number 7 Done by Heba Rababah Corrected by Muayad Azzam Doctor Hamad
Antibacterial therapy 1 Antibiotics are very common in our lives, most of us have taken antibiotics at one point or another or at least know them by name, such as Amoclan and Zomax; these are their commercial names. Each antibiotic has a commercial and a scientific name (in microbiology we focus more on the scientific name). Antibiotics also 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. Semisynthetic agents: Natural compounds that have been chemically modified to increase their activity and improve their pharmacokinetics, but they still contain native or nature component. Examples: Amoxycillin, Ampicillin, Cephalosporins and Carbapenems, Rifampicin Synthetic chemicals: completely synthesized in labs. Examples: Trimethoprim, linezolid and quinolones. *Note: Antibiotics are loosely applied to all antibacterial agents. History of antibiotics: Ancient Egyptians used honey for healing wounds, till now, bandages contain honey to help heal small wounds. The first time antibiotics were used and studied scientifically was in world war 2, by Alexander Fleming and Louis Pasteur. Unknown author described the 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." It is expected that older alternatives of antibiotics will be in use again; such as using roots. That comes as a result of the lack of new effective antibiotics able to kill bacteria; which is due to the microbe developing stronger resistance to the current antibiotics; which comes as a result of the abuse and misuse of said antibiotics. The bright side (Benefits vs risks): Since penicillin has been discovered, antibiotics played an important role in saving lives, yet even lifesavers may take lives. Antibiotics are dangerous drugs that have side effects that can be fatal for the kidney, heart, bones and joints etc. So be wise when prescribing them. Example on side effects: Broad spectrum antibiotics could kill the normal flora in addition to killing the bacteria, so there will be a problem if they are unnecessarily used (abuse). Exp: Pseudomembranous colitis. Pseudomembranous colitis: causes inflammation in colon due to the proliferation of a bacteria called clostridium difficle (c.difficile or c.deathicille; as they cause death), the overgrowth of c.difficile is due to the killing of normal flora by some antibiotics. Route of administration There are many factors that determine how to administer the antibiotic:
1. Nature of infection: is the infection severe or not,for example if the infection isn t severe,there s no need to administer it through IV. 2. Bioavailability and therapeutic index. 3. Tissue penetration: which tissue is the target. 4. Excretion. 5. Pharmacokinetics. Antibiotics may be given empirically (blindly): to give a broad-spectrum antibiotic without knowledge of the organism that is causing the infection but based on experience. Do not give antibiotics unnecessarily though; for colds and viral infections. When two or more antibiotics are given together, they might show synergistic effect; which means that when two antibiotics work together the total effect is greater than the sum of the individual antibiotics. For example: you have two antibiotics k1 and k2. k1 targets the cell wall, k2 targets the nucleus, when combined, 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 a major problem associated with antibiotics, which arises due to the abuse and misuse of them. 70 % of respiratory infections are caused by viruses, and most of those infections don t require antibiotics to be treated. So, we refrain from antibiotic use since they have side effects that may lead to more problems, and overusing them (abuse) may result in developing resistant generations of bacteria (as we will see in next lecture). Our role: The doctor is the most important person in the treatment process, pharmacists and chemists work for many years to discover and synthesize antibiotics, then the doctor comes and prescribes them to patients, so this prescription on what, when and how the antibiotic is used is of utmost importance.
