The Importance of Adherence

Factors Influencing Adherence

Measuring Adherence

HIV Therapy Adherence

Adherence Issues

Coping Strategies



The Importance of Adherence Next

Anti-HIV drugs must be taken reliably to ensure that they reach and are maintained at high enough concentrations in infected cells to inhibit HIV replication. A fall in the concentration of a drug to below a critical level allows the virus to continue replicating and provides ideal conditions for the development of drug resistance. This ultimately leads to a need for increasing drug concentrations to control viral replication (Figure 1).

Figure 1: The importance of regular dosing

As drug levels in the body drop, due to missed or delayed dosing, replication and mutation takes place. Mutations lead to drug resistance, which increases the amount of drug needed to prevent replication (IC100). The time spent when the body’s drug concentration is lower than the IC100 therefore increases, allowing replication to continue for longer. Eventually, the IC100 will rise above the maximum drug concentration in the body and the drug will have no affect on viral replication.


Adherence to prescription instructions is one of the most important factors in ensuring maximum benefit from drug treatment (Figure 2). This is important for all types of medication, including all types of anti-HIV drugs and treatments for opportunitistic infections such as CMV retinitis and candida. Adherence to drug schedules also allows individuals to play an active part in their treatment; providing an opportunity to participate in the management of their disease1 - something most people value.

This graphic clearly demonstrates the direct relationship between the number of daily doses taken (ie.adherence to therapy regimen) and the development of mutations and plasma viral load; when therapy is adhered to viral load declines, when doses are missed viral load rises.

Person A is relatively consistent in his/her medication taking, missing few doses during the 150 days monitored. Most of the viral replication is therefore suppressed and the viral load, which is represented by log RNA, declines accordingly. Person B does not adhere to the therapy regimen as well as Person A, missing many doses and at one point taking less then 2 doses a day. Viral replication takes place and the viral load rises.

(Adapted from JAMA, 1996:276;24)
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