Abacavir and Lamivudine (Page 4 of 7)

8.2 Lactation

Risk Summary
The Centers for Disease Control and Prevention recommends that HIV-1-infected mothers in the United States not breastfeed their infants to avoid risking postnatal transmission of HIV-1 infection. Abacavir and lamivudine are present in human milk. There is no information on the effects of abacavir and lamivudine on the breastfed infant or the effects of the drug on milk production. Because of the potential for (1) HIV-1 transmission (in HIV-negative infants), (2) developing viral resistance (in HIV-positive infants), and (3) adverse reactions in a breastfed infant similar to those seen in adults, instruct mothers not to breastfeed if they are receiving abacavir and lamivudine.

8.4 Pediatric Use

The dosing recommendations in this population are based on the safety and efficacy established in a controlled trial conducted using either the combination of EPIVIR and ZIAGEN or abacavir and lamivudine [see Dosage and Administration (2.3),Adverse Reactions (6.2), Clinical Studies (14.2)].

In pediatric patients weighing less than 25 kg, use of abacavir and lamivudine as single products is recommended to achieve appropriate dosing.

8.5 Geriatric Use

Clinical trials of abacavir and lamivudine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. In general, caution should be exercised in the administration of abacavir and lamivudine in elderly patients reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy [see Dosage and Administration (2.4),Use in Specific Populations (8.6,8.7)].

8.6 Patients with Impaired Renal Function

Abacavir and lamivudine is not recommended for patients with creatinine clearance less than 30 mL per min because abacavir and lamivudine is a fixed-dose combination and the dosage of the individual components cannot be adjusted. If a dose reduction of lamivudine, a component of abacavir and lamivudine, is required for patients with creatinine clearance less than 30 mL per min, then the individual components should be used [see Clinical Pharmacology (12.3)].

Patients with a creatinine clearance between 30 and 49 mL per min receiving abacavir and lamivudine may experience a 1.6- to 3.3-fold higher lamivudine exposure (AUC) than patients with a creatinine clearance ≥50 mL per min. There are no safety data from randomized, controlled trials comparing abacavir and lamivudine to the individual components in patients with a creatinine clearance between 30 and 49 mL per min who received dose-adjusted lamivudine. In the original lamivudine registrational trials in combination with zidovudine, higher lamivudine exposures were associated with higher rates of hematologic toxicities (neutropenia and anemia), although discontinuations due to neutropenia or anemia each occurred in <1% of subjects. Patients with a sustained creatinine clearance between 30 and 49 mL per min who receive abacavir and lamivudine should be monitored for hematologic toxicities. If new or worsening neutropenia or anemia develop, dose adjustment of lamivudine, per lamivudine prescribing information, is recommended. If lamivudine dose adjustment is indicated, abacavir and lamivudine should be discontinued and the individual components should be used to construct the treatment regimen.

8.7 Patients with Impaired Hepatic Function

Abacavir and lamivudine is a fixed-dose combination and the dosage of the individual components cannot be adjusted. If a dose reduction of abacavir, a component of abacavir and lamivudine, is required for patients with mild hepatic impairment (Child-Pugh Class A), then the individual components should be used [see Clinical Pharmacology (12.3)].

The safety, efficacy, and pharmacokinetic properties of abacavir have not been established in patients with moderate (Child-Pugh Class B) or severe (Child-Pugh Class C) hepatic impairment; therefore, abacavir and lamivudine is contraindicated in these patients [see Contraindications (4)].

10 OVERDOSAGE

There is no known specific treatment for overdose with abacavir and lamivudine. If overdose occurs, the patient should be monitored, and standard supportive treatment applied as required.

Abacavir: It is not known whether abacavir can be removed by peritoneal dialysis or hemodialysis.
Lamivudine: Because a negligible amount of lamivudine was removed via (4-hour) hemodialysis, continuous ambulatory peritoneal dialysis, and automated peritoneal dialysis, it is not known if continuous hemodialysis would provide clinical benefit in a lamivudine overdose event.

11 DESCRIPTION

Abacavir and Lamivudine

Abacavir and lamivudine tablets, USP contain the following 2 synthetic nucleoside analogues: abacavir (ZIAGEN, also a component of TRIZIVIR) and lamivudine (also known as EPIVIR or 3TC) with inhibitory activity against HIV-1.

Abacavir and lamivudine tablets, USP are for oral administration. Each orange colored, capsule-shaped, biconvex film coated tablet contains the active ingredients 600 mg of abacavir as abacavir sulfate USP and 300 mg of lamivudine USP, and the inactive ingredients magnesium stearate, microcrystalline cellulose, and sodium starch glycolate. The tablets are coated with a film (OPADRY orange YS-1-13065-A) that is made of FD&C Yellow No.6, hypromellose, polyethylene glycol 400, polysorbate 80, and titanium dioxide.

