Basics of Pharmacology: High-Yield Drug Concepts, Plasma Life and Routes Of Administration

• Pharmacology is the science dealing with drugs.(Greek: Pharmacon—drug; logos—discourse in).
• It deals with interaction of exogenously administered chemical molecules (drugs) with living systems, and any chemical substance which can produce a biological response is a ‘drug.’
• It is divided into several branches like pharmacokinetics, pharmacodynamics, pharmacotherapeutics, chemotherapy and toxicology etc.
• Pharmacokinetics :  (body does to a drug) the study of the absorption, distribution, metabolism and excretion of drugs, i.e. what the body does to the drug
• Pharmacodynamics: (drug does to a body) the study of the effects of the drugs on the body and their mechanisms of action, i.e. what the drug does to the body.
• Pharmacogenetics - Study of genetic basis for variability in drug response.
• Pharmacogenomics - Use of genetic information to guide choice of drug and dose on individual basis.
• Pharmacovigilance - Science and activities related to detection, assessment, understanding and prevention of adverse effects of drug or other drug related problems.
• Drug (Drogue—a dry herb in French) WHO definition— “A drug is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient.”

🔎 PLASMA LIFE:

• The plasma life of a drug is the time taken for its plasma concentration to be reduced to half of its original value.
• Types:
  – Alpha phase: This is due to distribution of drug. It is further divided into:
• Alpha 1 is due to distribution of drug into highly vascular organ.
• Alpha 2 is due to distribution of drug into less vascular organ.
  – Beta phase: This is due to elimination of drug.

🔎 ROUTES OF DRUG ADMINISTRATION:

👉 Local Routes include topical application on the skin and mucous membranes as well as the routes like intra-articular (e.g. hydrocortisone) and intrathecal (e.g. amphotericin B).
👉 Systemic Routes include oral, sublingual, transdermal, nasal, inhalational, rectal and other parenteral routes (intravenous, intramuscular, intradermal and subcutaneous).
• Oral route is safer and economical but several drugs are not effective by this route because of high first pass metabolism in the liver and intestinal wall (e.g. nitrates,
lignocaine, propanolol, pethidine).
• Sublingual route avoids first pass metabolism, can be used in emergencies, can be self administered and also after getting the desired action, rest of the drug can be spitted.
Drugs like nitroglycerine, isosorbide dinitrate, clonidine, nifedipine etc. can be administered by sublingual route.
• Transdermal route is used only for the drugs which are highly lipid soluble and can be absorbed through intact skin. By this route, there is a constant release of the drug and it may be administered less frequently. Nitroglycerine, nicotine, fentanyl and hyoscine are administered through transdermal patch.
• Drugs administered by Nasal route are nafarelin (GnRH agonist), calcitionin and desmopressin.
• Inhalational route is the route by which the rate of drug delivery can be controlled like I.V. infusion. The drugs administered by this route include drugs for asthma (e.g., salbutamol, ipratropium, montelukast and inhalational steroids) and inhalational anesthetic agents like nitrous oxide.
• Rectal route avoids first pass metabolism to 50% extent. Diazepam is given by this route in children for febrile seizures.
• Intravenous drugs can be given as bolus or via infusion. other parenteral routes include I.M. and S.C. routes.

• Drugs Administered by Various Routes

• SUBLINGUAL

• • nitroglycerine

• • isosorbide dinitrate

• • clonidine

• • nifedipine

• TRANSDERMAL

• • nitroglycerine

• • nicotine

• • fentanyl

• • hyoscine

• NASAL

• • Nafarelin (GnRH agonist)

• • calcitonin

• • desmopressin

• Inhalational route is the route by which the rate of drug delivery can be controlled like I.V. infusion.