NEET MDS Lessons
Pharmacology
CARDIAC GLYCOSIDES
Cardiac glycosides (Digitalis)
Digoxin
Digitoxin
Sympathomimetics
Dobutamine
Dopamine
Vasodilators
α-blockers (prazosin)
Nitroprusside
ACE-inhibitors (captopril)
Pharmacology of Cardiac Glycosides
1. Positive inotropic effect (as a result of increase C.O., the symptoms of CHF subside).
2. Effects on other cardiac parameters
1) Excitability
2) Conduction Velocity; slightly increased in atria & ventricle/significantly
reduced in conducting tissue esp. A-V node and His-Purkinje System
3) Refractory Period; slightly ^ in atria & nodal tissue/slightly v in ventricles
4) Automaticity; can be greatly augmented - of particular concern in ventricle
3. Heart Rate
-Decrease due to 1) vagal stimulation and 2) in the situation of CHF, due to improved hemodynamics
4 Blood Pressure
-In CHF, not of much consequence. Changes are generally secondary to improved cardiac performance.
-In the absence of CHF, some evidence for a direct increase in PVR due to vasoconstriction.
5. Diuresis
-Due primarily to increase in renal blood flow as a consequence of positive inotropic effect (increase CO etc.) Possibly some slight direct diuretic effect.
Mechanism of Action of Cardiac Glycosides
Associated with an interaction with membrane-bound Na+-K+ ATPase (Na-K pump).
Clinical ramifications of an interaction of cardiac glycosides with the Na+ K pump.
I. Increase levels of Ca++, Increase therapeutic and toxic effects of cardiac glycosides
II. Decrease levels of K+ , Increase toxic effects of cardiac glycosides
Therapeutic Uses of Cardiac Glycosides
- CHF
- CHF accompanied by atrial fibrillation
- Supraventricular arrhythmias
Etomidate -Intravenous Anesthetics
- A nonbarbiturate anesthetic used primarily to induce surgical anesthesia.
- It does not produce analgesia.
- Etomidate has minimal effect on the cardiovascular system and respiration during induction of anesthesia.
- Like the barbiturates, etomidate decreases cerebral blood flow, cerebral metabolic rate and intracranial pressure.
- No changes in hepatic, renal or hematologic function have been reported.
- Myoclonic muscle movements are relatively common.
- Postoperative nausea and vomiting are more common with etomidate than with barbiturates.
Chloramphenicol
derived from the bacterium Streptomyces venezuelae
Chloramphenicol is effective against a wide variety of microorganisms, but due to serious side-effects (e.g., damage to the bone marrow, including aplastic anemia) in humans, it is usually reserved for the treatment of serious and life-threatening infections (e.g., typhoid fever). It is used in treatment of cholera, as it destroys the
vibrios and decreases the diarrhoea. It is effective against tetracycline-resistant vibrios.It is also used in eye drops or ointment to treat bacterial conjunctivitis.
Mechanism and Resistance Chloramphenicol stops bacterial growth by binding to the bacterial ribosome (blocking peptidyl transferase) and inhibiting protein synthesis.
Chloramphenicol irreversibly binds to a receptor site on the 50S subunit of the bacterial ribosome, inhibiting peptidyl transferase. This inhibition consequently results in the prevention of amino acid transfer to growing peptide chains, ultimately leading to inhibition of protein formation.
Spectrum of activity: Broad-spectrum
Effect on bacteria: Bacteriostatic
Factors affecting onset and duration of action of local anesthetics
pH of tissue
pKa of drug
Time of diffusion from needle tip to nerve
Time of diffusion away from nerve
Nerve morphology
Concentration of drug
Lipid solubility of drug
Serotonin-norepinephrine reuptake inhibitors(SNRIs)
e.g. venlafaxine and duloxetine
- Inhibit the reuptake of both 5-HT and norepinephrine
- Has a more favourable adverse effect profile than TCAs
Norepinephrine reuptake inhibitor
e.g. bupropion, reboxetine
Monoamine receptor antagonists
e.g. mirtazapine, trazodone, mianserin
Barbiturates
1. Long-acting. Phenobarbital is used to treat certain types of seizures (see section on antiepileptic drugs).
2. Intermediate-acting. Amobarbital, pentobarbital (occasionally used for sleep), secobarbital.
3. Short-acting. Hexobarbital, methohexital, thiopental—rarely used as IV anesthetics.
Properties of inhalation anesthetics
The lower the solubility, the faster the onset and the faster the recoverability.
All general anesthetics:
1. inhibit the brain from responding to sensory stimulation.
2. block the sensory impulses from being recorded in memory.
3. prevent the sensory impulses from evoking “affect”.
Most general anesthetic agents act in part by interacting with the neuronal membranes to affect ion channels and membrane excitability.
· If the concentration given is too low:
1. Movement may occur
2. Reflex activity present (laryngeal spasm)
3. Hypertension
4. Awareness
Premedication of analgesic drugs and muscle relaxants are designed to minimise these effects
· If the concentration given is too high:
1. Myocardial depression
2. Respiratory depression
3. Delayed recovery