ART Guidelines

ART Guidelines


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  • ABBREVIATIONS
    /r ritonavir-boosted
    3TC lamivudine
    ABC abacavir
    ADR adverse drug reaction
    AKI acute kidney injury
    ALT alanine transaminase
    ANC antenatal care
    ART antiretroviral therapy
    ARV antiretroviral
    AST aspartate transaminase
    ATV atazanavir
    ATV/r ritonavir-boosted atazanavir
    AZT zidovudine
    bd twice daily
    CD4+ cluster of differentiation 4
    CM cryptococcal meningitis
    CNS central nervous system
    CrAg cryptococcal antigen
    CrCl creatinine clearance rate
    CSF cerebrospinal fluid
    CTX cotrimoxazole
    d4T stavudine
    ddI didanosine
    DILI drug-induced liver injury
    DNA deoxyribonucleic acid
    DRV darunavir
    DRV/r ritonavir-boosted darunavir
    DTG dolutegravir
    eGFR estimated glomerular filtration rate
    ELISA enzyme-linked immunosorbent assay
    ETR etravirine
    FBC full blood count
    FTC emtricitabine
    GI gastrointestinal
    Hb haemoglobin
    HBsAg hepatitis B surface antigen
    HBV hepatitis B virus
    HIV human immunodeficiency virus
    ICU intensive care unit
    INH isoniazid
    INR international normalised ratio
    InSTI integrase strand transfer inhibitor
    IPT isoniazid preventive therapy
    IRIS immune reconstitution inflammatory syndrome
    LAM lipoarabinomannan
    LDL-C low-density lipoprotein cholesterol
    LFT liver function test
    LP lumbar puncture
    LPV lopinavir
    LPV/r ritonavir-boosted lopinavir
    MDRD modification of diet in renal disease
    MTCT mother-to-child transmission of HIV
    MVC maraviroc
    NGT nasogastric tube
    NNRTI non-nucleoside reverse transcriptase inhibitor
    NRTI nucleoside reverse transcriptase inhibitor
    NTDs neural-tube defects
    NtRTI nucleotide reverse transcriptase inhibitor
    NVP nevirapine
    OI opportunistic infection
    PAS p-aminosalicylic acid
    PCR polymerase chain reaction
    PI protease inhibitor
    PI/r ritonavir-boosted protease inhibitor
    PMTCT prevention of mother-to-child transmission of HIV
    PPIs proton pump inhibitors
    PrEP pre-exposure prophylaxis
    QTc corrected QT interval
    RAL raltegravir
    RCTs randomised controlled trials
    RIF rifampicin
    RFB rifabutin
    RNA ribonucleic acid
    RPV rilpivirine
    RTV or /r ritonavir
    sCr serum creatinine
    sCrAg serum cryptococcal antigen
    TAF tenofovir alafenamide
    TAM thymidine analogue mutation
    TB tuberculosis
    TB-IRIS tuberculosis immune reconstitution inflammatory syndrome
    TBM tuberculosis meningitis
    TC total cholesterol
    TDF tenofovir disoproxil fumarate
    TG triglycerides
    TST tuberculin skin test
    UDP uridine 5’-diphospho
    ULN upper limit of normal
    VL viral load
    WHO World Health Organization
    WOCP women of childbearing potential








    Drug-drug interactions
            Key points
     
    • Whenever patients start or switch ARV drugs or start new concomitant medications, it is important to evaluate for potential drug interactions.
    • Many drugs and drug classes have clinically significant drug-drug interactions with ARVs.
    • There are also important drug interactions between several ARVs.
    • It is important to consult a regularly updated database to assess whether drugs can be co-administered and whether dose adjustment is required.
    • Herbal medications (e.g. St John's Wort, garlic) may also have interactions with ARVs, but data on herb-drug interactions are very limited.

    Mechanisms of drug interactions

    There are two main mechanisms of drug-drug interactions:

    Pharmacodynamic interactions occur when one drug influences the action of another drug without altering its concentrations. Such interactions may be beneficial, if drug effects are additive or synergistic; or harmful, if drug effects are antagonistic. Additive toxicity is also a pharmacodynamic interaction (e.g. AZT and linezolid both cause myelosuppression and should not be co-administered).

