Chemotherapy of Bacterial disease and classification of antibiotics

Lecture notes for medicine and allied health sciences students

1. DR. KABIRU ABUBAKAR CHEMOTHERAPY OF BACTERIAL DISEASES

2. CHEMOTHERAPY OF PARASITIC DISEASES Definition of chemotherapy: Difference between antimicrobials and antibiotics Concept of selective toxicity “magic bullet” General classification of antimicrobial agents Difference between Bactericidal and bacteriostatic agents with examples Concentration dependent and time dependent killing with examples Broad spectrum and narrow spectrum with examples Reasons for combining antimicrobials Factors that determine selection of appropriate antimicrobial agent Definition of Post Antibiotic Effect (PAE) and superinfection Resistance to antimicrobials and biochemical mechanism of resistance  

3. INTRODUCTION The word 'chemotherapy' comes from two words: Chemical & Therapy. It literally means 'drug treatment'. In cancer treatment, the term chemotherapy means treatment with cytotoxic drugs . Chemotherapy was a term introduced by Paul Ehrlich in the early 1900s Modern chemotherapy had its root from the discovery by Robert Koch and Loius Pasteur that specific microorganisms are linked to specific diseases. The 20 th century came with the characterization of different Microorganisms and different diseases they cause

4. Types of Chemotherapy 1. Anti-infective chemotherapy: Use of drugs to prevent (prophylaxis) or treat diseases caused by parasitic organisms and microorganisms. Relies on selective inhibition of target(s) in the infecting organism leading to inhibition of growth/death . 2. Cancer chemotherapy:Use of drugs to treat cancer. Usually relies on inducing a lethal cytotoxic event or apoptosis in the cancer cell. Ideally drugs should interfere only with cellular processes that are unique to malignant cells.

5. Difference between antimicrobials and antibiotics ANTIBIOTIC  is a low molecular substance produced by a microorganism that at a low concentration inhibits or kills other microorganisms . Ie show selective toxicity ANTIMICROBIAL  is any substance of natural, semisynthetic or synthetic origin that kills or inhibits the growth of microorganisms but causes little or no damage to the host. Disinfectants/antiseptics : compounds that kill microorganisms but which are too toxic for internal use in human patients. Therefore they are antimicrobials. Antibacterial chemotherapy: the use of antibacterial drugs to treat and cure bacterial infections of animals and humans . All antibiotics are antimicrobials, but not all antimicrobials are antibiotics

6. Bacteriostatic vs. Bactericidal Action Bacteriostatic action: a biological or chemical agent that stops bacteria from reproducing, while not necessarily harming them otherwise. Bactericidal action: a biological or chemical agent that kills bacteria, dead . Selectivity of Action ‒ Selective Toxicity: Selectivity of action is a central concept of antibacterial drug action. The growth of the infectious organism is selectively inhibited, or the organism is killed, without damage to the cells of the host . Selective toxicity is based on exploiting the differences in the structure or biochemistry of the infecting agent and the host cells.

7. The Ideal Antibiotic The ideal antibacterial drug would have no adverse effect on the patient but would be lethal to the organism. The agent does not get into mammalian cells as easily as it enters bacterial cells. The agent targets processes/structures in bacterial cells that are not present in mammalian cells. Agents target processes/structures in bacterial cells that are different in mammalian cells. Agent is a pro-drug that is only activated in bacteria; this means it will have little (preferably no) adverse effects on the host cell.

8. CONCENTRATION DEPENDENT VS TIME DEPENDENT KILLINGS Concentration-dependent/dose-dependent Certain classes of antibiotics, such as aminoglycosides and quinolones, use mainly concentration at the binding site to eradicate organisms. Unlike concentration-independent killing antibiotics, the aminoglycosides and fluoroquinolones eliminate bacteria most rapidly when their concentrations are appreciably above their MICs for organisms and, hence, their type of killing is referred to as CD/DD killers.

