number 7 Done by Heba Rababah Corrected by Muayad Azzam Doctor Hameed
Antibacterial therapy 1 Antibiotics are very common in our life, most us have taken antibiotic or at least know some of them, such as Amoclan, Zomax; these are commercial names of antibiotics. Each antibiotic has a commercial and scientific name, (in microbiology we focus more on the scientific name) Also, antibiotics have a dose and a route of administration. What are antibiotics? Natural products: derived from soil bacteria and fungi, Examples: Penicillin from penicillin notatum mould or Semisynthetic agents: Natural compounds that have been chemically modified to increase its activity and improve pharmacokinetic, but it still contain native or nature component Examples: Amoxycillin, Ampicillin, Cephalosporins and Carbapenems, Rifampicin or Synthetic chemicals: completely synthesized in lab Examples: Trimethoprim and linezolid, quinolones. *Note: Antibiotics are loosely applied to all antibacterial agent History of antibiotics: Ancient Egyptian used honey for healing wounds, till now, bandages involve honey to help heal small wounds. The first time antibiotics have been used and studied scientifically, was in world war 2,by Alexander Fleming and Louis Pasteur. Unknown author described development of antibiotics by saying: 2000 B.C. - "Here, eat this root." 1000 B.C. - "That root is heathen, say this prayer." 1850 A.D. - "That prayer is superstition, drink this potion." 1940 A.D. - "That potion is snake oil, swallow this pill."
1985 A.D. - "That pill is ineffective, take this antibiotic." 2000 A.D. - "That antibiotic is useless and artificial. Here, eat this root." We expect that we will start to find other alternatives for antibiotics such as returning to use of roots, as a result of lack of effective antibiotics able to kill bacteria due to microbe s developing strong resistance to current antibiotics as a result of abusive and misuse. The bright side (Benefits vs risks): Since penicillin has been discovered, antibiotics play a useful role in saving lives, yet even life savers may take lives, because antibiotics are dangerous drugs that have side effect that can be fatal for kidney, heart, bones, joints..etc, so be wise when prescribing antibiotics. Example on side effect: Broad spectrum of antibiotics could kill the normal flora in addition to bacteria, so there will be a problem if they are unnecessarily used(abuse), for example Pseudomembranous colitis. Pseudomembranous colitis: inflammation in colon due to proliferation of bacteria called clostridium difficle (c.difficile or c.deathicille as they cause death), the overgrowth of c.difficile is due to killing of normal flora by some antibiotics. Route of administration There many factors determine how to administer the antibiotic: 1. Nature of infection: is the infection severe or not, for example if infection isn t severe, there s no need to give it through IV. 2. Bioavailability and therapeutic index ( 3. Tissue penetration: which tissue is the target. 4. Excretion 5. Pharmacokinetics
Antibiotics can be given empirically (blindly): to give a broad-spectrum antibiotic without knowledge of the organism that is causing the infection based on experience. Do not give antibiotics unnecessarily though, like colds and viral infections. When two or more antibiotics given together, they might show synergistic effect, which mean that when two antibiotics work together the total effect is greater than the sum of individual antibiotics, for example: you have two antibiotics k1, k2, k1 antibiotic target the cell wall, k2 target nucleus, when the combine together, their effect will be more efficient than when both work separately, synergism looks like this equation 1+1>2 not 2. What are the problems related to antibiotics? Resistance is major problem associate with antibiotics due to abuse and misuse. 70 % of respiratory infection are caused by viruses, and most of those infections don t need antibiotics to recover (no need for antibiotics) So we refrain from antibiotic use since they have side effects that may cause more problems, and overuse (abuse) might develop resistant generations of the bacteria (as we will see in next lecture) Our role: You are the most important person in the treatment process, pharmacists and chemists work for many years to discover and synthesize antibiotics, then you come and prescribe them to patients, so your prescription on what and when and how the antibiotic is used is of utmost importance.
