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抗生素 賜復力生膠囊 (５００公絲) (賜福力欣)
CEFLEXIN CAPSULES 500mg (CEPHALEXIN) "VPP"
頭孢菌素(Cephalosporin)，又稱先鋒黴素，是一系列屬於β內醯胺類的抗生素。與頭黴素一併細分為頭孢烯。 頭孢菌素化合物最初是於1948年，由義大利科學家Giuseppe Brotzu從薩丁島排水溝中的頂頭孢提煉出來。他發現這些頂頭孢分泌出一些物質，可以有效抵抗引致傷寒的傷寒桿菌。牛津大學成功提煉出對β內醯胺酶穩定的頭孢菌素C，但卻未有足夠的效力作臨床使用。頭孢菌素的核心是7-氨基頭孢烯酸（簡稱7-ACA）是從頭孢菌素C中衍生出來，並已證實與青黴素的核心（即6-氨基青黴烷酸，6-APA）相似。對7-ACA的旁鏈作出修改，得出一些非常有用的抗生素，而第一種的頭孢噻吩便是由禮來公司於1964年發行。
DOSAGE AND ADMINISTRATION:
Usual Adult Dosage:
Type of Infection Dose / Frequency
Moderate to severe infections 500 mg to 1 gram every 6 to 8 hrs.
Mild infections caused by susceptible gram-positive cocci 250 mg to 500 mg every 8 hours
Acute, uncomplicated urinary tract infections 1 gram every 12 hours
Pneumococcal pneumonia 500 mg every 12 hours
Severe, life-threatening infections (e.g.,
endocarditis, septicemia)* 1 gram to 1.5 grams every 6 hours
*In rare instances, doses of up to 12 grams of Cefazolin Injection per day have been used.
Perioperative Prophylactic Use
To prevent postoperative infection in contaminated or potentially contaminated surgery, recommended doses are:
1. 1 gram IV administered one-half hour to 1 hour prior to start of surgery.
2. For lengthy operative procedures (e.g., 2 hours or more), 500 mg to 1 gram IV during surgery (administration modified depending on the duration of the operative procedure).
3. 500 mg to 1 gram IV every 6 to 8 hours for 24 hours postoperatively.
It is important that (1) the preoperative dose be given just (1/2 to 1 hour) prior to start of surgery so that adequate antibiotic levels are present in the serum and tissues at the time of initial surgical incision; and (2) cefazolin be administered, if necessary, at appropriate intervals during surgery to provide sufficient levels of the antibiotic at the anticipated moments of greatest exposure to infective organisms.
In surgery where the occurrence of infection may be particularly devastating (e.g., open-heart surgery and prosthetic arthroplasty), the prophylactic administration of cefazolin may be continued for 3 to 5 days following the completion of surgery.
Renal Dosing: ------------------------
Cefazolin Injection may be used in patients with reduced renal function with the following dosage adjustments: Patients with a creatinine clearance of 55 mL/min. or greater or a serum creatinine of 1.5 mg % or less can be given full doses. Patients with creatinine clearance rates of 35 to 54 mL/min. or serum creatinine of 1.6 to 3.0 mg % can also be given full doses but dosage should be restricted to at least 8 hour intervals.
Patients with creatinine clearance rates of 11 to 34 mL/min. or serum creatinine of 3.1 to 4.5 mg % should be given one-half the usual dose every 12 hours.
Patients with creatinine clearance rates of 10 mL/min. or less or serum creatinine of 4.6 mg % or greater should be given ½ the usual dose every 18 to 24 hours.
All reduced dosage recommendations apply after an initial loading dose appropriate to the severity of the infection.
The cephalosporins are a class of β-lactam antibiotics originally derived from the fungus Acremonium, which was previously known as "Cephalosporium". Together with cephamycins, they constitute a subgroup of β-lactam antibiotics called cephems. Cephalosporins were discovered in 1945 and were first sold in 1964.
Cephalosporins are indicated for the prophylaxis and treatment of infections caused by bacteria susceptible to this particular form of antibiotic. First-generation cephalosporins are active predominantly against Gram-positive bacteria, and successive generations have increased activity against Gram-negative bacteria (albeit often with reduced activity against Gram-positive organisms).
Common adverse drug reactions (ADRs) (≥ 1% of patients) associated with the cephalosporin therapy include: diarrhea, nausea, rash, electrolyte disturbances, and pain and inflammation at injection site. Infrequent ADRs (0.1–1% of patients) include vomiting, headache, dizziness, oral and vaginal candidiasis, pseudomembranous colitis, superinfection, eosinophilia, nephrotoxicity, neutropenia, thrombocytopenia, and fever.
