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Genvoya Approved in Canada: What You Need to Know

January 2016

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Understanding Drug Interactions

Sometimes one drug can interfere with the body's processing of another drug. Such an effect is called a drug-drug interaction or, more simply, a drug interaction. This can cause higher-than-normal levels of one or both drugs in the blood, resulting in side effects or worsening of pre-existing side effects. Alternatively, the interference of one drug on another can cause the levels of one or both drugs to fall below normal levels. This can result in the drug(s) losing effectiveness. In the case of anti-HIV meds, this fall in drug levels can cause HIV to develop the ability to resist one drug and, likely, other related drugs. This drug resistance limits future treatment options.

To minimize the development of drug resistance, all prescribed medicines should be taken every day, exactly as directed.

Always tell your doctor, nurse and pharmacist about all the drugs you are taking -- prescription and over the counter, supplements or herbs, and street drugs. Pharmacists in particular can be very helpful in checking for the possibility of drug interactions.


Genvoya and Drug Interactions

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Gilead Sciences recommends that the following medicines NEVER be used by someone who is taking Genvoya because they could lead to serious or life-threatening effects or they can weaken the anti-HIV activity of Genvoya:

  • anti-asthma drugs -- salmeterol (Advair, Serevent)
  • antihistamines -- astemizole, terfenadine
  • anti-tuberculosis (TB) drugs -- rifampin
  • anti-migraine drugs (ergot derivatives) -- dihydroergotamine (Migranal), ergotamine (Ergomar), ergonovine, methylergonovine
  • anti-anxiety drugs -- midazolam (Versed), triazolam (Halcion)
  • anti-seizure drugs -- carbamazepine, phenobarbital, phenytoin
  • gastrointestinal motility drugs -- cisapride (Prepulsid)
  • antifungal drugs -- voriconazole (Vfend), posaconazole (Posanol)
  • antipsychotic drugs -- pimozide (Orap)
  • herbs -- St. John's wort and its extracts (such as hypericin and hyperforin)
  • cholesterol-lowering medicines (statins) -- lovastatin and simvastatin
  • drugs for prostate problems -- alfuzosin
  • drugs for pulmonary hypertension -- Revatio (sildenafil)


Commonly Used Drugs and Their Interactions

Acid-reducing agents can lower levels of elvitegravir (in Genvoya) if taken at the same time as Genvoya. Therefore, Gilead Sciences recommends that you take Genvoya and antacid "at least two hours" apart from each other.

Genvoya can raise the level of erectile dysfunction drugs -- such as sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) -- in the blood, leading to side effects. Gilead provides the following advice for dosing these drugs in Genvoya users:

  • sildenafil -- no more than 25 mg in a 48-hour period should be used
  • tadalafil -- no more than 10 mg in a 72-hour period should be used
  • vardenafil -- no more than 2.5 mg in a 72-hour period should be used


Other Drug Interactions

In some cases, with advice and monitoring by your doctor and the use of lab and other tests, it can be possible for you to use some of the drugs listed below. Your doctors, including in some cases your specialist and pharmacist, can advise you how to take Genvoya safely with these drugs. The following drugs can interact with Genvoya and/or vice versa:

  • abnormal heart rhythm drugs -- amiodarone, bepridil, digoxin, disopyramide, flecainide, systemic lidocaine, mexiletine, propafenone, quinidine
  • antibiotics -- clarithromycin (Biaxin) and telithromycin
  • some antidepressants
  • antifungal agents -- itraconazole, ketoconazole, voriconazole
  • cholesterol drugs -- atorvastatin, lovastatin, rosuvastatin, simvastatin
  • corticosteroids (inhaled) -- fluticasone
  • corticosteroids (systemic) -- dexamethaxone
  • hormonal contraceptives (the Pill) -- norgestimate + ethinyl estradiol
  • drugs to prevent blood clots -- warfarin
  • drugs to treat higher-than-normal blood pressure -- amlodipine (Norvasc), diltiazem (Cardizem, Tiazac), felodipine, isradipine, nicardipine (Cardene SR), nifedipine (Procardia), nisoldipine (Sular), verapamil (Calan, Verelan, Covera-HS)
  • drugs to treat pulmonary arterial hypertension (PAH) -- bosentan
  • hepatitis C treatments -- Harvoni (sofosbuvir + ledipasvir), telaprevir, boceprevir
  • sedatives -- buspirone, zolpidem (Ambien)
  • anti-TB drugs -- rifabutin or rifapentine

