Nervous System Drugs Week 2 Ch 5 PDF

NERVOUS SYSTEM Chapter 5 DRUGS NERVOUS SYSTEM: ANATOMY AND PHYSIOLOGY Command center of the body Responsible for both automatic and deliberate responses Adapts to external stimuli but also maintains internal homeostasis CNS AND PNS Central Nervous System (CNS)  Brain and spinal cord Periph...

NERVOUS SYSTEM Chapter 5 DRUGS NERVOUS SYSTEM: ANATOMY AND PHYSIOLOGY Command center of the body Responsible for both automatic and deliberate responses Adapts to external stimuli but also maintains internal homeostasis CNS AND PNS Central Nervous System (CNS)  Brain and spinal cord Peripheral Nervous System (PNS)  Cranial and spinal nerves, as well as ganglia (clusters of nerve cells) Communication occurs when electrical impulses travel along nerves and inform both the CNS and PNS of a stimulus and elicit an appropriate response NERVOU S SYSTEM  Main functional cell of the nervous system Neuron anatomy  nucleus surrounded by cytoplasm  dendrites and axons  Dendrites are responsible for receiving messages and carrying them toward the cell body.  Axons carry messages away from the cell body.  Sensory neurons (afferent) carry electrical NEURO impulses toward the CNS while motor neurons (efferent) carry them away from the CNS. N  Associative neurons carry impulses from one neuron to another. ANATO  Synaptic bulbs allow the neurotransmitters to be received by MY the dendrites.  NEUROTRAN SMITTERS C H E M I C A L S U BS TA N C E S T H AT FAC I L I TAT E T H E M OV E M E N T OF AN IMPULSE FROM ONE NEURON TO ANOTHER PNS  ANS AND SNS 12 pairs of cranial nerves Spinal nerves connect the spinal cord to vital organs, skeletal muscle, and skin PNS is further divided: Afferent (sensory) and Efferent (motor)  Cranial and spinal nerves  Autonomic Nervous System (ANS) - involuntary  Somatic Nervous System - voluntary EFFECTS OF THE PNS AND SNS ON VARIOUS ORGANS  Involuntary or automatic functions Efferent nerves send impulses to AUTON cardiac, smooth muscles, and glands and elicit an automatic OMIC response NERVO Divided into two parts:  Sympathetic nervous system US  Parasympathetic nervous system SYSTEM ANS is responsible for heart rate and contraction, gastrointestinal (ANS) (GI) motility/secretions, pupillary response, glandular secretion, bladder control, and blood vessels AUTONO MIC NERVOU S SYSTEM  PARASYMPATHETIC AND SYMPATHETIC NERVOUS SYSTEMS When one system is stimulated, the other is inhibited Parasympathetic Nervous System  Cholinergic  Responsible for both rest and energy-conserving activities “Rest and Digest”  Affected by cholinergic drugs (anti-adrenergic) Sympathetic Nervous System  Adrenergic  “Fight or Flight” response  Affected by adrenergic drugs (AKA Anti-cholinergic) NERVOUS SYSTEM DRUGS Inhibit/block the effect of neurotransmitters (NT)  Bind to the receptor site  prevent binding to receptor  “-lytic” OR Mimic their effects  Bind to receptor sites, stimulating the release of the NT or inhibit the breakdown of the NT  “-mimetic”  Mechanisms of Action (MOA) Inhibitory and excitatory Cholinergic drugs aid in the response of the PNS, while anticholinergic drugs will inhibit SYMPATHETIC the binding of Acetylcholine (ACh) AND PARASYMPATH Adrenergic drugs will mimic the action of Epinephrine and ETIC Norepinephrine NEUROTRANS MITTERS SYMPATHETIC RECEPTORS PARASYMP ATHETIC RECEPTOR S PARASYMPATHO MIMETIC (CHOLINERGIC) AND PARASYMPATHO LYTIC (ANTICHOLINER GIC) DRUGS SYMPATHOM IMETIC (ADRENERG IC) AND SYMPATHOL YTIC (ANTIADREN ERGIC) DRUGS INHALANT ANESTHETICS Brought into the body by the lungs during respiration Distributed via circulation of blood to the brain and other tissues Exact mode of action is unknown  Perhaps increase the GABA neurotransmitters, thereby inhibiting nerve function  Perhaps dissolves in the nerve cell membrane, preventing it from conducting impulses Must cross the blood-brain barrier for the anesthetic action to occur  Concentration Gradient: Method