Antiemetics

 Antiemetic drugs are generally more effective in prophylaxis than treatment. Most antiemetic agents relieve nausea and vomiting by acting on the vomiting centre, dopamine receptors, chemoreceptors trigger zone (CTZ), cerebral cortex, vestibular apparatus, or a combination of these.
 
 Drugs used in the treatment of nausea and vomiting belong to several different groups. These include:
 
1. Phenothiazines, such as chlorpromazine, act on CTZ and vomiting centre, block dopamine receptors, are effective in preventing or treating nausea and vomiting induced by drugs, radiation therapy, surgery and most other stimuli (e.g. pregnancy).
They are generally ineffective in motion sickness.
Droperidol had been used most often for sedation in endoscopy and surgery, usually in combination with opioids or benzodiazepines

2. Antihistamines such as promethazine and Dimenhyrinate are especially effective in prevention and treatment of motion.

3. Metoclopramide has both central and peripheral antiemetic effects. Centrally, it antagonizes the action of dopamine. Peripherally metoclopramide stimulates the release of acetylcholine, which in turn, increases the rate of gastric. It has similar indications to those of chlorpromazine.

4. Scopolamine, an anticholinergic drug, is very effective in reliving nausea & vomiting associated with motion sickness.

5. Ondansetron, a serotonin antagonist, is effective in controlling chemical-induced vomiting and nausea such those induced by anticancer drugs. 

6. Benzodiazepines: The antiemetic potency of lorazepam and alprazolam is low. Their beneficial effects may be due to their sedative, anxiolytic, and amnesic properties

DOPAMINE

It is an immediate metabolic precursor of noradrenaline. It activates D1 receptors in several vascular beds, which causes vasodilatation. It acts on dopaminergic and other adrenergic receptors (α & β1).

Adverse effects of dopamine include nausea, vomiting, ectopic beats, anginal pain, tachycardia, palpitation and widened QRS.
Contraindications are atrial or ventricular tachyarrhythmias, hyperthyroidism and pheochromocytoma.

Fifth Generation:

These are extended spectrum antibiotics.

Ceftaroline, Ceftobiprole

Ketamine 
- Causes a dissociative anesthesia.
- Is similar to but less potent than phencyclidine.
- Induces amnesia, analgesia, catalepsy and anesthesia, but does not induce convulsions.
- The principal disadvantage of ketamine is its adverse psychic effects during emergence from anesthesia. These include: hallucinations, changes in mood and body image.
- During anesthesia, many of the protective reflexes are maintained, such as laryngeal, pharyngeal, eyelid and corneal reflexes.
- Muscle relaxation is poor.
- It is not indicated for intracranial operations because it increases cerebrospinal fluid pressure.
- Respiration is well maintained.
- Arterial blood pressure, cardiac output, and heart rate are all elevated.

PHARMACOLOGY OF VASOCONSTRICTORS

All local anesthetics currently used in dentistry today produce some degree of vasodilatation. This

characteristic results in the increased vascularity of the injected site and results in a shorter duration of local

anesthetic action due enhanced uptake of the local anesthetic into the bloodstream.

- Using a “chemical tourniquet” to prolong the effect of local anesthetics

- The vasoconstrictive action of epinephrine reduces uptake of local anesthetic resulting in a significant increase in the duration of local anesthetic action.

- the addition of vasoconstrictors in local anesthetic solutions will:

1. Prolong the effect of the local anesthetic

2. Increase the depth of anesthesia

3. Reduces the plasma concentration of the local anesthetic

4. Reduces the incidence of systemic toxicity

5. Reduces bleeding at surgical site

Local anesthetics containing epinephrine produce:

1. Localized

VASOCONSTRICTION MEDIATED BY ALPHA RECEPTOR ACTIVATION

 i. Hemostasis at surgical site

 ii. Ischemia of localized tissue

2. Systemic

HEART

 i. Increased heart rate (β1)

 ii. Increased force and rate of contraction (β 1)

 iii. Increased cardiac output

 iv. Increases oxygen demand

 v. Dilation of coronary arteries

 vi. Decreases threshold for arrhythmias 

LUNGS

 i. Bronchodilation (β2 )

SKELETAL MUSCLE
i. Predominately vasodilation (fight or flight response) (β 2 )

CNS

i. Minimal direct effect due to difficulty in crossing the blood-brain barrier. Most effects on the CNS are manifestations of the vasoconstrictor on other organs such as the heart.

Concentrations of vasoconstrictors

1. Epinephrine The most commonly used epinephrine dilution in dentistry today is 1:100000. However it appears that a 1:200000 concentration is comparable in effect to the 1:100000 concentration.

2. Levonordefrin Levonordefrin is a synthetic compound very similar in structure to epinephrine. It is the only alternate choice of vasoconstrictor to epinephrine. It is prepared as a 1:20000 (0.05mg/ml)(50 mcg/ml) concentration with 2 % mepivacaine.

Cardiovascular considerations

The plasma concentration of epinephrine in a patient at rest is 39 pg/ml.1 The injection of 1 cartridge of lidocaine 1:100000 epinephrine intraorally results in a doubling of the plasma concentration of epinephrine.

The administration of 15 mcg of epinephrine  increased heart rate an average of 25 beats/min with some individuals experiencing an increase of 70 beats/min.

Clinical considerations

It is well documented that reduced amounts of epinephrine should be administered to patients with:

HEART DISEASE (ANGINA HISTORYOF MI)

POORLY CONTROLLED HIGH BLOOD PRESSURE

It is generally accepted that the dose of epinephrine should be limited to 0.04 mg (40 mcg) for patients that have these medical diagnoses

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.