General pharmacology

• Pharmacology is the study of substances that interact with living systems through chemical processes, especially by binding to regulatory molecules and activating or inhibiting normal body processes
• Pharmacology deals with properties and effects of drugs in relation to their interaction with living systems
• Two basic areas of pharmacology:

  • Pharmacokinetics: deals with absorption, distribution, biotransformation and excretion of drugs
  • Pharmacodynamics: the study of biochemical and physiological effects of drugs and their mechanisms of action
• A drug is a chemical substance of known structure, other than a nutrient or an essential dietary ingredient, that when administered to living organisms produces a biological effect
• Drugs interact with specific molecules in a biological system that play a regulatory role (receptor)
• Drugs may be synthesized within the body (e.g., hormones) or may be chemicals not synthesized in the body (xenobiotics)
• Drugs may be administered to achieve a beneficial therapeutic effect on some process within the patient or for their toxic effects on regulatory processes in parasites infecting the patient
• Poisons are drugs that have almost exclusively harmful effects
• Toxins are poisons of biologic origin, synthesized by plants or animals
• Medicine is a chemical preparation that usually but not necessarily contains one or more drugs
• Pharmacotherapeutics is the use of drugs to diagnose, prevent, mitigate or treat disease or to prevent pregnancy
• Toxicology deals with undesirable effects of chemicals on living systems, from individual cells to complex ecosystems
• Clinical pharmacology is the study of drugs in humans (patients and healthy volunteers)
• Chemotherapy is the effect of drugs upon microorganisms, parasites, and neoplastic cells living and multiplying in living organisms
• Molecular Pharmacology is the study of the biochemical and biophysical characteristics of interactions between drug molecules and those of the cell
• Pharmacogenomics (pharmacogenetics) is the study of genetic variations that cause differences in drug response among individuals or populations
• Pharmacology originated as a branch of Physiology
• Oswald Schmiedeberg is considered the Father of Pharmacology
• Sources of drugs include plants, animals, microbes, mineral sources, synthetic or semi-synthetic products
• Plant origin drugs contain alkaloids, glycosides, and other active components
• Animal sources of drugs include hormones, vitamins, and immunoglobulins
• Microorganisms are a source of drugs like penicillin, streptomycin, erythromycin, and chloramphenicol
• Minerals and semi-synthetic/synthetic chemicals are also used as sources of drugs
• There are three common names for drugs: Chemical name, Generic name, and Brand name
• Routes of drug administration include Enteral (oral, sublingual, rectal) and Parenteral (subcutaneous, intramuscular, intravenous, intradermal)
• Oral route is the most commonly used route for drug administration, but has limitations such as slow drug action and inability to absorb certain drugs
• Sublingual administration involves placing highly lipid-soluble and nonirritating drugs under the tongue for rapid absorption
• Rectal administration is used for drugs that produce local or systemic effects, especially useful in patients who are vomiting or unable to take medication by mouth
• Parenteral routes involve injection of drugs directly into tissue fluid or blood, providing rapid action but with disadvantages like being less safe and more expensive
• Important parenteral routes include subcutaneous, intramuscular, intravenous, and intradermal administration
• Intravenous route is the most rapidly effective but also the most dangerous, reserved for emergencies when rapid action is required
• Intradermal route is employed for vaccination by injecting the drug into the skin raising a bleb
• Injection must usually be performed slowly and with constant monitoring of the patient
• Intradermal route:

  • Drug injected into the skin raising a bleb
  • Employed for vaccination e.g. BCG vaccine and for testing sensitivity e.g. penicillin injection
• Intra-arterial route:

  • Useful in diagnostic studies for arterial blood sample withdrawal for blood gas studies
  • Certain cytotoxic compounds administered by intra-arterial perfusion in localized malignancies
• Intrathecal or Intraspinal route:

  • Drugs injected directly into spinal subarachnoid space for local and rapid effect on meninges or cerebrospinal axis
  • Used for spinal anaesthesia or introduction of a radio-opaque contrast medium into the subarachnoid space for visualising the spinal cord
• Intracardiac route:

  • Adrenaline directly injected into the heart in sudden cardiac arrest and other cardiac emergencies by a long needle in the left fourth intercostal space close to the sternum
• Intraperitoneal route:

  • Common laboratory procedure, seldom employed clinically in infants for giving fluids like glucose/saline as the peritoneum offers a large surface for absorption
• Intra-articular route:

  • Certain drugs (i.e. glucocorticoids) administered directly into a joint space for the treatment of local conditions e.g. rheumatoid arthritis
• Inhalation Route:

  • Drugs administered as aerosols and gases when sprayed as fine droplets deposited over the mucous membrane
  • Advantages:
  • Avoidance of hepatic first-pass loss
  • Localize the action of the drug at the desired site of action
  • Rapid onset of action due to rapid access to circulation
  • Particularly effective and convenient for patients with respiratory complaints e.g. asthma
  • Disadvantages:
  • Needs special apparatus
  • Drugs may be irritants to the mucous membrane