PHYSIOCHEMICAL PROPERTIES OF A DRUG

• Drug


  A chemical substance intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease
• Types of drugs


  • Prescription drugs
  • Over-the-counter drugs
• Prescription drugs


  Drugs prescribed by a doctor which can be bought at any pharmacy, intended to be used by one person, regulated by FDA through the New Drug Application (NDA) process
• Over-the-counter drugs


  Drugs that DO NOT require doctor's prescription which can be bought off-the-shelf in stores, regulated by FDA through over-the-counter drug monograms
• Prescription drug categories


  • Antibiotics
  • Antidepressants
  • Antidiabetics
  • Antiepileptics
  • Bronchodilators
  • Cardiovascular
  • Hormone related
• Over-the-counter drug categories


  • Antacids
  • Antiemetic
  • Antihistamines
  • Cough medicine
  • Decongestant
  • Laxatives
  • Vitamins
  • Pain killers
  • Herbal products
• Uses of prescription drugs


  Easing pain, controlling blood sugar, lowering blood pressure, curing an infection
• Uses of over-the-counter drugs


  Treating minor illnesses like acne, facial pain, congestion, runny nose, fever, headache, hoarseness, itchy eyes, sneezing, sore throat cough and cold, pain, diarrhea and stomach discomfort, ulceration
• Physicochemical properties of drugs


  The ability of a chemical compound to elicit a pharmacological or a therapeutic effect which influence the various physical and chemical properties of the chemical substance on the biomolecule
• Physicochemical properties of drugs


  • Solubility
  • Partition coefficient
  • Dissociation constant
  • Hydrogen bonding
  • Ionization of drug
  • Redox potential
  • Complexation
  • Surface activity
  • Protein binding
  • Isosterism
• Solubility


  The concentration of the dissolved solute which is in equilibrium with the solid solute, affected by temperature, pH, pressure, nature of solute and solvent
• Methods to improve drug solubility


  Structural modification, usage of Cosolvents, employing surfactants, and complexation
• Importance of solubility


  Governs the preparation of liquid dosage form, drug must be in solution before being absorbed into the body to produce biological activity, must be in solution to interact with receptors
• Partition coefficient


  Equilibrium constant of drug concentration for unionized molecule in two phases (lipid and water), affects drug transport and distribution
• Factors affecting partition coefficient


  pH, Co solvents, Surfactant, and Complexation
• Dissociation constant (Kd)


  Rate of constant of dissociation at equilibrium, inversely proportional to association constant (Ka), indicates drug affinity for receptor
• Hydrogen bonding


  Special dipole-dipole interaction between hydrogen atom in a polar bond and electronegative atom, affects physical properties like boiling/melting point, water solubility, acid strength, spectroscopic properties, surface tension, viscosity, biological activity
• Types of hydrogen bonding


  • Intermolecular
  • Intramolecular
• Intermolecular hydrogen bonding


  Hydrogen bond made between two or more unlike molecules of similar or different types, e.g. solubility of alcohol in water
• Intramolecular hydrogen bonding


  Hydrogen bonding within the same molecule, results in cyclization and prevents association
• Complexation


  Formation of a coordination complex from a coordinating atom/ion and ligands, used to improve solubility and bioavailability of poorly water-soluble drugs
• Importance of complexation in medicine

  Antidote for metal poisoning, antibacterial/antifungal agent by complexing with iron/copper, reducing side effects caused by drug-metal chelation
• Ionization of drug


  Drugs can exist in ionized or unionized state, ionized molecules are hydrophilic and poorly lipid soluble, unionized molecules are lipid soluble and can diffuse across cell membranes
• Factors affecting ionization


  pKa value and pH of solution
• Redox potential


  Quantitative expression of a compound's tendency to give or receive electrons, characterizes ability to gain or lose electrons
• Surface activity


  Strong adsorption of materials at surfaces/interfaces in the form of an oriented monomolecular layer, affects drug absorption and pharmaceutical processes like tablet coating
• Surfactants


  Soluble in both water and oil, can reduce surface tension, affects drug absorption
• Applications of surfactants


  • Anthelmintic activity
  • Bactericidal activity
  • Disinfectant action
  • Enhancing dissolution of poorly water-soluble drugs
• Protein binding


  Ability of proteins to form bonds with drugs, can be reversible or irreversible, affects drug activity and elimination
• Isosterism


  Compounds with equal number and arrangement of electrons, have similar properties and molecular shapes/volumes
• Types of isosterism


  • Classical bioisosteres
  • Non-classical bioisosteres