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antimicrobial therapy 1 antimicrobial therapy 1 Presentation Transcript

  • Antimicrobial TherapyAntimicrobial Therapy Dr. Yahya Ibn Ilias
  • Antimicrobial agents  Are effective in the treatment of infections because of their selective toxicity i.e the ability to kill an invading micro organism without harming the cells of the host.  Antibiotic is the term used to describe any compound ( Synthetic / Natural) that inhibit of or kills micro organism.
  • Antimicrobial TherapyAntimicrobial Therapy • Selective destruction of the microorganism. • No or rare side effects on the host. • Antimicrobial substances should have a specific action against molecules or enzymes or metabolism of the microorganism only. Criteria that determine the effectivenessCriteria that determine the effectiveness of antimicrobial agents:of antimicrobial agents:
  • Antibiotic Sensitivity TestAntibiotic Sensitivity Test  During recent years, many bacteria have shown drug resistance against single or multiple drugs.  Once the organism is isolated from clinical sample, it is necessary to identify them and to test them against various antibiotics so as to choose the most effective one and in turn, to treat the patient in most rational way. Main purpose of Antibiotic Sensitivity Test:  To guide clinician in selecting the best antimicrobial agent in order to treat the patient.
  • Bacteriostatic Vs Bactericidal drugs  Bacteriostatic drugs arrest the growth and replication of bacteria at serum levels achievable in the patient ,thus limiting the spread of infection while the body’s immune system attacks, immobilizes and eliminates the pathogens.  Bacteriocidal drugs kill bacteria and decreases the total number of viable organism.  Eg: Chloramphenicol is static against gram-ve rods and cidal against pnemococci.
  • Antimicrobial Spectra  Antimicrobial spectra of a particular drug refers to the species of organisms affected by that drug. 1. Narrow spectrum: Antimicrobial agents acting only on a single or a limited group of micro organisms.  Eg: isoniazid is active only against mycobacteria.  Glycopeptides and bacitracin are only effective against Gram-positive bacteria, whereas polymixins are usually only effective against Gram negative bacteria.  Aminoglycosides and sulfonamides are only effective against aerobic organisms, while nitroimidazoles are generally only effective for anaerobes.
  • 2. Broad Spectrum: Drugs that affect a wide variety of species .  Eg: Tetracycline and chloramphenicol, fluoroquinolones, “third- generation” and “fourth-generation” cephalosporins.  Administration of broad spectrum antibiotics can drastically alter the nature of the normal bacteria flora and can precipitate a super infection of an organism.
  • Extended expectrum: Applied to antibiotics that are effective against gram +ve organisms and also against a significant number of gram -ve bacteria.  Eg: Ampicillin as it acts gram +ve and some gram-ve bacteria.
  • Combinations of Antimicrobial drugs  It is therapeutically advisable to treat with the single agent that is most specific for the infecting oraganism.  This strategy reduces the possibility of super infection, decreases the emergence of resistant organisms and minimizes toxicity.  However situations in which combinations of drugs are employed do exist. Eg: Rx of tuberculosis benefits from drug combinations.
  •  Advantages of drug combinations: Certain combinations of antibiotics such as b-lactams and aminogycosides show synergism i.e. combination is more effective than either of the drugs used separately. Disadvantages of drug combinations:  A number of antibiotics act only when organisms are growing. Thus concomitant administration of a second agent that results in bacteriostatic may interfere with the action of the first drug that is bactericidal.
  • Drug Resistance  Bacteria is said to be resistant if their growth is not halted by the maximal level of an antibiotic that is tolerated by the host.  Some organisms are inherently resistant to an antibiotic. Eg: gram – (ve) bacilli are resistant to Penicillin or M. Tuberculosis is insensitive to Tetracyclines.  However, microbial species normally responsive to a particular drug may develop resistant strains.  The emergence of these resistant strains has been ascribed to the inappropriate use of antibiotics in conditions that might resolve without treatment or which are amenable to antibiotic therapy. eg: Common cold.
  • Mechanism of Resistance  Susceptible bacteria can acquire resistance to AMAs by either Genetic mutation or by accepting Antimicrobial resistance gene from other bacteria.
  • A. Genetic alteration leading to drug resistant:  Resistance develops due to ability of DNA to: 1.Undergo spontaneous mutation 2.Move from one organism to another (resistance develop due to DNA transfer from one organism to another)  B. Altered expression of proteins in drug resistant organisms: 1.Alteration of the target site through mutation can confer resistance as occurs with the penicillin binding proteins in methicillin-resistant S.aureus.
