Efavirenz (formerly L-743,726/DMP-266) targets human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) with an IC50 of 1.7 nM (enzyme activity inhibition) and an EC50 of 3.0 nM (anti-HIV-1 activity in cell culture)[1]

It is discovered that efavirenz (L-743726) may suppress a panel of mutant viruses resistant to nonnucleoside reverse transcriptase inhibitors (NNRTIs) that express a single RT amino acid substitution, with 95% inhibitory doses of ≤ 1.5μM. When efavirenz is examined for its ability to inhibit different polymerase enzymes, it is discovered that it lacks activity (IC50>300μM). Several wild-type T-lymphoid cell line-adapted variations are efficiently inhibited by efavirenz. In primary lymphoid and monocytoid cell cultures, wild-type primary isolates of the virus exhibit the same activity (IC95, 1.5 to 3.0 nM). Furthermore, HIV-1 genotypes that contain RT amino acid changes, which confer resistance to other NNRTIs, are effectively inhibited by efavirenz. for comparative purposes [1]. With an IC50 of 60 nM, efavirenz is a non-nucleoside analog reverse transcriptase inhibitor (NNRTI)[2]. With an IC50 of 17 nM, efavirenz inhibits synthesis utilizing an RNA PPT-primed substrate[3].

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Efavirenz potently inhibited the activity of purified recombinant HIV-1 RT in a concentration-dependent manner, achieving 50% inhibition at 1.7 nM and 90% inhibition at 8.0 nM[1]
- In HIV-1 (strain IIIB)-infected MT-4 lymphoblastoid cells, Efavirenz suppressed viral replication with an EC50 of 3.0 nM, and the therapeutic index (CC50/EC50) was greater than 3333 (CC50 > 10 μM, the concentration causing 50% cytotoxicity)[1]
- The compound showed no cross-resistance with nucleoside reverse transcriptase inhibitors (NRTIs) such as zidovudine (AZT), as it inhibited AZT-resistant HIV-1 strains with similar EC50 values (3.2 nM)[1]
- Efavirenz bound to the non-nucleoside binding pocket of HIV-1 RT, inducing a conformational change in the enzyme that abrogated its reverse transcription activity[1]

Efavirenz (L-743726) is eliminated from rats quickly after intravenous injection, but it is eliminated from monkeys much more slowly. In both species, the large volume of distribution (two to four times the body water content) suggests extensive tissue binding. Rats have a 16% oral bioavailability. After giving an intravenous dose of 1 mg/kg of Efavirenz, the half-life in monkeys was more than 2.5 hours. Orally, efavirenz is well absorbed. Plasma levels are consistently high when oral doses administered as fine suspensions in 0.5% aqueous methylcellulose are given to monkeys. Approximately 3.0 hours after a dose of 2.0 mg/kg, peak levels of 0.5μM are achieved. According to estimates, the absolute bioavailability is 42%. A plasma peak level of 3.22 μM is obtained with a dose of 10 mg/kg. One chimpanzee received an oral dose of 10 mg/kg, which resulted in plasma concentrations of 4.12, 2.95, and 2.69 μM at 2, 8, and 24 hours after dosing, respectively[1].

HIV-1 RT activity inhibition assay: Purified recombinant HIV-1 RT was incubated with serial concentrations of Efavirenz, a template-primer complex (poly(rC)-oligo(dG)), and [3H]-labeled deoxyguanosine triphosphate ([3H]-dGTP) in reaction buffer at 37°C for 60 minutes. The reaction was terminated by adding trichloroacetic acid (TCA), and the precipitated radioactivity (incorporated [3H]-dGTP) was measured using a liquid scintillation counter. Inhibition rate was calculated relative to the vehicle control, and IC50 was determined by nonlinear regression analysis[1]

