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Pharmacology > 1.4 Pharmacokinetics > Flashcards

1.4 Pharmacokinetics Flashcards

1
Q

Pharmacokinetics

A

Movement of a drug into, through and out of the body

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2
Q

Four major processes involved

A

One absorption
Two distribution
Lthree metabolism
four excretion

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3
Q

Routes of administration

A
  • Before drug can be absorbed it must be administered
  • topical administration
  • Enteral administration
  • parenteral administration
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4
Q

Topical Administration - ON THE SKIN

A

-Large number of drugs can be applied to the skin to treat mild to moderate severity skin condition such as eczema acne and infections

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5
Q

Topical Administration- THROUGH THE SKIN

A

-Transdermal drug delivery is the application of a drug to the skin for absorption into the general circulation for a systemic affect this method is
-convenient
End it delivers a study drug supply for several days eliminating frequent oral dosing
-Bypasses the enzymes of the stomach intestines and liver
-Disadvantages it’s expensive and can cause local irritation

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6
Q

Topical Administration- INHALATION

A
  • Drugs are rapidly absorbed from the lungs and a number of both prescription and recreational drugs are administered this way
  • Drugs are administered through the lungs for both local and systemic affects
  • Gaseous anaesthetics administered by inhalation for a systemic affect
  • Steroids and other drugs for lung disease is administered for local effect in the lungs
  • Advantages the quantity of the drugs are small does avoiding the toxicity associated with oral ministration of the drug
  • disadvantage is that the method requires proper use by the patient
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7
Q

Enteral Administration

A

-Enter the blood through the gastrointestinal tract

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8
Q

Enteral administration – mouth

A
  • The mouth is commonly used to administer drugs for a number of reasons
  • Most convenient and least expensive
  • Noninvasive and can be self administered
  • More than 90% of all drugs are taking this way
  • Slow 30-min to > 1 hour
  • 5%-10% bioavailability
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9
Q

Enteral administration – rectum

A
  • Can be for systemic or local effect
  • can be used in patients who were nauseated or vomiting, or as a less invasive route for those who are comatose
  • Digestive enzymes of the stomach and intestine are bypassed
  • Disadvantages not all drugs are available as suppositories and absorption from the rectal mucosa is slow, incomplete, and variable, depending on the time the suppository is retained
  • slow and incomplete
  • 30-100% bioavailability
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10
Q

Enteral administration – sublingual and Buccal

A
  • Sublingual is under the tongue and buccal refers to in the cheek
  • Enzymes of the stomach, intestines and liver are bypassed by this route
  • Disadvantages not all drugs are adequately absorbed by this route and drugs may be swallowed and then the drug behaves as if it was taken orally
  • under the tongue, rapid 1-2 min, 30-100% bioavailability
  • in the cheek, intermediate 3-4min, 30-100% bioavailability
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11
Q

Parenteral administration

A

Injected into the body and enter the bloodstream

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12
Q

Parental Administration- Intravenous

A
  • The drug is placed directly into the blood
  • Can be used for drugs that are poorly absorbed providing that they can be made into a solution in water for injection
  • Disadvantages response is immediate, intense an irreversible (highest risk for drug reactions)
  • costly
  • Preparation must be sterile and free of fever producing substances (pyrogens)
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13
Q

Parenteral administration-intramuscular

A
  • The drug is injected deep into a muscle

- Volume of drug is limited to 5 to 10 mL in an adult

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14
Q

Parental administration-subcutaneous

A
  • The drug is injected into the deepest layer of the skin

- Drug preparations can be modified to control the timing of the release of the drug from SC injection sites

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15
Q

Absorption

A

-Movement of a drug from the site of administration into the blood
Endfor a drug to be absorbed and distributed to the sites of action, storage and excretion, it must be able to cross biological membranes

