β-Lactam Antibiotics: PDF Lecture Notes

β-lactam Antibiotics Lecture: 3 Dr. Tariq Aljarba  β-lactams A β-lactams is an internal amide with the amine in the β-position in relation to the carboxylic acid. All β-lactams will have similar mechanisms of action and many general properties...

β-lactam Antibiotics Lecture: 3 Dr. Tariq Aljarba  β-lactams A β-lactams is an internal amide with the amine in the β-position in relation to the carboxylic acid. All β-lactams will have similar mechanisms of action and many general properties     HOOC NH2 NH O  The largest group of antibiotics forms about 60% of total known antibiotics. The nitrogen atom is neutral (very weak base, amide nitrogen) because it’s lone pair electrons are delocalized by resonance and presence of carbonyl group The β- lactam ring is responsible for the following characters: Activity of antibiotics. Allergenicity Stability Stable for 7-14 days at 4C Stable for 1-2 days at room temp Dry form stable for up to 5 years  Penicillins They are the first group of antibiotics discovered Natural penicillin e.g. Penicillin G & Penicillin V. Semi-synthetic Penicillins divided into the following: Penicillinase resistant penicillins e.g. Methicillin, Nafcillin, Oxacillin, Cloxacillin, Dicloxacillin and Fluocloxacillin Broad spectrum penicillins e.g. Ampicillin, Amoxicillin, Bacampicillin. Mega-spectrum penicillins e.g. Carbencillin & Ticarcillin. Ureidopenicillins as Azalocillin, Mezlocillin and Piperacillin.  Stability The β-lactam ring is unstable (highly strained 4-membered ring) in the following: Presence of β-lactamase enzymes produced by resistant micro-organisms e.g. Staphyllococcus aureus, Heamophilus influenza and Neisseria gonorrhea. Presence of acid Presence of base  Common Characteristics All Penicillins are acids, with a pKa around 2.5 to 3. They are crystalline and should be protected from moisture If it is stored under dry conditions, it will be stable for years. They have an unpleasant taste. They are not suitable to formulate as a free acid, so used as sodium or potassium salts.  Generally safe in pregnancy and during lactation It will pass into the milk, so only precaution is to watch out for anaphylactic shock and diarrhea. Differ in their protein binding capability, between 20 and 90% protein bound This leads to a change in the free drug available in the bloodstream.  Common Characteristics Immunological reaction; an anaphylactic shock can occur in less than 0.1% of the population, or a rash in 5 - 7% This results from the reaction of the β-lactam ring with a terminal amine on a lysine in a polypeptide, leading to the formation of an allergen. O H H H N H N HS S O R N N R O O Lys-protein COOH COOH Lys-protein Allergen ❑ Antibodies are formed the first time the patient is exposed to the antibiotic, and the reaction will be severe in consequent times. ❑ If the preparation is not well purified, then residual proteins will cause the reaction to be more severe. ❑ First line of treatment is the use of Adrenaline to stabilize the blood pressure and relieve the bronco-constriction  Several drug interactions have been reported, such as oral contraceptives and the antigout, probenecid. Probenecid compound will compete with Penicillins for active tubular sites of active excretion, resulting in higher blood levels and may lead it to reach toxic levels.  Penicillin G Crystapen Source: Penicillium chrysogenum Mixture of compounds, including Penicillin G, K, V, O, and S are produced in the medium. We can obtain exclusively Penicillin G by the addition of phenyl acetic acid. It is used in units. In the USP one unit is equal to the antibiotic activity present in 0.6 µg. Essential Structural components of Penicillin G cis-orentation Amide H H H N S O N O COOH Carboxylic  -lactam ring Bicyclic system  Pharmaceutical Forms Water soluble salts: They are used IV, IV infusion or IM. Rapid onset and short duration ( t1/2 = 1/2 hour). Potassium preferred in hypertension. Sodium preferred in renal insufficiency (hyperkalemia & Cardiac arrest). Procaine Penicillin G (Wycillin®): Procaine (local anesthetic) :Pen.G = 1:1 Water Solubility (1:250 ml) used as IM suspension. Duration of action (up to 1 week)  Benzathine Penicillin G (Bicillin®) (Pencitard, Durapen, Penadur, Retaepen, Aqua Pen, Depo Pen) Benzathine:Pen.G =1:2 Water Solubility (1:5000 ml) used as IM suspension. Duration of action (up to 3-4 week) Metabolism by amine oxidase yields