in which the inhalant is distributed from the lungs into the bloodstream and eventually to the brain Travels from the alveoli (high INHALANT concentration) to the bloodstream (low concentration) ANESTHE Distributed via circulation to areas TICS with higher blood flow such as the brain Lipid soluble Anesthetic depth determined by the amount (partial pressure) of the anesthetic gas in the brain Directly correlates to the amount of the gas circulating in the blood and alveoli INHALANT ANESTHETICS: DEPTH Anesthetic planes are maintained by the amount of gas consistently inhaled When the anesthetic gas is turned down or off via the vaporizer, less gas is brought into the alveoli If the concentration level in the alveoli becomes too low the patient will begin to wake up INHALA Reverse the concentration gradient to begin waking patient NT from episode ANESTH 100% oxygen or room air ETICS: Bloodstream (high) and alveoli (low) REVERS Normal respirations causes E THE dissipation of inhalant anesthetic, allowing elimination of the drug GRADIE upon exhalation NT Concentration of anesthetic decreases in the blood so the gas leaves the brain, and the patient wakes up INHALANT DISTRIBUTION: VAPOR PRESSURE  Determined by how quickly the liquid anesthetic becomes a gas in the vaporizer  Directly dependent on the temperature at which the liquid version of the inhalant drug is transformed into a gas for inhalation  Room temperature (surgical room, etc.) liquids  Vaporizer specific to agent (use caution when refilling)  Precision vs. non-precision vaporizer  It is imperative to always use the correct vaporizer with the appropriate inhalant anesthetic  INHALANT DISTRIBUTION: SOLUBILITY Quantifies how well COEFFICIENT an inhalant is absorbed into the bloodstream or body tissues  Will determine how quickly a patient will be induced/recovered  Potency of the anesthetic needed Inhalants are lipid soluble – quickly leave the blood and enter the brain, causing the anesthetic effect Blood: gas solubility coefficient determines how rapidly the inhalant goes from the blood to the brain and alveoli Quick induction/recovery = lower blood: gas solubility coefficient Low coefficient = rapid response to vaporizer setting change INHALANT DISTRIBUTION: MINIMUM ALVEOLAR CONCENTRATION MAC of an anesthetic - lowest concentration of the anesthetic drug needed to inhibit a response in 50% of patients when exposed to painful stimuli Referred to as the potency or “strength” of the anesthetic agent itself Low MAC inhalant = requires less of the drug to inhibit this response (more potent than an inhalant with a high MAC)  Reversible depression of the CNS (dose-dependent) INHALA Muscle relaxation NT Slight analgesia (adjuncts ANESTH required) Respiratory depression (dose- ETICS: dependent) GENERA Slight cardiac depression L Potential cardiac arrhythmias, especially halothane EFFECTS Decreased blood pressure INHALANT ANESTHETICS: ADVERSE EFFECTS Adverse effects  Dose-related hypotension that can cause decrease in renal blood flow  GI effects, including nausea, vomiting, and ileus  Death (without diligent monitoring of patient vital signs) Inhalant anesthetics should be used with extreme caution in patients that are susceptible to malignant hyperthermia as well as patients that have suffered head trauma or have increased cerebral spinal fluid pressure  LOCAL ANESTHE TICS Commonly used for procedures that do not require general anesthesia or when general anesthesia may be detrimental to the patient Nerve blocks for diagnostic testing in horses Blocks pain receptors at the site of action and prevents nerve impulses from transmission back to the CNS Local anesthetic blocks:  Regional  Local  Ring  Inferior alveolar nerve  Epidural  Phenothiazines ANESTH Benzodiazepines Alpha-2 agonists ETICS Barbiturates DRUGS: Dissociatives CATEG Opioids ORIES Reversal agents  PHENOTHIAZINES Sedation, antiemetic, antiarrhythmic, pre-anesthetic, antihistamine (various forms for administration) Adverse effects  Hypotension  Lower the seizure threshold in epileptic patients (debatable)  Caution with geriatric patients  Hepatic or cardiac disease precautions  Boxers, sight hounds, and giant breeds are sensitive to these drugs (minimum dosage)  Prolapse of the 3rd eyelid, penile prolapse in stallions, and bradycardia BENZODIAZEPINES Anticonvulsant, muscle relaxant, appetite stimulant, sedation, anti-anxiety Also used in combination with other anesthetic agents  Diazepam + ketamine (dissociative) = slow IV induction  Caution in geriatric, pregnant animals, hepatic and renal disease Benzodiazepines can be reversed with flumazenil  ALPHA-2 AGONISTS Stimulates receptors in the CNS, heart, and blood vessels, decreasing levels of norepinephrine Sedation, pre-anesthetic, analgesia, emetic in cats (xylazine only – Ruminants are extremely sensitive to xylazine) Use with caution for animals with cardiac, liver, kidney disease; seizure disorders and patients that are debilitated Adverse effects:  Muscle tremors, bradycardia, respiratory depression, sensitivity to loud noises, and polyuria in cats  Sedatives, anticonvulsants, anesthetic induction, component in euthanasia solutions; CONTROLLED SUBSTANCES MUST be administered slowly; rapid IV induction can cause apnea BARBIT Cats are extremely sensitive to this class of drugs so caution must be utilized URATES Contraindicated for use in sight hounds; fat soluble Can cause dose-dependent cardiac and respiratory depression IV administration to prevent severe tissue sloughing if administered perivascularly  Anesthetic induction, short-term anesthesia, sedation; CONTROLLED SUBSTANCES Avoid using in patients with head traumas, seizure disorders, hypertension and cardiac disease, hepatic disease, renal disease, DISSOCIA glaucoma TIVES Can cause respiratory depression, increased salivation, muscle tremors, painful when given intramuscularly Typically combined with other anesthetic drugs  Derived from opium poppy alkaloids, opioid receptors are found throughout the body; most of these drugs work on receptors in the brain and spinal cord 4 types of receptors (mu, kappa, sigma, delta) OPIOID Responses are dependent on S which receptor is acted upon Drugs can be agonists, partial agonists, agonist-antagonists, or antagonist See Table 5.20 for opioid receptors and their function OPIOIDS: USES AND PRECAUTIONS Used as pre-anesthetic, analgesic, neuroleptic analgesic, and antitussive Caution with hepatic and renal disease, geriatric patients, hypothyroidism, hypoadrenocorticism, and respiratory disease Adverse effects can be constipation, nausea and vomiting, dependence, urine retention, and sensitivity to sound High potential for abuse in humans FENTANYL PATCHES Opiate narcotic medication used to treat patients suffering from moderate to severe pain Predominantly used in dogs and cats for postoperative pain control after major surgery, and chronic or severe pain from injury, disease or cancer Can be applied to lumbosacral region, lateral neck/thorax, rear limb below the hock, or inguinal areas Delay in time before medication takes effect, alternate analgesia until relief from pain occurs is recommended NON- CLASSIFIE D ANESTHETI CS These drugs do not fall into the chemical makeup of other classifications Unique compositions Uses are similar to other anesthetic and sedative drugs  Most anesthetic drugs are not all- inclusive DRUG Some have undesirable effects when used singularly, and lack COCKTA desired results ILS Anesthetic protocols often involve multiple drug combinations to achieve desired effects and optimize safety BEHAVIORAL MEDICATIONS Used to treat a variety of behavioral disorders in veterinary medicine Behavior modification + training + Rx:  Fears and phobias  Separation anxiety  Compulsive disorders  Cognitive dysfunction These drugs may not become effective for several weeks or more, and should not be discontinued abruptly