Antimicrobial Medications PDF

11/13/24 Today’s class …. This class should be almost entirely review – things you have seen before, but now all brought together. All the class queries I would normally ask are answered in the distributed notes – and blanking them out would eliminate too many slides. I will still blank...

11/13/24 Today’s class …. This class should be almost entirely review – things you have seen before, but now all brought together. All the class queries I would normally ask are answered in the distributed notes – and blanking them out would eliminate too many slides. I will still blank out the initial summary slide for some major sections. When we come to those, I strongly recommend you try to recall answers before reading ahead. Pre-quiz also tied in closely to content. For this quiz I will release answers by tomorrow. History of Medicine As long as there has been disease, there have been remedies. Some even worked… Others relied on placebo effect Willow bark vs chicken soup With discovery of microorganisms and linking to disease Efforts to stain for microscopy showed difference Dyes that stained some bacteria, but not our cells Triggered search for differential poisons – “silver bullet” 2  11/13/24 Search for Differential Poisons (anti- microbials) Guided by history and tradition Test old remedies on infectious agents – e.g., quinine, mercury Expanded to testing any poison – looking for therapeutic effect Can test against bacteria in culture (though might miss – e.g., sulfanilamide – arsenic compound!) Alexander Fleming’s bad lab technique led to discovery of “Antibiotics” – antimicrobial medications produced by microorganisms -- penicillin Continues to current time – looking for anti-microbial effects by organisms in all ecological niches. Best is still soil bacteria. – streptomycin. Addition of Science Modification of existing antibiotics to remedy initial shortcomings or overcome resistance. Resistance is continually evolving, reuiring new or evolved medication. Increasingly based on better understanding of mechanisms of both drugs and resistance. 3  11/13/24 Role of Money Anyone can propose new drugs – but takes investment to test and bring to market. Pharmaceutical Companies need to balance risks -- working with poisons -- what will “therapeutic” index be for ”normal” sick people What about interactions with other drugs or foods (erythromycin and grapefruit!) And rewards (factors that affect market)– How common is the disease/need? Acute vs chronic (or short-term vs long-term treatment) Cost to make vs cost people (or insurance) can/will pay How soon will microbial resistance arise? Is there an exclusive license? How long will exclusive license last? Golden Ticket – Rational Drug Design Ultimate goal is to use our scientific understanding of an organism to design new and specific anti-microbials (or any drug for that matter) Already seeing computers(AI!) test huge databases of chemical structures for possible specific interactions Still need to go through testing in animals and people. 4  11/13/24 Few drugs are curative on their own Bacteriostatic – inhibit bacterial growth. Give patient’s immune a chance to eliminate pathogen. Bactericidal – actually kill bacteria Until/unless resistance emerges in body. (or latency preserves live MOs) Again, a functioning immune system needed for full cure! Cases where immune system impaired (e.g., HIV/AIDS) require long-term, multi-drug regimens. Broad-Spectrum vs Narrow-Spectrum What do you know about the infective agent(s)? How fast do you need to start treatment Broad as more collateral damage, but faster Often start broad and move to specific as more known about the agent. 5  11/13/24 Drug interactions are an Increasing Issue Consider two medications that each help control an infections without harming the patient. If you take them together, they Can be additive – each still does its good thing at about the same level. Can be antagonistic – with one or both interfering the activity of the other Can be synergistic – greatly amplifying the effect of the other And the amplified effect might be worse for the patient than the MO! Each time you add another component, equation becomes more complicated. Think (don’t answer) – how many different pills, supplements, sweeteners, preservatives to you take each day? Location, Location, Location To be effective, medication has to get to where it can have an effect (and still be effective when it gets there) Oral – survive acid and enzymes, be taken up Injection – bypass stomach and absorption, they but have to survive in blood or deposit where needed. And still be effective (and remain effective) when it gets there Kidneys remove foreign materials Liver detoxifies Half-life of drug determines how much and