Azithromycin

Oral Antibiotics

Drug class: Macrolide Antibiotics

Azithromycin (ZITHROMAX)（中文：阿奇霉素）

Common Strengths of Azithromycin

• Tablet: 250 mg, 500 mg
• Powder for IV injection: 500 mg/vial
• Azithromycin eye-drops 1.5%

Drug Trade Names

Zithromax

Drug Usage

The macrolides have an antibacterial spectrum similar but not identical to penicillin; they are thus an alternative in penicillin-allergic patients.

Azithromycin is indicated for treating:

• Respiratory infections (e.g. pneumonia, bronchitis) - Ear infections
• Skin and soft-tissue infections
• Sexually transmitted infections (e.g. chlamydia)
• Sinusitis

Mechanism of Action

Azithromycin binds to the 50S ribosomal subunit of bacteria, inhibiting protein synthesis. This action prevents bacterial growth, making it primarily bacteriostatic, although it can exhibit bactericidal properties at higher concentrations.

Route of Administration

Azithromycin can be administered:

• Orally (tablets, capsules, liquid)
• Intravenously (in hospital settings)
• Topically (for eye infections)

Dosages

For adults, standard dosages are as follows:

• Normal individuals: 500 mg on day 1, followed by 250 mg daily for 4 days.
• Diabetic kidney disease: Generally, no renal dose adjustment is required as azithromycin is primarily eliminated via biliary excretion.

Side Effects

Frequency	Adverse reactions
Common Side Effects	Nausea
	Diarrhea
	Abdominal pain
	Disturbances in taste
Allergic reactions (e.g. rash, swelling)
	Liver dysfunction (e.g. jaundice)
	Cardiac arrhythmias (especially QT prolongation)

Pharmacokinetics

• Azithromycin has a long half-life of approximately 68 hours, allowing for once-daily dosing.
• It is well absorbed but works best on an empty stomach.
• Azithromycin is primarily eliminated through biliary excretion.
• The onset of action typically occurs within a few hours after oral administration.

Drug Precautions

Pregnancy

Advise use only if no suitable alternatives not available

Breastfeeding

Present in milk; use only if no suitable alternatives.

Children and Elderly

Dosages may vary; children as young as 6 months can be prescribed azithromycin for certain conditions. Elderly patients may be more susceptible to cardiac side effects.

Drug Monitoring Items

Monitor liver function tests and cardiac rhythm in susceptible populations.

Drug Interactions

Azithromycin interacts with numerous medications, including:

• Anticoagulants: There is an increased risk of bleeding when azithromycin is taken with apixaban, dabigatran, and warfarin.
• Statins: Co-administration with clarithromycin can lead to increased plasma concentrations of these statins, raising the risk of myopathy and rhabdomyolysis. It is advised to suspend these statins during clarithromycin treatment.
• Colchicine: Concomitant use can significantly increase colchicine levels, especially in patients with renal or hepatic impairment, leading to toxicity. This combination is contraindicated.
• Digoxin: There is a potential for increased digoxin levels when taken with azithromycin, which may lead to toxicity
• Antidepressants and antipsychotics: Medications such as citalopram and certain antipsychotics can also interact with azithromycin, increasing the risk of QT prolongation (a heart rhythm disorder) which may be serious or fatal.
• Nelfinavir: This HIV medication can increase azithromycin serum concentrations, necessitating careful monitoring for liver enzyme abnormalities and hearing impairment.

Disease Interactions:

Azithromycin has four notable disease interactions:

• QT Prolongation: Patients with existing heart rhythm issues are at increased risk for serious arrhythmias when taking azithromycin.
• Liver Disease: Azithromycin can exacerbate liver problems; monitoring liver function is recommended for patients with pre-existing liver conditions.
• Colitis: Antibiotic-associated colitis is a risk, particularly in patients with a history of gastrointestinal issues.
• Myasthenia Gravis: Azithromycin may worsen symptoms in patients with this neuromuscular disorder.

FAQ

How Should I Take the Tablet?

Take azithromycin with a full glass of water; it can be taken with or without food.

What Should I Avoid while Taking?

Avoid taking azithromycin with certain drugs that may increase the risk of serious side effects, such as pimozide and other QT-prolonging agents.

What Happens If I Miss a Dose?

If you miss a dose, take it as soon as you remember unless it is close to the time for your next dose. Do not double up on doses.