Amoxicillin, Uses, Dosage, Side Effects, Interactions, Pregnancy

Amoxicillin Anhydrous is the anhydrous form of a broad-spectrum, semisynthetic aminopenicillin antibiotic with bactericidal activity. Amoxicillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and results in the weakening of the bacterial cell wall and causes cell lysis.

A broad-spectrum semisynthetic antibiotic similar to ampicillin except that its resistance to gastric acid permits higher serum levels with oral administration. Amoxicillin is commonly prescribed with clauvanic acid (a beta lactamase inhibitor) as it is susceptible to beta-lacatamase degradation.

Mechanism of Action of Amoxicillin

Amoxicillin is a moderate-spectrum antibiotic active against a wide range of Gram-positive, and a limited range of Gram-negative organisms.Penicillins acylate the penicillin-sensitive transpeptidase C-terminal domain by opening the lactam ring. This inactivation of the enzyme prevents the formation of a cross-link of two linear peptidoglycan strands, inhibiting the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that amoxicllin interferes with an autolysin inhibitor.  It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other beta-lactam antibiotics. Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, and so may be given with clavulanic acid to increase its susceptability. The incidence of β-lactamase-producing resistant organisms, including E. coli, appears to be increasing. Amoxicillin is sometimes combined with clavulanic acid, a β-lactamase inhibitor, to increase the spectrum of action against Gram-negative organisms, and to overcome bacterial antibiotic resistance mediated through β-lactamase production.

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Indication of Amoxicillin

• Amoxicillin is used to treat infections due to bacteria that are susceptible to the effects of amoxicillin.
• Common bacterial infections that amoxicillin is used for include infections of the
  • middle ear,
  • tonsils,
  • throat,
  • larynx (laryngitis),
  • bronchi (bronchitis),
  • Lungs (pneumonia),
  • urinary tract, and
  • skin.
• It also is used to treat gonorrhea
• Bacterial Endocarditis Prophylaxis
• Chlamydia Infection
• Helicobacter pylori Infection
• Lyme Disease – Arthritis
• Lyme Disease – Carditis
• Lyme Disease – Erythema Chronicum Migrans
• Lyme Disease
• Dental abscesses (as addition to surgical management).
• Typhoid and paratyphoid fever.
• Pneumonia
• throat infections
• tonsillitis
• typhoid
• Bronchitis
• Sinusitis
• Dental abscess with spreading cellulitis
• Prosthetic joint infections
• Helicobacter pylori eradication
• Urinary Tract Infection
• Tonsillitis/Pharyngitis
• Skin and Structure Infection
• Cutaneous Bacillus anthracis
• Anthrax Prophylaxis
• For the treatment of infections of the ear, nose, and throat, the genitourinary tract, the skin and skin structure, and the lower respiratory tract due to susceptible (only b-lactamase-negative) strains of Streptococcus spp. (a- and b-hemolytic strains only), S. pneumoniae, Staphylococcus spp., H. influenzae, E. coli, P. mirabilis, or E. faecalis. Also for the treatment of acute, uncomplicated gonorrhea (ano-genital and urethral infections) due to N. gonorrhoeae (males and females).
• The product is indicated for use in clinical cases of mastitis including cases associated with infections with the following major pathogens – Staphylococci (including beta-lactamase producing strains) Streptococci (including S. agalactiae, S. dysgalactiae and S. uberis), Escherichia coli (including beta-lactamase producing strains
• Treatment and prophylaxis of several bacterial infections

