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CRIXIVAN

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Basic Informations

Crixivan is an anti-HIV medication. It is in a category of HIV medications called protease inhibitors (PIs). Crixivan prevents T-cells that have been infected with HIV from producing new HIV.

Crixivan, manufactured by Merck & Company, was approved for the treatment of HIV by the U.S. Food and Drug Administration (FDA) in 1996.

Crixivan must be used in combination with at least two other anti-HIV drugs.

Drugs Interactions

Crixivan is broken down (metabolized) by the liver, like many medications used to treat HIV and AIDS. This means that Crixivan can interact with other medications. Crixivan can lower or raise the levels of other medications in the body. Similarly, other medications can lower or raise the levels of Crixivan in the body. While many interactions are not a problem, some can cause your medications to be less effective or increase the risk of side effects.

Tell your doctors and pharmacists about all medicines you take. This includes those you buy over-the-counter and herbal or natural remedies, such as St. John’s Wort. Bring all your medicines when you see a doctor, or make a list of their names, how much you take, and how often you take them. Your doctor can then tell you if you need to change the dosages of any of your medications.

The following medications should not be taken while you are being treated with Crixivan:

  • Acid reflux/heartburn medications: Propulsid (cisapride)

  • Antimigraine medications: Methergine, Methylergometrine (methylergonovine); Ergostat, Cafergot, Ercaf, Wigraine (ergotamine); Ergotrate, Methergine (ergonovine); or D.H.E. 45, Migranal (dihydroergotamine)

  • Cholesterol-lowering drugs (statins): Zocor (simvastatin) and Mevacor (lovastatin)

  • Heart medications: Cordarone (amiodarone)

  • Antipsychotics: Orap (pimozide)

  • Sedatives: Versed (midazolam) and Halcion (triazolam)

  • Pulmonary Hypertension: sildenafil, used as Revatio

  • Herbal products: St. John's wort

If Crixivan is combined with low-dose Norvir, the following medications should also be avoided:

  • Antifungals: Vfend (voriconazole)

  • Antihistamines: Hismanal (astemizole) or Seldane (terfenadine)

  • Heart medications: Vascor (bepridil), Tambocor (flecainide), Rythmol (propafenone), or Quinaglute/Quinidex (quinidine)

  • Enlarged prostate: Uroxatral (alfuzosin)

Anticonvulsants, such as Tegretol ( carbamazepine), Luminal (phenobarbital), and Dilantin (phenytoin), decrease the amount of Crixivan in the bloodstream. Alternatives to these three anticonvulsants should be considered.

Anti-HIV protease inhibitors can interact with Crixivan. Norvir (ritonavir) increases Crixivan levels in the bloodstream (the usual dose is 800mg plus 100mg or 200mg Norvir, twice a day). Kaletra (lopinavir/ritonavir) also increases Crixivan levels (the recommended dose is 600mg Crixivan plus the standard dose of Kaletra, twice a day). Crixivan can increase blood levels of Invirase (saquinavir); Invirase does not impact Crixivan levels (no dosing recommendation has been made). Crixivan can increase Viracept (nelfinavir) levels and Viracept can increase Crixivan levels (no dosing recommendation has been made). Crixivan also increases Agenerase (amprenavir)—and probably Lexiva (fosamprenavir)—levels in the bloodstream (changes in doses do not appear to be necessary). Reyataz (atazanavir) should not be combined with Crixivan because both drugs can cause increased bilirubin levels.

Anti-HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs) can also interact with Crixivan. Sustiva (efavirenz) and Viramune (nevirapine) can decrease Crixivan levels in the bloodstream. If either of these drugs are combined with Crixivan, the Crixivan dose should be increased to 1000mg three-times daily. However, if low doses of Norvir (ritonavir) are also being used to "boost" Crixivan, the Crixivan dose should be 800mg twice a day. Rescriptor (delavirdine) increases Crixivan levels in the bloodstream (the Crixivan dose should be reduced to 600mg three times a day and the Rescriptor dose should remain the same).

It is also important to be careful when using the nucleotide reverse transcriptase inhibitor (NRTI) Videx (ddI) buffered tablets (not Videx EC capsules) with Crixivan. Videx buffered tablets can interfere with the absorption of Crixivan into the bloodstream. Because of this, the Videx buffered tablets must be taken either one hour before or one hour after taking Crixivan. It is okay to take Videx EC capsules and Crixivan at the same time.

Crixivan can interact with some medications used to treat TB, MAC and other bacterial infections. Rifadin (rifampin) decreases Crixivan levels in the bloodstream; these two drugs should not be used together. Crixivan can increase Mycobutin (rifabutin) levels and Mycobutin decreases Crixivan levels (the Mycobutin dose should be reduced to 150mg daily or 300 mg three times a week). Crixivan can increase Biaxin (clarithromycin) levels in the bloodstream (the Biaxin dose does not need to be changed).

