Pharmacodynamics is the study of physiological and biochemical effects of the drug on biological systems by discussing chemicals, biological receptors and relationship between drug concentration and its effect. It is summarized as what the drug does to the body.
Pharmacokinetics is the study of effects of biological systems on the drugs by discussing drug disposition which involves absorption, distribution, metabolism and excretion with emphasis on chemical changes effects and routes of excretion. It is summarized as what the drug does to the body (Leonard, 2003).
- Plasma protein binding is the formation of drug-plasma protein complex between the drug administered and plasma proteins such as serum albumin and globulins. These two dependent on the drug affinity for proteins and is either reversible or irreversible. Only the unbound drug undergoes metabolism, the more it dissociates from protein, the more it undergoes metabolism. Therefore, plasma protein binding is inversely proportional to metabolism (Woodrow, 2007).
- Warfarin is an anticoagulant; aspirin has the antiplatelet effect of inhibiting the production of thromboxane which normally binds the platelet patch, and inhibition is irreversible. The two drugs have the synergistic interaction which may result in complete impairment of clotting mechanism leading to excessive bleeding even in minor injuries (Prevost, 2005).
- Hepatic first pass effect is a phenomenon of drug metabolism that breaks down the drugs causing a decrease in drug concentration before it reaches the systemic circulation. It greatly reduces the bioavailability of drugs such as diazepam and morphine. It may also be an advantage since it activates prodrugs, for example, codeine, which is methylmorphine demethylated to its pharmacologically active form which is morphine (Leonard, 2003).
- Half-life is the time it takes for a drug or biological substance to lose half of its pharmacological or physiological activity. This may be due to the reduction of its plasma concentration to half its steady state. The implication on prescribers is that it dictates time taken to reach steady state concentration and determines the loading dosage, frequency of succeeding doses for optimal drug action and duration for complete drug elimination (Prevost, 2005).
- Steady state is the equilibrium obtained between the drug entering the body system and the drug eliminated and is often achieved at the end of a certain number of administrations. Steady state is achieved following that dose and frequency of administration are constant, and this is usually at the end of approximately five half-lives (Woodrow, 2007).
- Enzymes have several characteristics and properties, these are, for instance: denaturation, since they are protein in nature and denatured by extreme pH, temperature and strong ionic pull. They are also specific to the substrates and reactions they catalyze. Enzymes can be regulated either allosteric or covalently to control their rates of substrate turnover. Moreover, they are also inhibited by certain substances that may be particular to all enzymes.
In the case of competitive inhibition, the inhibitor and substrate race for the same enzyme which resembles the real substrate and cannot bind simultaneously. Also, Vmax is unchanged, while Km is raised. An example is methotrexate which competes with dihydrofolate reductase enzyme that catalyzes lessening of dihydrofolate to tetrahydrofolate. In non-competitive inhibition, inhibitor binds to enzyme simultaneously as substrate not compared to the active site. Also, it lowers Vmax whereas it is not overcome by raising Km. A good example is amino acid alanine that noncompetitively inhibits pyruvate kinase enzyme (Leonard, 2003).
- A drug antagonist reduces effects of a drug or blocks its actions by occupying receptors and therefore reducing the binding to receptors for action. Atropine is a competitive antagonist of muscarinic acetylcholine receptors M1, M2, M3, M4 and M5 reducing parasympathetic effects hence called parasympatolytic. Effects of atropine on the human body are mydriasis, photophobia, blurred vision, nausea, decreases bronchial, salivary, mucus, sweating and increasing heart rate (Woodrow, 2007).
- Cimetidine causes elevation of the steady state concentration of propranolol, hence synergistic to it. It also blocks the breakdown of propranolol by the liver, in addition, decreasing heart rate and increasing frequency and possibilities of chest pain (Woodrow, 2007).
- Cheddar cheese or broad beans have a compound called tyramine which causes the hypertensive crisis when administered together with Azilect. Azilect is an irreversible inhibitor of monoamine oxidase selective for MAO type B over type A by a factor of fourteen. Consumption of high levels of tyramine while on Azilect treatment may lead to perilous increases in blood pressure, a condition known as hypertensive crisis. A sudden and severe headache, blurred vision, confusion, seizures, chest pain, nausea or vomiting, sudden numbness or weakness (especially on one side of the body), fever, sweating, lightheadedness, and fainting during treatment with Azilect, as signs and symptoms of a hypertensive crisis (Woodrow, 2007).
- Tetracycline and antacids should not be administered together since they form insoluble complexes thus impair absorption and drug metabolism due to decreased bioavailability. Antacids containing aluminium and calcium reduce absorption of most tetracyclines and therefore curtail the actions of such drugs, and formed complexes may cause adverse reactions from the body’s immune system. Tetracyclines got the high affinity for chelates with polyvalent metallic cations such as Fe3+, Fe2+, Al3+, Mg2+ and Ca2+. Most of the tetracycline-metal complexes are whichever insoluble or poorly absorbable in the gastro-intestinal tract. These antacids having polyvalent cations, and various iron salts ingested concurrently with tetracycline derivatives, may interfere with tetracycline absorption by 90% or even more (Prevost, 2005).
- Diazepam is a benzodiazepine drug which possesses anxiolytic, anticonvulsant, hypnotic, sedative, skeletal muscle relaxant, and amnestic properties. It increases central depressive effects of alcohol and causes the synergistic enhancement of alcohol hypotensive properties (Woodrow, 2007).
Warfarin is an anticoagulant while cabbage has a high level of vitamin K which is a factor for coagulation; hence they have antagonistic effects on each other. This may result in neutralization or decreasing effects of either drug when administered concurrently. In that case, the effects may cause detrimental results which may result in pathological conditions of the affected individual (Woodrow, 2007).
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