Anesthetic Drugs (Veterinary)

ANESTHETIC DRUGS Anesthetic Drugs  Anesthetics: Render animal or person with no sensation  Two types of anesthesia: General and Local  General Anesthesia: Reversible loss of sensation associated with unconsciousness  Local Anesthesia: Reversible loss of sensation in a regional area of the body without loss of consciousness Anesthetic Drugs  Analgesia: Compounds designed to decrease the perception of pain but not necessarily cause total loss of sensation  Rimadyl/Aspirin: Example of analgesic, decreases pain associated with inflammation, but does not produce anesthesia Anesthetic Drugs    C-I: Has an extreme potential for abuse, has no approved medicinal purpose in the US. C-II: Has a high potential for abuse, may lead to severe dependency. Includes hydromorphone, pentobarbital, and morphine. C-III: Has some potential for abuse, may lead to low to moderate dependence or high psychologic dependence. (Buprenorphine) Anesthetic Drugs C-IV: Has a low potential for abuse, limited dependence, includes such drugs as phenobarbital and diazepam (Valium)  C-V: Is subject to state and local regulations, has low potential for abuse: Tylenol with Codeine  Anticholinergics  Atropine Blocks stimulation of vagus nerve Reduces salivation Reduces gastrointestinal activity Pupil dilation (mydriasis) Reduces tear production Promotes bronchodilation Will cross BBB and placenta  Route: IV, IM, or SC Anticholinergics  Glycopyrrolate Similar effects of atropine Onset of 2-3 min. after IV injection Longer duration (2-3 hours v.s. 60 minutes) Less likely to cause tachycardia Suppresses salivation more effectively Does not cross placental barrier Atropine still best for treatment of bradycardia  Route: IV, IM, or SC Phenothiazine  Acepromazine (Ace) Phenothiazine  Tranquilizer that produces mentally relaxed state Used to be used for storm anxiety, found to be that the animal is paralyzed, but still has massive anxiety Xanex now more often used for anxiety Phenothiazine Phenothiazine block alpha 1 receptors relaxation of smooth muscles and vasodilatation  Causing a sharp drop in blood pressure  No analgesic effects  Benzodiazepines  Benzodiazepine class: Diazepam (Valium) Zolazepam (Telazol) Midazolam (Versed) Benzodiazepines      Decrease risk of seizure activity Overall safe, few side effects Very effective when given intravenously Diazepam is absorbed irregularly when injected SQ or IM, very painful Midazolam pH is more basic, thus less painful when administered IM or SQ Benzodiazepines Very effective when given intravenously  Diazepam is absorbed irregularly when injected SQ or IM  Diazepam is painful when injected IM or SQ due to its acidic pH  Midazolam pH is more basic, thus less painful when administered IM or SQ  Benzodiazepine Reversal  Flumazenil: GABA antagonist Rare that these drugs ever need reversing  Used commonly in liver patients  Alpha-2 agonists  Alpha-2 Agonists Xylazine (Rompun) Detomidine (Dormosedan) Dexmedetomidine (Dexdomitor) Zenalpha (medetomidine +vatinoxan) Exert their effects by stimulating alpha-2 receptors  Compounds produce a calming effect  Dexdomitor the only one with analgesia effects  Alpha-2 agonists Xylazine is used in most species for sedation or may be combined with other drugs in a preanesthetic regimen  Cattle VERY sensitive, horse, dog/cats less, swine least sensitive  Xylazine sedative doses produces vomiting in about 90% of cats and 50% of dogs  Alpha-2 agonists      Vital to monitor blood pressure Many patients will become cyanotic!! Systolic above 90mmHg patient is safe, continue to monitor values If bradycardia is a concern, reverse drug Do not use anticholinergics!!! Alpha-2 antagonist       