how often a new dose is needed. Health of the patient also impacts turnover (e.g., kidney damage) 6  11/13/24 Specificity There are plenty of chemicals that will kill bacteria, fungi, protozoa, helminths, and viruses But most of those also kill us! General rule – antimicrobial medications are tailored to one group or to subgroups within the broader group. Consider separately Bacteria Viruses Fungi Protozoan parasites Helminth parasites Targets for Antibacterial Medications Cell wall synthesis Protein synthesis Nucleic acid synthesis Metabolic pathways Cell membranes 7  11/13/24 Cell Wall Synthesis Frequent target is Peptidoglycan and its components Includes beta-lactam antibiotics, glycopeptide antibiotics, and bacitracin Beta-Lactam antibiotics and deravatives All have beta-lactam ring All have VERY HIGH therapeutic index Competitively inhibit penicillin-binding proteins (PCPs) that catalyze formation of peptide bridges between adjacent glycan strands, disrupting cell wall synthesis Only effective against actively growing cells!! Penicillins – Penicillin G – natural enzyme Ampicillin – modified for higher Gram neg activity Augmentin as special combination. 8  11/13/24 Beta-Lactams cont Vary in activity, especially comparing Gram positive and Gram negative organisms. Also difference between aerobes and anaerobes. Resistance often by enzyme beta lactamase – destroys antibiotic catalytically. Gram negative more often than Gram positive. Different mechanism Cell Wall: glyopeptides Vancomycin NOT beta lactam based… Binds to amino acid side chain of peptide-glycan. Blocks peptidoglycan synthesis. Only effective against Gram positives (can’t cross outer membrane of Gram negatives) LOW therapeutic index (not a good thing) Normally injected Exception – intestinal infections – Why!!! Antibiotic of last resort for resistant Gram positives… 9  11/13/24 Bacitracin Affects cytoplasmic membrane, blocking transport of peptido- glycan precursors Very Toxic to human cells as well! Used in topical applications – why? Bacterial Protein Synthesis Ribosomes are main target! Prokaryotes have 70S, eukaryotes have 80S ribosomes Mitochondria also have 70S ribosomes May account for toxicity of some of these antibiotics 10  11/13/24 Protein synthesis Primary targets Many compounds with subtle differences in reactivity and interactions with other drugs. Side effects often limit to last resort or topical. For now, focus on subset: Binding large ribosome subunit (50S) – mostly bacteriostatic Erythromycin – effective Chloramphenicol – rare but fatal side effect; last resort or topical use Binding small ribosome subunit (30S) Streptomycin – block initiation and induce errors in translation. Aerobic required for uptake. Neomycin – extremely toxic but OTC topical use. Tetracyclines – block tRNA binding Nucleic Acid (both DNA & RNA) Synthesis. Some very specialized enzyme differences Target topoisomerases (aka helicase, gyrase). Floroquinolones. Specific for working with supercoiled DNA, but still severe side effects possible. – example: ciprofloxin. Target RNA polymerase initiation -- Rifamycins block initiation of bacterial transcription. Includes one of the first-line drugs for Mycobacterim tuberculosis -- Rifampin Book includes Metronidazole in this category. Active form of drug mutates all kinds of DNA – killing or causing cancer. Administered form of drug requires activation by anaerobic metabolism. Strong impact on many anaerobic (or microaerophilic) MOs! 11  11/13/24 Metabolic Pathways Many bacterial pathways are similar to Eukaryotes. Enzymes frequently related. Current focus is on pathway Humans do not have – Folate synthesis pathway! Sulfa drugs – competitive inhibitors (structurally similar to para-amino benzoic acid -- PABA) Membrane Integrity Membranes are awfully similar between bacteria and eukaryotes! Severe side effects possible. Example: Polymixins. Used in topical medicines. 12  11/13/24 Special Case: Mycobacterium Very different surface – waxy coat of mycolic acids Allow survival in dry conditions – including desiccated dust (or dust-like) suspensions in air – ideal for getting to smallest passages of the lung! Block uptake of many drugs! Slow growing – requires long term exposure to drugs (months) Allows for development of resistance during treatment First Line Drugs (ones that you hope will work…) Isoniazid (blocks mycolic acid synthesis. Ethambutol (blocks other specific cell wall components.) Rifampin (RNA polymerase, discussed earlier.) Summary – Anti-bacterial Medications Sufficient differences Cell Wall Ribosomes (protein synthesis) Nucleic Acid synthesis Metabolic pathways Cell membranes 13  11/13/24 Summary – Anti-bacterial Medications Broad Spectrum possible All related Two main groups – Gram positive and Gram