Pharmacokinetics

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Pharmacokinetics

• Pharmacology
• Chapter 2

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How Does medication Work in our Bodies?

• Pharmacokinetic Model
• Different cells are targeted to evoke a desired
  response
• Via chemical messangers.
• Can you name some?

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Receptors

• Cells communicate through the action of chemical
  messengers
• Target cell-(the cell that responds to the
  communication).
• Receptor is a protein molecule on the surface of
  or within a cell that recognizes and binds with
  specific molecules, thereby producing some effect
  within the cell.
• Specificity- the messenger has the same receptor
  structure as the target cell.
• Affinity- the strength by which a messenger binds
  to a receptor site.

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Mechanisms of Drug Action

• How a drug produces its effects.
• Agonist is a drug that binds to a particular
  receptor site and triggers the cells response in
  a manner similar to the action of the bodys own
  chemical messenger.
• Antagonists- Drugs that bind to a receptor site
  and block action of chemical messengers.
• Other drugs
• interact with non specific lipids
• combine with proteins
• Use Osmosis -how water is reabsorbed by the
  kidneys

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Pharmacokinetics

• The action of drugs in the body over a period of
  time .
• Pharmacokinetic Processes
• ADME Scheme of kinetics (Pharmacokinetic
  Modeling)
• Absorption
• Distribution
• Metabolism
• Elimination
• Considerations such as
• Levels of the drug in blood and tissues
• Overall distribution
• Reaction of the drugs with other drugs
• Patient compliance
• Life of the drug that includes bioavailability,
  half-life, bioequivalence

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Pharmacokinetics
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Absorption

• The process whereby a drug enters the circulatory
  system.
• Rate depends on ROA, solubility and physical
  properties.
• Dissolution the time necessary drug to be
  dissolved.
• Rate of dissolution depends on the chemistry,
  surface area, and mnf variables.
• Primary site of absorption- Small Intestine
• GI motility can affect the rate of absorption

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Distribution

• The process by which a drug moves from the blood
  into other body fluids and tissues.
• Factors that affect distribution
• Binding to Plasma Proteins
• Binding to Cellular Constituents
• Blood Brain Barrier
• Blood flow is the rate
• The distribution is not necessarily equal
  throughout the whole body

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Metabolism

• The process of converting drugs to compounds that
  are useful in the body.
• Factors that can alter metabolism
• Other medications
• Disease states, age, genetics

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Metabolism

• Most metabolism takes place in the liver
• Metabolism changes the chemical structure of the
  original drug
• There are different influences that can alter
  metabolism such as age, gender, genetics, diet,
  and other chemicals digested

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Excretion

• Occurs primarily in the kidney and bowel.
• Also exhalation, sweat glands, breast milk
• Clearance - rate at which a drug is eliminated
  from a specific volume of blood per unit of time.
• Excretion is the last phase of a drugs life in
  the body

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Important Pharmacokinetic Parameters

• Safe and effective drug therapy requires that
  drugs be delivered in concentrations that will
  treat the disease without toxicity.
• Bioavailability how much of the drug administered
  becomes active in the body.
• First Pass effect- drugs must first pass through
  the intestines and the liver before reaching
  target site.
• Ceiling effect -Greater doses are given until a
  point is reached when no improved clinical
  response occurs and increasing beyond this point
  can cause side effects, toxicity and death.

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Pharmacokinetics

• Dose-Response Curve

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• Therapeutic window - optimum response with the
  least probability of toxicity.
• Therapeutic level/Range -amount of drug in the
  blood that produces the desired effect.
• Duration of Action -The amount of time a drug is
  at this level
• Loading dose, the amount of drug needed to bring
  blood quickly to desired response.

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Pharmacokinetics

• Therapeutic Range

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Pharmacokinetics

• Duration of Action

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Maintenance Doses

• Given to maintain therapeutic levels

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Half Life

• The time it takes for the body to eliminate half
  the drug
• T1/2
• It takes a drug 5-7 times longer than its half
  life to be considered removed from the body
• 1000mg of Drug a has t ½ of 2 hours
• 12 am Take first dose
• 2am 500 mg left
• 4am 250 mg left
• 6 am 125 mg left
• 8 am 62 mg left
• 10 am 31 mg left
• 12pm 15 mg left
• 2 pm 7 mg left
• 4 pm drug eliminated
• 14 hours to rid the body of the medications

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Half Life
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Discussion

• How is a drugs volume of distribution,
  clearance, and half-life used in dosing drugs?
• Answer Volume of distribution is important for
  calculating the loading dose, clearance for
  calculating the maintenance dose, and half-life
  for determining the dosing interval.