Gilead notes that the following drugs do not have any "clinically significant interactions" with Genvoya:

  • entecavir
  • famciclovir
  • methadone
  • ribavirin
  • sertraline


Resistance and Other Integrase Inhibitors

Genvoya is meant to be taken once daily every day with food. If you have problems taking Genvoya exactly as directed, speak to your doctor and pharmacist. They can help you find ways to stick to your drug regimen. If you do not take Genvoya once every day, the level of anti-HIV drugs in your body will be reduced. When this happens, HIV can develop the ability to resist the medicines that make up Genvoya, which means that the medicines will no longer work. This could weaken your immune system and affect your body's ability to fight infections. Also, the development of HIV that is resistant to one or more of the medicines inside Genvoya can reduce your future treatment options.

The U.S. Department of Health and Human Services (DHHS) has been producing comprehensive HIV treatment guidelines for many years. These guidelines recommend that patients have resistance testing done prior to starting ART. Such testing can help reveal if HIV in your body has any resistance to the drugs in Genvoya.

Genvoya contains the integrase inhibitor elvitegravir. HIV that is resistant to elvitegravir is also usually resistant to another integrase inhibitor called raltegravir (Isentress). HIV that is resistant to elvitegravir or raltegravir is usually sensitive to another integrase inhibitor, dolutegravir (Tivicay and in Triumeq). Only a combination of resistance testing of a sample of your blood and a review of your treatment history can help your doctor determine which treatments are best for you.


Dosing

Gilead Sciences recommends that adults and adolescents who are at least 12 years and who weigh at least 35 kg can use Genvoya.

The recommended dose is one tablet once daily with food. The type of food does not matter.

Gilead Sciences advises the following when it comes to missed doses: If you miss "a dose of Genvoya within 18 hours of the time it is usually taken, [you] should take Genvoya with food as soon as possible, and then take the next dose of Genvoya at the regularly scheduled time." But, if you miss a dose of Genvoya "by more than 18 hours, [you] should not take the missed dose but resume the usual dosing schedule."


Access

Once Health Canada licenses a drug, physicians can prescribe it but patients must pay for it unless they have a private insurance plan that provides coverage. If left untreated, HIV infection leads to catastrophic disease that can affect one's ability to work and requires expensive care. Therefore, in Canada, provincial and territorial ministries of health heavily subsidize the cost of anti-HIV medications. Each ministry has a listing of drugs for which it is prepared to pay. These listings are called formularies.

In the months ahead, Gilead Sciences and provincial and territorial formularies will be negotiating the price of Genvoya. Your pharmacist or doctor can tell you when Genvoya is listed on your region's formulary.


References

  1. Gilead Sciences Canada. Genvoya (elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide). Product Monograph. 26 November 2015.
  2. Gilead Sciences Canada. Stribild (elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate). Product Monograph. 20 November 2015.
  3. Harris M, Larsen G, Montaner JS. Exacerbation of depression associated with starting raltegravir: a report of four cases. AIDS. 2008 Sep 12;22(14):1890-2.
  4. Abers MS, Shandera WX, Kass JS. Neurological and psychiatric adverse effects of antiretroviral drugs. CNS Drugs. 2014 Feb;28(2):131-45.
  5. Kheloufi F, Allemand J, Mokhtari S, et al. Psychiatric disorders after starting dolutegravir: report of four cases. AIDS. 2015 Aug 24;29(13):1723-5.
  6. Curtis L, Nichols G, Stainsby C, et al. Dolutegravir: clinical and laboratory safety in integrase-inhibitor-naive patients. HIV Clinical Trials. 2014 Sep-Oct;15(5):199-208.
  7. Lafay-Chebassier C, Chavant F, Favrelière S, et al. Drug-induced depression: a case/non case study in the French Pharmacovigilance Database. Therapie. 2015 Sep-Oct;70(5):425-32.
  8. Sax PE, Wohl D, Yin MT, et al. Tenofovir alafenamide versus tenofovir disoproxil fumarate, coformulated with elvitegravir, cobicistat, and emtricitabine, for initial treatment of HIV-1 infection: two randomised, double-blind, phase 3, non-inferiority trials. Lancet. 2015 Jun 27;385(9987):2606-15.
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This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication TreatmentUpdate. Visit CATIE's Web site to find out more about their activities, publications and services.
 

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