chapter 24-PCN

Question 1

PCN

Answer 1

• characterized by 6 aminopencillanic acid joined to beta-lactam ring
• diff. substrates attached to acid changes chemical compound and creates the subclasses: penicillinase-sensitive/natural PCN, penicillinase-resistant/antistaphylococcal PCN, aminopenicillins, and antipseudomonal/extended-spectrum PCN

Question 2

pharmacodynamics of PCN

Answer 2

• hinders bacterial growth by inhibiting biosynthesis of bacterial cell wall
• dependent on drug reaching pcn-binding proteins involved in the end stages of formation of wall
• wall weakens and lysis occurs
• most effective during active cellular multiplication

Question 3

sensitivity of natural pcn

Answer 3

• active against aerobic, gram positive organisms
• recommended for: steptococcus grp. A, S. pneumonia, enterococcus, legionella, neisseria meningitis, actinomyces, clostridium, peptostreptococcus, treponema pallidum

Question 4

sensitivity of penicillinase-resistant group/anti-staphylococcal pcn

Answer 4

-recommended for: salmonella, shigella, serratia marcescens, proteus mirabilis, proteus vulgaris, morganella species (only methicillin), brucella species, and penicillinase-producing s. aureus and staphylococcus epidermidis

Question 5

MRSA/MRSE

Answer 5

• methicillin resistant staph aureus and staph epidermidis are resistant to all penicillinase-resistant grp, pcn, and cephalosporins
• Vancomycin only single antibiotic effectivie

Question 6

beta-lactams

Answer 6

• unique four-member lactam ring

- includes: PCN, cephalosporins, monobactams, carbapentems, beta-lactam inhibitors

Question 7

sensitivity aminopenicillins

Answer 7

• broad-spectrum drug against similar organisms as natural pcn and penicillinase-sensitive group
• greater activity against gram negative bacteria-enhanced ability to penetrate outer membrane
  
  • esp. urinary and GI pathogens-e.coli, proteus mirabilis, salmonella, shigella, e.faecalis
• can be used for gram-negative respiratory-h.influenza type b

Question 8

sensitivity of antipseudomonal group

Answer 8

• gram-negative bacilli-pseudomonas aeruginosa, enterobacter, morganella, and providencia (gram-negative rods)
• activity against organisms to aminopenicillins

Question 9

PCN resistance

Answer 9

• due to: inactivation of beta-lactamases,
• alteration in target on bacterial cell wall
• permeability barrier preventing penetration of antibiotic to cell wall

Question 10

PCN absorption

Answer 10

• oral PCN absorbed in GI tract-but some are unstable in acid-must dose 3-4x more for these type of drugs and be taken on empty stomach
• oral PCN not used alone to fight systemic infection
• IM route unreliable and erratic for absorption; irritating to tissue
• bound to protein and well distributed to most tissues and body fluids
• crosses placenta and enters breast milk

Question 11

metabolism and excretion of PCN

Answer 11

• majority excreted in urine unchanged
• be careful with renal patients and toxicity
• probenecid-can prolong half life and therefore be taken concurrently for more severe infections

Question 12

ADR with PCN

Answer 12

• immediate reaction (2-30 min) for serious reactions
• can give desensitization therapy
• delayed reaction (7-10 days)-pruritic, maculopapular rash (not true allergic reaction)
• common reactions: GI upset, fungal overgrowth-give rx of diflucan, possible c.diff
• less common: hepatotoxicity (esp. with HIV patients), platelet dysfunction, irritability, seizures

Question 13

Drug interactions with PCN

Answer 13

-oral contraceptives potential reduced efficacy

Question 14

clinical use of PCN

Answer 14

• most frequently prescribed in primary care-usually drug of choice due to cost and minimal allergic reactions
• common uses: URI (pharyngitis, AOM, sinusitis, bronchitis), pneumonia, STIs, UTIs, wound infection
• can be given for endocarditis prophylaxis, for h. pylori, PUD, lyme’s disease

Question 15

rational drug selection for PCN

Answer 15

• indication-is use of antibiotic warranted? benefit-to-risk ratio
• use of definitive tests (rapid strep) warrants antibiotic
• culture and sensitivity-time consuming and costly-not ideal
• keep in mind: allergy hx, age, pregnancy, genetic factors, site of infection (enters poorly in CSF), immunocompromised status (may require bacterial drug tx and extended tx), affordability, convenience

Question 16

monitoring PCN

Answer 16

• alleviation of symptoms
• return to clinic if symptoms not improving or getting worse
• pt. education: overuse of abx, completing course of treatment, ADRs