9. Time dependent killings Certain antibiotics, such as β-lactams ( penicillins , cephalosporins , carbapenems , monobactams ), clindamycin, macrolides (erythromycin, clarith romycin ), oxazolidinones (linezolid), and vancomycin , employ mainly time at the binding site to eradicate organisms. Apparently, once the concentration exceeds a critical value, which appears to be about 2 to 4 times above the MIC for an organism, bacterial killing proceeds at a zero order rate and increasing the drug concentration does not increase the microbial death rate.

10. Broad spectrum and narrow spectrum with examples Broad-spectrum Broad spectrum antibiotics are formulated to destroy a large number of different types of bacteria. both gram-negative and gram-positive bacteria Amoxicillin , which is effective against a wide spectrum of bacteria, including Helicobacter, Streptococcus, Moraxella, Enterococcus, Bacillus subtilis , and Haemophilus . Another example is tetracycline, which is effective against a variety of bacteria that cause UTIs, skin infections such as acne, respiratory tract infections.

11. Narrow-spectrum Narrow-spectrum antibiotics, the range of bacteria that are targeted by the medication is fairly small. These antibiotics are designed only to treat a specific type of bacteria. The best example of a narrow-spectrum antibiotic is sodium fusidate , which is formulated to destroy staphylococcal strains of bacteria. Azithromycin, clarithromycin, clindamycin, erythromycin, and vancomycin are some of the medications that belong to this class of antibiotics.

12. Reasons for combining antimicrobials Use of a combination of antimicrobial agents may be justified : (1) For empirical therapy of an infection in which the cause is unknown, (2) For treatment of polymicrobial infections, (3) To enhance antimicrobial activity ( i.e. , synergism) for a specific infection, (4) To prevent emergence of resistance.

13. Factors that determine selection of appropriate antimicrobial agent 1.pharmacokinetics: ADME 2. effect of site of infection on therapy: (a) blood brain barrier: (b) plasma protein binding (ppb): (c) maintenance of MIC at the site of infection: d) route of administration:

14. Cont ………. 3 .   Host factors or status of patient: Innate host factors which apparently seem not to be related to infection being treated are prime determinants of the type of antimicrobial, its dose regimen and toxicity and expected therapeutic out come.  Such factors are Renal dysfunction, Hepatic dysfunction, A ge , Pregnancy and lactation. Drug Allergy Host Defense Mechanism: Disorders of Nervous System:

15. 4. Local factors: Local factors at the site of action may greatly influence the effectiveness of anti microbial in curing the disease. Pus (consisting of phagocytes, cellulose, debris, fibrin protein, micro organisms) reduces the antibacterial action of aminoglycosides by binding to them. 5. Cost of therapy: Very often, several drugs show the similar efficacy in treating an infection but they may vary greatly in cost. Sometimes there are many fold differences in the prices of different brands of the same drug. Thus cost of therapy may be taken into account, after accessing the socioeconomic status of patient, before making the final decision.

16. Superinfections /Post Antibiotic Effect superinfection , defined as the appearance of bacteriological and clinical evidence of a new infection during the chemotherapy of a primary one. This phenomenon is relatively common and potentially very dangerous because the microorganisms responsible for the new infection can be drug-resistant strains of Enterobacteriaceae , Pseudomonas , and Candida or other fungi . Superinfection is due to removal of the inhibitory influence of the normal flora, which produce antibacterial substances and also presumably compete for essential nutrients. The broader the antibacterial spectrum and the longer the period of antibiotic treatment, the greater is the alteration in the normal microflora , and the greater is the possibility that a single, typically drug-resistant microorganism will become predominant, invade the host, and produce infection.

