Aminoglycoside Antibiotics Prof R K Dixit Pharmacology and

Aminoglycoside Antibiotics Prof. R. K. Dixit Pharmacology and Therapeutics K. G. M. U. Lucknow

First member Streptomycin discovered by Waksman in 1944 Natural and semi-synthetic antibiotics Produced from Actinomycetes Ø Those obtained from Streptomyces – Have suffix mycin (eg. Streptomycin) Ø Those obtained from Micromonospora – Have suffix micin (eg. Gentamicin, )

Structure characterized by ØTwo aminosugars joined to ØOne aminocyclitol moiety by ØGlycosidic (-O-) bond In most of members aminoacyclitol moiety is 2 Deoxystreptamine. In streptomycin the aminocyclitol is Streptidine.

General character of Aminoglycosides Formulations are Sulfate or hydrochloric salts group Formulations are water soluble and stable Highly polar basic drugs. (Not absorbed from GIT) Ionize during dissolution Distribution inside the cells is minimal Penetration through BBB is minimal Least metabolized by hepatic enzymes Excretion is mainly renal (unchanged form, through glomerular filtration)

Bactericidal in nature More active in alkaline p. H MOA is by interfering with protein synthesis Attach with 30 S ribosomal subunit (ATT) Concentration dependent (PAE) Mainly gram negative (plus tuberculosis by streptomycin, Kanamycin, Amikacin) Cross resistance is partial Therapeutic index is narrow

Have NONE side effects ØNephrotoxic ØOtotoxic ØNeuromuscular blockage ØEtc. (Teratogenicity)

Nephrotoxicity Streptomycin is least nephrotoxic. Larger the number of NH 2 more nephrotoxicity. Nephrotoxicity is caused by Ø Inhibition of an intracellular lysosomal phospholipase-A 2 in renal brush border. Ø Leading to lysosomal distension, Ø Rupture and Release of acid hydrolases Ø Release of Free Aminoglycosides into cytosol. Ø This free drug binds to other cellular organelles (eg. In mitochondria it displaces Ca++ leading to mitochondrial degeneration and necrosis. ) Nephrotoxicity is reversible Verapamil and Ca++ can Reduce nephrotoxic potential But Also reduce antibacterial effect

KAN (Kanamycin, Amikacin, Neomycin) mainly damage cochlea rest vestibular damage All are teratogenic Neomycin and Framycetin have extreme systemic toxicity ( only topically used) Amikacin has widest spectrum Avoid concurrent use of other Ototoxic drugs ( Frusemide, Ethacrinic acid, Minocycline) Neomycin used orally for Hepatic Encephalopathy)

Avoid concurrent use of other nephrotoxic drugs (Amphotericin B, Vancomycin, Cephalothin, Cephradrine, Cyclosporin, Cisplatin) Be overcautious while using in extremes of age and renal compromised Be overcautious while using in operated patients (Received Curare)

Don’t mix with any other drug (Pharmaceutical Drug Interaction) Partially removed by peritoneal and haemodialysis The excretion is proportional to creatinine clearance. Half life increases in renal insufficiency. Dose adjustment is needed in renal insufficiency Most precise method for calculating dose is using creatinine clearance But in Practice most often used formula to calculate dose is

Members ØAmikacin Ø ØStreptomycin Ø Ø Sisomicin Ø Ø Spectinomycin Ø ØKanamycin Ø Ø Ispepamycin Ø Netilmicin ØGentamicin Ø Ø Ø Ribostamycin Arbekacin Bekanamycin Dibekacin Hygromycin Verdamicin Astromicin Paromomycin Ø Tobramycin ASKING Truth IS Great TASK

MOA Bactericidal (Gram Negative, No action on Anaerobes) Initial entry of Aminoglycosides through bacterial cell wall to periplasmic space ØThrough porin channels by passive diffusion (1) Later on further Entry across cytoplasmic membrane is carrier mediated (linked to electron transport chain, energy and oxygen dependent) ØActive transport (2) Advantage of adding Beta lactams ØBeta Lactam antibiotics weaken the bacterial cell wall ØFacilitate passive diffusion of Aminoglycoside. (Synergism)

