Azithromycin (Page 3 of 13)

Drug-Drug Interactions

Drug interaction studies were performed with azithromycin and other drugs likely to be co-administered. The effects of coadministration of azithromycin on the pharmacokinetics of other drugs are shown in Table 1 and the effect 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 PRECAUTIONS: Drug Interactions).

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/with- out azithromycin) of Co- adminis - tered Drug Pharmacokinetic Parameters (90% CI); No Effect = 1.00
Mean Cmax Mean AUC
*
-90% Confidence interval not reported

Atorvastatin

10 mg/day

x 8 days

500 mg/day

PO on days 6-8

12

0.83

(0.63 to

1.08)

1.01

(0.81 to

1.25)

Carbamazepine

200 mg/day

x 2 days,

then 200 mg

b.i.d. x

18 days

500 mg/day

PO for

days 16-18

7

0.97

(0.88 to

1.06)

0.96

(0.88 to

1.06)

Cetirizine

20 mg/day

x 11 days

500 mg PO

on day 7,

then 250 mg/

day on days 8-11

14

1.03

(0.93 to

1.14)

1.02

(0.92 to

1.13)

Didanosine

200 mg PO

b.i.d. x

21 days

1,200 mg/

day PO on

days 8-21

6

1.44

(0.85 to

2.43)

1.14

(0.83 to

1.57)

Efavirenz

400 mg/day

x 7 days

600 mg PO

on day 7

14

1.04*

0.95*

Fluconazole

200 mg PO

single dose

1,200 mg PO

single dose

18

1.04

(0.98 to

1.11)

1.01

(0.97 to

1.05)

Indinavir

800 mg t.i.d.

x 5 days

1,200 mg PO

on day 5

18

0.96

(0.86 to

1.08)

0.90

(0.81 to

1.00)

Midazolam

15 mg PO

on day 3

500 mg/day

PO x 3 days

12

1.27

(0.89 to

1.81)

1.26

(1.01 to

1.56)

Nelfinavir

750 mg t.i.d.

x 11 days

1,200 mg PO

on day 9

14

0.90

(0.81 to

1.01)

0.85

(0.78 to

0.93)

Rifabutin

300 mg/day

x 10 days

500 mg PO

on day 1, then

250 mg/day

on days 2-10

6

See

footnote

below

NA

Sildenafil

100 mg on

days 1 and 4

500 mg/day

PO x 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 PO

on day 7,

250 mg/day

on days 8-11

10

1.19

(1.02 to

1.40)

1.02

(0.86 to

1.22)

Theophylline

300 mg PO

b.i.d x

15 days

500 mg PO

on day 6, then

250 mg/ day

on days 7-10

8

1.09

(0.92 to

1.29)

1.08

(0.89 to

1.31)

Triazolam

0.125 mg

on day 2

500 mg PO

on day 1, then

250 mg/day

on day 2

12

1.06*

1.02*

Trimethoprim/

Sulfamethoxazole

160 mg/

800 mg/day

PO x 7 days

1,200 mg PO

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

PO x 21 days

600 mg/day

PO x 14 days

5

1.12

(0.42 to

3.02)

0.94

(0.52 to

1.70)

Zidovudine

500 mg/day

PO x 21 days

1,200 mg/day

PO x 14 days

4

1.31

(0.43 to

3.97)

1.30

(0.69 to

2.43)

NA — Not Available

Mean rifabutin concentrations one-half day after the last dose of rifabutin were 60 ng/mL when co-administered with azithromycin and 71 ng/mL when co-administered with placebo.

Table 2. Drug Interactions: Pharmacokinetic Parameters for Azithromycin in the Presence of Co-administered Drugs (See PRECAUTIONS: Drug Interactions)
Co- administered Drug Dose of Co- Administered Drug Dose of Azithromycin n Ratio (with/with- out Co- adminis - tered Drug) of Azithromycin Pharmacokinetic Parameters (90% CI); No Effect = 1.00
Mean Cmax Mean AUC
*
-90% Confidence interval not reported

Efavirenz

400 mg/day

x 7 days

600 mg PO

on day 7

14

1.22

(1.04 to

1.42)

0.92*

Fluconazole

200 mg PO

single dose

1,200 mg PO

single dose

18

0.82

(0.66 to

1.02)

1.07

(0.94 to

1.22)

Nelfinavir

750 mg t.i.d.

x 11 days

1,200 mg PO

on day 9

14

2.36

(1.77 to

3.15)

2.12

(1.80 to

2.50)

Rifabutin

300 mg/day

x 10 days

500 mg PO

on day 1, then

250 mg/day

on days 2-10

6

See

Footnote

Below

NA

NA — Not Available

Mean azithromycin concentrations one day after the last dose were 53 ng/mL when coadministered with 300 mg daily rifabutin and 49 ng/mL when coadministered with placebo.

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