  •  2. Efflux systems : That pumps out the drugs (tetracycline)  3. The ability to destroy or inactivate the antimicrobial agent also can confer resistance on microorganisms. Eg:b-lactamase destroy many penicillins and cephalosporins, acetyltransferase can convert chloramphenicol to an inactive compound.  C. Decreased penetrability of an agent can protect organisms against that antibiotic because it is unable to gain access to the site of action due to the presence of lipopolysaccharide layer (gram-ve bacteria).
  • Complications of Antibiotic Therapy  1.Hypersensitivity: Hypersensitivity reactions to antimicrobial drugs or their metabolic products frequently occur. Eg: Penicillins despite their almost absolute selective microbial toxicity can cause serious hypersensitivity problems, ranging from urticaria to anaphylactic shock.  2.Direct Toxicity: High serum levels of certain antibiotics may cause toxicity by affecting cellular processes in the host directly. Eg: Aminoglycosides can cause ototoxicity by interfering with membrane function in the hair cells of the organ of corti.
  •  3.Superinfections:  Drug therapy, particularly with broad spectrum antimicrobials or combinations of agents, can lead to alterations of the normal flora of the upper respiratory, intestinal and genitourinary tracts, permitting the overgrowth of opportunistic organisms, especially fungi or resistant bacteria. These infections are often difficult to treat.  An additional infection occurring during the course of an existing infection, usually caused by opportunistic microorganisms resistant to the antimicrobial agents used in treating the first infection
  • Misuses of Antibiotics  TREATMENT OF NONRESPONSIVE INFECTIONS  Most viral diseases are self-limited and do not respond to any of the currently available anti-infective compounds. Thus, antibiotic therapy of at least 90% of infections of the upper respiratory tract and many GI infections is ineffective.  THERAPY OF FEVER OF UNKNOWN ORIGIN  Fever of short duration in the absence of localizing signs usually is associated with undefined viral infections. Antimicrobial therapy is unnecessary, and resolution of fever usually occurs spontaneously within a week.  Fever persisting for 2 or more weeks, commonly referred to as fever of unknown origin, has a variety of causes; only about one quarter of these are infections.  Moreover, some of these infections (e.g., tuberculosis,disseminated fungal infections) may require antibiotics that are not typically used for bacterialinfections.  Inappropriately administered antibiotics may mask an underlying infection, delay the diagnosis, and prevent the identification of the infectious pathogen by culture.
  •  IMPROPER DOSAGE  Dosing errors with antibiotics are common. Excessive dosing can result in significant toxicities, while too low a dose may result in treatment failure and is most likely to select for antibiotic resistance.  INAPPROPRIATE RELIANCE ON CHEMOTHERAPY ALONE  Infections complicated by abscess formation or the presence of necrotic tissue or a foreign body often cannot be cured by antibiotic therapy alone.  Drainage, debridement, and removal of the foreign body are at least as important as the choice of antibiotic agent.  As a general rule, when an appreciable quantity of pus, necrotic tissue, or a foreign body is present, the most effective therapy is an antimicrobial agent given in adequate dose plus a properly performed surgical procedure.
  • CLASSIFICATION AND MECHANISM OF ACTION  Antimicrobial agents are classified based on proposed mechanism of action as follows:  (1) Agents that inhibit synthesis of bacterial cell walls, including the b-lactam class and other agents such as Vancomycin;  (2) Agents that act directly on the cell membrane to increase permeability and cause leakage of intracellular compounds;  (3) Agents that disrupt function of ribosomal subunits to reversibly inhibit protein synthesis (e.g., chloramphenicol, the tetracyclines, erythromycin, and clindamycin);
  •  (4) Agents that bind to the 30S ribosomal subunit and alter protein synthesis (e.g., the aminoglycosides);  (5) Agents that affect bacterial nucleic acid metabolism by inhibiting RNA polymerase (e.g., rifampin) or Topoisomerase / DNA gyrase (e.g., the quinolones);  (6) The antimetabolites, including trimethoprim and the sulfonamides, which block essential enzymes (PABA) of folate metabolism.
  • Summary of Targets
  • Inhibitors of Cell Wall Synthesis  B-lactam Antibiotics: A. Penicillins (Penicillin G, Penicillin V, Methicillin, Nafcillin, Oxacillin, Cloxacillin, Ampicillin, Amoxycillin, Carbenicillin, Ticarcillin, Pipercillin, Azlocillin) B. Cephalosporins: Ist generation: cefazolin, cefadroxil, cephalexin 2nd generation: cefaclor, cefoxitin, cefuroxime 3rd generation: cefixime, ceftriaxone, cefotaxime 4th generation: cefepime
  • C. Carbapenems: Imipenem, Meropenem, Ertapenem D. Monobactams: Aztreonam Other Antibiotics: Vancomycin, Bacitracin B-Lactamase Inhibitors: Clavulanic acid, sulbactam and tazobactam
  • Penicillins  Most widely effective antibiotics and are among the least toxic drugs known.  Bactericidal Mechanism of action (MOA):  Bacterial cell wall is cross linked polymer of polysaccharides and pent peptides.  Penicillin interact with penicillin binding protein(PBP) on cytoplasmic membrane to inhibit transpeptidation reactions involved in cross linking of peptidoglycan chains, the final step in cell wall synthesis.
