Stribild

Uses

Cobicistat is a CYP3A inhibitor used to increase the systemic exposure of atazanavir or darunavir in combination with other antiretroviral agents in the treatment of HIV-1 infection.

Cobicistat is a CYP3A inhibitor indicated to increase systemic exposure of atazanavir or darunavir (once daily dosing regimen) in combination with other antiretroviral agents in the treatment of HIV-1 infection. It is not interchangeable with ritonavir to increase systemic exposure of darunavir 600 mg twice daily, fosamprenavir, saquinavir, or tipranavir due to lack of exposure data. The use of cobicistat is not recommended with darunavir 600 mg twice daily, fosamprenavir, saquinavir or tipranavir. Complex or unknown mechanisms of drug interactions preclude extrapolation of ritonavir drug interactions to certain cobicistat interactions. Cobicistat and ritonavir when administered with either atazanavir or darunavir may result in different drug interactions when used with concomitant medications.

Elvitegravir is an antiretroviral agent used in combination with other antiretrovirals for the treatment of HIV-1 infection in antiretroviral treatment-experienced adults.

Elvitegravir in combination with an HIV protease inhibitor coadministered with ritonavir and with other antiretroviral drug(s) is indicated for the treatment of HIV-1 infection in antiretroviral treatment-experienced adults.

Emtricitabine is a nucleoside reverse transcriptase inhibitor used for the treatment and prophylaxis of HIV.

Emtricitabine is indicated in combination with other medications for the treatment of HIV-1 infections; treatment of HIV-1 infections in pediatric patients 25-35kg, treatment of HIV-1 infections in adult patients ≥35kg, for pre exposure prophylaxis of HIV-1 in adolescent and adult patients excluding those who have receptive vaginal sex; treatment of HIV-1 infections in pediatric and adult patients ≥17kg, pre exposure prophylaxis in adolescents and adults ≥35kg; treatment of HIV-1 in patients ≥12 years and ≥35kg; treatment of HIV-1 in patients weighing ≥35kg; treatment of HIV-1 in patients weighing ≥25kg; and treatment of HIV-1 in patients weighing ≥40kg.

This is used for the treatment of:

• Chronic hepatitis B virus infection in adults
• HIV infected adults in combination with other anti retroviral agents

Stribild is also used to associated treatment for these conditions: Human Immunodeficiency Virus (HIV) Infections, Human Immunodeficiency Virus Type 1 (HIV-1) InfectionHuman Immunodeficiency Virus Type 1 (HIV-1) InfectionHIV Transmission, Human Immunodeficiency Virus (HIV) Infections, Human Immunodeficiency Virus Type 1 (HIV-1), Human Immunodeficiency Virus Type 1 (HIV-1) Infection

How Stribild works

Cobicistat is a mechanism-based inhibitor of cytochrome P450 3A (CYP3A) isoforms. Inhibition of CYP3A-mediated metabolism by cobicistat increases the systemic exposure of CYP3A substrates atazanavir and darunavir and therefore enables increased anti-viral activity at a lower dosage. Cobicistat does not have any anti-HIV activity on its own.

Elvitegravir is an HIV-1 integrase strand transfer inhibitor (INSTI). Integrase is an HIV-1 encoded enzyme that is required for viral replication. Inhibition of integrase prevents the integration of HIV-1 DNA into host genomic DNA, blocking the formation of the HIV-1 provirus and propagation of the viral infection. Elvitegravir does not inhibit human topoisomerases I or II.

Emtricitabine is a cytidine analog which, when phosphorylated to emtricitabine 5'-triphosphate, competes with deoxycytidine 5'-triphosphate for HIV-1 reverse transcriptase. As HIV-1 reverse transcriptase incorporates emtricitabine into forming DNA strands, new nucleotides are unable to be incorporated, leading to viral DNA chain termination. Inhibition of reverse transcriptase prevents transcription of viral RNA into DNA, therefore the virus is unable to incorporate its DNA into host DNA and replicate using host cell machinery. This reduces viral load.

Once tenofovir is activated by a bi-phosphorylation it acts as an antiviral acyclic nucleoside phosphonate. It is a potent inhibitor of the viral reverse transcriptase with an inhibitory constant of approximately 0.022 micromolar.

Once activated, tenofovir acts with different mechanisms including the inhibition of viral polymerase causing chain termination and the inhibition of viral synthesis. All these activities are attained by its competition with deoxyadenosine 5'-triphosphate in the generation of new viral DNA. Once tenofovir is incorporated in the chain, it induces a chain termination which in order inhibits viral replication. The safety of tenofovir relies on its low affinity towards the cellular DNA polymerase including the mitochondrial DNA polymerase gamma.

Dosage

Stribild dosage

The recommended dose of Tenofovir in chronic hepatitis B virus infection in adults 18 years of age and older with adequate renal function is 300 mg once daily with or without food.

Side Effects

The most common side effects are nausea, vomiting, diarrhea and flatulence.

Toxicity

The most common adverse reactions reported during clinical trials were jaundice (13%), ocular icterus (15%), and nausea (12%).

The most common adverse reactions reported for elvitegravir use during clinical trials include nausea, vomiting, and diarrhea. Less common side effects occurring in <2% of patients, include abdominal pain, dyspepsia, fatigue, insomnia, rash, depression, suicidal ideation, and suicidal attempt.

The LD₅₀ of emtricitabine is not readily available.[9019,L9818]

Symptoms of emtricitabine toxicity include hepatotoxicity with steatosis, as well as lactic acidosis. Treat overdose with symptomatic and supportive measures, including hemodialysis.