pen.G + Oxalic acid (toxic metabolite). Must be used with urine alkalinser to prevent crystallization of calcium oxalate formed  Pharmacokinetics Route of administration IM, IV, but not orally. Distribution to almost all body tissues and fluid. It penetrate to CSF in case of meningitis. Concurrent administration of probencid, kidney will excrete probenecid before Pen G leads to increase blood level concentration of Pen G five times  Mechanism of Action Inhibition of transpeptidation leading to loss of murine layers during cell division. Inhibits stage III and thus prevents cross-linking of peptidoglycan Less effective against Gram negative bacteria due to the presence of outer mucopolysaccharide membrane  Antimicrobial Spectrum Narrow spectrum (effective against limited number of micro-organisms, mostly Gram positive) : Staph. aureus Soft tissues infections. Osteomylelitis ( infection of bone marrow and hard tissues) Pen G is effective but not drug of choice. Toxic Shock Syndrome (TSS), during menstruation or wound infection with Staph. aureus Streptococci Sterpt. viridans: non-pathogenic, one of the normal flora it can passes to the blood stream causing sub-acute bacterial endocarditis. Treatment by benzathine Pen. Sterpt. Pneumonia: Besides causing pneumonia, can cause meningitis in adult. Treatment, with pen G Strept. pyogenes Tonsillitis, boils, sore throat, scarlet fever, endocarditis and rheumatic fever. Treatment with Pen G  Enterococci Sterpt. faecalis, normal large intestine flora, can causes UTI and endocarditic. Treatment by Pen G and streptomycin Corynbacterium diphtheria (Diphtheria). Treatment by Pen G Clostridium tetani (Tetanus). Treatment by Pen G  Gram negative bacteria: Neisseria meningitides (Meningitis): When the blood-brain barrier (BBB) is normal, most beta- lactam agents (eg: penicillin G) penetrate poorly. However, in the presence of meningeal inflammation, CSF penetration is enhanced likely as a result of separation of intercellular tight junctions, raising the level of Pen G in the CSF. In case of allergy or penicillin-resistant strain, third-generation cephalosporins are the beta-lactams of choice in the empiric treatment of meningitis (ceftriaxone or cefotaxime are used). N. gonorrheae (Gonorrhea) Treponema pallidum (Syphilis)  Properties of penicillin G Active versus Gram-positive bacteria (e.g. staphylococci, meningitis, and gonorrhoea) and limited activity against Gram-negative cocci. Non-toxic Narrow spectrum. Ineffective when taken orally since it breaks down in the acid conditions of the stomach. Sensitive to all known -lactamases. These are enzymes produced by penicillin resistant bacteria which catalyze the degradation of penicillins. Allergic reactions are suffered by some individuals.  Penicillin V (Ospen, Pen os) Production: from P. chrysogenum by the addition of phenoxyacetic acid instead of phenyl-acetic acid. H H N S C Me O O N Me O COOH  Properties Penicillin V Relatively acid stable, given orally due to: Electron withdrawing group makes the side chain carbonyl less electronegative and can not attack the lactam carbonyl. Blood level concentration (BLC) of Pen V is moderate so it is not the good choice for treating N.gonorrheae and Strept. pneumonia infections.  Clinical Uses Prophylactic against sub-acute endocarditis and in rheumatic fever. Prophylaxis in sickle cell babies against pneumococcal infections. Mouth infections. Treatment of tonsillitis and sore throat. Semisynthetic Penicillins  Aim Increase the Spectrum Improve cell wall permeability by adding polar groups. Decrease Penicillinase susceptibility Steric hinderness by bulky group close to the β-lactam ring. Increase Acid liability Electron withdrawing groups at the side chain. How they are produced ? In 1959 6-aminopenicillanic acid (6-APA) was obtained by: Action of acylase enzyme on Pen G Chemical hydrolysis H H2N S Me N Me O COOH  H H2N S Me O N Me R-C-Cl O COOH O H H R-C N S Me N Me O COOH Structure-Activity Relationship (SAR) 1-position, if the sulfur is oxidized to the sulfone/sulfoxide, gives it better acid stability, but becomes less active. 2-position, any change will lower activity. 3-position, the carboxylic acid is a must. If changed to an alcohol/ester, it will be inactive. R H H N 6 1 S C Me 5 2 O N Me 7 4 3 O COOH 4-position, must have a nitrogen. 5-position, no substitutions allowed. 