Azithromycin (Page 4 of 8)

8.4 Pediatric Use

[see Clinical Pharmacology (12.3), Indications and Usage (1.2), and Dosage and Administration (2.2)]

Safety and effectiveness in the treatment of pediatric patients with acute otitis media, acute bacterial sinusitis and community-acquired pneumonia under 6 months of age have not been established. Use of azithromycin for the treatment of acute bacterial sinusitis and community-acquired pneumonia in pediatric patients (6 months of age or greater) is supported by adequate and well-controlled trials in adults.

Pharyngitis/Tonsillitis: Safety and effectiveness in the treatment of pediatric patients with pharyngitis/tonsillitis under 2 years of age have not been established.

8.5 Geriatric Use

In multiple-dose clinical trials of oral azithromycin, 9% of patients were at least 65 years of age (458/4949) and 3% of patients (144/4949) were at least 75 years of age. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in response between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

Elderly patients may be more susceptible to development of torsades de pointes arrhythmias than younger patients [ see WARNINGS AND PRECAUTIONS (5.4)].


Adverse reactions experienced at higher than recommended doses were similar to those seen at normal doses particularly nausea, diarrhea, and vomiting. In the event of overdosage, general symptomatic and supportive measures are indicated as required.


Azithromycin tablets, USP contain the active ingredient azithromycin, USP a macrolide antibacterial drug, for oral administration. Azithromycin has the chemical name (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl) oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6-trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one. Azithromycin is derived from erythromycin; however, it differs chemically from erythromycin in that a methyl-substituted nitrogen atom is incorporated into the lactone ring. Its molecular formula is C38 H72 N2 O12 , and its molecular weight is 749. Azithromycin has the following structural formula:

(click image for full-size original)

Azithromycin as the dihydrate, is a white or almost white powder with a molecular formula of C38 H72 N2 O12 •2H2 O and a molecular weight of 785.02.

Azithromycin tablets, USP are supplied for oral administration as pink modified capsule shaped, film-coated tablets containing azithromycin dihydrate equivalent to 500 mg azithromycin, USP and the following inactive ingredients: anhydrous dibasic calcium phosphate, croscarmellose sodium, hydroxypropyl cellulose, magnesium stearate, sodium lauryl sulfate, lactose monohydrate, hypromellose, titanium dioxide, triacetin and D&C Red #30 Aluminum Lake. FDA approved dissolution specification differs from the USP dissolution specification.


12.1 Mechanism of Action

Azithromycin is a macrolide antibacterial drug [see Microbiology (12.4)].

12.2 Pharmacodynamics

Based on animal models of infection, the antibacterial activity of azithromycin appears to correlate with the ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC) for certain pathogens (S. pneumoniae and S. aureus). The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with azithromycin.

Cardiac Electrophysiology

QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthy subjects who received either chloroquine (1000 mg) alone or in combination with oral azithromycin (500 mg, 1000 mg, and 1500 mg once daily). Coadministration of azithromycin increased the QTc interval in a dose-and concentration-dependent manner. In comparison to chloroquine alone, the maximum mean (95% upper confidence bound) increases in QTcF were 5 (10) ms, 7 (12) ms and 9 (14) ms with the co-administration of 500 mg, 1000 mg and 1500 mg azithromycin, respectively.

12.3 Pharmacokinetics

Following oral administration of a single 500 mg dose (two 250 mg tablets) to 36 fasted healthy male volunteers, the mean (SD) pharmacokinetic parameters were AUC0-72 =4.3 (1.2) mcg•hr/mL; Cmax =0.5 (0.2) mcg/mL; Tmax =2.2 (0.9) hours. Two azithromycin 250 mg tablets are bioequivalent to a single 500 mg tablet.

In a two-way crossover study, 12 adult healthy volunteers (6 males, 6 females) received 1500 mg of azithromycin administered in single daily doses over either 5 days (two 250 mg tablets on day 1, followed by one 250 mg tablet on days 2 to 5) or 3 days (500 mg per day for days 1 to 3). Due to limited serum samples on day 2 (3-day regimen) and days 2 to 4 (5-day regimen), the serum concentration-time profile of each subject was fit to a 3-compartment model and the AUC0-∞ for the fitted concentration profile was comparable between the 5-day and 3-day regimens.

3-DayRegimen 5-DayRegimen
Pharmacokinetic Parameter [mean (SD)] Day 1 Day 3 Day 1 Day 5
Cmax (serum, mcg/mL) 0.44(0.22) 0.54(0.25) 0.43(0.2) 0.24(0.06)
Serum AUC0-∞ (mcg•hr /mL) 17.4 (6.2)* 14.9 (3.1)*
Serum T1/2 71.8 hr 68.9 hr

*Total AUC for the entire 3-day and 5-day regimens.