Abacavir Sulfate, USP

The chemical name of abacavir sulfate, USP is ( 1S, 4R)- 4-[2-amino-6-(cyclopropylamino)-9H -purin-9­yl]-2-cyclopentene-1-methanol sulfate (salt) (2:1). Abacavir sulfate is the enantiomer with 1S , 4R absolute configuration on the cyclopentene ring. It has a molecular formula of (C14 H18 N6 O)2 •H2 SO4 and a molecular weight of 670.74 g per mol. It has the following structural formula:

abacavir structure
(click image for full-size original)

Abacavir sulfate, USP is a white to almost white powder and is soluble in water.

In vivo , abacavir sulfate dissociates to its free base, abacavir. Dosages are expressed in terms of abacavir.

Lamivudine, USP

The chemical name of lamivudine, USP is (2(1H)-Pyrimidinone,4-amino-1-[2-(hydroxymethyl)-1,3-oxalathiolan-5-yl]-, (2Rcis)-. Lamivudine, USP is the (-)enantiomer of a dideoxy analogue of cytidine. Lamivudine, USP has also been referred to as (-)2′,3′-dideoxy, 3′-thiacytidine.. It has a molecular formula of C8 H11 N3 O3 S and a molecular weight of 229.26 g per mol. It has the following structural formula:

lamivudine structure
(click image for full-size original)

Lamivudine, USP is a white to almost white solid and is soluble in water, sparingly soluble in methanol, slightly soluble to practically insoluble in 96% ethanol and practically insoluble in acetone.

FDA approved dissolution test specifications differ from USP.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Abacavir and lamivudine is an antiretroviral agent with activity against HIV-1 [see Microbiology (12.4)].

12.3 Pharmacokinetics

Pharmacokinetics in Adults
In a single-dose, 3-way crossover bioavailability trial of 1 abacavir and lamivudine tablet versus 2 ZIAGEN tablets (2 x 300 mg) and 2 EPIVIR tablets (2 x 150 mg) administered simultaneously in healthy subjects (n = 25), there was no difference in the extent of absorption, as measured by the area under the plasma concentration-time curve (AUC) and maximal peak concentration (Cmax ), of each component.

Abacavir: Following oral administration, abacavir is rapidly absorbed and extensively distributed. After oral administration of a single dose of 600 mg of abacavir in 20 subjects, Cmax was 4.26±1.19 mcg per mL (mean ± SD) and AUC was 11.95 ± 2.51 mcg•hour per mL. Binding of abacavir to human plasma proteins is approximately 50% and was independent of concentration. Total blood and plasma drug-related radioactivity concentrations are identical, demonstrating that abacavir readily distributes into erythrocytes. The primary routes of elimination of abacavir are metabolism by alcohol dehydrogenase to form the 5’-carboxylic acid and glucuronyl transferase to form the 5’-glucuronide.

Lamivudine: Following oral administration, lamivudine is rapidly absorbed and extensively distributed. After multiple-dose oral administration of lamivudine 300 mg once daily for 7 days to 60 healthy subjects, steady-state Cmax (Cmax ,ss ) was 2.04 ± 0.54 mcg per mL (mean ± SD) and the 24-hour steady-state AUC (AUC24 ,ss ) was 8.87 ± 1.83 mcg•hour per mL. Binding to plasma protein is low. Approximately 70% of an intravenous dose of lamivudine is recovered as unchanged drug in the urine. Metabolism of lamivudine is a minor route of elimination. In humans, the only known metabolite is the trans-sulfoxide metabolite (approximately 5% of an oral dose after 12 hours).
In humans, abacavir and lamivudine are not significantly metabolized by cytochrome P450 (CYP) enzymes. The pharmacokinetic properties of abacavir and lamivudine in fasting subjects are summarized in Table 2.

Table 2. Pharmacokinetic Parametersa for Abacavir and Lamivudine in Adults
a Data presented as mean ± standard deviation except where noted.b Approximate range.
Parameter Abacavir Lamivudine
Oral bioavailability (%) 86 ±25 n = 6 86 ±16 n = 12
Apparent volume of distribution (L/kg) 0.86 ±0.15 n = 6 1.3 ±0.4 n = 20
Systemic clearance (L/h/kg) 0.80 ±0.24 n = 6 0.33 ±0.06 n = 20
Renal clearance (L/h/kg) 0.007 ±0.008 n = 6 0.22 ±0.06 n = 20
Elimination half-life (h) 1.45 ±0.32 n = 20 13 to 19b

Effect of Food on Absorption of Abacavir And Lamivudine

Abacavir and lamivudine may be administered with or without food. Administration with a high-fat meal in a single-dose bioavailability trial resulted in no change in AUClast , AUC , and Cmax for lamivudine. Food did not alter the extent of systemic exposure to abacavir (AUC ), but the rate of absorption (Cmax ) was decreased approximately 24% compared with fasted conditions (n = 25). These results are similar to those from previous trials of the effect of food on abacavir and lamivudine tablets administered separately.

