Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1     Pharmacodynamic properties
Pharmacotherapeutic group: Antivirals for systemic use, non-nucleoside reverse transcriptase inhibitors, ATC code J05AG01.

Mechanism of action

Nevirapine is a NNRTI of HIV-1. Nevirapine is a non-competitive inhibitor of the HIV-1 reverse transcriptase, but it does not have a biologically significant inhibitory effect on the HIV-2 reverse transcriptase or on eukaryotic DNA polymerases α, β, γ, or δ.

Antiviral activity in vitro

Nevirapine had a median EC50 value (50% inhibitory concentration) of 63 nM against a panel of group M HIV-1 isolates from clades A, B, C, D, F, G, and H, and circulating recombinant forms (CRF), CRF01_AE, CRF02_AG and CRF12_BF replicating in human embryonic kidney 293 cells. In a panel of 2,923 predominantly subtype B HIV-1 clinical isolates, the mean EC50 value was 90nM. Similar EC50 values are obtained when the antiviral activity of nevirapine is measured in peripheral blood mononuclear cells, monocyte derived macrophages or lymphoblastoid cell line. Nevirapine had no antiviral activity in cell culture against group O HIV-1 isolates or HIV-2 isolates.

Nevirapine in combination with efavirenz exhibited a strong antagonistic anti-HIV-1 activity in vitro (see section 4.5) and was additive to antagonistic with the protease inhibitor ritonavir or the fusion inhibitor enfuvirtide.
Nevirapine exhibited additive to synergistic anti-HIV-1 activity in combination with the protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, saquinavir and tipranavir, and the NRTIs abacavir, didanosine, emtricitabine, lamivudine, stavudine, tenofovir and zidovudine. The anti-HIV-1 activity of nevirapine was antagonized by the anti-HBV medicinal product adefovir and by the anti-HCV medicinal product ribavirin in vitro.
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Resistance
HIV-1 isolates with reduced susceptibility (100 - 250-fold) to nevirapine emerge in cell culture. Genotypic analysis showed mutations in the HIV-1 RT gene Y181C and/or V106A depending upon the virus strain and cell line employed. Time to emergence of nevirapine resistance in cell culture was not altered when selection included nevirapine in combination with several other NNRTIs
Genotypic analysis of isolates from antiretroviral naïve patients experiencing virologic failure (n=71) receiving nevirapine once daily (n=25) or twice daily (n=46) in combination with lamivudine and stavudine for 48 weeks showed that isolates from 8/25 and 23/46 patients, respectively, contained one or more of the following NNRTI resistance-associated substitutions: Y181C, K101E, G190A/S, K103N, V106A/M, V108I, Y188C/L, A98G, F227L and M230L.
Cross-resistance
Rapid emergence of HIV-strains which are cross-resistant to NNRTIs has been observed in vitro. Cross resistance to delavirdine and efavirenz is expected after virologic failure with nevirapine. Depending on resistance testing results, an etravirine-containing regimen may be used subsequently. Cross-resistance between nevirapine and either HIV protease inhibitors, HIV integrase inhibitors or HIV entry inhibitors is unlikely because the enzyme targets involved are different. Similarly the potential for cross-resistance between nevirapine and NRTIs is low because the molecules have different binding sites on the reverse transcriptase.

Clinical results

Viramune has been evaluated in both treatment naïve and treatment experienced patients.
Studies in treatment naïve patients
2NN study
The double non-nucleoside study 2 NN was a randomised, open-label, multicentre prospective study comparing the NNRTIs nevirapine, efavirenz and both medicinal products given together.
1,216 antiretroviral-therapy naïve patients with plasma HIV-1 RNA > 5,000 copies/ml at baseline were assigned to Viramune 400 mg once daily, Viramune 200 mg twice daily, efavirenz 600 mg once daily, or Viramune (400 mg) and efavirenz (800 mg) once daily, plus stavudine and lamivudine for 48 weeks.
The primary endpoint, treatment failure, was defined as less than 1 log10 decline in plasma HIV-1 RNA in the first 12 weeks, or two consecutive measurements of more than 50 copies/ ml from week 24 onwards, or disease progression.
Median age was 34 years and about 64% were male patients, median CD4 cell count was 170 and 190 cells per mm3 in the Viramune twice daily and efavirenz groups, respectively. There were no significant differences in demographic and baseline characteristics between the treatment groups.
The predetermined primary efficacy comparison was between the Viramune twice daily and the efavirenz treatment groups.
The nevirapine twice daily regimen and the efavirenz regimen were not significantly different (p= 0.091) in terms of efficacy as measured by treatment failure, or . any component of treatment failure including virological failure.

