Antibiotics

BC Yang

Antibiotics and vaccines are among the biggest medical advances since 1000. (Culver Pictures)

For lecture only

A brief history of antibiotics 1495, mercury to treat syphilis. 1630, quinine (chinchona tree) for malarial fever by South Americ

an Indians. 1889, Buillemin defined antibiosis. 1910, Paul Ehrlich developed arsenical compound (Salvarsan) for

syphilis, term: the chemical knife. 1929, Alexander Fleming found penicillin. 1935, Gerhard Domagk showed the value of sulfonamides. 1940, Ernst Chain and Howard Flory demonstrated the effect of p

enicillin. 1940-1970, then searching for new antibiotics ~ recent year: modifying old drugs, finding new discipline in antib

acterial combats Early time in war: thanks penicillin, we can go home now Now a day……….Oh eh?!

For lecture only BC Yang

Thanks to work by Alexander Fleming (1881-1955), Howard Florey ( 1898-1968) and Ernst Chain (1906-1979), penicillin was first produced on a large scale for human use in 1943. At this time, the development of a pill that could reliably kill bacteria was a remarkable development and many lives were saved during World War II because this medication was available.

E. Chain H. FloreyA. Fleming

For lecture only BC Yang

A tale by A. Fleming• He took a sample of the

mold from the contaminated plate. He found that it was from the penicillium family, later specified as Penicillium notatum. Fleming presented his findings in 1929, but they raised little interest. He published a report on penicillin and its potential uses in the British Journal of Experimental Pathology.

For lecture only BC Yang

Scenario of penicillin action on E. coli

1 2 3

456

1: ordinary appearance 2-4: globular extrusions emerge5: rabbit-ear forms6: Ghost form

For lecture only BC Yang

Natural products, including: toxins, antibiotics (about 70% of all known antibiotics) , antifungals, etc, have historically been isolated and characterized from heterotrophic bacteria (e.g. Streptomyces). This was primarily due to the ease with which these organisms can be grown and manipulated in the laboratory.

For lecture only BC Yang

In 2001, the problem of antimicrobial resistance posed a global threat to the effective treatment of many bacterial diseases. In developed countries, as many as 60% of hospital-acquired infections are caused by drug-resistant microbes. These infections are no longer found only in hospital or nursing home wards but are active in the community at large.

Evaluation by BUSINESS COMMUNICATIONS COMPANY, INC.,

For lecture only BC Yang

An ideal antibiotics

Broad-spectrum Did not induce resistance Selective toxicity, low side effects Preserve normal microbial flora

For lecture only BC Yang

Susceptibility test Tube dilution method

Minimal inhibitory concentration (MIC): the smallest amount of chemotherapeutic agent required to inhibit the growth of organism in vitro

Disk diffusion method Zone of inhibition (ZOI):

the correlation of ZOI and MIC has been established by FAD

ETest. This commercially-prepared strip creates a gradient of antibiotic concentration when placed on an agar plate

For lecture only BC Yang

Guidance of antimicrobial therapy

Minimum inhibitory concentration: lowest concentration of antibiotic that inhibits visible growth

Minimum bactericidal concentration: lowest concentration of antibiotic that kills 99.9% of the inoculum

Serum bactericidal title: dilution of serum that kills 99.9% of the inoculum

Synergy test: synergistic activity of multiple antibiotics

For lecture only BC Yang

Use of antibiotics; is it properly applied?

Acute infections in outpatients

Acute infections in hospitalized patients

Chronic infection (tuberculosis, AIDS)

Agriculture/veterinary medicine

For lecture only BC Yang

In vitro: Factors for optimal antibiotic action

pH of environment: Nitrofurantoin is more active in acid pH; sulfonamides and

aminoglycoside are more active in alkaline pH. Components of medium:

Anionic detergents inhibit aminoglycosides, serum proteins bind to penicillin in varying degrees.

Stability of drug: Aminoglycosides and chloramphenical are stable for long p

eriod in vivo. Size of inoculums:

The larger the bacterial inoculum, the greater the chance for resistnat mutant to emerge.

Metablic activity of microorganisms: Actively and rapidly growing organisms are more susceptib

le to drug action

For lecture only BC Yang

Affecting factors in vivo

Abscess: circulation is blocked off.

Foreign bodies: obstruction of the uri

nary, biliary or respiratory tracts etc.

Immunity.

For lecture only BC Yang

Diagrammatic representation of the results of treatment related to specific chemotherapy

Patients with normal immunity and uncomplicated mild to moderate infections

Patients with serious life-threatening infections

For lecture only BC Yang

Sites of action

For lecture only BC Yang

Modes of action (1) Inhibitors of cell wall synthesis.

Penicillins, cephalosporin, bacitracin, carbapenems and vancomycin.

Inhibitors of Cell Membrane.Polyenes - Amphotericin B, nystatin, and condicidin.Imidazole - Miconazole, ketoconazole and clotrimazole.Polymixin E and B.

Inhibitors of Protein Synthesis.Aminoglycosides - Streptomycin, gentamicin, neomycin and kanamycin.Tetracyclines - Chlortetracycline, oxytetracycline, doxycycline and minocycline.Erythromycin, lincomycin, chloramphenicol and clindamycin.

Amphotericin

Tetracyclines

Aminoglycosides

vancomycin

For lecture only BC Yang

Modes of action (2)

Inhibitors of metabolites (Antimet

abolites).Sulfonamides - Sulfanilamide, sulfadiazine silver a

nd sulfamethoxazole.

