What Happens After A Drug Has Been Administered

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Chapter 4

• What Happens After A Drug Has Been Administered

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Pharmocokinetics

• Describes how the body handles drugs
• Drug movement
• Absorption
• Distribution
• Metabolism
• Excretion

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Drug Movement

• Absorption process of involving the movement of
  a substance from the site of administration
  across one or more body membranes
• Occurs across the skin, associated mucous
  membranes or across membranes that line blood
  vessels

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Drug Movement

• Distribution process by which drugs are
  transported after they have been absorbed or
  administered directly into the bloodstream
• Factors that affect movement binding of drugs
  and substances present in the bloodstream (plasma
  proteins) such as albumin
• Barriers brain, placenta, and testes (require
  lipid soluble substances)

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Drug Movement

• Blood brain- barrier - some medications do
  cross, like antianxiety, sedatives, and
  psychoactive drugs
• Blood placental barrier regulates substances
  from the mother to the fetus, there are certain
  drugs that do cross and cause harm
• Blood-testicular barrier between the blood
  supply and the male reproductive tissue

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Drug Movement

• Metabolism process occurs at almost every cell
  with the liver (the primary site), kidneys, and
  the intestinal tract
• First-pass effect intestinal wall, enter the
  blood vessels (hepatic portal circulation-
  carries blood to the liver)

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Drug Movement

• Oral drugs go to the liver via veins in the upper
  digestive tract, this causes as much as 90 to be
  deactivated
• Other factors that affect metabolism Age, kidney
  and liver disease, genetics
• Enzyme activity is decreased in children and the
  elderly making them more sensitive to medications

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Drug Movement

• Excretion process of removing drugs from the
  body, via urination, exhalation, defecation,
  and/or sweating
• Via kidneys, respiratory tract, or glandular
  activity
• Main organ kidney
• Drugs that become gaseous are excreted via the
  respiratory tract

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Drug Movement

• Affected by gas exchange (diffusion, gas
  solubility, blood flow)

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Drug Movement

• Enterohepatic recirculation- bile is recirculated
  back to the liver which are metabolized in the
  liver and excreted by the kidneys, what is not
  recirculated is excreted in the feces
• Glands saliva, sweat eliminate substances
  naturally as urea or other waste products,
  substances that cross membranes in the breast may
  affect the infant if breast feeding

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Rate of Elimination

• Amount of drug removed per unit of time from the
  body by normal physiological processes
• Determines amount of time it stays in the
  bloodstream and its effect

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Rate of Elimination

• Half life length of time required for a drug to
  decrease concentration in the plasma by one-half
• The larger the half-life value the longer it
  takes to be eliminated
• Plasma half-life will increase with renal and
  hepatic disease

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Pharmacodynamics

• Mechanism of action or how the drug exerts its
  effects
• Things that influence therapy are the rate of
  administration, frequency of dosing, and a change
  in medical condition

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Receptors

• Structural component of a cell to which a drug
  binds in a dose related manner in order to
  produce a response
• To treat disease drug must interact with specific
  receptors

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Receptors

• Agonists are capable of binding with receptors
  and inducing a cellular response, they are
  facilitators of cellular action
• Antagonists inhibit or block the responses of
  agonists, called blockers

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Potency

• Potency drugs strength at a certain
  concentration or dose
• The higher the potency will produce a more
  intense effect
• A smaller dose may be needed to produce the same
  effect as another drug

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Efficacy

• Efficacy ability of a drug to produce a more
  intense response as the concentration is
  increased
• if the doses of two similar acting drugs are
  increased, they produce the same intense effect,
  but one will have a maximum intensity that is
  lower than the other drug

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Efficacy

• Lower efficacy - The one with the lower maximum
  intensity
• It is better to have a drug with a higher
  efficacy than one with a higher potency

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End