antibiotics Flashcards
antibiotic
traditionally referred to substances produced by microorganisms to suppress the growth of other microorganisms
antimicrobials
broader, refers to antibiotics synthesized in the laboratory as well as those synthesized by other microorganisms
bacteriocidal
-antimicrobial drug that kills sensitive organisms. Organism falls rapidly after drug exposure. Induce lethal changes in microbial metabolism or block activities essential for viability. Less likely to cause resistance. Includes most antimicrobial drugs ( Lactams, quinolones, aminoglycosides (AMG), advanced macrolides)
bacteriostatic
Inhibits growth of bacteria but does not kill. Number of organisms remains relatively constant after drug exposure. Require immunologic mechanisms to eliminate organism. Inhibit a metabolic rxn needed for cell growth but not necessary for viability. More likely to cause resistance. Examples of bacteriostatic drugs include sulfonamides, tetracyclines and erythromycin macrolides
-the problem is bacteria can become resistant
antimicrobial spectrum
-Narrow Spectrum Drugs - have activity against a single species or a limited group of pathogens (Penicillin)
-Broad spectrum - have activity against a wide range of drugs (Fluoroquinolones)
-broad can be gram -/+, anarobic/aerobic
-** always choose the narrowest spectrum 1st, when possible, less likely to cause superinfection and development of bacterial resistance**
culture and sensitivity
-Determines the exact organism responsible for an infection and the antibiotics that it is sensitive or resistant too. Takes 72 hours for result – therefore start with empiric therapy and switch after results. Organism classified as having susceptibility, intermediate sensitivity or resistance based on minimum inhibitory concentration. (MIC) to the drug tested. MIC – lowest concentration of the drug that inhibits bacterial growth.
microbial resistance
-Can be innate or acquired. Resistance often develops overtime due to misuse of drug (i.e. short duration, dose too low, infection recurs -> resistance)
-Resistance occurs by the following three primary mechanisms
-Inactivation by microbial enzymes (beta Lactamase)
-Decreased accumulation of drug by microbe
-Reduced affinity of the target molecule by the drug
choosing antimicrobial drugs
-1. type of infection
-based on lab results or knowledge of most common organisms causing various types of infections and drugs of choice for these infections (empiric therapy). Empiric therapy is used initially until lab results are available or for Tx of minor URI and UTI b/c of predictability of causative organism(s) and their sensitivity
-2. status of patient
-Pregnancy
-Allergy history- ask what the allergy is, diarrhea isnt an allergy
-Immune status
-Age
-Renal impairment-call the pharm, adjust dose
-Hepatic insufficiency
-Abscesses
-Presence of indwelling catheters- take it out, put antibx in catheter
-3. drug properties
-Pharmacokinetics:
-Drug concentrations low in bone, pts with osteomyelitis must be treated for several weeks
-Route of elimination – renally excreted drugs good for UTI, however may accumulate in pts with renal impairment and cause increased toxicity (i.e. AMG)
-adjust dose
-Adverse effect profile – risk to benefit ratio
-Cost - consider total cost (drug + administration + monitoring.)
-Convenience – consider frequency and duration
classes of antimicrobials
Sulfonamides
Penicillins
Miscellaneous beta lactams (PCN-like compounds)
Cephalosporins
Fluoroquinolones
Macrolides
Tetracyclines
Aminoglycosides
Miscellaneous
sulfonamides
-MOA - inhibits one of the sequential steps in the production of folic acid
-Often combined with trimethoprim (TMP) for synergistic effect (b/c TMP inhibits 2nd sequential step in the production of folic acid)
-Not used as often b/c of increased resistance and allergy
-Spectrum: S. Aureus, including MRSA, some gram – coverage.
-Indications: !community acquired- MRSA, UTI! and minor URI, !PCP treatment and prophylaxis!, topical for burns, sulfasalazine for IBD
-make sure pt hydrates -> urine crystals can form
-static
-good for staph
-Ex
-Sulfamethoxazole/trimethoprim (Bactrim, Septra)
-Silver sulfadiazine (Silvadene) – topical for burns
sulfonamides ADRs, DDIs, pregnancy
-ADRs:
-Skin rashes, dermatitis, erythema mulitiforme or Steven Johnson Syndrome
-GI reactions, headache
-Renal damage (crystalluria, peripheral nephritis)
-Liver damage (hepatitis), kernicterus in newborn
-Bone Marrow Suppression
-DDIs – CYP 2D6 inhibitor, highly protein bound. Contraindicated w/ methanamine.
