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Prezista (Darunavir)

Articles on Prezista
Full US Prescribing Information (20-page PDF)


What is Prezista?
How does Prezista work?
Who should not take Prezista?
How should I take Prezista?
What are the possible side effects?
Important Safety Information
Clinical Trials
Resistance
Pregnancy
Drug and Food Interactions
Contraindications
Sources
www.prezista.com

PREZISTAÖ is always used with 100 mg ritonavir (Norvir«) in combination with other HIV medicines for the treatment of HIV infection in treatment-experienced adult patients, such as those with HIV resistant to more than one PI.


Articles on Prezista

FDA Approves New Darunavir Dose and Etravirine Strength
1-7-2011

Boosted Darunavir Monotherapy Maintains Viral Suppression in Most People with HIV
11-19-2010

Boosted Darunavir (Prezista) Monotherapy Provides Durable Viral Suppression for Most HIV Patients
8-17-2010

Darunavir/ritonavir increases rosuvastatin concentrations but does not alter lipid lowering effect in healthy volunteers
7-23-2010

Effect of adherence on virological response to once-daily versus twice-daily darunavir/ritonavir in treatment-experienced, HIV-1-infected patients with no darunavir resistance-associated mutations: ODIN 48-week data
7-23-2010

Effects of once-daily versus twice-daily darunavir/ritonavir on lipid parameters at Week 48 in treatment-experienced, HIV-1-infected patients with no darunavir resistance-associated mutations in the ODIN study
7-23-2010

METABOLIK (Metabolic Evaluation in Treatment-na´ves Assessing the impact of two Boosted protease inhibitors on LIpids and other marKers): Comparison of the Metabolic Effects of Darunavir/ritonavir versus Atazanavir/ritonavir over 12Weeks
7-23-2010

Suboptimal Adherence Has Less Effect on Boosted Darunavir (Prezista) than Lopinavir/ritonavir (Kaletra)
7-02-2010


Fat Tissue Distribution Changes in HIV-infected Patients with Viral Suppression Treated with Darunavir/ritonavir (DRV/r) monotherapy versus 2 NRTIs + DRV/r in the MONOI-ANRS 136 Randomized Trial : Results at 48 weeks
3-06-2010

Lack of Interaction between Etravirine and Raltegravir plus Darunavir/Ritonavir when Combined in Treatment Experienced Patients:a Substudy of the ANRS 139 TRIO
3-06-2010

Darunavir Concentrations in Seminal Plasma in patients receiving Darunavir/ritonavir(DRV/r) monotherapy: a MONOI-ANRS 136 substudy
3-06-2010

The Prevalence of Darunavir Associated Mutations in PI-naive and PI-experienced HIV-1 Infected Children in the UK
2-23-2010

The Binary Protease Inhibitor, Darunavir, Has a High Genetic Barrier to the Emergence of Resistant HIV-1 Variants
2-23-2010

Darunavir (DRV) concentrations exceed the Protein-corrected (PC) EC50 for wild type HIV in the semen of HIV-1 infected Men
2-23-2010

FDA Announces Label Changes for Darunavir (Prezista), Didanosine (Videx), and Lopinavir/ritonavir (Kaletra)
2-02-2010

MONET Study Finds Boosted Darunavir (Prezista) Monotherapy Maintains HIV Suppression as well as Standard Combination Antiretroviral Therapy
1-19-2010

Boosted Darunavir (Prezista) Monotherapy Works Well as Maintenance Therapy, but Not So Well as Initial Regimen
11-24-2009

Raltegravir (Isentress), Etravirine (Intelence), and Boosted Darunavir (Prezista)
Is Highly Effective for Treatment-experienced Adolescents
11-17-2009


Raltegravir (Isentress) and Darunavir (Prezista) Appear to Reach Therapeutic Levels in Cerebrospinal Fluid
10-16-2009

Raltegravir (Isentress), Etravirine (Intelence), and Ritonavir-boosted Darunavir (Prezista) Is a Safe and Successful Salvage Regimen
10-06-2009