7-position, must have the carbonyl R H H N 6 1 S C Me 5 2 O N Me 7 4 3 O COOH 6-position, specifically the R group: If add an electron withdrawing group (NO2, Cl, Fl..), then the amide oxygen will be less nucleophillic and will thus give the compound better acid stability. If a bulky group (ph, diph,…) is added close to the ring, then it makes the drug better resistant to β-lactamases If a polar group(NH2, COOH, OH) is added, its spectrum becomes broader, since it can pass through the porin in the Gram negative bacterial cell walls. R H H N 6 1 S C Me 5 2 O N Me 7 4 3 O COOH Classes of Semisynthetic Penicillins Penicillinase – Resistant Penicilins (PRP). Broad Spectrum Penicillins (BSP). Mega – Spectrum Penicillins (MSP). Penicillinase-Resistant Penicillins 1- Methicillin Dimethoxy groups increase resistance of the drug to penicillinase, but also increase the acid – sensitivity as the OCH3 group as electron releasing group. O OMe H H N S Me OMe N Me O COOH  Uses It is used for treatment of infection caused by penicillinase producing Staph. aureus. Treatment of respiratory, urinary tracts infections, skin, bone and joint infections due to Staph. aureus penicillinase producing strains. Toxicity Hypersensitivity reactions. Nephropathy in a large i.v. dose.  2- Nafcillin Penicilinase stable. Acid stable. More lipophilic. Penetrates CSF. O H H O N S Me N Me O COOH Side effects: Reversible neutropenia (abnormally low number of neutrophil granulocytes), platelets dysfunction leading to abnormal bleeding time. Very irritant at injection site (causes phlebitis).  3- Isoxazolyl Penicillins R1 O H N H S Me R2 N Me N Me O O COOH R1 R2 Oxacillin H H Cloxacillin = Prostaphlin H Cl Dicloxacillin Cl Cl Flucloxacillin = Fluxapen F Cl Characters: Resistant to β-lactamas enzymes. Resistant to gastric acidity. Active against Staphylococcal infections. Toxicity: Hypersensitivity. GIT side effects Hepatotoxicity Neurotoxicity Neutropenia Cloxacillin (Prostaphlin): Oral and parenteral Cloxacillin + Ampicillin = Hi Flucil, Ampiclox, Rivaclox Dicloxacillin Oral only. Most potent due to higher lipid solubility. Dicloxacillin + Ampicillin = Cloxapen, Dipebacid Flucloxacillin (Fluapen) Oral only Flucloxacillin + Ampicillin = Ampiflux Broad Spectrum Penicillins 1- Ampicillin = Amino-pencillin G (Epicocillin) Penicillinase sensitive penicillin. Acid Stable Forms an Zwitter ion at PH = 7 leading to increases the penetration of the Gram negative bacterial cell walls (Broad Spectrum). NH3 H H N S Me O N Me O COO Spectrum: Gram (+ve) micro-organisms that are susceptible to penicillin G. Gram (-ve) micro-organisms: E. coli which causes UTI Proteus mirabilis cause UTI Brucella spp. Haemophilus influenzae causes infections of upper respiratory tract (URT). Gardnerella vaginalis (bacterial infection) causing vaginitis Pharmacokinetics: Less bound to plasma proteins. Rapidly excreted through kidney. 35- 50% only absorbed. Actively transported in the intestine as phenylalanine. Should be taken 1 hr before meals or 2 hr after meal. Adverse effects: Mild Diarrhea Loosely stool (5-6 times/ day of diarrhea) Watery stool (15-20 times/ day). Treatment must be stopped and replaced with amoxycillin. Sever Diarrhea (Bloody stool). Decrease level of hormones in contraceptive pills. Ampicillin rash due to hypersenstivity. Pseudomembraneous colitis (PMC) Pseudomembraneous colitis (PMC): On treatment with Ampicillin suppression of the normal intestinal flora occurs leading to super infection with Clostridium difficile (ampicillin resistant bacteria). This bacteria produces two toxins A and B and causing diarrhea. Treatment: Cholestyramine to absorbs the toxin. Lactobacillus organisme to Re-establish normal flora Vancomycin, metronidazole or bacitracin Ampicillin Combinations: Unasyn (ampicillin: sulbactam sodium salt = 2:1): (Ampictam, Sabect, Unictam, Ampictam, Ultracillin, Synerpen) Sulbactam is inactive penicillin analogue that bind irreversibly to penicillinase active site leading to deactivation of the enzyme. Unasyn is used usually as i.v. or i.m. Unasyn prepared as sodium salt, caution of hypertension Unasyn is effective against E. coli and H. influenza O O S Me N Me O COO Na  Ampicillin Pro-Drug Bacampicillin: It is more absorbed than ampicillin and undergo hydrolysis with esterase enzymes in plasma to release ampicillin in high yield NH2 H H N S Me O N Me O Esterase in plasma COO-CH(CH3)-O-CO-CH2-CH3 AMPICILLIN + CH3CHO + CO2 + CH3CH2 OH  2- Amoxycillin Amoxil- E mox- Hymox- Ospamox- Glomox- Remox- Julphamox