Beta-Lactams PDF

DEFINITIONS - Beta-lactamases Bacterial enzymes (penicillinases, cephalosporinases) that hydrolyze the beta-lactam ring of certain penicillins and cephalosporins. - Beta-lactam inhibitors Potent inhibitors of some bacterial beta- lactamases used in combinations to protect...

DEFINITIONS - Beta-lactamases Bacterial enzymes (penicillinases, cephalosporinases) that hydrolyze the beta-lactam ring of certain penicillins and cephalosporins. - Beta-lactam inhibitors Potent inhibitors of some bacterial beta- lactamases used in combinations to protect hydrolyzable penicillins from inactivation. - Penicillin-binding proteins (PBPs) Bacterial cytoplasmic membrane proteins that act as the initial receptors for penicillins and other beta-lactam antibiotics. - Peptidoglycan Chains of polysaccharides and polypeptides that are cross-linked to form the bacterial cell wall. - Transpeptidases Bacterial enzymes involved in the cross- linking of linear peptidoglycan chains, the nal step in cell wall synthesis. - Selective toxicity More toxic to the invader than to the host. A drug that kills harmful microbes without damaging the host - The log phase is also the stage where bacteria are the most susceptible to the action of disinfectants and common antibiotics that a ect protein, DNA, and cell-wall synthesis. Bacterial growth may be inhibited following exposure to an antibiotic even after the drug concentration has fallen below the MIC. This is known as the postantibiotic e ect (PAE) ff ff fi CLASSIFICATION Bacteriocidal - kill bacteria Bacteriostatic - prevent growth of bacteria High doses of bacteriostatic drugs may act as Bacteriocidal agent  β-LACTAMS - All BETA-LACTAM antibiotics are BACTERICIDAL in nature - Drugs → bind to speci c receptors on bacterial cell membrane (Penicillin Binding Proteins, PBPs) → inhibit TRANSPEPTIDASE enzyme → prevents CROSS- LINKING of PEPTIDOGLYCAN chains - Bacteria formed in the presence of beta-lactams → lack CELL-WALL - Since cell-wall is vital for providing rigidity to the cell → lack of cell-wall in susceptible bacteriae causes IMBIBITION of water → causes death of susceptible organisms! - Bacteria like MYCOPLASMA → lack CELL-WALL → thus, INTRINSICALLY RESISTANT TO BETA-LACTAMS & VANCOMYCIN!! Beta –Lactam has heteroatomic ring structure with 3 carbon, one nitrogen atom Penicillins Chephalosporins Carbapenems Monobactams PENICILLINS - most widely e ective antibiotics and also the least toxic drugs known, but increased resistance has limited their use. - Members of this family di er from one another in the R substituent attached to the 6-aminopenicillanic acid residue. The nature of this side chain a ects the antimicrobial spectrum, stability to stomach acid, and susceptibility to bacterial degradative enzymes (β- lactamases). MOA 1- Penicillin (or other cell wall synthesis inhibitor) is added to the growth medium. 2- The cell begins to grow, but is unable to synthesize new cell wall. 3- cytoplasm covered by plasma membrane begins to squeeze out through the gap(s) in the cell wall. 4- Cell wall integrity is further violated. The cell continues to increase in size, but is unable to "pinch o " the extra cytoplasmic material into two daughter cells. 5- The loss of the cell wall also causes the cell to lose control over its shape, Finally, the fact that the cell disrupts homeostasis, which usually leads to the cell's death ü ü ü ü ff ff fi ff ff 1. Penicillin-binding proteins: Penicillins inactivate numerous proteins on the bacterial cell membrane. These penicillin-binding proteins (PBPs) are bacterial enzymes involved in the synthesis of the cell wall and in the maintenance of the morphologic features of the bacterium. Binding of PBP prevents peptide cross linking, cell wall weakened, bacteria undergoes lysis. 2. Inhibition of transpeptidase: Penicillins inhibit this transpeptidase-catalyzed reaction, thus hindering the formation of cross-links essential for cell wall integrity. As a result of this blockade of cell wall synthesis. 