2.Formulation
factors
Any drug it is possible to alter its bioavailability
considerably by formulation modification, a drug must be in solution to be
absorbed from the GIT, and you may expect the bioavailability of drug to
decrease in the order solution› suspension › capsule › tablet ›
coated tablet this order may not always be followed but it is a useful guide.
Solutions
In most cases absorption from an oral
solution is rapid and complete compare with in any other oral dosage form, the Rate
limiting step is the rate of gastric emptying.
Suspensions
Is second only to a solution in term of
superior bioavailability, Absorption may be dissolution limited the
addition of a surface active agent
will improve dispersion of a suspension & may improve the
absorption of very fine particle size suspensions, otherwise caking may be
problem.
Capsules
·
Hard gelatin capsules:
are usually filled with a powder blend that contains the drug, after ingestion
the gelatin shell softens, swells, and begins to dissolved in the GIT the is
release rapidly dispersed easily and has a good bioavailability
·
Soft gelatin capsules: may
contain a non aqueous solution, or a suspension of a drug.
Therefore
soft gelatin capsule that contains the drug dissolved in a hydrophobic vehicle
such as a vegetable oil may have slower bioavailability than a compressed
tablet formulation.
Tablets
The tablet is the most commonly used oral dosage form.
The biggest problem is overcoming the reduction in
effective surface area produced during the compression process. One may start
with the drug in a very fine powder then proceeds to compress it into a single
dosage unit.
Coated tablets are used to mask an unpleasant
taste, to protect the tablet ingredients during storage, or to improve the
tablets appearance.
Tablet coatings are of several types & for several
purposes:
1.
Coating are employed to protect the drug from
moisture, light, air and mask the bitter taste of drugs such as sugar.
2.
Enteric coating (delayed-release dosage
forms): are employed to permit safe passage of a tablet through the acid of
stomach.
3.Routs of
Drug Administration
An alternation method of classifying these routes of administration is enteral and
parenteral
·
Enteral mean to do
with GI tract and includes oral, buccal, & rectal
· Parnteral means not through the alimentary canal and
refer to injections such as IV, IM and SC also include topical and inhalation.
1.
Oral Routes:
Disadvantage
·
The slow drug response
compared with parenteral route
·
The drug may not be absorbed
completely from the GIT
·
The destruction of certain
drug by the gastric fluid, or by GI enzymes or inactive by the first pass
effect in the liver.
2.
Buccal and Sublingual Administration:
The buccal and sublingual mucosa is the oral cavity provides an excellent alternative for the
delivery of certain drugs
Advantages:
·
There is no loss of drug by
first pass effect mean Bioavilability is high
·
Rapid absorption because of
the good blood supply to the area absorption is usually quite rapid
Disadvantage:
·
Used only for potent drugs
(small doses) because of its small surface area
3.
Nasal Route:
The nasal route is used for the local action of drug
Advantages:
·
Ease of administration
·
Rapid absorption and avoidance of hepatic
first pass effect
Disadvantage:
·
Used only for potent drugs
(small doses) because of its small surface area
4.
Inhalation (Aerosols):
An aerosol can administer drug rapidly into
the bronchial region (liquid or solid particles)
o Local effect- bronchodilators
o Systemic effect- general anesthesia
Advantages:
·
Rapid absorption and
avoidance of hepatic first pass effect
5.
Rectal Route:
The rectal rout is used primarily for constipation
treatment by suppository or enema.
Advantages:
·
Rapid absorption and
avoidance of hepatic first pass effect.
· This route may be most useful for
patients unable to take drugs orally or with younger children.
Disadvantage:
·
Absorption is often
incomplete.
·
Not well accepted.
6.
Vaginal Route:
The major advantage is possibility of avoiding
first-pass effect following its
absorption through the vaginal epithelium.
Disadvantage:
·
The drug absorption changes
with change in the thickening of the vaginal epithelium and blood circulation
in this region through menstrual cycle and age.
7.
Ocular Route:
The topical application of the drug to the eye
8.
Parenteral Route:
The parenteral routes are the principal
routes for the systemic delivery of the drugs.
Advantage:
·
Rapidly and complete
absorption, Small dose and
avoidance of first pass effect.
9.
Skin /Transdermal Rout
Drugs
are administrated topically to provide either local or systemic effects.
The
major advantage is possibility of avoiding first-pass
The main limitation of this route is the size of the
penetrating drug molecules.
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