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Foundations of Medicine > Drug Therapy > Flashcards

Drug Therapy Flashcards

1
Q

What factors affect oral absorption bioavailability?

A

Formulation

The ability of drug to pass physiological barriers - particle size, lipid solubility, degree of ionisation

Gastrointestinal effects - gut mobility, food, illness

First-pass metabolism

Transport across membranes - passive diffusion (most important), protein-mediated transport, filtration, bulk flow

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2
Q

What is first pass metabolism?

A

A phenomenon of drug metabolism whereby the concentration of a drug, specifically when administered orally, is greatly reduced before it reaches the systemic circulation.

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3
Q

What is the most frequent transport mechanism of drugs?

A

Passive diffusion down a concentration gradient

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4
Q

How do lipid soluble drugs diffuse?

A

By dissolving in the lipoidal matrix of the membrane

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5
Q

Do drugs ionise in water?

A

Most drugs do not completely ionise in water

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6
Q

What does the degree of drug ionisation depend on?

A

As most drugs are weak acids or bases the degree of ionisation depends on the pH of the environment

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7
Q

In respect to ionisation, what does not cross the membrane?

A

Both ionised and un-ionised forms will be present.

The ionised drug does not cross the membrane

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8
Q

What should un-ionised drugs do at the membrane?

A

The un-ionised form should distribute across the membrane until the equilibrium is reaches - an equal concentration at each side

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9
Q

What does a drug have to be in order to cross a lipid layer?

A

In solution and lipid soluble

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10
Q

What key factors affect passive transport?

A

Molecular size
Lipid solubility
Polarity
Degree of ionisation
pH of environment

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11
Q

Where does filtration normally occur?

A

Through channels in the cell membrane

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12
Q

What is filtration the normal method for?

A

Water-soluble molecules with a molecular weight of <100

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13
Q

Where does bulk flow of liquid occur?

A

Through inter-cellular pores

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14
Q

What is active transport?

A

Energy-dependent transport across membranes against a concentration gradient

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15
Q

What do drugs must do to undergo active transport?

A

Resemble naturally occurring compounds

The drug is reversibly bound to a carrier system

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16
Q

What physiological barrier on the GI tract in necessary for drugs to pass from one side into the other to get into circulation?

A

Lipid membranes that contain receptors, ion channels and a variety of proteins.

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17
Q

What does the speed of gastric emptying affect?

A

The speed at which the drug reaches the site of absorption

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18
Q

Where are most drugs absorbed?

A

Small intestine

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19
Q

How does food impact rate of absorption?

A

Can enhance or impair rate of drug absorption

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20
Q

How can malabsorption impact rate of absorption?

A

Can increase or decrease rate of absorption

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21
Q

How do migranes impact the rate of absorption of analgesic drugs?

A

Reduces rate of stomach emptying and increase rate of absorption

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22
Q

What can knowledge of first pass metabolism assist in?

A

Deciding on doses and dose schedules

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23
Q

What routes can be taken to avoid first pass metabolism?

A

Subcutaneous and intra-muscular

Inhalation and nasal

Sublingual absorption - under tongue

Rectal

Transdermal - drug administered via patch or ointment

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24
Q

What route can be affected by first pass metabolism?

A

Oral

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25
Q

Discuss the stages of first pass metabolism

A
  1. Drug taken orally travels to lumen of GI tract
  2. Drug moves to hepatic portal system, consisting of capillary network and hepatic portal vein
  3. The hepatic portal vein takes the drug to the liver
  4. The liver metabolises the drug and then the drug moves into systemic circulation
  5. Remaining amount (often little) travels into systemic circulation

Little amount of drug absorbed

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26
Q

What is the main organ of the body that metabolises drugs?

A

The liver

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27
Q

What does the hepatic portal system consist of?

A

Capillary network surrounding stomach and small intestine

Hepatic portal vein

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28
Q

What does the hepatic portal vein do?

A

Receives blood from the body and transports it into the liver for filtration and processing

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29
Q

What is the heavy first pass effect?

A

Drug taken orally are so substantially removed by the liver that it results in very little of the drug reaching systemic circulation

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30
Q

What is bioavailability?

