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INTRODUCTION TO CNS PHARMACOLOGY

INTRODUCTION TO CNS PHARMACOLOGY. An overview of the CNS with a focus on Most drugs that affect the central nervous system (CNS) act by altering some step in the neurotransmitters mediating the physiological and pathological responses is essential for understanding neuropharmacology.

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INTRODUCTION TO CNS PHARMACOLOGY

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  1. INTRODUCTION TO CNS PHARMACOLOGY

  2. An overview of the CNS with a focus on Most drugs that affect the central nervous system (CNS) act by altering some step in the neurotransmitters mediating the physiological and pathological responses is essential for understanding neuropharmacology.

  3. Nature of Centrally acting Drugs • Drug first needs to cross the blood-brain barrier, so it needs to be lipophilic and unionized, • or it could be actively transported across the barrier. • This ability to cross the blood-brain barrier is essential of the drug because without this,the drug will not be effective.

  4. Ion channels & NT receptors Voltage-gated channels Respond to AP Fast action potentials Include the sodium channels responsible for action potential propagation Ligand-gated channels (Inotropic) Chemically-gated Respond to chemical neurotransmitters (NTAs) that bind to receptor subunits of the channel

  5. G-protein coupled receptors (Metabotropic) • NTAs also bind to G protein-coupled receptors • Direct opening voltage-channel through SM

  6. CNS PHARMACOLOGY ROLE OF THE ION CURRENT CARRIED BY THE CHANNEL SYNAPSE- communication EXCITATORY POSTSYNAPTIC POTENTIALS 2.INHIBITORY POSTSYNAPTIC POTENTIALS

  7. CNS PHARMACOLOGY EXCITATORY POSTSYNAPTIC POTENTIALS (EPSPs) Depolarizing potential change Generated by Opening of sodium or calcium channels Closing of potassium channels

  8. CNS PHARMACOLOGY EXCITATORY POSTSYNAPTIC POTENTIALS (EPSPs) Na+, K+, Ca+2 -70 mV

  9. CNS PHARMACOLOGY INHIBITORY POSTSYNAPTIC POTENTIALS (IPSPs) Hyperpolarizing potential change Generated by Opening of potassium or chloride channels

  10. CNS PHARMACOLOGY INHIBITORY POSTSYNAPTIC POTENTIALS (IPSPs) K+ , Cl- at the postsynaptic , Ca+2 at the presynaptic -70 mV

  11. CNS PHARMACOLOGY SITES AND MECHANISMS OF DRUG ACTION Some drugs exert their effect through direct interactions with molecular components of ion channels on axons Carbamazepine Phenytoin Local anesthetics and somedrugs usedfor general anesthesia

  12. CNS PHARMACOLOGY SITES AND MECHANISMS OF DRUG ACTION Most drugs exert their effect mainly at the synapses

  13. CNS PHARMACOLOGY SITES AND MECHANISMS OF DRUG ACTION May alter Neurotransmitter Synthesis Storage Release Reuptake Metabolism

  14. CNS PHARMACOLOGY SITES AND MECHANISMS OF DRUG ACTION Activate or block Pre- and postsynaptic receptors for specific transmitters

  15. CNS PHARMACOLOGY CNS ORGANIZATION Major excitatory transmitters Aspartate Glutamate

  16. CNS PHARMACOLOGY CNS ORGANIZATION 2 TYPES OF NEURONAL SYSTEM Major inhibitory transmitters: Gamma amino butyric acid (GABA) Glycine

  17. CNS DRUGS CLASSIFICATION Chemical structure Benzodiazepines, Butyrophenones Pharmacological MAO inhibitors, SSRI, Clinical use Antidepressants, Antipsychotic agents

  18. Classification sedatives –hypnotics drugs “Drugs that reduce anxiety and cause sleep” Examples Barbiturates, benzodiazepines

  19. Classification 2. Antipsychotic drugs (neuroleptics, anti-schizophrenia “Drugs that are effective in relieving symptoms of schizophrenic illness” Examples Clozapine, Haloperidol

  20. Classification 3. Antidepressant drugs “ Drugs that alleviate the symptoms of depressive illness” Examples TCA, MAOI, SSRI

  21. Classification 4. Psychomotor stimulants (Psychostimulants) “Drugs that can cause wakefulness and euphoria” Examples Amphetamines, Cocaine, and caffeine

  22. 5. Anticonvulsants: Drugs that prevent or suppress convulsions. 6.Analgesics: Drugs that relieve pain without causing loss of consciousness. 7. General anesthetics: Drugs that produce reversible depression of the CNS leading to loss of consciousness and loss of sensations surgical operations.

