tetracyclines/macrolides 68 Flashcards

1
Q

tetracyclines (group)

oral absorption

A
4-ringed structure
oral absorption:
30% chlortetracycline absorbed
60-70%: tetra
95-100% for doxy, mino!

do not take 1-2 hrs before bed or laying down, take with water, due to risk of esophageal ulceration, don’t take w. dairy

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2
Q

tetracycline

A

Short acting (T 1⁄2 = 6 - 12 hours approximately)

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3
Q

Doxycycline (generic, Vibramycin, Monodox)

A

Long-Acting (T 1⁄2 = 16 – 18 hours approximately)
preferred for serious infections, can be used IV
-avoids GI upset
excreted NON-renally, good for renal failure pts
NOT pumped out by Tet(K) efflux pump in Staph!

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4
Q

Minocycline (generic, Minocin, Arrestin, Dynacin, Myrac)

A

Long-Acting (T 1⁄2 = 16 – 18 hours approximately)
NOT pumped out by Tet(K) efflux pump in Staph!
-more lipid soluble, used as alt. (to Rifampin) to eliminate meningococcal carrier state

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5
Q

tetracyclines bind to ??

A

Ca2+ and multivalent cations in antacids, dec. oral abs. of the drugs
don’t admin tetras w. dairy or antacids
abx tx failure bc these abx often cause GI upset

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6
Q

tissue dist./excretion

A

widely, cross placenta

exc. via kidney, also bile and elimated in feces
- some drug my be reabsorbed via enterohepatic circulation

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7
Q

tetra pharmko

A
  • enter bac by passive diffusion and active transport
  • inhibit protein synthesis by binding 30S ribosomal unit
  • block binding of aa containing aminoacyl-tRNA to acceptor site of ribosome, prevents adding new aa
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8
Q

mechs of tetra resistance

A

efflux pumps that “spit” drug out of bacteria

  • Tet(AE) pump in G- bac
  • doxy and mino NOT pumped out by Tet(K) efflux pump in Staph!
  • Tet(M) ribosomal protection protein in G+ (prevents drug from binding)

tetra resistant usually marker of MDR
other resistance mechs: enzymatic inactivation, use in animal feed

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9
Q

tetra spectrum

A

broad spec but lots of resistance:

  • G+: resistance to Staph, strep, some pneumococci, *not the drug of choice for many G+ aerobic infections
  • G-: pseudomonals, gonorrheae, enterobacter are resistant, active against Brucella, Vibrio spp., CA-E.coli
  • anaerobes are resistant (B. fragilis-use metronidazole)
  • used for Spirochetes, Rickettsiae, Mycoplasma, Chlamydia
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10
Q

tetra use

A

Rickettsial-doxy
Mycoplasma-doxy (erythromycin for preggos, kiddos)
Chlamydia-doxy (can also use macrolides)
Spirochetes-doxy (drug of choice for Lyme)
Periodontitis-doxy tablests, or mino microspheres (inhibit enzyme collagenase)
Acne-(tetra, doxy, mino)
Cholera
others: UTIs, non-TB mycobac inf.
-alternative for: H. pylori (tetra)
used to be used for bac gastroent, pneumonias, bac UTIs, but resistance now a big problem

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11
Q

tetra SEs

A
  • GI upset: reduce by giving food (NOT dairy/Ca2+)
  • Superinfections: C. diff, candida
  • CONTRAINDICATED during pregnancy and kiddos younger than 8:
  • can bind Ca2+, can be deposited in teeth and bone: teeth discoloration, fluorescence, enamel deformities, inhibit bone growth, and cause bone deformities (when used in pregnancy)
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12
Q

tetra tox

A
  • renal damage: outdated tetras can become nephrotoxic and cause renal tubular acidosis and renal damage (throw old pills away!)
  • demeclocycline can inhibit actions of ADH in kidney and cause diabetes insipid us like state (peeing too much)
  • photosensitivity, sun-burn prone
  • impaired liver function in preggos, liver damage pts
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13
Q

Tigecycline (Tygacil)

A

IV admin, newer, eliminated by non-renal mechs
same MOA as tetras BUT
-not effectively pumped out of bacteria by the Tet(AE) or Tet(K) efflux pumps, which makes it useful in some tetra-resistant bac
-G+ Tet(M) ribosomal protection protein does not effectively block Tigecycline from binding to the 30S ribosomal subunit

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14
Q

Macrolide absorption/metab/excr

A
  • erythromycin base: poor oral absorption, broken down by acid
  • clarithromycin and azithromycin have ESTERS in their base: demonstrate improved oral absorption
  • erythromycin can be used IV
  • IM avoided (painful)
  • distr. to most tissues, but DO NOT ENTER CNS: not used for meningitis
  • crosses placenta