The simultaneous use of nevirapine (400 mg) plus efavirenz (800 mg) was associated with the highest frequency of clinical adverse events and with the highest rate of treatment failure (53.1%). As the regimen of nevirapine plus efavirenz did not have additional efficacy and caused more adverse events than each medicinal product separately, this regimen is not recommended.

Twenty per cent of patients assigned to nevirapine twice daily and 18% of patients assigned to efavirenz had at least one grade 3 or 4 clinical adverse event. Clinical hepatitis reported as clinical adverse event occurred in 10 (2.6%) and 2 (0.5%) patients in the nevirapine twice daily and efavirenz groups respectively. The proportion of patients with at least one grade 3 or 4 liver-associated laboratory toxicity was 8.3% for nevirapine twice daily and 4.5% for efavirenz. Of the patients with grade 3 or 4 liver-associated laboratory toxicity, the proportions


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coinfected with hepatitis B or hepatitis C virus were 6.7% and 20.0% in the nevirapine twice daily group, 5.6% and 11.1% in the efavirenz group.

2NN Three-year follow-up-study

This is a retrospective multicentre study comparing the 3-year antiviral efficacy of Viramune and efavirenz in combination with stavudine and lamivudine in 2NN patients from week 49 to week 144.
Patients who participated in the 2NN study and were still under active follow-up at week 48 when the study closed and were still being treated at the study clinic, were asked to participate in this study. Primary study endpoints (percentage of patients with treatment failures) and secondary study endpoints as well as backbone therapy were similar to the original 2NN study.



A durable response to Viramune for at least three years was documented in this study, and equivalence within a 10 % range was demonstrated between Viramune 200 mg twice daily and efavirenz with respect to treatment failure. Both, the primary (p = 0.92) and secondary endpoints showed no statistically significant differences between efavirenz and Viramune 200 mg twice daily.

Studies in treatment experienced patients

NEFA study
The NEFA study is a controlled prospective randomised study which evaluated treatment options for patients who switch from protease inhibitor (PI) based regimen with undetectable load to either Viramune, efavirenz or abacavir.
The study randomly assigned 460 adults who were taking two nucleoside reverse-transcriptase inhibitors and at least one PI and whose plasma HIV-1 RNA levels had been less than 200 c/ml for at least the previous six months to switch from the PI to Viramune (155 patients), efavirenz (156), or abacavir (149).
The primary study endpoint was death, progression to the acquired immunodeficiency syndrome, or an increase in HIV-1 RNA levels to 200 copies or more per millilitre.

At 12 months, the Kaplan–Meier estimates of the likelihood of reaching the endpoint were 10 % in the Viramune group, 6 % in the efavirenz group, and 13 percent in the abacavir group (P=0.10 according to an intention-to-treat analysis).

The overall incidence of adverse events was significantly lower (61 patients, or 41%) in the abacavir group than in the nevirapine group (83 patients, or 54%) or the efavirenz group (89 patients, or 57%). Significantly fewer patients in the abacavir group (9 patients, or 6%) than in the nevirapine group (26 patients, or 17%) or the efavirenz group (27 patients, or 17%) discontinued the medicinal product because of adverse events Perinatal Transmission


Numerous studies have been performed examining the use of Viramune in regards to perinatal transmission, most notably HIVNET 012. This study demonstrated a significant reduction in transmission using single dose nevirapine
(13.1% (n = 310) in the Viramune group, versus 25.1% (n = 308 in the ultra-short zidovudine group (p = 0.00063)).


Monotherapy with Viramune has been associated with the development of NNRTI resistance. Single dose nevirapine in mothers or infants may lead to reduced efficacy if an HIV treatment regimen using nevirapine is later instituted within 6 months or less in these patients. Combination of other antiretrovirals with single-dose nevirapine attenuates the emergence of nevirapine resistance. Where other antiretroviral medicines are accessible, the single dose Viramune regimen should be combined with additional effective antiretroviral medicines (as recommended in internationally recognized guidelines).
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The clinical relevance of these data in European populations has not been established. Furthermore, in the case Viramune is used as single dose to prevent vertical transmission of HIV-1 infection, the risk of hepatotoxicity in mother and child cannot be excluded.

