Azithromycin Monohydrate (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)]

10 OVERDOSAGE

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.

11 DESCRIPTION

Azithromycin tablets USP contain the active ingredient azithromycin, 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 C 38 H 72 N 2 O 12 , and its molecular weight is 749.00. Azithromycin has the following structural formula:

structural formula
(click image for full-size original)

Azithromycin, as the monohydrate, is a white to almost white crystalline powder with a molecular formula of C 38 H 72 N 2 O 12 •H 2 O and a molecular weight of 767.00.

Azithromycin is supplied as tablets containing azithromycin monohydrate equivalent to either 250 mg or 500 mg azithromycin and the following inactive ingredients: croscarmellose sodium, dibasic calcium phosphate, hydroxypropyl methyl cellulose, lactose monohydrate, magnesium stearate, sodium lauryl sulfate, titanium dioxide, triacetin and D&C Red #30.

Organic Impurities Test Pending.

12 CLINICAL PHARMACOLOGY

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). Co-administration 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 AUC 0-72 =4.3 (1.2) mcg·hr/mL; C max =0.5 (0.2) mcg/mL; T max =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 AUC 0-∞ for the fitted concentration profile was comparable between the 5-day and 3-day regimens.

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

3-Day Regimen

5-Day Regimen

Pharmacokinetic Parameter [mean (SD)]

Day 1

Day 3

Day 1

Day 5

C max (serum, mcg/mL)

0.44 (0.22)

0.54 (0.25)

0.43 (0.20)

0.24 (0.06)

Serum AUC 0-∞ (mcg·hr/mL)

17.4 (6.2) *

14.9 (3.1) *

Serum T 1/2

71.8 hr

68.9 hr

Absorption
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 C max by 23% but had no effect on AUC.

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

Distribution
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.

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

Elimination
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 1.0 g dose of azithromycin (4 x 250 mg capsules), mean C max and AUC 0-120 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 C max and AUC 0-120 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 C max =0.216 mcg/mL, T max =1.9 hr, and AUC 0-24 =1.822 mcg·hr/mL for the 1 to 5-year-old group and were C max =0.383 mcg/mL, T max =2.4 hr, and AUC 0-24 =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/kg for 5 days)

N

17

C max (mcg/mL)

0.5 (0.4)

T max (hr)

2.2 (0.8)

AUC 0-24 (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 C max and AUC of azithromycin. No dosage adjustment of azithromycin is recommended when administered with drugs listed in Table 2. [see DRUG INTERACTIONS ( 7.3)]

*
-90% Confidence interval not reported

Table 1. Drug Interactions: Pharmacokinetic Parameters for Co-administered Drugs in the Presence of Azithromycin

Co-administered Drug

Dose of Co-administered Drug

Dose of Azithromycin

n

Ratio (with/without azithromycin) of Co-administered Drug Pharmacokinetic Parameters (90% CI); No Effect = 1.00

Mean C max

Mean AUC

Atorvastatin

10 mg/day for 8 days

500 mg/day orally on days 6 to 8

12

0.83 (0.63 to 1.08)

1.01 (0.81 to 1.25)

Carbamazepine

200 mg/day for 2 days, then 200 mg twice a day for 18 days

500 mg/day orally for days 16 to 18

7

0.97 (0.88 to 1.06)

0.96 (0.88 to 1.06)

Cetirizine

20 mg/day for 11 days

500 mg orally on day 7, then 250 mg/day on days 8 to 11

14

1.03 (0.93 to 1.14)

1.02 (0.92 to 1.13)

Didanosine

200 mg orally twice a day for 21 days

1200 mg/day orally on days 8 to 21

6

1.44 (0.85 to 2.43)

1.14 (0.83 to 1.57)

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 (0.98 to 1.11)

1.01 (0.97 to 1.05)

Indinavir

800 mg three times a day for 5 days

1200 mg orally on day 5

18

0.96 (0.86 to 1.08)

0.90 (0.81 to 1.00)

Midazolam

15 mg orally on day 3

500 mg/day orally for 3 days

12

1.27 (0.89 to 1.81)

1.26 (1.01 to 1.56)

Nelfinavir

750 mg three times a day for 11 days

1,200 mg orally on day 9

14

0.90 (0.81 to 1.01)

0.85 (0.78 to 0.93)

Sildenafil

100 mg on days 1 and 4

500 mg/day orally for 3 days

12

1.16 (0.86 to 1.57)

0.92 (0.75 to 1.12)

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 (1.02 to 1.40)

1.02 (0.86 to 1.22)

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 (0.92 to 1.29)

1.08 (0.89 to 1.31)

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/800 mg/day orally for 7 days

1200 mg orally on day 7

12

0.85 (0.75 to 0.97)/ 0.90 (0.78 to 1.03)

0.87 (0.80 to 0.95)/ 0.96 (0.88 to 1.03)

Zidovudine

500 mg/day orally for 21 days

600 mg/day orally for 14 days

5

1.12 (0.42 to 3.02)

0.94 (0.52 to 1.70)

Zidovudine

500 mg/day orally for 21 days

1200 mg/day orally for 14 days

4

1.31 (0.43 to 3.97)

1.30 (0.69 to 2.43)

*
-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-administered Drug

Dose of Azithromycin

n

Ratio (with/without co-administered drug) of Azithromycin Pharmacokinetic Parameters (90% CI); No Effect = 1.00

Mean C max

Mean AUC

Efavirenz

400 mg/day for 7 days

600 mg orally on day 7

14

1.22 (1.04 to 1.42)

0.92 *

Fluconazole

200 mg orally single dose

1,200 mg orally single dose

18

0.82 (0.66 to 1.02)

1.07 (0.94 to 1.22)

Nelfinavir

750 mg three times a day for 11 days

1,200 mg orally on day 9

14

2.36 (1.77 to 3.15)

2.12 (1.80 to 2.50)

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