Review of Pharmacology - 9E (2015)

Review of Pharmacology
Urinary Antiseptics
These are oral drugs that are rapidly excreted in the urine and suppress the bacterial growth
in urinary tract. These are more effective in acidic urine because low pH is an independent inhibitor
of bacterial growth. Nitrofurantoin, methanamine mandelate and nalidixic acid are three
important urinary antiseptic drugs.
Nitrofurantoin
After reduction by bacterial enzymes, nitrofurantoin result in DNA damage. It is active against
most urinary pathogens except pseudomonas and proteus. Resistance against it develops slowly.
Now it is used infrequently. Adverse effects include diarrhea, phototoxicity, neurotoxicity
and hemolysis in G-6-PD deficient patients.
Chemotherapy A: General Considerations and Non-specific...
Methanamine Mandelate
Methanamine release formaldehyde at low pH (below 5.5), which is the major compound having
antibacterial activity. Mandelate salt is used because it itself is urine acidifying agent. This drug
is not effective against proteus because it releases NH 3
and alkalinizes the urine. Insoluble
complex forms between formaldehyde and sulfonamides, so methanamine should not be used
with sulfonamides.
Nalidixic Acid
This is a quinolone drug and acts by inhibiting DNA gyrase. This too is not effective against
pseudomonas and proteus. Resistance emerges rapidly and main adverse effect is neurotoxicity.
Phenazopyridine
It is not a urinary antiseptic but possesses analgesic action and alleviates symptoms of dysuria,
frequency, burning and urgency.
Other Antibacterial Drugs
These include daptomycin, mupirocin, polypeptide antibiotics, fusidic, acid, teicoplanin and
glycylcyclines.
Daptomycin
It is a lipopeptide bactericidal drug that acts by causing depolarization of bacterial cell membranes
with K + efflux and rapid cell death. It is used for serious gram positive infections including
penicillin resistant pneumococci, MRSA and VRSA. It is also effective against organisms
resistant to linezolid and streptogramins. Myopathy is the dose limiting toxicity of this drug.
Pulmonary surfactant antagonizes daptomycin, therefore, the latter should not be used to treat
pneumonia.
Mupirocin (psudomonic acid)
It acts on gram positive organisms by inhibiting protein synthesis due to binding with
isoleucyl-tRNA. It is active against most gram positive cocci including MRSA (but not
enterococci). It is used topically or nasally for eliminating staphylococcal nasal carriage.
Polypeptide Antibiotics
These include polymyxin B, bacitracin, colistin and tyrothricin. All of these except bacitracin
affect cell membrane. Bacitracin inhibits cell wall synthesis. Because of neurotoxicity and renal
damage, these antibiotics are used only topically.
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Fusidic Acid
It acts by blocking protein synthesis and is used topically for staphylococcal infections.
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