-Pregnancy – all category C in 1st & 2nd trimester, category D in 3rd except topical agents
penicillins (PCN)
-Beta lactam drug
-Can be used in pregnancy (category B)
-MOA – inhibit bacterial cell wall synthesis
-Further divided:
-Narrow spectrum
-Extended spectrum
-Penicillinase resistant
-Beta- lactamase inhibitor
safe for pregnancy: PCM
-penicillin
-cephalosporin
-Macrolides- erythromycin
penicillin ADRs
-Overall – they are fairly non-toxic. Common derm reactions include itching, skin rash. When taken orally the most common side-effects are !GI (N, V, D) – Augmentin has higher incidence of diarrhea!
-1% patients are allergic – ask pt to describe rxn. (anaphylactic rxn: hypotension, bronchoconstriction, hives)
-cross reactivity allergy with cephalosporin
-ampicillin and amoxicillin can cause skin rashes that are not allergic in nature.
-hepatic & renal damage, neutropenia is rare
-Secondary infections (superinfection) caused by upsetting the normal flora can occur:
-Note – secondary infections can occur with any/all the different classes of antibiotics!!!!!!!:
-candida albicans – oral & vaginal yeast infections
-Clostridium dificile- pseudomembranous colitis – severe diarrhea
->Treat with anti anaerobic antibiotic like -> !Vancomycin (Vancocin) – PO – Drug of Choice!! OR Fidaxomycin!
narrow spectrum penicillins
-mostly cover gram+ organisms, except for the gram cocci N. meningitis
-Common indications – pharyngitis!, neonatal meningitis/sepsis, endocarditis, meningitis, CAP, syphillis!
-Examples:
-PCN G (IVP) - can only be given as a bolus
-Benzathine PCN G (Bicillin CR) (IM only) - long acting; q3-4 weeks -> for long term STDs
-PCN V (Pen Vee K) - oral form of PCN G
extended spectrum penicillin
-mostly cover strep organisms and gram (-) incl E. coli, H influenzae and proteus)
-Examples
-ampicillin (Polycillin, Omnipen) (PO, IV, IM) - broader (more gram neg). Esp. good for listeria, meningitis
-ampicillin needs to be taken many times a day
-amoxicillin (Amoxil) (PO) - more rapidly absorbed, higher blood levels
-Used for !sinusitis, otitis media, dental prophylaxis!
-Antipseudomonal pcn – piperacillin and ticarcillin, often combined w/ beta-lactamase inhibitor. Used for nosocomial pneumonias!
penicillinase-resistant penicillins
-can treat penicillinase or beta lactamase producing bacteria (1 degree staphylococci)
-Indications – serious staph infections like endocarditis and osteomyelitis where these organisms are common
-Examples
-methicillin (Staphcillin)(IV)
-nafcillin/oxacillin (Unipen)(PO, IV)
-dicloxacillin (Dynapen) (PO)
beta-lactamase inhibitors
-Inhibits beta-lactamase enzyme, no antimicrobial activity given alone!!!!!!!!!, must be combined with beta-lactam antibiotic
-Indications - All good for Tx of beta-lactamase producing bacterial infections. (staphylococci, gonococci, H. influenzae, sinusitis, !bite wounds, diabetic foot ulcers)!
-when someone becomes resistant to amoxicillin we can use augmentin
-after I&D you give this to prevent infection as a precaution
-Examples
-amoxicillin + clavulanate (Augmentin) (PO)
-ticaricillin + clavulanate (Timentin) (IV)
-ampicillin + sulbactam (Unasyn) (IV)
-piperacillin + tazobactam (Zosyn) (IV)
MISC. BETA-LACTAMS (PCN – LIKE COMPOUNDS): Aztreonam (Azactam) (IV)
-monocyclic beta-lactam (monobactam)
-good for gram neg (esp multidrug rst P. aeruginosa)
-Can be used in PCN allergic pts!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! bc its monobactam
-ADRs – N/V/D, seizures, leucopenia
