Schizophrenia: drugs

Synaptic transmission Mechanisms of drug action Drugs used with schizophrenia

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Neurones

Sou

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Neuronal cell bodies

Synapses occur at the junctions

Axons psyc

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Synapses

Neurones transmit signals electrically along their axons

The synapses (junctions between neurones) transmit signals chemically

Most drugs act by interfering with events at the synapse

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Synapse

Vesicles filled with neurotransmitter

Location of receptors (post-synaptic density)

Synaptic cleft

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edu

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Vesicles release neurotransmitter into synaptic cleft

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Neurotransmitter binds to receptors & activates them

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Enzymes are released to break down the neurotransmitter

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Excess neurotransmitter is taken up by the pre-synaptic neurone

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Vesicles are replenished with new & reused neurotransmitter

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Drug Therapies

Increase synaptic activity by: Causing more neurotransmitter to be

released Introducing a chemical that acts like the

neurotransmitter Preventing breakdown of neurotransmitter Preventing reuptake of neurotransmitter

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Drug therapies

Decrease activity by: Increasing rate of neurotransmitter

breakdown Blocking off receptors

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Antipsychotic medication

Neuroleptics (e.g. chlorpromazine) bind to DA receptors without activating them

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Effectiveness

Older (typical) drugs (e.g. chlorpromazine) Short term beneficial effect in 75% of

patients (Davis et al, 1989) Long term beneficial effect in 55-60%

(Davis et al, 1993) Most effective against positive symptoms High risk of side effects

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Side effects

Extrapyramidal side effects (EPS) Parkinson’s-type symptoms Postural & motor abnormalities

Other side effects Sedation Weight gain Seizures

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Effectiveness

Newer (atypical) drugs (e.g. clozapine) As effective as typical drugs on positive

symptoms; better for negative symptoms (Bilder et al, 2002)

More effective with treatment-resistant patients (DeNayer et al, 2003)

Less risk of EPS, but other side effects may occur (e.g. blood disorders)

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Typical vs. atypical

DA receptor

tightly bound; slow release

from receptor

loosely bound; fast release

from receptor

Drug

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