Drug Nomenclature

• Drug nomenclature refers to the different names used to identify drugs.
• Drugs generally have three names: chemical, non-proprietary, and proprietary.

Chemical Name

• Assigned when a new chemical entity (NCE) is developed following IUPAC rules.
• Provides the precise arrangement of atoms and atomic groups.
• Primarily useful for chemists or technical personnel, not for clinical or marketing purposes.

Non-Proprietary Name

• A short name not subject to proprietary rights.
• It is usually concise and meaningful.
• Approved names are given by bodies such as USAN and BAN soon after introduction.
• Official names are approved by the National Pharmacopeia Commission and included in the Pharmacopeia, and are identical to the approved name.

Proprietary Name

• Given by the pharmaceutical firm selling the drug.
• A single drug can be sold under many proprietary names by different firms.
• Written with a capital initial letter and often distinguished by a superscript ®.
• Clinicians often refer to drugs by their proprietary names.
• Paracetamol's chemical name is N-(4-hydroxyphenyl)acetamide.
• Paracetamol's Approved names include British Approved Name (BAN) as paracetamol and United States Adopted Name (USAN) as acetaminophen.
• Paracetamol's Proprietary names include Panadol, Calpol, Adol, or Tylenol.

Drug Classification

• Essential for reducing drugs into manageable groups.
• Drugs are classified based on different uses or perspectives like those of a Chemist, Pharmacologist, Pharmacist, or Clinician.
• The Anatomical Therapeutic Chemical Classification System (ATC) is widely used in pharmacology and medicine, assigning drugs a unique alphanumeric ATC code.
• The Biopharmaceutics Classification System (BCS) classifies drugs by solubility, permeability, or absorption properties.
• Classifications can be based on chemical structures, mechanism of action, mode of action, or treatment of the same disease.

Classification Based on Chemical Nature

• Inorganic drugs include metals and their salts like Ferrous Sulphate, Zinc Sulphate, Magnesium Sulphate, and non-metals like sulphur.
• Organic drugs include alkaloids like atropine, morphine, strychnine, glycosides such as digitoxin and digoxin, proteins like insulin and oxytocin, and others like esters, amide, alcohol, and glycerides.

Classification Based on Source

• Natural sources include plants like morphine, atropine, digitoxin, animals like bovine Insulin, and micro-organisms like penicillin.
• Synthetic sources examples are sulphonamide.
• Semi-synthetic sources examples are amoxicillin, ampicillin, and doxycycline.
• Biosynthetic Sources examples are recombinant Human erythropoietin and Recombinant bovine somatotropine.

Classification Based on Target Organ

• Central nervous system examples are diazepam, phenobarbitone.
• Respiratory system examples are bromhexaine.
• Cardiovascular system examples are digitoxin, digoxin.
• Gastrointestinal system examples are omeprazole, kaoline.
• Urinary System examples are magnesium sulphate, lasix.
• Reproductive system examples are oxytocin, oestrogen.

Classification Based on Mode of Action

• Inhibitors of bacterial cell wall synthesis examples are penicillin.
• Inhibitors of bacterial protein synthesis examples are tetracycline.
• Calcium channel blockers examples are verapamil or nifedipine.

Classification Based on Therapeutic Use

• Antimicrobials/antibacterials examples are penicillin, streptomycin, quinolones, macrolides.
• Antihypertensives examples are clonidine, hydralazine, enalapril.
• Antidiarrheals examples are lopramide, kaoline.
• Antiemetics examples are domperidone, meclizine, metoclopramide.

Classification Based on Physiological System

• Sympathomimetics examples are adrenaline and noradrenaline.
• Parasympathomimetics examples are carbachol, pilocarpine, neostigmine.
• Neuromuscular blockers examples are suxamethonium, gallamine.

Characteristics of Drugs

• Can be synthesized within the body (hormones) or outside the body.
• Generally act on regulator molecules (receptors).
• Must have specific size, shape, atomic configuration, and electrical charge to interact with a receptor.
• Necessary properties to travel to its site of action.
• Must be easily inactivated or excreted after use.
• Can be solid (aspirin), liquid (ethanol), or gas (nitrous oxide).
• Physical nature affects administration.
• Can be carbohydrates, lipids, or proteins, affecting administration route.
• Addition of a chemical group can significantly alter drug interactions.

