Amoxicillin-clavulanate is one of the most frequently used antibiotics in emergency departments and primary care offices throughout the country. It is a combination of two separate drugs, amoxicillin, and clavulanic acid, and is commonly known as Augmentin. Amoxicillin is a penicillin derivative and has similar activity against both gram positive and gram negative bacteria, including Enterococcus species, Listeria monocytogenes, Streptococcus species, Haemophilus influenzae, Moraxella catarrhalis, Corynebacterium diphtheria, Escherichia coli, Klebsiella pneumoniae, Salmonella, Shigella, and Borrelia species. Furthermore, with the addition of clavulanic acid, the spectrum is increased to include all beta-lactamase producing strains of the previously mentioned organisms, as well as broadening the coverage to include methicillin-sensitive Staphylococcus aureus, Neisseria species, Proteus species, Pasteurella multocida, and Capnocytophaga canimorsus, among others.
Amoxicillin-clavulanate has FDA approval for the treatment of aspiration pneumonia, community-acquired pneumonia, acute bacterial rhinosinusitis, urinary tract infections, acute otitis media, and skin and soft tissue infections. Off-label uses include the treatment of human or animal bite wounds, group A streptococcal infections, impetigo, acute exacerbations of chronic obstructive pulmonary disease and bronchiectasis, diabetic foot infections, odontogenic infections, and peritonsillar cellulitis/abscess.
Amoxicillin is a broad-spectrum beta-lactam antibiotic, originally derived from penicillin. It is a bactericidal agent which targets and kills bacteria by inhibiting the biosynthesis of the peptidoglycan layer of the bacterial cell wall. This layer makes up the outermost portion of the cell wall and is responsible for the structural integrity of the cell. Peptidoglycan synthesis involves the facilitation of enzymes called DD-transpeptidases, which are a type of penicillin-binding protein (PBP). Amoxicillin works by binding to these PBPs and inhibiting peptidoglycan synthesis, which interrupts the construction of the cell wall and ultimately leads to the destruction, or lysis, of the bacteria.
Clavulanic acid is a beta-lactamase inhibitor often used in conjunction with amoxicillin to further broaden its spectrum and combat resistance. It has little to no antimicrobial activity of its own and instead works by preventing bacterial destruction of antibiotics. Over the years, certain bacteria have evolved to develop resistance to standard beta-lactam antibiotics through the production of enzymes called beta-lactamases. These enzymes target and hydrolyze the beta-lactam ring, which is necessary for penicillin-like antibiotics to work. Clavulanic acid prevents this degradation by binding and deactivating the beta-lactamases, thus restoring the antimicrobial effects of amoxicillin.
Amoxicillin-clavulanate is only available in oral formulations and like most bactericidal antibiotics, needs to be administered at regularly scheduled intervals to minimize differences in the antibiotic’s peaks and troughs. This helps maintain consistent serum concentrations over the minimum inhibitory concentration (MIC) needed to effectively destroy the targeted organism. This is generally accomplished by a twice or three times daily administration of the medication. Oral formulations of this antibiotic are available as immediate or extended-release tablets, reconstituted suspensions, or chewable tablets. The reconstituted solution should be kept in the refrigerator and shaken well before the administration to maximize its longevity and effectiveness. It is recommended to take this antibiotic with food to enhance its absorption as well as minimize any adverse GI symptoms.
Amoxicillin-clavulanate is largely safe and well tolerated in the general population with the vast majority of adverse effects being only mild gastrointestinal symptoms. The single most common complaint is diarrhea, but others include nausea, vomiting, loose stools, and abdominal discomfort. Of note, the incidence of diarrhea is higher in amoxicillin-clavulanate compared with amoxicillin alone. Additionally, there is a moderately increased risk of secondary Clostridium difficile colitis when compared with other classes of antibiotics. Female's taking this medication can also develop vaginitis secondary to vaginal mycosis or candidiasis.
Dermatologic effects are less common and generally related to hypersensitivity reactions. These reactions can present anywhere on the spectrum of disease, ranging from simple pruritis or urticaria to severe and life-threatening manifestations, such as anaphylaxis, Steven-Johnson syndrome or toxic epidermal necrolysis. Classically, a morbilliform rash will present shortly after initiation of amoxicillin in patients misdiagnosed as strep pharyngitis, when in fact they have infectious mononucleosis.