3. Production of autolysins: Many bacteria, particularly the gram-positive cocci, produce degradative enzymes (autolysins) that participate in the normal remodeling of the bacterial cell wall. Resistance to Penicillins and other B lactams 1. - One way that gram-negative bacteria defend themselves is by preventing the penicillin from penetrating the cell layers by altering the porins - gram-negatives have an outer lipid bilayer around their peptidoglycan - The antibiotic must be the right size and charge to be able to sneak through the porin channels, and some penicillins cannot pass through this layer - Because gram-positive bacteria do not have this perimeter defense, this is not a defense that gram- positives use 2. - Both gram-positive and gram-negative bacteria can have beta-lactamase enzymes that cleave the C-N bond in the beta-lactam ring - Gram-positive bacteria (like Staphylococcus aureus ) secrete the beta-lactamase (called penicillinase) and thus try to intercept the antibiotic outside the peptidoglycan wall - Gram-negative bacteria, which have beta-lactamase enzymes bound to their cytoplasmic membranes, destroy the beta-lactam penicillins locally in the periplasmic space 3. - Bacteria can alter the molecular structure of the transpeptidase so that the beta-lactam antibiotic will not be able to bind - Methicillin-resistant Staphylococcus aureus (MRSA) defends itself in this way, making it resistant to ALL of the penicillin family drugs 4. - Both gram positive and gram negative bacteria may also develop the ability to actively pump out the beta-lactam before it can bind to the transpeptidase enzyme - This one is called an "e ux" pump ffl  CLASSIFICATION 1.Natural penicillins ( Penicillin G, Penicillin V) Greatest activity against gram-positive organisms gram-negative cocci Non-ß-lactamase anaerobes Susceptible to hydrolysis by ß-lactamases 2. Antistaphylococcal penicillins ( nafcillin) Activity against Staphylococci Streptococci Resistant to Staphylococcal ß-lactamases 3. Extended-spectrum penicillins (aminopenicillins and antipseudomonal penicillins semi synthetic Same spectrum as penicillins, better activity against gram-negative organisms Still Susceptible to ß-lactamases 4. Antipseudomonal/carboxypenicillins -carbencillin, piperacillin, ticarcillin -Active against gram-negative organisms including P. aeruginasa 1.Natural penicillins PENICILLIN G→ commercially obtained from Penicillium chrysogenum PENICILLIN G → only NATURAL OCCURRING PENICILLIN!!! Important limitations of clinical use of Penicillin G include: 1. Drug → undergoes rapid breakdown by acid inside stomach → hence, NOT EFFECTIVE ORALLY! 2. Drug → rapidly excreted from kidney, via TUBULAR SECRETION → thus, has SHORT DURATION OF ACTION! 3. Drug → covers mainly GRAM-POSITIVE BACTERIA → has NARROW SPECTRUM OF ACTIVITY! 4. Most of following reasons: the Gram-positive bacteria have become resistant to Penicillin G, due to the: a. Development of BETA-LACTAMASE(penicillinase) b. b. Development of altered PBPs!! 5. Penicillin G → can cause severe hypersensitivity reactions!! ü ü ü ü STRATEGIES to overcome Penicillin G shortcomings: a. Development of ACID-RESISTANT PENICILLINS: Newer penicillins have been developed that are ACID-RESISTANT → thus can be given orally! Include OXACILLIN, PENICILLIN V, DICLOXACILLIN, CLOXACILLIN, AMOXICILLIN, AMPICILLIN, etc b. Pn G is SHORT-ACTING. Strategies to overcome this problem include: - Addition of BENZATHINE/ PROCAINE group to Pn G → can make it long-acting - BENZATHINE PN G → longest-acting penicillin! - PROBENECID→if given with Penicillin G → tubular secretion of latter will be inhibited! Since Pn G has WIDE THERAPEUTIC INDEX → HIGH INITIAL doses of drug can be used!! c. Strategy to overcome narrow-spectrum activity of Pn G: - Several new penicillins, with extended-spectrum have been developed - Include AMINOPENICILLINS, CARBOXYPENICILLINS, UREIDOPENICILLINS d. Strategy to overcome resistance issues with Penicillin G: -Beta-lactamase inhibitors → if added to Penicillin G → causes inhibition of bacterial enzyme → penicillins escape degradation! - Administration of PENICILLINASE-RESISTANT PENICILLINS, like CLOXACILLIN OXACILLIN, NAFCILLIN, DICLOXACILLIN & METHICILLIN. e. Strategies, to prevent risk of hypersensitivity with Pn G: -Hypersensitivity reactions can occur with ANY PENICILLIN - PENICILLINS →most common drugs responsible for ANAPHYLACTIC SHOCK - If a person is severely allergic to any penicillin → NO BETA-LACTAM ANTIBIOTIC SHOULD BE ADMINISTERED TO THAT PERSON!! (Except AZTREONAM) - To prevent severe allergic reactions → INTRA-DERMMAL SKIN TESTING can be opted! KINETICS Absorption of most oral penicillins (amoxicillin being an exception) is impaired by food, and the drugs should be administered at least 1–2 hours before or after a meal Penicillin G IV prefered than IM, because of irritation pain By IM route Half lives usually 30-60 minutes Ampicillin and the extended-spectrum penicillins are secreted more slowly than penicillin G and have half-lives of 1 hour Rapidly excreted ( unchanged ) by kidneys Some clearance via biliary excretion Nafcillin is primarily cleared by biliary excretion Oxacillin, dicloxacillin, and cloxacillin are eliminated by both the kidney and biliary excretion, and no dosage adjustment is required for these drugs in patients in renal failure  All beta- lactam antibiotics distribute easly - Cross placenta - Not teratogenic Penetration into the eye, the prostate, bone and CNS poor BUT When they get in amed (Meningitis) – permeability increases USES Oral penicillins should be given 1–2 hours before or after a meal; They should not be given with food to minimize binding to food proteins and acid inactivation Amoxicillin may be given without regard to meals Blood levels of all penicillins can be raised by probenecid which impairs renal tubular secretion of weak acids such as β-lactam compounds PROCAINE PENICILLIN Procaine penicillin is a suspension of procaine and PENICILLIN G complex, which is poorly soluble Procaine penicillin is always given by intramuscular route Virtually the injection is painless Since Procaine is released at the site of injection slowly to produce local anesthetic action A standard dose of Procaine penicillin can act up to 21-48hr BENZATHINE PENICILLIN long-acting preparation of PENICILLIN G, which acts for 32 days after 1.2 mega unit deep intramuscular dose This preparation should not be used for acute and severe infection This distinct advantages Avoid repeated injections Local trauma is reduced Reduces the cost fl NATURAL PENICILLIN USES (penicillin G and penicillin V) PENICLLIN G ( BENZYL PENILLIN) - for infections caused by a number of grampositive and gram-negative cocci, gram-positive bacilli, and spirochetes. Penicillins are susceptible to inactivation by β-lactamases (penicillinases) PENICLLIN V (ORALLY) - similar spectrum to that of penicillin G, but it is not used for treatment of bacteremia because of its poor oral absorption - Pneumococcal infections: pneumonia, meningitis and osteomyelitis due to penicillin-sensitive, pneumococci PnG is the DOC - Streptococcal infections: Pharyngitis, sinusitis, pneumonia, meningitis and endocarditis are all treated with penicillin - Infective endocarditis due to Strep. Viridans is treated with high dose PnG in combination with an AMG - Meningococcal infections : PnG is the DOC for all Meningococcal infections - Staphylococcal infections: Since most Staphylococci produce penicilinase, a penicilinase-resistant penicillin should be used - Diphtheria: Antitoxin is only e ective treatment. - PnG eliminates state –PP6 given for 10-12 days - Anaerobis infecios: Pulmonary, periodontal and barin abscesses due to anaerobes respond to PnG - Penicillin remains the drug of choice for the treatment of gas gangrene (Clostridium perfringens) Antitoxin is the treatment for tetanus- but PnG has adjuvant value and syphilis (Treponema pallidum) - EXAMPLE: Benzathine penicillin G, 2.4 million units IM – for syphilis once a week for 1–3 weeks - Actinomycosis: PnG is the DOC for all forms of Actinomycosis 12 to 20 MU should be given for 6 week - Other infections: PnG is the DOC for infections like anthrax, trenc mouth , rat bite fever and listeria infections ff  Antistaphylococcal penicillins Penicillins Resistant to Staphylococcal Beta- Lactamase (Methicillin, Nafcillin, and Isoxazolyl Penicillins-oxacillin, dicloxacillin) Their use is restricted to the treatment of infections caused by penicillinase-producing staphylococci including