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Flashcards in Pharmacology Deck (588)
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What are they drug administration routes?

Oral (per os; p.o.)
Intravenous (i.v.) - immediately into circulation
Intramuscular (i.m.) - slow release
Subcutaneous (s.c.) - under skin surface into fat tissue
Buccal - cheek
Transdermal - through skin i.e. nicotine patch
Intracerebroventricular (i.c.v.) - into ventricles open brain


Describe oral administration

Easy; no sterile preparations, special skill or apparatus
Convenient and preferred by patients


What are some of the problems associated with oral administration?

Stomach acidity - acid labile (cleaved) drugs broken down in stomach e.g. benzyl penicillin
Proteolytic enzymes - protein drugs digested by enzymes e.g. insulin
Poor absorption - erratic e.g. pyridostigmine
No absorption - quaternary amine (permanently charged) e.g. tubocurarine
Pre-systemic metabolism - absorbed but metabolised in 1st-pass e.g. glyceryl trinitrate


What are the benefits of intravenous administration?

Immediately enters systemic circulation
Know exactly how much is absorbed, all does enters circulation
Instantaneous peak plasma conc.
Slow injection/infection, can be stopped at anytime if adverse reactions


Describe some of the disadvantages of iv administration?

Needs sterile apparatus and skill


Give examples of iv drugs

Tubocurarine - muscle relaxant during surgery
Pyridostigmine - reverse effects of tubocurarine
Thiopental - GA


Discus the advantages and disadvantages of intramuscular and subcutaneous administration and give examples

Advantages - avoid some oral problems, absorbed from injection, less skill than iv
Disadvantages - slow to reach peak conc., sterile prep. and equipment
SC - insulin, sustained release
IM - diazepam, absorption is slow and erratic


Discuss sublingual/buccal administration

Advantages - absorbed drugs doN'T enter portal vein, enter vena cava (to heart), avoid 1st-pass metabolism
Glyceryl trinitrate rapidly absorbed to relieve angina


Discuss rectal administration

Useful when other routes are not suitable
Nausea - prochlorperazine
Child epilepsy - diazepam
Asthma - aminophyline
Arthritis - indomethacin


Describe transdermal administration

Through skin thus limited to potent, lipophilic drugs
Depot (slow over numerous weeks) release
Usually in plaster
Trinitrin (glyceryl trinitrate)
Hyoscine - motion sickness
Nicotine - smoking cessation


Discuss inhalation administration

Large SA, rapid absorption and onset
Gaseous/volatile anaesthetics - halothane
Bronchodilators - salbutamol


What is the importance of first-pass (pre-systemic) metabolism?

Metabolise any drug taken up through portal vein
Parent drug is broken down to metabolites: useful in case of aspirin as active compound is v acidic so prodrug aspirin given, metabolites are active


Describe the process of first pass metabolism

Drug absorbed from GIT enter mesenteric capillary network
Drug carried to liver via portal vein
Extensive hepatic metabolism by hepatic enzymes
Metabolites enter systemic circulation


What are the methods of transport across biological membranes? (PHARM)

Filtration - through gaps
Passive - through cell wall
Facilitated (saturable) - Na/glucose, absorption of vit. B12
Active (saturable) - levodopa (L-DOPA)
Pinocytosis - absorption of botulinum toxin


What factors affect absorption from the GIT?

Changing pH of tract - alters ionisation state of drugs (pH>pKa will ionise)
Gastric emptying - stomach-intestines, faster less absorption
Varying transporter expression - patterns, amounts at different areas
GIT motility - digestion, faster less absorption
Interaction with food - won't be taken up


Describe absorption from muscle

Perfusion limited thus slow absorption as larger blood flow, faster absorption
Capillary wall fenestrations - drugs move past endothelial cells, ionisation isn't an issue
Little effect on molecular size


What are the two phases of metabolism?

Phase 1: functionalisation
Phase 2: conjugation


Describe phase 1 of metabolism

Introduce groups that undergo phase 2 reactions
Mainly oxidation - also reductions, hydrolyses
Often increase polarity


Describe phase 2 metabolism

Addition of large, heavy groups: glucuronic acid, sulphate, AAs, make large so not absorbed well, can't bind receptor
Marked increase in polarity
Increase rate of excretion as tag for removal


What are the two main sites of excretion?

Kidney - urine
Liver - bile, faeces
(Lungs - volatile anaesthetics, ethanol
Milk - lactating mothers)


What is the functional unit of the kidneys?

The nephron


Describe entry of drugs in the kidney

Drugs filtered at glomerulus
Active secretion of drugs at proximal convoluted tubule - separate carriers for acids and bases


Describe the reabsorption of drugs in the kidney

Active re-uptake at glomerulus
Passive reabsorption of lipophilic molecules along proximal convoluted tubule


How are weak electrolytes excreted and how is this aided?

pH-partition - non-ionised passively reabsorbed thus more ionised, more remains in tubular fluid, more excreted
Aided by altering pH (of urine) to cause greater ionisation of drug


Give examples of excretion of weak electrolytes

Salicylic acid (aspirin metabolite) - pKa 3.0
Increase excretion by making urine more alkaline using sodium bicarbonate, sodium lactate

Amphetamine - pKa 9.8
Make urine acidic using ammonium chloride


Describe the excretion of penicillin and how it can be manipulated

Actively secreted into tubular fluid, short t1/2 ~30mins
pKa = 2.7
Lower pH - lower degree of ionisation
Non-ionised form passively reabsorbed from urine
Effective increase t1/2


Describe excretion of drugs in bile

Passive diffusion
3 active mechanisms dependent on: MW, polar, acidic, glucuronide metabolites usually good substrates
High MW drugs excreted unchanged e.g. oubain


Describe the process of enterohepatic recirculation

Drug absorbed, carried to liver
Converted to glucuronide conjugate
Conjugate secreted in bile
Bile containing conjugate secreted in response to food
Conjugate hydrolysed by B-glucuronidase in GI flora
Drug reabsorbed


Define drug

Substance that affects the body, elicits a change in physiology


Explain receptor theory

Drug will not have activity unless binds to specific receptor thus inducing response