A

The fraction (or %) of a drug that reaches systemic circulation

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31
Q

What is the bioavailability of intravenous route?

A

100%

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32
Q

What is the bioavailability of oral route?

A

40%

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33
Q

What are the benefits of intravenous medication?

A

Eliminates the process of drug absorption and breakdown by directly depositing it into the blood.

This results in the immediate elevation of serum levels and high concentration in vital organs, such as the heart, brain, and kidneys.

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34
Q

What are the benefits of tropical medication?

A
  • Low risk of systemic adverse events and drug interactions
  • Higher concentration of the antibiotic when applied to the affected area
  • Smaller amount of drug is used
  • Lack of effect on intestinal florae
  • Low cost
  • Ease of administration to a young child
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35
Q

What are the benefits of inhaled medication?

A

Inhaled drugs are localized to the target organ, which generally allows fora lower dose than is necessary with systemic delivery(oral or injection), and thus fewer and less severe adverse effects.

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36
Q

What are the four basic factors of pharmacokinetics?

A

Absorption
Distribution
Metabolism
Elimination

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37
Q

What is pharmacokinetics?

A

Describes what a body does to a drug

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38
Q

What is Tmax?

A

Time to peak concentration

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39
Q

What is Cmax?

A

Peak concentration

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40
Q

What is AUC?

A

Area under the drug concentration-time curve

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41
Q

What are the phases of metabolism?

A

Phase one
Phase two

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42
Q

What processes take place in phase one metabolism?

A

Oxidation
Reduction
Hydrolysis

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43
Q

What does phase one metabolism provide for phase two metabolism?

A

Increases the polarity of the compound and provides an active site for phase two metabolism

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44
Q

Regarding phase one metabolism:

What are the most important superfamily of metabolising enzymes?

A

The cytochrome P-450 enzymes

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45
Q

Regarding phase one metabolism:

What is drug specificity determined by?

A

The isoform of the cytochrome p-450 - specificity is relative rather than absolute

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46
Q

Regarding phase one metabolism:

What enzyme in the liver contributes to the metabolism of a wide range or drugs?

A

CYP3A4 - also found in gut and is responsible for the pre-systemic metabolism of several drugs

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47
Q

Regarding phase one metabolism:

What are examples of drugs that CYP3A4 metabolises pre-systemically?

A

Diazepam, methadone, simvastatin, CCBs

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48
Q

Regarding phase one metabolism:

What is CYP2D6 responsible for?

A

The metabolism of some antidepressants, antipsychotics and the conversion of codeine to morphine

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49
Q

Regarding phase one metabolism:

What % of the population have reduced or absent expression and what does this mean?

A

5-10%

Which means they may be immune to the analgesic actions of codeine

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50
Q

Regarding phase one metabolism:

What is CYP1A2 induced by and what is it important in?

A

By smoking and is important in the metabolism of theophylline

Therefore smokers require a higher dose of theophylline than non-smokers

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51
Q

Regarding phase two metabolism:

What does phase two metabolism involve?

A

Conjugation which increases the water solubility and enhances exertion of the metabolised compound

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52
Q

Regarding phase two metabolism:

What does conjugation involve?

A

Conjugation involves the attachment of glucuronic acid, glutathione, sulphate or acetate to the metabolite generated by phase 1

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53
Q

Regarding phase two metabolism:

What does conjugation usually result in?

A

Inactivation however a small number of drug metabolites may be active

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54
Q

What are the patterns of drug metabolism?

A

Parent molecule - Phase 1 metabolsim

Phase 1 metabolite - Phase 2 metabolism

Parent molecule - Phase 2 metabolism

Phase 2 metabolite - Phase 1 metabolism

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55
Q

What is cytochrome P450 present in?

A

Most tissues of the body

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56
Q

What does cytochrome P450 play an important role in?

A

Hormone synthesis and breakdown(including oestrogen and testosterone synthesis and metabolism)

Cholesterol synthesis

Vitamin D metabolism

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57
Q

What does enzyme induction involve?

A

Increased enzyme synthesis and therefore increased activity

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58
Q

What are the most common enzyme inducers?

A

Alcohol and smoking

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59
Q

What drugs can induce metabolising enzymes?