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16
Q

Transfer across membranes- DIFFUSION THROUGH AQUEOUS PORES

A
  • Drugs with small molecular weights of 150 or less that are water soluable can move across membranes by first resolving in the aqueous fluids surrounding cells and then by passing through the small openings between cells
  • drugs flow down these water passages from an area of higher concentration to an area of lower concentration
17
Q

Transfer across membranes- DIFFUSION THROUGH LIPIDS

A
  • biological membranes are composed of a lipid bilayer structure which consists of proteins interspersed throughout a double layer of lipid the fast majority of drugs have molecular weights greater than 150 and do not pass through aqueous pores but rather pass through the membrane by dissolving in the lipid portion of the membrane these drugs still flow down a concentration gradient to the other side of the cell membrane the ability of a drug to cross a membrane and be absorbed depends on its lipid solubility diffusion through lipid is the most important process that drugs use to cross membranes
18
Q

transport across membranes - Active Transport

A

-a number of drugs bind to proteins termed carried proteins or transporters which carry molecules across a membrane once bound the drug carrier complex moves across the membrane and releases the drug on the other side of the membrane transporter mediated drug transfers can move down a concentration gradient but can also be an active process requiring energy and can move a drug against a concentration gradient these carrier proteins for drugs and their matobilites play an important role in removal of metabolites from the liver and kidney

19
Q

Distribution/redistribution

A

-The movement of a drug from the blood to the site of action and other tissues
Most drugs reach all tissues and organs regardless of the target site of action
-Concentrations of drug at the sites of distribution equilibrium with its concentration in the blood
-If the concentration in the blood drops below the concentration of any of the distribution sites the drug will move from that site to the blood to maintain the equilibrium
-The greater the blood flow to an organ in the more rapidly drugs reach that organ and vice versa

20
Q

Metabolism

A
  • Conversion of a drug to a different chemical compound
  • Products are called metabolites, and they are usually, but not always, devoid of pharmacological action
  • To be eliminated from the body by the kidneys a drug must be water soluble
  • Without metabolism some chemicals that are very lipid soluble will never be excreted from the body
  • The liver is the organ where most metabolism reactions occur but some metabolism also occurs in the kidneys, intestine, lungs, skin, and most other organs
  • Divided into phase 1 and phase 2 reactions
21
Q

Phase 1 bio transformation reactions

A

-Purpose is to add or unmask a functional group on the drug so that the phase 2 reactions can add a large water soluble molecule, usually glucuronic acid or sulfate, making the product more water soluble for excretion by the kidney

22
Q

P450

A
  • Enzymes capable of bio transforming drugs are found in most tissues, but are present in high concentrations in the liver
  • The liver is the organ that is responsible for the majority of drug biotransformation
  • The cytochrome P450 family of enzymes by transforms the vast majority of clinically used drugs
23
Q

Phase 2 bio transformation reactions

A

-Add a large water soluble part or functional group or a molecule (moiety) To the product resulting from phase 1, making him a tablet water soluble for excretion by the kidney

24
Q

Excretion

A

-Moving the dragon it’s metabolites out of the body

25
Q

Excretion – kidney

A
  • The majority of drugs are illuminated by the kidney
  • drugs of sufficient water solubility will be excreted in the urine
  • lipid soluble drugs can be reabsorbed from the kidney back into the blood
26
Q

Excretion – Gastrointestinal tract

A

-Some drugs may be excreted by the gastrointestinal tract( feces) after they undergo biotransformation of the liver

27
Q

Excretion - lungs

A

-Drugs that are volatile or in a gaseous form can be excreted by the lungs (gaseous anaesthetic and alcohol)

28
Q

Excretion - breastmilk

A
  • Drugs are often found in the breastmilk of nursing mothers
  • while this is a minor route of elimination of the drug from the mother the nursing infant can be exposed to a therapeutic or toxic dose of the drug
29
Q

Excretion-saliva and sweat

A
  • Drugs are also found in saliva in sweat

- Often the presence of drugs of abuse can be detected in the saliva of the abuser