17. Resistance to antimicrobials and biochemical mechanism of resistance Antibiotic resistance is the ability of bacteria and other microorganisms to resist the effects of an antibiotic to which they were once sensitive . ( i) Antibiotic inactivation – direct inactivation of the active antibiotic molecule ; (ii) Target modification – alteration of the sensitivity to the antibiotic by modification of the target ; (iii) Efflux pumps and outer membrane (OM) permeability changes – reduction of the concentration of drug without modification of the compound itself ; (iv) Target bypass – some bacteria become refractory to specific antibiotics by bypassing the inactivation of a given enzyme. This mode of resistance is observed in many trimethoprim- and sulfonamide-resistant bacteria. The example is in bypassing inhibition of dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) enzymes (involved in tetrahydrofolate biosynthesis).

18. PENICILLINS Penicillin are a group of antibiotics derived from Penicillium fungi. Penicillin antibiotics were among the first drugs to be effective against many previously serious diseases, such as syphilis and infections caused by staphylococci and streptococci . Penicillins are still widely used today, though many types o f bacteria have now become resistant . All penicillins are B-lactam antibiotics and are used in the treatment of bacterial infections caused by susceptible , usually Gram-positive, organisms. Several enhanced penicillin families also exist, effective against additional bacteria: these include the antistaphylococcal penicillins , aminopenicillins and the more-powerful antipseudomonal penicillins . Types: penicillin G (IV use), penicillin V (oral use), procaine penicillin, and benzathine penicillin (intramuscular use)

19. BETA LACTAM B-Lactam antibiotics inhibit the formation of peptidoglycan cross-links in the bacterial cell wall; This is achieved through binding of the four-membered B-lactam ring of penicillin to the enzyme DD- transpeptidase . As a consequence, DD- transpeptidase cannot catalyse formation of these cross-links, and an imbalance between cell wall production and degradation develops, causing the cell to rapidly die. The peptidoglycan is composed of glycan chains, which are linear strands of two alternating amino sugars ( N - acetylglucosamine and N - acetylmuramic acid) that are cross-linked by peptide chains.

20. Mechanisms of action All β-lactam antibiotics interfere with the synthesis of the bacterial cell wall peptidoglycan . After attachment to binding sites on bacteria (termed penicillin-binding proteins (PBP) of which there may be seven or more types in different organisms), they inhibit the transpeptidation enzyme that cross-links the peptide chains attached to the backbone of the peptidoglycan. The final bactericidal event is the inactivation of an inhibitor of the autolytic enzymes in the cell wall; this leads to lysis of the bacterium.

21. PENICILLIN CONT…….. The first penicillin was the naturally occurring benzylpenicillin and its congeners such as phenoxymethylpenicillin . Benzylpenicillin is active against a wide range of organisms and is the drug of first choice for many infections. Its main drawbacks are poor absorption in the GIT (which means it must be given by injection) and its susceptibility to bacterial β-lactamases.

22. Various semisynthetic penicillins have been prepared by adding different side-chains to the penicillin nucleus (at R 1. In this way β- lactamase-resistant penicillins (e.g. flucloxacillin ) and broad-spectrum penicillins (e.g. ampicillin , pivampicillin and amoxicillin ) have been produced. Extended-spectrum penicillins (e.g. carbenacillin , ticarcilin and aziocillin ) with antipseudomonal activity have also been developed and have gone some way to overcoming the problem of serious infections caused by P. aeruginosa .

23. Pharmacokinetics When given orally, different penicillins are absorbed to differing degrees depending on their stability in acid and their adsorption to food . Penicillins can be given by intramuscular or intravenous injection. Intrathecal administration is inadvisable, particularly with benzylpenicillin , as it can cause convulsions. The drugs are widely distributed in the body fluids, passing into joints, into pleural and pericardial cavities, into the bile, the saliva and the milk and across the placenta .

