Question

Learning Task 19-04 - Drugs in the Body

Create a chart that summarizes how drugs get into, are distributed, and do their job in the body. Make a note of some of the challenges to getting drugs where they are needed. Include information about the following in your chart :

Circulatory System	Liver
Stomach and Stomach Acid	Small Intestine
Enzymes	Protein
Fat	Receptors
Cells

Answer 1

Drugs in the Body

1.Route of administartion

Route through which the drug is inserted into the body. Drug can be inserted in many ways mainly divided into

i) Systemic ii) Local

i) Systemic	ii) Local
a)Enteral	b)Parentral	Topical skin
Oral	Inhalation	Deeper tissue
Rectal	Injections
Sublingual

2. Absorption

The name reffers to the movement of drug from the site of administration to the blood stream. Different route of administartion takes different route of absorption.

Route	Absorption
Oral route:	Most commonly used,inexpensive and safest way of administration. Drug is taken in through oral cavity. However the drug moves to the stomach and from there to the intestine and liver before reaching the circulation. This is called First pass Metabolisam. This reduces the quantity or avilability of drug.
Intravenous Injection:	Administrated directly into the blood stream resulting in 100% bioavilablility of the drug. Effect can be expected within a very short span of time.
Intramuscular Injection	Slower when compaired with intravenous type. Lipidsoluble drug are passively diffused into the blood circulation. Water soluble drug are not redly absorbed into the circulation through special pores called capillary pores.
Sublingual:	Drug absorbed across the oral mucosa through passive diffusion. Only possible route for lipid soluble drugs.
Rectel route:	Only used in younger and older age individuals. Slower rate of absorption Absorption through passive diffusion. Fecal matter in rectum decreases the rate of absorption.
Topical Application:	Avilable in from of gel,ointment, lotion etc. slower rate as it has to penetrate many layers of cell. Effect remains only for a limited period of time. If applied to obtain an systemic effect then called transdermal or percutaneous administration.

3.Distribution

It is the passage of drug from the circulation into the target tissues.It is a reversible process.Several factors affect the distribution like

Factors
Blood flow	more circulation more distribution
Permiability of the membrane	Lipid soluble drugs are eaily permiable
lipid solubility of the drug	Lipid soluble drug can cross the membrane but water soluble drug remains in the extracellular fluid.
Molecular weight of drug	Low molecular weight high rate of penetration
Blood Brain Barrier	Only few drugs can cross the blood brain barrier and reach the central nervous system. Capillary membrane are deprived of the slits between the endothelial cell making it a tight junction impermiable tpo many substances. THis is a form of protective mechnaisam. Lipid soluble drugs can cross the blood brain barrier.

Consist of two steps

i) Penetration of the drug from blood stream into the interstitial space crossing the capillary membrane

ii) Penetration of the tissue membrane to reach the inside of cell or intercellular fluid.

Drug receptor: They are cellular receptors on the extra cellular membrane of the target tissue or cell to which the specifc drug interacts. Receptors are mainly glycoproteins. The ineracting drug is called as a lingand. The binding of the drug to the membrane causes a cascade of changes exhibited by the protein complexes inside the cell which bring about the desired effect on the target tissues.

Challenges in Drug Delivery

Identifing the target by the drug ligand is one of the main challenge.

common target in the body are proteins likes enzymes,ion channel,receptors and nucleic acid.

The binding of the drug to target brings about some conformational changes in the target disabeling its binding with other substances like hormones etc. Few mechanisam of inhibition are receptor antagonisam, enzyme inhibition and channel blockage,

Druing development of a drug it is important to identify the specific target binding to which can bring about the desired effect. This brought about using Reverse pharmacology approach.

Other challenges include reduction of the bioavilability of the drug by first pass metabolisam,incapability to reach the desired target, inability to cross the membrane etc.

Oral route - First pass metabolism

Oral administrated drug after reached in the stomach. Few acidic drugs are absorbed in the stomach.The unabsorbed basic drug passes into the small intestine were is it absorbed and passed on the portal circulation. Upon reaching the Liver through portal circulation these drugs undergo metabolisam in the liver. Reducing the bioavilability of the drug. The active drug after the metabolisam passes to the systemic circulation.