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==Introduction==
This is a large group of antibiotics that are made up of a sugar group and an amino group. As this is a large and diverse group we shall firstly discuss general characteristics and then one by one go through each drug to show and explain their differences.
This is a large group of antibiotics that are made up of a sugar group and an amino group. As this is a large and diverse group we shall firstly discuss general characteristics and then one by one go through each drug to show and explain their differences.
==General Group Characteristics==
==General Group Characteristics==
===Mechanism of Action===
===Mechanism of Action===
The drug must first enter the bacterial cell which it does via a oxygen-dependent active transport system. Thus it is unable to work against any anaerobic species. Once inside the cell it disrupts protein synthesis by acting directly on the ribosome. Unlike the other antibiotics that act at the level of protein synthesis these drugs are '''bactericidal''' and are concentration dependent killers. They will act synergistically with any antibiotic that disrupts cell wall synthesis, ie any of the beta-lactams.
The drug must first enter the bacterial cell which it does via a oxygen-dependent active transport system. Thus it is unable to work against any anaerobic species. Once inside the cell it disrupts protein synthesis by acting directly on the ribosome. Unlike the other antibiotics that act at the level of protein synthesis these drugs are '''bactericidal''' and are concentration dependent killers. They will act synergistically with any antibiotic that disrupts cell wall synthesis, ie any of the beta-lactams.
===Spectrum of Activity===
===Spectrum of Activity===
* They are active mainly against gram-negative species, including some of the hardier species.
* They are active mainly against gram-negative species, including some of the hardier species.
* There is variable gram-positive activity.
* There is variable gram-positive activity.
* They tend not to work well in purulent material.
* They tend not to work well in purulent material.
* If the local tissue environment is acidic the efficacy of the drug will be reduced.
* If the local tissue environment is acidic the efficacy of the drug will be reduced.
===Pharmacokinetic Considerations===
===Pharmacokinetic Considerations===
Aminoglycosides are very hydrophilic molecules and weak bases and so aren't very well absorbed in the gastrointestinal tract. They distribute poorly and are confined to mainly extracellular fluid. Elimination is performed by the kidneys and the drugs are excreted unchanged in the urine and so have very short half-lives. They also bind to renal tissue and so shouldn't be used in patients with renal failure.
Aminoglycosides are very hydrophilic molecules and weak bases and so aren't very well absorbed in the gastrointestinal tract. They distribute poorly and are confined to mainly extracellular fluid. Elimination is performed by the kidneys and the drugs are excreted unchanged in the urine and so have very short half-lives. They also bind to renal tissue and so shouldn't be used in patients with renal failure.
===Side Effects and Contraindications===
===Side Effects and Contraindications===
* They tend to be nephrotoxic and shouldn't be used if any renal pathology is suspected. To try and avoid this problem give one large single dose daily rather than splitting the dose up as accumulation of the drug will be increased in the kidney.
* They tend to be nephrotoxic and shouldn't be used if any renal pathology is suspected. To try and avoid this problem give one large single dose daily rather than splitting the dose up as accumulation of the drug will be increased in the kidney.
* Ototoxicity is a problem with the Vestibulocochlear Nerve (Cranial Nerve VIII) affected.
* Ototoxicity is a problem with the Vestibulocochlear Nerve (Cranial Nerve VIII) affected.
* They can create non-depolarising neuromuscular junction blocks leading to acute paralysis and cardiovascular collapse if given intravenously.
* They can create non-depolarising neuromuscular junction blocks leading to acute paralysis and cardiovascular collapse if given intravenously.
==Streptomycin==
==Streptomycin==
* Reistance to this drug is widespread.
* Reistance to this drug is widespread.
* It's use is limited by its toxicity, especially in cats. It is main toxicity problem is with ototoxicity. If used post-anaesthesia there is a higher risk of the patient experiencing a neuromuscular block.
* It's use is limited by its toxicity, especially in cats. It is main toxicity problem is with ototoxicity. If used post-anaesthesia there is a higher risk of the patient experiencing a neuromuscular block.
==Neomycin==
==Neomycin==
* More active than Streptomycin but still not very active. Good activity against ''S.aureus'' but is poor against other gram-positives. Though it is active against most gram-negatives including ''Pseudomona''.
* More active than Streptomycin but still not very active. Good activity against ''S.aureus'' but is poor against other gram-positives. Though it is active against most gram-negatives including ''Pseudomona''.
* This is the most toxic of all aminoglycosides and is mainly nephrotoxic and toxic to the cochlear.
* This is the most toxic of all aminoglycosides and is mainly nephrotoxic and toxic to the cochlear.
==Kanamycin==
==Kanamycin==
* It has a wider therapeutic index than neomycin, but the normal toxicity risks still stand.
* It has a wider therapeutic index than neomycin, but the normal toxicity risks still stand.
* Cross-resistance exists with neomycin.
* Cross-resistance exists with neomycin.
==Gentamicin==
==Gentamicin==
* It is very nephrotoxic and shouldn't be used for more than seven days and it is recommeneded to only give once daily doses.
* It is very nephrotoxic and shouldn't be used for more than seven days and it is recommeneded to only give once daily doses.
* Resistance is currently uncommon in veterinary pathogens.
* Resistance is currently uncommon in veterinary pathogens.
==Amikacin==
==Amikacin==
* More active than Kanamycin but not as broad spectrum as Gentamicin.
* More active than Kanamycin but not as broad spectrum as Gentamicin.
* Standard concerns about toxicity remain.
* Standard concerns about toxicity remain.
==Tobramycin==
==Tobramycin==
* Similar level activity against pathogens as Gentamicin but with the least toxicity of all aminoglycosides.
* Similar level activity against pathogens as Gentamicin but with the least toxicity of all aminoglycosides.
* It is currentlt too expensive to use in the veterinary field.
* It is currentlt too expensive to use in the veterinary field.
==Aminocyclitols==
==Aminocyclitols==