What happens if you miss a dose of Human Immunodeficiency Virus (HIV) antivirals?

Consequences of Missing HIV Antiretroviral Doses

Missing doses of HIV antiretroviral medication can lead to viral rebound, development of drug resistance, and increased morbidity and mortality if it becomes a pattern of nonadherence. 1

Immediate Consequences of Missed Doses

• Suboptimal adherence is the strongest predictor for failure to achieve viral suppression below detectable levels 1
• Studies indicate that 90-95% of doses must be taken for optimal viral suppression, with lesser degrees of adherence associated with virologic failure 1
• The risk of viral rebound increases with each consecutive day off therapy, with each treatment interruption lasting more than 2 days significantly increasing this risk 2

Impact Based on Pattern of Missed Doses

• Sustained treatment interruptions pose a greater risk of virologic rebound than the same number of interspersed missed doses, especially at low-to-moderate adherence levels (below 80%) 2
• Each additional consecutive day off therapy increases the risk of virologic rebound by 34% 2
• Each additional treatment interruption lasting more than 2 days increases the risk of virologic rebound by 38% 2

What To Do After Missing a Dose

• If doses are missed by 1-2 days, resume the normal dosing schedule as soon as possible rather than doubling up on medication 3
• Contact your healthcare provider if you've missed multiple doses or if you're unsure about how to proceed 3
• Do not stop taking medication completely if doses are missed, as this increases the risk of viral rebound and resistance 3

Factors Affecting the Impact of Missed Doses

• The consequences of missed doses depend on the specific antiretroviral regimen, as some medications have longer half-lives that provide more forgiveness for occasional missed doses 3
• Non-nucleoside reverse transcriptase inhibitor (NNRTI) based regimens are particularly vulnerable to resistance development with sustained treatment interruptions 2
• Each 10% decrease in average adherence increases the risk of virologic rebound significantly 2

Common Reasons for Missing Doses

• The most frequent reason for missing doses is simply forgetting (53%), followed by ART-related hunger or not having enough food (30%), and medication side effects (12%) 4
• Other factors associated with missed doses include:
  • Lack of trust between clinician and patient 1
  • Active drug and alcohol use 1
  • Active mental illness such as depression 1
  • Lack of patient education about medications 1
  • Lack of reliable access to medical care or medication 1

Strategies to Improve Adherence

• Use daily or weekly pillboxes, timers with alarms, smartphone reminders, and other devices to help maintain adherence 1, 3
• Consider switching to once-daily regimens or fixed-dose combinations to decrease pill burden if adherence is challenging 1
• Incorporate medication taking into daily routines to improve consistency 3
• Enhanced adherence counseling is strongly recommended for individuals who have difficulty maintaining their ARV schedule 3
• Personal telephone and text message reminders have been shown to improve adherence 1, 3

Monitoring After Missed Doses

• Regular viral load monitoring is essential to ensure that occasional missed doses haven't affected treatment efficacy 3
• If a pattern of nonadherence develops, the patient should be closely monitored for viral rebound and renewed immunologic deterioration 1
• Patients should honestly report adherence challenges to their healthcare provider to develop appropriate support strategies 1, 3

Special Considerations

• For post-exposure prophylaxis (PEP), completing the full 28-day course without interruption is particularly important for maximum effectiveness 1
• If you anticipate difficulty adhering to your medication schedule (due to travel, work, etc.), discuss strategies with your healthcare provider in advance 3
• If taking PrEP (pre-exposure prophylaxis), missing doses increases the risk of HIV-1 infection 5