  •  Penicillins are only effective against rapidly growing organisms that synthesize a peptidoglycan cell wall.  Consequently they are inactive against organisms devoid of this structure, such as mycobacteria, protozoa, fungi and viruses.  Activation of autolytic enzymes(autolysins) that destroy the existing cell wall.
  • B-lactam ring is present in penicillin. B-lactamase is the enzyme that hydrolyzes the cyclic amide bond of the B- lactam ring, which results in loss of bactericidal activity.
  • Subgroups and Antimicrobial Activity: Narrow spectrum, B-lactamase sensitive: 1. Penicillin G (natural penicillins) Acid labile 2. Penicillin V (acid stable )  Spectrum:  Streptococcal infection ( Pharyngitis, Otitis media, Rheumatic fever),  Pneumococcal infection :  Meningococcal infection : like meningitis, Gonorrhea**  Gram + (ve) bacilli : B. Antharcis, C. Diphtheriae  All clostridia are highly sensitive, so are Spirochetes.
  • Very narrow spectrum, b-lactamase resistant:  Nafcillin, Methicillin, Cloxacillin  Spectrum: known or suspected staphylococci Extended spectrum : - b-lactamase sensitive: ampicillin and amoxycillin  Spectrum: gram +ve cocci (not staph), E.coli, H.influenza, listeria monocytogens. - Others b-lactamase sensitive: Ticarcillin, piperacillin, azlocillin  Spectrum: gram –ve rods including pseudomonas Beta lactamase inhibitors : Clavulanic acid, sulbactam, Tazobactam
  • Mechanisms of Resistance: 1. Production of beta- lactamase by the organism:  Penicillin -- beta-lactamase ---------- penicillonic acid (no antibacterial activity) ---- break lactam ring structure. eg: staphylococcal 2. Structural change in PBPs: methicillin resistant s. aureus, penicillin resistant pneumococci. 3. Reduction in the permeability of the outer membrane of the bacteria to penicillins.
  • RESISTANCE TO ANTIBIOTICS- PENICILLIN NH O COOH CH3 CH3 NH O COOH CH3 CH3 +H20 β-LACTAM RING PENICILLOIC ACID OH N NH Hydrolysis of β-lactam bond β-LACTAMASE
  • Pharmacokinetics Administration: oral (amoxycillin), iv (methicillin, ticarcillin, carbenicillin, piperacillin) or im route (procaine penicillin and benzathine penicillin). Absorption: most of the penicillins are incompletely absorbed after oral administration and reach the intestine in sufficient amount to affect the composition of the intestinal flora. Distribution: distribution of the drug throught the body is good.
  •  Metabolism: metabolism of these drugs by the host is usually insignificant, but some metabolism of penicillin G has been shown to occur in patients with impaired renal function.  Excretion: most are eliminated through active tubular secretion. Nafcillin and oxacillin eliminated largely in bile.  Plasma half life : usually < 2 hours
  • Narrow spectrum Penicillins
  • Benzylpenicillin (penicillin G) Properties :  Narrow spectrum  Bactericidal in action and very high activity  Destroyed by gastric HCL  Destroyed by beta – lactamase  Short duration of action  Highly water soluble Indications :  Pneumococcal, streptococcal (infective endocarditis), meningococcal meningitis, tetanus, gas gangrene, syphillis, gonorrohea
  • Penicillin V (acid resistant) Properties :  Same as penicillin G but  Less potent activity  Acid resistant (orally active)  Short duration of action  Destroyed by beta – lactamase Indications :  Boil, abscess  Pneumonia  Prophylaxis before and after surgery
  • Beta – lactamase resistant penicillins  The penicillins that are resistant to hydrolysis by beta lactamase (penicillinase) are called beta – lactamase resistant penicillins. Properties :  Narrow spectrum of activity, but less potent then benzylpenicillin  Acid resistant (except methicillin)  Food interferes absorption of drugs (administered 1 hour before or after meal)  Indication is infections caused by penicillinase producing Staphylococci, for which they are the drug of choice except in area where methcillin resistant Staph. aureus (MRSA)
  • Flucloxacillin  Narrow spectrum beta-lactam antibiotic  Used to treat infections caused by susceptible Gram- positive bacteria Mode of action  Acts by inhibiting the synthesis of bacterial cell walls.  It inhibits cross-linkage between the peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria.