-conc. in liver and exc. in bile
*metab by hep p450 enzymes (p4503A, DYP3A)
5% excredted in urine
worry about hepatic dysfunction

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15
Q

macros pharmko

A
  • bacteriostatic, any high conc. may be tidal
  • bind to 50S subunit, prevent movement of pp chain from acceptor site to donor site–>prevents protein synthesis
  • close to binding site for chloramphenicol-competition!*
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16
Q

macrolide resistance mechs

A

most important mech:
-modifications of 50S subunit by
mutation or by a macrolide-inducible/constitutive enzyme (Methylase, erm genes) which alters the binding site and prevents the drug from binding.
also:
-dec. influx or active efflux
-breakdown by esterases (i.e. Enterobacteriaceae)

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17
Q

erythromycin spectrum

A

G+: GAS, PCN sus strp, MRSA, Corynebacterium, B. antracis
G-: M. cat, N. gon, Legionella, Campy, B. pertussis, Haemophilus ducreyi
-mycoplasmas, chlamydiae, spirochetes

  • many H. flu strains are resistant
  • Enterobacteriaceae are resistant (E. coli, Klebsiella, Enterobacter)
  • Anaerobes: active against some but B. fragalis is resistant, generally not a good anaerobic agent
18
Q

macro uses

A
  • Mycoplasma pneumonia(use macrolide in pregnancy over tetra!) (test question)
  • Legionella-Legionaires’ pneumonia
  • CAP
  • nonstrep pharyngigtis
  • Chlamydial inf (resp, neonatal, ocular, genital) erythromycin 1st line in pregnancy for UG inf
  • tx/ppx for whooping cough (B. pertussis)
  • alternative for pts w. allergies to B-lactam abx (PCN): staph, strep (PCN-resistant S. pneumo are usually also resistant to erythromycin)
  • preventing bac endocarditis with dental procedures, and prophylaxis for RF
  • Campy gastroenteritis
19
Q

macro SEs

A

GI upset due to direct stim of GI motility, use therapeutically to inc. gastric emptying

20
Q

more macro adverse

A
  • liver toxicity (esp. estolate form of erythromycin: cholestatic hepatitis)
  • allergic rxn: fever, rash, rarely anaphylaxis
  • cytP450 inhibitors increase levels of erythromycin–>ventricular arrhythmias, QT prolongation
  • erythromycin can inhibit cyt P450 enzymes, increase serum levels of other drugs (theophylline, oral anticoagulants, antihistamines: terfenadine, astemizole pulled)
21
Q

new macros: clarithromycin and azithromycin

A

more acid stable, better abs, less GI intolerance, clarith more $$ than erythromycin

  • longer 1/2 life: vs. eryth (1.5 hrs) clarithromycin (6 hrs), azith (3 days!)
  • azith: slow release from tissue stores, dose for 5 days
  • clarithromycin inhibits cyt P450 enzymes, azithromycin does NOT!
22
Q

new macro uses

A

clarith and azith active against Mycobacterium avium complex infections in AIDS pts

  • both better activity against H. flu (azith)
  • Azith: highly active against Chlamydia (see notes)
    clarith: RTIs, skin inf.
23
Q

Telithromycin (Ketek)

A

sim to macros
CAP, activity against methyl’s prod. G+ cocci
SE: inhib of cup P4503A4, reserved for serious pneumonias

24
Q

case 2: 24 yo male naval officer, stationed in Philippines, complains of dysuria and profuse yellow urethral discharge, started sev. days ago

A

N. gonorrhea

how to tx:
1st line:
Ceftriaxone
+ azithromycin OR + doxycycline

2nd line: Cefixime + azithromycine

tx for confection w. Chlamydia: 2 g oral azithromycin, or doxycycline will cover both!

FQs will cover Chlamydia but not Neisseria

25
Q

Macrolides: Erythromycins

A
Erythromycin base (generic, ERY, PCE) Film coated
Erythromycin Estolate
Erythromycin Stearate
Erythromycin Ethylsuccinate
Erythromycin Lactobionate – IV use
26
Q

Clarithromycin (generic, Biaxin)

A

macrolide
used for:
-Pharyngitis/tonsillitis: Strep progenies (PCN is the drug of choice)
-Acute maxillary Sinusitis: due to Strep. Pneumo
-Bronchitis: acute exacerbations of chronic bronchitis caused by S.
pneumo, M. catarrhalis, and H. flu
-CAP: Mycoplasma pneumo and Strep pneumo
-Uncomplicated skin infections: Strep pyogenes and Staph aureus
-Prevention and treatment of Mycobacterium avium complex (MAC)

