Pharmacotherapeutics

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Lecture 4

• Pharmacotherapeutics
• Pharmacokinetics
• Pharmacodynamics

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Pharmacotherapeutics / Indications

• Purposes of giving a drug
• Prevent illness
• Diagnose illness
• Relieve symptoms
• Treat and cure illness

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Effective concentration is influenced by

• Pharmaceutical phase
• Pharmacokinetic phase
• Pharmacodynamic phase

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Pharmaceutic Disintegration and dissolution
Rate limiting
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Pharmaco kinetics

• How the body processes the drug
• Absorption
• Metabolism
• Distribution
• elimination

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Pharmacokinetics

• Absorption
• Processes of drug absorption

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Absorption is dependent on -Route of
administration

• Enteral route length of time in the stomach,
  consumption of alcohol, solubility of the drug,
  stability in gastric ph, interactions with other
  food/ drugs, circulation in the GIT, surface area
  for absorption
• Parenteral route solubility, surface area for
  absorption and circulation

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Metabolism / biotransformation

• Occurs in two phases
• Phase 1 drug breakdown
• Phase 2 conjugation
• Hepatic first pass phenomena
• Enterohepatic cycling
• Extrahepatic phenomena

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BIOAVAILABILITY

• Bioavailability
• fraction of administered drug that reaches the
  systemic system
• Factors which affect it
• Factors which affect the absorption
• Route of administration
• Changes in liver metabolism

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BIOAVAILABILITY
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Distribution process by which drug is carried
in the blood and delivered to the tissues and
cells

• Protein binding
• Lipid solubility
• Tissue affinity
• Amount of drug present in the tissues
• Cardiac output and blood supply
• Density of blood vessels in the tissues
• Placenta and blood brain barrier

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Distribution (contd)
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Distribution (contd)
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Elimination

• Via the kidneys ( primarily), liver , GIT tract,
  lungs , sweat glands, skin and breast milk

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Half life (t ½)

• Half life
• time for plasma concentration of drug to be
  eliminated by 50
• Affected by
• Metabolism
• Elimination

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Pharmacodynamics

• Dose-response and maximal efficacy
• Onset, peak, and duration of action

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Pharmacodynamics (contd)

• Receptor theory

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Pharmacodynamcis

• Drug receptor activity
• Drug Receptor -gt Drug Receptor Complex -gt
  Response
• Drug receptor affinity affects potency.
• An agonist is a drug capable of combining with
  receptors to initiate a drug response.
• An antagonist is a drug that opposes or prevents
  receptor response.

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Agonists and Antagonists
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Pharmacodynamics (contd)

• Nonspecific drug effect

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Pharmacodynamics (contd)

• Nonselective drug effect

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Pharmacodynamics (contd)

• Categories of drug action
• Stimulation or depression
• Replacement
• Inhibition or killing of organisms
• Irritation

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• Therapeutic index
• the ratio of effective dose to lethal dose. A
  wide TI means the drug is relatively safe.

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Therapeutic Index
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Therapeutic Index (contd)

• Therapeutic range (therapeutic window)
• Peak and trough levels, see Table 1-4
• Loading dose
• Side effects, adverse reactions, and toxic effect
• Pharmacogenetics
• Tachyphylaxis
• Placebo effect

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Drug Effects

• To achieve therapeutic effect the drug must be
  in appropriate concentration

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Effects of Dosing on Pharmacokinetic Processes

• Steady state
• even distribution of drug concentration
• administration rate rate of clearance
• dependent on half-life

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• Loading maintenance doses
• higher than usual dose needed to sustain
  therapeutic effect
• faster therapeutic effect than can be achieved
  with steady state
• Volume of distribution
• hypothetical volume of fat, blood, and total body
  water in which drug appears distributed.
• Highly water soluble drugs have a low Vd and
  reach high serum levels. Drugs with high Vd are
  more widely distributed in tissues. Figure is
  used to help determine drug dose.

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• Clearance
• rate of removal of drug from the body
• Tolerance
• successively larger doses of a drug are required
  to maintain the same level of effect.

Tacyphlaxis when drug tolerance occurs
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Implications for Nursing Management

• Maximizing therapeutic effect
• understand principles of drug action
• assess core patient variables to see if drug
  action is typical
• assess appropriateness of therapeutic regime
• assess appropriateness of administration site,
  route, probable effects
• assess drug to be given and time of
  administration

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Nursing Management cont.

• Minimize Adverse Effects
• make appropriate modifications to promote
  effective action
• monitor drug level
• assess for early signs of adverse effects

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Summary