A

Many drugs and herbals such as:

Phenytoin
Carbamazepine
Rifampicin
St John’s Wort

60
Q

How long can induction take?

A

Weeks or even months

61
Q

What are common inhibitors of enzymes?

A

Cimetidine, valproate, erythromycin, clarithromycin, ketoconazole, CBBs and grapefruit juice

62
Q

What can pharmacokinetics allow?

A

Safer and more accurate clinical trials can be designed by scientists.

63
Q

What can gene mutations result in?

A

In excess or deficiencies or complete absence of a particular metabolising enzyme activity

64
Q

What is the purpose of metabolism?

A

Deactivate compounds and increase water solubility and so aid exertion.

65
Q

Define drug metabolism

A

Biochemical modification of pharmaceutical substances by living organisms usually through specialised enzymatic activity.

66
Q

What are the effects of drug metabolism?

A
  • Loss of pharmacological activity
  • Decrease in activity, with metabolites that sow some activity
  • Increase in activity, more active metabolites - activation of a prodrug
  • Production of toxic metabolites - direct toxicity, carcinogenic, tetragenic
67
Q

What is the relationship between the number of drugs a patient takes and the frequency of ADRs?

A

Increasing the number of medications a patient is taking increases the frequency of ADRs.

68
Q

What is the frequency of ADRs for patients on 6-10 meds?

A

10%

1 in 10

69
Q

What is the frequency of ADRs for patients on 11-15 meds?

70
Q

What is the frequency of ADRs for patients on 16-20 meds?

71
Q

How many people die annually in the US and UK as a result of ADRs?

A

US - 100,000

UK - 12-15,00

72
Q

What are the classifications of ADRs?

A

Type A - Augmented

Type B - Bizarre

Type C - Chronic

Type D - Delayed

Type E - End of treatment

Type F - Failure of treatment

73
Q

Define adverse drug reaction

A

A harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product.

74
Q

Give an example type A adverse drug reaction

A

Bradycardia with beta-blockers

Hypoglycaemia with sulphonylureas or insulin

Respiratory depression with opioids

Bleeding with warfarin.

75
Q

Give an example type B adverse drug reaction

A

Anaphylaxis with penicillin
Skin rashes with antibiotics

76
Q

Define type A ADR

A

Augmented

Result from an exaggeration of a drug’s normal pharmacological actions

Predicted, management is to reduce dose

77
Q

Define type B ADR

A

Bizarre

Novel responses that are not expected from the known pharmacological actions of the drug

Not predicted, management is to discontinue therapy

78
Q

Define type C ADR

A

Chronic/continuing

Persist for a relatively long time

79
Q

Define type D ADR

A

Delayed

Become apparent some time after the use of a medicine

80
Q

Define type E ADR

A

End of use

Associated with the withdrawal of a medicine.

81
Q

Give an example of type C ADR

A

Osteonecrosis of the jaw with bisphosphonates

82
Q

Give an example of type D ADRs

A

Leucopoenia, which can occur up to six weeks after a dose of lomustine.

83
Q

Give an example of type E ADRs

A

Insomnia, anxiety and perceptual disturbances following the withdrawal of benzodiazepines.

84
Q

What is the most common ADR?

A

Type A - 80%

85
Q

What are the features of type A ARDs?

A

Easily reversible on reducing dose and not usually life threatening

86
Q

What are the two types of Type A ARDs?

A
  1. Augmentation of the primary effect
  2. Secondary effects
87
Q

What are the reasons for Type A ADRs?

A

Too high or too low a dose

Pharmacokinetic variation (ADME)

Pharmacodynamic variation

Last two commonly occur as a result of disease

88
Q

What is pharmacokinetic variation related to?

A

Related to absorption distribution, metabolism and elimination of drug.

Decreased absorption may occur with food, formulation of drug, GI mobility and first-pass metabolism.

89
Q

What is the result of ARDs that arise through absorption problems?

A

Result in therapeutic failure - often a failure to achieve proper absorption and proper therapeutic drug levels.

90
Q

What diseases are important when drugs have a narrow therapeutic index?

A

Liver and renal

91
Q

What are the primary methods of detecting and reporting ARDs?