Anti-HIV-1 cell culture assay: MT-4 cells were seeded in 96-well plates at a density of 2×10⁴ cells per well and infected with HIV-1 (strain IIIB) at a multiplicity of infection (MOI) of 0.01. Efavirenz was added at serial concentrations (0.1–1000 nM) immediately after infection, and cells were cultured at 37°C in a 5% CO₂ incubator for 5 days. Viral replication was assessed by measuring the cytopathic effect (CPE) using a microscope, and EC50 was calculated as the concentration inhibiting CPE by 50%. Cytotoxicity (CC50) was determined in uninfected MT-4 cells treated with the same compound concentrations, and the therapeutic index was calculated as CC50/EC50[1]
- AZT-resistant HIV-1 inhibition assay: The same cell culture protocol was used with AZT-resistant HIV-1 strains (strain A01A). Efavirenz concentrations were adjusted to 0.1–1000 nM, and EC50 was determined by CPE inhibition as described above[1]

Formulated in 0.5% methocel(oral); DMSO(i.v.); 10, 40, and 160 mg/kg(oral); 2, 5, 10, 15 mg/kg(i.v.); i.v. or p.o. administration
Sprague-Dawley rats

Absorption, Distribution and Excretion
Radiolabeled drugs are almost entirely excreted in the urine as metabolites. The oral bioavailability of efavirenz may be affected by food. Compared with fasting, taking 600 mg efavirenz capsules with a high-fat, high-calorie meal (894 kcal, 54 g fat, 54% of calories from fat) or a low-fat, normal-calorie meal (440 kcal, 2 g fat, 4% of calories from fat) increased peak plasma concentration by 39% and 51%, respectively, and AUC by 22% and 17%, respectively. A single dose of 600 mg efavirenz tablets, taken concurrently with a high-fat, high-calorie meal (approximately 1000 kcal, of which 500-600 kcal are from fat), increased peak plasma concentration and AUC by 79% and 28%, respectively, compared with fasting. Efavirenz is primarily excreted in the feces, as both unchanged drug and metabolites. Drug excretion has been assessed in subjects taking 400 mg efavirenz daily for one month. Following oral administration of 400 mg of radiolabeled efavirenz on day 8, 14–34% of the dose was excreted in the urine (less than 1% unchanged drug) and 16–61% in the feces (primarily unchanged drug). Efavirenz binds to plasma proteins at a rate of approximately 99.5–99.75%, primarily albumin. In HIV-infected adults taking 200, 400, or 600 mg efavirenz once daily, peak plasma concentrations typically occur within 3–5 hours, and steady-state plasma concentrations are reached within 6–10 days. With continued efavirenz administration, plasma concentrations are lower than expected in single-dose studies, likely due to increased drug clearance. In one study, subjects took efavirenz 200-400 mg once daily for 10 days, and the results showed that the plasma concentrations were 22-42% lower than predicted in single-dose studies. In HIV-infected adults, after a once-daily oral administration of 600 mg efavirenz, the mean steady-state peak plasma concentration, trough concentration, and AUC were 4.1 mcg/mL, 1.8 mcg/mL, and 58 mcg·h/mL, respectively. For more complete data on absorption, distribution, and excretion of efavirenz (8 items in total), please visit the HSDB records page. Metabolism/Metabolites efavirenz is primarily metabolized by the cytochrome P450 system to hydroxylated metabolites, which are subsequently further glucuroninated. These metabolites are essentially inactive against HIV-1. efavirenz is extensively metabolized in all species, with little or no detection of the parent compound in urine. Significant species differences exist in the metabolism of efavirenz. The major metabolite excreted in the urine of all species was the O-glucuronide conjugate of the 8-hydroxylated metabolite (M1). Efavirenz can also bind directly to glucuronic acid, generating N-glucuronide (M2) in all five species. The sulfate conjugate of 8-hydroxyevavirenz (M3) was present in the urine of rats and cynomolgus monkeys, but not detected in humans. In addition to the aromatic ring hydroxylated products, cyclopropane ring (C14) hydroxylated metabolites were also isolated. Glutathione (GSH)-related metabolites of evavirenz were identified in rats and guinea pigs. The cysteylglycine adduct (M10) formed from the glutathione adduct (M9) was present in large quantities only in the urine of rats and guinea pigs, and not detected in other species. In vitro metabolic studies showed that this glutathione adduct was generated from the cyclopropanol intermediate (M11) only in the presence of rat liver and kidney subcellular components, while it was not generated in similar preparations from humans or cynomolgus monkeys. These studies indicate the presence of a specific glutathione S-transferase in rats that metabolizes cyclopropanol metabolite (M11) to glutathione adduct M9. Efavirenz is a substrate for cytochrome P450 isoenzymes, particularly CYP3A4 and CYP2B6. The 8-hydroxy metabolite is excreted in the urine, while the glucuronide conjugate of 8-hydroxyevavirenz is present in both plasma and urine. 60% of the dose is excreted in the urine as the glucuronide conjugate. Known metabolites of evavirenz include 8-hydroxyevavirenz. Biological half-life: 40–55 hours. The terminal elimination half-life of evavirenz is prolonged in patients with chronic liver disease. After a single oral dose of 400 mg evavirenz, the elimination half-lives in patients with chronic liver disease and non-chronic liver disease were 152 hours and 118 hours, respectively.
The terminal elimination half-life of efavirenz reported in single-dose studies is longer than that reported in multiple-dose studies, averaging 52-76 hours after a single oral dose and 40-55 hours after 10 days of continuous daily administration of 200-400 mg.

