1 - Antibiotics Flashcards
Intro
-inhibition of protein synthesis
Bacteria = 70S ribosomes (50S + 30S)
30S = aminoglycosides and tetracyclines (buy AT 30)
50S = Chlorampenicol, macrolides (Erythro, azithrom clarithro), clinda/Lincomycin (CEL at 50)
Penicillins: Amoxicillin, Dicloxacillin
- adverse reactions
- cross-sensitivity
1:HS rxns
-T1: anaphylaxis, urticaria (IgE-mediated rxns)
-T4: contact derm
Others: render oral contraceptives ineffective, Stevens-Johnson syndrome (amoxi)
Pens + Cephs have beta-lactam ring
-C = 6-member ring
-P = 5-member ring
If pt is allergic to PCN, theres ~1% risk will also be allergic to 1st gen cephs (rx with caution)
Both: contraindicated in pts with IgE-mediated T1 HS (urticaria, anaphylaxis)
Sulfonamides: Sulfisoxazole, Sulfacetamide, Sulfamethoxazole, Sulfadiazine
- opthalmic indications/adverse effects
- systemic indications/adverse effects
Ophthalmic
- use: topical ophth rarely used (previously rxd for bleph and conj-itis)
- SE: burning, stinging, contact derm, local photosensitization (sunburn on eyelid margins)
Systemic
-use: sulfadiazine + pyrimethamine tx’s toxoplasmosis
—Bactrim = sulfamethoxazole + trimethoprim
-SE:
—kernicterus in infants (bilirubin accum in brain) = contraindicated in pregnancy
—may induce myopic shift (think sulfa, CAIs, pilo)
—Stevens-Johnson syndrome
Trimethoprim, Pyrimethamine
- clinical indications
- adverse effects
Topical ophth trimethoprim: gram(+) and (-) infections
- not effective against pseudomonas
- available in combo with polymyxin B = Polytrim (bacterial conj-itis, esp kids)
Pyrimethamine: oral for ocular toxoplasmosis (with sulfadiazine (di and py for toxo))
Oral trimethoprim can cause bone marrow suppression (Treats Marrow Poorly) -> aplastic anemia (recall chloramphenicol also), leukopenia, granulocytopenia
Pyrimethamine can have similar toxicity
Tetracyclines: Tetracycline, Doxycycline, Minocycline
- MOA
- clinical indications
Protein synthesis inhibitor - binds to 30S subunit and prevents access for aminoacyl tRNA, bacteriostatic
Doxy:
-meibomianitis, acne rosacea: alters configuration of oil glands, decr release of irritating free FAs
-chlamydial ocular infections (trachoma, adult inclusion)
-RCE: decr risk of recurrences (inhibits MMPs)
Mino:
-RXd in low doses for long-term management of acne vulgaris
Cephalosporins: Cephalexin, Ceftriaxone
- MOA
- clinical indications (lexin vs triaxone)
Cell wall inhibitor - blocks mortar/glue (transpeptidase)
All have good gram(+)
1st gen (cephalexin): commonly used for skin infections, which are primarily caused by gram(+) (think staph)
-includes dacryoadenitis/cystitis, preseptal
3rd gen (ceftriaxone): also has gram(-) coverage, esp used against gonorrhea (gram neg diplococci) as IM injection
-IV cef is the TOC for gonococcal conj-itis + orbital cellulitis (H. flu)
Aminoglycosides: Tobramycin, Gentamicin
- MOA
- clinical indications
Protein synthesis inhibitor - binds to 30S
Effective against gram(+) and (-), with better (-) coverage
Used to be first-line against ocular bacterial infections before fluoros
Tobra: avail in topical gtt and ung form
Both: available in fortified concentrations
-RXd with fortified cefazolin for tx of sight-threatening corneal ulcers
Macrolides: Erythro/Azithro/Clarithromycin
- MOA
- clinical indications
Protein synthesis inhibitor - binds to 50S subunit
Oral azithro: safe in pregnancy, chlamydial infections (trachoma, adult inclusion), convenient single 1g dose, take on empty stomach
Topical ophthalmic azithro (Azasite): bacterial conj-itis and blepharitis, dose BID x 2days, then QD x 5days (recall: preserved with BAK = no CLS during tx)
Topical opthalmic erythro: uncommonly rxd due to poor resistance, used for prophylaxis, dosed at night, also prophylaxis of gonococcal opthalmia neonatorum (recall: used in place of silver nitrate; ophth neo usually chlamydial)
Oral clarithro: respiratory infections
Cephalosporins: Cephalexin, Ceftriaxone
- adverse effects
- coverage of cephs by generations
HS rxns
May destroy normal microflora -> alters absorption of vit K -> excessive thinning of blood in pts taking warfarin (K-antagonist)
-recall K is needed for “klotting”
1st: (+)
2nd: (+), some (-)
3rd/4th: (+) and (-)
Bacitracin
- MOA
- clinical indications
- combos
Cell wall synth inhibitor - blocks bricks (peptidoglycan) from growing cell wall
Gram(+) only, ung only, blepharitis (staph)
Polysporin = bacitracin(+) + polymyxin B(-) Neosporin = polysporin + neomycin
Trimethoprim, Pyrimethamine
-MOA
Interfere with bacterial DNA - inhibit dihydrofolate reductase (DHF red)
-enzyme that converts DHF acid to tetrahydrofolic acid (THF) in the second step of folic acid synth
Sulfonamides: Sulfisoxazole, Sulfacetamide, Sulfamethoxazole, Sulfadiazine
-MOA
Interfere with bacterial DNA - inhibit dihydropteroate synthase (DHD synth)
- enzyme that converts PABA to dihydrofolic acid (DHF) in the first step of folic acid synth
- bacteriostatic
- gram(+) and (-)
Tetracyclines: Tetracycline, Doxycycline, Minocycline
- pharmacokinetics
- adverse effects
Absorbed in GI tract: impaired by cations in dairy, antacids, iron-containing compounds
Excreted via kidneys: contraindicated with renal failure
*Exception: doxycyline can be taken with food, is eliminated in fecal matter
Contraindications: pregnancy, children
SE: pseudotumor cerebri, slows bone growth, teeth discoloration
Minocycline = blue sclera, pigmented cysts on conj (think a minnow, but actually a big BLUE shark that comes and bites you)
Pregnancy and drugs
“FAT PAC: she’s not fat, she’s just pac-ing a baby”
Avoid FAT, give PAC
Fluoros (bones), Aminoglycos (nephro/ototox), Tets
Pcns, Azithro*, Cephs
*safest
Fluoroquinolones
- adverse effects
- ages approved for
Oral fluoroquinoLONES hurt the BONES
- can cause tendonitis, damage to cartilage formation, inhibition of bone growth
- contraindicated in pregnancy, children, adolescents (<18)
All topical ophth fluoros EXCEPT LEVO are approved for use in pts 1 year and older
