Antibacterials are the subclass of antibiotics, which can be naturally obtained from fungal sources, semi‐synthetic members which are chemically altered natural product and or synthetic. Cephalosporins, cefamycins, benzylpenicillin, and gentamicin are well‐known examples of natural antibiotics/antibacterials. Natural antibiotics/antibacterials often exhibit high toxicity than synthetic antibacterials. Ampicillin and amikacin are semi‐synthetic antibiotics, which were developed to show low toxicity and increase effectiveness. Synthetic antibiotics are also designed to have even greater effectiveness and less toxicity and, thus, have an advantage over the natural antibiotics that the bacteria are not exposed to the compounds until they cipro 750mg prices are released. Moxifloxacin and norfloxacin are promising synthetic antibiotics [3].

2.3. Classification based on spectrum of activity
This is another way of classification of antibiotics or antibacterial agents, which is based on their target specification. In this category, the antibacterials may be either narrow or broad spectrum. The terms narrow spectrum and broad spectrum have been interpreted not specifically since their use in antibiotic history, but recently these acquired clear meanings in academic and industrial fields [4, 5]. The narrow spectrum antibacterials are considered to be those which can work on a narrow range of microorganisms, that is, they act against Gram‐positive only or Gram‐negative only bacteria. Unlike narrow spectrum antibacterial, the broad spectrum antibacterial affects a wide range of pathogenic bacteria, including both Gram‐positive and Gram‐negative bacteria. Usually, the narrow spectrum antibacterials are considered ideal antibacterials and are preferred over the broad‐spectrum antibacterials. The reason is that the narrow‐spectrum antibiotics do not kill as many of the normal microorganisms in the body as the broad‐spectrum antibiotics and thus has less ability to cause superinfection. Also, the narrow‐spectrum antibiotic will cause less resistance of the bacteria as it will deal with only specific bacteria.

Based on the spectrum of activity, both of these groups have a large and diverse library of antibacterials. Table 2 shows all the well‐known examples of these categories.

Broad‐spectrum antibacterials (examples) Narrow‐spectrum antibacterials (examples)
Ampicillin and its derivative amoxicillin are broad‐spectrum antibacterials. Amoxicillin/clavulanic acid (common name co‐amoxiclav) is an antibiotic useful for the treatment of a number of bacterial infections β‐Lactamase‐sensitive, first generation include penicillin G, benzathine penicillin G, penicillin V, procaine penicillin, propicillin, pheneticillin, azidocillin, clometocillin, and penamecillin are considered in narrow‐spectrum antibacterial category
Quinolones [6] such as Maxaquin (lomefloxacin), Floxin (ofloxacin), Noroxin (norfloxacin), Tequin (gatifloxacin), Cipro (ciprofloxacin), Avelox (moxifloxacin), Levaquin (levofloxacin), Factive (gemifloxacin), Cinobac (cinoxacin), NegGram (nalidixic acid), Trovan (trovafloxacin), and Zagam (sparfloxacin) are considered as broad‐spectrum antibacterials β‐Lactamase‐resistant, Ist generation include;
Cloxacillin (dicloxacillin flucloxacillin), methicillin, nafcillin, oxacillin and temocillin are narrow‐spectrum antibacterials
Aminoglycosides which are broad‐spectrum antibacterials include kanamycin A, amikacin, tobramycin, dibekacin, gentamicin, sisomicin, netilmicin, neomycins B, C and neomycin E (paromomycin) [7] Cephalosporins (first generation and second generation) antibacterials are relatively narrow spectrum
Cephalosporins (third, fourth, and fifth generations) are relatively extended to the broad spectrum of activity Vancomycin, clindamycin, isoniazid, rifampin, ethambutol, pyrazinamide, bacitracin, polymixins, sulfonamides, glycopeptide and nitroimidazoles are counted in this group
Carbepenems (e.g. imipenems) show a broad pattern of activity [8]
Macrolides such as erythromycin, roxithromycin, clarithromycin, azithromycin, and dirithromycin are considered in this category [9]
Tetracycline, chlortetracycline, oxytetracycline, demeclocycline, lymecycline, meclocycline, methacycline, minocycline, and tigecycline are considered as broad‐spectrum antibacterials
Chloramphenicol
Ticarcillin, a carboxypenicillin, also has a broad spectrum of activity
Rifamycins also exhibited broad coverage [10]
Table 2.
List of broad‐ and narrow‐spectrum antibacterials.

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2.4. Classification based on chemical structure
Different skeleton‐containing antibiotics display different therapeutic behaviour; therefore, it is an ultimate need to classify antibacterials on the basis of their chemical structure. This classification is also very important as similar structural units have similar patterns of toxicity, effectiveness, and other related where can i buy phenergan properties. Usually on a structural basis, antibacterials have been classified into two groups: group A (β‐lactams) and group B (aminoglycosides). However, in a more elaborated way, the antibacterials can be classified into β‐lactams, β‐lactam/β‐lactamase inhibitor combinations, aminglycoside, macrolides, quinolones, and flouroquinolones.

2.4.1. β‐Lactams
Beta‐lactams are a popular class of drugs, having a four‐membered lactam ring (Figure 1), known as β‐lactam ring; however, they vary by side chain attached or additional cycles. Penicillin derivatives, cephalosporins, monobactams, and carbepenems, e.g. imipenems, all belong to this class.


Figure 1.
Basic structure of the β‐lactam ring, penicillins (Penam skeleton) and cephalosporins (Cephem skeleton). R in Penam and Cephem nucleus represents the side chain that could be different for different penicillins and cephalosporins, while R′ denotes another side chain in the Cephem nucleus.
Usually, alterations were made to the basic penam and cephem structural units such that enhanced antimicrobial potential is achieved. Among such modified agents, some are clavulanate, latamoxef, loracarbef, etc. On the cephalosporins unit, most changes have been made at positions 7 and 3. Cephalothin, cephaloridine, and cephazolin are among some of the modified cephalosporins, which have shown good activity against Gram positive with the exception of enterococci‐ and methicillin‐resistant staphylococci. Some other examples include preparation of microbiologically active oxacephems and carbacephems (Figure 2) by modification of the cephalosporin nucleus [11].


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