Therapeutic Indications

• Infections of the Ear, Nose, and Throat: Amoxicillin capsules are indicated in the treatment of infections due to susceptible (ONLY beta-lactamase-negative) isolates of Streptococcus species. (alpha- and beta-hemolytic isolates only), Streptococcus pneumoniae, Staphylococcus spp., or Haemophilus influenzae.
• Infections of the Genitourinary Tract: Amoxicillin capsules are indicated in the treatment of infections due to susceptible (ONLY beta-lactamase-negative) isolates of Escherichia coli, Proteus mirabilis, or Enterococcus faecalis.
• Infections of the Skin and Skin Structure: Amoxicillin capsules are indicated in the treatment of infections due to susceptible (ONLY beta-lactamase-negative) isolates of Streptococcus spp. (alpha- and beta-hemolytic isolates only), Staphylococcus spp., or E. coli
• Infections of the Lower Respiratory Tract: Amoxicillin capsules are indicated in the treatment of infections due to susceptible (ONLY beta-lactamase-negative) isolates of Streptococcus spp. (alpha- and beta-hemolytic isolates only), S. pneumoniae, Staphylococcus spp., or H. influenzae.
• Amoxicillin capsules in combination with clarithromycin plus lansoprazole as triple therapy, is indicated for the treatment of patients with Helicobacter pylori infection and duodenal ulcer disease (active or 1-year history of a duodenal ulcer) to eradicate H. pylori. Eradication of H. pylori has been shown to reduce the risk of duodenal ulcer recurrence.
• Oral amoxicillin has been shown to be effective for the treatment of acute, uncomplicated urinary tract infections (UTIs) in some women when given as a single dose.
• Amoxicillin and ampicillin have been used orally for the treatment of uncomplicated gonorrhea and disseminated gonococcal infections caused by nonpenicillinase-producing strains of N. gonorrhoeae; however, penicillins are no longer recommended for the treatment of uncomplicated or disseminated gonococcal infections and are not included in current CDC guidelines for treatment of the disease.
• Ampicillin and amoxicillin are used in adults or children for the treatment of typhoid fever (enteric fever) caused by susceptible strains of Salmonella typhi.
• Amoxicillin is considered a drug of choice for the treatment of erythema migrans and certain other manifestations of early or late Lyme disease.
• Oral amoxicillin is recommended by the CDC and other clinicians for the treatment of uncomplicated urethral, endocervical, or rectal infections caused by Chlamydia trachomatis in pregnant women who cannot tolerate erythromycins; however, experience with amoxicillin therapy in this infection is limited.
• Amoxicillin and ampicillin are used for prophylaxis in adults and children who have certain cardiac conditions that put them at high or moderate risk of enterococcal endocarditis and who are undergoing certain GI, biliary, or genitourinary tract surgery or instrumentation likely to cause transient bacteremia and increase their risk of developing enterococcal endocarditis.
• Amoxicillin and ampicillin are used for prophylaxis of bacterial endocarditis in adults and children with congenital heart disease, rheumatic or other acquired valvular heart dysfunction (even after valvular surgery), prosthetic heart valves (including bioprosthetic and allograft valves), surgically constructed systemic pulmonary shunts or conduits, hypertrophic cardiomyopathy, mitral valve prolapse with valvular regurgitation and/or thickened leaflets, or previous bacterial endocarditis (even in the absence of heart disease) who undergo certain dental and upper respiratory tract procedures likely to cause transient bacteremia and increase the risk of endocarditis caused by viridans streptococci or certain GI, biliary, or genitourinary procedures likely to cause transient bacteremia and increase the risk of enterococcal endocarditis.
• Amoxicillin and ampicillin are the preferred anti-infectives for prophylaxis of bacterial endocarditis in patients undergoing certain dental and upper respiratory tract procedures who have cardiac conditions that put them at high or moderate risk of endocarditis.
• Amoxicillin is used as an alternative agent for postexposure prophylaxis following exposure to Bacillus anthracis spores, for the treatment of anthrax when a parenteral regimen is not available (e.g., when there are supply or logistic problems because large numbers of individuals require treatment in a mass casualty setting), and for the treatment of cutaneous anthrax.
• Amoxicillin and clavulanate potassium is a fixed combination of amoxicillin trihydrate (an aminopenicillin antibiotic) and the potassium salt of clavulanic acid (a beta-lactamase inhibitor); clavulanic acid synergistically expands amoxicillin’s spectrum of activity against many strains of beta-lactamase-producing bacteria.

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Contra Indications of Amoxicillin

• History of severe hypersensitivity (e.g. anaphylactic reaction) to any other type of betalactam antibacterial agent (penicillins, monobactams and carbapenems).
• Hemolytic anemia
• Liver problems
• Interstitial nephritis
• Subacute cutaneous lupus erythematosus
• Systemic lupus erythematosus
• use should be avoided in pregnant or lactating women, and in children with developing teeth because they may result in permanent staining (dark yellow-gray teeth with a darker horizontal band that goes across the top and bottom rows of teeth), and possibly affect the growth of teeth and bones.

Dosage of Amoxicillin

Strengths: 125 mg; 200 mg; 400 mg; 500 mg, 875 mg;600 mg; 775 mg 200 mg/5 mL; 400 mg/5 mL;

Bacterial Endocarditis Prophylaxis

American Heart Association (AHA) recommendations

• Immediate-release: 2 g orally as a single dose 30 to 60 minutes prior to procedure

Chlamydia Infection

US CDC recommendations

• 500 mg orally 3 times a day for 7 days in pregnant patients as an alternative to azithromycin

Helicobacter pylori Infection

Immediate-release

• Dual Therapy: 1 g orally every 8 hours for 14 days in combination with lansoprazole
• Triple Therapy: 1 g orally every 12 hours for 14 days in combination with clarithromycin and lansoprazole

Pneumonia

Immediate-release

• Mild, moderate, or severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA and American Thoracic Society (ATS) recommendations ,Pneumonia

• Immediate-release: 1 g orally 3 times a day

Bronchitis

Immediate-release

• Mild, moderate, or severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA and American Thoracic Society (ATS) recommendations ,Pneumonia

• Immediate-release: 1 g orally 3 times a day

Sinusitis

Immediate-release

• Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
• Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Urinary Tract Infection

Immediate-release

• Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
• Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Tonsillitis/Pharyngitis

Extended-release

• 775 mg orally once a day within 1 hour after a meal for 10 days

Skin and Structure Infection

Immediate-release

• Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
• Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Pediatric Skin or Soft Tissue Infection

Immediate-Release Formulations ,Mild, Moderate, or Severe Infection

• 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

Immediate-Release Formulations:Mild to Moderate Infection:4 months or older

• Less than 40 kg: 20 mg/kg/day orally in divided doses every 8 hours or 25 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 250 mg orally every 8 hours or 500 mg every 12 hours

Severe Infection ;4 months or older

• Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours.

