Types of Neurons (Function)

•There are 3 general types of neurons (nerve cells): 

1-Sensory (Afferent ) neuron:A neuron that detects changes in the external or internal environment and sends information about these changes to the CNS. (e.g: rods and cones, touch receptors). They usually have long dendrites and relatively short axons. 

2-Motor (Efferent) neuron:A neuron located within the CNS that controls the contraction of    a muscle or the secretion of a gland. They usually have short dendrites and long axons. 

2-Interneuron or association neurons: A neuron located entirely within the CNS in which they form the connecting link between the afferent and efferent neurons. They have short dendrites and may have either a short or long axon.

Mixed Narcotic Agonists/Antagonists

These drugs all produce analgesia, but have a lower potential for abuse and do not produce as much respiratory depression.

A. Pentazocine

• Has a combination of opiate analgesic and antagonist activity.
• Orally, it has about the same analgesic potency as codeine.
• In contrast to morphine, cardiac workload tends to increase due to an increase in pulmonary arterial and cerebrovascular pressure. Blood pressure and heart rate both also tend to increase.
• Adverse reactions to Pentazocine

• Nausea, vomiting, dizziness.

• Psychotomimetic effects, such as dysphoria, nightmares and visual hallucinations.

• Constipation is less marked than with morphine.

B. Nalbuphine

• Has both analgesic and antagonist properties.
• Resembles pentazocine pharmacologically.
• Analgesic potency approximately the same as morphine.
• Appears to be less hypotensive than morphine.
• Respiratory depression similar to morphine, but appears to peak-out at higher doses and to reach a ceiling.
• Like morphine, nalbuphine reduces myocardial oxygen demand. May be of value following acute myocardial infarction due to both its analgesic properties and reduced myocardial oxygen demand.
• Most frequent side effect is sedation.

C. Butorphanol

• Has both opiate agonist and antagonist properties.Resembles pentazocine , pharmacologically., 3.5 to 7 times more potent than morphine., Produces respiratory depression, but this effect peaks out with higher doses. The respiratory depression that does occur lasts longer than that seen following morphine administration.
• Butorphanol, like pentazocine, increases pulmonary arterial pressure and possibly the workload on the heart.
• Adverse reactions include sedation, nausea and sweating.

D. Buprenorphine

• A derivative of eto`rphine. Has both agonist and antagonist activity. 20 to 30 times more potent than morphine.Duration of action only slightly longer than morphine, but respiratory depression and miosis persist well after analgesia has disappeared.
• Respiratory depression reaches a ceiling at relatively low doses.
• Approximately 96% of the circulating drug is bound to plasma proteins.
• Side effects are similar to other opiates:
  • sedation, nausea, vomiting,
  • dizziness, sweating and headache.

Antiarrhythmic Drugs

Cardiac Arrhythmias 
Can originate in any part of the conduction system or from atrial or ventricular muscle.
Result from
– Disturbances in electrical impulse formation (automaticity) 
– Conduction (conductivity) 
– Both

MECHANISMS OF ARRHYTHMIA
ARRHYTHMIA – absence of rhythm
DYSRRHYTHMIA – abnormal rhythm

ARRHYTHMIAS result from:
1. Disturbance in Impulse Formation
2. Disturbance in Impulse Conduction
- Block results from severely depressed conduction
- Re-entry or circus movement / daughter impulse

Types of Arrhythmias

• Sinus arrhythmias 
– Usually significant only 
– if they are severe or  prolonged 

• Atrial arrhythmias 
– Most significant in the presence of underlying heart disease
– Serious: atrial fibrillation can lead to the formation of clots in the heart 

• Nodal arrhythmias 
– May involve tachycardia and increased workload of the heart or bradycardia from heart block 

• Ventricular arrhythmias 
– Include premature ventricular contractions (PVCs), ventricular tachycardia, and ventricular fibrillation 

Indications
• To convert atrial fibrillation (AF) or flutter to normal sinus rhythm (NSR) 
• To maintain NSR after conversion from AF or flutter 
• When the ventricular rate is so fast or irregular that cardiac output is impaired
– Decreased cardiac output leads to symptoms of decreased systemic, cerebral, and coronary circulation 
• When dangerous arrhythmias occur and may be fatal if not quickly terminated 
– For example: ventricular tachycardia may cause cardiac arrest 

Mechanism of Action 
• Reduce automaticity (spontaneous depolarization of myocardial cells, including ectopic pacemakers) 
• Slow conduction of electrical impulses through the heart
• Prolong the refractory period of myocardial cells (so they are less likely to be prematurely activated by adjacent cells 
 

Topical Anesthetics

Benzocaine

Benzocaine is a derivative of procaine, an ester type local anesthetic, and is poorly soluble in water and is

available only as a topical anesthetic.

