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AMA-_Miscellaneous_Antibiotics.pdf

The document provides an overview of various antibiotics including vancomycin, spectinomycin, clindamycin, polymyxins, and bacitracin, detailing their mechanisms of action, uses, side effects, and resistance issues. It highlights vancomycin's role against gram-positive bacteria, spectinomycin's use for gonorrhea, clindamycin's applications in anaerobic infections, and the toxicity concerns associated with polymyxins and bacitracin. Additionally, it emphasizes the importance of careful use to prevent resistance and adverse reactions.

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Sanjaya Mani Dixit Assistant Prof of Pharmacology Miscellaneous Antibiotics
Contents • Vancomycin Cell wall synthesis inhibitor • Spectinomycin (AGs) Protein Synthesis Inhibitors • Clindamycin Protein Synthesis Inhibitors • Polymyxin-B Causing leakage of cell membrane Bacitracin Cell wall synthesis inhibitor
Mechanisms of Axn of Antibiotics
Vancomycin • A glycopeptide antibiotic discovered in 1956 • Bactericidal on Gram +ve cocci, Neisseria, Clostridia and diptheroids. • Gram –ve bacilli are inherently non-responsive to Vancomycin. • Importance is due to its efficacy against MRSA, Strep viridans, Enterococcus and Cl. difficile.
Vancomycin Mechanism of action Inhibition of bacterial cell wall synthesis Binds to the terminal di-peptide D-ala-D-ala sequence of peptidoglycan units Prevents its release from the bactoprenol lipid carrier so that assembly of the units at the cell membrane and their cross linking to form the cell wall cannot take place.
Vancomycin PK Not absorbed orally- used for GI problems orally IV administration Wide distribution penetrates inflamed meninges Excreted mainly by glomerular filtration T1/2 of 6 hrs Dose must be reduced in case of renal insufficiency
Vancomycin Uses Oral Second choice drug to Metronidazole for antibiotic associated pseudomembranous entero-colitis caused by C. difficile. Staphylococcal enterocolitis
Vancomycin Uses--IV Serious MRSA infections Enterococcal endocarditis with gentamicin as penicillin substitute Gram +ve organism caused SSTIs Emperical therapy of bacterial meningitis with IV ceftriaxone or cefotaxime Penicillin resistant pneumococcal infections Diptheroid infections Surgical prophylaxis in MRSA prevalent areas
Vancomycin Side Effects High systemic toxicity Plasma concentration dependent nerve deafness, which may be permanent Dose related kidney damage Skin allergy and hypotension during IV injection Red man syndrome- rapid IV inj causes chills, fever, uritcaria and intense flushing as a result of histamine release by direct action on mast cells
Vancomycin Resistance Extensive use of Vancomycin in hospitals for prophylaxis has resulted in VRSA and VRE. Enterococcal resistance to vancomycin is due to plasmid mediated alteration of the dipeptide target site, reducing its affinity for vancomycin.
Spectinomycin • Its an Aminocyclitol antibiotic and is a Aminoglycoside like drug, produced by bacterium Streptomyces spectabilis. • Narrow spectrum- inhibits limited number of Gram –ve bacteria, N. gonorrhoeae • Mechanism involves inhibiting the synthesis of proteins –Bacteriostatic • Spectinomycin binds to the 30S subunit of the bacterial ribosome and interrupts protein synthesis.
Spectinomycin • It is given parenterally to treat gonorrhea, especially in patients who cannot be given the first line agents (B- lactam/macrolides,etc.) due to allergy to penicillins, or in resistant cases. • However, N. gonorrhoeae resistance against Spectinomycin has been seen since 1982 itself. • Used in veterinary medicine to combat bacterial infections. • Intramuscular injection
Spectinomycin– Adverse Effects • Itching, chills, stomach-ache, and red rash. • Pain at the injection site • Occasionally fever and nausea. • Repeated doses- Hepatotoxicity, Nephrotoxicity and anemia
Clindamycin • A potent lincosamide antibiotic. • Similar in MOA (inhibits protein synthesis by binding to 50S ribosome) and spectrum of activity to erythromycin with which it exhibits partial cross resistance.
Clindamycin Spectrum It inhibits most gram-positive cocci (including penicillinase producing Staph., but not MRSA), • C. diphtheriae, • Nocardia, • Actinomyces, • Toxoplasma • Highly efficient against a variety of anaerobes, especially Bact. fragilis.