A
  1. Voluntary organised reporting - Yellow card system
  2. Intensive event monitoring system - Green card system
92
Q

Who can use the yellow card system?

A

Doctors, pharmacists, pharma companies, members of public

93
Q

What is the yellow cards system for?

A

All drugs including vaccines

94
Q

What does the yellow card system collect information on?

A

Side effects, medical device adverse incidents

95
Q

What is the advantage of the yellow card system?

96
Q

What is the disadvantage of the yellow card system?

A

Under-reporting & reporting bias by “bandwagon” effect.

Only 10% of serious drug reactions are reported.

Bandwagon effect ig if a new med is in the news such as vaccines for babies which were incorrectly linked to autism then the yellow card reports will increase dramatically by several thousandfold.

97
Q

Describe the green card reporting system of ADRs

A

Very organised and chooses certain populations to be studied for a short time but it will only pick up ADRs for the medicines being studied at the time

98
Q

What are drug interactions and what do they account for?

A

Drug-drug interactions occur when two or more drugs react with each other.

Drug interactions are common and account for significant patient morbidity and mortality.

99
Q

What is morbidity?

A

The condition of suffering from a disease or medical condition

100
Q

What is morality?

101
Q

In what groups does the risk of drug-drug interactions increase?

A
  • Elderly
  • Very young
  • Critically ill
  • Patients undergoing complicated surgical procedures

Patients with chronic conditions:

  • Liver disease
  • Renal impairment
  • Diabetes
  • Epilepsy
  • Asthma

Interactions which are minor in normal patients can be severe in such patients

102
Q

Define DDI

A

Modification of a drug effect by proper or concomitant administration of another drug, herb, food or drink.

103
Q

What are the types of DDI

A

Types:

  • Drug-drug interactions (DDI)
  • Herb-drug interactions
  • Food-drink interaction
  • Drink-drug interactions
  • Pharmacodynamic interactions

All have caused significant patient morbidity and mortality.

104
Q

What factors affect DDIs?

A

Remember the precipitant (factors):

  • Drugs
  • Smoking
  • Herbs
  • Food
  • Alcohol
105
Q

In what illnesses do DDIs increase?

A
  • Hypertension
  • Ischaemic heart disease
  • Parkinsonism with carbidopa and levodopa
106
Q

What are patient specific risk factors of DDIs?

A
  • Advanced age
  • Genetic polymorphisms
  • Comorbidities
  • Polypharmacy
107
Q

What are drug specific factors of DDIs?

A
  • Polypharmacy
  • Narrow therapeutic range
  • Dose
108
Q

What are other factors of DDIs?

A
  • Multiple prescribing drs
  • Self-prescription
  • Prolonged hospitalisation
109
Q

What are the aims of therapeutic drug monitoring?

A

For selected drugs therapeutic drug monitoring aimsto enhance drug efficacy, reduce toxicity or assist with diagnosis.

110
Q

What are the four key factors of bioavailability?

A

Dose of drug

Frequency of administration - less frequent the better

Timing of administration

Desired speed of onset - depends on disease treated

111
Q

What are the ways drugs can be absorbed through the GI tract?

A

Oral
Sublingual
Buccal - placing a drug between your gums and cheek
Rectal

112
Q

What is an example of a drug administered via buccal and sublingual routes?

113
Q

How do buccal and sublingual drugs work?

A
  • Small and dissolve slowly under the tongue or in the buccal cavity
114
Q

What is the ideal method for drugs that have extensive pre-systemic or first pass metabolism?

A

Buccal or sublingual

115
Q

In what cases would drugs be administered rectally?

A
  • Treat local conditions such as proctitis
  • To achieve systemic absorption (benzodiazepines)
  • Useful in the young or old
  • Patients unable to swallow
  • By-pass pre-systemic metabolism
116
Q

What are examples of medications taken orally?

A
  • Tablets
  • Capsules
  • Solutions & Suspensions
  • Modified release tablets
117
Q

Features of solutions and suspensions

A
  • Useful in the young, elderly and patients who can’t swallow
  • It May be given via nasogastric or PEG tube
  • Absorbed very quickly
  • Absorption depends on gastric emptying and is most rapid in the small intestine
118
Q

What is the rate limiting step in absorption?

