Azithromycin

The selected oral label covers adult bacterial exacerbations of chronic bronchitis, bacterial sinusitis, mild CAP appropriate for oral therapy, uncomplicated skin infections, second-line streptococcal pharyngitis/tonsillitis, urethritis/cervicitis, and chancroid in men. Pediatric scope includes otitis media and CAP from age 6 months and second-line pharyngitis/tonsillitis from age 2 years. Its dosage and population sections also describe pediatric bacterial sinusitis from age 6 months.

Selected IV Zithromax is labeled for adult CAP or PID requiring initial IV treatment; add anaerobic coverage for PID when such organisms are suspected. Oral therapy is inappropriate for moderate/severe pneumonia or important risk factors such as bacteremia, hospitalization need, cystic fibrosis, nosocomial infection, substantial debility, or impaired host response.

CDC does not recommend azithromycin for routine adult bacterial sinusitis because of pneumococcal resistance, and uncomplicated acute bronchitis generally needs no antibiotic. Doxycycline is CDC’s preferred adult/adolescent chlamydia regimen; azithromycin is an alternative with lower rectal efficacy. Gonorrhea treatment uses ceftriaxone-based guidance rather than azithromycin monotherapy. Use current syndrome-specific guidance and local susceptibility before choosing a labeled course.

Tablets and immediate-release suspension may be taken with or without food. The 1 g and 2 g totals are doses, not proof that a particular packet or ER bottle is interchangeable. For pregnancy-associated chlamydia, CDC recommends 1 g orally once; the complete diagnosis and follow-up plan remain necessary.

Verify weight and concentration: 100 mg/5 mL and 200 mg/5 mL are different. The label does not establish 1- or 3-day pediatric CAP regimens, or 1- or 5-day pediatric sinusitis regimens. Safety of re-dosing after vomiting the 30 mg/kg otitis dose is not established; contact the clinician rather than repeat it automatically. For confirmed group A strep in penicillin-allergic patients, CDC lists a different azithromycin course: 12 mg/kg (maximum 500 mg) once on day 1, then 6 mg/kg (maximum 250 mg) daily for 4 more days. Penicillin/amoxicillin remain preferred; macrolide resistance varies. The table above preserves the FDA label regimen, not a universal preferred course.

Switch according to clinical response. Infuse 1 mg/mL over 3 hours OR 2 mg/mL over 1 hour; never give an IV bolus or IM injection. Reconstitution alone is not ready for infusion: further dilution is mandatory.

These are label courses, not default current practice. CDC places azithromycin PID therapy among alternatives when cephalosporin allergy, low gonorrhea risk/prevalence, and reliable follow-up permit it. ATS’s 2025 public summary conditionally supports <5 days, minimum 3, for adult CAP outpatients who reach clinical stability. It does not authorize every patient to stop early or convert the pediatric CAP regimen.

Have the exact bottle constituted using its label: 300 mg and 600 mg bottles each use 9 mL water; 900 mg uses 12 mL; 1,200 mg uses 15 mL. Resulting total volumes are 15, 15, 22.5, and 30 mL respectively; only the 300 mg bottle makes 100 mg/5 mL. Shake well before each use and measure in mL. Severe renal impairment increases exposure; hepatic-impairment PK is unestablished. Neither selected label provides a validated numeric adjustment table for these conditions.

Known hypersensitivity to azithromycin, erythromycin, another macrolide, or a ketolide; and prior azithromycin-associated cholestatic jaundice or hepatic dysfunction. Existing liver disease alone is not the same wording as this specific prior-drug-injury contraindication.

The selected current U.S. Zithromax oral and IV labels do not carry a boxed warning. Their serious cardiac, hepatic, allergic, and C. difficile warnings still apply.

Diarrhea, nausea, abdominal pain, and vomiting are common; tolerability differs by dose and course. IV treatment also causes infusion-site pain or inflammation. Postmarketing reports include hearing impairment, severe skin reactions, arrhythmias, and liver injury; spontaneous reports cannot establish frequency.

Other QT-prolonging drugs, including class IA or III antiarrhythmics, compound the warning risk. Review the full medication list and correct relevant electrolyte disturbances as part of clinician-directed risk management.

Monitor prothrombin time with warfarin: postmarketing potentiation has been reported despite no effect in the dedicated interaction study. Nelfinavir increases azithromycin exposure; no routine dose change is recommended, but monitor liver abnormalities and hearing effects. For digoxin, colchicine, or phenytoin, dedicated azithromycin studies are lacking; the label advises careful monitoring based on other macrolides.

Do not take immediate-release oral azithromycin simultaneously with aluminum- or magnesium-containing antacids. The selected label does not specify a universal number of hours for separation; follow pharmacist instructions.