methicillin sensitive Staphylococcus aureus (MSSA) METHICILLIN IS NOT USED AS A DRUG (causes Interstitial nephritis) JUST USED IN LABS TO IDENTIFY MRSA The penicillinase- resistant penicillins have minimal to no activity against gram-negative infections EXAMPLE: dicloxacillin - is suitable for treatment of mild to moderate localized staphylococcal infections (Non - MRSAs) Extended-spectrum Penicillins Extended-Spectrum Penicillins (Aminopenicillins, Carboxypenicillins, and Ureidopenicillins) Ampicillin and amoxicillin same spectrum as for penicillin G but are more e ective against gram negative bacilli Ampicillin (with or without the addition of gentamicin) is the drug of choice for the gram-positive bacillus Listeria monocytogenes and susceptible enterococcal species respiratory infections; Amoxicillin is employed prophylactically by dentists in high-risk patients for the prevention of bacterial endocarditis Resistance to these antibiotics is now a major clinical problem because of inactivation by plasmid-mediated penicillinases. [Note: Escherichia coli and Haemophilus in uenzae are frequently resistant.] Formulation with a β-lactamase inhibitor, such as clavulanic acid or sulbactam, protects amoxicillin or ampicillin, respectively, from enzymatic hydrolysis and extends their antimicrobial spectra Example: without the β-lactamase inhibitor, MSSA is resistant to ampicillin and amoxicillin Antipseudomonal penicillins Piperacillin and ticarcillin are called antipseudomonal penicillins because of their activity against Pseudomonas aeruginosa Only PARENTERAL Piperacillin is the most potent of these antibiotics E ective against many gram-negative bacilli, but not against Klebsiella because of its constitutive penicillinase Formulation Ticarcillin/clavulanic acid; Piperacillin/tazobactam extends the antimicrobial spectrum of these antibiotics (for example, most Enterobacteriaceae and Bacteroides species) ff fl ff  CLINICAL USES Urinary tract infections Respiratory tract infections Meningitis To treat Gonorrhea, Syphilis, typhoid, bacillary dysentery Sub acute bacterial endocarditis. Bone and joint infections. Bronchitis, Pneumonia. Skin and Soft tissue infections. Adverse e ects of penicillins Neurotoxicity – irritating neuronal tissue – provokes seizures especially if given intrathecally (epileptic pts at risk!!) Hematologic toxicities – Decreased coagulation especially with high doses (Most common agents – piperacillin, ticarcillin, PCN G, nafcillin) More than 2 weeks Tx regimen – cytopenias – should chech CBC weekly (Complete blood count) Jarisch – Herxheimer reaction Happens when you treat Spirochete infections with PCN (Classically with syphilis, common in secondary) Also in Borellioisis, Leptospirosis and Brucelosis) Fever, Chills, Flushing, hyperventilation Usually happens 2 hours after starting treatment BACTERIAL CELL LYSIS – immune response Treatment –NSAID and Corticosteroides DRUG INTERACTIONS With Tetracyclines, Chloramphenicol, Erythromycin- - Antagonism Penicillin with Aminoglycosides-- Synergism. Penicillin and Aminoglycosides or Penicillin and hydrocortisone in same syringe - Inactivate each other (Pharmaceutical) Ampicillin with Allopurinol -- High incidence of non-urticarial maculopapular rashes Penicillin with Probenecid - Prolongs action of penicillin by decreasing tubular secretion Oral contraceptives – Penicillins may interact with oral contraceptives and decrease the e ectiveness of the oral contraceptives. Penicilin+spironolactone = hyperkalemia ff ff  PENICILIN RESISTANCE β-lactamases Enzymes produced by some bacteria -Hydrolyse beta-lactam ring on beta-lactam antibiotics, inactive them -can administer beta-lactamase inhibitors Alteration in PBPs-can provide organism resistance to penicillins E ux -Some bacteria have developed e ux mechanisms to actively pump antibiotics out Impaired penetration -In gram-negative bacteria beta-lactam antibiotics cross outer membrane via membrain protein channels called porins -Resistance can be built up via downregulation of porins -As porins are downregulated, more di cult for antibiotics reach cell wall β-LACTAMASE INHIBITORS CLAVULANIC ACID SULBACTAM TAZOBACTAM β-lactamases