Alpha-2 antagonist: Dexmedetomidine: ATIPAMEZOLE Xylazine: YOHIMBINE/TOLAZOLINE Detomidine: YOHIMBINE/TOLAZOLINE Atipamezole is only given IM/SQ Yohimbine/Tolazoline: IV Atipamezole IV or IM Dissociative Anesthetics Ketamine  Tiletamine  Short acting injectable anesthetics Produce anesthesia in which the animals feels dissociated from its body  Cats given Ketamine, eyes remain open and unblinking *Be sure to use eye lubricant on these  Patients’ maintain laryngeal reflexes Dissociative Anesthetics  Produce good somatic (peripheral tissue) analgesia and suitable for superficial surgery  N-methly-D-aspartate (NMDA) antagonist Reverses “windup”  Less effective in blocking visceral pain and should not be used alone as anesthesia for internal procedures Dissociative Anesthetics  These recovering animals do best when placed in areas with little visual or auditory stimulation, loud noises or bright lights  Because of the Dissociative nature loud noises may precipitate violent reactions or even seizures  Ketamine is well absorbed through the mucous membranes of the mouth and nasal cavity Propofol Propofol is an injectable anesthetic agent unrelated to barbiturates  Marketed as an emulsion drug made from egg lecithin and soybean oil  Injected by in IV bolus, leading to rapid induction/short period of unconsciousness  Provides sedation with no analgesic effects  Etomidate Selective hypnotic drug occasionally used for induction in cats and dogs  Good muscle relaxation but no analgesia  Minimal effect on cardiovascular function best for cardiac cases and animals in shock  Alfaxalone     Water-soluble neuroanaesthetic C-IV Rapidly metabolized by the liver Minimal side-effects  Clinical use and properties compared to propofol  Unlike propofol, little or no cardiovascular effects Narcotics  Receptors (five classes) Mu: pain regulating areas of the brain, alagesia, euphoria, resp. depression, hypothermia Kappa: cerebral cortex, spinal cord; alagesia, sedation, miosis (pupil constrict) Sigma: struggling, whining, hallucinations, mydriatic effects (dilate pupil) Delta and Epsilon: unknown April 23, 2025 25 Opioids  Mode of action Bind to receptors in the brain and spinal cord Four different opioid receptors ○ Mu ○ Kappa ○ Sigma ○ Delta Mimic endorphins and enkephalins Opioids  Referred to as Agonist ○ pure agonist if bind to all 4 receptors Partial agonists ○ bind to some of the four receptors Agonist-antagonist ○ stimulate some receptors, blocks other receptors Antagonist ○ Blocks all four receptor sites Analgesics Partial agonists: Butorphanol Generally have weaker opioid effects Used for cough control in small animals and for reduction of colic pain in horses  Sedation/anxiolytic effects    Analgesics Buprenorphine:  Buprenorphine (Burprenex)/Simbadol/Zoribrum is a partial agonist and antagonist with moderately strong analgesic properties  Good efficacy when given transmucosaly in cats  Analgesics  Fentanyl is a potent opioid with an analgesic effect 250 times greater than morphine  Respiratory effects of fentanyl, no vomiting  Meperidine (Demerol) is a fairly weak analgesic and sedative and is fairly safe when injected subcutaneously to restrain cats Fentanyl Placement for fentanyl patches  12mcg/hr patch ingested by 3 year old can potentially be fatal  Caution when sending home with owner’s, need to return the patch  How to destroy?  Analgesics Morphine, Hydromorphone, Oxymorphone all like that of fentanyl.  