Boosted Darunavir (Prezista) Monotherapy May Be a Viable Alternative for Patients with Stable Suppressed Viral Load
7-24-2009

Once Daily Darunavir/ritonavir: Experience in a Single Centre
7-21-2009

Treatment Strategies Using Boosted Darunavir (Prezista) and Raltegravir (Isentress) for Highly Treatment-experienced HIV Patients
6-12-2009


Suboptimal Adherence May Have Less Detrimental Effect in Patients Taking Boosted
Darunavir (Prezista)
4/17/09


Factors affecting virologic response to darunavir/ritonavir and lopinavir/ritonavir in treatment-na´ve HIV-1-infected patients in ARTEMIS at 96 weeks
2/10/09

Once-daily Darunavir (Prezista) Approved in Europe for Patients Starting First-line HIV Treatment
2/10/09


HIV Mutations Can Both Reduce and Enhance Virological Response to Boosted Darunavir (Prezista)
1/30/09

Changes in Darunavir (Prezista) Resistance Score after Previous Failure of Boosted Tipranavir (Aptivus) in Multidrug-resistant HIV Patients
1/27/09

Darunavir (Prezista) and Abacavir (Ziagen) Approved for Children with HIV
1/06/09



What is Prezista?

PREZISTA (darunavir), is a prescription medicine. It is one treatment option in the class of HIV (human immunodeficiency virus) medicines known as protease inhibitors (PI).

PREZISTA is always used with 100 mg ritonavir (Norvir ® ) in combination with other HIV medicines for the treatment of HIV infection in adults

The use of other medicines active against HIV in combination with PREZISTA/ritonavir (Norvir ® ) may increase the likelihood of your overall treatment response. Your health care professional will work with you to find the right combination of other HIV medicines.

The long-term effects of PREZISTA therapy are unknown at this time. It is important that you remain under the care of your health care professional.


How does Prezista work?

PREZISTA™ blocks HIV protease, an enzyme which is needed for HIV to multiply. When used with other anti-HIV medicines, PREZISTA™ may reduce the amount of HIV in your blood (called "viral load") and increase your CD4 (T) cell count. HIV infection destroys CD4 (T) cells, which are important to the immune system. The immune system helps fight infection. Reducing the amount of HIV and increasing the CD4 (T) cell count may improve your immune system and, thus, reduce the risk of death or infections that can happen when your immune system is weak (opportunistic infections).

PREZISTA™ is always taken with and at the same time as 100 mg of ritonavir (Norvir), in combination with other anti-HIV medicines.


Who should not take Prezista?

Together with your doctor, you need to decide whether taking PREZISTAÖ is right for you.

Do not take PREZISTAÖ if you:

are allergic to darunavir or any of the other ingredients in PREZISTAÖ

are allergic to ritonavir (Norvir « )

take any of the following types of medicines because you could experience serious side effects:

Type of Drug
Examples of Generic Names (Brand Names)
Antihistamines
(to treat allergy symptoms)
astemizole (Hismanal ® )
terfenadine (Seldane ® )
Ergot Derivatives
(to treat migraine and headaches)
dihydroergotamine (D.H.E. 45 ® , Migranal ® )
ergonovine
ergotamine (Wigraine ® , Ergostat ® , Cafergot ® , Ergomar ® )
methylergonovine
Gastrointestinal Motility Agent
(to treat some digestive conditions)
cisapride (Propulsid ® )
Neuroleptic
(to treat psychiatric conditions)
pimozide (Orap ® )
Sedative/hypnotics
(to treat trouble with sleeping and/or anxiety)
midazolam (Versed ® )
triazolam (Halcion ® )


How should I take Prezista?

Take PREZISTA™ tablets every day exactly as prescribed by your doctor. You must take ritonavir (Norvir ® ) at the same time as PREZISTA™. The usual dose is 600 mg (two 300 mg tablets) of PREZISTA™, together with 100 mg (one 100 mg capsule) of ritonavir (Norvir ® ), twice daily every day. It may be easier to remember to take PREZISTA™ and ritonavir (Norvir ® ) if you take them at the same time every day. If you have questions about when to take PREZISTA™ and ritonavir (Norvir ® ), your doctor can help you decide which schedule works for you.