negative Some outliers -- Mycobacteria Resistance Mutation for evolutionary development PLASMIDS! For rapid exchange and multi-resistance (retirement comment) New drugs Cost/Risk ratio not good When new anti-microbials, try and hold back Targets for Anti-Viral Drugs What targets? Uses host machinery for ALL metabolism, ALL protein synthesis, All lipid synthesis, etc. à no way to target without targeting host! When look at special corners of viral life cycle à DIFFERENT FOR EACH VIRUS TYPE or GROUP Remember: Cellular life arose once and evolved. Still a common thread throughout. à but viruses arose many times, inventing rules from scratch each time! 14  11/13/24 Viral entry Viral uncoating Nucleic Acid Synthesis (genome integration) Virus assembly Virus release àActive only during virus replication àSpecific for particular virus types or groups Virus entry First step is to bind to a specific receptor on surface of target cell. Idea is to block that binding, either by reacting with virus protein or cell target. Extremely specific for each virus type or group. Relatively easy for virus to mutate and resist Examples in book are all for HIV Our immune system (if we have a functioning one) does this better and faster than drug companies… 15  11/13/24 Virus uncoating Not common Anti-Influenza – amantadine (and rimantadine), but very broad resistance already exists. Anti HIV Capsid (both disassembly and assembly) – Lenacapavir Used for patients with multi-drug-resistant infections. Number 1 Target è Nucleic Acid Synthesis Many viruses code for their own, special nucleic acid polymerase. All RNA viruses MUST code for this activity! DOES NOT MEAN THAT ONE DRUG CAN TREAT MOST VIRUSES! Closest to a universal silver bullet – nucleic acid analogs. Analogs get incorporated into growing chain, resulting in defective or terminated DNA. Virus polymerase (no error checking) incorporates more often. Replicating viruses also doing more replication more quickly! Examples: Herpes viruses (all types) – Acyclovir HIV – Azidothymidine (AZT) 16  11/13/24 Nucleic Acid Synthesis (and integration) Polymerase Inhibitors – examples for Herpes viruses & HCV Reverse Transcriptase inhibitors – examples for HIV & HBV Integrase inhibitors – example of HIV Again – very specific for specific virus types and groups. Proteinase inhibitors…. REMEMBER – Bacterial Operons (lac operon) Make one RNA strand that codes for multiple proteins, all needed at once. Only possible because bacteria ribosomes bind to an RNA SEQUENCE Eukaryotic ribosomes bind to N-terminal Cap – means only one protein per RNA. Viruses that want to use that strategy in eukaryotes have a new twist. Make a large mRNA that codes for several proteins all at once. Then make a protease that will cut specifically between the proteins! If you block the protease – prevent assembly! 17  11/13/24 Protease Inhibitors (cont.) HIV – Ritonavir (in combo with at least two other drugs)– both protease and a CYP3A inhibitor… COVID-19 – PAXLOVID© (Ritonavir plus nirmatrelvir) Other drug category Specific for influenza -- Neuraminidase inhibitors Why do we keep seeing HIV drugs? Most anti-microbials do not cure! Controls or slows infection, allowing time for immune system to kick in. But if patient is immune-compromised, we ask anti-microbials to do more. Generally, means long term (or life-long) treatments, including replacements when resistance develops to first-line drugs. Long-term users changes the cost/risk analysis by pharmaceutical companies to favor investment in new medications. And HIV infections make a person immunocompromised… 18  11/13/24 Speaking of Immune system -- Antibodies are being regularly used as “medicines” Passive immunization – injection of ANTIBODIES from recovered/protected people is a time-honored way of saving lives. Natural transfer from mother to child via placenta and colostrum. Rho gamma globulin for Rn-negative mothers at childbirth Artificial transfer of immune globulin – such as recovered Ebola patients Antivenom for snake bite (or spider bite) victims! Also have developed ways to produce MONOCLONAL ANTIBODIES in the laboratory Specific antibodies (usually high-titer IgG) against a known target, used as a drug Actually, examples of such use were listed in the book Either method presents a mature, humoral immune response for immediate effects. Danger with using too often – patient can develop antibodies to the donor antibodies… There is a better way... Vaccines Develop a mature immune response (humoral and/or cell based) before you need it by exposing the body to key ANTIGENS in a controlled fashion. Inactivated Micro-organisms Take whole organism, kill it (formalin), mash it up, and inject Some viral vaccines still in this mode (influenza, rabies, hepatitis A) Subunit vaccines Purify one or a few key proteins or protein fragments and inject. Make key proteins using recombinant technoloy Make virus-like-particles (empty capsids) -- HPV. Acellular pertussis (aP) vaccine an example Toxoid vaccines Purify toxins, destroy toxic part, but keep epitopes. Diphtheria & tetanus are examples. Much fewer side effects. 