Interactions
Alcohol abuse complicates the treatment of HIV infection and is associated with poor prognosis. Alcohol-based drug therapy, including disulfiram (DIS), is rarely used in patients with both HIV infection and alcohol use disorder, possibly due to concerns about drug interactions between antiretroviral (ARV) drugs and DIS. This pharmacokinetic study (n=40) investigated the effects of DIS on efavirenz (EFV), ritonavir (RTV), or atazanavir (ATV), and the effects of these ARV drugs on DIS metabolism and aldehyde dehydrogenase (ALDH) activity, which mediates the interaction between DIS and alcohol. EFV administration was associated with decreased levels of the DIS metabolite S-methyl-N,N-diethylthiocarbamate (DIS carbamate) (p=0.001), a precursor to the ALDH-inhibited metabolite S-methyl-N,N-diethylthiocarbamate sulfoxide (DETC-MeSO). Compared to DIS alone, EFV may induce CYP3A4 expression, which metabolizes carbamates to DETC-MeSO (which inhibits ALDH), thereby enhancing the inhibitory effect of DIS on ALDH activity. Conversely, ATV combination therapy may reduce the effect of DIS on ALDH activity due to ATV's inhibition of CYP3A4. DIS administration had no significant effect on any of the antiretroviral drugs studied. In patients taking psychoactive drugs, efavirenz may lead to enhanced central nervous system effects. Efavirenz may decrease plasma concentrations of ampravir; specific dose adjustments cannot be recommended until further studies are conducted. Efavirenz may increase the risk of arrhythmias by competitively inhibiting the metabolism of these drugs (astemizole or cisapride) with CYP3A4 isoenzymes; contraindicated. For more complete data on drug interactions of efavirenz (15 in total), please visit the HSDB record page.

[1]. L-743, 726 (DMP-266): a novel, highly potent nonnucleoside inhibitor of the human immunodeficiency virus type 1 reverse transcriptase. Antimicrob Agents Chemother. 1995 Dec;39(12):2602-5.

[2]. Differential susceptibility of HIV-1 reverse transcriptase to inhibition by RNA aptamers in enzymatic reactions monitoring specific steps during genome replication. J Biol Chem. 2006 Sep 1;281(35):25712-22.

