Testing for Resistance

Healthcare providers (HCPs) can do genotypic testing and/or phenotypic testing to help detect resistance to antiretroviral drugs.

Genotypic testing
Genotypic tests look for changes in HIV that are associated with drug resistance. These tests help your HCP find out if and how your virus has changed and which drugs are not likely to work.

Genotyping can be used to help determine the potential for drug resistance by looking at the reverse transcriptase and protease enzymes of a person’s virus.

A single mutation may mean resistance to more than one drug or an entire drug class.

The genotypic testing process
Step 1—A blood sample is taken.
Step 2—Copies of the virus are made from the blood sample.
Step 3—Genes within the virus are evaluated for mutations.
Step 4—Mutations found in the virus are compared with known resistance mutations.

If the type and number of mutations present in a person’s HIV match pre-established mutation patterns for a particular drug, that individual’s virus has probably developed resistance to that drug.

If genotypic testing reveals drug resistance mutations in a person’s HIV, certain antiviral drugs may be less likely to work for him or her. The specific type and placement of the mutations dictate to which drugs the virus may be resistant. Once an HCP understands which drugs are less likely to work for his or her patient, he or she can develop a treatment plan that avoids the use of those drugs. This results in a therapy regimen that is more likely to be effective for a longer period of time.

Phenotypic testing
Phenotypic tests directly measure the amount of resistance that HIV has to each drug. This test is done for most HIV medicines you are taking, or may take, to learn which drugs may work well for you.

Phenotypic testing directly exposes a person’s virus to many of the currently available antiviral drugs. The virus is exposed to a specific drug and then evaluated to determine how much of the drug is required to block viral activity.

The phenotypic testing process
The phenotypic testing process can be summarized in two key phases: making the HIV copy and measuring phenotypic resistance.

Making the HIV copy
Step 1—A sample of blood is taken from the patient.
Step 2—From the sample, key portions of the genes in the patient’s virus are copied.
Step 3—The copied genes are inserted into a laboratory sample of HIV.
Step 4—The laboratory HIV becomes a genetic copy of the patient’s HIV.

After a copy of the HIV is made, phenotypic resistance can be measured.

Measuring phenotypic resistance
Step 1—The copies of the patient’s virus made in the previous steps are exposed to antiretroviral drugs.
Step 2—The ability of the virus to grow (or not grow) in the presence of each antiretroviral drug is evaluated.
Step 3—The results help HCPs determine how much of a particular drug is needed to stop the patient’s HIV from reproducing.

Once an HCP has a complete understanding of a person's resistance status and therapy options, he or she can develop a treatment plan that avoids the use of ineffective drugs. This results in a therapy regimen that is more likely to be effective for a longer period of time.

Important Safety Information for APTIVUS

• Patients taking APTIVUS may develop severe liver disease that can cause death. If you develop any of the following symptoms of liver problems, you should stop taking APTIVUS treatment and CALL your HCP right away: tiredness, general ill feeling or “flu-like” symptoms, loss of appetite, nausea (feeling sick to your stomach), yellowing of your skin or whites of your eyes, dark (tea-colored) urine, pale stools (bowel movements), or pain, ache, or sensitivity on your right side below your ribs. If you have chronic hepatitis B or C infection, your HCP should check your blood tests more often because you have an increased chance of developing liver problems. Tell your HCP if you have liver disease, are infected with hepatitis B or C infection, or reduced liver function because you may have increased chance of liver disease problems while taking APTIVUS.
• Patients taking APTIVUS may develop severe bleeding in the brain that can cause death. You should report any unusual or unexplained bleeding to your HCP if you are taking APTIVUS.
• APTIVUS capsules and oral solution are always taken with Norvir^® (ritonavir)
• APTIVUS taken with ritonavir capsules or solution can be taken with or without meals
• APTIVUS taken with ritonavir tablets must only be taken with meals
• Your HCP will prescribe at least 2 other anti-HIV medicines with APTIVUS. This usually will increase the likelihood of treatment response.
• Baseline HIV resistance may affect your response to APTIVUS. Therefore, your HCP should conduct resistance tests and know your treatment history before prescribing APTIVUS.
• Tell your healthcare professional about all the medications you take. Taking APTIVUS with certain drugs can reduce the effectiveness of your treatment and can result in serious or life-threatening events.
• Tell your HCP if you have hemophilia or other medical conditions that increase the chances of bleeding. Tell your HCP about medicines you are taking to find out if they may increase your chance of bleeding.
• If you are taking APTIVUS oral solution, which contains vitamin E, you should not take additional vitamin E other than that contained in a standard multivitamin.
• Tell your HCP immediately if you develop or if you suspect you have a skin rash. APTIVUS should be used with caution in patients with a known sulfa allergy.
• Patients may develop new or worsening diabetes, high blood sugar (hyperglycemia), immune reconstitution syndrome, changes in body fat, and elevated lipids. Your HCP may monitor your cholesterol and triglycerides before starting APTIVUS and while on treatment.
• Women taking APTIVUS and estrogen-based hormonal contraceptives are advised to use alternative methods of contraception during therapy with APTIVUS. Women using estrogens for birth control or hormone replacement have an increased chance of developing a skin rash while taking APTIVUS. If a rash occurs, it is usually mild to moderate, but you should call your HCP.
• Tell your HCP if you are thinking about becoming pregnant, if you are pregnant, or are thinking about breast-feeding. Breastfeeding can result in passing the HIV virus to your baby.
• The most common side effects of APTIVUS include diarrhea, nausea, fever, vomiting, tiredness, headache, and stomach pain. Rash was seen more frequently in children.
• APTIVUS should not be used in children under 2 years of age.