  • Indications 1. Staphylococcal skin infections and cellulitis including  Impetigo, Otitis externa, folliculitis, boils, carbuncles, and mastitis 1. Pneumonia 2. Osteomyelitis, septic arthritis 3. Septicaemia 4. Empirical treatment for endocarditis 5. Surgical prophylaxis
  • Precautions/contraindications  Previous history of allergy to penicillins, cephalosporins or carbapenems  Should also not be used in the eye  Used with caution in the elderly, patients with renal impairment, where a reduced dose is required; and those with hepatic impairment, due to the risk of cholestatic hepatitis.
  • Adverse effects  An allergic reaction (shortness of breath; swelling of lips, face, or tongue; rash; or fainting);  Seizures;  Severe watery diarrhea and abdominal cramps; or  Unusual bleeding or bruising.
  • Resistance  Methicillin-resistant Staphylococcus aureus (MRSA) has developed resistance to flucloxacillin and other penicillins by having an altered penicillin binding protein Note : Oxacillin, Nafcillin, Cloxacillin and Dicloxacillin are similar to Flucloxacillin.
  • Cloxacillin  Acid resistant  Taken in empty stomach  Plasma protein binding > 90%  Elimination : kidney, partially by liver  Plasma half life : about 1 hour
  • Broad spectrum penicillins  Ampicillin, Amoxicillin, Carbenicillin, ticarcillin, azlocillin. Properties :  These are semisynthetic penicillin  Acid resistant (not destroyed by HCL)  Destroyed by beta – lactamase  Less potent than benzylpenicillin  Short duration of action (4 – 6 hours) and plasma t1/2 I hour  Usually given with beta lactamase inhibitors Adverse effects : Superinfection, hypersensitivity, GI upset (loose motion)
  • Indications  Respiratory tract infections (RTI):  Sinusitis, Otitis media, tonsillitis, bronchitis  Urinary tract infection (UTI)  Meningitis due to H.influenza, meningococci  Gonorrhoea  Enteric fever  Bacillary dysentry
  • Beta – lactamase inhibitors  Are family of enzymes produced by many gram + and gram – bacteria that inactivates beta – lactam antibiotics by opening the beta – lactam ring . Clavulanic acid :  Inhibits a wide variety of beta lactamase produce by both gram + and gram – bacteria  It is a progressive inhibitor: binding with beta – lactamase is reversible initially, but becomes covalent later – inhibition increasing with time and called sucide inhibitor.
  • Pharmacokinetics :  Rapid oral absorption  Bioavailability 60 %  t1/2 1 hour  Eliminated through kidney but not affected by probenecid. ADR : same as amoxicillin Uses : addition of clavulanic acid re- establishes the activity of amoxicillin against beta lactamase producing resistant Staph. Aureus, H. influenza, N. gonorrhoea, E. coli, proteus, Klebsiella, Salmonella, and shigella
  • Penicillin + Probenecid  Probenecid inhibit the tubular secretion of penicillin, so probenecid causes :  Raises the plasma concentration of penicillin  Prolongation of the action of penicillin Penicillin +Aspirin  Penicillin is excreted through kidney by tubular secretion, when aspirin is administered with penicillin, it inhibits the tubular secretion of penicillin, so prolonged the action (increased bioavailibility)
  • Adverse Reactions of penicillin  1. Hypersensitivity: most important adverse effect of the penicillins; ranges from maculopapular rash to angioedema and anaphylaxis.  2. GI Distress: nausea, vomitting and diarrhoea  3. Nephritis  4. Neurotoxicity
  • CEPHALOSPORINS  B-lactams antibiotics that are closely related both structurally and functionally to penicillins.  Like the penicillins, cephalosporins have a beta- lactam ring structure that interferes with synthesis of the bacterial cell wall and so are bactericidal.
  • To be continued……
  • Mechanism of action (MOA):  Cephalosporins are bactericidal agents and have the same mode of action as other beta-lactam antibiotics (as penicillins).  All bacterial cells have a cell wall that protects them.  Cephalosporins disrupt the synthesis of the peptidoglycan layer of bacterial cell walls, which causes the walls to break down and eventually the bacteria die.