Crixivan can interact with some medications used to treat thrush (candidiasis) and other fungal infections. Crixivan can increase Nizoral (ketoconazole) levels in the bloodstream. Because of this, the dose of Crixivan needs to be lowered while taking Nizoral, from 800mg three-times-daily to 600mg three-times-daily.

Crixivan can increase the blood levels of oral contraceptives/birth-control pills. No changes in dosing have been recommended.

Crixivan can increase blood levels of cochicine, which is used to treat gout. Lower doses of colchicine are recommended, and the two drugs should not be used together in people with liver or kidney impairment.

Crixivan can increase blood levels of Advair, Flovent, or Flonase (fluticasone), the inhalable medications that are used to treat allergies and asthma. Alternatives to these drugs should be considered, especially for long-term use. Crixivan can also increase blood levels of an asthma medication called Serevent (salmeterol), a drug that is used to open the air passages in the lungs during an asthma attack. This can result in heart rhythm problems. Use of the two drugs together is not recommended.

Crixivan can increase the blood levels of UroXatral (alfuzosin), a drug used to treat enlarged prostate glands. Increased alfuzosin blood levels can increase the risk of high blood pressure.

Cholesterol-lowering drugs, also known as "statins," can interact with Crixivan. There are two statins that should not be used with Crixivan: Zocor (simvastatin) and Mevacor (lovastatin). Levels of these two drugs can become significantly increased in the bloodstream if they are combined with Crixivan, which increases the risk of side effects. The two statins that are considered to be the safest in combination with Crixivan are Pravachol (pravastatin) and Lescol (fluvastatin). It is also possible to take Crixivan with Lipitor (atorvastatin), although Crixivan can increase Lipitor levels in the bloodstream. If Lipitor is prescribed, it's best to begin treatment with the lowest possible dose of the drug and then increase the dose if necessary. Little is known about the newest statin, Crestor (rosuvastatin), although it is not expected to have any serious drug interactions with Crixivan or the other protease inhibitors.

There is a class of drugs, known as PDE-5 inhibitors that are used to treat both erectile dysfunction and pulmonary arterial hypertension. Their brand names differ, depending on their use. Prezista/Norvir can significantly increase blood levels of these drugs.
When used to treat erectile dysfunction, it is best to use a lower dose of Viagra (sildenafil), Levitra (vardenafil) and Cialis (tadalafil) in order to reduce the risk of side effects. When used to treat pulmonary arterial hypertension, the dose of tadalafil (Adcirca) must be reduced if combined with Prezista/Norvir. Revatio (sildenafil) and Prezista/Norvir should not be used together.

Herbal products can also interact with Crixivan. St. John's wort should not be used with Crixivan, since it can greatly reduce the amount of Crixivan in the bloodstream. HIV-positive people should also be cautious about using garlic supplements or milk thistle with Crixivan—test tube studies suggest that both herbal products can interact with the same liver enzyme system (cytochrome P450 3A4) responsible for metabolizing Crixivan. This may alter the amount of Crixivan in the bloodstream. These and other herbal products should be used with caution, until further studies are conducted.

A number of other negative drug interactions are possible if Crixivan is combined with Norvir (ritonavir).

Side Effects

Crixivan forms crystals in the urine, which occurs in as many as 40% of people taking this drug. This can cause kidney stones (nephrolithiasis), pain when urinating, and back pain. To reduce the risk of these side effects, it is advised that people taking Crixivan drink at least six eight-ounce glasses of water a day (at least 48 ounces).

Some side effects of Crixivan involve the skin. People taking Crixivan are more likely to experience rash, dry skin, patches of dark skin (hyperpigmentation), hair loss, dry lips, and brittle fingernails and toenails.

Crixivan can cause creatinine levels to increase in the bloodstream. Creatinine is a marker of muscle function. Increased creatinine levels, caused by Crixivan use, is not believed to be dangerous.

Crixivan can cause bilirubin levels in the bloodstream to increase. Bilirubin is the waste product that results from the breakdown of hemoglobin molecules from worn out red blood cells. Crixivan can block the liver's removal of bilirubin from the bloodstream, which can cause bilirubin levels to become elevated and lead to jaundice (yellowing of the skin, eyes, and under the nails). Crixivan should not be combined with Reyataz (atazanavir), another protease inhibitor that can cause increased bilirubin levels.

Anti-HIV drug regimens containing protease inhibitors, including Crixivan, can cause increased fat levels (cholesterol and triglycerides) in the blood, abnormal body-shape changes (lipodystrophy; including increased fat around the abdomen, breasts, and back of the neck, as well as decreased fat in the face, arms, and legs), and diabetes. These side effects of anti-HIV drug therapy are reviewed in our lessons on Lipodystrophy, Facial Lipoatrophy, and Risks To Your Heart (Hyperlipidemia).

Short-term side effects include appetite loss, headaches, feeling crummy (malaise), diarrhea, nausea, and vomiting. Very often, these side effects improve within a few months/weeks of starting Crixivan.