Pharmacokinetics l Pharmacology MCQs for dental students

 

Pharmacokinetics: The Absorption, Distribution, and Fat at e of Drugs l Pharmacology  MCQs (multiple choice question) for dental students 

Introduction, kinetics and Dynamics

• Pharmacology It is the science that deals with the effects of drugs on living system.
• Drug ‘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’.
• Pharmacokinetics It means the movement of the drug within the body; it includes the processes of absorption (A), distribution (D), metabolism (M) and excretion (E). It means ‘what the body does to the drug’.
• Pharmacodynamics It is the study of drugs effect —their mechanism of action, pharmacological actions and their adverse effects. It covers all the aspects relating to ‘what the drug does to the body’.
• Therapeutics It is the aspect of medicine that is concerned with the treatment of diseases.
• Chemotherapy It deals with the treatment of infectious diseases/cancer with chemical compounds that have relatively selective toxicity for the infecting organism/ cancer cells.
• Toxicology It is the study of poisons, their actions, detection, prevention and the treatment of poisoning.

 

Sources of Drugs

• Plants:

1.      Alkaloids, e.g. morphine, atropine.
2.      Glycosides, e.g. digoxin.

• Animals: Insulin, heparin.
• Minerals: Ferrous sulphate, magnesium sulphate.
• Microorganisms: Penicillin, streptomycin, griseofulvin.
• Semisynthetic: Hydromorphone, hydrocodone.
• Synthetic: Most of the drugs used today are synthetic, e.g. aspirin , paracetamol.
• Genetic engineering (DNA recombinant technology), e.g. human insulin, human growth hormone, hepatitis B vaccine.

 

Pharmacokinetics (ADME)

• It is derived from two words: Pharmacon meaning drug and kinesis meaning movement. In short, it is ‘what the body does to the drug’.
• It includes absorption (A), distribution (D), metabolism (M) and excretion (E) of a drug. All these processes involve movement of the drug molecule through various biological membranes . All biological membranes are made up of lipid bilayer.

Drugs cross various biological membranes by the following mechanisms:

1. Simple ( passive ) diffusion: It is a bidirectional process. The drug molecules move from a region of higher concentration to lower concentration until equilibrium is attained. Lipid-soluble drugs are transported across the membrane by Simple ( passive ) diffusion. It does not require energy.
2. Filtration: Filtration depends on the molecular size and weight of the drug. If the drug molecules are smaller than the pores, they are filtered easily through the membrane.(Kidney )
3. Active transport: The drug molecules move from a region of lower to higher concentration against the concentration gradient. It requires energy, e.g. transport of sympathomimetic amines into neural tissue, transport of choline into cholinergic neurons .
4. Facilitated diffusion: This is a type of carrier-mediated transport and does not require energy. The drug attaches to a carrier in the membrane, which facilitates its diffusion across the membrane. The transport of molecules is from the region of higher to lower concentration, e.g. transport of glucose across muscle cell membrane by a transporter GLUT4.

 

Drug Absorption

• The movement of a drug from the site of administration into the blood stream is known as absorption.

 

Factors Influencing Drug Absorption

 Physicochemical properties of the drug:

•      Physical state: Liquid form of the drug is better absorbed .
•      Lipid-soluble and unionized form of the drug is better absorbed than the water-soluble and         ionized form.
•      Particle size: Drugs with smaller particle size are absorbed better than larger ones.
•      Others.

 Route of drug administration:

1. A drug administered by intravenous route bypasses the process of absorption, as it directly enters the circulation.
2. Some drugs are highly polar compounds, ionize in solution and are not absorbed through GI tract( oral ) ; hence are given parenterally, e.g. gentamicin.
3. Drugs like insulin are administered parenterally because they are degraded in the GI tract on oral administration.

 pH and ionization:

• Most drugs have groups that can be ionized
• Many drugs are weak acids or weak bases and can exist in either non ionized or ionized forms in an equilibrium, depending on the PH of the environment and the PKa = pH at which the molecule is 50% ionized and 50% non ionized)
• Only the non ionized (uncharged) form of a drug can cross biomembranes.
• Ionized form is better renally excreted because it is water soluble

• So ;

•         For weak acids and weak bases:

1.                 ionized = water soluble
2.                 Non ionized- lipid soluble

•         ionization decrease passage across lipid membranes .
•         ionization increases solubility and renal clearance of drug