Antidepressants Flashcards

1
Q

What is psychosis?

A

can be SPLIT into SCHIZOPHRENIA and the AFFECTIVE DISORDERS (mania and depression)

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2
Q

What are the emotional and biological symptoms of depression?

A

EMOTIONAL SYMTPOMS:

  • misery, apathy
  • pessimism
  • low self-esteem
  • loss of motivation
  • anhedonia

BIOLOGICAL SYMPTOMS:

  • slowing of thought and action
  • loss of libido, loss of appetite
  • sleep disturbance
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3
Q

What are the features of unipolar depression (/depressive disorder)?

A
  • Mood swings are in same direction
  • Relatively late onset (adulthood)
  • Unipolar depression can be split into reactive depression (75%) and endogenous depression (25%)

Reactive depression: depression in response to stressful life events, that is non-familial
Endogenous depression: depression that is unrelated to external stresses, with a familial pattern

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4
Q

What are the features of bipolar depression (/manic depression)?

A
  • Oscillating depression and mania (hyper-excitability with symptoms opposite to depression)
  • This is less common than unipolar depression, and tends to have an early adult onset
  • There is a strong hereditary tendency
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5
Q

What are the treatments for unipolar and bipolar depression?

A

uni polar: drug treatment (same for reactive and endogenous depression)

bipolar : lithium

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6
Q

What is the monoamine theory of depression?

A

Noradrenaline & 5-HT are the two monoamines involved in this hypothesis

The changes in NA and 5-HT that we see are rapid – there is a rapid onset

However, the clinical effect can take weeks, before we see the optimal action of the drug

There is a dissociation in between the neurochemical change and the antidepressant effect

  • In response to many antidepressant drugs, we see a down-regulation: α2, β, 5HT receptors - often correlates in a more timely fashion with the onset of clinical drug effectiveness

It may be these changes therefore, that are responsible for the clinical drug effects

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7
Q

What are TCAs?

A

tri-cyclic anti-depressant
e.g amitriptyline

  • two main chemical groups: the dibenzazepines and dibenzcycloheptenes
  • TCAs are three-ringed structures
  • All are neuronal monoamine re-uptake inhibitors
  • prevent reuptake of NA and 5-HT much more so than dopamine -> potentiate the action of these monoamines for much longer

*delayed down-regulation of b-adrenoceptors and 5HT2 receptors

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8
Q

What are the pharmacokinetic factors of TCAs?

A
  • Rapid oral absorption – all TCAs are given orally and absorbed orally
  • Highly plasma protein bound (90 – 95% of TCAs are PPB)
  • Hepatic metabolism - this generates active metabolites (weaker) -> then undergo renal excretion (as glucuronide conjugates)
  • Plasma t1/2 (10-20 hours) – relatively long half life, so can be given once a day (long duration of action)
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9
Q

What are the unwanted effects of TCAs at therapeutic dosage?

A
  • Atropine-like effects with amitriptyline: dry mouth, blurred vision, constipation, urinary retention
  • Amitriptyline seems to have more muscarinic antagonist activity than some of the other TCAs
  • Postural hypotension (mediated through the vasomotor centre) – this is a CENTRAL EFFECT
  • Sedation (TCAs cause H1 antagonism) – patients feel drowsy during the day - Many depressed patients have trouble sleeping, so this can be taken advantage of
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10
Q

What are the unwanted side effects of TCAs at acute toxicity?

A
  • CNS: excitement, delirium, seizures -> coma and respiratory depression
  • CVS: cardiac dysrhythmias -> ventricular fibrillation and sudden death
  • With TCAs that are muscarinic antagonists, we also affect vagal input to the heart

*commonly utilised in attempted suicid

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11
Q

What are some interactions that TCAs undergo?

A
  • PPB: we see increased TCA effects with co-administration with aspirin and phenytoin (anti-convulsant)
  • Warfarin can displace TCAs from their binding sites, which moves plasma levels of TCA into a toxic range
  • Hepatic microsomal enzymes metabolise TCAs, so TCA effects increase if co-administered with drugs that are metabolised by the same enzyme system (e.g. neuroleptics and oral contraceptives)
  • Potentiation of CNS depressants with TCAs (alcohol in particular)
  • There is an interaction with antihypertensive drugs (monitor BP closely) – difficult to predict
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12
Q

What are MOAIs?