are a family of enzymes produced by many gram-positive and gram-negative bacteria that inactivate β-lactam antibiotics by opening the β-lactam ring. Inhibitors contain a beta-lactam ring Do not have anti-bacterial activity Given with beta-lactam antibiotics Di erent β-lactamases di er in their substrate a nities. § § § § ffl ff ff ffl ffi ffi  CLAVULANIC ACID Obtained from Streptomyces clavuligerus, it has a β- lactam ring but no antibacterial activity of its own. It inhibits a wide variety (class II to class V) of β- lactamases (but not class I cephalosporinase) produced by both gram-positive and gram-negative bacteria. Clavulanic acid is a ‘progressive’ inhibitor :binding with β- lactamase is reversible initially, but becomes covalent later—inhibition increasing with time. Called a ‘suicide’ inhibitor, it gets inactivated after binding to the enzyme. PHARMACOKINETICS Clavulanic acid has rapid oral absorption and a bioavailability of 60%; can also be injected Its elimination t½ of 1 hr and tissue distribution matches amoxicillin with which it is used (called co-amoxiclav). It is eliminated mainly by glomerular ltration and its excretion is not a ected by probenecid. Also, it is largely hydrolysed and decarboxylated before excretion, while amoxicillin is primarily excreted unchanged by tubular secretion. USES ddition of clavulanic acid re-establishes the activity of amoxicillin against β-lactamase producing resistant Staph. aureus (but not MRSA that have altered PBPs), H. in uenzae, N. gonorrhoeae, E. coli, Proteus, Klebsiella, Salmonella and Shigella. Bact. fragilis and Branhamella catarrhalis are not responsive to amoxicillin alone, but are inhibited by the combination. Amoxicillin sensitive strains are not a ected by the addition of clavulanic acid. Co-amoxiclav is indicated for: Skin and soft tissue infections, intra-abdominal and gynaecological sepsis, urinary, biliary and respiratory tract infections: especially when empiric antibiotic therapy is to be given for hospital acquired infections. Gonorrhoea (including PPNG) single dose amoxicillin 3 g + clavulanic acid 0.5 g +probenecid 1 g is highly curative. Adverse e ects : They are the same as for amoxicillin alone; g.i. tolerance is poorer—especially in children. Candida stomatitis/ vaginitis Rashes Hepatic injury in some case with the combination. v v v v v v v v v v v v v ff fi ff fl ff  SULBACTAM It is a semisynthetic β-lactamase inhibitor, related chemically as well as in activity to clavulanic acid. It is also a progressive inhibitor, highly active against class II to V but poorly active against class I β-lactamase. On weight basis, it is 2–3 times less potent than clavulanic acid for most types of the enzyme, but the same level of inhibition can be obtained at the higher concentrations achieved clinically. Sulbactam does not induce chromosomal β-lactamases, while clavulanic acid can induce some of them. Oral absorption of sulbactam is inconsistent. Therefore, it is preferably given parenterally. It has been combined with ampicillin for use against β- lactamase producing resistant strains. Absorption of its complex salt with ampicillin— sultamicillin tosylate is better, which is given orally. Indications : PPNG gonorrhoea; sulbactam per se inhibits N. gonorrhoeae. Mixed aerobic-anaerobic infections, intraabdominal,gynaecological, surgical and skin/soft tissue infections, especially those acquired in the hospital. Main Adverse E ects : Pain At Site Of Injection Thrombophlebitis Of Injected Vein Rash Diarrhea TAZOBACTAM Similar to sulbactam. Its pharmacokinetics matches with piperacillin with which it has been combined for use in severe infections like peritonitis, pelvic/urinary/respiratory infections caused by β-lactamase producing bacilli. However, the combination is not active against piperacillin-resistant Pseudomonas, because tazobactam (like clavulanic acid and sulbactam) does not inhibit inducible chromosomal β-lactamase produced by Enterobacteriaceae. It is also of no help against Pseudomonas that develop resistance by losing permeability to piperacillin. Dose: 0.5 combined with piperacillin 4 g injected i.v. over 30 min 8 hourly. v v v v v ü ü ü ü ü v v v v ff