  • CLASSIFICATION I Generation: Predominantly active against gram positive pathogens II Generation: Moderate activity against gram positive & gram negative pathogens III Generation: Predominantly active against gram negative pathogens IV Generation: wider spectrum
  • First Generation Cephalosporins  Active against gram + cocci, pneumococci, streptococci and staphylococci. The first generation cephalosporins are:  Cephradine  Cefadroxil  Cephalexin  Cefazolin  Cephalothin  Cephapirin
  • Pharmacokinetics and dosage A. Oral : Cephalexin, cephradine, cefadroxil (500mg)  Excretion by kidney and tubular secretion into the urine.  Probenecid block the tubular secretion (increase the serum level) B. Parenteral :  Cefazolin : only first generation parenteral
  • Clinical uses  Relatively nontoxic.  Oral drugs : UTI, cellulitis or soft tissue abscess Cefazolin penetrates the most tissues.  Drug of choice for surgical prophylaxis.  Streptococcal or staphylococcal infections who have history of penicillin allergy.  Does not penetrate the CNS
  • Second generation cephalosporins  Are active against organism inhibited by 1st generation drugs and extended gram negative coverage. The second generation cephalosporins are:  Cefaclor,  Cefuroxime,  Cefonicid,  Cefoxitin  Ceforanide  Cefprozil  Cefmetazole, and cefotetan active against anaerobes.
  •  Cefaclor, Cefuroxime, cefamandole, cefonicid, and ceforanide ------- active against H. influenzae  Cefoxitin and ----- active against B fragilis.
  • Pharmacokinetics and dosage : A . Oral : - Cefaclor, Cefuroxime, cefprozil,. Dosage : Adult (10-15mg/kg/d x 4 x divided dose; Children (20-40mg/kg/d up ot 1 g/d)  Cefuroxime (not active against penicillin-resistant pneumococci)  Cefaclor (susecptible to beta- lactamase hydrolysis) B. Parenteral : excreted by kidney  I.M is very painful so I.V is used.
  • Clinical uses : Oral : beta-lactamase producing H influenzae, Moraxella catarrhalis. Tx of sinusitis, otitis or lower respiratory tract infections.  Cefuroxime for community- acquired pneumonia.
  • Third generation cephalosporins  Third generation cephalosporins have a broad spectrum of activity and expanded gram-negative coverage, and some are able to cross the BBB.  Effective against beta – lactamase producing strains of haemophilus and neisseria.  Most enter CNS and are important in emperic management of meningitis and sepsis.
  • The third generation cephalosporins are: Oral  Cefixime  Cefdinir  Cefpodoxime proxetil,  Ceftibuten  Moxalactam.  Cefpodoxime proxetil Parenteral  Ceftriaxone  Cefotaxime,  Cefoperazone,  Ceftazidime,  Ceftizoxime
  •  Cefoperazone, ceftadizime are only two drugs with activity against P aeruginosa.  Ceftizoxime and moxalactam (B. fragilis)
  • Pharmacokinetics  Penetrate body fluids and tissues well . Half life :  Ceftriaxone 15-50mg/kg/d (t1/2 : 7-8 hrs) x od  1g dose is sufficient for most serious infections  4g x od for meningitis  Cefoperazone 25-100mg/kg/d (t1/2:2 hrs) x8-12hrs.  Remaining drugs (t1/2 : 1-1.7hrs)  Cefixime x p/o x 200mg (bd) or 400mg (od) for RTI or UTI. Excretion : renal except cefoperazone and ceftriaxone through biliary tract (no dose adjustment in renal disease)
  • Clinical uses  Ceftriaxone and cefotaxime (meningitis)- caused by pneumococci, meningococci, H influenzae and suspected gram negative rods, but not by L monocytogenes.  Sepsis of unknown cause.  Ceftriaxone and cefotaxime for meningitis (cross the BBB)
  • 4th generation cephalosporins  Fourth generation cephalosporins are extended spectrum agents with similar activity against gram-positive organisms as first generation cephalosporins.  Many can cross blood brain barrier and are effective in meningitis.  Highly active against haemophilus and neisseria.  Plasma half life (2 hrs) and excreted by kiney. The fourth generation cephalosporins are:  Cefepime  Cefluprenam
  •  Ceftobiprole, Ceftaroline has been described as "fifth-generation" cephalosporin, though acceptance for this terminology is not universal.  Ceftobiprole has powerful anti pseudomonal characteristics and appears to be less susceptible to development of resistance.  Ceftaroline has also been described as "fifth-generation" cephalosporin, but does not have the anti-pseudomonal coverage as Ceftobiprole .