Very rare complications of amoxicillin-clavulanate use include prolonged prothrombin time, vasculitis, thrombocytopenia, cholestatic jaundice, elevated serum alkaline phosphatase, hepatitis, and hepatotoxicity.
Caution is warranted when treating patients on hemodialysis or with severe renal impairment with creatinine clearance less than 30 mL/minute. As this antibiotic is primarily excreted by the kidneys, individuals with renal disease will need dose adjustments and closer monitoring.
There are no guidelines for dosing in hepatic impairment, but extreme caution should be exercised when considering use in this population. This medication is absolutely contraindicated in any patient with a prior history of amoxicillin or clavulanic acid-induced hepatic dysfunction.
Lastly, use in patients with previous hypersensitivity reactions to amoxicillin, clavulanic acid, or other beta-lactam antibiotics is contraindicated. As amoxicillin is a penicillin derivative, there is a high likelihood of crossover hypersensitivity in patients with a documented penicillin allergy. In this population, alternative antibiotic options should be entertained.
Patients taking amoxicillin-clavulanate should be monitored at the beginning of therapy for signs of hypersensitivity and throughout the course for signs of secondary infection, such as C. difficile colitis or candidiasis. Prolonged therapy, or use greater than 10-14 days, will also require intermittent monitoring of hepatic, renal, and hematologic function. Patients with hepatic impairment should receive regular monitoring of liver enzymes up to several weeks after discontinuation of the antibiotic.
Although amoxicillin-clavulanate is an excellent antibiotic, it is one of the most frequent causes of idiosyncratic drug-induced hepatic injury. Men are at increased risk when compared to women, as well as patients greater than 50 years of age. Other factors include genetic polymorphisms, HIV patients on antiretroviral therapy, or concomitant use of medications that influence the cytochrome P450 pathway. Time of symptom onset is generally 2-3 weeks after the initial dose, but may occur more rapidly or even be delayed up to 12 weeks. Treatment involves immediate discontinuation of the offending agent and limiting the use of other hepatotoxic drugs. N-acetylcysteine and corticosteroids can also be considered, however, the benefits are likely marginal. Administration of a bile acid sequestrant, such as cholestyramine, may provide symptomatic relief from pruritis. Full recovery, although prolonged, is achieved by the majority of patients; however, a select few will go on to develop liver failure requiring a liver transplant to survive.
All drug-related reactions, including drug-induced hepatic injury, pose a real threat to society and have the potential to lead to significant morbidity or mortality if not appropriately identified and managed. Open and effective interprofessional communication is essential among all members of the medical team. Proper management begins in the primary care office or emergency department with physicians maintaining broad differentials and a high index of suspicion through clinical gestalt and information gained from a thorough history and physical exam. Appropriate investigative tests then need to be ordered and properly interpreted to identify possible drug reactions as the explanation for a patient’s presenting symptoms. In the case of drug-induced hepatic injury secondary to antibiotic use, a patient will likely present with liver injury days to weeks after completing a course of antibiotics, and a direct correlation may not be easily made. If there is suspicion for drug-induced hepatic injury, identifying and discontinuing the offending agent is the main goal of treatment. (Level I) Involvement of a specialist, such as a hepatologist, can be beneficial especially when there is a concern for acute liver failure, chronic liver disease, or the diagnosis remains unclear after the initial evaluation. Furthermore, in patients with evidence of liver failure or who are at high risk, early transport to liver transplant facilities can be advantageous. (Level I) Other treatment modalities include corticosteroids and N-acetylcysteine, however, the benefits are likely marginal and they should be used in conjunction with a specialist. (Level III)
In summary, proactive instead of reactive methods are always more valuable. Proper antibiotic stewardship can decrease unnecessary use of antibiotics, and therefore decrease the incidence of drug-related adverse effects as well as limit the rate of antibiotic resistance. Information sharing between emergency medicine and primary care physicians can further help with early identification of suspected adverse reactions as well as improve appropriate antibiotic selection for individuals who must undergo treatment. When a serious adverse reaction has occurred, the early involvement of a specialist can limit the severity of disease and increase the chance of a full and uneventful recovery.
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