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121 > 1.2 > Flashcards

1.2 Flashcards

1
Q

What are the 4 types of receptors?

A

Ion channel
Enzyme associated
Nuclear receptor
G-protein coupled

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2
Q

How do ion channels work?

A

Allow ions into cell

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3
Q

What are G-protein receptors made up of?

A

7 transmembrane protein receptor which is associated with a G-protein intracellularly

The G-protein is made up of 3 subunits (alpha, beta, gamma)

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4
Q

How are G-protein receptors activated and inactivated?

A 
Inactive - with GDP bound
Activated - GTP
- An agonist binds extracellularly 
- This leads to conformational change
- Ligand (GTP) exchanged for GDP
- The normally alpha subunit dissociates from beta-gamma subunits and goes on to perform effector functions
- Alpha subunit has an intrinsic GTPase
- GTPase cleaves GTP and then it re-associates with other subunits in it's inactive state
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5
Q

What are these examples of: adrenoceptors, muscarinic receptors.

A

G-protein coupled receptors

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6
Q

What are the 4 ways drugs are handled by the body?

A

ADME mnemonic

  • Absorption
  • Distribution
  • Metabolism
  • Elimination
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7
Q

What is bioavailability?

A

Percentage of total oral dose of a drug that reaches plasma

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8
Q

What affects absorption of a drug?

A

Lipid-water solubility

1st pass metabolism (hepatic degradation of portal blood)

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9
Q

What are high bioavailability drugs used for in general?

A

Treating systemic pathology (e.g. atherosclerosis)

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10
Q

What are low bioavailability drugs used for in general?

A

Treating GI infection (e.g. oral vancomycin)

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11
Q

What is the bioavailability of an IV drug?

A

100% because all of the drug ends up in the plasma

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12
Q

What is vancomycin?

A

An glycopeptide antibiotic

Very useful against gram positive bacteria (especially MRSA)

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13
Q

Side effects of vancomycin.

A

Ototoxicity
Renal toxicity

And when given intravenously as a bolus it causes red man syndrome (allergic response, massive rash)

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14
Q

List two characteristics of a high partition drug (one that passes epithelium easily).

A

Small, non-ionised

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15
Q

Drugs are weak acids or bases, what does their ionisation depend on?

A

pH

- Acid: more ionised in alkaline environment and less ionised in acidic environment

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16
Q

What does pKa describe?

A

Relative ionisation

17
Q

Where along the GIT are weakly acidic drugs mainly absorbed?

A

The gastric mucosa (pH 3.5)

Because equilibrium shifts to favour the non-ionised HA rather than the ionised H+ and A= (dissociative state)

18
Q

What is the 2 phases of drug metabolism?

A

Phase 1: oxidation and hydroxylation

Phase 2: glucuronate/sulphate conjugation

19
Q

Which enzymes are involved in phase 1 drug metabolism (oxidation/hydroxylation)?

A

CYP450

20
Q

Why are the byproducts of oxidation/hydroxylation important?

A

They can be toxic

E.g. paracetamol undergoes phase 1 hydroxylation and rearrangement. The product is NAPQI which can undergo toxic reactions with proteins and nucleic acids at high levels

21
Q

What is the purpose of glucuronate and sulphate conjugation?

A

Stabilise and increase solubility

22
Q

Some drugs can interact with the CYP450 mono-oxygenase system. This system is responsible for number of phase 1 drug metabolisms.

Which drugs are potent inducers of the CYP450 system?

A

There are many cytochrome P450 enzymes each affected by slightly different drugs.

Rifampin (antibiotic) and carbamazepine (anticonvulsant + analgesic) are a potent inducer of CYP1A2, CYP2C9, CYP2C19, CYP3A4, CYP3A5

Other potent inducers:
- Phenobarbital (epilepsy treatment)
- Phenytoin (anticonvulsant)
Hypericum perforatum (St. John’s wort)

23
Q

Some drugs can interact with the CYP450 mono-oxygenase system. This system is responsible for number of phase 1 drug metabolisms.

Which drugs are potent inhibitors of the CYP450 system?

A
  • Amiodarone
  • Cimetidine
  • Ciprofloxacin
  • Fluvoxamine
  • Trimethoprim
  • Metronidazole
  • Paroxetine
  • Terbinafine
  • Quinidine
  • Fluoxetine
  • Clarithromycin
24
Q

Define elimination and excretion.

A

Elimination: removal of active drug from the body

Excretion: removal of drug from the body by loss

25
Q

Where does water and lipid soluble drugs get eliminated from the body?

A

Water soluble - urine (in CKD, drug activity increased)

Lipid soluble - bile

26
Q

Define affinity and efficacy.

A

Affinity: ability to bind to a receptor

Efficacy: ability to generate a response

27
Q

Define full agonist and partial agonist.

A

Full agonist: can generate maximum response

Partial agonist: cannot generate maximum response

28
Q

What does the following describe:

  • an antagonist which dissociates away
  • can be overcome
A

A competitive antagonist (same binding site as agonist)

29
Q

What does the following describe:

  • an antagonist which removes receptor once bound
  • increasing agonist has no effect
A

Non-competitive (irreversible (covalent))

30
Q

What are allosteric agonists or inhibitors.

A

THey bind at different site

31
Q

What are G-proteins activated by?

A

GTP, causing subunit dissociation

32
Q

Increased ionisation of drugs does what?

A

Reduces transmembrane passage

33
Q

What is zero order elimination?

A

Has a fixed amount remove per hour, with variable half-life

34
Q

How can competitive antagonists be overcome?

A

By increasing agonist concentration

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