Today we are going to discuss about aminoglycosides (and i try to keep it simple, promise)

Aminoglycosides are the antibiotics derived from the soil actinomycetes (a strain of soil bacteria).

Streptomycin was the first member which was discovered in 1944 by Waksman and his colleagues.

It was the first antibiotic which can be used for the treatment of tuberculosis and later Waksman was awarded by Nobel prize for this breakthrough discovery.

Structurally they are the amino sugars joined by glycoside linkage (i am just saying that they are polar compounds).

Now we know that they are polar compounds, highly water soluble (now if you recall your pharmacokinetics you can easily conclude that they have difficulty in crossing the cell membrane). Aminoglycosides are neither absorbed nor destroyed in the GIT.

Aminoglycosides are not absorbed orally – ALL AMINOGLYCOSIDES ARE GIVEN PARENTRALLY (by i.v or i.m route)

They have very less penetration in Blood brain barrier.

They act by inhibiting protein synthesis (bactericidal drugs).

They bind to 30 s ribosome and

1) Freeze initiation of protein synthesis,

2) Misreading of the code (by entering one or more amino acid in peptide chain)

3) Interfere with polysome formation.

Aminoglycosides are not metabolize in the body hence excecated by kidney in unchanged form.

They all produce nephrotoxicity, ototoxicity and neuromuscular blockade as adverse effects.

Nephrotoxicity is almost reversible, during ototoxicity, cochlear damage causes deafness and it is permanent while vestibular damage started as headache, later causes nystagmus, vertigo and ataxia which can take months in recovery (often incomplete).

Examples and uses of aminoglycosides are-

Aminoglycosides should be avoided during pregnancy as they can cause ototoxicity in fetus.

These drugs exhibit concentration dependent killing and have prolong time dependent killing hence can be administration as single daily dosage.

They show synergistic effects when combined with Beta lactam antibiotics or vancomycin against gram positive bacteria.

So, if you with me till now, i think we have understand some very basic concepts about aminoglycosides.

Have a nice day, happy learning.

Neomycin is an aminoglycoside antibiotic.

Due to its extreme nephrotoxicity, we cannot use it by intravenous or intramuscular route.

By giving orally it is not absorbed nor metabolized. If you want to read more about aminoglycosides you can clink on the link (Must Know Interesting Points About Aminoglycosides)

Use of Neomycin in hepatic coma-

In normal circumstances the NH3 produced by colonic bacteria is detoxified by the liver. Liver convert NH3 into urea, which is excreted by kidneys.

But in hepatic coma patient, the NH3 produced by colonic bacteria is not detoxified by the liver and NH3 level increases which further causes encephalopathy.

When we give neomycin orally. it kills the gut bacterial flora and due to less NH3 formation, the condition improves, usually it takes 48 hours to act.

Note- Now a days we prefer less toxic agent in hepatic coma like lactulose. (to know more click on the link- Lactulose use in hepatic coma )

Other uses of Neomycin

1. Orally we can use neomycin to reduce aerobic gut flora before surgery (preparation of bowel before surgery).

To cover the anaerobic infections we combined it with metronidazole, which help in reducing postoperative infections.

2) It is most extensively used topically for wounds – burn cases, ear infections, eye infections (here it is commonly combined with polymyxin, bacitracin etc. for better coverage)

Q. Why does pyridoxine is used with isoniazid in Tuberculosis treatment ?

Answer- As we know that isoniazid is an anti-tubercular drug. It acts by inhibition of synthesis of mycolic acid (which is an important component of mycobacterial cell wall).

Though isoniazid is well tolerated by the patients, but in some, it can cause neurotoxicity such as peripheral neuritis and other neurological manifestations like paresthesia, numbness, mental disturbance etc.

So, we use pyridoxine to prevent and also to treat the neurotoxicity.

The prophylactic dose of pyridoxine is 10 mg/day whereas isoniazid induced neurotoxicity is treated by pyridoxine 100 mg/ day.

Hepatotoxicity is also a major adverse effect of isoniazid, which is dose related and is reversible when the drug is stopped.

Some extra interesting points about Isoniazid-

• Its is an excellent antitubercular drug which acts on TB bacilli extracellularly and intracellularly.
• It is also one of the cheapest antitubercular drug.
• Specifically fast multiplying organisms are killed rapidly.
• It is an essential component of all antitubercular regimens (unless it is intolerable or resistant).
• It is also used in prophylaxis of tuberculosis (given for six months, daily)

Hope, this post is helpful to you in understanding this basic concept.

Have a nice day, happy learning………..