Penicillin narrow-spectrum

The natural penicillins also have a fairly narrow spectrum of activity, which means that they are effective against only a few strains of bacteria Newer penicillins have been developed to combat this problem. These penicillins are a result of chemical treatment of a biologic precursor to penicillin. Because of their chemical modifications, they are more slowly excreted... 

The antibiotic of choice for group B streptococcal disease is penicillin G, although ampicillin is an alternative.43 No resistance to either agent has been reported, and their narrow spectrum of activity makes them ideal choices.43 Resistance has developed with the use of alternative choices for penicillin-allergic patients. A treatment algorithm for group B Streptococcus is shown in Fig. 44—3, and dosing recommendations are shown in Table 44-5. 

The answer is a. (Hardman, pp 1084-1085J Amoxicillin is classified as an aminopenicillin along with ampicillin. Because it is less affected than ampicillin by the presence of food, it has a superior absorption in the GI tract. It is sensitive to penicillinase and has a narrow spectrum of activity toward certain Gram-positive and Gram-negative organisms, but not Pseudomonas. Because it is in the penicillin family, hypersensitivity reactions are a possibility... 

The answer is b. (Hardman, p 1077.) Oxacillin is classified as a penicillinase-resistant penicillin that is relatively acid-stable and, therefore, is useful for oral administration. Major adverse reactions include penicillin hypersensitivity and interstitial nephritis. With the exception of methi-cillin, which is 35% bound to serum proteins, all penicillinase-resistant penicillins are highly bound to plasma proteins. Oxacillin has a very narrow spectrum and is used primarily as an anti staphylococcal agent... 

Three broad groupings, of the antibiotic substances presently used in animal production, include (a) broad-spectrum antibiotics, including penicillins and tetracyclines, which are effective against a wide variety of pathogenic and non-pathogenic bacteria (b) several narrow-spectrum antibiotics that are not used in human medicine and. (c) the ionophore antibiotics, monensin. lasalocid and salinomycin Monensin and lasalocid are used as rumen fermentation regulators in beef cattle, and the three ionophores are used as coccidiostats in poultry production. The ionophores. which are not used in human medicine, were first introduced in the 1970 s and account for most of the increase in antibiotic usage in animal production since the 1960 s. 

Semisynthetic penicillins are produced by combining the specific side chains in place of benzyl side chain. They have been produced to overcome the shortcomings of benzyl penicillin like poor bioavailability, susceptibility to penicillinase and narrow spectrum of activity. 

Novobiocin (Fig. 3.9) is a narrow-spectrum antibiotic with antibacterial activity against many gram-positive pathogens. It is frequently used, in combination with penicillin, for treatment of bovine mastitis by intramammary infusion of 200 mg/ quarter in two quarters, and to control fowl cholera and staphylococcal infections in chickens and turkeys at a level of 200-350 g/ton in feed. 

Correct answer a D. Amoxicillin plus clavulanic acid is an extended spectrum formulation that is penicillinase resistant because of the presence of a p-lactamase inhibitor, and is stable in acid. Methicillin, an antistaphylococcal penicillin, is penicillinase resistant but is not stable in acid. Carbeniciliin and piperacillin, antipseudomonai penicillins, are neither penicillinase resistant nor stable in acid. Penicillin V is a narrow spectrum antibiotic that is not penicillinase resistant but is stable in acid. 

Penicillin V is a narrow-spectrum penicillin and has similar antibacterial activity to benzylpenicillin. It is active against many streptococcal infections, but it is inactivated by penicillinases. Flucloxacillin is a penicillinase-resistant antibiotic and is effective against infections caused by penicillin-resistant staphylococci. In comparison to penicillin V, attachment of carbocyclic/heterocyclic ring directly to the C6 carbonyl group confers resistance to beta-lactamases due to steric hindrance around the amide group. 

The natural penicillins, primarily G and V, have a relatively narrow spectrum. They act mostly on gram-positive organisms. The fact that proper selection of precursors could lead to new variations in the penicillin side chain offered the first source of synthetic penicillins. Penicillin V, derived from a phenoxy-acetic acid precursor, attracted clinical use because of its greater acid tolerance, which made it more useful in oral administration. Also, the widespread use of penicillin eventually led to a clinical problem of penicillin-resistant staphylococci and streptococci. Resistance for the most part involved the penicillin-destroying enzyme, penicillinase, which attacked the beta-lactam structure of the 6-aminopenicillanic acid nucleus (6-APA). Semisynthetic penicillins such as ampicillin and carbenicillin have a broader spectrum. Some, such as methicillin, orafi-cillin, and oxacillin, are resistant to penicillinase. In 1984, Beecham introduced Augmentin, which was the first combination formulation of a penicillin (amoxicillin) and a penicillinase inhibitor (clavulanic acid). Worldwide production of semisynthetic penicillins is currently around 10,000 tons/year, the major producers are Smith Kline Beecham, DSM, Pfizer, and Toyo Jozo. 

Narrow spectrum (natural penicillins) benzylpenicillin. phenoxymethylpenicillin... 

Clearly, there are several problems associated with the use of penicillin G, the most serious being acid sensitivity, sensitivity to penicillinase, and a narrow spectrum of activity. The purpose of making semisynthetic penicillin analogues is therefore to find compounds which do not suffer from these disadvantages. 

The mechanisms of action of penicillins, the bacterial modes of resistance to penicillins, the penicillin subgroups, their biodisposition, and adverse affects are provided. The subgroups discussed are the penicillins that are p-lactamase susceptible with a narrow spectrum of activity, p-lactamase-resistant penicillins having a very narrow spectrum of activity, and J3-lactamase—susceptible penicillins with a i wider spectrum of activity. The common penicillins and their susceptible organisms are listed for each I subgroup. 

Answer B. Indications for the use of penicillin G are currently limited for a number of reasons. The drug has a narrow spectrum, is susceptible to beta-lactamases, and may cause hypersensitivity, and alternative antibiotics are available. However, penicillin G remains the drug of choice in syphilis, usually given IM as benzathine penicillin G, but as the Na or K salt IV in neurosyphilis. What would you do for patients who are highly allergic to penicillins (Consider tetracyclines, or possibly desensitization.)... 

Streptococcal infections caused by Streptococcus sp. including group A beta-hemolytic Streptococcus and S. pneumoniae however, such infections are ordinarily treated with more narrow-spectrum penicillins... 

Narrow spectrum, beta-lactamase sensitive penicillin G and penicillin V... 

Very narrow spectrum, penicillinase-resistant drugs This subclass of penicillins includes methicillin (the prototype), nafcillin, and oxacillin. Their primary use is in the treatment of known or suspected staphylococcal infections. Methicillin-resistant staphylococci (MRSA) are resistant to other members of this subgroup and may be resistant to multiple antimicrobial drugs. 

Figure 7.8 Neisseria meningitides and N. gonorrhea are the only gram negatives that are susceptible to penicillin G and other narrow spectrum penicillins. Ceftriaxone has now replaced penicillin as the drug of choice for N. gonorrhea due to the emergence of penicillin-resistant strains.

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