Trimethoprim, ethambutol, isoniazid.

Inhibitors of nucleic acids (DNA/R

NA polymerase).Quinolones - Nalidixic acid, norfloxacin and ciprof

loxacin.

Rifamycin and flucytosine. 

rifamycin

For lecture only BC Yang

Penicillin: an extensively studied example

For lecture only BC Yang

Action mechanism of penicillin

Action target: cell wall on penicillin binding proteins (PBPs) Transpeptidases (form cross-links in peptid

oglycan) Beta-lactam ring attached to 5-membered t

hiazolidine ring Accessibility of PBPs differ in gram+ and gra

m- bacteria Amino acyl side chain groups determine spectr

um, adsorption, susceptibility to lactamase Bactericidal inhibitors

For lecture only BC Yang

Pharmacokinetics of penicillins

Adsorption: can be oral

Stability in acid condition: PenG (no) Pen V (yes) Ampicillin (yes)

Distribution: to most body sites; not in

CSF unless inframmed meninges Excretion: rapid eliminated by renal s

ecretion

Amoxacillin (yes) Nafcillin (yes) Peperacillin (no)

For lecture only BC Yang

Clinical status of Penicillins Pen G (Pen V): natural

Common strptococci (S. pneumoniae; S. pyrogenes); URTI, pneumonia meningitis, prophylaxis of rheumatic fever

Nafcillin: penicillinase-resistant Staphylococci epidemic; bacteremia, septiemia

Ampicillin: Gram- spectrum: E. coli; H. influenzae;Salmonella, shigella

pharngitis, otitis media, UTI, gastroenteritis Peperacillin:

Expanded spectrum/antipsuedomonal, enteric bacilli; Systemic infection in hospitalized patients (gram-, P aeruginoma)

Combinations with -lactamase inhibitors:URTI, pneumonias, meningitis, bactermia

For lecture only BC Yang

Resistance

B-lactamaseTypes:

Different substrate specificity Penicillinases cephalosporinases

Location: Gram+: extracellularly Gram-: periplasmic space

Serine--Lactamase

Metallo--Lactamase

By Dr. Osnat HerzbergUniversity of Maryland Biotechnology Institute (UMBI)

Failure to bind to PBPs Cannot penetrate porins (gram-) Production of lactamase (penicillinase) Lack autolytic enzyme

For lecture only BC Yang

Adverse effects

Wickens K, Pearce N, Crane J, Beasley R. Antibiotic use in early childhood and the development of asthma. Clin Exp Allergy 1999;29:766-771.

Thrombophlebitis Allergic reactions Superinfections (dia

rrhea) Seizures (rare)

For lecture only BC Yang

Before on antibiotics:

–Antibiotics act as powerful selective factors in the emergence and spread of resistant microoraganism.

For lecture only BC Yang

聯合報 八十五年 四月十三日 頭版新聞

In Rwanda

For lecture only BC Yang

1953: Shigella outbreak in Japan, multiple drug resistance

1950: M tuberculosis largely resistant to streptomycin

For lecture only BC Yang

Resistances

Natural (inherent) resistanceStructural barrelLack of targetTransport system

Acquired resistanceMutationGene exchange (conjugation in most)

For lecture only BC Yang

Transferable antibiotic resistance in bacteria

Reduced uptake into cell (chloramphenicol) Active efflux from cell (tetracycline) Modification of antibiotic targets (-lactam, erythrom

ycin) inactivation of antibiotic by anzymic modification:

hydrolysis (-lactam, erythromycin); derivatization (aminoglycosides)

Sequestration of antibiotic by protein binding (-lactam)

Metabolic bypass (sulfonamides) Overproduction of antibiotic target (titration: sulfo

namides)

For lecture only BC Yang

Spread of resistanceIn most:

Day-care, nursing homes, correctiona

l facilities Sanitation, animal feeds (fecal-oral) Sexual/ Respiratory transmission International travel Immunosuppression

For lecture only BC Yang

Some probable overuse/misuse of antibiotics

Prophylatic use before surgery Empiric use (blinded use) Increased use of broad spectrum agents Pediatric use for viral infections Patients who do not complete course (chro

nic disease, eg. TB, AIDS) Antibiotics in animal feeds

For lecture only BC Yang

Policy to deal drug resistance (1)

Ideally, bacteriological management of clinical infection should involve:

1. Identification of causative organism2. Sensitivity test3. Follow-up the drug effect4. Monitor antibiotic level to avoid toxicity.

In reality, most patients requiring antimicrobial therapy are treated empirically. In serious infections immediate chemotherapy may be life-saving.

For lecture only BC Yang

Policy to deal drug resistance (2)

Periodic changes of antibiotics used might change selective pressure and thus avoid the emergence of resistance and retain the therapeutic value of antibiotics over a longer period.

The unnecessary prophylactic or animal feeds use should be discouraged.

Distribution of information on current/updated infectious microbes (consult microbiologists): use more targeted antibiotics

Patient education ( 不隨便吃藥 , 停藥 )

For lecture only BC Yang

New antibiotics development

Pharmaceutical industry putting resources

back into discovery Liaisons with university researches Discoveries in microbial physiology and

genetics offering new targets, new

disciplines Combinational chemistry (mass screening)

For lecture only BC Yang