[3]. HIV-1 reverse transcriptase plus-strand initiation exhibits preferential sensitivity to non-nucleoside reverse transcriptase inhibitors in vitro. J Biol Chem. 2007 Mar 16;282(11):8005-10.

Therapeutic Uses
Anti-HIV drugs; reverse transcriptase inhibitors. Due to persistent neuropsychiatric adverse events in some patients receiving efavirenz (EFV), switching to other non-nucleoside reverse transcriptase inhibitors may be considered. Rilpivirine (RPV) has been formulated as a single-tablet combination (STR) with emtricitabine/tenofovir disoproxil fumarate (FTC/TDF), and its efficacy has been proven to be non-inferior to EFV+FTC/TDF, with good tolerability and high adherence. After discontinuation of EFV, EFV continues to induce cytochrome P450 (CYP) 3A4; switching to RPV may reduce RPV exposure, thus adversely affecting clinical efficacy. This study aimed to investigate the clinical significance of reduced RPV exposure (concurrent administration of emtricitabine/tenofovir disoproxil fumarate [FTC/TDF]) and decreased EFV exposure when switching from the EFV/FTC/TDF regimen to the RPV/FTC/TDF regimen in patients intolerant to efavirenz (EFV). This 48-week phase IIb, open-label, multicenter study evaluated the efficacy and safety of switching from EFV/FTC/TDF (treatment duration ≥3 months) to the RPV/FTC/TDF regimen. The study assessed virologic suppression (HIV-1 RNA <50 copies/mL), safety, and the pharmacokinetics of EFV and RPV. At weeks 12 and 24, all 49 subjects receiving RPV/FTC/TDF maintained virologic suppression. At week 48, 46 (93.9%) subjects remained virologically suppressed, and 2/49 (4.1%) subjects experienced virologic failure, but no resistance developed. Within weeks of discontinuing efavirenz (EFV), EFV concentrations remained above the 90th percentile of the inhibitory concentration (IC90); approximately two weeks after switching to another drug, rilpivirine (RPV) exposure reached levels observed in the Phase 3 studies. No subjects withdrew from the study due to adverse events. For virologically suppressed HIV-infected individuals who are intolerant to EFV and wish to continue monotherapy, switching from EFV/FTC/TDF to RPV/FTC/TDF is a safe and effective option. efavirenz is indicated for the treatment of HIV-1 infection in combination with other antiretroviral agents. /Included on US Product Label/

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Drug Warning
A case of acquired long QT syndrome has been reported, which, after ruling out all other possible causes, is likely associated with treatment with the novel nonnucleoside reverse transcriptase inhibitor efavirenz. In controlled clinical trials, approximately 53% of adult patients treated with efavirenz (600 mg once daily) reported central nervous system adverse reactions, such as abnormal dreams, thought disorders, agitation, amnesia, confusion, depersonalization, dizziness, euphoria, hallucinations, poor concentration, insomnia, somnolence, and coma; these adverse reactions were reported by 25% of adult patients in the control group who did not receive efavirenz. Among patients treated with efavirenz, 33.3% reported mild adverse reactions (not affecting daily life), 17.4% reported moderate adverse reactions (potentially affecting daily life), 2% reported severe adverse reactions (disruption of daily activities), and 2.1% required discontinuation of the drug. 28.1% of patients reported dizziness, and 16.3% reported insomnia. 6.2% to 8.3% of patients reported poor concentration, somnolence, or abnormal dreams, and 1.2% reported hallucinations. Serious psychiatric adverse reactions are rare in adult patients treated with efavirenz. In controlled clinical trials, 0.4% to 1.6% of patients treated with efavirenz reported major depression, suicidal ideation, nonfatal suicide attempts, aggressive behavior, delusional reactions, or manic reactions. In the control group not receiving medication, up to 0.6% of patients reported these psychiatric symptoms. In patients with a history of mental illness, the incidence of each psychiatric symptom ranged from 0.3% (manic reaction) to 2% (major depression or suicidal ideation), and these patients appeared to be more prone to these symptoms than other patients. Other reported psychiatric symptoms in controlled clinical trials of adults treated with efavirenz included depression (15.8%), anxiety (11.1%), and tension (6.3%); in the control group not receiving medication, the incidence of these symptoms was 13.1%, 7.6%, and 2%, respectively. While a causal relationship between efavirenz and these symptoms has not been established, there have been occasional post-marketing reports of suicidal ideation, delusions, or psychotic-like behavior in patients treated with efavirenz. In addition, adverse reactions such as aggression, agitation, mood instability, mania, neurosis, and delusions were reported during postmarketing surveillance. There is no evidence that patients experiencing central nervous system adverse reactions (e.g., dizziness, insomnia, poor concentration, abnormal dreams) during efavirenz treatment have a higher risk of developing psychiatric symptoms. In clinical studies, up to 7% of adult patients treated with efavirenz reported fatigue. Other neurological adverse reactions reported during postmarketing surveillance included coordination disorders, ataxia, seizures, hypoesthesia, paresthesia, neuropathy, and tremor. In clinical studies, 18% of children treated with efavirenz experienced central nervous system adverse reactions.
For more complete data on drug warnings for efavirenz (21 in total), please visit the HSDB record page.

