Azithromycin (Page 3 of 14)

Drug-Drug Interactions

Drug interaction studies were performed with azithromycin and other drugs likely to be coadministered. 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.

Coadministration 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 coadministered with azithromycin.

Coadministration 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 Coadministered Drugs in the Presence of Azithromycin
*
– 90% Confidence interval not reported

Coadministered Drug

Dose of Coadministered Drug

Dose of Azithromycin

n

Ratio (With/Without Azithromycin) of Coadministered Drug Pharmacokinetic Parameters (90% CI); No Effect = 1

Mean Cmax

Mean AUC

Atorvastatin

10 mg/day x 8 days

500 mg/day PO on days 6 to 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 BID x 18 days

500 mg/day PO for days 16 to 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 to 11

14

1.03 (0.93 to 1.14)

1.02 (0.92 to 1.13)

Didanosine

200 mg PO BID x 21 days

1,200 mg/day PO on days 8 to 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 TID x 5 days

1,200 mg PO on day 5

18

0.96 (0.86 to 1.08)

0.90 (0.81 to 1)

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 TID x 11 days

1,200 mg PO on day 9

14

0.9 (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 to 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 to 11

10

1.19 (1.02 to 1.4)

1.02 (0.86 to 1.22)

Theophylline

300 mg PO BID x 15 days

500 mg PO 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 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)/0.9 (0.78 to 1.03)

0.87 (0.8 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 1.7)

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 coadministered with azithromycin and 71 ng/mL when coadministered with placebo.

Table 2. Drug Interactions: Pharmacokinetic Parameters for Azithromycin in the Presence of Coadministered Drugs (see PRECAUTIONS, Drug Interactions).
*
– 90% Confidence interval not reported

Coadministered Drug

Dose of Coadministered Drug

Dose of Azithromycin

n

Ratio (With/Without Coadministered Drug) of Azithromycin Pharmacokinetic Parameters (90% CI); No Effect = 1

Mean Cmax

Mean AUC

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 TID x 11 days

1,200 mg PO on day 9

14

2.36 (1.77 to 3.15)

2.12 (1.8 to 2.5)

Rifabutin

300 mg/day x 10 days

500 mg PO on day 1, then 250 mg/day on days 2 to 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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