24. Pharmacokinetics Being lipid insoluble they do not enter mammalian cells. They, therefore, do not cross the blood-brain barrier unless the meninges are inflamed, in which case they readily reach therapeutically effective concentrations in the CSF. Elimination of most penicillins is mainly renal and occurs rapidly, 90% being by tubular secretion. The relatively short plasma half-life is a potential problem in the clinical use of benzylpenicillin , although since penicillin works by preventing cell wall synthesis in dividing organisms, intermittent rather than continuous exposure to the drug can be an advantage

25. Unwanted effects Penicillins are relatively free from direct toxic effects (other than their proconvulsant effect when given intrathecally ). The main unwanted effects are hypersensitivity reactions, caused by the degradation products of penicillin, which combine with host protein and become antigenic. Skin rashes and fever are common;. Much more serious is acute anaphylactic shock, which may, in some cases, be fatal but is fortunately very rare. Penicillins , particularly the broad-spectrum type given orally, alter the bacterial flora in the gut. This can be associated with gastrointestinal disturbances and, in some cases, with superinfection by microorganisms not sensitive to penicillin.  

26. Classification of the Penicillins 1. Penicillin G and its close congener penicillin V are highly active against sensitive strains of gram-positive cocci , but they are readily hydrolyzed by penicillinase . Thus they are ineffective against most strains of S. aureus . 2. The Penicillinase -Resistant Penicillins The penicillins described in this section are resistant to hydrolysis by staphylococcal penicillinase . Their appropriate use should be restricted to the treatment of infections that are known or suspected to be caused by staphylococci that elaborate the enzyme, ¾ which now includes the vast majority of strains of this bacterium that are encountered clinically. These drugs are much less active than is penicillin G against other penicillin-sensitive microorganisms, including non- penicillinase -producing staphylococci.

27. Classification of the Penicillins 3.The Aminopenicillins : Ampicillin, Amoxicillin, and Their Congeners These agents have similar antibacterial activity and a spectrum that is broader than the antibiotics heretofore discussed. They all are destroyed by b-lactamase (from both gram-positive and gram-negative bacteria ). 4.Antipseudomonal Penicillins : The Carboxypenicillins and the Ureidopenicillins The carboxypenicillins , carbenicillin and ticarcillin and their close relatives, are active against some isolates of P. aeruginosa and certain indole -positive Proteus spp. that are resistant to ampicillin and its congeners.

28. Ureidopenicillins The ureidopenicillins , mezlocillin and piperacillin , have superior activity against P. aeruginosa compared with carbenicillin and ticarcillin . In addition, mezlocillin and piperacillin are useful for treatment of infections with Klebsiella . The carboxypenicillins and the ureidopenicillins are sensitive to destruction by b-lactamases.

29. Cephalosporins History and Source. Cephalosporium acremonium , the first source of the cephalosporins , was isolated in 1948 by Brotzu Crude filtrates from cultures of this fungus were found to inhibit the in vitro growth of S. aureus and to cure staphylococcal infections and typhoid fever in human beings. Culture fluids in which the Sardinian fungus was cultivated were found to contain three distinct antibiotics, which were named cephalosporin P, N, and C. With isolation of the active nucleus of cephalosporin C,7-aminocephalosporanic acid, and with the addition of side chains, it became possible to produce semisynthetic compounds with antibacterial activity very much greater than that of the parent.

30. Mechanism of action The mechanism of action of these agents is the same as that of the penicillins -interference with bacterial peptidoglycan synthesis after binding to the β-lactam-binding proteins. Pharmacokinetics : Some cephalosporins may be given orally but most are given parenterally , After absorption they are widely distributed in the body. Some, such as cefoperazone , cefotaxime , cefuroxime and ceftriaxone, also cross the blood-brain barrier. Excretion is mostly via the kidney, largely by tubular secretion, but 40% of ceftriaxone and 75% of cefoperazone is eliminated in the bile.

