NEET MDS Lessons
Pharmacology
Excretion
Routes of drug excretion
The most important route of drug elimination from the body is via the kidney
Renal Drug Excretion
- Glomerular Filtration
- Passive Tubular Reabsorption: drugs that are lipid soluble undergo passive reabsorption from the tubule back into the blood.
- Active Tubular Secretion
Factors that Modify Renal Drug Excretion
- pH Dependent Ionization: manipulating urinary pH to promote the ionization of a drug can decrease passive reabsorption and hasten excretion.
- Competition for Active Tubular Transport
- Age: Infants have a limited capscity to excrete drugs.
Nonrenal Routes of Drug Excretion
Breast Milk
Bile, Lungs, Sweat and Saliva
The kidney is the major organ of excretion. The lungs become very important for volatile substances or volatile metabolites.
Drugs which are eliminated by the kidney are eliminated by:
a) Filtration - no drug is reabsorbed or secreted.
b) Filtration and some of the drug is reabsorbed.
c) Filtration and some secretion.
d) Secretion
By use of the technique of clearance studies, one can determine the process by which the kidney handles the drug.
Renal plasma clearance = U x V ml/min U / Cp = conc. of drug in urine
Cp = conc. of drug in plasma
V = urine flow in ml/min
Renal clearance ratio = renal plasma clearance of drug (ml/min) / GFR (ml/min)
Total Body Clearance = renal + non-renal
Diphenoxylate (present in Lomotil)
- A meperidine congener
- Not absorbed very well at recommended doses.
- Very useful in the treatment of diarrhea.
Miconazole
Miconazole is an imidazole antifungal agent commonly used in topical sprays, creams and ointments applied to the skin to cure fungal infections such as Athlete's foot and Jock itch. It may also be used internally to treat vaginal yeast infection.
When used by a person taking the anticoagulant medication warfarin, Miconazole may cause an adverse reaction which can lead to excessive bleeding or bruising.
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.
Buspirone
1. Short half-life (2–4 hours).
2. Relieves anxiety.
3. Does not act as an anticonvulsant.
4. Is not a good muscle relaxant.
5. Minimum abuse potential.
Azithromycin
Azithromycin is the first macrolide antibiotic belonging to the azalide group. Azithromycin is derived from erythromycin by adding a nitrogen atom into the lactone ring of erythromycin A, thus making lactone ring 15-membered.
Azithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Hemophilus influenzae.
azithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids.
Main elimination route is through excretion in to the biliary fluid, and some can also be eliminated through urinary excretion
PHARMACOLOGY OF LOCAL ANESTHETICS
Characteristics
1. Block axon conduction (nerve impulse) when applied locally in appropriate concentrations.
2. Local anesthetic action must be completely reversible; however, the duration of the anesthetic block should be of sufficient length to allow completion of the planned treatment.
3. Produce minimal local toxic effects such as nerve and muscle damage as well as minimal systemic toxic effects of organ systems such as the cardiovascular and central nervous system.