Take PREZISTA™ and ritonavir (Norvir ® ) with food. The type of food is not important. Swallow the tablets whole with a drink such as water, milk, or any other nutritional drink. Do not chew the tablets.

Continue taking PREZISTA™ and ritonavir (Norvir ® ) unless your doctor tells you to stop. Take the exact amount of PREZISTA™ and ritonavir (Norvir ® ) that your doctor tells you to take, right from the very start. To help make sure you will benefit from PREZISTA™ and ritonavir (Norvir ® ), you must not skip doses or interrupt therapy. If you don't take PREZISTA™ and ritonavir (Norvir ® ) as prescribed, the beneficial effects of PREZISTA™ and ritonavir (Norvir ® ) may be reduced or even lost.

If you miss a dose of PREZISTA™ or ritonavir (Norvir ® ) by more than 6 hours, wait and then take the next dose of PREZISTA™ and ritonavir (Norvir ® ) at the regularly scheduled time. If you miss a dose of PREZISTA™ or ritonavir (Norvir ® ) by less than 6 hours, take your missed dose of PREZISTA™ and ritonavir (Norvir ® ) immediately. Then take your next dose of PREZISTA™ and ritonavir (Norvir ® ) at the regularly scheduled time.

You should always take PREZISTA™ and ritonavir (Norvir ® ) together with food.

If a dose of PREZISTA™ or ritonavir (Norvir ® ) is skipped, do not double the next dose. Do not take more or less than your prescribed dose of PREZISTA™ or ritonavir (Norvir ® ) at any one time.


What are the possible side effects of Prezista?

Like all prescription drugs, PREZISTA™ can cause side effects. The following is not a complete list of side effects reported with PREZISTA™ when taken either alone or with other anti-HIV medicines. Do not rely on this leaflet alone for information about side effects. Your doctor can discuss with you a more complete list of side effects.

Your healthcare professional should do blood tests prior to initiating combination treatment including PREZISTA. Patients with liver diseases such as hepatitis B and hepatitis C may have worsening of their liver disease with PREZISTA™ and may need more frequent monitoring of blood tests. PREZISTA™ has been reported to cause liver problems which may be life-threatening. It was not always clear if PREZISTA™ caused these liver problems because some patients had other illnesses or were taking other medicines.

Mild to moderate rash has been reported in 7% of subjects receiving PREZISTA™. In some patients, PREZISTA has been reported to cause a severe or life-threatening rash. Contact your healthcare provider if you develop a rash. Your healthcare provider will advise you whether your symptoms can be managed on therapy or whether PREZISTA™ should be stopped.

As with other protease inhibitors, PREZISTA may cause side effects, including:

high blood sugar (hyperglycemia) and diabetes. This can happen in patients taking PREZISTA™ or other protease inhibitor medicines. Some patients have diabetes before starting treatment with PREZISTA™ which gets worse. Some patients get diabetes during treatment with PREZISTA™. Some patients will need changes in their diabetes medicine. Some patients may need new diabetes medicine.

increased bleeding in patients with hemophilia. This may happen in patients taking PREZISTA™ as it has been reported with other protease inhibitor medicines.

changes in body fat. These changes can happen in patients taking anti-HIV medicines. The changes may include an increased amount of fat in the upper back and neck, breast, and around the back, chest, and stomach area. Loss of fat from the legs, arms, and face may also happen. The exact cause and long-term health effects of these conditions are not known.

immune reconstitution syndrome. In some patients with advanced HIV infection (AIDS) and a history of opportunistic infection, signs and symptoms of inflammation from previous infections may occur soon after anti-HIV treatment is started. It is believed that these symptoms are due to an improvement in the body's immune response, enabling the body to fight infections that may have been present with no obvious symptoms.


