NEET MDS Lessons
Pharmacology
Lithium carbonate: 1st choice (controls mania in bipolar disorders); delay before onset of therapeutic benefit; no psychotropic effects in normal humans
i. Mechanism: blocks enzymes in inositol phosphate signaling pathway; no consistent effects of lithium on NE, 5-HT, and DA
ii. Side effects: severe CNS (ataxia, delirium, coma, convulsions) and CV (cardiac dysrhythmias)
Glucocorticoids
Cortisol (hydrocortisone) and its synthetic derivatives
|
Drug |
Duration |
| Cortisol | Short |
| Prednisone | Medium |
| Triameinolone | Intermediate |
| Betamethasone | Long |
| Dexamethasone | Long |
Mechanism
↓ the production of leukotrienes and prostaglandins - inhibits phospholipase A2 , inhibits expression of COX-2 , will also stimulate the bone marrow to produce neutrophils resulting in leukocytosis
halts inflammatory cascade
↓ leukocyte migration
↓ capillary permeability
↓ phagocytosis
↓ platelet-activating factor
↓ interleukins (e.g. IL-2)
may trigger apoptosis in dividing and non-dividing cells
used in cancer chemotherapy
Clinical use
anti-inflammatory
immunosuppression
cancer chemotherapy (prednisone most common)
CLL
Hodgkin's lymphomas
part of MOPP regimen
Addison disease
asthma
Toxicity
1) must taper dose to avoid toxicity
2) suppression of ACTH → shock state if abrupt withdrawal - > cortical atrophy, malaise, myalgia, arthralgia, fever
3) iatrogenic Cushing syndrome ->buffalo hump, moon facies, truncal obesity, muscle weakness and atrophy, thin skin, easy bruising, acne
4) osteoporosis - vertebral fractures, aseptic hip necrosis, ↓ skeletal growth in children
5) hyperglycemia (diabetes) -due to ↑ gluconeogenesis , glaucoma, cataracts, and other complications can subsequently result
6) ↑ GI acid release -ulcers
7) Na+ retention -> edema, HTN, hypokalemia alkalosis, hypocalcemia
8)↓ wound healing
9) ↑ infections
10) mental status changes
11) cataracts
Clotrimazole: Clotrimazole is a potent, specific inhibitor of p450 enzymes.
It is used in some antifungal medications, and in the treatment of yeast infections.
Sedative-Hypnotic Drugs
Sedative drug is the drug that reduce anxiety (anxiolytic) and produce sedation and referred to as minor tranquillisers.
Hypnotic drug is the drug that induce sleep
Effects: make you sleepy; general CNS depressants
Uses: sedative-hypnotic (insomnia ), anxiolytic (anxiety, panic, obsessive compulsive, phobias), muscle relaxant (spasticity, dystonias), anticonvulsant (absence, status epilepticus, generalized seizures—rapid tolerance develops), others (pre-operative medication and endoscopic procedures, withdrawal from chronic use of ethanol or other CNS depressants)
1- For panic disorder alprazolam is effective.
2- muscle disorder: (reduction of muscle tone and coordination) diazepam is useful in treatment of skeletal muscle spasm e.g. muscle strain and spasticity of degenerative muscle diseases.
3-epilepsy: by increasing seizure threshold.
Clonazepam is useful in chronic treatment of epilepsy while diazepam is drug of choice in status epilepticus.
4-sleep disorder: Three BDZs are effective hypnotic agents; long acting flurazepam, intermediate acting temazepam and short
acting triazolam. They decrease the time taken to get to sleep They increase the total duration of sleep
5-control of alcohol withdrawals symptoms include diazepam, chlordiazepoxide, clorazepate and oxazepam.
6-in anesthesia: as preanesthetic amnesic agent (also in cardioversion) and as a component of balanced anesthesia
Flurazepam significantly reduce both sleep induction time and numbers of awakenings and increase duration of sleep and little rebound insomnia. It may cause daytime sedation.
Temazepam useful in patients who experience frequent awakening, peak sedative effect occur 2-3 hr. after an oral dose.
Triazolam used to induce sleep in recurring insomnia and in individuals have difficulty in going to sleep, tolerance develop within few days and withdrawals result in rebound insomnia therefore the drug used intermittently.
Drugs and their actions
1. Benzodiazepines: enhance the effect of gamma aminobutyric acid (GABA) at GABA receptors on chloride channels. This increases chloride channel conductance in the brain (GABA A A receptors are ion channel receptors).
2. Barbiturates: enhance the effect of GABA on the chloride channel but also increase chloride channel conductance independently of GABA, especially at high doses
3. Zolpidem and zaleplon: work in a similar manner to benzodiazepines but do so only at the benzodiazepine (BZ1) receptor type. (Both BZ1and BZ2 are located on chloride channels.)
4. Chloral hydrate: probably similar action to barbiturates.
5. Buspirone: partial agonist at a specific serotonin receptor (5-HT1A).
6. Other sedatives (e.g., mephenesin, meprobamate, methocarbamol, carisoprodol, cyclobenzaprine):
mechanisms not well-described. Several mechanisms may be involved.
7. Baclofen: stimulates GABA linked to the G protein, Gi , resulting in an increase in K + conductance and a decrease in Ca2+ conductance. (Other drugs mentioned above do not bind to the GABA B receptor.)
8. Antihistamines (e.g., diphenhydramine): block H1 histamine receptors. Doing so in the CNS leads to sedation.
9. Ethyl alcohol: its several actions include a likely effect on the chloride channel.
Kinins
Peptide that are mediated in the inflammation.
Action of kinin:
On CVS: vasodilatation in the kidneys, heart, intestine, skin, and liver. It is 10 times active than histamine as vasodilator.
On exocrine and endocrine glands: kinin modulate the tone of pancreas and salivery glands and help regulate GIT motility, also affect the transport of water and electrolytes, glucose and amino acids through epithelial cell transport.
Gabapentin (Neurontin): newer; for generalized tonic-clonic seizures and partial seizures (partial and complex)
Mechanism: unknown but know doesn’t mimic GABA inhibition or block Ca currents
Side effects: dizziness, ataxia, fatigue; drug well-tolerated and no significant drug interactions
Effects and Toxic Actions on Organ Systems
1. Local anesthetics (dose dependent) interfere with transmission in any excitable tissue (e.g. CNS and CVS).
2. CNS effects
a. Central neurons very sensitive.
b. Excitatory-dizziness, visual and auditory disturbances, apprehension, disorientation and muscle twitching more common with ester type agents.
c. Depression manifested as slurred speech, drowsiness and unconsciousness more common with amide type agents (e.g. lidocaine).
d. Higher concentrations of local anesthetic may eventually produce tonic-clonic[grand mal] convulsions.
e. Very large doses may produce respiratory depression which can be fatal. Artificial respiration may be life-saving.
3.CVS effects
a. Local anesthetics have direct action on the myocardium and peripheral vasculature by closing the sodium channel, thereby limiting the inward flux of sodium ions.
b. Myocardium usually depressed both in rate and force of contraction. Depression of ectopic pacemakers useful in treating cardiac arrhythmias.
c. Concentrations employed clinically usually cause vasodilation in area of injection.
d. Vasoconstrictors such as epinephrine may counteract these effects on myocardium and vasculature.
4. Local Tissue Responses
a. Occasionally focal necrosis in skeletal muscle at injection site, decreased cell motility and delayed wound healing.
b. Tissue hypoxia may be produced by action of excessive amounts of vasoconstrictors.