Test Two: Penicillin Alternatives Flashcards
1st gen cephalosporins
Cephalexin: Good for gram+ aerobes and MSSA. Less active for gram- and no enterococci activity. Good for soft tissue infxn and surgical prophy
What is the mechanism of action of cephalosporins?
Inhibit cell wall peptidoglycan synthesis by blocking transpeptidase and carboxypeptidase
2nd gen cephalosporins
Cefamandole: mainly gram- with less staph activity and some anaerobic effect
3rd gen cephalosporins
Cefoperazone: Mostly Gm –ve, penicillin resistant streptococcus pneumoniae, with a subset effective against pseudomonas. Not used much in dentistry
4th gen cephalosporins
Cefepime: Wider antibacterial spectrum (pseudomonas, penicillin resistant Streptococcus pneumoniae, MRSA, enterococcus, and hyper β-lactamase producing organism). Administered IV
What cephalosporin penetrates the CSF for meningitis?
Cephotaxime
How do 1st gen cephs respond to beta lactamase?
Very sensitive to hydrolysis
Dosing for 1st gen ceph?
500mg qid. T1/2 is 1 hr
2nd gen ceph kinetics
Lower peak plasma level than 1st. T1/2 1-1.5 hrs. 200-400 mg bid. Not widely used
What are some adverse rxns for cephalosporins?
- Hypersensitivity (cross allergy with penicillin(~20%)
- Maculopapular rashes
- Transient increase in liver function.
- Inhibit hemostasis (hypoprothrombinemia)
- Alcohol intolerance
Carbapenems (imipenem and miropenem)
Broad spectrum, beta lactamase resistant, used as alt for MRSA and strep pneumoniae, has cross allergenicity
Monobactams (aztreonam)
Aerobic gram-, only injected, sensitive to beta lactamase, no cross allergenicity
Examples of macrolides and mechanism of action
Erythromycin, clarithromycin, azithromycin, bind to 50s ribosomal subunit to block translation, hardly any allergies
Erythromycin spectrum and dosage
Gram+ aerobes and facultatives, 250-500 mg q6h as enteric coated tablets bc of poor acid resistance, excreted in urine, does not reach brain or CSF
Erythromycin adverse rxns
Epigastric pain, ventricular arrhythmia, hepatotoxicity (hepatic microsomal enzyme inhibitor-helps prolong action of other drugs)
Clarithromycin diff from erythromycin
Similar spectrum but mainly gram+ anaerobes, rapid absorption, less GI problems, dosing is 250-500 bid, liver and kidney excretion
Azithromycin
Rapid absorption, more active against strep/staph but mainly gram- anaerobes, stays in tissue for slow release (take 250 qd), excreted by liver
When should macrolides be used?
1- Best alternative for B-lactam –allergic patient for acute orofacial infections
2- treat acquired bacterial pneumonia
3- chronic sinusitis
4- Asthma complications
What are contraindications for macrolides?
Patient with cholestatic hepatitis and cardiac arrhythmia
Clindamycin spectrum and mechanism of action
Gram+ and gram- anaerobes, binds to 50s subunit
Clindamycin kinetics
- Completely absorbed after oral administration
- Widely distributed, penetrate well into bones
- Metabolized in the liver and its metabolites have also antimicrobial activity
- Excreted in urine and feces
Clindamyin dosage and uses
150-300 q6h, Mainly used for bone infection, female genital
tract, pelvic and abdomenal infection.
- For acute orofacial infections for oral microbial resistance to the β-lactam antibiotics.
Side effect of clindamycin
Some develop diarrhea and can get pseudomembranous colitis
Vancomycin spectrum and mechanism of action
Effective against gram+ like MRSA, gram- bacilli are resistant, binds to terminal amino acids to block carboxypeptidase
Vancomycin dosage and administration
Poorly absorbed oral, given iv, t1/2 is 6hr, 500 q6h
Vancomycin side effects
Can have hypersensitivity like penicillin, can also cause nephrotoxicity esp in combo with other drugs
Metronidazole uses
1-Protozoal infections (Giardiasis, Trichomoniasis, amebiasis)
2-Anerobia bacterial causing orofacial infection (periodontitis, acute necrotizing ulcerative gingivitis)
Metronidazole kinetics
completely absorbed from GIT- oral intake attains peak level in 1-2 hours, widely distributed with excellent CNS penetration ( half
life= 8 hours)
Side effect of metronidazole with alcohol
Disulfiram like action-blocks alcohol dehydrogenase which causes a buildup of acetaldehyde–> nausea, vomiting, flushing, tachycardia
Fluoroquinolone mechanism of action
Inhibits bacterial gyrase and topoisomerase to prevent supercooling of DNA which stops replication
Uses and dosage for fluoroquinolones
or UTIs, respiratory infections, GIT, bone, prophylaxis, 250-750 bid (very long 1/2 life, 10-12hrs, good for fewer dosages needed)
Most commonly prescribed fluoroquinolones
Ciprofloxacin 250-500 bid, ofloxacin (topical), levofloxacin 250-500-750 qd (all 2nd generation bc there are generic forms)
Side effects with fluoroquinolones
most imp is arrythmia–can disturb ECG, be careful when taking with anti arrhythmic drugs, theophylline or NSAIDs (CNS toxicity)
