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Common sulfa drugs

•Trimethoprim/Sulfamethoxazole (1:5 ratio TMP:SMX, “trim-sulfa”, co-trimoxazole); oral

•Other examples of sulfonamides for protozoal infections:

•Sulfadiazine or Sulfadoxine-pyrimethamine (pyrimethamine is another drug used to treat protozoal infections, similar to TMP, targets DHFR)•Plasmodium falciparum (malaria) if choloquine resistant

•Sulfadiazine-pyrimethamine•Toxiplasma gondii

•Dapsone (diamino-diphenyl sulfone; not formally a sulfonamide):•Pneumocystis jiroveci: fungus

•Mycobacterium leprae (leprosy): a bacterium; among bacteria,

•only has high affinity for M. leprae’s dihyodropteroate synthase PABA binding site

These agents in protozoa are believed to act by targeting homologous enzymes, thus inhibiting folic acid synthesis in the mitochondria (which are related to bacteria)

TMP-SMX adverse reactions•Crystallurea

•Kernicterus

•In G6PD-deficient patients, risk of hemolytic anemia

•Drug-interactions

•Hypersensitivity allergic reaction:•Rash

•Urticaria (hives)

•Steven-Johnson Syndrome

•Toxic epidermal necrolysis

Adverse reactions to TMP-SMX in HIV individuals•As high as 25-50% of HIV+ patients receiving therapy report adverse reactions vs upper

limits of 6-8% in non-infected individuals

•HIV+ patients are observed to have greater rates of hypersensitivity skin disease including those resulting from adverse reactions to drugs; ~5x more physician visits for skin reactions than non-infected individuals

• TMP-SMX reactions in 149/1000 courses

• Sulfadiazine 200/1000

• TMP-Dapsone 156/1000

• Aminopenicillins 93/1000

• About 10x higher than normal population

• In about 50% of cases, the adverse reactions are significant enough to lead to a change in therapy

•As immune system deteriorates (i.e. diagnosis of AIDS), the reactions worsen

•Some studies found that the severe reactions were also more frequent, other found severe reactions were relatively infrequent. All studies showed that adverse reactions were dramatically more prevalent in HIV+, and in particular AIDS patients.

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Adverse reactions to TMP-SMX in HIV individuals•Anti-microbial therapy is used as prophylaxis in HIV+ patients with depressed immune

function (diagnosed with AIDS, CD4+<200/!L)

•Pneumocystis jiroveci (a.k.a. P. carinii): fungal pneumocystis (carnii) pneumonia (PCP). The most common, life-threatening infection in patients with advanced HIV; untreated 20-40% mortality.

•TMP-SMX

•Dapsone or Dapsone+pyrimethamine+folinic acid (can be converted to tetrahydrofolate)

•Pentamidine

•Atovaquone

•Mycobacterium avium complex (MAC):

•Azithromycin, clarithromycin

•Toxoplasma gondii: toxoplasmic encephalitis (TE)

•TMP-SMX

•Dapsone+pyrimethamine+folinic acid

•Atovaquone or Atovaquone + pyrimethamine + folinic acid

Adverse reactions to TMP-SMX in HIV individuals•So, why are these drug still used? Basically because they are the best option to prevent

potentially life-threatening infections.

•Pneumocystis jiroveci (a.k.a. P. carinii): fungal pneumocystis pneumonia (PCP); most common, life-threatening infection in patients with advanced HIV

•TMP-SMX

•Dapsone or Dapsone+pyrimethamine+folinic acid (can be converted to tetrahydrofolate)

•Pentamidine

•Atovaquone

• In a comparative study of TMP-SMX, Dapsone, and Pentamidine PCP prophylaxis:

•0% developed pneumonia while on TMP-SMX

•15% while on Dapsone

• 17% while on Pentamidine

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Tetracyclines

OH O OHOH

OC NH 2O

OHN (CH3)2

HOHH3C

7 6 5 4

Tetracycline !

OH O OHOH

OC NH 2O

OHN (CH3)2

HOHCl H

7 6 5 4

Demeclocycline !

OH O OHOH

OC NH 2O

OHN (CH3)2

HN(CH3)2

7 6 5 4

Minocycline !

OH O OHOH

OC NH 2O

OHN (CH3)2

HOHH3C H

7 6 5 4

Doxycycline !

OH O OHOHO

OHH

NH

CHN

CH3C

H3C CH3

O

N(CH3)2 N(CH3)2

NH2

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•First tetracycline isolated 1945 from Streptomyces aureofaciens, chlortetracycline (though apparently the Egyptians 1600 years ago may have benefitted from tetracyclines in their beer and bread).