To avoid abuse and misuse of antibiotics, more restrictions should be applied in health systems. We don t have strict restrictions on antibiotics off the shelf, so any one could go to a pharmacy and buy them without prescription. However, in the UK, this is not the case; even if a physician wants to write a prescription for a patient, he\she must write their phone number, address, GMC (general medical council), the patient s address and then the prescription. After that this information will be submitted to the medical council. Also, the physician should follow the guidelines when prescribing antibiotics. Let s take chest infection for an example, with guidelines you will know from where to start; is the patient immunocompromised* or not? So, safe use of antibiotics is necessary 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-effectiveness. Spectrum of activity Activity of antibiotics could be for different types of bacteria or a specific type 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. What determines when narrow or broad spectrum antibiotics should be used? If a specimen for an unknown bacteria is present, broad spectrum antibiotics should be administered until the lab results are ready ( may require 2-3 days) this is called Blind therapy. After that, a narrow spectrum antibiotic must be selected and administered to avoid resistance, especially if it s given through IV. Terms related to antibiotic use: -Selective toxicity: Killing or inhibition of the growth of microorganisms without harming human tissue; carried out by targeting structures in bacteria that aren t found in human cells such as the bacterial cell-wall. Antibiotics should have this trait to prevent damage to human cells. -Bacteriostatic vs Bactericidal: Bacteriostatic: used to describe antibiotics that prevent growth of bacteria and allow for natural immunity to deal with the microbe. Bactericidal: describes antibiotics that kill the bacteria. *Note: Bactericidal may lead to the 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 needed for inhibition of bacterial growth. MLC (Minimum lethal concentration): the smallest concentration needed to kill bacteria. Used for Bactericidal only. Antibiotic susceptibility testing:
Bacteria still diffused towards streptomysine, indicating it wasn t inhibited and instead resisted. This clear zone is an indication of the power of inhibition for the antibiotic. 1.) Disk Diffusion Test: - Bacteria with specific type and concentration was grown in a culture. It is then placed in a 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 on the surface of the medium (the black circles in the diagram). After incubation, it will be observed that bacteria have grown in different areas, covering the entire petri dish, except for some clear zones around SOME antibiotics. This indicates that that specific antibiotic inhibited that type of bacteria. Meaning: the use of this antibiotic against that bacteria can be effective. The diameter of the clear zone is measured and compared against a reference standard, which contains measurement ranges and their equivalent qualitative categories of susceptible, intermediate or resistant. For example: 0-5: resistant. 5-15: intermediately resistant. >15: susceptible or sensitive. When can intermediate antibiotics be used? 1.If the choice was between two antibiotics one intermediate and the other resistant, the intermediate antibiotic is the right choice for the targeted bacteria. However, if a sensitive antibiotic was available it should be the first choice against said bacteria.
2.antibiotic categories might be changed as mediums differ, for example; In Vitro, antibiotics could be intermediate,but in Vivo the same antibiotic could be sensitive. 2.) Determination of MIC: You have various test tubes, each is planted with bacteria of certain concentration. In these tubes you add the same antibiotic but with different concentrations; 0%,1%,2%,4%,8% then you observe the tubes. The tube which has turbidity indicates growth of bacteria while the tube which is clear with non-visible growth indicates inhibition of it. For example, we assume tubes with concentrations of 2%,4% and 8% don t have any turbidity. So, the MIC (Minimum inhibitory concentration) will be the tube with the concentration of 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 be equal to MLC. So how to decide? bacteria is taken from each tube that didn t show any visible growth (2,4,8) and then is planted in a plate. The plate in which bacteria doesn t grow would have killed the bacteria. So, the minimum concentration at which this happened will be the MLC.
This figure shows: -Red line indicates Bacteria is growing normally without any added antibiotics. -Blue shows the effect of using tetracycline in inhibiting bacterial growth when the drug is added as bacteriostatic. -Green shows penicillin effect in killing bacteria and stopping growth (number is decreasing) when the drug is added as bactericidal. There are some cases of infection in which a bactericidal 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 structures(nerves) in that opening resulting in herniation (the brain will try to squeeze out) so you need bactericidal to prevent further deadly
infections, as you can t leave the task for the immune system to do it in this case. Infective endocarditis: an inflammation caused by bacteria in heart valves causing damage to them. It results in heart failure, so this bacteria has to be eliminated by a bactericidal. There are some scenarios that direct you to choose a specific antibiotic (bactericidal or bacteriostatic), the route of administration (IV or orally), and if the antibiotic reaches the bone. To sum up, some infections such as meningitis, infective endocarditis and some immunocompromised patients require using a bactericidal. Antibiotics are used for treatment. However, they can be used for prevention (prophylaxis) in certain cases: Immunocompromised people who are vulnerable against infections more than others. They take antibiotics for prevention. Before certain operations, antibiotics are given to prevent probable infections. Some people lose their spleen (in an accident or as a result of sickle-cell diseases) which is very important for protection against capsulated bacteria, in this case individuals must be protected by giving vaccines and prophylactic antibiotics to avoid disastrous outcomes. When you give the antibiotic remember precaution: History of hypersensitivity: in remote areas, patients should be asked if they ve previously experienced sensitivity toward any antibiotic (especially penicillin, since it might cause respiratory shock) (Sensitivity: if he/she had taken it and started to have swellings or allergic reactions.) Do not mix up hypersensitivity with mild side effects; some side effects are normal and controllable. Based on the patient s answer the proper antibiotic should be