  • Adverse reactions:  Hypersensitivity reactions (anaphylaxis, fever, skin rashes, nephritis and hemolytic anemia)  Patients with history of anaphylaxis to penicillins should not receive cephalosporins.  Thrombophlebitis after IV and local irritation after IM  Renal toxicity; interstitial nephritis  common side effects involve mainly the digestive system: mild stomach cramps or upset, nausea, vomiting, and diarrhea.  Incidence of resistance is lower than penicillins
  • Some common uses of cephalosporins  Hospital-acquired pneumonias - Cefotaxime  Meningitis - Cefotaxime, Ceftriaxone  Sepsis (initial Tx) - 3rd and 4th generation cephalosporins  Gonorrhoea  Acute urinary tract infections (UTI)
  • Monobactams  Aztreonam  Used as IV every 8 hrly, 1-2 g  Half life (1- 2 hrs)  Narrow spectrum – Gram(-) rods  Highly resistant to β-lactamases  Penicillin – allergic patients tolerate aztreonam. ADR: - May causes skin rashes.  Alternative to aminoglycosides and 3rd generation cephalosporins
  • Carbapanems  Imipenem, Meropenem, Ertapenem  Antimicrobial Activity  Imipenem, like other b-lactam antibiotics, binds to PBPs, disrupts bacterial cell wall synthesis, and causes death of susceptible microorganisms.  It is very resistant to hydrolysis by most b-lactamases.  The activity of imipenem is excellent for a wide variety of aerobic and anaerobic microorganisms. Streptococci (including penicillin-resistant S. pneumoniae), staphylococci (including penicillinase-producing strains), and Listeria are all susceptible.  Although some strains of methicillin-resistant staphylococci are susceptible, many are not. Activity is excellent against the Enterobacteriaceae, including organisms that are cephalosporin-resistant.
  •  Imipenem is inactivated by dehydropeptidases in renal tubules, resulting in low urinary concentrations. Consequently, it is administered together with an inhibitor of renal dehydropeptidase, Cilastatin, for clinical use.  Therapeutic Uses  Imipenem–cilastatin is effective for a wide variety of infections, including urinary tract and lower respiratory infections; intra-abdominal and gynecological infections; and skin, soft tissue, bone, and joint infections.  The combination appears to be especially useful for the treatment of serious infections caused by cephalosporin- resistant nosocomial bacteria, as may be seen in hospitalized patients who have recently received other b-lactam antibiotics.
  •  Meropenem has slightly greater activity against gram-negative aerobes and slightly less activity against gram-positives. It is not significantly degraded by renal dehydropeptidase and does not require an inhibitor.  Its toxicity and clinical efficacy are similar to imipenem, except that it may be less likely to cause seizures.  Ertapenem is less active than meropenem or imipenem and it is not degraded by renal dehydropeptidase.
  •  Carbapenems penetrate body tissues and fluids well, including the cerebrospinal fluid.  Cleared renally, and the dose must be reduced in patients with renal insufficiency.  Imipenem Dose : 0.25–0.5 g given intravenously every 6–8 hours (half-life 1 hour).  Meropenem Dose : 1 g intravenously every 8 hours.  Ertapenem Dose : 1 g intravenously or intramuscularly ,half- life (4 hours) and is administered as a once-daily.
  • Most common adverse effects : - Imipenem—nausea, vomiting, diarrhea, skin rashes, and reactions at the infusion sites. Excessive levels of imipenem in patients with renal failure may lead to seizures. - Meropenem and Ertapenem are less likely to cause seizures than imipenem. - Patients allergic to penicillins may be allergic to carbapenems as well.
  • Vancomycin  Is an antibiotic produced by Streptococcus orientalis  With the single exception of flavobacterium, it is active only against gram-positive bacteria, particularly staphylococci.  water-soluble and quite stable.
  • Mechanisms of Action  Inhibits the transglycosylase, preventing further elongation of peptidoglycan and cross-linking. The peptidoglycan is thus weakened and the cell becomes susceptible to lysis. The cell membrane is also damaged, which contributes to the antibacterial effect. Antibacterial Activity :  Vancomycin is bactericidal for gram-positive bacteria.  Synergistic with Gentamicin and Streptomycin
  • Pharmacokinetics  Poorly absorbed from the intestinal tract and is administered orally only for the treatment of antibiotic-associated enterocolitis caused by Clostridium difficile.  90% of the drug is excreted by kidney.  Half-life of vancomycin is 6–10 days.  Parenteral doses must be administered intravenously
  • Clinical Uses  Indication for parenteral vancomycin is sepsis or endocarditis caused by methicillin resistant staphylococci  Combination with gentamicin is an alternative regimen for treatment of enterococcal endocarditis in a patient with serious penicillin allergy  dosage is 30 mg/kg/d in two or three divided doses  Children is 40 mg/kg/d in three or four divided doses.  Oral vancomycin, 0.125–0.25 g every 6 hours, is used to treat antibiotic-associated enterocolitis caused by Clostridium difficile.
  • Adverse Reactions  In about 10% of cases  Phlebitis at the site of injection  Chills and fever  Ototoxicity is rare and nephrotoxicity uncommon  "red man" or "red neck’’ syndrome (infusion-related flushing is caused by release of histamine) - prevented by prolonging the infusion period to 1–2 hours or increasing the dosing interval
  • Bacitracin  Active against gram-positive microorganisms  Inhibits cell wall formation by interfering with dephosphorylation in cycling of the lipid carrier that transfers peptidoglycan subunits to the growing cell wall.  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  Poorly absorbed and local antibacterial activity without significant systemic toxicity. Use :- irrigation of joints, wounds, or the pleural cavity.
