SUSTIVA (Page 7 of 10)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Efavirenz is an antiviral drug [see Clinical Pharmacology (12.4) ].

12.3 Pharmacokinetics

Absorption

Peak efavirenz plasma concentrations of 1.6-9.1 μM were attained by 5 hours following single oral doses of 100 mg to 1600 mg administered to uninfected volunteers. Dose-related increases in Cmax and AUC were seen for doses up to 1600 mg; the increases were less than proportional suggesting diminished absorption at higher doses.

In HIV-1-infected patients at steady state, mean Cmax , mean Cmin , and mean AUC were dose proportional following 200-mg, 400-mg, and 600-mg daily doses. Time-to-peak plasma concentrations were approximately 3-5 hours and steady-state plasma concentrations were reached in 6-10 days. In 35 patients receiving SUSTIVA 600 mg once daily, steady-state Cmax was 12.9 ± 3.7 μM (mean ± SD), steady-state Cmin was 5.6 ± 3.2 μM, and AUC was 184 ± 73 μM•h.

Effect of Food on Oral Absorption:

Capsules: Administration of a single 600-mg dose of efavirenz capsules with a high-fat/high-caloric meal (894 kcal, 54 g fat, 54% calories from fat) or a reduced-fat/normal-caloric meal (440 kcal, 2 g fat, 4% calories from fat) was associated with a mean increase of 22% and 17% in efavirenz AUC and a mean increase of 39% and 51% in efavirenz Cmax , respectively, relative to the exposures achieved when given under fasted conditions. See Dosage and Administration (2) and Patient Counseling Information (17.3).

Tablets: Administration of a single 600-mg efavirenz tablet with a high-fat/high-caloric meal (approximately 1000 kcal, 500-600 kcal from fat) was associated with a 28% increase in mean AUC of efavirenz and a 79% increase in mean Cmax of efavirenz relative to the exposures achieved under fasted conditions. See Dosage and Administration (2) and Patient Counseling Information (17.3).

Distribution

Efavirenz is highly bound (approximately 99.5-99.75%) to human plasma proteins, predominantly albumin. In HIV-1 infected patients (n=9) who received SUSTIVA 200 to 600 mg once daily for at least one month, cerebrospinal fluid concentrations ranged from 0.26 to 1.19% (mean 0.69%) of the corresponding plasma concentration. This proportion is approximately 3-fold higher than the non-protein-bound (free) fraction of efavirenz in plasma.

Metabolism

Studies in humans and in vitro studies using human liver microsomes have demonstrated that efavirenz is principally metabolized by the cytochrome P450 system to hydroxylated metabolites with subsequent glucuronidation of these hydroxylated metabolites. These metabolites are essentially inactive against HIV-1. The in vitro studies suggest that CYP3A and CYP2B6 are the major isozymes responsible for efavirenz metabolism.

Efavirenz has been shown to induce CYP enzymes, resulting in the induction of its own metabolism. Multiple doses of 200-400 mg per day for 10 days resulted in a lower than predicted extent of accumulation (22-42% lower) and a shorter terminal half-life of 40-55 hours (single dose half-life 52-76 hours).

Elimination

Efavirenz has a terminal half-life of 52-76 hours after single doses and 40-55 hours after multiple doses. A one-month mass balance/excretion study was conducted using 400 mg per day with a 14 C-labeled dose administered on Day 8. Approximately 14-34% of the radiolabel was recovered in the urine and 16-61% was recovered in the feces. Nearly all of the urinary excretion of the radiolabeled drug was in the form of metabolites. Efavirenz accounted for the majority of the total radioactivity measured in feces.

Special Populations

Gender and race: The pharmacokinetics of efavirenz in patients appear to be similar between men and women and among the racial groups studied.

Renal impairment: The pharmacokinetics of efavirenz have not been studied in patients with renal insufficiency; however, less than 1% of efavirenz is excreted unchanged in the urine, so the impact of renal impairment on efavirenz elimination should be minimal.

