Acyclovir is a widely used antiviral medication, particularly for treating infections caused by the herpes simplex virus [1]. However, the frequency of acyclovir resistance can vary depending on several factors.

According to a study published in the Journal of Infectious Diseases, the prevalence of acyclovir resistance among immunocompetent adults is relatively low, with estimates ranging from 0.1% to 7.7% [2]. However, the resistance rate can be significantly higher in immunocompromised patients or those who have been taking the drug for an extended period. For instance, the resistance rate can reach up to 30% in patients with advanced HIV infection [3].

It is also essential to note that mutations in the virus can lead to acyclovir resistance. These mutations may affect the virus's ability to bind with and incorporate the drug, reducing its effectiveness [1].

In summary, while acyclovir resistance is not overly common in the general population, certain factors such as immunocompromised status or prolonged drug use can increase the likelihood of resistance. It is always best to consult with healthcare professionals regarding any concerns about medication effectiveness or potential side effects.

Sources:
[1] <https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR>
[2] <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC145299/>
[3] <https://www.nature.com/articles/ijos20163>