31. Clinical use/Unwanted effects Septicaemia (e.g. cefuroxime , cefotaxime ) Pneumonia caused by susceptible organisms Meningitis (e.g. cefriaxone , cefotaxime ) Biliary and UTI (especially in pregnancy, or in patients unresponsive to other drugs) Sinusitis (e.g. cefadroxil) Unwanted effects Hypersensitivity reactions, very similar to those that occur with penicillin, may be seen. Some cross-reactions occur; about 10% of penicillin-sensitive individuals will have allergic reactions to cephalosporins . Nephrotoxicity has been reported (especially with cefradine ) as has intolerance to alcohol. Diarrhoea can occur with oral cephalosporins and cefoperazone

32. Classification ` The large number of cephalosporins makes a system of classification most desirable. Although cephalosporins may be classified by their chemical structure, clinical pharmacology, resistance to b-lactamase, or antimicrobial spectrum, the well-accepted system of classification by "generations" is very useful, although admittedly somewhat arbitrary. Classification by generations is based on general features of antimicrobial activity. The first-generation cephalosporins , epitomized by cephalothin and cefazolin , have good activity against gram-positive bacteria and relatively modest activity against gram-negative microorganisms

33. Classification cont ….. The second-generation cephalosporins have somewhat increased activity against gram-negative microorganisms but are much less active than the third-generation agents. A subset of second-generation agents ( cefoxitin , cefotetan , and cefmetazole ) also is active against the B. fragilis group. Third-generation cephalosporins generally are less active than first-generation agents against gram-positive cocci , but they are much more active against the Enterobacteriaceae , including b-lactamase-producing strains. A subset of third-generation agents ( ceftazidime and cefoperazone ) is also active against P. aeruginosa but less active than other third-generation agents against gram-positive cocci

34. Classification cont ….. Fourth-generation cephalosporins , such as cefepime , have an extended spectrum of activity compared with the third generation and have increased stability from hydrolysis by plasmid and chromosomally mediated b-lactamases. It is important to remember that none of the cephalosporins has reliable activity against the following bacteria: penicillin-resistant S. pneumoniae , methicillin-resistant S. aureus , methicillin-resistant S. epidermidis and other coagulase-negative staphylococci, Enterococcus, L. monocytogenes , Legionella pneumophila , L. micdadei , C. difficile , Xanthomonas maltophilia , Campylobacter jejuni , and Acinetobacter spp

35. FIFTH GENERATION CEPHALOSPORIN Also referred to as advanced cephalosporin. An example is ceftaroline can be used to treat bacteria, including resistant S. aureus (MRSA) and Streptococcus species that are resistant to penicillin antibiotics. It is the only 5 th generation cephalosporin available in the USA.

36. FLUOROQUINOLONES The fluoroquinolones include the broad-spectrum agents ciprofloxacin, levofloxacin , ofloxacin , norfloxacin , acrosoxacin and pefloxacin , and the narrower-spectrum drugs used in urinary tract infections- cinoxacin , and nalidixic acid . (the first quinolone and is not fluorinated). MOA: These agents inhibit topoisomerase II (a DNA gyrase ), the enzyme that produces a negative supercoil in DNA and thus permits transcription or replication.

37. Antibacterial spectrum and clinical use Ciprofloxacin is the most commonly used fluoroquinolone and will be described as the prototype agent . It is a broad-spectrum antibiotic, effective against both Gram-positive and Gram-negative organisms. It has excellent activity against the Enterobacteriaceae (the enteric Gram-negative bacilli), including many organisms resistant to penicillins , cephalosporins and aminoglycosides, and it is also effective against H. influenzae , penicillinase -producing N. gonorrhoeae , Campylobacter sp. and pseudomonads. Of the Gram-positive organisms, streptococci and pneumococci are only weakly inhibited and there is a high incidence of staphylococcal resistance. Ciprofloxacin should be avoided in methicillin-resistant staphylococcal infections .