Important Safety Information

PREZISTA, together with NORVIR, has rarely been observed to cause liver problems, which may be life-threatening. It was not always clear if PREZISTA caused these liver problems because some patients had other illnesses or were taking other medicines. Your health care professional should do blood tests prior to initiating combination treatment including PREZISTA. If you have chronic hepatitis B or C infection, your health care professional should check your blood tests more often because you have an increased chance of developing liver problems.

Talk to your healthcare professional about the signs and symptoms of liver problems. These may include yellowing of your skin or whites of your eyes, dark (tea colored) urine, pale colored stools (bowel movements), nausea, vomiting, loss of appetite, or pain, aching or sensitivity on your right side below your ribs.

Skin rashes have been reported in patients taking PREZISTA. Rarely, PREZISTA has been reported to cause a severe or life-threatening rash. Contact your health care professional if you develop a rash.

Taking PREZISTA with certain medicines could cause serious and/or life-threatening side effects or may result in loss of its effectiveness. Do not take PREZISTA if you are taking the following medicines:

dihydroergotamine (D.H.E.45 ® , Migranal ® ), ergonovine, ergotamine (Wigraine ® , Ergostat ® , Cafergot ® , Ergomar ® ), methylergonovine, cisapride (Propulsid ® ), pimozide (Orap ® ), oral midazolam, triazolam (Halcion ® ), rifampin (Rifadin ® , Rifater ® , Rifamate ® ), indinavir (Crixivan ® ), lopinavir/ritonavir (Kaletra ® ), saquinavir (Invirase ® ), lovastatin (Mevacor ® ), pravastatin (Pravachol ® ), simvastatin (Zocor ® ), or products containing St. John's Wort.

Before taking PREZISTA, tell your health care professional if you are taking sildenafil (Viagra ® ), vardenafil (Levitra ® ), tadalafil (Cialis ® ), atorvastatin (Lipitor ® ), atorvastatin/amlodipine (Caduet ® ), or rosuvastatin (Crestor ® ). This is not a complete list of medicines. Be sure to tell your health care professional about all the medicines you are taking or plan to take, including prescription and nonprescription medicines, vitamins, and herbal supplements.

Tell your health care professional if you are taking estrogen-based contraceptives (birth control). PREZISTA might reduce the effectiveness of estrogen-based contraceptives. You must take additional precautions for birth control such as condoms.
Before taking PREZISTA, tell your health care professional if you have any medical conditions, including allergy to sulfa medicines, diabetes, liver problems (including hepatitis B or C) or hemophilia.


Tell your health care professional if you are pregnant or planning to become pregnant, or are breastfeeding.

The effects of PREZISTA on pregnant women or their unborn babies are not known. You and your health care professional will need to decide if taking PREZISTA is right for you.

Do not breastfeed if you are taking PREZISTA. You should not breastfeed if you have HIV because of the chance of passing HIV to your baby.

High blood sugar, diabetes or worsening of diabetes, and increased bleeding in people with hemophilia have been reported in patients taking protease inhibitor medicines, including PREZISTA.

Changes in body fat have been seen in some patients taking HIV medicines, including PREZISTA. The cause and long-term health effects of these conditions are not known at this time.

As with other protease inhibitors, taking PREZISTA may strengthen the body's immune response enabling it to begin to fight infections that have been hidden. Patients may experience signs and symptoms of inflammation that can include swelling, tenderness or redness.

The most common side effects related to taking PREZISTA include diarrhea, nausea, headache, and abdominal pain. Uncommon but severe side effects such as inflammation of the pancreas and increased blood fat levels have also been rarely reported. This is not a complete list of all possible side effects. If you experience these or other symptoms, talk to your health care professional. Do not stop taking PREZISTA or any other medicines without first talking to your health care professional.

Please refer to the ritonavir (Norvir ® ) Product Information (PI and PPI) for additional information on precautionary measures.

PREZISTA should always be taken at the same time with 100 mg Norvir ® , in combination with other HIV medicines as prescribed by your health care professional. PREZISTA should also be taken with food (the type of food is not important).


