| What factors modify GI absorption (gastric factors)? | Factors accelerating gastric emptying increase absorption (hunger, exercise, diluted solutions)
Factors delaying gastric emptying (anticholinergics, antihistamines)
Gastric secretions (insulin is destroyed)
Some drugs are coated in order to not cause gastric irritations (NSAIDs and aspirin) |
| What are the stages of pharmacokinetics? | Absorption (entry to plasma)
Distribution (Leaving bloodstream into interstitial and intercellular)
Metabolism (Biotransformation in liver or other tissues)
Elimination (through urine/feces) |
| What is bioavailability? | It is the percentage of administered drugs that reach bloodstream.
It is the quantity reaching circulation/ quantity administered |
| Why is their a lost quantity of the disease? | Since it will pass through liver where some administered drugs is metabolized.
So if the liver has a great metabolic activity on the drug, its bioavailability will be reduced largely
Note that IV drugs have 100% bioavailability |
| What do we mean by first-pass liver metabolism? | Entry of drugs through portal veins into the liver before being distributed to the desired target (this usually occurs for toxins as a protective measure detox)
So a fraction of the administered drugs is inactivated
(Non-enteral routes are not subjected to first pass) |
| What is the are under the curve (AUC)? | It is a quantification of the amount of drugs getting administered to the bloodstream
(Curve is of amount of drug in bloodstream versus time) |
| What are the factors influencing drug bioavailability? | First pass liver metabolism (nitroglycerin has 10% bioavailability due to first pass)
Solubility of drug (Hydrophilic products are poorly absorbed, extremely lipophillic are also poorly absorbed since they cannot circulate in the blood - this is why drugs are either weak acids or bases)
Chemical Instability (Degrarded by enzymes (insulin) and acidity (penicillin))
Nature of drug Formulation (size, shape, crystrallization, coating) |
| What kinds of effects can a drug have? | Local (if drug acts near site of admin)
Systemic (If it need to go to circulation) |
| What routes of entry possess systemic effects? | Enteral routes (Oral, sublingual and rectal)
PRL
Skin (nitroglycerin patches avoiding first pass effect)
Nose (like cocaine and desmopressin)
Vagina/rectum
Lung (like general anesthesia) |
| What routes of entry posses local effects? | Skin (corticosteroids like hydrocortisone to decrease inflammation)
Nose (decongestants like otrivin nasal spray)
Rectum (hemmorrhoids preparation H and procto synalar vasoconstrictors)
Lung (salbutamol beta agonist bronchodilator)
Eye (atropine to dilate pupil) |
| What factors affect the oral administration of drugs? | Site characteristics (blood flow to site of absorption and surface area of absorption)
Drug characteristics (physical state of drug, water or lipid solubility, and concentration administered) |
| What are the premium conditions for drug absorption? | Solid forms are governed by the rate of dissolution and water solubility (if low water solubility and dissolution very limited)
absorption is favored by non-ionized lipophilic forms
Weak acids are better absorbed in stomach while basic substance are absorbed in intestines (pH=7) |
| What is the difference between abosption in stomach and intestine? | Stomach (thick epithelium and small surface area and acidic)
Intestine (thin mucosa, large area, and basic |
| What factors modify GI absorption (gastric factors)? | Factors accelerating gastric emptying increase absorption (hunger, exercise, diluted solutions)
Factors delaying gastric emptying (anticholinergics, antihistamines)
Gastric secretions (insulin is destroyed)
Some drugs are coated in order to not cause gastric irritations (NSAIDs and aspirin) |
| What factors modify GI absorption (intestinal factors)? | Time of preservation in intestine (larger favors absorption like antidiarrhea drugs decreasing peristalsis)
Increasing peristalsis decreases absorption (laxatives) |
| What are the advantages and disadvantages of oral administration? | Advantages (easy, safe, cheap, convenient)
Dis (limit absorption, emesis, destruction of drugs, irregular absorption due to food, metabolized by first pass) |
| What is meant by therapeutic window? | When the dosage of effectiveness of a drug is very close to the toxic dose (like digoxine) |
| Describe sublingual route of administration. | It is absorption through oral mucosa, limited area, but goes into superior vena cava directly without first pass
Like nitroglycerin (very effective in sublingual and potent) |
| Describe rectal route of administration. | When pt is unconscious or vomiting, more than 50% bypasses liver (superior rectal vein goes to inf mesenteric), others go to inferior vena cava (middle and inferior rectal veins go to inferior pudental vein to vena cava) |