Paediatric population
Results of a 48-week analysis of the South African study BI 1100.1368 confirmed that the 4/7 mg/kg and 150 mg/m2 nevirapine dose groups were well tolerated and effective in treating antiretroviral naive paediatric patients.
A marked improvement in the CD4+ cell percent was observed through Week 48 for both dose groups. Also, both dosing regimens were effective in reducing the viral load. In this 48-week study no unexpected safety findings were observed in either dosing group.

Pharmacokinetic Properties

5.2     Pharmacokinetic properties
Viramune tablets and oral suspension have been shown to be comparably bioavailable and interchangeable at doses up to 200 mg.
Absorption: Nevirapine is readily absorbed (> 90 %) after oral administration in healthy volunteers and in adults with HIV-1 infection. Absolute bioavailability in 12 healthy adults following single-dose administration was 93 ± 9 % (mean SD) for a 50 mg tablet and 91 ± 8 % for an oral solution. Peak plasma nevirapine concentrations of 2 ± 0.4 µg/ml (7.5 µM) were attained by 4 hours following a single 200 mg dose. Following multiple doses,
nevirapine peak concentrations appear to increase linearly in the dose range of 200 to 400 mg/day. Data reported in the literature from 20 HIV infected patients suggest a steady state Cmax of 5.74 µg/ml (5.00-7.44) and Cmin of 3.73 µg/ml (3.20-5.08) with an AUC of 109.0 h*µg/ml (96.0-143.5) in patients taking 200 mg of nevirapine bid.
Other published data support these conclusions. Long-term efficacy appears to be most likely in patients whose nevirapine trough levels exceed 3.5 µg/ml.
Distribution: Nevirapine is lipophilic and is essentially nonionized at physiologic pH. Following intravenous administration to healthy adults, the volume of distribution (Vdss) of nevirapine was 1.21 ± 0.09 l/kg, suggesting that nevirapine is widely distributed in humans. Nevirapine readily crosses the placenta and is found in breast milk. Nevirapine is about 60 % bound to plasma proteins in the plasma concentration range of 1-10 µg/ml.

Nevirapine concentrations in human cerebrospinal fluid (n = 6) were 45 % (± 5 %) of the concentrations in plasma; this ratio is approximately equal to the fraction not bound to plasma protein.
Biotransformation and elimination: In vivo studies in humans and in vitro studies with human liver microsomes have shown that nevirapine is extensively biotransformed via cytochrome P450 (oxidative) metabolism to several hydroxylated metabolites. In vitro studies with human liver microsomes suggest that oxidative metabolism of nevirapine is mediated primarily by cytochrome P450 isozymes from the CYP3A family, although other isozymes may have a secondary role.
In a mass balance/excretion study in eight healthy male volunteers dosed to steady state with nevirapine 200 mg given twice daily followed by a single 50 mg dose of 14C-nevirapine, approximately 91.4 ± 10.5 % of the radiolabelled dose was recovered, with urine (81.3 ± 11.1 %) representing the primary route of excretion compared to faeces (10.1 ± 1.5 %). Greater than 80 % of the radioactivity in urine was made up of glucuronide conjugates of hydroxylated metabolites. Thus cytochrome P450 metabolism, glucuronide conjugation, and urinary excretion of glucuronidated metabolites represent the primary route of nevirapine biotransformation and elimination in humans. Only a small fraction (< 5 %) of the radioactivity in urine (representing < 3 % of the total dose) was made up of parent compound; therefore, renal excretion plays a minor role in elimination of the parent compound.
Nevirapine has been shown to be an inducer of hepatic cytochrome P450 metabolic enzymes. The pharmacokinetics of autoinduction is characterised by an approximately 1.5 to 2 fold increase in the apparent oral clearance of nevirapine as treatment continues from a single dose to two-to-four weeks of dosing with 200-400 mg/day. Autoinduction also results in a corresponding decrease in the terminal phase half-life of nevirapine in plasma from approximately 45 hours (single dose) to approximately 25-30 hours following multiple dosing with 200-400 mg/day.