Advantages: Acid stable but pencillinase sensitive. More absorbed than ampicillin by tyrosine active transport (75% absorbed). High absorption from GIT decrease incidence of diarrhea and PMC Food will not interfere with absorption. Longer t1/2 due retain in polar body fluids (long acting). NH3 H H N S Me HO O N Me O COO Spectrum: Amoxycillin is more active against Salmonella typhi (Typhoid) but not DOC. Amoxycillin is active against Helicobacter pylori (gastric and duodenal ulcer) in combination (Amoxycillin + Clarithromycin + Omeprozole). Amoxycillin is less active against Shigella spp. (Shigellosis bacillary dysentery). Excretion: Amoxicillin is excreted by urine. Amoxycillin Combination: Augmentin- Julmentin- Megamox- Klavox- Curam: Amoxycillin + clavulanate potassium (250mg/125mg, 500/125, and 875/125) Sodium free so no risk for hypertensive patients. Clavulanic acid is a β-lactam penicillin analog inactivate β- lactamases by blocking the active sites of these enzymes. Spectrum: Lower respiratory tract infections (such as pneumonia) Ear Infections Sinus Infections Skin Infections UTI such as bladder infections or kidney infections.  Mega Spectrum Penicillins (Extended Spectrum Penicillins) (Antipseudomonal Penicillins) Mega Spectrum Penicillins A) α- Carboxy penicillins Carbenicillin O H S Me N H N Me O Na OOC COO Na  Characteristics Acid and penicillinase sensitive. Active against ampicillin resistant Pseudomonas aeruginosa, Proteus and Providenica spp. More effective against gram (-ve) Bacilli due to the COOH that provide better penetration to their cell walls. Combination with Gentamycin for serious Pseudomonal and Coliform infections. However, the two drugs are incompatible chemically and should never be combined in the same i.v. solution.  Carindacillin Geocillin It is indenyl ester (pro-drug) of carbenicillin sodium salt absorbed orally and hydrolyzed by esterase enzyme to yielded carbenicillin. One of few antibiotics that active against Pseudomonas aeruginosa orally. O H S Me CH N H N Me OC O O COO Na  Ticarcillin Thienyl O H S S N Me COO Na H N Me O COO Na Advantages: Not used orally, but i.v. or i.m. Give higher serum levels more than carbenicillin. Longer duration of action, replacing carbenicillin in clinical uses. Greater potency against gram (-ve) Bacilli Ps. aeruginosa and Bacteroid fragilis. Timentin consists of Ticarcillin sodium salt and clavulanate potassium (3 g+100 mg)  Mega Spectrum Penicillins B) Ureidopenicillins They contain ureido group (NH-CO-NH) These antibiotics are highly polar, high penetration power and high potency. They are too polar to be absorbed orally so they administered parentrally. They are penicillinase sensitive, therefore they are reserved for use with hospital acquired infections. They bind more to proteins so have high potency and mega-spectrum activity  Low MIC, so low therapeutic doses Low toxic effect on platelets DOC for meningitis caused by Pseudomonas aeruginosa as a combination with Gentamycin.  They have expanded spectrum against the following gram (-ve) bacteria: E. coli. Pr. mirabilis. H. influenzae. Ps. aeruginosa. Klebsiella pneumoniae. Bacteroides fragilis. Enterobacter spp.  Piperacillin H S CH CO NH Me NH N Me O CO COOH N C=O C=O N CH2-CH3 NH-CO- group in the side chain make it mega spectrum for a many types of bacteria. The most potent ureidopenicillin antipseudomonal antibiotic MIC = 4µg/ml. Synergistic with amino-glycosides against Enterobacteriacea which are resistant to the amino- glycoside and β -lactam antibiotics. Zosyn- Tazocin (Piperacillin + Tazobactam), (2 g + 0.25 g). Tazobactam is a strongest suicidal substrate (penicillinase inhibitor).  Toxicity Hypersensitivity reactions. Neuro-toxicity in massive doses. Bleeding disorder through platelets function disturbance. Reversible neutropenia. Electrolyte and acid- base balance disturbance.  -Lactam Monobactam β-lactam ring is alone and not fused to another ring. They work only against aerobic Gram negative bacteria (e.g., Neisseria, Pseudomonas ). No cross-hypersensitivity reactions with penicillin Resistant to some beta-lactamases 1- Aztreonam (Azactam- Cayston) Administration: I.M., I.V., Inhalation. Active against Gram-negative bacteria, including Pseudomonas aeruginosa. It has no useful activity against Gram-positive bacteria or anaerobes. Side Effects: Injection site reactions. Gastrointestinal side effects generally include diarrhea, nausea and vomiting