Pharmacokinetics

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Pharmacokinetics

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Pharmacokinetics

• Examines the movement of a drug over time through
  the body
• The clinician most recognize that the speed of
  drug action
• Intensity of drugs effect and duration of drug
  action are controlled by 4 fundamental pathways
  of drug movement and modification in the body

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• Absorption ( input )
• Distribution
• Metabolism
• Elimination ( output )

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Absorption

• Drug absorption from the site of administration (
  input ) permits entry the therapeutic agent (
  either direct or indirect ) into the plasma

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Distribution

• The drug may then reversibly leave the blood
  stream and distribute into the interstitial and
  intracellular fluids

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Metabolism

• The drug may by metabolized by the liver kidney ,
  or other tissues

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Elimination

• The drug and its metabolites are eliminated from
  the body ( output ) in urine , bile and feces

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Routes of Drug Administration

• The rout of administration is determined
  primarily by the prosperities of the drug ( for
  example , water or lipid solubility , ionization
  etc ) and by the therapeutic objectives ( for
  example , desirability of a rapid onset of action
  or the need for long-term administration or
  restriction to local site )

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There are 3 major routs for given the drug
B- Parenteral
C- others
A- Enteral
Oral
Inhalational
Intravenous
Sublingual
Intramuscular
Intranasal
Rectal
Intrathorasic
Subcutaneous
Topical
Transdermal
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Oral

• Giving the drug by the mouth is the
  most common rout of administration , same dug are
  absorbed from the stomach however , the
  duodenum is the major site of entry to the
  systemic circulation because of its larger
  absorptive surface.

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• Note - most drugs absorbed from gastrointestinal
  tract enter the portal circulation and encounter
  the liver before they are distributed into the
  general circulation ,this case called first-pass
  metabolism by intestine or liver limits the
  efficacy of many drugs when taken orally for
  example , more than ninety percent of
  nitroglycerin is cleared during a single passage
  through the liver
• Note 2 Ingestion of drugs with food can
  influence absorption .
• Note 3 enteric coating of a drug protects it
  form the irritation , depending on the
  formulation .

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Sublingual

• Placement under the tongue allows a drug to
  diffuse into the capillary network and therefore
  , to enter the systemic circulation directly

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Rectal

• This rout is very useful if the drug induces
  vomiting when given orally or if the patient is
  already vomiting and advantage that they prevent
  the destruction of the drug by internal enzyme or
  by low PH in the stomach .

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Parenteral

1. Used for drug that are poorly absorbed from GIT .
2. Used for agents such as insulin that are unstable
   in GIT.
3. Used for treatment of unconscious patient .
4. Used for circumstance that required rapid onset
   of action.
5. Provides the most control over the actual dose of
   drug .

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• There are 3 major routes -
• Intravenous.
• Intramuscular.
• Subcutaneous.

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Intravenous

• most common parentral rout for the drug that are
  not absorbed orally, this permit rapid effect and
  a maximal degree of control , it may also induce
  hemolysis or cause other adverse reaction by
  too-rapid , therefore the rate of infusion most
  be carefully controlled

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Intramuscular

• Drug administered IM. Can be aqueous solution or
  specialized depot preparations often suspension
  of drug in a non aqueous vehicle, such as
  polyethylene glycol ,absorption of drug in
  aqueous solution in fast ,where as that from
  depot preparations is slow.

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Subcutaneous

• This route used for slowering time of absorption
  as uses silastic capsule that containing the
  contraceptive that are implanted for long-term
  activity or uses minute amount of epinephrene
  that combine with lidocaine that are decrease
  removal the drug from site of area by acting
  vasoconstrector.

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Other

1. Inhalation.
2. Intranasal.
3. Intratracheal.
4. Topical.
5. Transdermal

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Inhalation

• provide the rapid delivery of a drug across the
  large surface area of the mucous membrane of the
  respiratory tract and pulmonary epithelium
  producing an effect almost as rapidly as with IV
  injection, this rout use for gases such as some
  anesthetic and convent patient with respiratory
  complaints example asthma .

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Intranasal

• salmon calcitonin , a peptide hormone used in
  treatment of osteoporosis or abused drug cocaine
  , is generally taken by sniffing

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Intrathecal or intraventicular

• Its sometimes necessary to introduce drugs
  directly to cerebrospinal fluid for examples
  ,amphotercin B is used in treatment cryptococcal
  meningitis.

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Topical

• Application is used when a local effect of the
  drug desired, such as atropine is instilled
  directly into the eye to dilate pupil.

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Trans dermal

• This rout of administration achieves systemic
  effects by application of the drug to the skin,
  usually via a dermal patch , that depending in to
  physical characteristic of the skin such as
  nitroglycerine that act antianginal drug.