There haven't been reports regarding the LD50 of the parent compound nor the effects of an overdose. However, based on the reports with the derivative that most rapidly transforms into tenofovir, tenofovir disoproxil, it is recommended to monitor overdose patients. As well, it is widely known that tenofovir is efficiently removed by hemodialysis.

Administration of high doses of tenofovir has been reported to produce bone toxicity reported as osteomalacia and reduced bone mineral density and to produce some degree of renal toxicity.

To know more about the carcinogenicity and mutagenic potential of tenofovir, as well as the effect on fertility, please visit the drug entries for the derivatives tenofovir disoproxil and tenofovir alafenamide.

Precaution

Co-administration with other drugs: Tenofovir should not be administered concurrently with Emtricitabine & Tenofovir combination or Adefovir Dipivoxil.

Lactic Acidosis & Severe Hepatomegaly with Steatosis: Though the risk of occurrence of lactic acidosis is low for Tenofovir, treatment should be suspended in any patient who develops lactic acidosis or hepatotoxicity.

Exacerbation of hepatitis after discontinuation of treatment: Discontinuation of Tenofovirtherapy may be associated with severe acute exacerbation of hepatitis.

Interaction

Co-administration of Tenofovir with anti-retroviral, entecavir, lamivudine, methadone, oral contraceptives, ribavirin and tacrolimus did not result in significant drug interactions. The effects of co-administration of Tenofovir with other drugs that are renally eliminated or are known to affect renal function have not been evaluated.

Volume of Distribution

The apparent central volume of distribution is 42.3L and the peripheral volume of distribution is 55.4L.

Accumulation of tenofovir in plasma is related to the presence of nephrotoxic effects. It is reported that tenofovir presents a volume of distribution of 0.813 L/kg.

Elimination Route

Median peak plasma concentrations were observed at 3.5 hours post-dose.

Following oral administration of elvitegravir and ritonavir with food, in HIV-1 infected subjects, peak elvitegravir plasma concentrations were observed approximately 4 hours post-dose.

Emtricitabine reaches a C_max of 1.8±0.7µg/mL with a T_max of 1-2 hours, and has an AUC of 10±3.1µg*hr/mL. The bioavailability of emtricitabine capsules is 93% and the bioavailability of the oral solution is 75%. Taking emtricitabine with food decreases the C_max by 29%.[L9019

Tenofovir as the active moiety presents a very low bioavailability when orally administered. Hence, the administration of this active agent is required to be under its two prodrug forms, tenofovir disoproxil and tenofovir alafenamide. This reduced absorption is suggested to be related to the presence of two negative charges among its structure. This negative charge limits its cellular penetration, and its passive diffusion across cellular membranes and intestinal mucosa hindering its availability for oral administration.

Intravenous tenofovir has been shown to produce a maximum plasma concentration of 2500 ng/ml with an AUC of 4800 ng.h/ml.

Half Life

The terminal plasma half-life of cobicistat is approximately 3 to 4 hours.

The median terminal plasma half-life following administration of elvitegravir and ritonavir was approximately 8.7 hours.

The half life of emtricitabine is approximately 10 hours.

The reported half-life of tenofovir is of 32 hours.

Clearance

Emtricitabine has an apparent elimination rate of 15.1L/h. This rate is closely linked to creatinine clearance.

The clearance of tenofovir is highly dependent on the patient renal stage and hence the clearance rate in patients with renal impairment is reported to be of 134 ml/min while in patients with normal function the clearance rate can be of 210 ml/min.

Elimination Route

With single dose administration of [14C] cobicistat after multiple dosing of cobicistat for six days, the mean percent of the administered dose excreted in feces and urine was 86.2% and 8.2%, respectively.

Following oral administration of [14C]elvitegravir/ritonavir, 94.8% of the dose was recovered in feces, while 6.7% was recovered in urine as metabolites.

Emtricitabine is 86% recovered in the urine and 14% recovered in feces. 13% of the dose is recovered in the urine as metabolites; 9% as 3'-sulfoxide diastereomers and 4% as 2'-O-glucuronide.

Tenofovir is eliminated in the urine by tubular secretion and glomerular filtration. The elimination of this compound is driven by the activity of the human organic anion transporters 1 and 3 and its secretion is mainly ruled by the activity of the multidrug resistance-associated protein 4.

Pregnancy & Breastfeeding use

Pregnancy: Pregnancy category B. It should be used during pregnancy only if clearly needed.

Lactation: It is not known whether it is excreted in human milk. Mothers should be instructed not to breast feed if they are taking Tenofovir.

Contraindication

Tenofovir is contraindicated in patients with known hypersensitivity to Tenofovir or any component of the product.

Special Warning

Pediatric use: Safety and effectiveness of Tenofovir in pediatric patients below the age of 18 years have not been established.Geriatrics use: Clinical studies of Tenofovir did not include sufficient numbers of subjects aged 65 years and over to determine whether they respond differently from younger subjects. But care should be taken in dose selection, and it may be useful to monitor renal function.Renal Impairment: Haemodialysis patients: 300 mg once every 7 days or after a cumulative total of 12 hr of dialysis.

• CrCl (10-29 mL/min): 300 mg 72-96 hrly.
• CrCl (30-49 mL/min): 300 mg 48 hrly.

Hepatic impairment

: No dose adjustment is required in patients with hepatic impairment.

Acute Overdose

There is no experience of Tenofovir overdose reported in patients

Storage Condition

Store in a cool and dry place, protected from light and moisture. Keep the medicine out of the reach of children.

Innovators Monograph

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