Penetration is dependent on Maintenance of polarized membrane Oxygen dependent active process ØNot active in absence of oxygen ØNot effective against anaerobes ØNot effective in presence of big abscess p. H alteration. Alkalization favors penetration into cell

Prevent polysome formation (accumulation of nonfunctional monosomes) Inside the bacterial cell Aminoglycoside bind with 30 S ribosome subunit ( or at the interface of 30 S and 50 S) Inhibit formation of initiation complex Inhibit protein synthesis Misreading of m. RNA Codon Entry of wrong amino acid in the chain Formation of wrong peptide chain (Check the growth of bacteria, Bacteriostatic)

How Cidal action is achieved Ans- Defective proteins incorporated in cell membrane. Due to secondary changes in the integrity of bacterial cell membrane. (Increase permeability for ions, amino acids, proteins- Leading to leaking of these out side) Bonus of incorporation of defective protein in cell membrane More entry of antibiotic occurs in to the cell. Further increasing affectivity Death Of Bacteria

Resistance development (Conjugation and transfer of plasmid) Development and synthesis of plasmid mediated bacterial transferase enzyme (Acetyltransferase, Phosphotransferase, Adenylyltransferase), which inactivates Aminoglycosides. Impermeability of porins, Impaired active transport Inactivating enzymes in the cell membrane – Phosphorylate / Adenylate / Acetylate and inactivate Aminoglycosides Phosphorylated / Adenylated / Acetylated conjugates of Aminoglycoside can not bind at target ribosomal subunit and site. Decreased affinity of ribosomal proteins for binding with Aminoglycosides

Side effects and Toxicity Ototoxic- ◦ Concentrated in labyrinthine fluid ◦ Released from there when plasma concentration decreases. Less seen in routine dose. (High dose, long time high chance) Damage of sensory and hair cells Vestibular- ◦ Presents with Vertigo, Ataxia, Nystagmus ◦ (Headache, Nausea, Vomiting, Dizziness) ◦ Recover slowly ( Least recovery in elderly) Cochlear- ◦ Starts from base spreads to apex. ◦ High frequency affected first ◦ Recovery is very poor. ◦ Deafness may be permanent, more in elderly ◦ Presents with tinnitus (reversible) followed by hearing loss (irreversible)

Nephrotoxicity- ØMore damage of cortical nephrons ØRelated to total exposure ØMore in Elderly ØMore in pre-existing renal disease ØReversible ØTubular damage (Loss of concentrating mechanism) ØReduction in GFR (Interference with the prostaglandin production in kidney) ØUrine contains albumin and casts ØNitrogen retention in body Nephrotoxicity- Reduced clearance of Aminoglycosides – High blood levels of Aminoglycosides – High chances of Ototoxicity

Neuromuscular Blockade More with Neomycin and Streptomycin Ø Reduce Acetylcholine release from Motor Endings Ø Interfere with mobilization of synaptic vesicles Ø By antagonizing calcium Ø Decreased sensitivity of the muscle end plates to Ach. Non significant in otherwise normal cases in routine § Dangerous in § Myasthenia gravis § Direct administration of Aminoglycosides into pleural and peritoneal cavities § If patient received curare like muscle relaxant during surgical procedure Partially antagonized by IV calcium

Streptomycin Narrow spectrum (Gram negative + M. tuberculosis) Uses ØTuberculosis (First drug to show antitubercular activity) Ø(PESRI-25, 20, 15, 10, 5 mg/kg) Acts against extracellular bacilli (due to poor penetration in the cell) Also active against Atypical Mycobacterium (M. kansasii and M. avium intracellulare. ) Resistance develops fast (Never use streptomycin alone as antitubercular) SABE Plague – (Streptomycin {Tetracycline} Tularemia- (DOC {Tetracyclines alternate} Brucellosis

Tularemia (rabbit fever, deer fly fever, and Ohara's fever)is caused by the bacterium Francisella tularensis a gram-negative, nonmotile coccobacillus. Depending on the site of infection, tularemia has six characteristic clinical symptoms: ulceroglandular , glandular, oropharyngeal, pneumonic, oculoglandular, and typhoidal. Brucellosis, also called Bang's disease, Crimean fever, Gibraltar fever, Malta fever, Mediterranean fever, rock fever, or undulant fever is a highly contagious zoonosis caused by ingestion of unsterilized milk or meat. Transmission from human to human, through sexual contact or from mother to child, is rare but possible. Brucella are small, gram-negative, non-motile, non-spore-forming, rod shaped (coccobacilli) bacteria. They function as facultative intracellular parasites. Plague is a deadly infectious disease that is caused by the enterobacteria Yersinia pestis. The symptoms of plague depend on the concentrated areas of infection in each person: such asbubonic plague in lymph nodes, septicemic plague in blood vessels, pneumonic plague in lungs, and so on. It is treatable if detected early.