To avoid abuse and misuse of antibiotics, more restriction should be applied in our health systems. We don t have strict restrictions on antibiotics(off the shelf), so any one could go to pharmacy and buy antibiotics without prescription. However, in UK, you can t do this,even if you are physician and you want to write prescription for someone, you have to write your phone number, address, your JMS (general medical council), patient address, and your prescription,then these information will be submitted to the medical council. Also, physician should follow the guideline when prescribing antibiotics. Let s take chest infection as example, with guidelines you will know from where to start, if the patient immunocompromised or not? So safety use of antibiotics is necessary in order for them to be effective. * A person who has an immunodeficiency of any kind is said to be immunocompromised. To prevent Abuse we must consider: -Side effects -Resistance -Cost-effectivness Spectrum of activity Activity of antibiotics could be for many types of bacteria or specific types only, so we categorize them into: 1. Narrow spectrum antibiotics: antibiotics that have limited activity and affect only G-positive bacteria for example. 2. Broad spectrum antibiotics: antibiotics that affect wide groups of bacteria, G-positive and G-negative, aerobic and anaerobic bacteria. When you should use narrow or broad spectrum antibiotics? If you have a specimen for unknown bacteria, you should give broad spectrum antibiotics until the lab result reach (requires 2-3 days) (Blind therapy) after that, you have to be select a narrow spectrum antibiotic to avoid resistance especially if given through IV.
Terms related to antibiotics use: -Selective toxicity: Kill or inhibit the growth of microorganism without harming human tissue by targeting structure in bacteria that aren t found on in cell such as cell wall. We want the antibiotic to have this trait to prevent damage to our cells. -Bacteriostatic vs Bactericidal : Bacteriostatic: term used to describe antibiotics that stop growth of bacteria and allow for natural immunity to deal with the microbe. Bacteriocidial: describe antibiotics that kill the bacteria *Note: Bactericidial may lead to release of toxins and microbial contents from the microbe itself leading to subsequent illness and inflammatory responses. Static vs cidal (MIC vs MLS): MIC( minimum inhibitory concentration ): the smallest concentration is needed for inhibit growth of bacteria. MLC( Minimum lethal concentration ): the smallest concentration is needed for kill bacteria. Used for Bactericidial only Antibiotic susceptability testing: Bacteria still diffusion towards streptomysine,so it wasn t inhibited, it resistant This clear zone indication to power of inhibition of antibiotics
1.) Disk Diffusion Test: -You have bacteria with specific type and concentration that has grown in a culture. You put it in medium. (In the diagram the grey area in the petri dish is the bacteria) A filter paper disk containing a measured quantity of antibiotic is placed of surface of medium (the black circles in the diagram). After incubation, you will see that the bacteria have grown in different area. (cover the entire petri dish) except for some clear zones around SOME the antibiotics. This indicates that, that specific antibiotic inhibited that type of bacteria. Meaning: the use of this antibiotic towards that bacteria may be effective. The diameter of bacteria clear zone is measured and compared against a reference standard which contains measurement ranges and their equivalent qualitative categories of susceptible, intermediately resistant, for example, diameter of zone could be : 0-5: resistant 5-15 : intermediately resistant >15 : susceptible or sensitive Intermediate resistant is useful when the result of your bacteria is intermediate resistant for azithromycine and you see this the right option t, you are free to use if other options is resistant and intermediate, but if you have antibiotics which bacteria is sensitive for you must use, also in some case the same antibiotic could be intermediate vitro but sensitive to vivo.????????????????????????????????????????????????????? 2.)Determination of MIC: You have various test tubes, each is planted with bacteria of certain concentration. In these tube you add the same antibiotic with different concentration 0,1,2,4,8, then observe the tubes. Tube which has turbidity indicate growth of bacteria while tube which is clear with non visible growth seem to inhibit growth for example w, assume tube with concentration of 2,4,8 don t have any turbidity. So MIC ( MINIMUM inhibitory concentration) will tube which concentration is 2 since it is the minimum concentration that prevented microbes from growing) How to estimate if the MIC is also MLC?