Hepatic impairment: A multiple-dose study showed no significant effect on efavirenz pharmacokinetics in patients with mild hepatic impairment (Child-Pugh Class A) compared with controls. There were insufficient data to determine whether moderate or severe hepatic impairment (Child-Pugh Class B or C) affects efavirenz pharmacokinetics.

Drug Interaction Studies

Efavirenz has been shown in vivo to cause hepatic enzyme induction, thus increasing the biotransformation of some drugs metabolized by CYP3A and CYP2B6. In vitro studies have shown that efavirenz inhibited CYP isozymes 2C9, 2C19, and 3A4 with Ki values (8.5-17 μM) in the range of observed efavirenz plasma concentrations. In in vitro studies, efavirenz did not inhibit CYP2E1 and inhibited CYP2D6 and CYP1A2 (Ki values 82-160 μM) only at concentrations well above those achieved clinically. The inhibitory effect on CYP3A is expected to be similar between 200-mg, 400-mg, and 600-mg doses of efavirenz. Coadministration of efavirenz with drugs primarily metabolized by 2C9, 2C19, and 3A isozymes may result in altered plasma concentrations of the coadministered drug. Drugs which induce CYP3A activity would be expected to increase the clearance of efavirenz resulting in lowered plasma concentrations.

Drug interaction studies were performed with efavirenz and other drugs likely to be coadministered or drugs commonly used as probes for pharmacokinetic interaction. The effects of coadministration of efavirenz on the Cmax , AUC, and Cmin are summarized in Table 8 (effect of efavirenz on other drugs) and Table 9 (effect of other drugs on efavirenz). For information regarding clinical recommendations see Contraindications (4.2) and Drug Interactions (7.1).

