561P10_Elmer_penicillins1

561P10_Elmer_penicillins1 - I. ANTIBIOTICS INHIBITORY...

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14 I. ANTIBIOTICS INHIBITORY BACTERIAL CELL WALL BIOSYNTHESIS A. PENICILLINS 1. Introduction a) still a widely prescribed and useful group of antibiotics b) are potent, nontoxic, and have fairly broad spectrum with use of beta-lactamase inhibitors 2. Chemistry a) Structure/Activity Relationships considerations 1. need conformation, intact β -lactam ring 2. can modify 5-membered ring and replace R groups 3. Production 1928 - Fleming, P. notatum 1938 - Flory and Chain 1941-49 - international cooperation with U.S. and England mainly using P. chrysogenum 1959 - England - Beecham developed process for forming 6-APA which lead to commercial development of semisynthetic derivatives 4. General Properties of Penicillins a) stability in stomach acid varies; Pen G is labile and has low bioavailability so is only rarely used orally; amoxicillin has high stability and bioavailability and is only used orally. b) susceptibility to Gram + β -lactamses (penicillinase) varies; Pen G, Pen V, amox, ampi are very susceptible but modification of side chain can lead to penicillinase resistance, e.g. dicloxacillin (a "penicillinase resistant penicillin") c) susceptibility to Gram (–) β -lactamases – highly susceptible unless β -lactamases inhibitors are present d) bacteriocidal
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15 e) allergy This is considered the "major determinant" of penicillin allergy. The "minor determinants" are a variety of other penicillin breakdown products. 1) immediate - urticaria, pruritus, shock; occurs within 60 min – rare but highly feared; 1gE mediated and directed against minor determinants 2) accelerated - rash; occurs within 72 h - common (5-10% of treated); 1g M and 1g E directed against major determinant 3) late - fever, urticaria; occurs > 72 h – rare; 1g M and 1g E 4) incidence - 5% show (+) reaction with skin test using penicilloyl polylysine. Note: This skin test is no longer commercially available (2010). 50-70% of (+) have clinical Sx on amin. of penicillins - mostly rash <1% of (+) have serious reaction; overall incidence is about <.02%, <.0014% death semisynthetic show reactions; oral show reactions relative to parenteral doses but an allergy to one penicillin means that the patient would be assumed to have a problem with any penicillin allergy to penicillin does not necessarily mean allergy to cephalosporins but cross reactivity does occur (~10%); rule: if patient has serious reaction to a penicillin, don't give any beta lactam except aztreonam ampicillin 9.5% allergy; this is due, in part, to the chemical nature of ampicillin, i.e. not all ampicillin induced rashes are true penicillin allergies. Amoxicillin has a somewhat lower incidence densensitization protocols can be employed if infection requires penicillin therapy for an allergic patient a rare interstitial nephritis is sometimes seen which may be a type of allergic reaction
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16 5) precautions on penicillin allergy a) ask about prior reactions b) ask about the type of allergic reaction (i.e. symptoms of anaphylaxis)
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561P10_Elmer_penicillins1 - I. ANTIBIOTICS INHIBITORY...

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