It s not necessary for MIC to equal MLC. So how do we check? we take bacteria from each tube that doesn t show any visible growth(2,4,8) and plant them in a plate. The plate that bacteria doesn t grow in would have killed the bacteria. So the minimum concentration at which this happens will be the MLC. This figure show : -Red line indicate Bacteria is growing normally without any added antibiotics -Blue shows the effect of use tetracycline to inhibit growth when drug added as bacteriostatic -Green show penicillin effect in killing bacteria and stoping growth (number is decreasing) when drug added as bacteriocidial There are some cases of infection, bacteriocidial must be used :
In meningitis (an infection), there s inflammation that leads to an increase in intracranial pressure, so you need to get rid of this pressure, how? In the skull there is an opening for nerves to leave, so this pressure will affect the structure in that opening result in herniation(brain wil try to squeeze out) so you need bacteriocidial to prevent further deadly infections, as you can t leave the task for immunosystem to do it in this case. Infective endocarditis: it s an inflammation in heart valve causing damage to these valves by a bacteria. This results in heart failure, so you need to kill this bacteria by bacteriocidial So, there are some scenarios that direct you to choose the antibiotic (whether bacteriocidal or bacteriostatic), route of administration ( give it IV or orally), and if the antibiotic reaches the bone for example, as good penetration disruption? Or does it reach the brain or not? To sum up, some infections such as meningitis, infective endocarditis or immunocompromised patients where Bactericidal is a must Antibiotics is used for treatment, however it can be used for prevention prophylaxis such as : For immunocompromised people who are vulnerable for infection more than others. They take antibiotics for prevention. Before certain operations, antibiotics are given to the patient to prevent probable infections. Some people lost their spleen, which is very important for protection against capsulated bacteria, (in an accident or as a result of sickle cell)the people must be protected to some extent by giving vaccines and prophylaxis antibiotics to avoid disastrous outcomes. When you give the antibiotics beware about precaution: History of hypersensitivity: if you are in a remote area you should ask that patient if he had a sensitivity to any antibiotic(especially penicillin, since it
might cause respiratory shock) in his previous experiences (if he had taken it and started to have swollen or allergic reactions.) Do not mix up hypersensitivity with mild side effects; some side effects are normal and controllable. Based on his answer you will give him the proper antibiotic. If you are in a hospital,you should be sure about his sensitivity by doing a sensitivity test. Glandular fever (Epstein-Barr virus infection), cytomegalovirus infection greatly increase the risk of developing a penicillin-induced rash. Impaired liver and kidney functions, as the liver and kidney are the sites of secretion of antibiotics, so people with kidney and liver problems shouldn t be given the same dose as normal people. Pregnancy, breastfeeding and children: drug move from palcenta to embryo or through the breast milk. If antibiotics reach the embryo many problems such as : discoloration of the tooth or might pass to cartilage and prevent ossification so he will be short. If you know the antibiotic might cause harm to the patient try to stay away from the entire antibiotic family and choose another safer alternative. ***You are responsible, so be wise when we prescribe antibiotics,be wary from side effects and remember history is very useful Mechanism of action: Target of antibacterial agent: o Cell wall : as it has a unique structure for bacteria which is peptidoglycan. o Protein synthesis: 70 s ribosome found in bacteria and mitochondria while 80s ribosome present in human cell. However, mitochondria has 70s so some side effects might occur if we target 70s however they are minimal. o Folate synthesis: Bacteria manufacture its own folates while human obtain it in food.
* Folic acid is the synthetic form of folate that is found Bacteria. Bacteria use folic acid in order to synthesize the nucleic acids that make up their DNA. So targeting the synthesis mechanism is an excellent way of protection. o Nucleic acid synthesis o Other sites such as bacterial cell membrane In this lecture we will talk about targeting the cell wall: -Most bacteria possess a cell wall to protect from osmotic pressures -Microbe divides needs to create a new cell wall -Interrupt this leads to new microbes being susceptible to external influences -Cell ruptures leading to Microbe death As you remember that cell wall of bacteria contains peptidoglycans that are composed of repeating disaccharide (NAM-NAG) units crosslinked with amino acids (peptides). The enzyme that catalyzes this linkage is called a transpeptidase, so if we have antibiotic that target this protein will prevent crosslinking, it will damage peptidoglycan, and lead to death of bacteria, so antibiotics that target cell wall is bactericidal. There two families of this type glycopeptides(antibiotic) and beta lactam agents. Glycopeptides : prevent NAM from transfering to peptidoglycan so chain is defective. B lactam agent: prevent crosslinking. Beta lactam agents Have Beta lactam ring which is necessary to bind to penicillin binding proteins.
