Amoxicillin

Action

Inhibits cell-wall synthesis during bacterial multiplication, leading to cell death. Shows enhanced activity toward gram-negative bacteria compared to natural and penicillinase-resistant penicillins.

Availability

Capsules: 250 mg, 500 mg

Powder for oral suspension: 50 mg/ml and 125 mg/5 ml (pediatric), 200 mg/5 ml, 250 mg/5 ml, 400 mg/5 ml

Tablets: 500 mg, 875 mg

Tablets for oral suspension: 200 mg, 400 mg

Tablets (chewable): 125 mg, 200 mg, 250 mg, 400 mg

Indications and dosages

➣ Uncomplicated gonorrhea

Adults and children weighing at least 40 kg (88 lb): 3 g P.O. as a single dose

Children ages 2 and older weighing less than 40 kg (88 lb): 50 mg/kg P.O. given with probenecid 25 mg/kg P.O. as a single dose

➣ Bacterial endocarditis prophylaxis for dental, GI, and GU procedures

Adults: 2 g P.O. 1 hour before procedure

Children: 50 mg/kg P.O. 1 hour before procedure

➣ Lower respiratory tract infections caused by streptococci, pneumococci, non-penicillinase-producing staphylococci, and Haemophilus influenzae

Adults and children weighing more than 20 kg (44 lb): 875 mg P.O. q 12 hours or 500 mg P.O. q 8 hours

Children weighing less than 20 kg (44 lb): 45 mg/kg/day P.O. in divided doses q 12 hours or 40 mg/kg/day P.O. in divided doses q 8 hours

➣ Ear, nose, and throat infections caused by streptococci, pneumococci, non-penicillinase-producing staphylococci, and H. influenzae; GU infections caused by Escherichia coli, Proteus mirabilis, and Streptococcus faecalis

Adults and children weighing more than 20 kg (44 lb): 500 mg P.O. q 12 hours or 250 mg P.O. q 8 hours

Children weighing less than 20 kg (44 lb): 45 mg/kg/day P.O. in divided doses q 12 hours or 20 to 40 mg/kg P.O. in divided doses q 8 hours

➣ Eradication of Helicobacter pylori to reduce risk of duodenal ulcer recurrence

Adults: 1 g P.O. q 12 hours for 14 days in combination with clarithromycin and lansoprazole, or in combination with lansoprazole alone as 1 g t.i.d. for 14 days

➣ Postexposure anthrax prophylaxis

Adults: 500 mg P.O. t.i.d. for 60 days

Children: 80 mg/kg/day P.O. t.i.d. for 60 days

➣ Skin and skin-structure infections caused by streptococci (alpha- and beta-hemolytic strains), staphylococci, and E. coli

Adults: 500 mg P.O. q 12 hours to 250 mg P.O. q 8 hours. For severe infections, 875 mg P.O. q 12 hours or 500 mg P.O. q 8 hours.

Children older than age 3 months: 25 mg/kg/day P.O. in divided doses q 12 hours or 20 mg/kg/day P.O. in divided doses every 8 hours. For severe infections, 45 mg/kg/day P.O. in divided doses q 12 hours or 40 mg/kg/day P.O. in divided doses every 8 hours.

Dosage adjustment

• Renal impairment

• Hemodialysis

• Infants ages 3 months and younger

Off-label uses

• Chlamydia trachomatis infection in pregnant patients

Contraindications

• Hypersensitivity to drug or any penicillin

Precautions

Use cautiously in:

• severe renal insufficiency, infectious mononucleosis, hepatic dysfunction

• pregnant patients.

Administration

☞ Ask about history of penicillin allergy before giving.

• Give with or without food.

• Store liquid form in refrigerator when possible.

• Know that maximum dosage for infants ages 3 months and younger is 30 mg/kg/day divided q 12 hours.

Adverse reactions

CNS: lethargy, hallucinations, anxiety, confusion, agitation, depression, dizziness, fatigue, hyperactivity, insomnia, behavioral changes, seizures (with high doses)

GI: nausea, vomiting, diarrhea, bloody diarrhea, abdominal pain, gastritis, stomatitis, glossitis, black "hairy" tongue, furry tongue, enterocolitis, pseudomembranous colitis

GU: vaginitis, nephropathy, interstitial nephritis

Hematologic: eosinophilia, anemia, thrombocytopenia, thrombocytopenic purpura, leukopenia, hemolytic anemia, agranulocytosis, bone marrow depression

Hepatic: cholestatic jaundice, hepatic cholestasis, cholestatic hepatitis, nonspecific hepatitis

Respiratory: wheezing

Skin: rash

Other: superinfections (oral and rectal candidiasis), fever, anaphylaxis

Interactions

Drug-drug. Allopurinol: increased risk of rash

Chloramphenicol, macrolides, sulfonamides, tetracycline: decreased amoxicillin efficacy

Hormonal contraceptives: decreased contraceptive efficacy

Probenecid: decreased renal excretion

Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, eosinophils, lactate dehydrogenase: increased levels

Granulocytes, hemoglobin, platelets, white blood cells: decreased values Direct Coombs' test, urine glucose, urine protein: false-positive results

Drug-food. Any food: delayed or reduced drug absorption

Drug-herbs. Khat: decreased antimicrobial efficacy

Patient monitoring

• Monitor for signs and symptoms of hypersensitivity reaction.

☞ Evaluate for seizures when giving high doses.

• Monitor patient's temperature and watch for other signs and symptoms of superinfection (especially oral or rectal candidiasis).

Patient teaching

☞ Instruct patient to immediately report signs and symptoms of hypersensitivity reactions, such as rash, fever, or chills.

• Tell patient he may take drug with or without food.

• Tell patient not to chew or swallow tablets for suspension, because they're not meant to be dissolved in mouth.

• Advise patient to minimize GI upset by eating small, frequent servings of food and drinking plenty of fluids.

• Tell patient taking hormonal contraceptives that drug may reduce contraceptive efficacy. Suggest she use alternative birth control method.

• Inform patient that drug lowers resistance to other types of infections. Instruct him to report new signs and symptoms of infection, especially in mouth or rectum.

• Tell parents they may give liquid form of drug directly to child or may mix it with foods or beverages.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and herbs mentioned above.