Endocrine Drugs and Medications Q 17
Which of the following drugs will decrease the effects of vasopressin?
A. digoxin (Lanoxin)
B. lithium (Lithane)
C. penicillin (Pen-Vee-K)
D. azithromycin (Zithromax)
Correct Answer: B. lithium (Lithane)
Lithium is known to decrease the effects of vasopressin. Lithium is a salt, and antidiuretic hormone acts on the water that influences the sodium/water balance. Lithium modifies sodium transport in nerve and muscle cells. It alters the metabolism of neurotransmitters, specifically catecholamines and serotonin. It may alter intracellular signaling via second messenger systems by inhibition of inositol monophosphate. This inhibition, in turn, affects neurotransmission through the phosphatidylinositol secondary messenger system.
Option A: Digoxin has two principal mechanisms of action which are selectively employed depending on the indication. It increases the force of contraction of the heart by reversibly inhibiting the activity of the myocardial Na-K ATPase pump, an enzyme that controls the movement of ions into the heart. Digoxin induces an increase in intracellular sodium that will drive an influx of calcium in the heart and cause an increase in contractility. Digoxin has vagomimetic effects on the AV node. By stimulating the parasympathetic nervous system, it slows electrical conduction in the atrioventricular node, therefore, decreases the heart rate.
Option C: Penicillin inhibits the cross-linking of peptidoglycan in the cell wall. The catalyst for this reaction is penicillin-binding proteins, such as the enzyme DD-transpeptidase. Penicillin’s four-membered ?-lactam ring can bind to DD-transpeptidase to irreversibly inactivate it. The bacteria, therefore, are unable to build their cell walls even while other proteins continue to break down the wall.
Option D: Azithromycin is a broad-spectrum macrolide antimicrobial and is among the most prescribed antimicrobial drugs in the United States. It is a derivative of erythromycin with greatly enhanced activity against gram-negative bacteria (including Enterobacteriaceae) and provides coverage of many gram-positive organisms. As an inhibitor of bacterial protein synthesis (rather than a peptidoglycan cell-wall inhibitor like beta-lactam agents), azithromycin is effective against many “atypical” bacteria such as chlamydiae (e.g., Chlamydia trachomatis and Chlamydophila psittaci), legionella (i.e., Legionella pneumophila), mycoplasma (e.g., Mycoplasma pneumoniae), and mycobacteria (e.g., Mycobacterium avium).