    Pharmacokinetic interactions occur when a perpetrator drug alters the concentrations of a victim drug by affecting its absorption, distribution, metabolism or excretion. Inhibition is a direct chemical effect when a drug binds to the active site of drug-metabolising enzyme or drug transporter – typically only one or a few enzymes or transporters are inhibited. Inhibition is maximal when the inhibiting drug reaches steady state and wanes rapidly when the inhibiting drug is stopped. Strong inhibitors (e.g. ritonavir, clarithromycin, itraconazole) can cause marked increases in concentrations of victim drugs, resulting in toxicity. Induction results in transcriptional activation of many genes involved in drug metabolism and transport, which takes about 2 weeks to be maximal and wanes in a similar timeframe. Strong inducers (e.g. RIF, carbamazepine, phenytoin) can caused marked decreases in concentrations of victim drugs, resulting in reduced efficacy. Pharmacokinetic interactions are occasionally beneficial (e.g. RTV markedly increases the concentrations of other PIs). Data on herb-drug interactions are very limited – both St John’s Wort and garlic are known inducers. Clinically significant pharmacokinetic interactions require dose adjustment of the victim drug or, if the interaction is severe, avoiding co-administration with the perpetrator drug.

    Overview of drug-drug interactions by antiretroviral class
    • NRTIs are generally neither victims nor perpetrators of clinically significant pharmacokinetic interactions.
    • PIs: RTV is a potent inhibitor of the key cytochrome P450 (CYP) enzyme 3A4 and the drug efflux transporter P-glycoprotein; it also induces several other drug-metabolising enzymes and drug transporters. Therefore, RTV-boosted PIs are frequent perpetrators of pharmacokinetic interactions, but can also be victims of such interactions when co-administered with strong inducers – co-administration with strong inhibitors does not add significantly to the inhibition by RTV. ATV/r requires an acid pH in the stomach for absorption – it should be taken 2 hours before or 1 hour after antacids, and administration with PPIs is not advised.
    • NNRTIs differ by individual drug. EFV is a moderate inducer. RPV can be the victim when co-administered with strong inducers. Although inhibitors increase exposure to RPV, it is seldom necessary to adjust the dose. ETR induces CYP3A4 and also inhibits two CYP enzymes; it can also be the victim when co-administered with strong inducers.
    • InSTIs: Polyvalent cations (calcium, magnesium, iron, aluminium) bind to InSTIs, reducing their absorption. InSTIs can be taken 2 hours before or 6 hours after polyvalent cations. However, calcium and iron can be co-administered with InSTIs if taken with a meal, but not in the fasted state. InSTIs are victim drugs when co-administered with strong inducers. InSTIs are not perpetrator drugs, except DTG inhibits an efflux transporter important in the elimination of metformin (metformin dose should not exceed 500 mg 12-hourly).
       

    There are many important pharmacokinetic drug interactions between ARVs and other drugs, as well as between different ARVs. Some of these drug-drug interactions are discussed in other sections of these guidelines (e.g. interactions with RIF in Module 18). The full list of all potential drug interactions is very long and beyond the scope of these guidelines.

    Knowledge of drug interactions is constantly evolving. Clinicians are advised to seek reliable information on drug-drug interactions when using non-standard ART regimens and when drugs are co-administered, using one or more of the resources listed in Box 4.
     

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    Common pitfall: Not checking for interactions between concomitant drugs and current or newly initiated ARVs. Concomitant drugs may need dose adjustment or discontinuation when ART is switched, e.g. switching from a moderate inducer (such as EFV) to a strong inhibitor (such as a PI/r), or from either of these to an InSTI.

    Common pitfall: Not considering marked increases in statin considerations when used concomitantly with PIs. There are major interactions between PIs and many statins resulting in marked increases in statin concentrations. Low-dose atorvastatin (not exceeding 10 mg, which will give equivalent exposure to ~60 mg) can be used with PIs, but simvastatin cannot be used.