Table 8: Effect of Efavirenz on Coadministered Drug Plasma Cmax , AUC, and Cmin
Coadministered Drug Dose Efavirenz Dose Number of Subjects Coadministered Drug(mean % change)
Cmax (90% CI) AUC(90% CI) Cmin (90% CI)
↑ Indicates increase ↓ Indicates decrease ↔ Indicates no change or a mean increase or decrease of <10%.
a Compared with atazanavir 400 mg qd alone.
b Comparator dose of indinavir was 800 mg q8h x 10 days.
c Parallel-group design; n for efavirenz + lopinavir/ritonavir, n for lopinavir/ritonavir alone.
d Values are for lopinavir; the pharmacokinetics of ritonavir in this study were unaffected by concurrent efavirenz.
e 95% CI.
f Soft Gelatin Capsule.
g Tenofovir disoproxil fumarate.
h 90% CI not available.
i Relative to steady-state administration of voriconazole (400 mg for 1 day, then 200 mg po q12h for 2 days).
j Not available because of insufficient data.
NA = not available.
Atazanavir 400 mg qd with a light meal d 1‑20 600 mg qd with a light meal d 7‑20 27 ↓ 59%(49-67%) ↓ 74%(68-78%) ↓ 93%(90-95%)
400 mg qd d 1‑6, then 300 mg qd d 7‑20 with ritonavir 100 mg qd and a light meal 600 mg qd 2 h after atazanavir and ritonavir d 7‑20 13 ↑ 14%a (↓ 17-↑ 58%) ↑ 39%a (2-88%) ↑ 48%a (24-76%)
300 mg qd/ritonavir 100 mg qd d 1‑10 (pm), then 400 mg qd/ritonavir 100 mg qd d 11‑24 (pm) (simultaneous with efavirenz) 600 mg qd with a light snack d 11‑24 (pm) 14 ↑ 17%(8-27%) ↓ 42% (31-51%)
Indinavir 1000 mg q8h x 10 days 600 mg qd x 10 days 20
After morning dose b ↓ 33%b (26-39%) ↓ 39%b (24-51%)
After afternoon dose b ↓ 37%b (26-46%) ↓ 52%b (47-57%)
After evening dose ↓ 29%b (11-43%) ↓ 46%b (37-54%) ↓ 57%b (50-63%)
Lopinavir/ ritonavir 400/100 mg capsuleq12h x 9 days 600 mg qd x 9 days 11,7c d ↓ 19%d (↓ 36-↑ 3%) ↓ 39%d (3-62%)
600/150 mg tabletq12h x 10 days withefavirenz compared to400/100 mg q12h alone 600 mg qd x 9 days 23 ↑ 36%d (28-44%) ↑ 36%d (28-44%) ↑ 32%d (21-44%)
Nelfinavir 750 mg q8h x 7 days 600 mg qd x 7 days 10 ↑ 21%(10-33%) ↑ 20%(8-34%)
Metabolite AG-1402 ↓ 40%(30-48%) ↓ 37%(25-48%) ↓ 43%(21-59%)
Ritonavir 500 mg q12h x 8 days 600 mg qd x 10 days 11
After AM dose ↑ 24%(12-38%) ↑ 18%(6-33%) ↑ 42%(9-86%)e
After PM dose ↑ 24%(3-50%)e
Saquinavir SGCf 1200 mg q8h x 10 days 600 mg qd x 10 days 12 ↓ 50%(28-66%) ↓ 62%(45-74%) ↓ 56%(16-77%)e
Lamivudine 150 mg q12h x 14 days 600 mg qd x 14 days 9 ↑ 265%(37-873%)
Tenofovirg 300 mg qd 600 mg qd x 14 days 29
Zidovudine 300 mg q12h x 14 days 600 mg qd x 14 days 9 ↑ 225%(43-640%)
Maraviroc 100 mg bid 600 mg qd 12 ↓ 51%(37-62%) ↓ 45%(38-51%) ↓ 45%(28-57%)
Raltegravir 400 mg single dose 600 mg qd 9 ↓ 36%(2-59%) ↓ 36%(20-48%) ↓ 21%(↓ 51-↑ 28%)
Boceprevir 800 mg tid x 6 days 600 mg qd x 16 days NA ↓ 8%(↓ 22-↑ 8%) ↓ 19%(11-25%) ↓ 44%(26-58%)
Telaprevir 750 mg q8h x 10 days 600 mg qd x 20 days 21 ↓ 9%(↓ 18-↑ 2%) ↓ 26%(16-35%) ↓ 47%(35-56%)
