Pharma

• Skeletal muscle relaxants


  Drugs that act peripherally at neuromuscular junction/muscle fibre itself or centrally in the cerebrospinal axis to reduce muscle tone and/or cause paralysis
• Skeletal Muscle Relaxants


  • Peripherally acting
  • Centrally acting
• Peripherally acting skeletal muscle relaxants


  • Neuromuscular blocking agents
  • Directly acting agents
• Neuromuscular blocking agents


  • Nondepolarizing blockers
  • Depolarizing blockers
• Nondepolarizing blockers


  • Long acting (D-Tubocurarine)
  • Intermediate acting (Vecuronium, Atracurium)
  • Short acting (Mivacurium)
• Depolarizing blockers


  Succinyl choline
• Directly acting agents


  Dantrolene sodium
• Centrally acting skeletal muscle relaxants

  • Mephenesin congeners (Chlorzoxazone)
  • Benzodiazepines (Diazepam)
  • Gaba mimetic (Baclofen)
  • Central a2 agonist (Tizanidine)
• Neuromuscular blocking agents - Mechanism of Action

  1. Competitive block (Nondepolarizing block)

  2. Depolarizing block
• Uses of neuromuscular blocking agents

  • Adjuvants to general anaesthesia
  • Assisted ventilation of critically ill patients
  • Convulsions and trauma from electroconvulsive therapy
  • Severe cases of tetanus and status epilepticus
• Toxicity of neuromuscular blocking agents

  • Respiratory paralysis and prolonged apnoea
  • Flushing
  • Fall in BP and cardiovascular collapse
  • Cardiac arrhythmias and even arrest
  • Precipitation of asthma
  • Postoperative muscle soreness
• Centrally acting muscle relaxants

  • Decrease muscle tone without reducing voluntary power
  • Selectively inhibit polysynaptic reflexes in CNS
  • Cause some CNS depression
  • Given orally, sometimes parenterally
  • Used in chronic spastic conditions, acute muscle spasms, tetanus
• Peripherally acting muscle relaxants

  • Cause muscle paralysis, voluntary movements lost
  • Block neuromuscular transmission
  • No effect on CNS
  • Practically always given i.v.
  • Used for short-term purposes (surgical operations)
• Thiocolchicoside


  GABA mimetic and glycinergic muscle relaxant
• Tizanidine


  Central a2 adrenergic agonist, inhibits release of excitatory amino acids in spinal interneurones, facilitates inhibitory transmitter glycine
• Side effects of Tizanidine

  • Dry mouth
  • Drowsiness
  • Night-time insomnia
  • Hallucinations
  • Dose-dependent elevation of liver test values
• Uses of centrally acting muscle relaxants

  • Acute muscle spasms
  • Torticollis, lumbago, backache, neuralgias
  • Anxiety and tension associated with increased muscle tone and bruxism
  • Spastic neurological diseases
  • Tetanus
  • Electroconvulsive therapy
  • Orthopaedic manipulations
• General Anesthesia (GA)

  Drug-induced reversible loss of sensation and a complete loss of consciousness "awareness" that feels like a very deep sleep
• Five important benefits of GA

  • Analgesia (loss of pain sensation)
  • Lack of awareness (consciousness)
  • Amnesia (memory loss)
  • Sedation and reduced anxiety
  • Skeletal muscle relaxation and Suppression of undesirable reflexes
• Balanced Anesthesia


  Use of multiple drugs (IV-anesthetics for induction, inhalational anesthetics for maintenance, sedative hypnotics, opioids "analgesics", neuromuscular blocking drugs) to minimize the adverse effects of using single anesthetic agent
• First reliable documentation of an operation performed under general anesthesia by Japanese surgeon Hanaoka Seishu


  1804
• Dr. Horace Wells


  • Pioneer of the modern surgical anesthesia, demonstrated the use of nitrous oxide gas "laughing gas" in the prevention of pain during surgery
• Dr. William Morton


  • Credited for the first anesthetic (known as Ether Day) and solidified the foundation for the use of anesthetics in dental practice, demonstrated the use of Ether vapors for the removal of a jaw tumor
• Dr. Greene Vardeman Black