30
Q

Half life

A
  • The time needed for the liver and kidney to remove half the drug from the body
  • If we give a person 100 mg of Tylenol, after 1/2 life, 50 mg would remain in the body and after two half-lives, 25 mg would remain
31
Q

Absorption, DisDistribution, metabolism and excretion working together

A

-First the drug has to be absorbed from the gastrointestinal tract ones the drug crosses the membranes of the small intestine it will be in the blood designated as the central compartment in this figure in the blood the drug can exist as free drug and it can exist bound to proteins free drug will be available to move to other tissues but not the drug that is bound to protein. The drug can distribute to tissue reservoir such as fat or muscle this drug may be free and bound at these sites. The drug will also distribute throughout the body some of these sites will be unwanted sites of action for example an anhistomine causes drowsiness because it distributed through the brain as well as through the nasal passages. Then the drug gets to the site of action and acts on the receptor and should produce an effect. The magnitude of the effect is proportional to the concentration of the free drug at the site of action. It should be obvious that drug bound in fat distributed elsewhere will reduce the amount of drug available to distribute to the site of action and will control the drug concentration at the site of action it should also be noted that all these distribution pathways are reversible and the drug moves from site to site. There are 2 processes that remove the drug from the body
Biotransformation is the process where a drug is converted into another chemical the products of these biotransformational reactions are called metabolites. And usually but not always they are devoid of pharmacological action. A metabolite is usually more water soluble than the original drug and will then be available for excretion by the kidney. The kidney filters a large amount of blood each minute and any drug that is in the blood in a water soluble form will have the potential to be removed from the body by the kidney. Bio transformation and excretion are two processes that eliminate the drug from the body

32
Q

Variation in drug response

A

–The recommended dose of a drug is the amount of drug that will cause the desired effect in most people, but it will not cause the desired effect in all people
Dash of a difference in response to a drug exist within a population, which is why drug does it sometimes need to be adjusted based on the individuals response

33
Q

Variations in drug response- genetic factors

A
  • Genetic variability exist in the receptors for which the job buns, and in the manner in which the body handles and illuminates drugs
  • some individuals are considered slow bio transformers and others first biotransformers
34
Q

Variations in drug response - environmental factors

A

–Exposure to certain chemicals can increase the enzymes in the liver responsible for the bio transformation of drugs, therefore these persons eliminate the drug more rapidly than the unexposed portion of the population
Dash for example alcohol use increases the amount of one of the enzymes involved in drug biotransformation

35
Q

Variations in drug response – other disease states

A

–The presence of a disease state will alter the manner in which drugs are handled by the body. -Patients with liver disease will metabolize drugs at a slower rate than patients with normal liver function.
- Cardiovascular and kidney disease also alter the manner in which the body handles drugs.

36
Q

Variations in drug response - altered physiological states

Age of the patient

A
  • the elderly are more susceptible To drug action then young adults, especially to drugs acting on the central nervous system. As we age, we lose some of the reverse, or redundancy, and neural function and drugs have a greater effect than expected based on the response in the young adult.
    Ashliver and kidney function also decreases with age, which reduces the rate at which the elderly eliminate some drugs.
37
Q

Variations in drug response- altered physiological states-pregnancy

A

–The body undergoes a number of changes during pregnancy that influence drug response; increase in blood volume, cardiac output, and rate of rental excretion. It must be kept in mind that when treating a pregnant woman with drugs, two patients are receiving the drug, both the mother and the baby.

38
Q

Variation and drug response - other drugs present

A

-When multiple drugs are taken together, it is possible for one drug to change the biological effect of a second drug, leading to variability in drug response.

39
Q

Therapeutic range

A

-If the drug concentration is above the therapeutic range, Toxic Effects to the drug will occur, whereas of the drug concentration is below the therapeutic range, the patient will not be getting the full benefit of the drug

Pharmacology (11 decks)

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