Azithromycin 600 mg single dose 400 mg qd x 7 days 14 ↑ 22%(4-42%) NA
Clarithromycin 500 mg q12h x 7 days 400 mg qd x 7 days 11 ↓ 26%(15-35%) ↓ 39%(30-46%) ↓ 53%(42-63%)
14-OH metabolite ↑ 49%(32-69%) ↑ 34%(18-53%) ↑ 26%(9-45%)
Fluconazole 200 mg x 7 days 400 mg qd x 7 days 10
Itraconazole 200 mg q12h x 28 days 600 mg qd x 14 days 18 ↓ 37%(20-51%) ↓ 39%(21-53%) ↓ 44%(27-58%)
Hydroxy-itraconazole ↓ 35%(12-52%) ↓ 37%(14-55%) ↓ 43%(18-60%)
Posaconazole 400 mg (oral suspension) bid x 10 and 20 days 400 mg qd x 10 and 20 days 11 ↓ 45%(34-53%) ↓ 50%(40-57%) NA
Rifabutin 300 mg qd x 14 days 600 mg qd x 14 days 9 ↓ 32%(15-46%) ↓ 38%(28-47%) ↓ 45%(31-56%)
Voriconazole 400 mg po q12h x 1 day, then 200 mg po q12h x 8 days 400 mg qd x 9 days NA ↓ 61%h ↓ 77%h NA
300 mg po q12h days 2‑7 300 mg qd x 7 days NA ↓ 36%i (21-49%) ↓ 55%i (45-62%) NA
400 mg po q12h days 2‑7 300 mg qd x 7 days NA ↑ 23%i (↓ 1-↑ 53%) ↓ 7%i (↓ 23-↑ 13%) NA
Atorvastatin 10 mg qd x 4 days 600 mg qd x 15 days 14 ↓ 14%(1-26%) ↓ 43%(34-50%) ↓ 69%(49-81%)
Total active (including metabolites) ↓ 15%(2-26%) ↓ 32%(21-41%) ↓ 48%(23-64%)
Pravastatin 40 mg qd x 4 days 600 mg qd x 15 days 13 ↓ 32%(↓ 59-↑ 12%) ↓ 44%(26-57%) ↓ 19%(0-35%)
Simvastatin 40 mg qd x 4 days 600 mg qd x 15 days 14 ↓ 72%(63-79%) ↓ 68%(62-73%) ↓ 45%(20-62%)
Total active (including metabolites) ↓ 68%(55-78%) ↓ 60%(52-68%) NAj
Carbamazepine 200 mg qd x 3 days, 200 mg bid x 3 days, then 400 mg qd x 29 days 600 mg qd x 14 days 12 ↓ 20%(15-24%) ↓ 27%(20-33%) ↓ 35%(24-44%)
Epoxide metabolite ↓ 13%(↓ 30-↑ 7%)
Cetirizine 10 mg single dose 600 mg qd x 10 days 11 ↓ 24%(18-30%) NA
Diltiazem 240 mg x 21 days 600 mg qd x 14 days 13 ↓ 60%(50-68%) ↓ 69%(55-79%) ↓ 63%(44-75%)
Desacetyl diltiazem ↓ 64%(57-69%) ↓ 75%(59-84%) ↓ 62%(44-75%)
N- monodesmethyl diltiazem ↓ 28%(7-44%) ↓ 37%(17-52%) ↓ 37%(17-52%)
Ethinyl estradiol/ Norgestimate 0.035 mg/0.25 mg x 14 days 600 mg qd x 14 days
Ethinyl estradiol 21
Norelgestromin 21 ↓ 46%(39-52%) ↓ 64%(62-67%) ↓ 82%(79-85%)
Levonorgestrel 6 ↓ 80%(77-83%) ↓ 83%(79-87%) ↓ 86%(80-90%)
Lorazepam 2 mg single dose 600 mg qd x 10 days 12 ↑ 16%(2-32%) NA
Methadone Stablemaintenance 35-100 mg daily 600 mg qd x 14-21 days 11 ↓ 45%(25-59%) ↓ 52%(33-66%) NA
Bupropion 150 mg single dose(sustained-release) 600 mg qd x 14 days 13 ↓ 34%(21-47%) ↓ 55%(48-62%) NA
Hydroxy- bupropion ↑ 50%(20-80%) NA
Paroxetine 20 mg qd x 14 days 600 mg qd x 14 days 16
Sertraline 50 mg qd x 14 days 600 mg qd x 14 days 13 ↓ 29%(15-40%) ↓ 39%(27-50%) ↓ 46%(31-58%)
Table 9: Effect of Coadministered Drug on Efavirenz Plasma Cmax , AUC, and Cmin
Efavirenz(mean % change)
Coadministered Drug Dose Efavirenz Dose Number of Subjects Cmax (90% CI) AUC(90% CI) Cmin (90% CI)