The commonly quoted figure of 10% of patients with allergic hypersensitivity to penicillins and/or carbapenems also having cross-reactivity with cephalosporins originated from a 1975 study looking at the original cephalosporins, and subsequent "safety first" policy meant this was widely quoted and assumed to apply to all members of the group. Hence, it was commonly stated that they are contraindicated in patients with a history of severe, immediate allergic reactions (urticaria, anaphylaxis, interstitial nephritis, etc.) to penicillins, carbapenems, or cephalosporins. This, however, should be viewed in the light of recent epidemiological work suggesting, for many second-generation (or later) cephalosporins, the cross-reactivity rate with penicillin is much lower, having no significantly increased risk of reactivity over the first generation based on the studies examined. The British National Formulary previously issued blanket warnings of 10% cross-reactivity, but, since the September 2008 edition, suggests, in the absence of suitable alternatives, oral cefixime or cefuroxime and injectable cefotaxime, ceftazidine, and ceftriaxone can be used with caution, but the use of cefaclor, cefadrocil, cefalexin, and cefradine should be avoided.
Overall, the research shows that all beta lactams have the intrinsic hazard of very serious hazardous reactions in susceptible patients. Only the frequency of these reactions vary, based on the structure. Recent papers have shown that a major feature in determining frequency of immunological reactions is the similarity of the side chains (e.g., first generation cephalosporins are similar to penicillins), and this is the reason the β-lactams are associated with different frequencies of serious reactions (e.g., anaphylaxis).
Several cephalosporins are associated with hypoprothrombinemia and a disulfiram-like reaction with ethanol. These include latamoxef, cefmenoxime, moxalactam, cefoperazone, cefamandole, cefmetazole, and cefotetan. This is thought to be due to the N-methylthiotetrazole side-chain of these cephalosporins, which blocks the enzyme vitamin K epoxide reductase (likely causing hypothrombinemia) and aldehyde dehydrogenase (causing alcohol intolerance).
Mechanism of Action
Cephalosporins are bactericidal and have the same mode of action as other β-lactam antibiotics (such as penicillins), but are less susceptible to β-lactamases. Cephalosporins disrupt the synthesis of the peptidoglycan layer forming the bacterial cell wall. The peptidoglycan layer is important for cell wall structural integrity. The final transpeptidation step in the synthesis of the peptidoglycan is facilitated by transpeptidases[disambiguation needed] known as penicillin-binding proteins (PBPs). PBPs bind to the D-Ala-D-Ala at the end of muropeptides (peptidoglycan precursors) to crosslink the peptidoglycan. Beta-lactam antibiotics mimic the D-Ala-D-Ala site, thereby irreversibly inhibiting PBP crosslinking of peptidoglycan.
Resistance to cephalosporin antibiotics can involve either reduced affinity of existing PBP components or the acquisition of a supplementary β-lactam-insensitive PBP. Currently, some Citrobacter freundii, Enterobacter cloacae, Neisseria gonorrhoeae, and Escherichia coli strains are resistant to cephalosporins. Some Morganella morganii, Proteus vulgaris, Providencia rettgeri, Pseudomonas aeruginosa, and Serratia marcescens strains have also developed resistance to cephalosporins to varying degrees.
The cephalosporin nucleus can be modified to gain different properties. Cephalosporins are sometimes grouped into "generations" by their antimicrobial properties. The first cephalosporins were designated first-generation cephalosporins, whereas, later, more extended-spectrum cephalosporins were classified as second-generation cephalosporins. Each newer generation has significantly greater Gram-negative antimicrobial properties than the preceding generation, in most cases with decreased activity against Gram-positive organisms. Fourth-generation cephalosporins, however, have true broad-spectrum activity.
The classification of cephalosporins into "generations" is commonly practised, although the exact categorization is often imprecise. For example, the fourth generation of cephalosporins is not recognized as such in Japan. In Japan, cefaclor is classed as a first-generation cephalosporin, though in the United States it is a second-generation one; and cefbuperazone, cefminox, and cefotetan are classed as second-generation cephalosporins. Cefmetazole and cefoxitin are classed as third-generation cephems. Flomoxef and latamoxef are in a new class called oxacephems.
Most first-generation cephalosporins were originally spelled "ceph-" in English-speaking countries. This continues to be the preferred spelling in the United States, Australia, and New Zealand, while European countries (including the United Kingdom) have adopted the International Nonproprietary Names, which are always spelled "cef-". Newer first-generation cephalosporins and all cephalosporins of later generations are spelled "cef-", even in the United States.
Some state that cephalosporins can be divided into five or even six generations, although the usefulness of this organization system is of limited clinical relevance.
Fourth-generation cephalosporins as of March, 2007, were considered to be "a class of highly potent antibiotics that are among medicine's last defenses against several serious human infections" according to the Washington Post.
The mnemonic "LAME" is used to note organisms against which cephalosporins do not have activity: Listeria, Atypicals (including Mycoplasma and Chlamydia), MRSA, and enterococci.
Fifth-generation cephalosporins are effective against MRSA, however.