  • Father of modern dentistry, founding dean of Northwestern School of Dentistry, and general anesthesia educator, developed the carious lesion classification system used by dentists to this day, lectured on the "Introduction of Bromide of Ethyl as an Anesthetic for Dental Purposes or Any Very Short Operation" in 1883
• Dr. Charles Teeter


  • Introduced the first anesthesia machine capable of delivering N2O/O2, ether, and chloroform
• Dr. Adrian Hubbell


  • Pioneered and popularized the intravenous office-based outpatient general anesthesia among OMFS by administering barbiturates, advocated the utility and safety of recovering patients on their side or abdomen postoperatively to prevent aspiration of vomitus
• Dr. John Lundy


  • Introduced the concept of the balanced anesthesia
• John Lytle


  • Authored many early OMS anesthesia safety articles in the professional literature
• Indications for General Anesthesia in Dentistry

  • Mentally challenged patients
  • Children where attempts to use local anesthesia alone or with conscious sedation has been unsuccessful or the child does not cooperate
  • Patients allergic to local anaesthetic
  • Prolonged traumatic procedures
  • Inability to safely inject the local anesthesia (e.g., severe trismus)
• Settings for General Anesthesia in Dentistry

  • Dental chair anesthesia "Office based anesthesia" on outpatient basis
  • Day care anesthesia (patient is admitted and discharged on the same day) for oral surgical procedures lasting not more than one hour
  • Inpatient anesthesia for extensive procedures
• Phases of General Anesthesia

  • Before Surgery (Premedication)
  • During Surgery
  • After Surgery (Recovery)
• Steps of General Anesthesia

  1. IV-Induction

  2. Intubation

  3. Maintenance
• Properties of Ideal Anesthetic Agent

  • Inexpensive
  • Environmentally safe
  • Doesn't react with other compounds (e.g., plastic pipes and metal tubes or cylinders)
  • Non-flammable (non-explosive and doesn't support combustion)
  • Long shelf life (i.e., stable over a range of temperatures, doesn't degraded by light and doesn't require a preservative)
  • Pleasant (non-pungent) and non-irritant (non-painful)
  • Easy and controllable administration (titratability)
  • Potent at low concentration
  • Provide adequate sedation, analgesia, muscle relaxation and amnesia
  • Wide margin of safety
  • Smooth induction and recovery
  • Minimal effects on cardiovascular functions (cardiostability) and bronchodilator
• Inhalational Anesthetics


  Anesthetics which are administered in a gaseous form, used primarily for maintenance of anesthesia after administration of an IV agent
• General Characteristics of Inhalational Anesthetics

  • Easy administration with the ability to change the depth of anesthesia by changing the inhaled concentration
  • Nonflammable and nonexplosive agents
  • They have very steep dose–response curves
  • They have a very narrow therapeutic indices (i.e., the difference in concentrations causing surgical anesthesia and severe cardiac and respiratory depression is small)
  • They have no antagonists
  • They are delivered in a recirculation system containing absorbents that remove carbon dioxide and allow rebreathing of the agents in order to minimize waste of the potent inhaled agents and decrease cost
• Types of Inhalational Anesthetics

  • Nonvolatile Anesthetic (Exist as a gas at room temperature): Nitrous Oxide, Nobel Gases (Xenon, Helium)
  • Volatile Liquids (Halogenated Gases): Halothane, Isoflurane, Enflurane, Desflurane, Sevoflurane
• Mechanism of Action of Inhalational Anesthetics

  • Activation of Gamma-aminobutyric acid (GABA) receptors
  • Opening the two pore potassium channels
  • Inhibition of N-methyl-D-aspartate (NMDA) receptors
  • Lipid Solubility (Mayer-Overton Theory)
• Minimum Alveolar Concentration (MAC)


  The minimum concentration of an anaesthetic in alveoli required to produce immobility in response to a painful stimulus (e.g., incision) in 50% patients
• Inhalation administration


  Provides a rapid increase in the lung concentration and access to the blood stream without necessitating intravenous access
• Diffusion of the inhaled anesthetic gas from the lung alveoli to blood


  1. Depends on the partial pressure between the alveoli (air) and blood

  2. Depends on the partition coefficient between tissues

  3. Depends on cardiac output to pulmonary and cerebral blood vessels