•Ring substitutions to positions 5, 6, and 7 change pharmacokinetic properties, but not spectra

•Broad spectrum, Gm+ and Gm-, plus some “unusual” pathogens. But significant resistance developing (except tigecycline)

•Chelates, forms an insoluble complex with, calcium• Tooth discoloration of child if administered to pregnant mother, or to children < 8 y.o.

• Incorporates into bone, may affect bone growth in fetus

•Drug breaks down into antimicrobially inactive compounds that may increase renal toxicity; use full course and do not store.

•Possibly antagonistic with amino-penicillins; they diminish each others’ activities.

Tetracycline features

•Researcher hoping to study osteoporosis in mummies examined bone samples from Nubian and Egyptian mummies under a fluorescent microscope. Observed distinct fluorescence associated with tetracyclines

•Extracted compounds from the bone, and they still were active, killing bacteria

•Distribution in the bone indicated that the tetracycline had been deposited for throughout most of the mummy’s life. Similar to therapeutic levels today.

•Consumed in their diet, but where did it come from?

• Probably from grains contaminated with Streptomyces used in bread and beer making. Normally Streptomyces if happy doesn’t produce much tetracycline, but if stressed, e.g. in competition with yeast in the fermenting bread dough, it pumps out a lot.

• They fermented the bread that was likely contaminated with Streptomyces, mixed it with the fermented grain mash. Drank the beer.

• Looked for evidence of increasing bacterial resistance that might show up as increase in bone infections, but did not see any sign of it over centuries.

Tetracyclines in human diets since ~2000 years ago

figure by Stephen Douthwaite, University of Southern Denmark

30s 50s

aminoglycosidestetracyclines

macrolideschloramphenicol

lincosamidesstreptogramins

linezolid

Tetracyclines MOA

•Target the 30s small ribosomal subunit in bacteria, inhibit protein synthesis• Bacteriostatic: shuts down protein synthesis, but doesn’t lead to nonsense proteins (like

aminoglycosides). As a result damage to cells is less severe.

• Prevents aminoacyl-tRNA from docking

figure by David Goodsell

Tetracyclines MOA

•Target the 30s small ribosomal subunit in bacteria, inhibit protein synthesis• Bacteriostatic: shuts down protein synthesis, but doesn’t lead to nonsense proteins (like

aminoglycosides). As a result damage to cells is less severe.

• Prevents aminoacyl-tRNA from docking

AP

E

•Significant resistance

•Overuse and significant use in agriculture, significant amount released to environment

•Resistance genes (“tet” genes) encoded on mobile elements: plasmids, transposons, integrons (gene for recombination + a gene casette).

•Active macrolide efflux pumps

•Modification of 30s binding site

•RNA or protein mutation

•Some bacteria express “protection proteins” that can rescue the ribosomal function even if a tetracycline is bound

•Very rarely enzymatically inactivated/modified like beta-lactams or macrolides

•Cross-resistance among tetracyclines, except for tigecycline

• Tigecycline was selected to overcome typical tetracycline resistance mechanisms

Tetracycline resistance

•Mostly the same for all tetracyclines, except tigecycline overcomes some resistance

•Aerobic Gram+:• S. pyogenes• S. pneumoniae• S. aureus: MSSA, CA-MRSA (@ UW, ~90% sensitive still)

•Aerobic Gram-: many are becoming resistant• N. gonorrhea (significant resistance)• H. influenzae• Enterobacteriacea: Klebsiella, Shigella, E. coli, Salmonella

• “Atypicals”:• Chlamydia trachomatis (STD) and Chlamydia (aka Chlamydophilia) pneumoniae• Rickettsia rickettsii: Rocky Mountain spotted fever• Borellia burgdoferi: Lyme disease• Pasturella multocida: from animal bites• Mycoplasma pneumoniae: walking pneumonia• Brucella spp.• Vibrio cholerae• Bacillus anthracis: anthrax; 2 months treatment (spores)• Treponema pallidum: syphilis• Plasmodia spp.: malaria prophylaxis• Entamoeba histolytica

Spectrum of activity

•AUC/MIC most important metric: i.e. total exposure of bug to drug

•Post-antibiotic effect observed

•High absorption; up to 95% orally bioavailable. Doxycline, minocycline not hindered by food, others are absorbed less + food.