Immediate-Release Formulations;Mild to Moderate Infection4 months or older

• Less than 40 kg: 20 mg/kg/day orally in divided doses every 8 hours or 25 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 250 mg orally every 8 hours or 500 mg every 12 hours

Severe Infection 4 months or older

• Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours

Urinary Tract Infection

Immediate-Release Formulations ,Mild, Moderate, or Severe Infection

• 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

Pediatric Pneumonia

Immediate-Release Formulations ,Mild, Moderate, or Severe infection

• 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

4 months or older

• Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA and the Pediatric Infectious Diseases Society recommendatio ,Immediate-release formulations ,4 months or older

• Empiric therapy for presumed bacterial pneumonia: 90 mg/kg/day orally in 2 divided doses; maximum 4 g/day
• Streptococcus pneumoniae (penicillin minimum inhibitory concentration of 2 mcg/mL or less): 90 mg/kg/day orally in 2 divided doses or 45 mg/kg/day in 3 divided doses
• Group A Streptococcus: 50 to 75 mg/kg/day orally in 2 divided doses
• Haemophilus influenza typeable (A to F) or nontypeable: 75 to 100 mg/kg/day orally in 3 divided doses

Pediatric Dose for Bronchitis

Immediate-Release Formulations:Mild, Moderate, or Severe infection

• 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

4 months or older

• Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
• At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA and the Pediatric Infectious Diseases Society recommendations
Immediate-release formulations:4 months or older

• Empiric therapy for presumed bacterial pneumonia: 90 mg/kg/day orally in 2 divided doses; maximum 4 g/day
• Streptococcus pneumoniae (penicillin minimum inhibitory concentration of 2 mcg/mL or less): 90 mg/kg/day orally in 2 divided doses or 45 mg/kg/day in 3 divided doses
• Group A Streptococcus: 50 to 75 mg/kg/day orally in 2 divided doses
• Haemophilus influenza typeable (A to F) or nontypeable: 75 to 100 mg/kg/day orally in 3 divided doses

Tonsillitis/Pharyngitis

12 years or older

• Extended-release: 775 mg orally once a day within 1 hour after a meal for 10 days

IDSA recommendations

• Immediate-release: 50 mg/kg (maximum 1000 mg) orally once a day or 25 mg/kg (maximum 500 mg) twice a day

Side Effects of Amoxicillin

The most common side effects 

• allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue
• leukopenia/leukemia
• hemolytic anemia
• agranulocytosis
• pain, swelling, irritation where injected
• Abdominal pain
• sweating
• skin color change, mild diarrhea
• mild nausea
• loss of appetite
• vaginal discharge and itching
• swelling of feet or legs
• chest pain
• constipation
• a cough
• diarrhea or loose stools
• difficulty with breathing
• dizziness
• heartburn

More common

• Abdominal or stomach pain, discomfort, or tenderness
• chills or fever
• a headache, severe and throbbing
• joint or back pain
• muscle aching or cramping
• muscle pains or stiffness
• chest pressure or squeezing pain in the chest
• excessive sweating
• feeling of heaviness, pain, warmth and/or swelling in a leg or in the pelvis
• sudden tingling or coldness in an arm or leg
• sudden slow or difficult speech
• sudden drowsiness or need to sleep
• fast breathing
• sharp pain when taking a deep breath
• fast or slow heartbeat
• coughing up blood
• decreased amount of urine

Rare

• Anxiety
• change in vision
• seizures
• tremors
• weight loss
• chest pain or tightness
• confusion
• cough
• Agitation
• blurred vision
• chest pain or discomfort
• convulsions
• extra heartbeats
• hallucinations
• a headache
• irritability
• lightheadedness
• mood or mental changes
• muscle pain or cramps

Drug Interactions of Amoxicillin

Amoxicillin may interact with following drugs, supplements, & may change the efficacy of drugs

• antacids that contain aluminum, calcium, or magnesium
• birth control medications
• bismuth subsalicylate
• calcium supplements
• digoxin
• Rosuvastatin
• Duloxetine
• Albuterol
• Topiramate
• Carbamazepine
• Vitamin D3 (cholecalciferol)
• Alprazolam
• Cetirizine
• insulin
• iron supplements
• penicillin
• vitamin A derivatives (e.g. isotretinoin)
• warfarin
• zinc sulfate or gluconate

Pregnancy & Lactation Amoxicillin

FDA Pregnancy Category B

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