19  11/13/24 Other “inactivated” Vaccines Conjugate Vaccines – polysaccharides linked to proteins Makes polysaccharides into T-debendent antigens (good thing!) Haemophilus inflluenzae nearly eliminated Hib meningitis in children Streptococcus pneumoniae also strong protection. Nucleic acid-based vaccines Best known variety à mRNA vaccines (for COVID-19) mRNA incorporated into cells For a short time, express key antigens on cell surface, triggering immune response. Flexible. Quickly developed in response to new agents Require a “freezer chain” for delivery Attenuated Vaccines Find or create a weakened form of pathogen Infect Normal host No disease results But long-lasting immunity develops Can transmit to others, spreading the effect of the immunization Infect immunocompromised host Sometimes will cause disease Also, can revert or mutate, becoming pathogenic Measles, mumps, rubella, chickenpox, yellow fever, rotovirus are all examples. 20  11/13/24 Effectiveness for Bacteria and Viruses Cases per Year Before Decrease After Immunization Immunization Disease Diphtheria 175,885 (1920 to 1922) Nearly 100% Haemophilus influenzae type b 20,000 (estimated) 98.8% invasive disease Measles 503,282 (1958 to 1962) Nearly 100% Mumps 152,209 (1968) 99.2% Pertussis (whopping cough) 147,271 (1922 to 1925) 90% Poliomyelitis 16,316 (1951 to 1954) 100% Rubella (German measles) 50,230 (1966 to 1969) Nearly 100% Smallpox 48,164 (1900 to 1904) 100% Tetanus 1,314 (1922 to 1926) 98% Problems Come with Success People forget what it was like before vaccine. Remember sore arms and headaches. Think we have won, and no longer need. “if everyone else is vaccinated, my kids are safe” à instead, they are at increased risk if there is an outbreak The only disease we have eliminated on this planet is SmallPox 21  11/13/24 CEC Vaccinations recommended for Bacterial Diseases Diphtheria (infants – preschool) Hemophilus influenza type b (children or high risk) Meningococcal disease (adolescents or high risk) Pertussis (whooping cough) (infants – preschool) Bacterial pneumonia (65. high risk) Tetanus (everyone, 10 yr boost) CDC recommended Vaccinations for Viral Diseases COVID-19 Mumps Hepatitis A Polio Hepatitis B Rotavirus HPV Rubella (German Measles) Influenza Shingles Measles Chickenpox 22  11/13/24 Non-routine Vaccines (for special cases) Adenovirus Anthrax Cholera Dengue Ebola Japanese Encephalitis Rabies Tuberculosis Typhoid fever Yellow Fever Anti-Fungal Medications Fungi are Eukaryotes – makes finding differences with human cells difficult! Fungal cytoplasmic membrane Cell Wall synthesis Cell division Nucleic acid synthesis Protein synthesis. 23  11/13/24 Ergosterol vs Cholesterol Same function Almost same structure Ergosterol Cholesterol Most antifungal chemicals target ergosterol Azoles inhibit ergosterol synthesis, membrane leaks Three families Imidazoles, Triazoles, and Tetrazoles Newer less toxic triazoles used to treat systemic infections and nail infections Others used in topical applications Polyenes (from Streptomyces) can actually BIND TO ergosterol containing membranes, causing leakage Amphotericin B – strongest systemic drug we have – and strong side affects! Used as last resort. Nystatin – even more toxic, but used in creams, lozenges, and oral suspension (not absorbed!) for local treatment 24  11/13/24 Cell Wall synthesis Target is a unique bets-1,3 glucan linkage Target drug resistant fungal infections Other Cell Division – one example (Griseofulvin) blocks tubulin – which human also have! Slow uptake by human cells Concentrates in keratinized dead cells of skin Effective against fungal infections on keratinized skin (nail infections) Nucleic Acid Synthesis Flucytosine Inactive form taken up, but converted by yeast enzyme to active form that inhibits nucleic acid synthesis. Bad side effects. Last resort. 25  11/13/24 Parasitic Protozoa Some specialized metabolic pathways or structures allow for repurposed drugs Metronidazole can treat anaerobic (or microaerophilic) protists Tetracycline derivatives seem to work on apicompliexan protozoa. Amphotericin B used with life-threatening Leishmania infections No financial incentive for new drugs (e.g., diseases are not a major problem in developed world) Parasitic Helminths Neuro inhibitors(!) First-world (read money) needs center on pets! E.g., dog and cat heartworm Translation to third-world raises political issues Ivermectin example 26