John Ray
Department of Clincal Pharmacology

Therapeutic Drug Monitoring of HIV Drug Therapy

Preamble

Pharmaceutical care is defined as “the responsible provision of drug therapy for the purpose of achieving definite outcomes that improve a patients’ quality of life”. A ‘one-size fits all’ dosing strategy is an inflexible approach to individualising the drug dose. Response to a drug is determined by pharmacokinetic (absorption, distribution, metabolism..) and pharmacodymanic (e.g. affinity for an enzyme) variability. Thus, the plasma concentration of a drug rather than the dose is a more appropriate surrogate marker of drug effect when the effect cannot be measured directly.

The aim of therapeutic drug monitoring (TDM) is to ensure that plasma drug concentrations are used to adjust dose to achieve maximum therapeutic benefit with minimal drug related toxicity. TDM is useful as a marker early in therapy to ensure adequate plasma drug concentrations, to evaluate therapeutic failure and to aid dose adjustment when a second, interacting, drug is administered.

Tests Available

    Amprenavir    Lopinavir    Nelfinavir     Ritonavir
    Saquinavir    Efavirenz    Indinavir         Nevirapine
    Atazanavir

Sample Collection & Transport

• Collect a morning trough sample (just before the morning dose).
• Efavirenz collect a morning 12 hour sample.
• Collect 1 X 5 mL EDTA (purple top) tube with NO gel separator.
• One tube is adequate for any combination of drugs but you must send 2.0 mL plasma.
• Separate the plasma within 24 hours of collection/store blood at 4oC.
• Transport plasma aliquot in an eski with an ice brick (4oC).
• Send sample and any request form with Pharmacology, St. Vincent’s Hospital, address printed on request. Use your pathology provider as the courier.

Interpretation

Time/date of last dose, time/date of sample collection and when HIV drug therapy commenced must be considered when interpreting drug results. Please put this information on request form.

Cost

    Currently, we are charging Medicare only.
    NOTE: a Medicare assignment form must accompany the request to allow billing.

Contact

    John Ray
    Clinical Pharmacology & Toxicology
    NSW Referral Laboratory for Therapeutic Drug Monitoring    
    A Division of SydPath    Phone:      (02) 8382 9190
    St. Vincent’s Hospital,    Fax:     (02) 8382 3016
    Victoria Street, Darlinghurst NSW 2010    E-mail: jray@stvincents.com.au