The absolute bioavailability of azithromycin 250 mg capsules is 38%.

In a two-way crossover study in which 12 healthy subjects received a single 500 mg dose of azithromycin (two 250 mg tablets) with or without a high fat meal, food was shown to increase Cmax by 23% but had no effect on AUC.

When azithromycin oral suspension was administered with food to 28 adult healthy male subjects, Cmax increased by 56% and AUC was unchanged.


The serum protein binding of azithromycin is variable in the concentration range approximating human exposure, decreasing from 51% at 0.02 mcg/mL to 7% at 2 mcg/mL.

The antibacterial activity of azithromycin is pH related and appears to be reduced with decreasing pH, However, the extensive distribution of drug to tissues may be relevant to clinical activity.

Azithromycin has been shown to penetrate into human tissues, including skin, lung, tonsil, and cervix. Extensive tissue distribution was confirmed by examination of additional tissues and fluids (bone, ejaculum, prostate, ovary, uterus, salpinx, stomach, liver, and gallbladder). As there are no data from adequate and well-controlled studies of azithromycin treatment of infections in these additional body sites, the clinical significance of these tissue concentration data is unknown.

Following a regimen of 500 mg on the first day and 250 mg daily for 4 days, very low concentrations were noted in cerebrospinal fluid (less than 0.01 mcg/mL) in the presence of noninflamed meninges.


In vitro and in vivo studies to assess the metabolism of azithromycin have not been performed.


Plasma concentrations of azithromycin following single 500 mg oral and IV doses declined in a polyphasic pattern resulting in a mean apparent plasma clearance of 630 mL/min and terminal elimination half-life of 68 hr. The prolonged terminal half-life is thought to be due to extensive uptake and subsequent release of drug from tissues. Biliary excretion of azithromycin, predominantly as unchanged drug, is a major route of elimination. Over the course of a week, approximately 6% of the administered dose appears as unchanged drug in urine.

Specific Populations

Patients with Renal Impairment

Azithromycin pharmacokinetics was investigated in 42 adults (21 to 85 years of age) with varying degrees of renal impairment. Following the oral administration of a single 1 g dose of azithromycin (4 x 250 mg capsules), mean Cmax and AUC0-120 increased by 5.1% and 4.2%, respectively, in subjects with mild to moderate renal impairment (GFR 10 to 80 mL/min) compared to subjects with normal renal function (GFR >80 mL/min). The mean Cmax and AUC0-120 increased 61% and 35%, respectively, in subjects with severe renal impairment (GFR <10 mL/min) compared to subjects with normal renal function (GFR >80 mL/min).

Patients with Hepatic Impairment

The pharmacokinetics of azithromycin in subjects with hepatic impairment has not been established.

Male and Female Patients

There are no significant differences in the disposition of azithromycin between male and female subjects. No dosage adjustment is recommended based on gender.

Geriatric Patients

Pharmacokinetic parameters in older volunteers (65 to 85 years old) were similar to those in young adults (18 to 40 years old) for the 5-day therapeutic regimen. Dosage adjustment does not appear to be necessary for older patients with normal renal and hepatic function receiving treatment with this dosage regimen [see Geriatric Use (8.5)].

Pediatric Patients

In two clinical studies, azithromycin for oral suspension was dosed at 10 mg/kg on day 1, followed by 5 mg/kg on days 2 through 5 in two groups of pediatric patients (aged 1 to 5 years and 5 to 15 years, respectively). The mean pharmacokinetic parameters on day 5 were Cmax =0.216 mcg/mL, Tmax =1.9 hr, and AUC0-24 =1.822 mcg•hr/mL for the 1 to 5-year-old group and were Cmax =0.383 mcg/mL, Tmax =2.4 hr, and AUC0-24 =3.109 mcg•hr/mL for the 5 to 15-year-old group.

In another study, 33 pediatric patients received doses of 12 mg/kg/day (maximum daily dose 500 mg) for 5 days, of whom 31 patients were evaluated for azithromycin pharmacokinetics following a low fat breakfast. In this study, azithromycin concentrations were determined over a 24 hr period following the last daily dose. Patients weighing above 41.7 kg received the maximum adult daily dose of 500 mg. Seventeen patients (weighing 41.7 kg or less) received a total dose of 60 mg/kg. The following table shows pharmacokinetic data in the subset of pediatric patients who received a total dose of 60 mg/kg.

Pharmacokinetic Parameter [mean (SD)] 5-Day Regimen (12 mg/kgfor 5 days)
N 17
Cmax (mcg/mL) 0.5 (0.4)
Tmax (hr) 2.2 (0.8)
AUC0-24 (mcg•.hr/mL) 3.9 (1.9)

Single dose pharmacokinetics of azithromycin in pediatric patients given doses of 30 mg/kg have not been studied [see Dosage and Administration (2)].

