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2025

The Long Haul: Watching the Kidneys on Acyclovir

Modern medicine offers some fantastic tools for managing chronic conditions that used to cause significant distress. Take recurrent genital herpes, for example. For patients plagued by frequent, painful outbreaks, suppressive antiviral therapy – taking a low dose of medication like Acyclovir every day – can be life-changing, preventing recurrences and vastly improving quality of life. But with any medication taken long-term, 'the long haul' as I sometimes think of it, comes the responsibility of vigilant monitoring. Our bodies aren't static, and we need to keep an eye out for subtle shifts or potential impacts over time.

Mr. Peterson is a perfect example. He's a gentleman in his late 70s, sharp wit, keeps active gardening. I've been his urologist for well over a decade. Early on, he suffered terribly with frequent herpes outbreaks. We started him on daily low-dose Acyclovir years ago, and it worked wonders. The outbreaks virtually stopped. He came in for routine check-ups, mostly for prostate health monitoring, feeling generally well and incredibly grateful for the relief the Acyclovir provided.

Part of these routine check-ups always includes basic blood work, including kidney function tests – specifically, serum creatinine. For years, Mr. Peterson's creatinine level was stable, well within the normal range for his age. But over the last year or two, I started noticing a subtle trend. Each time we checked, the number was just a tiny bit higher than the last. Not jumping into danger zones, nothing acute, but a slow, undeniable upward creep. His calculated kidney function, the eGFR, was correspondingly drifting downwards.

Now, a gradual decline in kidney function isn't entirely unexpected in someone approaching their 80s. Age itself can take a toll. He also had well-controlled hypertension, another factor to consider. But my mind immediately went to his daily medication. Could this be related to the Acyclovir?

While generally considered safe, especially at suppressive doses, potential Acyclovir side effects do include effects on the kidneys. It's not common with low-dose oral therapy, but Acyclovir is cleared by the kidneys, and in certain situations – particularly dehydration or higher doses – it can crystallize in the renal tubules, potentially impairing function over time. This is known as crystal nephropathy. Elderly patients can be more susceptible; their baseline kidney function might be lower, and they can sometimes struggle with maintaining adequate hydration.

During his next visit, after reviewing the latest labs showing another small increment upwards in his creatinine, I broached the subject carefully. "Mr. Peterson," I began, "your kidney function numbers are still in a reasonable range, but I've noticed they've been trending up slowly over the past year or so. There are a few possible reasons for this, including just age-related changes. But one thing we need to consider is your long-term Acyclovir use."

I explained the potential mechanism simply. "The medication itself is processed by the kidneys. Rarely, especially if hydration isn't optimal, tiny crystals can form, which might make the kidneys work a bit harder over time. It's usually more of a concern with high IV doses, but it's something we need to keep in mind with long-term use, particularly as we get older."

He listened intently, understandably concerned but also pragmatic. The Acyclovir had drastically improved his life. Stopping it wasn't an appealing prospect.

"So, what do we do?" he asked.

"First," I said, "we focus on hydration. Making absolutely sure you're drinking plenty of fluids every day is the most important step. That helps keep everything flushed through." We discussed practical tips for reminding himself to drink regularly. "Second, we'll continue monitoring your kidney function closely, perhaps a bit more frequently for a while. If the trend continues despite good hydration, we might need to consider adjusting the Acyclovir dose slightly, finding the lowest possible dose that still prevents your outbreaks effectively, based on your current kidney function level."

Stopping the drug entirely would be a last resort, given its benefit to him. It was about finding the right balance – maximizing the quality of life benefits while minimizing potential long-term risks through careful observation and proactive management.

Mr. Peterson appreciated the clear explanation and the plan. It's a reminder that managing chronic conditions with chronic medications isn't a 'set it and forget it' situation. It requires partnership, ongoing assessment, and sometimes, subtle adjustments along the way to ensure the treatment remains both effective and safe over the long haul, especially for our older, more vulnerable patients.

by Dr. Gregory J. Lowe on 2025-05-01 04:03:07