Hydromorphone: Can cause “hydro panting” animal feels warm so pants to decrease temperature  Cats: transient hyperthermia with hydromorphone  Morphine causes vomiting/defecation/histamine release  Analgesics Naloxone is considered a “pure” narcotic antagonist because when it combines with u- and k-receptors  Reverses: Sedation, analgesia, and respiratory depression  May need multiple re-dosing  NSAIDS Block cyclooxygenase (COX)  Two forms  Cox 1 ○ Modulation of renal blood flow ○ Synthesis of gastric mucosa Cox 2 ○ Formation of prostaglandin Salicylates Aspirin: acetylsalicylic acid  Actions  analgesia, antipyrexia, anti-inflammatory reduction of platelet aggregation block cyclooxygenase  Adverse effects gastric irritation cats very sensitive to aspirin April 23, 2025 35 Pyrazolone Derivatives (Bute)  Phenylbutazone mild to moderate pain anti-inflammatory antipyrexia  Adverse effects gastrointestinal bleeding ( stomach ulcers)  Dosage forms tablets, paste, injectable, etc Give injections IV route only April 23, 2025 36 Flunixin Meglumine Banamine  Actions  analgesia antipyrexia anti-inflammatory  Adverse effects swelling at injection site sweating GI ulcerations April 23, 2025 37 Dimethyl Sulfoxide  DMSO commercial solvent anti-inflammatory carrier of other agents vasodilation at topical site of application  Adverse effects garlic taste, skin irritation birth defects, liver disorders  Use gloves when applying April 23, 2025 38 Acetaminophen Limited antipyretic and anti-inflammatory action  Adverse effects  cats: ○ methemoglobinemia ○ cyanosis ○ anemia ○ liver damage dogs: GI bleeding April 23, 2025 39 Carprofen Rimadyl (Pfizer)  Actions: Cox inhibitor  analgesic anti-inflammatory antipyretic  Adverse effects GI disorders, liver damage April 23, 2025 40 Deracoxib  Coxib class Cox 2 inhibitor Control of pain and inflammation  Forms: Deramaxx  Adverse side effects  GI upset Renal dysfunction Firocoxib  Coxib class Cox 2 inhibitor Treats pain and inflammation  Forms: Previcox  Adverse side effects  GI upset Renal dysfunction Meloxicam Cox 2 inhibitor  Use  Pain, inflammation Labeled for cats Forms: Metacam  Adverse side effects  GI upset and renal dysfunction Robenacoxib Cox 2 selective  Onsior  For both dogs and cats  Use Pain, inflammation Galliprant Grapiprant: NSAID specific for canine O.A.  Prostaglandin E2 (PGE2) EP4 receptor antagonist  Non-cyclooxygenase inhibiting, nonsteroidal  Vomiting, diarrhea, not eating/less lethargy.  Solensia  Frunevetmad Specific for feline osteoarthritis Minimal liver/kidney Well tolerated by feline patients SQ injection (monthly) in place of oral medication Cerenia  Maropitant: Neurokinin-1 antagonist Receptor ○ Used as antiemetic and motion sickness ○ Inhibits Substance-P in CNS ○ Substance-P are stimulated by Neurokinin1which is blocked. ○ Works well for visceral pain  Can be given SQ or PO Zofran  Ondansetron Vagal nerve terminals and chemoreceptor trigger zone (CRTZ)  May mask ileus or gastric foreign body, distention Narcotics  Forms Tramadol ○ Synthetic Mu receptor ○ Not regulated as is not an opioid ○ Ultram ○ Used safely with NSAIDS ○ Used for mild to moderate pain  Why this is not a good drug for dogs! April 23, 2025 49 Other Centrally Acting Drugs  Gabapentin Molecule of GABA Initially developed as antiepileptic drug Very little effect for acute pain Very useful for chronic pain Very good for long term neuropathic pain control April 23, 2025 50 Local Anesthetics   Results: block depolarization of nerve fiber Sensation disappears in the following order pain, cold, warmth, touch, joint, and deep pressure. April 23, 2025 51 Local Anesthetics  Epinephrine vasoconstriction delays absorption ○ reduces toxicity and increases safety increase intensity and prolong activity April 23, 2025 52 Local Anesthetics   Ester linked Procaine: Novocain Amide linked Lidocaine hydrochloride Mepivacaine: Carbocaine Bupivacaine: Maracaine April 23, 2025 53