A

Dissolution of tablet/capsule breakdown

119
Q

What are advantages of tablets and capsules?

A
  • Convenience
  • Accurate
  • Reproducibility of dose
  • Drug stability
  • Ease of mass production
120
Q

Why are some drugs coated?

A

Protect drug from stomach acid (omeprazole)

Protect the stomach from the drug (aspirin)

121
Q

What do modified tablets-enteric coated delay?

A

Delays disintegration of the tablet until it reaches small intestine

122
Q

Discuss percutaneous absorption

A
  • Creams, ointments and skin patches
  • Achieve local effect however the steroid will still be absorbed and may produce systemic effects
123
Q

What do skin patches allow?

A

Allow release of drug from a reservoir into the skin and then into the systemic circulation

124
Q

What are possible to obtain via skin patches?

A

Controlled, sustained blood levels of the drug such as nicotine, nitroglycerin, GRT, contraception

125
Q

What are transdermal drug delivery systems?

A

Adhesive patches containing the drug are applied on the skin

126
Q

How do drugs work in transdermal delivery systems?

A

Adhesive patches containing the drug are applied on the skin

127
Q

What do transdermal delivery systems bypass?

A

First pass hepatic metabolism

128
Q

What is inhalation of drugs used for?

A

To deliver drugs directly to lung for local effect (eg salbutamol) or to achieve a systemic effect (eg inhaled anaesthetics)

129
Q

How are inhaled drugs delivered?

A

Medicine administered via a pressurised aerosol, breath-actuated aerosol, nebuliser or dry powder device

130
Q

What are the advantages of inhaled drug delivery?

A
  • Drug delivered directly to site of action
  • Rapid effect
  • Small doses used
  • Little systemic absorption
  • Reduced adverse effects
131
Q

What are the disadvantages of inhaled drug delivery?

A

Patient education is essential

132
Q

What is meant by error?

A

Any error in the prescribing, dispensing or administration of a drug, irrespective of whether such errors lead to patient harm

133
Q

Define medication

A

A drug or other form of medicine that is used to treat or prevent disease.

134
Q

Define prescribing error

A

Incorrect drug selection for a patient

135
Q

What are the cons of prescribing errors?

A
  • Patient safety
    • Collegues
    • Unprofessional
    • Legal issues
    • Bad publicity for healthcare if gone public
136
Q

What is a medication error?

A

Mistakes may be defined as errors in the planning of an action

137
Q

How can a medication error be made?

A

Knowledge based
Rule based

138
Q

What is a rule based medication error?

A

Misapplication of a good rule (eg injecting a medication into a non-preffered site) or the application of a bad rule or the failure to apply a good rule such as using an excessive dose of a drug

139
Q

What is a knowledge based medication error?

A

Giving a medication without having established whether the patient is allergic to that medicine

140
Q

What is a slip?

A

An erroneous performance

Writing up the incorrect medicine

141
Q

What is a lapse?

A

An erroneous memory

Giving a drug that a patient is already known to be allergic to

142
Q

What is a prescribing error?

A

Incorrect dose, quantity, indication or prescribing of a contained drug

143
Q

What can lead to a prescribing error?

A
  • Illegible handwriting
  • Inaccurate medication history taking
  • Confusing with drug name
  • Inappropriate use of decimal points
  • Use abbreviations (eg AZT has lead to confusing between zidovudine and azathioprine)
  • Use of verbal orders
144
Q

What factors contribute to prescribing errors?

A

Lack of knowledge on of the prescribed drug, its recommended dose and patient details

Tired

145
Q

What can minimise the occurrence and impact of medication/prescribing errors?

A

Before prescribing consider:

  • Patient’s medication history
  • Other factors that might alter the benefits and risks of treatment
  • Select effective, safe and cost-effective medicines
    individualised for the patient
  • Adhere to national guidelines and local formularies
  • Monitor the beneficial and adverse effects of medicines
  • Communicate and document prescribing describing
  • Prescribe within the limitations of your knowledge, skills and experience
146
Q

What is the major mechanism through which drugs cross the capillary walls?

A

Bulk flow of liquid

Foundations of Medicine (56 decks)

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