Clinical Trials

Evidence of the efficacy of darunavir and ritonavir in antiretroviral treatment-experienced HIV positive adults is shown in analyses of 24- and 48-week data in two randomized, Phase IIb trials, POWER 1 (TMC114-C213) and POWER 2 (TMC114-C202).

Both of these trials consisted of 2 parts: an initial partially-blinded, dose-finding part and a second long-term part in which all patients were randomized to either darunavir and ritonavir or an investigator-selected antiretroviral regimen, then received the recommended dose of darunavir 600 mg and ritonavir 100 mg.

Participants were required to have a baseline HIV RNA (viral load) of greater than 1000 copies/ml, had previous treatment with PIs, non-nucleoside reverse transcriptase inhibitors (NNRTIs), and nucleoside reverse transcriptase inhibitors (NRTIs), and have at least one primary PI mutation at screening, and to be currently taking a stable PI-containing regimen at screening for at least 8 weeks prior to study entry.

24-week Primary Analysis Findings

Analyses included 318 patients in TMC114-C213 and 319 patients in TMC114-C202. At 24 weeks, the virologic response rate was evaluated in patients receiving darunavir and ritonavir plus an optimized background regimen (OBR) versus a control group receiving an investigator-selected PI-containing regimen plus an OBR.

The primary analysis from POWER 1 and 2 showed that at 24 weeks, patients in the darunavir/r arm were significantly more likely to achieve a virologic response, achieve undetectable viral load (less than 50 copies/mL) and have an increase in CD4+ cell counts from baseline compared to the patients in the control arm. An intent-to-treat analysis demonstrated the following:

69.5 percent vs. 21 percent achieved a virologic response defined as equal to or greater than 1.0 log10 reduction (90 percent reduction) in viral load from baseline;
45 percent vs. 12.1 percent achieved undetectable viral load (less than 50 copies/mL); and
Patients experienced a CD4+ cell mean increase of 92 cells/mm3 vs.17 cells/mm3 from baseline.

Analysis of Patients Reaching 48 Weeks of Treatment

Among 110 patients who had reached 48 weeks of treatment in the darunavir/r arm (total n=131) vs. 120 patients who had reached 48 weeks of treatment in the control arm (total n=124), intent-to-treat data showed the following:

61 percent vs. 15 percent had a virologic response defined as equal to or greater than 1.0 log10 reduction (90 percent reduction) in viral load from baseline
46 percent vs. 10 percent reached undetectable viral load (less than 50 copies/mL)
Patients experienced a CD4+ cell mean increase of 102 cells/mm3 vs.19 cells/mm3 from baseline

Among patients reaching 48 weeks, the most commonly reported adverse events among patients in the darunavir/r arm vs. control arm were diarrhea (20 percent vs. 28 percent), nausea (18 percent vs. 13 percent), headache (15 percent vs. 20 percent), nasopharyngitis (14 percent vs. 11 percent) and fatigue (12 percent vs. 17 percent). Discontinuations because of adverse events were seven percent in the darunavir/r arm vs. five percent in the control arm.

 

Pooled POWER 1 and 2 Virologic Response Rates

 

Week 24

Week 48

Efficacy parameter

TMC114/r 600/100mg bid (n=131)

CPI
(n=124)

P-value

TMC114/r 600/100mg bid (n=110)

CPI
(n=120)

P-value

Patients with HIV RNA >=1.0 log10 reduction (%)

70

21

<0.001

61

15

<0.001

Patients with HIV RNA <50 copies/mL (%)

45

12

<0.001

46

10

<=0.003

Mean HIV RNA log10 reduction (copies/mL)

- 1.89

- 0.48

<0.001

- 1.63

- 0.35

<0.001

Mean CD4 increase (cells/mm3)

92

17

<0.001

102

19

<=0.005

* Lazzarin et al. TMC114 provides durable viral load suppression in treatment-experienced patients: POWER 1 and 2 combined week 48 analysis. 16th International AIDS Conference. August 13-18, 2006. Toronto, Canada. Abstract TUAB0104 (oral).