Specific Populations

Patients with Renal Impairment: The pharmacokinetics for the individual lamivudine component of abacavir and lamivudine has been evaluated in patients with renal impairment (see the U.S. prescribing information for the individual lamivudine components).
Patients with Hepatic Impairment: The pharmacokinetics for the individual components of abacavir and lamivudine have been evaluated in patients with varying degrees of hepatic impairment (see the U.S. prescribing information for the individual abacavir and lamivudine components).

Pregnant Women: Abacavir: Abacavir pharmacokinetics were studied in 25 pregnant women during the last trimester of pregnancy receiving abacavir 300 mg twice daily. Abacavir exposure (AUC) during pregnancy was similar to those in postpartum and in HIV-infected non-pregnant historical controls. Consistent with passive diffusion of abacavir across the placenta, abacavir concentrations in neonatal plasma cord samples at birth were essentially equal to those in maternal plasma at delivery.

Lamivudine: Lamivudine pharmacokinetics were studied in 36 pregnant women during 2 clinical trials conducted in South Africa. Lamivudine pharmacokinetics in pregnant women were similar to those seen in non-pregnant adults and in postpartum women. Lamivudine concentrations were generally similar in maternal, neonatal, and umbilical cord serum samples.

Pediatric Patients: Abacavir and Lamivudine: The pharmacokinetic data for abacavir and lamivudine following administration of

abacavir and lamivudine in pediatric subjects weighing 25 kg and above are limited. The dosing recommendations in this population are based on the safety and efficacy established in a controlled trial conducted using either the combination of EPIVIR and ZIAGEN or abacavir and lamivudine. Refer to the EPIVIR and ZIAGEN USPI for pharmacokinetic information on the individual products in pediatric patients [see Dosage and Administration (2.3), Adverse Reactions (6.2),Clinical Studies (14.2)].

Geriatric Patients: The pharmacokinetics of abacavir and lamivudine have not been studied in subjects over 65 years of age.

Male and Female Patients: There are no significant or clinically relevant gender differences in the pharmacokinetics of the individual components (abacavir or lamivudine) based on the available information that was analyzed for each of the individual components.

Racial Groups: There are no significant or clinically relevant racial differences in pharmacokinetics of the individual components (abacavir or lamivudine) based on the available information that was analyzed for each of the individual components.
Drug Interaction Studies

The drug interactions described are based on trials conducted with abacavir or lamivudine as single entities; no drug interaction trials have been conducted with abacavir and lamivudine.

Effect of Abacavir and Lamivudine on the Pharmacokinetics of Other Agents: In vitro studies have shown that abacavir has potential to inhibit CYP1A1 and limited potential to inhibit metabolism mediated by CYP3A4. Lamivudine does not inhibit or induce CYP3A4. Abacavir and lamivudine do not inhibit or induce other CYP enzymes (such as CYP2C9 or CYP2D6). Based on in vitro study results, abacavir and lamivudine at therapeutic drug exposures are not expected to affect the pharmacokinetics of drugs that are substrates of the following transporters: organic anion transporter polypeptide (OATP)1B1/3, breast cancer resistance protein (BCRP) or P-glycoprotein (P-gp), organic cation transporter (OCT)1, OCT2, OCT3 (lamivudine only), or multidrug and toxic extrusion protein (MATE)1 and MATE2-K.

Riociguat: Coadministration of a single dose of riociguat (0.5 mg) to HIV-1–infected subjects receiving fixed-dose abacavir/dolutegravir/lamivudine is reported to increase riociguat AUC(∞) compared with riociguat AUC(∞) reported in healthy subjects due to CYP1A1 inhibition by abacavir. The exact magnitude of increase in riociguat exposure has not been fully characterized based on findings from two studies [see Drug Interactions (7.3)].