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Pharmacodynamics
Efavirenz (dideoxyinosine, ddI) is an oral nonnucleoside reverse transcriptase inhibitor (NNRTI). It is a synthetic purine derivative, similar to zidovudine, zalcitabine, and stavudine. Efavirenz was initially approved for the treatment of HIV-infected patients who had failed zidovudine treatment. Currently, the U.S. Centers for Disease Control and Prevention (CDC) recommends that efavirenz be included as part of a three-drug combination therapy for HIV infection, which also includes another nucleoside reverse transcriptase inhibitor (such as lamivudine, stavudine, or zidovudine) and a protease inhibitor or efavirenz.

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Efavirenz (code name L-743,726/DMP-266) is a novel and highly effective non-nucleoside reverse transcriptase inhibitor (NNRTI) for the treatment of HIV-1 infection [1]
- Its mechanism of action is to bind to the non-nucleoside binding pocket of HIV-1 reverse transcriptase, thereby inducing structural changes in the enzyme and blocking its ability to catalyze the reverse transcription of viral RNA into cDNA [1]
- The selectivity of this compound against HIV-1 reverse transcriptase is much higher than that against human cell DNA polymerases (α, β, γ), with an IC50 value greater than 10 μM, minimizing the potential risk of infection. Cytotoxicity to host cells [1]

C14H9CLF3NO2

315.67

315.027

154598-52-4

(Rac)-Efavirenz-d4;1246812-58-7;Efavirenz-d5;1132642-95-5;Efavirenz-13C6;1261394-62-0

64139

White to off-white solid powder

1.5±0.1 g/cm3

422.7±55.0 °C at 760 mmHg

139-141ºC

209.4±31.5 °C

0.0±1.1 mmHg at 25°C

1.582

3.72

1

5

1

21

519

1

C1CC1C#C[C@]2(C3=C(C=CC(=C3)Cl)NC(=O)O2)C(F)(F)F

XPOQHMRABVBWPR-ZDUSSCGKSA-N

InChI=1S/C14H9ClF3NO2/c15-9-3-4-11-10(7-9)13(14(16,17)18,21-12(20)19-11)6-5-8-1-2-8/h3-4,7-8H,1-2H2,(H,19,20)/t13-/m0/s1

(4S)-6-chloro-4-(2-cyclopropylethynyl)-4-(trifluoromethyl)-1H-3,1-benzoxazin-2-one

DMP-266, DMP 266; Efavirenz; Sustiva; Stocrin; DMP-266; DMP 266; trade name: efavirenz; L-743,726; L-743726; DMP266; EFV; L 743726

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.08 mg/mL (6.59 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (6.59 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (6.59 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)