Resistance and Cross Resistance

In analyses of 3 different Phase IIb studies using darunavir, multiple PI-resistant HIV-1 isolates were collected from highly treatment-experienced patients who received darunavir 600 mg and ritonavir 100 mg twice daily and experienced virologic failure either by rebound or by never being fully suppressed. These patients developed amino acid substitutions that were associated with decreased susceptibility to darunavir.

Cross resistance to other PIs has been observed. Darunavir has a less than tenfold decreased susceptibility in cell culture against 90% of 3309 clinical isolates resistant to amprenavir (Agenerase), atazanavir (Reyataz), indinavir (Crixivan), lopinavir (Kaletra), nelfinavir (Viracept), ritonavir (Norvir), saquinavir (Invirase), and/or tipranavir (Aptivus) showing that viruses to these PIs remain susceptible to darunavir.

Darunavir-resistant viruses were not susceptible to amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, or saquinavir in cell culture. However, six of nine darunavir-resistant viruses selected in cell culture from PI-resistant viruses showed a fold change in EC50 values less than 3 for tipranavir, indicative of limited cross resistance between darunavir and tipranavir. Of the viruses isolated from patients experiencing virologic failure taking darunavir 600 mg and ritonavir 100 mg twice daily, greater than 50% were still susceptible to tipranavir, while less than 5% were susceptible to the other PIs.

Cross resistance between darunavir and NNRTIs, NRTIs, and fusion inhibitors is unlikely because the viral targets are different.


Pregnancy

Darunavir is in FDA Pregnancy Category B. There are no adequate and well-controlled studies conducted in pregnant women. Reproduction studies conducted with darunavir have shown no embryotoxicity or teratogenicity in mice, rats, and rabbits.

To monitor maternal-fetal outcomes of pregnant women exposed to zidovudine (or other antiretrovirals), an Antiretroviral Pregnancy Registry has been established. Physicians may register patients at http://www.APRegistry.com or by calling 1-800-258-4263. It is not known whether darunavir is excreted in human milk; it is excreted in the milk of lactating rats. Because of the potential for HIV transmission and for serious adverse effects from darunavir to the breastfed infant, women should be instructed not to breastfeed while taking darunavir.


Drug and Food Interactions

Darunavir must always be taken with ritonavir 100 mg in combination with other antiretroviral drugs.

Coadministration of darunavir and ritonavir with efavirenz (Sustiva) caused a decrease in darunavir AUC by 13% and minimum serum concentrations (Cmin) by 31%, while the AUC and Cmin of efavirenz increased by 21% and 17%, respectively. The clinical significance has not been established; however, this combination of drugs should be used with caution.

Because didanosine (Videx) must be administered on an empty stomach, didanosine should be administered one hour prior to or two hours after darunavir and ritonavir dosing with food.

Coadministration of darunavir and ritonavir with indinavir (Crixivan) resulted in a serum concentration increase in both darunavir and indinavir. The appropriate dose of indinavir in combination with darunavir and ritonavir has not been established.

Coadministration of darunavir with lopinavir/ritonavir (Kaletra) resulted in a 53% decrease in darunavir AUC. Coadministration of darunavir and ritonavir with saquinavir (Invirase) resulted in a 26% decrease in darunavir AUC. Coadministration of these drugs with darunavir is not recommended.

Both darunavir and ritonavir are inhibitors of CYP3A. Coadministration of darunavir and ritonavir with drugs primarily metabolized by CYP3A may result in increased plasma concentrations of such drugs, which could increase or prolong their therapeutic effect and adverse effects.

Carbamazepine, phenobarbital, phenytoin, and rifampin are inducers of CYP450 enzymes and should not be used in combination with darunavir and ritonavir. St. John's wort should also not be used concomitantly with darunavir and ritonavir. Coadministration of these drugs may cause significant decreases in darunavir plasma concentrations and a loss of therapeutic effect to darunavir.

