Amoxicillin, also spelled amoxycillin is an antibiotic useful for the treatment of a number of bacterial infections. It is the first line treatment for middle ear infections. It may also be used for strep throat, pneumonia, skin infections, and urinary tract infections among others. It is taken by mouth, or less commonly by injection.

Molecular Structure

Class of Drug

Antibiotic, penicillin family, aminopenicillin.

Mechanism of Action

Inhibits bacterial cell wall synthesis.

Susceptible organisms in vivo: [same as ampicillin] Streptococcus pneumoniae, beta-hemolytic streptococci, Enterococcus faecalis, viridans streptococci, Escherichia coli, Hemophilus influenzae, Neisseriagonorrhoeae,Proteus mirabilis,Salmonella (often resist-ant), Shigella (often resistant), Listeria monocytogenes, Neisseria meningitidis.

Indications / Dosage / Route

Routes of Administration: Oral only.

Condition: Ear, nose, and throat infections, mild/moderate; GU tract infections, mild/moderate

Dose: Adults: 500 mg ql2h.

         Children: >3 months: 25 mg/kg/d, divided doses ql2h.

Condition: Ear, nose and throat infections, severe; GU tract infections, severe

Dose: Adults: 875 mg ql2h.

         Children: >3 months: 45 mg/kg, divided doses ql2h.

Condition: Lower respiratory tract infections

Dose: Adults: 875 mg ql2h.

          Children >3 months: 45 mg/kg, divided doses ql2h.

Condition: Skin, skin structure infections, mild/moderate

Dose: Adults 500 mg ql2h.

         Children >3 months: 25 mg/kg/d, divided doses ql2h.

Condition: Skin, skin structure infections, severe

Dose: Adults 875 mg ql2h.

         Children: >3 months: 45 mg/kg/d, divided doses q8h.

Condition: Acute gonorrhea, uncomplicated anogenital and urethral infections

DoseAdults: 3 mg as single dose

Children >2 years: 50 mg/kg plus 25 mg probenecid as single dose.

Adjustment of Dosage

Kidney disease: creatinine clearance 10-30 mL/min: 250 or 500 mg ql2h; creatinine clearance <10 mL/minute: 250 or 500 mg q24h.

Liver disease: None.

Elderly: None

Pediatric: Contraindicated for children <2 years.

Food and Drug Interactions

Food: No restrictions.

Pregnancy: Category B.

Lactation: Appears in breast milk. Considered compatible by American Academy of Pediatrics

Contraindications: Hypersensitivity to penicillin or cephalosporins.

Warnings / Precautions

> Use with caution in patients with mononucleosis.

> Allergic reactions are more likely to occur in patients with the following conditions: asthma, hay fever, allergy to cephalosporins, history of allergy to penicillin. Consider skin testing, with major and minor antigenic components, of penicillin hypersensitivity in patients with β-lactamase allergy who require amoxicillin for life-threatening infections, to assess possibility of a hypersensitivity reaction. If patient is given drug parenterally, observe for at least 20 minutes for possible anaphylactic reaction. Negative history of penicillin hypersensitivity does not prelude a patient from reacting to the drug.

> Administer at least 1 h before a bacteriostatic agent is given (eg, tetracycline, erythromycin, chloramphenicol).

> For IV infusion: Make sure no other drugs are added or mixed into the infusing solution. Do not use solution containing precipitates or foreign matter.

> Do not use a penicillin to test Enterobacter or Citrobacter infections because of inducible β-lactamase.

Clinically Important Drug Interactions

> Drugs that increase effects/toxicity of penicillins: probenecid, disufiram(increase levels).

> Drugs that decrease effects/toxicity of penicillins: antacids, tetracyclines.

> Penicillins increase effects of following drugs: oral anticoagu-lants, heparin.

> Penicillins decrease effects of following drugs: oral contra-ceptives.

Adverse Reactions

> Common: None.

> Serious: Stevens-Johnson syndrome, anaphylaxis, angioedema, laryngospasm, pseudomembraneous colitis.

Parameters to Monitor

> Signs and symptoms of anaphylactic shock.

> Signs and symptoms of allergic reaction.

> Signs and symptoms of pseudomembranous colitis.

> Patient’s intake/output of fluid.

> Renal, hepatic, and hematologic status for patients on high- dose prolonged therapy.

Advice to Patient

> If you are using an oral contraceptive, use an additional method of birth control as efficacy of oral contraceptive may be reduced.

> If you are allergic to a penicillin or cephalosporin, carry an identification card with this information.

Further Useful Info

> Amoxicillin is preferred over ampicillin for oral use because incidence of diarrhea is less. Ampicillin is preferred for intra-venous use.

> Amoxicillin and ampicillin are the first choice for Enterococcus faecalis and Listeria monocytogenes infections. Amoxicillin is also used orally for prophylaxis of endocarditis after dental procedures in high-risk patients. Dosage is 2 g PO 1 h prior to procedure.

> The American Association of Pediatrics recommends amoxi-cillin for the treatment of otitis media due to cost-effectiveness. However, resistant organisms are clearly an important problem.

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