  • Protein synthesis inhibitors  The bacterial ribosome is composed of 30s and 50s subunits.  30s ribosomal subunit inhibitors: aminoglycosides and tetracyclines  50s ribosomal subunit inhibitors: Macrolides, chloramphenicol, clindamycin
  • AMINOGLYCOSIDES  Bactericidal MOA:  Inhibit protein synthesis ( 30 s subunit ) by interfering with the initiation complex of peptide formation induce misreading of mRNA, resulting in nonfuctional protein  Eg: Streptomycin, Neomycin, Kanamycin, Amikacin, Gentamicin, Tobramycin, Sisomicin.
  • MECHANISM OF RESISTANCE: 1. Produce enzyme that inactivate the aminoglycoside (acetyltransferases, phosphotransferase) 2. Impaired entry of aminoglycoside into the bacteria. 3. Alteration of drug binding site (30s ribosomes) by chromosomal mutation.
  • Common properties of aminoglycosides  Water soluble and more active at alkaline pH  Extracellular distribution only, cannot cross the BBB  Can cross the placenta (teratogenicity)  Narrow therapeutic index  All show common toxicities (ototoxicity, nephrotoxicity, neurotoxicity)
  • Indications Gram negative bacillary infections: 1. Septicaemia (gentamycin, amikacin) 2. Abdominal and pelvic sepsis  Bacterial endocarditis (gentamycin + penicillin)  Tuberculosis, plague, brucellosis Topical uses (Neomycin) 1. Conjunctival infection 2. Infection of external ear 3. Prior to bowel surgery (to reduce the intestinal flora)
  • Adverse effects 1. Hypersensitivity : rash, fever, eosinophilia, hemolytic anemia 2. Ototoxicity : 8th cranial nerve damage 3. Nephrotoxicity : 4. Neurotoxicity 5. Teratogenecity : risk of 8th cranial nerve damage
  • Common toxicities 1. Ototoxicity : Damage of 8th CN (vestibular and auditory damage) by toxic effects on sensory hair cells of cochlea and vestibular organ. a) Vestibular damage : comes earlier, usually reversible, headache (first), nausea, vomiting, dizziness, nystagmus, vertigo b) Auditory disturbance : comes lately; usually irreversible, tinnitus, deafness, headache
  • 2. Nephrotoxicity : excreted unchanged mainly by glomerular filtration; so attain high concentration in urine and accumulate in renal tubule : a) - damage to renal tubules (reversible) b) - proteinuria and haematuria c) - rising serum creatinin level 3. Neurotoxicity : Prevent release of acetylcholine.
  • Streptomycin  Bactericidal (high dose)  Bacterostatic (low dose)  Second or third line drugs of tuberculosis Indications :  Serious form of tuberculosis  Plague, brucellosis  Subacute bacterial endocarditis  Urinary and respiratory tract infections
  • Gentamicin  Sensitive strains : bactericidal against pseudomonas, proteus, klebsiella, enterobactor.  More potent than streptomycin  Spectrum: broad spectrum then streptomycin  More nephrotoxic Indications : septicaemia, bacterimia, abdominal and pelvic abscess, bacterial endocarditis, infected burns, pneumonia, peritonitis Route of administration : IV, IM and topical (creams, ointments)
  • Neomycin  Broad spectrum antibiotic  Susecptible : E. coli, enterobacter, klebsiella pneuminiae, Staph. aureus, M. tuberculosis  Poorly absorbed from the gut and excreted by kidney. Indications :  Topical : infected burn, wound, ulcers  Oral : preparation of the bowel for surgery
  • TETRACYCLINES  Source : streptomyces grasius (soil organism)  Broad spectrum antibiotics  Bacterostatic in nature  Acts by inhibiting bacterial protein synthesis Drugs : 1. Natural : oxytetracycline, chlortetracycline, demeclocyclin (short acting : 4-6hrs) 2. Semisynthetic : doxycycline, minocycline, methacycline, tetracycline (longer acting : 12- 24 hrs)
  • Mechanism of action  Tetracyclines enter microorganisms ( by passive diffusion and active transport)------ Susceptible cells concentrate the drug intracellularly------- once inside the cell, tetracyclines bind reversibly to the 30S subunit of the bacterial ribosome, blocking the binding of aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex .This prevents addition of amino acids to the growing peptide.