-  Localized allergic reactions are sometimes encountered    

-  Overdosing is unlikely as benzocaine is poorly absorbed into the blood, which decreases the likelihood of systemic toxicity.

- The onset of surface anesthesia is rapid requiring less than one minute.

Tetracaine

- Tetracaine is an ester type local anesthetic

-  Topically applied tetracaine as opposed to benzocaine has a prolonged duration of action.

Cocaine

- Cocaine is a ester type anesthetic that is used exclusively as a topical agent.

- Cocaine is unique among topical and injectable anesthetics in that it has vasoconstrictive as well as anesthetic properties. It is used sparingly because of its abuse potential but is still used when hemostasis of mucous membranes is essential.

- Cocaine is generally available in concentrations of 2-10 % solution.

Lidocaine

- Lidocaine is an amide local anesthetic that is available in injectable and topical formulations.

- It is available in gel, viscous solution, ointment and aerosol preparations in concentrations ranging from 2-10 %.

- The onset of anesthesia is slower relative to benzocaine but, the duration is about the same.

- Absorption into the bloodstream is greater than benzocaine providing a greater risk of systemic toxicity.

ISOPRENALINE

It is beta-receptor stimulant, which stimulates the heart and causes tachycardia.
It relaxes the smooth muscles particularly the bronchial and GIT. It is mainly used in bronchial asthma, in the treatment of shock and as a cardiac stimulant in heart block. 

ORCIPRENALINE
Is a potent β-adrenergic agonist.
Receptor sites in the bronchi and bronchioles are more sensitive to the drug than those in the heart and blood vessels.

AMPHETAMINE 

increases the systolic and diastolic blood pressure. Amphetamine is a potent CNS stimulant and causes alertness, insomnia, increased concentration, euphoria or dysphoria and increased work capacity.

Amphetamines are drugs of abuse and can produce behavioural abnormalities and can precipitate psychosis. 

PHENYLEPHRINE
It is used as a nasal decongestant and mydriatic agent and also in the treatment of paroxysmal supraventricular tachycardia.

UTERINE RELAXANTS (TOCOLYTICS)

ISOXSUPRINE
Isoxsuprine has a potent inhibitory effect on vascular and uterine smooth muscle and has been used in the treatment of dysmenorrhoea, threatened abortion, premature labour and peripheral vascular diseases. 
 

Routes of Drug Administration

Intravenous

• No barriers to absorption since drug is put directly into the blood.
• There is a very rapid onset for drugs administered intravenously.  This can be advantagous in emergency situations, but can also be very dangerous.
• This route offers a great deal of control in respect to drug levels in the blood.
• Irritant drugs can be administer by the IV route without risking tissue injury.
• IV drug administration is expensive, inconvenient and more difficult than administration by other routes.
• Other disadvantages include the risk of fluid overload, infection, and embolism.  Some drug formulations are completely unsafe for use intravenously.

Intramuscular:

• Only the capillary wall separates the drug from the blood, so there is not a significant barrier to the drug's absorption.
• The rate of absorption varies with the drug's solubility and the blood flow at the site of injection.
• The IM route is uncomfortable and inconvenient for the patient, and if administered improperly, can lead to tissue or nerve damage.

Subcutaneous

Same characteristics as the IM route.

Oral

• Two barriers to cross: epithelial cells and capillary wall.  To cross the epithelium, drugs have to pass through the cells.

• Highly variable drug absorption influenced by many factors:  pH, drug solubility and stability, food intake, other drugs, etc.
• Easy, convenient, and inexpensive.  Safer than parenteral injection, so that oral administration is generally the preferred route.
• Some drugs would be inactivated by this route
• Inappropriate route for some patients.
• May have some GI discomfort, nausea and vomiting.
• Types of oral meds = tablets, enteric-coated, sustained-release, etc.
• Topical, Inhalational agents, Suppositories