Clindamycin-Uses • Because of potential toxicity, use of clindamycin is restricted to anaerobic and mixed infections, especially by Bact. fragilis causing abdominal, pelvic and lung abscesses. • To treat staphylococcal infections of bones and joints. • Given topically, as eye drops, for staphylococcal conjunctivitis. • Diabetic foot infections • Acne ( 1% topical gel & lotion )
Clindamycin--Side effects • Rashes & Urticaria • Abdominal pain, diarrhoea & potentially fatal pseudomembranous enterocolitis. • Hepatotoxicity & bone marrow suppression- rare Pseudomembranous enterocolitis This is a super-infection comprising of an acute inflammation of the colon caused by a necrotising toxin produced by a clindamycin-resistant organism, Clostridium difficile, which may form part of the normal faecal flora. The drug should be promptly stopped and metronidazole (altematively Vancomycin) given to treat it.
Clindamycin • It is generally combined with aminoglycoside or cephalosporin for enhanced actions. • Metronidazole and chloramphenicol are the alternatives to clindamycin for covering the anaerobes.
Polymyxins • The polymyxins are a family of lipopeptides produced by Bacillus polymyxa and related bacteria. • They are bactericidal agents • Only polymyxins B and E are used therapeutically. • Polymyxin E is called Colistin. • Polymyxins B is given parenterally unless infection is in the GIT (unabsorbed).
Polymyxin B and Colistin • Both the drugs were discovered in the late 1940s • Polymyxin B from Bacillus polymyxa • Colistin from B. colistinus • They are both active against Gram –ve bacteria only; all except Proteus, Serratia and Neisseria • Colistin is more potent on Pseudomonas, Salmonella and Shigella
Polymyxin-MOA • They act like cationic detergents by binding to the cell membrane and causing the leakage of essential cytoplasmic contents, thus bactericidal in action. • They have high affinity for phospholipids • The peptide molecules (or their aggregates) orient between the phospholipid and protein films in Gram negative bacterial cell membrane causing membrane distortion and pseudopore formation • Results in leakage of ions, aminoacids– Cell death • May also inactivate the bacterial endotoxin • Exhibit synergism with many other AMAs by helping with penetration into the bacterial cell.
Polymyxin-Uses Typical uses are Topically In combination with other AMAs for skin infections, burns, otitis externa, conjunctivitis, corneal ulcer caused by Gram –ve bacteria including Pseudomonas Orally Gram –ve bacillary diarrhoea (E. coli, Salmonella, Shigella), especially in infants and children Pseudomonas superinfection enteritis
Polymyxin S/Es Systemic toxicity is high- causes histamine release from mast cells • Nephrotoxic>> Neurotoxic • Dizziness, muscle weakness, flushing, facial and peripheral paraesthesia, partial deafness, visual disturbances, vertigo, confusion, hallucinations, seizures and ataxia, NM blockade • Used only as a last resort if modern antibiotics are ineffective or are contraindicated. • Little or no absorption from oral route or even from ulcers when applied topically on skin, so are safe. • Oral route- occasional nausea, vomiting, diarrhoea.
Bacitracin • Bacitracin is a mixture of related cyclic polypeptides produced by Bacillus subtilis. • These peptides disrupt both Gram +ve and Gram -ve bacteria, by interfering cell wall and phospholipid synthesis. • Most active against Gram +ve bacteria, including Staph. (producing B- lactamase) & Streptococci
Bacitracin • Mechanism of action – Inhibition of cell wall synthesis – It is bactericidal. • It acts by inhibiting cell wall synthesis at a step earlier than that inhibited by penicillin. Subsequently, it increases the efflux of ions by binding to cell membrane causing cell death. • It is active mainly against gram-positive organisms (both cocci and bacilli). Neisseria and H. influenzae are also affected.
Bacitracin--Clinical uses – Not used systemically (kidney toxicity high) – Used for suppression of mixed bacterial flora in skin, wounds or mucus membranes. – Topical for infections of mouth, nose, eye and skin – Use is restricted to topical application for infected wounds, ulcers, eye infections- generally in combination with neomycin, polymyxin, etc. – Solutions of bacitracin containing 100–200 units/mL in saline can be employed for irrigation of joints, wounds, or the pleural cavity.
Bacitracin • Bacitracin is markedly nephrotoxic if administered systemically, producing proteinuria, hematuria, and nitrogen retention. • Because of its marked toxicity when used systemically, it is limited to topical use. • Topical application results in local antibacterial activity without significant systemic toxicity. • Hypersensitivity reactions (eg., skin rashes) are rare. • Rarely other types of skin infections (such as fungal or other bacterial infections).
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AMA-_Miscellaneous_Antibiotics.pdf