A

monoamine oxidase inhibitors e.g phenelzine

  • The mechanism of action involves monoamine oxidase-A (NA & 5-HT) and monoamine oxidase-B (DA)
  • MAO-A has a preference for NA and 5-HT, whereas MAO-B has a preference for dopamine
  • The inhibition is irreversible, which leads to a long duration of action (patients need to take these daily)

We see rapid neurochemical changes: rapid increase in cytoplasmic NA & 5-HT
-This is because we are blocking the breakdown of NA and 5-HT with MAOIs – enhanced activity in brain

  • delayed effects with these drugs, in terms of the clinical response
  • down-regulation of β-adrenoceptors & 5-HT2 receptors - corresponds with the onset of the clinical effectiveness of the drug
  • MAOIs are not ENTIRELY SELECTIVE – they result in the inhibition of other enzymes
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13
Q

Describe the chemical structure of MAOI?

A
  • All of the MAOIs have got a single ring structure
  • There is a range of different chemical classes.

Phenelzine is a hydrazine. It has a single ring with a carbon side chain. On the end is a hydrazine functional group. This group is VERY REACTIVE. It is this functional group that forms the covalent bonds with the MAO enzyme (irreversible inhibition).

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14
Q

What are the pharmacokinetic features of MAOIs?

A
  • Rapid oral absorption (MAOIs are taken orally, either once a day or every other day)
  • Short plasma t1/2 (few hours) but longer duration of action due to irreversible inhibition
  • Metabolised in the liver and excreted in the urine
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15
Q

What are the unwanted effects of MAOIs?

A
  • Atropine-like effects (much less than with TCAs)
  • Postural hypotension (common) – probably a vasomotor mediated effect
  • Sedation with long-term usage (and seizures in over dose)
  • Weight gain (possibly excessive) – associated with increase appetite with MAOIs
  • Hepatotoxicity (due to hydrazines) – this is rare (e.g. 1 in 10,000 patients)
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16
Q

Why are the drug interactions of MAOIs? a serious problem?

A

TYRAMINE: an indirectly acting sympathomimetic amine (has actions similar to activation of the SNS)

  • Under normal circumstances, there are not sufficient levels of tyramine in the body to cause problems
  • However, tyramine is metabolised by MAOs (so if they are being inhibited, we may encounter problems)
  • ‘Cheese reaction’: Tyramine-containing foods + MAOI leads to a hypertensive crisis
    > Throbbing headache, increased blood pressure and intracranial haemorrhage
  • MAOIs can react with TCAs to produce hypertensive episodes (avoid)
  • MAOIs can react with pethidine to cause hyperpyrexia, restlessness, coma & hypotension
17
Q

What is moclobemide?

A

a reversible MAO-A inhibitor (RIMA) – it is SELECTIVE

- has fewer drug interactions, but a shorter duration of action (taken 2-3 times a day)

18
Q

What are SSRIs?

A

selective serotonin reuptake inhibitor e.g fluoxetine

  • Selective 5-HT re-uptake inhibition (SSRIs selectively inhibit the reuptake of 5-HT)
  • propose less troublesome side effects, so they are safer in the case of overdose
  • But they are less effective against severe depression
19
Q

What are the pharmacokinetics of SSRIs?

A
  • Oral administration of SSRIs
  • Plasma t1/2 (18-24 hours) – given once a day, orally
  • There is a delayed onset of action (2-4 weeks before we see the optimal anti-depressant action of SSRIs)
  • Fluoxetine competes with TCAs for the hepatic enzymes (so avoid co-administration
20
Q

Describe the structure of SSRIs

A

There are a couple of ring structures with an aliphatic side chain

21
Q

What are the unwanted effects of SSRIs?

A
  • There are fewer unwanted effects than TCAs/MAOIs
  • 10% of patients complain of GI side effects (nausea, diarrhoea)
  • Some people complain of insomnia and 30% of patients complain of loss of libido
  • SSRIs can interact with MAOIs (avoid co-administration)
22
Q

What is venlafaxine?

A

(an SNRI): This drug shows dose-dependent Reuptake inhibition of both 5-HT and NA

  • 5HT > NA (SNRI) – we can increase the dose to get increase of NA reuptake inhibition
  • If you give a very high dose of venlafaxine, you can inhibit the dopamine transporter too
  • This is 2nd line treatment for severe depression
23
Q

What is mirtazapine?

A

α2 Receptor antagonist

  • increases NA & 5HT release in the brain
  • Other receptor interactions may contribute to antidepressant activity (sedative – histamine antagonism)
  • Useful in SSRI-intolerant patients