Effect of Other Agents on the Pharmacokinetics of Abacavir or Lamivudine: Abacavir and lamivudine are not significantly metabolized by CYP enzymes; therefore, CYP enzyme inhibitors or inducers are not expected to affect their concentrations. In vitro , abacavir is not a substrate of OATP1B1, OATP1B3, OCT1, OCT2, OAT1, MATE1, MATE2-K, multidrug resistance-associated protein 2 (MRP2) or MRP4; therefore, drugs that modulate these transporters are not expected to affect abacavir plasma concentrations. Abacavir is a substrate of BCRP and P-gp in vitro ; however, considering its absolute bioavailability (83%), modulators of these transporters are unlikely to result in a clinically relevant impact on abacavir concentrations.
Lamivudine is a substrate of MATE1, MATE2-K, and OCT2 in vitro. Trimethoprim (an inhibitor of these drug transporters) has been shown to increase lamivudine plasma concentrations. This interaction is not considered clinically significant as no dose adjustment of lamivudine is needed.
Lamivudine is a substrate of P-gp and BCRP; however, considering its absolute bioavailability (87%), it is unlikely that these transporters play a significant role in the absorption of lamivudine. Therefore, coadministration of drugs that are inhibitors of these efflux transporters is unlikely to affect the disposition and elimination of lamivudine.

Abacavir: Lamivudine and/or Zidovudine: Fifteen HIV-1-infected subjects were enrolled in a crossover-designed drug interaction trial evaluating single doses of abacavir (600 mg), lamivudine (150 mg), and zidovudine (300 mg) alone or in combination. Analysis showed no clinically relevant changes in the pharmacokinetics of abacavir with the addition of lamivudine or zidovudine or the combination of lamivudine and zidovudine. Lamivudine exposure (AUC decreased 15%) and zidovudine exposure (AUC increased 10%) did not show clinically relevant changes with concurrent abacavir.

Lamivudine: Zidovudine: No clinically significant alterations in lamivudine or zidovudine pharmacokinetics were observed in 12 asymptomatic HIV-1-infected adult subjects given a single dose of zidovudine (200 mg) in combination with multiple doses of lamivudine (300 mg every 12 h).

Other Interactions

Ethanol: Abacavir has no effect on the pharmacokinetic properties of ethanol. Ethanol decreases the elimination of abacavir causing an increase in overall exposure.

Interferon Alfa: There was no significant pharmacokinetic interaction between lamivudine and interferon alfa in a trial of 19 healthy male subjects.

Methadone: In a trial of 11 HIV-1-infected subjects receiving methadone-maintenance therapy (40 mg and 90 mg daily), with 600 mg of ZIAGEN twice daily (twice the currently recommended dose), oral methadone clearance increased 22% (90% CI: 6% to 42%) [see Drug Interactions (7)]. The addition of methadone has no clinically significant effect on the pharmacokinetic properties of abacavir.

Ribavirin: In vitro data indicate ribavirin reduces phosphorylation of lamivudine, stavudine, and zidovudine. However, no pharmacokinetic (e.g., plasma concentrations or intracellular triphosphorylated active metabolite concentrations) or pharmacodynamic (e.g., loss of HIV-1/HCV virologic suppression) interaction was observed when ribavirin and lamivudine (n = 18), stavudine (n = 10), or zidovudine (n = 6) were coadministered as part of a multi-drug regimen to HIV-1/HCV co-infected subjects.
Sorbitol (Excipient): Lamivudine and sorbitol solutions were coadministered to 16 healthy adult subjects in an open-label, randomized-sequence, 4-period, crossover trial. Each subject received a single 300-mg dose of lamivudine oral solution alone or coadministered with a single dose of 3.2 grams, 10.2 grams, or 13.4 grams of sorbitol in solution. Coadministration of lamivudine with sorbitol resulted in dose-dependent decreases of 20%, 39%, and 44% in the AUC(0 to 24) ; 14%, 32%, and 36% in the AUC(∞) ; and 28%, 52%, and 55% in the Cmax ; of lamivudine, respectively. The effects of other coadministered drugs on abacavir or lamivudine are provided in Table 3.

Table 3. Effect of Coadministered Drugs on Abacavir or Lamivudine
↑= Increase; ↔= No significant change; AUC = Area under the concentration versus time curve; CI = Confidence interval.a The drug-drug interaction was only evaluated in males.
Coadministered Drug and Dose Drug and Dose n Concentrations of Abacavir or Lamivudine Concentration of Coadministered Drug
AUC Variability
Ethanol 0.7 g/kg Abacavir Single 600 mg 24 ↑41% 90% CI: 35% to 48% a
Nelfinavir 750 mg every 8 h x 7 to 10 days Lamivudine Single 150 mg 11 ↑10% 95% CI: 1% to 20%
Trimethoprim 160 mg/ Sulfamethoxazole 800 mg daily x 5 days Lamivudine Single 300 mg 14 ↑43% 90% CI: 32% to 55%

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