38. Pharmacokinetic Given orally, the fluoroquinolones are well absorbed. The half-life of ciprofloxacin and norfloxacin is 3 hours, that of ofloxacin is 5 hours and that of perfloxacin is 10 hours. The drugs concentrate in many tissues, particularly in the kidney, prostate and lung. All quinolones are concentrated in phagocytes. Most do not cross the blood-brain barrier except for pefloxacin and ofloxacin , which reach, in the CSF, 40% and 90%, respectively, of their serum concentrations. Aluminium and magnesium antacids interfere with the absorption of the quinolones . Elimination of ciprofloxacin, norfloxacin and enofloxacin is partly by hepatic metabolism by P450 enzymes (which they can inhibit, giving rise to interactions with other drugs) and partly by renal excretion. Pefloxacin is metabolised to norfloxacin .

39. Clinical uses of the fluoroquinolones Clinical Uses Complicated urinary tract infections, respiratory infections in patients with cystic fibrosis, Invasive external otitis osteomyelitis Gonorrhoea , Bacterial prostatitis and Cervicitis. Unwanted effects Unwanted effects are infrequent, usually mild and disappear if the agents are withdrawn. They consist mainly of gastrointestinal disorders and skin rashes. Arthropathy has been reported in young individuals. CNS symptoms-headache, dizziness-have occurred and, less frequently, convulsions, which have been associated with CNS pathology or concurrent use of theophylline or a non-steroidal anti-inflammatory drug.

40. Classification of Quinolones They are also classified into generations such as First generation- Nalidixic acid Second generation- Ciprofloxacin Third generation- Levofloxacin Fourth generation- Trovafloxacin with activity against anaerobes. First generation achieve minimal serum levels, 2 nd increased gram negative and systemic activity, 3 rd expanded activity against g positive bacteria and atypical pathogens while 4 th have activity against anaerobes eg actinomyces . propionibacterium , clostridium etc

41. MACROLIDES For 40 years, erythromycin was the only macrolide antibiotic in general clinical use. Several additional macrolide and related antibiotics are now available, the two most important of which are clarithromycin and azithromycin . Mechanism of action : The macrolides inhibit bacterial protein synthesis by an effect on translocation. Their action may be bactericidal or bacteriostatic, the effect depending on the concentration and on the type of microorganism. The drugs bind to the 50S subunit of the bacterial ribosome; the binding site is the same as that of chloramphenicol and clindamycin and the three types of agent could compete, if given concurrently

42. Antimicrobial spectrum The antimicrobial spectrum of erythromycin is very similar to that of penicillin and it has proved to be a safe and effective alternative for penicillin-sensitive patients. Erythromycin is effective against Gram-positive bacteria and spirochaetes but not against most Gram-negative organisms, exceptions being Neisseria gonorrhoeae and, to a lesser extent, H. influenzae . Azithromycin is less active against Gram-positive bacteria than erythromycin , is considerably more effective against H. influenzae and may be more active against Legionella . It has excellent action against Toxoplasma gondii . Clarithromycin is as active, and its metabolite is twice as active, against H. influenzae as erythromycin; and it may be useful in leprosy and against Helicobacter pylori.

43. Pharmacokinetic The macrolides are administered orally, azithromycin and clarithromycin being more acid stable than erythromycin . They all diffuse readily into most tissues but do not cross the blood-brain barrier and there is poor penetration into synovial fluid. Macrolides enter and are concentrated within phagocytes-azithromycin concentrations in phagocyte lysosomes can be 40 times higher than in the blood-and they can enhance phagocyte killing of bacteria. Erythromycin is partly inactivated in the liver; azithromycin is more resistant to inactivation and clarithromycin is converted to an active metabolite. Effects on the P450 cytochrome system can affect the bioavailability of other drugs. The major route of elimination is in the bile

44. Unwanted effects Gastrointestinal disturbances are common and unpleasant but not serious. With erythromycin , the following have also been reported: hypersensitivity reactions such as skin rashes and fever, transient hearing disturbances, and, rarely, with treatment longer than 2 weeks, cholestatic jaundice. Opportunistic infections of the gastrointestinal tract or vagina can occur