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Bioequivalence

• This is the comparison between drugs either from
  different manufacturers or in the same company
  but from different batches of a drug
• Generic drug manufacturers strive to achieve the
  same equivalence as brand name manufacturers for
  competition

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Drug Effects

• Effects of drugs can be beneficial or detrimental
  and dangerous.
• Site of action- location in the body where a drug
  exerts its therapeutic effect.
• Beneficial Responses
• Therapeutic Effect
• effect-The desired action of a drug in treatment
  or symptom of a disease.
• Local Effect
• Confined to a specific part of the body
• Systemic Effect
• Generalized, all-inclusive effect on entire body

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Drug Effects

• When choosing a drug for a patient, a healthcare
  practitioner considers
• Indications
• diseases, symptoms, and conditions for which the
  drug is known to be of benefit
• Contraindications
• conditions for which the drug will not be
  beneficial and may do harm

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Drug Effects

• Side Effects
• secondary responses to a drug other than its
  intended effect.
• Allergic responses
• Drug dependence, addiction, abuse, and tolerance

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Harmful Responses

• An allergic response can be a local or general
  immune response.
• an overreaction to a harmless substance.
• Can be mild to severe
• Anaphylactic response- characterized by
  respiratory distress, vascular collapse and
  shock.
• Idiosyncratic reactions- unusual or unexpected
  reactions to a medication.
• Drug dependence- physiological and/or
  psychological need for a drug
• Addiction- A perceived need for a drug
• Abuse The use of a drug for purposes other than
  prescribed and or in amounts not directed.
• Tolerance -Decreased response to the effects of a
  drug do to its continued use.

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Drug Interactions

• Combined effect of two or more drugs.
• Common Drug relationships
• Addition
• 1 1 2
• Antagonism
• 1 1 1
• Potentiation
• 0 1 gt 1
• Synergism
• 1 1 gt 2

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Discussion

• Name a common drug-food interaction.
• Answer Grapefruit juice can affect drugs for up
  to a day following ingestion.

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Discussion

• Why is it important for the pharmacy to have a
  complete list of all of the prescription drugs,
  OTC medications, vitamins, and herbal remedies
  that a patient is taking?
• Answer Such a list will help healthcare
  professionals identify potential drug
  interactions.

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Factors that Influence Drug Effects

• Age
• Gender
• Disease/Medical condition
• Other-psychological, genetics, allergies.

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Geriatric Pharmacology

• Factors that affect the rate of aging
• Genetics
• Nutrition
• exercise
• injury
• disease
• environment
• Geriatric over 65,
• Most elderly patients will take 4 different RXs.
• This increases the chance of adverse reactions or
  drug-drug interactions.

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Physiological Effects of Aging on Pharmacokinetic
Process

• Loss of lean body mass
• Decrease in of body water
• Increased of body fat
• Absorption- is slowed and a delay in the onset of
  drug action occurs.
• Distribution - drugs can become more concentrated
  within the system. Increased body fat can slow
  the excretion of fat soluble drugs.
• Metabolism-is reduced and there is an increase in
  the duration of drug actions
• Elimination - Reduced blood flow and surface area
  can cause delays in excretion.

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Drug Compliance in the Elderly

• The elderly can easily become confused by their
  dosing regiments and can have difficulty
  remembering what meds are for what.
• Polypharmacy- multiple drug prescriptions.
• Increased side effects,
• Forgetting to take prescribed dose
• Continuing to take D/C Meds
• Difficult dosage form
• Small print on drug labels
• Look alike pills
• An average of six diseases coexist in older
  persons.

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Pediatric Patients

• Children undergo constant physiologic changes
  that can affect the ADME scheme of Kinetics.
• Could cause over or under dosing, resulting in
  failure of therapy, adverse reactions and death.
• Age and or weight is the least reliable guideline
  for dosing,
• BSA

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Lets Try it!

• Child weighs 13.9 kg and is 85 cm tall
• What is the BSA?
• 13.9 x 85
• 1181.5
• 1181.5/3600 (hit the before next step!)
• 0.3281944
• 0.3281944 v
• 0.572 m2

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Once More with Feeling!

• Child weighs 12.2 lb and is 24 inches tall
• What is the BSA?
• 12.2 x 24
• 292.8
• 292.8/3131 (hit the before next step!)
• 0.0935164
• 0.0935164 v
• 0.305 m2

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Discussion

• What can the pharmacy technician do to help
  patients manage their medications properly?

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Teaching Patients To Manage Their Medications

• Patients failure to follow drug regimen is often
  caused by a lack of understanding or unclear
  information.
• The pharmacy technician can positively affect
  patient compliance by providing clearly written
  instructions and aids.
• Techs are responsible for gathering and
  maintaining patient information such as medical
  history and possible allergies to prevent drug
  interactions and duplications.
• Obtain information about OTC medications.

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• Techs should type full , clear directions on the
  prescription label this includes.
• Name and strength of medication ( Brand and
  Generic if applicable)
• Qty ( 1 tablet , 5 ml, 1 teaspoonful)
• Route ( po, pr)
• Time ( tid, qid )
• Any extra information. ( dx) Unwrap etc)
• Axillary labels
• 1 qd
• Take 1 every day?
• Take 1 tablet orally every day.

NO!!!
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Teaching Patients Medication Management
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Teaching Patients Medication Management