Drug Interaction Studies

Drug interaction studies were performed with azithromycin and other drugs likely to be co-administered. The effects of co-administration of azithromycin on the pharmacokinetics of other drugs are shown in Table 1 and the effects of other drugs on the pharmacokinetics of azithromycin are shown in Table 2.

Co-administration of azithromycin at therapeutic doses had a modest effect on the pharmacokinetics of the drugs listed in Table 1. No dosage adjustment of drugs listed in Table 1 is recommended when co-administered with azithromycin.

Co-administration of azithromycin with efavirenz or fluconazole had a modest effect on the pharmacokinetics of azithromycin. Nelfinavir significantly increased the Cmax and AUC of azithromycin. No dosage adjustment of azithromycin is recommended when administered with drugs listed in Table 2 [see Drug Interactions (7.3)].

Table 1. DrugInteractions:Pharmacokinetic Parameters for Co-administeredDrugs in the Presence ofAzithromycin
Co-administered Drug Dose of Co-administeredDrug Dose of Azithromycin n Ratio (with/without azithromycin)ofCo­administeredDrugPharmacokineticParameters (90% CI); No Effect = 1
Mean C max Mean AUC
Atorvastatin 10 mg/dayfor 8 days 500 mg/day orally on days 6 to 8 12 0.83 (0.63to1.08) 1.01 (0.81to1.25)
Carbamazepine 200 mg/day for 2 days, then 200mg twice a day for 18 days 500 mg/day orally fordays 16 to 18 7 0.97 (0.88to1.06) 0.96 (0.88to1.06)
Cetirizine 20 mg/dayfor 11 days 500 mg orally on day 7, then 250 mg/day on days 8 to 11 14 1.03 (0.93to1.14) 1.02 (0.92to1.13)
Didanosine 200 mg orally twice a day for 21 days 1200 mg/day orally on days8 to 21 6 1.44 (0.85to2.43) 1.14(0.83to1.57)
Efavirenz 400 mg/day for 7 days 600 mg orally on day 7 14 1.04* 0.95*
Fluconazole 200 mg orally single dose 1200 mg orally single dose 18 1.04(0.98to1.11) 1.01(0.97to1.05)
Indinavir 800 mg three times a day for 5 days 1200 mg orally on day 5 18 0.96(0.86to1.08) 0.9(0.81to1)
Midazolam 15 mg orally on day 3 500 mg/day orally for 3 days 12 1.27(0.89to1.81) 1.26(1.01to1.56)
Nelfinavir 750 mg three times a day for 11 days 1,200 mg orally on day 9 14 0.9(0.81to1.01) 0.85(0.78to0.93)
Sildenafil 100 mg on days 1 and 4 500 mg/day orally for 3 days 12 1.16(0.86to1.57) 0.92(0.75to1.12)
Theophylline 4 mg/kg IV on days 1, 11, 25 500 mg orally on day 7, 250 mg/day on days 8 to 11 10 1.19(1.02to1.4) 1.02(0.86to1.22)
Theophylline 300 mg orally twice a day for 15 days 500 mg orally on day 6, then 250 mg/day on days 7 to 10 8 1.09(0.92to1.29) 1.08(0.89to1.31)
Triazolam 0.125 mg on day 2 500 mg orally on day 1, then 250 mg/day on day 2 12 1.06* 1.02*
Trimethoprim/Sulfamethoxazole 160 mg/800mg/day orally for 7 days 1200 mg orally on day 7 12 0.85(0.75to 0.97)/0.9 (0.78to1.03) 0.87(0.8to0.95)/0.96(0.88to1.03)
Zidovudine 500 mg/day orally for21days 600 mg/day orally for14 days 5 1.12(0.42to3.02) 0.94(0.52to1.7)
Zidovudine 500 mg/day orally for21days 1200 mg/day orally for 14 days 4 1.31(0.43to3.97) 1.3(0.69to2.43)

* -90% Confidence interval not reported

Table 2. Drug Interactions: Pharmacokinetic Parameters for Azithromycin in the Presence of Co-administered Drugs [see Drug Interactions (7)].
Co-administered Drug Dose of Co-administeredDrug Dose of Azithromycin n Ratio (with/without azithromycin)ofCo­administeredDrug PharmacokineticParameters (90% CI); No Effect = 1
Mean C max Mean AUC
Efavirenz 400 mg/day for 7 days 600 mg orally on day 7 14 1.22(1.04to1.42) 0.92*
Fluconazole 200 mg orally single dose 1,200 mg orally single dose 18 0.82(0.66to1.02) 1.07(0.94to1.22)
Nelfinavir 750 mg three times a day for 11 days 1,200 mg orally on day 9 14 2.36(1.77to3.15) 2.12(1.8to2.5)

* -90% Confidence interval not reported

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