  • Pharmacokinetics Absorption after oral administration :  30% - chlortetracycline;  60–70% - tetracycline, oxytetracycline, demeclocycline, and methacycline; and  95–100% - doxycycline and minocycline  Absorption occurs mainly in the upper small intestine and is impaired by food (except doxycycline and minocycline); by divalent cations (Ca2+,Mg2+, Fe2+) ; by dairy products and antacids, which contain multivalent cations; and by alkaline pH
  •  Distributed widely to tissues and body fluids .  Minocycline reaches very high concentrations in tears and saliva.  Tetracyclines cross the placenta and excreted in milk. As a result of chelation with calcium, tetracyclines are bound to— and damage—growing bones and teeth.  Carbamazepine, phenytoin, barbiturates, and chronic alcohol ingestion may shorten the half-life of doxycycline 50% by induction of hepatic enzymes that metabolize the drug.  Excreted mainly in bile, feces and urine
  •  Some of the drug excreted in bile is reabsorbed from the intestine (enterohepatic circulation) and contributes to maintenance of serum levels.  Ten to 50 percent of various tetracyclines is excreted into the urine, mainly by glomerular filtration.  Ten to 40 percent of the drug in the body is excreted in feces.  Doxycycline, in contrast to other tetracyclines, is eliminated by nonrenal mechanisms, does not accumulate significantly in renal failure, and requires no dosage adjustment, making it the tetracycline of choice for use in the setting of renal insufficiency.
  • Adverse Reactions Hypersensitivity reactions (drug fever, skin rashes) Gastrointestinal: - Nausea, vomiting, and diarrhea are the most common, direct local irritation of the intestinal tract, - Nausea, anorexia, and diarrhea can usually be controlled by administering the drug with food
  • Bony Structures and Teeth  Tetracyclines are readily bound to calcium deposited in newly formed bone or teeth in young children.  When the drug is given during pregnancy, it can be deposited in the fetal teeth, leading to discoloration, and enamel dysplasia.  it can also be deposited in bone, where it may cause deformity or growth inhibition.  If the drug is given for long periods to children under 8 years of age, similar changes can result.
  • Liver Toxicity  Especially during pregnancy, in patients with preexisting hepatic insufficiency and when high doses are given intravenously.  Hepatic necrosis has been reported with daily doses of 4 g or more intravenously. Kidney Toxicity :Renal tubular acidosis and Fanconic syndrome (patient ingesting outdated and degraded tetracycline) resulting in nitrogen retention (except doxycycline) Local Tissue Toxicity: IV lead to venous thrombosis. IM painful local irritation
  • Photosensitization  Systemic tetracycline administration, demeclocycline, can induce sensitivity to sunlight or ultraviolet light  Vestibular Reactions :Dizziness, vertigo, nausea, and vomiting (doxycycline at doses above 100 mg).  Superinfection : caused by Candida (angular stomatitis, sore throat; Proteus (UTI)
  • Indications Drug of first choice  Chlamydial infections (PID)  Mycoplasmal infection (pneumonia)  Cholera  Rickettsial infections (Typus, relapsing fever) Drug of second choice  Diarrhoea (campylobacter)  Dysentry (shigella)  Abscess (actinomyces)  Respiratory tract infection
  • Contraindications  Children below 8 years of age  Pregnancy : early (teratogenicity) ; late (fetal bone deformity, discoloration of teeth of offspring)  Nursing mother  Renal failure (except doxycycline)
  • Drug interactions  Antacids : decrease effectiveness by chelating  Iron : decrease absorption of tetracycline
  • Comparative study between Tetracycline 1. Natural 2. Irregularly absorbed from gut 3. Plasma half life : 12 hrs 4. Excretion : renal route 5. Renal failure : Contraindication Doxycycline 1. Semisynthetic 2. Completely absorbed from gut 3. Plasma half life : 16 hrs 4. Excretion : non renal route 5. Renal failure : effective
  • MACROLIDES Mechanism of action  Inhibit protein synthesis by binding to the 50 s subunit Antibacterial activity  Bactericidal or bacteriostatic, depending on the concentration and type of bacteria Example : Erythromycin, Azithromycin and clarithromycin, Roxythromycin  Clarithromycin and azithromycin are semisynthetic derivatives of erythromycin.
  • Antibacterial spectrum:  Erythromycin:  Drug of choice in corynebacterial infections (diphtheria, corynebacterial sepsis); in respiratory, neonatal, ocular, or genital chlamydial infections; and in treatment of community-acquired pneumonia  Gram +ve cocci  Atypical organisms (chlamydia, mycoplasma, ureaplasma species)  Camphylobacter jejuni  Azithromycin: similar spectrum but more active in respiratory infections including mycobacterium avium  Clarithromycin: has more activity against M.avium and H.pylori.
  • To be continued…..