•Chelates with cations including calcium; becomes insoluble and not absorbed• Avoid antacids, dairy, iron products for 2 hours (containing calcium, aluminum, iron,

magnesium, zinc)• Doxycyline less susceptible, due to weaker interaction w/ calcium• In breast milk, but chelated by calcium, so not bioavailable to infant

•Good penentration of tissues, ranked by lipophilicity• Minocycline>doxycoline>tetracycline• Gets incorporated into bone and teeth in developing fetus, children; adults not affected• Some to CNS

Distribution

•Clearance:

•Bile, urine, feces

•T1/2 tetracycline: ~6h; renal filtration, unmodified

•T1/2 demeclocycline: ~10-17h; liver metabolized to inactive products

•T1/2 doxycyline: ~18-22h; 80% fecal, 20% renal, unmodified

•T1/2 minocycline: ~11-22h; liver metabolized to inactive products

•T1/2 tigecycline: 42h; all most all through fecal route, unchanged

Distribution

•PO

•Frequent dosing (QID)

•Uses:

•Rocky mountain spotted fever (Rickettsia)

• Lyme disease (Borellia burgdorferi)

•Chlamydia (but now azithromycin is preferred)

•Can be used as a bone marker to measure growth. Take advantage of the compound’s fluorescence, and permanent deposition in the bone

Tetracycline

OH O OHOH

OC NH 2O

OHN (CH3)2

HOHH3C

7 6 5 4

Tetracycline !

•PO or IV

•“Long acting”, less frequent dosing (BID)

•Gram+ coverage including MRSA

•Uses:• Rocky mountain spotted fever

• H. pylori: stomach ulcers

• Lyme disease

• Plasmodium: malaria prophylaxis

•Chlamydia (but now azithromycin is preferred)

• Acne

• Pelvic inflammatory disease (PID)

• Syphilis (Penicillin is the drug of choice)

Doxycyline

OH O OHOH

OC NH 2O

OHN (CH3)2

HOHH3C H

7 6 5 4

Doxycycline !

•PO or IV

•“Long acting”, less frequent dosing (once a day)

•Somewhat broader spectrum than other tetracyclines

•Uses:• More lipophilic than others, better penetration to brain

• Greater likelihood of CNS-related side effects such as vertigo

•Not much renal clearance, so poor choice for UTI

•CA-MRSA

• Lyme disease

• Acinetobacter

• Asymptomatic carriers of N. meningiditis (not recommended due to side effects and other options e.g. ceftriaxone)

Minocycline

OH O OHOH

OC NH 2O

OHN (CH3)2

HN(CH3)2

7 6 5 4

Minocycline !

•IV only, poor oral bioavailability

•A drug reserved for challenging infections, multi-drug resistant•MRSA•VRE•Bacteriodes•Gram-:

• E. coli

• Klebsiella

• Enterobacteriacea bearing NDM-1 are susceptible still susceptible

• Pasteurella multocida

• Serratia marcescens

• Stenotrophomonas maltophilia

• Acinetobacter baumanii

•Can still bind tightly to 30s ribosome, even if it is mutated, and even in presence of protection proteins

•Can resist efflux

Tigecycline (Tygacil®)

OH O OHOHO

OHH

NH

CHN

CH3C

H3C CH3

O

N(CH3)2 N(CH3)2

NH2

•Approved indications:

•Complicated skin and skin structure infections (e.g. MRSA)•Complicated intrabdominal infections (e.g. Bacteriodes)•In UW formulary, restricted for treatment of multi-drug resistant

infections

Tigecycline (Tygacil®)

•Do not use outdated products due to higher chance of renal toxicity (Fanconi syndrome: numerous small molecule nutrients are not reabsorbed)• Less of a problem with current formulations

•Accumulates in growing bone and teeth in fetuses and children. Permanently discolors the teeth and can affect bone growth.•Not recommended for children < 8 y.o. or pregnant women (Pregnancy category D)

•Chelates cations: avoid dairy, iron, antacid products for 2 hours

•Avoid taking with food: doxycyline OK

•Esophagitis: drink a lot of water and remain upright for 30 minutes

•Photosensitivity

Adverse reactions to Tetracyclines

•Bind to 30s ribosomal subunit, shut down protein synthesis. Bacteriostatic•Cross-resistance among tetracyclines, except Tigecycline

•Resistance through efflux pumps, alteration of 30s ribosome binding sites, protection proteins.

•Broad spectrum, includes coverage of numerous “atypicals, but resistance is a growing problem (less so for Tigecycline)

•Accumulates in growing bone and teeth in fetuses and children. Permanently discolors the teeth and can affect bone growth.•Not recommended for children < 8 y.o. or pregnant women (Pregnancy category D)

•Otherwise, generally safe

Tetracylines summary