ATT Pyrazinamide (25)– Cidal, Intra, Inhibition of Mycolic Acid, Hyperuricemia, Hepatotoxicity Ethambutol (20)– Static, Inhibits arabinosyl transferase and inhibit Mycolic acid incorporation, Hyperuricemia, Optic Neuritis Streptomycin (15)- NONE Rifampicin (10)- Red discoloration, Cidal, Both Extra and Intra, Inhibition of DNA dependent RNA polymerase, Inducer, Hepatitis Isoniazid (5)- Peripheral neuropathy , Pyridoxine, Inhibition of Mycolic Acid of cell wall, Cidal to multiplying, Both Extra and Intra

Gentamicin (Gentamicin) Most commonly used Aminoglycosides (Jantamycin) Obtained from Micromonospora purpurea Broader spectrum ( But not effective in T. B) Synergism with Beta lactams Activity decreases in presence of pus Uses -Usually in combination with Penicillin, Cephalosporin or Fluoroquinolones, (BA, CA, FA with or without M) SABE Usually in peritoneal dialysate in topical creams for dressing and eye preparations combined with Ticarcillin for Pseudomonas

ØGentamicin-PMMA (Polymethyl methacrylate) ØA new drug delivery system for Osteomyelitis. Ø Small acrylic beads impregnated with gentamicin. ØThreaded over surgical wire and implanted in bone cavity ØLeft for 10 days. ØThen removed along with wire.

Amikacin Semisynthetic derivative of Kanamycin Next to gentamicin regarding use Resistant is less Widest spectrum ( Second line ATT) Reserve drug as alternate to Gentamicin More hearing loss

Kanamycin Highly Ototoxic Highly Nephrotoxic) Narrow spectrum Rarely used now ( Second line anti-tubercular drug)

Tobramycin More active against Pseudomonas and Proteus Reserve alternative of Gentamicin

Sisomicin (Not Sisomycin) Obtained from Micromonospora Same as gentamicin Greater efficacy against Pseudomonas

Netilmicin (Not Netilmycin) Semisynthetic derivative of Sisomicin Similar to Gentamicin but wider spectrum Effective in Gentamicin resistant cases of Proteus, Pseudomonas, Klebsiella, E. coli

Paromomycin To treat intestinal amoebiasis Cryptosporidiosis in immunocompromised (AIDS patients) Spectinomycin Chlamydial treatment along with Doxycycline

Framycetin (Soframycin) Too toxic for systemic use Topically as ointment, cream, eye drops, etc.

Neomycin Wide spectrum Highly Cochlear Toxic, and Nephrotoxic Most common use is topical, ointment, eye and ear drops ◦ ( in combination with Polymyxin, Bacitracin as Nebasulf, Polybiotic cream, etc) Neomycin with Polymyxin-B solution is used as an irrigant in urinary bladder to prevent bacteriuria associated with use of indwelling catheter.

Oral neomycin has damaging effect on intestinal villi- Malabsorption syndrome. Damages colonic flora- deficiency of vit. K Superinfection Not used systemically ( Except for preparation of bowel for surgery and in Hepatic Coma or Hepatic Encephalopathy)

Hepatic coma (Hepatic Encephalopathy) Colonic bacteria produce NH 3 can cross BBB NH 3 is toxic to nervous system NH 3 is converted to Urea by Liver (Urea does not cross BBB) In hepatic failure conversion of NH 3 to Urea does not occur Increased level of NH 3 produces encephalopathy. Neomycin suppresses colonic flora NH 3 production in colon is reduced NH 3 level in blood is reduced Other drug used for this purpose is Lactulose