fetal abnormalities, and potential risk clearly outweigh possible benefit
Estrogens, isotretinoin, ergometrine
- Pharmacovigilance: Defined by WHO in 2002 as the science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other drug related problems.
- Therapeutic window phenomenon: Some drugs show sub-optimal efficacy below a certain concentration and also beyond a certain concentration. Classical example is clonidine which shows optimum BP lowering between blood levels of 0.2 to 2.0 ng/mL.
- Clinical trial: According to WHO, clinical trial is any research study that prospectively assigns human participants or groups of humans to one or more health related interventions to evaluate the effects on health outcomes. Summary of clinical trials:
Blinding and control
Human pharmacology and safety
Healthy volunteers (20–100)
Open Label (No binding)
100–150 patients (homogeneous population)
Single blind controlled
Up to 5000 patients from several centers (heterogeneous population)
Double blind randomized controlled
Large number of patients being treated by practicing physicians
Healthy volunteers (small number)
Very low dose 1/100 of human dose; max 100 mg of drug is administered to know pharmacokinetics. This could avoid costly phase I studies for candidate drugs with unsuitable pharmacokinetics
- Autacoids: These are diverse substances produced by a wide variety of cells in the body, having intense biological activities but generally act locally (e.g. within inflammatory pockets) at the site of synthesis and release. The classical autacoids are: amine autacoids (histamine, 5-HT), lipid derived autacoids (PGs, leukotrienes, PAFs) and peptide autacoids (bradykinin, angiotensin).
- Bronchial asthma: It is a heterogeneous disease, usually characterized by chronic airway inflammation. It is defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable expiratory airflow limitation (GINA).
- Status asthmaticus: It is a life threatening acute exacerbation of bronchial asthma wherein bronchospasm is not relieved with aggressive therapy within 30–60 minutes and attacks follow without any pause.Blood gas progression in status asthmaticus:
- Minimal alveolar concentration: The lowest concentration of the anesthetic in pulmonary alveoli needed to produce immobility in response to a painful stimulus in 50% individuals.
- Second gas effect: During induction of general anesthesia, when a large volume of a gas (e.g. nitrous oxide) is taken up from alveoli into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased. This results in effects known as the “concentration effect” and the second gas effect where the gas mixture will be sucked in independent of ventilatory exchange; thus gas flow will be higher than tidal volume.
- Diffusion hypoxia: During discontinuation of N2O after prolonged anesthesia the reverse of second gas effect occurs leading to dilution of the alveolar air and finally PP of oxygen is reduced, this resulting hypoxia is called diffusion hypoxia.
- Epilepsy: The term ‘epilepsy’ denotes any disorder characterized by recurrent unprovoked seizures (CMDT 2017). Seizure is defined as a paroxysmal event due to abnormal excessive or synchronous neuronal activity in the brain.
- Status epilepticus: It refers to continuous seizures or repetitive, discrete seizures with impaired consciousness in the inter-ictal period. The duration of seizure activity sufficient to meet the definition of status epilepticus has traditionally been specified as 15–30.
- Hypertensive urgency: SBP>220 mm Hg or DBP>120 mm Hg without overt signs of end organ damage.
- Diuretics (Natriuretics): These are drugs which cause a net loss of Na+ and water in urine.
- Free water clearance: It is defined as the volume of urine excreted per unit time in excess of that required to excrete the contained solute isosmotically with plasma.
- Positive free water clearance: Urine is dilute wrt plasma.
- Negative free water clearance: Urine is concentrated wrt plasma.
- Zero free water clearance: Isosmotic with plasma.
- Hematinics: These are substances required in the formation of blood and are used for the treatment of anemias, e.g. iron, folic acid, etc.Unconventional hematinics: Erythropoietin, lithium, thyroxine.
- Laxatives and purgatives: Chemical agents that promote evacuation of bowel and are primarily used to treat constipation or when loose stools are desirable. Based on their intensity of action they are classified as:
- Laxatives or aperients: Milder action and thus lead to elimination of soft but formed stools.