Use of some HMG-CoA reductase inhibitors, including lovastatin and simvastatin, may require dose adjustment if taken concurrently with darunavir and ritonavir because of the potential of serious reactions such as myopathy, including rhabdomyolysis. Coadministration of darunavir and ritonavir with other HMG-CoA reductase inhibitors, such as atorvastatin and pravastatin, should be given at the lowest possible dose of the statin with careful patient monitoring.

Caution must be used when antiarrhythmics, including bepridil, lidocaine, quinidine, and amiodarone, are used concurrently with darunavir and ritonavir. Concentrations of antiarrhythmic drugs may increase. Therapeutic concentration monitoring should be used, if available, to guide patient treatment.

Concurrent use of darunavir and ritonavir with warfarin may decrease warfarin plasma concentrations, and patients should be monitored carefully if they are taking such a regimen.

Concomitant use of trazodone and darunavir and ritonavir may increase plasma concentrations of trazodone, leading to nausea, dizziness, hypotension, and syncope. A lower dose of trazodone should be considered in patients who require this combination of drugs.

Concurrent use of darunavir and ritonavir with clarithromycin may require dose adjustment of the clarithromycin dose in patients with impaired renal function.

Ketoconazole and itraconazole are potent inhibitors as well as substrates of CYP3A. Plasma concentrations of these two drugs may increase in the presence of darunavir and ritonavir. When coadministration is required, the daily dose of azole should not exceed 200 mg. Concurrent use of darunavir and ritonavir with voriconazole has not been studied. However, concomitant use of voriconazole and 100 mg ritonavir twice daily decreased voriconazole AUC by 39%. Therefore, patients receiving darunavir and ritonavir should not receive voriconazole unless the potential benefit outweighs the risk to the patient.

Rifabutin is an inducer and substrate of CYP450 enzymes. Concomitant use of rifabutin with darunavir and ritonavir is expected to increase rifabutin plasma concentrations. It is recommended to administer rifabutin at a dosage of 150 mg rifabutin once every other day when coadministered with darunavir and ritonavir.

Plasma concentrations of calcium channel blockers, including felodipine, nifedipine, and nicardipine, may increase when given concurrently with darunavir and ritonavir. Caution is warranted and clinical monitoring of patients is recommended.

Plasma concentrations of immunosuppressants, including cyclosporine, tacrolimus, and sirolimus, may be increased when coadministered with darunavir and ritonavir. Therapeutic concentration monitoring for the immunosuppressive agent is recommended when these drugs are taken concurrently.

When methadone is coadministered with darunavir and ritonavir, patients should be monitored for abstinence syndrome, as ritonavir is known to induce the metabolism of methadone, leading to a decrease in methadone's concentrations. An increase in methadone dosage may be considered based on the clinical response.

Plasma concentrations of ethinyl estradiol may be decreased when it is used with darunavir and ritonavir due to the induction of its metabolism by ritonavir. Alternative or additional contraceptive measures should be used when estrogen-based contraceptives are coadministered with darunavir and ritonavir.

Concomitant administration of darunavir and ritonavir with PDE-5 inhibitors, including sildenafil, vardenafil, and tadalafil, should be done with caution. PDE-5 inhibitor dosing should not exceed the doses as indicated by the manufacturer.

Darunavir and ritonavir with selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine should be taken concomitantly with caution. The recommended approach is a careful dose titration of the SSRI based on a clinical assessment of antidepressant response. In addition, patients on a stable dose of sertraline and paroxetine who start treatment with darunavir and ritonavir should be monitored for antidepressant response.


Contraindications

Darunavir must always be taken with ritonavir 100 mg in combination with other antiretroviral drugs.

Both darunavir and ritonavir are both inhibitors of CYP3A. Coadministration of darunavir and ritonavir with drugs primarily metabolized by CYP3A may result in increased plasma concentrations of such drugs, which could increase or prolong their therapeutic effect and adverse effects (See section on Drug Interactions above)