  23. Definitions…. • Tolerance A decreasing response to repetitive drug doses. Higher doses are needed to produce the same effect. • Cross tolerance:means that individuals tolerant to one drug will be tolerant to other drugs in the same class or other classes

  24. Dependence a state of relying on or chronic need, as for a drug • A physiologic or psychological need for a drug

  25. physical dependence (physiological dependence)  in which the drug is used to prevent withdrawal symptoms • psychological dependence in which the drug is used to obtain relief from tension or emotional discomfort; called also emotional dependence.

  26. Anxiolytic and Hypnotic Drugs

  27. Sedative – Hypnotics • Anxiety disorders • Is unpleasant state of tension, apprehension or uneasiness . “ A fear that seems to arise from a sometimes unknown source” .

  28. Anxiety is a universal human characteristic which serves as adaptive mechanism to warn about an external threat by activating the sympathetic NS. Anxiety is in many cases secondary to organic disease (e.g MI, angina, peptic ulcers) which themselves require specific therapy. Or due to Drug-Induced. or Drug Withdrawal

  29. Manifestations of anxiety: • Verbal complaints. The patient says he/she is anxious, nervous. • Somatic and autonomic effects. The patient is restless and agitated, has tachycardia, increased sweating, breathlessness, tremor, fatigue, disturbed sleep. . • Social effects. Interference with normal productive activities.

  30. Anxiety become pathological when: 1.Fear is greatly out-of-proportion to risk/ severity of threat. 2.Response continues beyond existence of threat. 3.Social or occupational functioning is impaired.

  31. insomnia is "difficulty initiating or maintaining sleep, or both" or the perception of poor quality sleep.

  32. BASIC PHARMACOLOGY OF SEDATIVE-HYPNOTICS • An effective sedative(anxiolytic) agent should reduce anxiety and exert a calming effect with little or no effect on motor or mental functions. • A hypnotic drug should produce drowsiness and encourage the onset and maintenance of a state of sleep that as far as possible resembles the natural sleep state.

  33. General anesthetic: the drug which causes reversible and controllable loss of consciousness associated with absence of response to pain. • Sedation Hypnosis  Anesthesia  Coma and death. After progressive dose increments.

  34. BASIC PHARMACOLOGY OF SEDATIVE-HYPNOTICS • Hypnotic effects involve more pronounced depression of the central nervous system than sedation, and this can be achieved with most sedative drugs simply by increasing the dose. • Graded dose-dependent depression of central nervous system function is a characteristic of sedative-hypnotics.

  35. Classification of anxiolytic and hypnotic drugs 1. Benzodiazepines “most important class” 2. Hydroxyzine – H1 blocker. 3. β – receptor antagonist “propranolol”. • Use to treat some forms of anxiety, particularly when physical (autonomic) symptoms (sweating, tremor, tachycardia) are severe. 4. barbiturates

  36. SEDATIVE/HYPNOTICSANXYOLITICS GABAergic SYSTEM

  37. Ⅰ.Benzodiazepines

  38. Ⅰ.Benzodiazepines • Classification • Short acting  e.g. Midazolam • Intermediate acting  e.g. Alprazolam • Long acting  e.g. Diazepam • The BNZ for most part, end in “pam” or “lam’

  39. MOA of Benzodiazepines (BDZ)

  40. Mechanism of action of the benzodiazepines

  41. Benzodiazepines MOA

  42. The main effects of benzodiazepines are: 1. Reduction of anxiety at low doses. 2. Sedation and hypnosis at higher doses. 3. Anterograde amnesia: temporary impairement of memory ,decreased person’s ability to learn and form new memories. 4. Anticonvulsant. 5. Muscle relaxant .

  43. Therapeutic Uses of BDZs 1. Anxiety disorders: for continued sever anxiety and NOT to alleviate the normal stress of every day of life. Only for short period. Addiction potential. • Benzodiazepines with intermediate or long durations of action are favored • Alprazolam for Phobic and panic attacks

  44. Therapeutic Uses of(BDZ) 2. Sleep disorders: • latency of sleep onset is decreased. • total duration of sleep is increased. Both effects decline after prolonged use. Nursing points • Dependence can occur with long –term use of all hypnotics. use the minimum dose for the minimum time… • Depression can cause insomnia

  45. Therapeutic Uses of(BDZ) 3. Anticonvulsant: clonazepam diazepam and lorazepam. 4. Preanesthetic medication: to produce amnesia in anxiety provoking and unpleasant procedures as endoscopy and dental procedures.

  46. 5.Muscular disorders: in skeletal muscle spasm , spasticity of multiple sclerosis and cerebral palsy. 6. Control of ethanol and other hypnotic withdrawal.

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