- Purgatives or cathartics: Stronger action resulting in fluid evacuation.
- Chelating agents: These are drugs that can form ring structures within their molecule with metallic ions thus producing stable, non-toxic and easily excretable complexes.Orally active iron chelator- deferiprone, deferasirox.
- Vaccine/sera: These are biological products which act by reinforcing the immunological defence of the body against foreign agents mostly infective organisms or their toxins.
- Toxoid: A toxoid is a bacterial toxin (usually an exotoxin) whose toxicity has been inactivated or suppressed, while other properties, typically immunogenicity, are maintained. Thus, when used during vaccination, an immune response is mounted and immunological memory is formed against the molecular markers of the toxoid without resulting in toxin-induced illness.
- Antisera: These are purified and concentrated preparations of serum of horses actively immunized against a specific antigen.
- Antiseptic and disinfectant: These two terms connote an agent which inhibits or kills microbes on contact. Conventionally, agents used on living surfaces are called antiseptics while those used on inanimate objects are called disinfectants.
- Irritant: These are drugs that stimulate sensory nerve endings and induce inflammation at the site of application.
- Counter irritant: Certain irritants also produce a remote effect which tends to relieve pain and inflammation in deeper organs, e. g. clove oil, methyl salicylate.
- Vesicant: Stronger irritants which in addition increase capillary permeability and cause collection of fluid under the epidermis forming vesicles, e. g. vancomycin.
- Rubefacient: Irritants which cause local hyperemia with little sensory competent, e. g. capsaicin.
- Emollient: These are bland oily substances which soothe and soften skin, e.g. olive oil.
- Demulcent: Inert substances which soothe inflamed or denuded mucosa or skin by preventing contact with air/irritants in the surroundings, e. g. glycyrrhiza, methylcellulose
- Adsorbents and protectives: These are finely powdered, inert and insoluble solids capable of binding to their surface (adsorbing) noxious and irritant substances, e. g. talc, aloe vera.
- Ointment: It is a semisolid preparation containing medicinal ingredients for external use only on skin/mucous membranes.
- FTU (Fingertip unit): It is the unit of application of ointments. 1 FTU ~ 0.5 g/area of 2 palms. 20 FTU ~ whole body.
- Antibiotic: These are substances produced by microorganisms, which selectively suppress the growth of or kill other microorganisms at very low concentrations.
- Antimicrobial agent (AMA): This is a common term to designate both synthetic and naturally derived drugs that attenuate microorganisms.Thus, all antibiotics are also antimicrobials but the reverse is not true. For example, silver
- Anticancer: These are drugs that either kill cancer cells or modify their growth.
- DOTS: Directly observed treatment short-course (DOTS) is a domiciliary treatment strategy to ensure cure of TB by providing most effective regimen of medicines and also confirming that medicines are taken.
- Monoresistance TB: Resistance to one 1st line anti-TB drug only.
- Polydrug resistance TB: Resistance to more than one 1st line anti-TB drug (other than INH and rifampicin).
- Multidrug resistance TB: Resistance to at least both INH and rifampicin (i.e. may have resistance of other 1st line drugs).
- Extensive drug resistance TB: Resistance to any fluoroquinolone and at least one of the 2nd line injectable drugs (capreomycin, amikacin, kanamycin); in addition to multidrug resistance.
- MIC: Minimum inhibitory concentration (MIC) is the lowest concentration of an antibiotic which prevents visible growth of a bacterium after 24 hrs incubation in micro-well culture plates using serial dilutions of the antibiotic.
- Post-antibiotic effect: The lag period in growth resumption when after a brief exposure to an antibiotic, the organism is placed in an antibiotic free medium; it starts multiplying again, is called post-antibiotic effect. It depends on the antibiotic as well as the organism.
- Break point concentration: It is defined as the concentration of antibiotic that demarcates between sensitive and resistant bacteria.