27
Q

Azithromycin (Zithromax)

A

macrolide: longest half-life (3 days)
- penetrates tissues well (not CNS) 10-100x higher conc. than plasma, not used for bacteremia/sepsis
- may use single dose for uncomplicated genital chlamydial inf. (as effective as a 7-day course with doxy!)
- slightly less active against staph and strep than eryth/clarith, but more active against H. flu
* does not interfere with cytP450 enzymes*

28
Q

Telithromycin (Ketek)

A

macrolide (like macrolide in structure)

  • approved in ‘04 for bac respiratory infections (CAP)
  • admin orally(+/- food, 1x/d) metab./elim by liver
  • macrolide-resistant bac may be susceptible to telithro
  • activity against some methylase (erm genes) producing G+ cocci since it can bind to a part of the 50 S ribosomal subunit that is not inhibited by methylase
  • poor substrate for the efflux pump
  • inhibitor of CYP3A4 and will increase serum concentrations of other drugs metabolized by CYP3A4 (e.g. Simvastatin, Lovastatin, Atorvastatin)
  • limited by potential to cause severe liver toxicity
29
Q

Chloramphenicol (not emphasized in class)

A
  • nitrobenzene moiety and is a derivative of dichloroacetic acid
  • oral administration (active drug and a prodrug (palmitate)), broken down to active in duodenum
  • parenteral: Chloramphenicol succinate
  • widely distributed, penetrates CSF: useful for meningitis and brain abscesses
  • secreted in breast milk, crosses placenta, 50% plasma protein bound
30
Q

chloramphenicol metabolism/excretion

A

metab. in liver to the inactive glucorinide conjugate, excreted in urine
* adjust for liver but not kidney failure*
* lower dose for premies and newborns less than 1 week old (decreased liver metabolic function)

31
Q

Chloramphenicol prevents ??
can also inhibit ??
bacteriostatic or cidal??

A

Protein Synthesis by reversibly binding to the 50S subunit of the bacterial 70S ribosome

  • mitochondrial protein synthesis in mammalian cells: responsible for many of its toxic effects
  • mostly bacteriostatic. but appears to be bactericidal for H. flu, N. meningitidis, and S. pneumo
32
Q

resistance to chloramphenicol caused by ??

A

bac production of an enzyme acetyltransferase which acetylates chloramphenicol and prevents the drug from binding to the bacterial ribosome (acq. via conjugation)

other mechs: dec. perm of drug, mutations in ribosome that prevent binding

33
Q

chloramphenicol is limited due to ??

A

its toxic side effects (e.g. aplastic anemia)

  • only used in infections for which the benefits of the drug outweigh the risks of potential toxicities
  • not a first line agent and is used for life threatening bacterial meningitis or rickettsial infections*
34
Q

chloramphenicol spectrum of activity

A

G+: most, not MRSA
G-: N. meningitidis, H. flu (including Amp-resistant) (NOT pseudomonas)
anaerobes: including B. fragilis
Rickettsiae: RMSF, Q fever, typhus

35
Q

clinical uses of chloramphenicol

A
  • alternative for meningitis from N. meningitides, H. flu, S. pneumo in pts. w. allergies to PCNs, cephs
  • brain abscesses (+ PCN or + metronidazole)
  • Rickettsial diseases (Rocky mountain spotted fever, murine typhus, tick bite fever, Q fever)
  • usually tetracyclines are preferred, but chloramphenicol can be used in preggos, kiddos
36
Q

chloramphenicol SEs

A

bone marrow toxicity
gray baby syndrome
GI: N/V/D w. oral admin

37
Q

chloramphenicol drug interactions

A
  • phenobarbitol and rifampin (induce liver enzymes–>dec. levels)
  • can inhibit microsomal cytochrome P450 enzymes and prolong the half-life of drugs metabolized by this system (e.g. phenytoin, tolbutamide).
38
Q

chloramphenicol: bone marrow tox

A
  • reversible BM suppression: anemia, leukopenia, thrombocytopenia (dose/time-dep, inc. risk in neonates, liver dis.)
  • aplastic anemia: deficient RBC production (rare but fatal, not dose related) (time/incidence-dependent), genetic
39
Q

chloramphenicol: gray baby syndrome

A

premies/neonates can’t conjugate/excrete due to deficient glucuronyl transferase, also decreased renal excretion
-occures 2-9 days after tx: vomiting, inc. RR, abd. distention, cyanosis–>ashen gray (death in 40%)

40
Q

Tigecycline spectrum/uses

A
  • MRSA, B-lactamase producing G- s, Acintobacter sp.

- skin/skin structure and intra-abdominal infections