↑ Indicates increase ↓ Indicates decrease ↔ Indicates no change or a mean increase or decrease of <10%.
a Parallel-group design; n for efavirenz + lopinavir/ritonavir, n for efavirenz alone.
b 95% CI.
c Soft Gelatin Capsule.
d Tenofovir disoproxil fumarate.
e 90% CI not available.
f Relative to steady-state administration of efavirenz (600 mg once daily for 9 days).
NA = not available.
Indinavir 800 mg q8h x 14 days 200 mg qd x 14 days 11
Lopinavir/ ritonavir 400/100 mg q12h x 9 days 600 mg qd x 9 days 11,12a ↓ 16%(↓ 38-↑ 15%) ↓ 16%(↓ 42-↑ 20%)
Nelfinavir 750 mg q8h x 7 days 600 mg qd x 7 days 10 ↓ 12%(↓ 32-↑ 13%)b ↓ 12%(↓ 35-↑ 18%)b ↓ 21%(↓ 53-↑ 33%)
Ritonavir 500 mg q12h x 8 days 600 mg qd x 10 days 9 ↑ 14%(4-26%) ↑ 21%(10-34%) ↑ 25%(7-46%)b
Saquinavir SGCc 1200 mg q8h x 10 days 600 mg qd x 10 days 13 ↓ 13%(5-20%) ↓ 12%(4-19%) ↓ 14%(2-24%)b
Tenofovird 300 mg qd 600 mg qd x 14 days 30
Boceprevir 800 mg tid x 6 days 600 mg qd x 16 days NA ↑ 11%(2-20%) ↑ 20%(15-26%) NA
Telaprevir 750 mg q8h x 10 days 600 mg qd x 20 days 21 ↓ 16%(7-24%) ↓ 7%(2-13%) ↓ 2%(↓ 6-↑ 2%)
Telaprevir, coadministered with tenofovir disoproxil fumarate (TDF) 1125 mg q8h x 7 days 600 mg efavirenz/300 mg TDF qd x 7 days 15 ↓ 24%(15-32%) ↓ 18%(10-26%) ↓ 10%(↓ 19-↑ 1%)
1500 mg q12h x 7 days 600 mg efavirenz/300 mg TDF qd x 7 days 16 ↓ 20%(14-26%) ↓ 15%(9-21%) ↓ 11%(4-18%)
Azithromycin 600 mg single dose 400 mg qd x 7 days 14
Clarithromycin 500 mg q12h x 7 days 400 mg qd x 7 days 12 ↑ 11%(3-19%)
Fluconazole 200 mg x7 days 400 mg qd x 7 days 10 ↑ 16%(6-26%) ↑ 22%(5-41%)
Itraconazole 200 mg q12h x 14 days 600 mg qd x 28 days 16
Rifabutin 300 mg qd x 14 days 600 mg qd x 14 days 11 ↓ 12%(↓ 24-↑ 1%)
Rifampin 600 mg x7 days 600 mg qd x 7 days 12 ↓ 20%(11-28%) ↓ 26%(15-36%) ↓ 32%(15-46%)
Voriconazole 400 mg po q12hx 1 day, then 200 mg po q12hx 8 days 400 mg qd x 9 days NA ↑ 38%e ↑ 44%e NA
300 mg po q12h days 2-7 300 mg qd x 7 days NA ↓ 14%f (7-21%) f NA
400 mg po q12h days 2-7 300 mg qd x 7 days NA f ↑ 17%f (6-29%) NA
Atorvastatin 10 mg qd x4 days 600 mg qd x 15 days 14
Pravastatin 40 mg qd x4 days 600 mg qd x 15 days 11
Simvastatin 40 mg qd x4 days 600 mg qd x 15 days 14 ↓ 12%(↓ 28-↑ 8%) ↓ 12%(↓ 25-↑ 3%)
Aluminum hydroxide 400 mg, magnesium hydroxide 400 mg, plus simethicone 40 mg 30 mL single dose 400 mg single dose 17 NA
Carbamazepine 200 mg qd x 3 days, 200 mgbid x 3 days, then 400 mg qd x 15 days 600 mg qd x 35 days 14 ↓ 21%(15-26%) ↓ 36%(32-40%) ↓ 47%(41-53%)
Cetirizine 10 mg single dose 600 mg qd x 10 days 11
Diltiazem 240 mg x14 days 600 mg qd x 28 days 12 ↑ 16%(6-26%) ↑ 11%(5-18%) ↑ 13%(1-26%)
Famotidine 40 mg single dose 400 mg single dose 17 NA
Paroxetine 20 mg qd x 14 days 600 mg qd x 14 days 12
Sertraline 50 mg qd x 14 days 600 mg qd x 14 days 13 ↑ 11%(6-16%)

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