Available observational pregnancy data have not identified a drug-associated major-birth-defect or miscarriage signal, but cannot exclude risk. CDC recommends azithromycin 1 g once for chlamydia during pregnancy and a test of cure at about 4 weeks; retest at 3 months. Azithromycin enters milk: weigh maternal need and breastfeeding benefits, and monitor the infant for diarrhea, vomiting, or rash.

Oral otitis media, sinusitis, and CAP safety/effectiveness below 6 months and pharyngitis/tonsillitis below 2 years are unestablished. Selected IV pediatric safety/effectiveness are unestablished. Neonatal regimens for specific infections require separate specialist guidance. Older adults may be more susceptible to torsades; age alone does not eliminate the need to review illness severity and organ function. Each selected IV vial contains 114 mg (4.96 mEq) sodium, which contributes to the total sodium load in heart failure or other salt-sensitive conditions.

Single-dose PK studies show little change at GFR 10–80 mL/min, but at GFR <10 mL/min mean peak concentration and AUC rose approximately 61% and 35%. These studies do not establish a universal severe-renal dosing rule. Hepatic-impairment PK is not established; assess benefit and risk, watch for hepatitis, and avoid use after prior azithromycin-associated hepatic injury.

Azithromycin binds bacterial 23S rRNA in the 50S ribosomal subunit, inhibiting protein synthesis. Ribosomal target modification is a common resistance mechanism; cross-resistance with erythromycin occurs. Use culture, susceptibility, and local epidemiology when selecting therapy.

Long tissue persistence helps explain studied dosing schedules; it is not permission to invent a shorter regimen. IV and oral exposure differ, and food effects depend on formulation.

Peak after 500 mg tablets

About 2.2 hours in the label study

Terminal half-life

Approximately 68 hours

Major elimination route

Biliary excretion, predominantly unchanged drug

Tissue distribution

Extensive uptake and later release

Zmax is a distinct 2 g extended-release suspension bottle described in archived FDA labeling, not a Z-Pak or a 2 g immediate-release dose. The archived label requires an empty stomach (at least 1 hour before or 2 hours after food) and states it is not interchangeable with immediate-release courses. Current supply and current complete prescribing information were not verified here; this historical product is excluded from the dosing tables. Do not apply these fasting instructions to reviewed immediate-release tablets or suspension.

Review diagnosis, allergy history, prior azithromycin liver injury, QT-risk conditions and medicines, relevant electrolytes, and clinical response. ECG, laboratory testing, and organ monitoring depend on patient risk rather than a universal routine schedule. Monitor INR with warfarin and assess new hepatic, hearing, infusion-site, or diarrheal symptoms.

• Take the exact prescribed course; do not share, save for another illness, or use for a cold.
• Immediate-release tablets/suspension can be taken with or without food. Shake suspension well, verify concentration, and use a calibrated mL device. Avoid simultaneous aluminum/magnesium antacids.
• Get prompt assessment for fainting/palpitations, jaundice, severe rash, breathing difficulty, or persistent watery/bloody diarrhea.
• For STI treatment, complete testing, partner management, abstinence advice, and follow-up. Azithromycin is not reliable syphilis treatment.

CDC advises no sex for 7 days after single-dose chlamydia treatment and until partners are treated; retest at about 3 months. Persistent symptoms or possible rectal infection need reassessment. Excess doses chiefly intensify GI effects; management is supportive. U.S. Poison Control: 1-800-222-1222; call 911 for collapse, inability to awaken, or impaired breathing.

The reviewed label lists both imprint presentations. Confirm the actual NDC, strength, manufacturer, and package; photographs alone cannot establish identity.

Strength / form

250 mg film-coated oral tablet

Appearance

Pink, modified capsular shape

Imprint

PFIZER / 306 OR Pfizer / ZTM 250

Package example

Z-Pak of six 250 mg tablets; selected Pfizer label

Reviewed oral Zithromax: 250 mg and 500 mg tablets; constituted suspension 100 mg/5 mL or 200 mg/5 mL. Reviewed IV Zithromax: 500 mg single-dose vial requiring reconstitution and dilution. Separate 600 mg/MAC products, 1 g packet products, ophthalmic products, and historical Zmax have their own labeling and are not covered as interchangeable formulations.

Tablets: 15–30°C (59–86°F). Dry oral powder: below 30°C (86°F). Constituted immediate-release suspension: 5–30°C (41–86°F), tightly closed; use within 10 days and discard after completion of dosing.

Unreconstituted IV vials: at or below 30°C. Reconstituted 100 mg/mL solution: 24 hours below 30°C. After labeled dilution to 1–2 mg/mL: 24 hours at or below 30°C, or 7 days at 5°C. Inspect for particles, follow aseptic preparation policy, and do not add or simultaneously infuse other drugs through the same line. Label chemical stability does not replace sterile-compounding requirements.