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Renal impairment: The single-dose pharmacokinetics of nevirapine has been compared in 23 patients with either mild (50 ≤ CLcr < 80 ml/min), moderate (30 ≤ CLcr < 50 ml/min) or severe renal dysfunction (CLcr < 30 ml/min), renal impairment or end-stage renal disease (ESRD) requiring dialysis, and 8 patients with normal renal function (CLcr > 80 ml/min). Renal impairment (mild, moderate and severe) resulted in no significant change in the pharmacokinetics of nevirapine. However, patients with ESRD requiring dialysis exhibited a 43.5 % reduction in nevirapine AUC over a one-week exposure period. There was also accumulation of nevirapine hydroxy- metabolites in plasma. The results suggest that supplementing nevirapine therapy with an additional 200 mg dose of Viramune following each dialysis treatment would help offset the effects of dialysis on nevirapine clearance.
Otherwise patients with CLcr ≥ 20 ml/min do not require an adjustment in nevirapine dosing.

Hepatic impairment: A steady state study comparing 46 patients with mild (n=17: Ishak Score 1-2), moderate (n=20; Ishak Score 3-4), or severe (n=9; Ishak Score 5-6, Child-Pugh A in 8 pts., for 1 Child-Pugh score not applicable) liver fibrosis as a measure of hepatic impairment was conducted.

The patients studied were receiving antiretroviral therapy containing Viramune 200 mg twice daily for at least 6 weeks prior to pharmacokinetic sampling, with a median duration of therapy of 3.4 years. In this study, the multiple dose pharmacokinetic disposition of nevirapine and the five oxidative metabolites were not altered.

However, approximately 15% of these patients with hepatic fibrosis had nevirapine trough concentrations above 9,000 ng/ml (2 fold the usual mean trough). Patients with hepatic impairment should be monitored carefully for evidence of medicinal product induced toxicity.

In a 200 mg nevirapine single dose pharmacokinetic study of HIV-negative patients with mild and moderate hepatic impairment (Child-Pugh A, n=6; Child-Pugh B, n=4), a significant increase in the AUC of nevirapine was observed in one Child-Pugh B patient with ascites suggesting that patients with worsening hepatic function and ascites may be at risk of accumulating nevirapine in the systemic circulation. Because nevirapine induces its own metabolism with multiple dosing, this single dose study may not reflect the impact of hepatic impairment on multiple dose pharamcokinetics (see section 4.4).

Gender and elderly
In the multinational 2NN study, a population pharmacokinetic substudy of 1077 patients was performed that included 391 females. Female patients showed a 13.8% lower clearance of nevirapine than did male patients. This difference is not considered clinically relevant. Since neither body weight nor Body Mass Index (BMI) had influence on the clearance of nevirapine, the effect of gender cannot be explained by body size Nevirapine pharmacokinetics in HIV-1 infected adults does not appear to change with age (range 19-68 years) or race (Black, Hispanic, or Caucasian). Nevirapine has not been specifically investigated in patients over the age of 65.

Paediatric population

Data concerning the pharmacokinetics of nevirapine have been derived from two major sources: a 48 week paediatric study in South Africa (BI 1100.1368) involving 123 HIV-1 positive, antiretroviral naïve patients aged 3 months to 16 years; and a consolidated analysis of five Paediatric AIDS Clinical Trials Group (PACTG) protocols comprising 495 patients aged 14 days to 19 years.

Pharmacokinetic data on 33 patients (age range 0.77 – 13.7 years) in the intensive sampling group demonstrated that clearance of nevirapine increased with increasing age in a manner consistent with increasing body surface area. Dosing of nevirapine at 150 mg/m2 BID (after a two-week lead in at 150 mg/m2 QD) produced geometric mean or mean trough nevirapine concentrations between 4-6 µg/ml (as targeted from adult data). In addition, the observed trough nevirapine concentrations were comparable between the two methods.

The consolidated analysis of Paediatric AIDS Clinical Trials Group (PACTG) protocols 245, 356, 366, 377, and   403 allowed for the evaluation of paediatric patients less than 3 months of age (n=17) enrolled in these PACTG studies. The plasma nevirapine concentrations observed were within the range observed in adults and the remainder of the paediatric population, but were more variable between patients, particularly in the second month of age.