Examples: Penicillins, cephalosporins, monobactams, carbapenems and beta lactamase inhibitors How they work? For example penicillin bind to enzyme transpeptidase, that we call penicillin binding protein, preventing crosslinking so cell ruptures,lead to its death. How bacteria develop resistance for this type? Each b lactam agents have a beta lactam ring ( it s the heart of thes types of antibiotics) Bacteria produce enzyme called beta lactamase or its called penicillinase that breaks antibiotics beta lactam ring preventing binding so,producesa resistance Amoxicillin is a beta lactam agent that has B lactam ring Lactamase cleaves the ring so amoxicillin becomes inactive, so how do we develop antibiotics to prevent this? We develop amoxicillin mixed with cavulinic acid in what we know as Amoclan (co-amoxiclan) Cavulinic acid is B- lactamase inhibitor while amoxicillin works on bacteria Why we start to synthesize penicillin? Examples: Penicillin: Benzylpenicillin and penicillin G o Penicillin barrier: Narrow spectrum Short acting Resistance by beta lactamases So we develop synthetic penicillins.
Example of Synthetic penicillins: Penicillin V like Flucloxacillin and methicillin. These don t get inhibited by b-lactmase of Staphylococcus aureus (s.aureus) as they rearrange its lactam ring to not be recognized by s.ureus. ***How S.aureus develops resistance? S.ureus change methicillin target in cell wall by alter the molecular structure of transpeptidase (on a genetic level) so methacillin will not be able to bind. This type of S.ureus is called methacillin resistant staphylococcus aureus ( MRSA) this is a very prevalent name you will hear in hospitals especially. Monobactam such as Aztreonam used mostly against serious aerobic and Facultative G-ve infection Carbapenem which is the strongest antibiotic in b-lactam family such as imipenem & meropenem. They have Broad Spectrum that affects G- and G+, aerobic and anaerobic. Penicillinase-R causes resistance against Carbapenem. Cephalosporins: has a lactam ring, however with 6 atoms rather than 5 atoms as penicillin, this makes it have Broader spectrum and Less hypersensitivity reactions Cephalosporins have 5 Different generations: 1 st (1960) Cephalexin, Cephradine, work on spectrum G+. 2 nd (70s) Cefoxitin, Cefuroxime, work on Broad spectrum, both G- and G+ 3 rd (80s) Ceftriaxone, Cefotaxime.. work on mainly G-ve Enteric bacteria. Usually taken as IV form. Has high penetrating for blood capillary barriers so particularly useful for infections in CFS as they are able to reach it. 4 th (1990s) Cefepime.. work on mainly G-ve, GPC (gram positive cocci) and pseudomonas( which is bad bacteria) 5 th generation 2000s: ceftaroline work on MRSA
Glycopeptides: they differ from b a- lactam as they are Large molecules. As a result they are unable to penetrate the outer membrane of Gram-negative bacteria, and the spectrum is consequently restricted to Gram-positive organisms. Their action is mainly against Gram positive cocci with multiple resistance to other drug. Start with penicillin, if staphylococcus appear to be resistant move to flucloxacillin,if resistant continue use vancomysine, then glucopeptides. Gram-positive cocci with multiple resistance to other drugs such as Enterococci and staphylococci, including MRSA, that exhibit resistance or reduced sensitivity to glycopeptides are being reported more frequently. Moving away from B-latam antibiotics we have other antibiotics that affect the cell membrane: Essentially, affect cell membrane s ability of transportation in and out Increases permeability of membrane, so external influences have greater effect causing bacteria death They are bacteriocidial Example: Polymyxin, Colistin These agents are more toxic systemically (affect our cells) than those agents that inhibit cell wall synthesis نعم نحن ندفن بالطب أعوام ا تحت التراب, حتى نصبح يوم ا أشجار ا مثمرة فوق التراب