administered. If you are in a hospital, you need to be sure about the sensitivity by carrying out a sensitivity test. Glandular fever (Epstein-Barr virus infection) and cytomegalovirus infection greatly increase the risk of developing a penicillin-induced rash. Impaired liver and kidney functions: the liver and kidney are the sites of excretion of antibiotics, so individuals with kidney and liver problems shouldn t be given the same dose as healthy people. Pregnancy, breastfeeding and children: the drug can move from the placenta to the embryo or reach the infant through the breast milk. If antibiotics reach the embryo many problems might occur: discoloration of the tooth or the antibiotic might pass to cartilage and prevent ossification causing the fetus to 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 you prescribe antibiotics, be careful of side effects and remember history is very useful. Mechanism of action: Targets of antibacterial agents: o Cell-wall: it has a unique structure for bacteria which is peptidoglycan. o Protein synthesis: 70s ribosomes are found in bacteria and mitochondria while 80s ribosomes are present in human cells. However, mitochondria also have 70s ribosomes, so some side effects might occur if we target 70s, still they are minimal. o Folate synthesis: Bacteria manufactures its own folates while humans obtain it in food. * Folic acid is the synthetic form of folate that is found in Bacteria. Bacteria use folic acid 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. Next, we will discuss targeting the cell wall: -Most bacteria possess a cell wall to protect from osmotic pressure. - when a microbe divides the need to create a new cell-wall arises. -Interrupting this process leads to new microbes being susceptible to external influences. - The cell might ruptures then leading to the Microbe s death. As you remember bacterial cell-wall 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 an antibiotic that targets this protein it will prevent crosslinking, which will damage the peptidoglycans and lead to death of bacteria. So, antibiotics that target the cell-wall are bactericidal. There re two families of this type: glycopeptides(antibiotic) and beta lactam agents. Glycopeptides : prevent NAM from transforming to peptidoglycan so the chain becomes defective. B lactam agents: prevent crosslinking. Beta lactam agents Have Beta lactam ring which is necessary for binding to penicillin binding proteins. Examples: Penicillins, cephalosporins, monobactams, carbapenems and beta lactamase inhibitors
How do they work? For example, penicillin binds to a transpeptidase enzyme, which we call penicillin binding protein, which prevents the crosslinking and causes the cell to rupture leading to its death. How do bacteria develop resistance for this type? Each b lactam agents have a beta lactam ring (it s the heart of these types of antibiotics) Bacteria produce an enzyme called beta lactamase or penicillinase that breaks the antibiotic s beta lactam ring preventing binding which produces 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 did we start to synthesize and modify penicillin? Penicillin was first discovered as a natural product; Benzylpenicillin and penicillin G. o But, there re some barriers that limit the use of natural Penicillin such as: Narrow spectrum. Short acting. Resistance by beta lactamases. So, we developed synthetic penicillin.
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 their lactam ring to not be recognized by s.ureus. ***How S.aureus develops resistance? S.ureus changes methicillin target in cell wall by altering 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) and is a very prevalent name you will hear in hospitals especially. Monobactam such as Aztreonam used mostly against serious aerobic and Facultative G-ve infections. 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 bacteria. Penicillinase-R causes resistance against Carbapenem. Cephalosporins: have a lactam ring, however with 6 atoms rather than 5 atoms as penicillin, this causes it to have Broader spectrum and Less hypersensitivity reactions. Cephalosporins have 5 Different generations: 1 st (1960) Cephalexin, Cephradine, works on spectrum G+. 2 nd (70s) Cefoxitin, Cefuroxime, works on Broad spectrum, both G- and G+ 3 rd (80s) Ceftriaxone, Cefotaxime.. works mainly on G-ve Enteric bacteria. Usually taken in IV form. Has high penetrating capacity for blood capillary barriers, making it particularly useful for infections in CFS as they can reach it. 4 th (1990s) Cefepime.. works mainly on G-ve, GPC (gram positive cocci) and pseudomonas (which is bad bacteria).
5 th generation 2000s: ceftaroline works on MRSA Glycopeptides: they differ from a b- 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 drugs. Start with penicillin, if staphylococcus appears to be resistant move to flucloxacillin, if resistant continues use vancomysine which is a 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, those antibiotics affect the cell membrane s ability of transportation in and out. Increase the permeability of the membrane, so external influences have greater effect leading to bacterial death. They are bactericidal. 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 الت ر اب,ح ر ت نصبح يوم ا أشجار ا مثمرة فوق الت ر اب