Summarize the following text to main points and sub-points and make detailed explain for them:

Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
1
Principles of Drug Therapy
Pharmacology: The science that deals with the study of the interaction of drugs with 
living organisms.
Systemic Pharmacology: studying the effect of a drug or group of drugs on a 
determined system of living organisms. Ex, Neuropharmacology, Cardiovascular 
pharmacology…etc.
Molecular pharmacology deals with the biochemical and biophysical 
characteristics of interactions between drug molecules and those of the cell.
Clinical pharmacology: is the application of pharmacodynamics and 
pharmacokinetics to patients with diseases.
Pharmacokinetics: what the body does to the drug.
Pharmacodynamics: what the drug does to the body.
Toxicology: is that branch of pharmacology, which deals with the undesirable 
effects of chemicals (poisons) or toxins on living systems.
Routes of drug administration:
1. Enteral (Oral) like Tablets, Solutions, Suspensions,
2. Parenteral by injections
It is classified according to the speed of stimulation to the drug into four ways those 
are:-
A. Intravenous injection (i.v.).                              B. Intraperitoneal injection (i.p.). 
C. Intramuscular injection (i.m.).                       D. Subcutaneous injection (s/c).
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
2
3. Topical administration or (local) 
And includes: - (on skin, in the eye, Intravaginal) 
4. Other special routes include - Inhalation (Respiratory system), Intrathecal 
(epidural anesthesia in the spinal cord), and Sublingual.
Methods of transport of drug across the cell membrane:
1. Passive diffusion (simple diffusion). Depends on lipid solubility. Example 
(weak acids, weak basis).
2. Through aqueous pores. Example lithium.
3. Carrier-mediated transport (facilitated diffusion). Example Amino acids.
4. Active transport. Example (execration of penicillin through the proximal 
convoluted tubules).
Pharmacokinetics: 
Movement of a drug through the body including several available routes.
Absorption from the site of administration permits entry of the therapeutic 
agent (either directly or indirectly) into plasma. 
Distribution the drug may then reversibly leave the bloodstream and 
distribute into the interstitial and intracellular fluids. 
Metabolism the drug may be metabolized by the liver, kidney, or other 
tissues.
Elimination of the drug and its metabolites are removed from the body in 
urine, bile, or feces.
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
3
Absorption:
Most drugs are absorbed into the systemic circulation via passive diffusion and 
other mechanisms of absorption include active transport, facilitated diffusion 
absorption rate, and amount depending on 
1. local blood flow at the administration site: (e.g. sublingual vessels provide 
significant blood flow therefore rapid absorption)
2. Lipid solubility: greater lipid solubility = increased rate of diffusion 
through membranes E.g. anesthetics are very lipid soluble therefore 
have a rapid onset of action
4. Molecular size: small size, water-soluble drugs can pass through 
channels 
in 
membranes, 
Large 
molecules 
cannot 
e.g. 
aminoglycosides are large molecules and are not absorbed through 
the intestinal 
mucosa and are therefore not orally active
5. local pH and drug ionization: charged molecules do not cross 
membranes e.g. lactulose ionizes ammonia to ammonium and keeps 
it in the bowel
6. Total surface area for absorption: the small intestine has villi, 
which increase the surface area for absorption, and hence is the 
primary site of absorption for most oral drugs.
Henderson-Hasselbach Equation:
           The proportion of the total drug concentration that is present in either ionized 
or un-ionized form is dictated by the drug’s dissociation or ionization constant (K) 
and the local pH of the solution in which the drug is dissolved. The relationship of 
pKa and the ratio of acid-base concentrations to pH is expressed by the Henderson-
Hasselbalch equation:
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
4
Effect of pH on drug absorption: 
Most drugs are either weak acids or weak bases. Acidic drugs (HA) release an 
H+ causing a charged anion (A-) to form
Weak bases (BH+) can also release an H+. However, the protonated form of basic 
drugs is usually charged, and the loss of a proton produces the uncharged base (B):
 Passage of an uncharged drug through a membrane: A drug passes through 
membranes more readily if it is uncharged. Thus, the uncharged HA can permeate 
through membranes for a weak acid, and A- cannot. The uncharged form, B, 
penetrates through the cell membrane for a weak base, but BH+ does not. The ratio 
between the two forms is, in turn, determined by the pH at the absorption site and 
by the strength of the weak acid or base, represented by the pKa (Figure 1).
PKa is a measure of the strength of the interaction of a compound with a proton. 
The lower the pKa of a drug, the more acidic it is. Conversely, the higher the pKa, 
the more basic is the drug.
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
5
Factors that affect drug absorption:
1. The chemical nature of the drug.
2. Pharmaceutical form of the drug.
3. Dissociation constant PKa of the drug.
4. PH of the medium.
5. Presence or absence of food.
6. Movement of the gastrointestinal tract (G.I.T.).
7. Nature of the food.
Bioavailability:
             Is the fraction of administered drug that reaches the systemic circulation. 
For example, if 100 mg of a drug is administered orally and 70 mg of this drug is 
absorbed unchanged, the bioavailability is 0.7 or seventy percent.
First Pass Effect: 
Metabolism of orally administered drug in the liver before it reaches the 
systemic circulation. If a drug with high first-pass effect, it means low 
bioavailability. Drugs with a high first-pass effect include: chlorpromazine 
levodopa, morphine, propranolol, lidocaine, hydralazine, nortriptyline, and organic 
nitrates, drugs with low hepatic extraction (little or no first-pass effect) include: 
diazepam, digoxin, phenylbutazone, phenytoin, theophylline, tolbutamide, and 
warfarin.
Distribution:
            Movement of drug from intravascular to extravascular compartment or 
process by which drugs are carried throughout the body to reach target sites of action.
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
6
Factors affecting drug distribution: 
1. Blood flow: drug molecules are highly distributed to the highly vascularized 
tissues like the brain, liver, and kidney.
2. Capillary permeability: capillaries of some organs (Brain, Testes, and Placenta) 
have tight pores so only lipid-soluble materials can pass by simple diffusion.
3. Chemical nature of the drug: It plays an important role in drug distribution, so 
the non-polar drugs are well distributed across tissues while polar drugs are not well 
distributed across tissues.
4. Binding of the drug to plasma proteins: Drug molecules may bind to plasma 
proteins (usually albumin). Bound drugs are pharmacologically inactive; only the 
free, unbound drug can act on target sites in the tissues, elicit a biological response, 
and be available to the processes of elimination. 
✓Drugs with high affinity to bind to plasma proteins have low distribution, and 
this binding will slow their transfer out the vascular compartment, Albumine 
tends to bind to acidic drugs while Globuline tends to bind with basic drugs.
Volume of Distribution (Vd): The volume of distribution (Vd) relates the amount 
of drug in the body to the concentration of drug (C) in the blood. This volume does 
not necessarily refer to an identifiable physiological volume but rather to the fluid 
volume that would be required to contain the entire drug in the body at the same 
concentration measured in the blood:
Dose (mg/kg)
(Vd) =
liter/kg
Concentration mg/liter
Asst. Lecturer                                                 Lecture No. (1)                            M.Sc. Pharmacology & Toxicology
Hayder H. AL-kaabi
7
Metabolism or Biotransformation: 
              Chemical transformation of drug, Alteration of drugs by the liver. Drugs 
can be metabolized from active to inactive or from inactive to active. Generally, 
drugs are made more hydrophilic by the process. The liver is the principal organ of 
drug metabolism. Other tissues that display considerable activit

Summary :