Drug Size

• Molecular size varies from very small (lithium ion, MW 7) to very large (alteplase, MW 59,050).
• Must be unique to have effects at receptors, which are specific for size, charge, shape, and atomic configuration.
• Lower limit of drug size is about 100MW, determined by the need to interact with receptors.
• Drugs must diffuse to needed compartments.
• Drugs larger than 1000MW do not diffuse readily.
• Drugs larger than 1000MW can be used if directly injected into the compartment where they act.
• Alteplase (MW 59,050) must be injected directly to the vascular compartment.
• Drugs must be unique to a receptor (above 100 MW) but still move to target cells (below 1000MW).

Drug Shape

• Important for drug-receptor interaction.
• Interacts with a structural binding region of the receptor (typically a protein).
• The specific nature of the interaction determines whether the drug acts as an agonist or antagonist.
• Must be a perfect shape to “fit” into the receptor.
• Must have a configuration allowing it to be chemically active and react with a receptor.

Chirality (Stereoisomerism)

• Chiral refers to a molecule with a center of three-dimensional asymmetry.
• Chirality or "handedness" refers to representing molecules that are not superimposable on their mirror image.
• Achiral molecules can be superimposed on their mirror image. -A chiral molecule rotates plane-polarized light and has no plane of symmetry.
• All molecules are chiral when they have one stereogenic (asymmetric) carbon.
• Stereoisomers have the same substituent bonding pattern but different 3D arrangement of the atoms and may be enantiomers or diastereomers.
• Many drugs (50%) are chiral (existing as enantiomeric pairs).
• Enantiomers are mirror images that cannot be superimposed.
• Enantiomers are chemically identical but rotate polarized light differently.
• Chemical identity is associated with true enantiomers, i.e., associated with a single asymmetric molecular center.
• If the molecule has 2 asymmetric centers, the molecule is referred to as a diasteriomer.
• Diastereomers have differing arrangement of atoms in space such as Cis-Trans isomers.
• Drugs with two asymmetric centers have four diasteriomers (e.g., labetalol, trandate, normodyne): an alpha and beta-receptor antagonist).
• One enantiomer is usually more effective than its mirror structural image.
• S(+)- methacholine enantiomer is 250 times more potent than the R(-) enantiomer form.
• Ketamine (Ketalar): (+) enantiomer is more potent and less toxic then the (-) enantiomer; however, the drug is used as the racemate (includes both enantiomeric forms).
• Thalidomide's chirality is significant, where one form causes sedation and the other causes foetal abnormalities.
• Thalidomide is used to treat leprosy, particularly erythema nodosum leprosum, and is effective in treating certain cancers.

Drug Permeability

• Permeability across biological membranes is a key factor in the absorption and distribution of drugs.
• Poor permeability arises from structural features and membrane-based efflux mechanisms.
• Poor permeability leads to poor absorption across the gastrointestinal mucosa or poor distribution throughout the body.
• The membrane lipid bilayer is the most important barrier for drug permeation.
  • Lipid: aqueous drug partition coefficients describes the ease with which a drug moves between aqueous and lipid environments
  • lonization state of the drug is an important factor: charged drugs diffuse-through lipid environments with difficulty.
  • pH and the drug pKa (dissociation or ionization constant which is the pH at which half of the substance is ionized and the other half unionized) are important in determining the ionization state, and influence significantly transport (ratios of lipid-to aqueous-soluble forms for weak acids and bases described by the Henderson-Hasselbalch equation.
• Uncharged forms are lipid-soluble, while charged forms are soluble in aqueous solution and are not lipid soluble, so they pass through biological membranes with difficulty.

Drug Design

• Drug design, also referred to as rational drug design is the inventive process of discovering new medications based on the knowledge of a biological target.
• This drug would most likely be an organic small molecule that either activates or inhibits the function of the biological target which is usually a biomolecule such as a protein, the effect of this potential drug then results in a therapeutic benefit to the patient.
• Drug design involves the design of molecules that are complementary in shape and charge to the biomolecular target with which they interact and therefore will bind to it.
• Drug design frequently but not necessarily relies on computer modelling techniques.
• Computer-based modelling is referred to as computer-aided drug design.
• Drug design may also rely on the knowledge of the three-dimensional structure of the biomolecular target in this case this is known as structure-based drug design.

This lesson covers the different types of drug names, including chemical, non-proprietary, and proprietary names. It also discusses the bodies that assign these names and the importance of maintaining congruence between official and non-proprietary names.