Pharmacokinetics is the study of absorption, distribution, metabolism and excretion of drug. The main concept of pharmacokinetics is elimination of chemical xenobiotic from the body. Pharmacodynamics is that the study of the biochemical and physiological effects of drug with the body. The interaction of drug with the receptors located either in the cell membrane or intercellular fluids.
Pharmaceutical equivalents are drug products in identical dosage forms and route(s) of administration that contain identical amounts of the identical active drug ingredient, i.e., an equivalent salt or ester of the same therapic moiety, or, with in the case of modified-release dosages that need a reservoir, such forms as prefilled syringes where the volume may vary, that delivers identical amounts of the active ingredient over the identical dosing period; it don't necessarily contain an equivalent inactive ingredients; and meet the identical compendial or other applicable standard of identity, strength, quality, and purity, including potency and, where applicable, content uniformity, disintegration times, and/or dissolution rates.2 They will differ in characteristics like shape, scoring configuration, release mechanisms, packaging, excipients (including colours, flavours, preservatives), expiration date/time, and, within certain limits, labelling.
Factors affecting bioavailability are differentiated into pharmaceutical and pharmacological factors. Disintegration, dissolution and absorption affects the bioavailability of drugs. Pharmaceutical factors are particle size, nature of excipients and adjuvants, degree of ionization...Pharmacological factors are gastric emptying and gastrointestinal motility, gastro intestinal diseases, food and other substances, first pass metabolism, drug-drug interactions, and route of administration.
The first pass effect is a phenomenon in which a drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug upon reaching its site of action or the circulation. The first pass effect is usually related to the liver, as this is often a serious site of drug metabolism. Let’s take a example of 100 drug molecules that are ingested in pill form. Only 90 of those molecules survive the alimentary canal . Then 81 make it past the gut wall and into the hepatic portal vein . Of the 81 that enters the liver, only 41 can make it to the systemic circulation. Thus the bioavailability is 41/100 = 41%. We also know the fraction that was passed through the gut (90/100 = 90%), the gut wall (81/90 = 90%), and the liver (41/81 = 50%). If you multiply each of these fractions together (90% * 90% * 50% = 41%) you reach the overall bioavailability for the drug. However, the primary pass effect also can occur within the lungs, vasculature, GI tract, and other metabolically active tissues within the body. This effect can become augmented by various factors like plasma protein concentrations, enzymatic activity, and gastrointestinal motility. The extent to which a patient may experience the first pass effect varies from patient to patient, and this must even be taken into consideration when determining appropriate dosing. If the first-pass effect is exceptionally prominent in patient, the drug may require administration via different route to bypass the first-pass effect.
Compares the bioavailability of the active drug in systemic circulation following Non-intravenous administration with an equivalent drug following intravenous administration for drugs administered intravenously, bioavailability is 100%. Determination of the best administration route
Compares the bioavailability of a formulation (A) of particular drug in comparison with another formulation (B) of an equivalent drug
One of the most challenging advanced research areas in pharmacology with in the new millennium is to know why every individual respond differently to drug therapy and to what extent that individual variability in disposition is liable for the observed differences in therapeutic efficacy and adverse reactions. Drug metabolism reactions are of two stages: stage 1 (functionalization) reactions like oxidation, hydrolysis; and stage II (conjugation) reactions like glucuronidation, sulfate conjugation. Newly introduced drugs are associated with 551 bioactivity points from ChEMBL (65.5%), manual curation from literature (24.14%), the Guide to Pharmacology (6.17%) and approved drug labels (4.17%), respectively; as well as 109 mechanism of action (MoA or Tclin proteins—vide infra) targets, with kinases (26%) and enzymes (21%) representing the major target categories, followed by G-protein-coupled receptors—GPCRs (17%) and tumor-associated antigens (9%).