Acyclovir Tablets at a Glance
How Oral Acyclovir Works — The Systemic Advantage Over Topical Cream
Oral acyclovir uses the same viral thymidine kinase (TK) selectivity mechanism as the cream — but achieves something the cream cannot: systemic drug levels that penetrate nerve tissue where HSV replicates during outbreaks originating from ganglia.
Dosage by Indication — Complete Reference for Acyclovir 200mg Tablets
Acyclovir 200mg tablets are used across several distinct clinical indications with different dosing schedules. Using the wrong dose for the wrong indication is a common patient error:
| Indication | Dose | Frequency | Duration | Notes |
|---|---|---|---|---|
| Genital herpes — first episode | 200mg | 5× daily | 10 days | First episodes are typically more severe and prolonged. Start as soon as diagnosis is confirmed. With or without food. |
| Genital herpes — recurrent episodes | 200mg | 5× daily | 5 days | Start at very first sign of prodrome (tingling, burning). Timing is as critical as with the cream. Delays reduce benefit significantly. |
| Suppressive therapy (chronic daily) | 400mg | 2× daily | Ongoing — reassess every 12 months | For patients with ≥6 outbreaks/year or severe psychosocial impact. Reduces recurrences 70–80%. Also reduces asymptomatic shedding and transmission risk to partners. |
| Oral herpes (cold sores) — severe | 200mg | 5× daily | 5 days | Oral tablets for cold sores when topical cream is insufficient — immunocompromised patients, extensive facial involvement, or frequent severe outbreaks. |
| Herpes zoster (shingles) | 800mg | 5× daily | 7 days | Higher dose required for VZV. Start within 72 hours of rash onset — efficacy drops sharply after this window. Reduces severity, duration, and risk of post-herpetic neuralgia. |
| Varicella (chickenpox) — adults | 800mg | 5× daily (4× daily in some protocols) | 5 days | Recommended for adults and adolescents >12 years where chickenpox is more severe than in children. Start within 24 hours of rash onset for maximum benefit. Not routinely recommended for healthy children. |
Renal impairment — dose adjustment is mandatory: Acyclovir is eliminated by the kidneys. In patients with impaired renal function, drug levels accumulate — causing neurological toxicity (confusion, tremor, seizures) and nephrotoxicity. If your GFR is below 25–50 mL/min, your physician must adjust the dose or extend the dosing interval. Always inform your prescriber about any kidney disease before starting acyclovir tablets.
Acyclovir 200mg vs Valacyclovir 500mg — The Honest Comparison
Valacyclovir (Valtrex) is the prodrug of acyclovir — it converts to acyclovir in the body after absorption. The key difference is bioavailability and dosing convenience:
| Factor | Acyclovir 200mg (Zoviclovir) | Valacyclovir 500mg (Valtrex) |
|---|---|---|
| Oral bioavailability | ~15–20% | ~54% |
| Dosing for recurrent genital herpes | 200mg × 5 daily for 5 days | 500mg × 2 daily for 3–5 days |
| Suppressive therapy dosing | 400mg × 2 daily | 500mg × 1 daily |
| Adherence challenge | High — 5 times daily dosing is difficult to maintain consistently | Low — once or twice daily is far easier to sustain |
| Active compound in body | Acyclovir (directly) | Converted to acyclovir after absorption |
| Efficacy | Clinically equivalent when doses are taken correctly | Clinically equivalent — but higher bioavailability means more consistent drug levels |
| Cost | Lower — generic acyclovir is significantly cheaper | Higher — but generic valacyclovir is now widely available in Canada |
| Best suited for | Cost-sensitive patients who can reliably take 5 doses daily. Short episodic courses. | Most patients — simpler adherence, especially for long-term suppressive therapy. |
From Dr. Sarah Mitchell, RPh: In Canadian clinical practice, valacyclovir has largely replaced acyclovir for most HSV indications because of its simpler dosing schedule. Missing doses of acyclovir during a 5× daily episodic course is very common and significantly reduces efficacy. If cost is not the primary concern, valacyclovir is generally the preferable choice. Acyclovir tablets remain an effective, well-evidenced option — particularly for patients where cost matters or for short-term episodic courses where adherence can be maintained.
When Oral Tablets Are Necessary vs When Cream Is Sufficient
Side Effects
Common — usually mild
- Nausea and vomiting
- Headache
- Diarrhoea
- Abdominal discomfort
- Dizziness
- Fatigue
Less common — report to doctor
- Elevated creatinine / kidney function changes
- Elevated liver enzymes (transient)
- Rash or photosensitivity
- Hair loss (prolonged high-dose use)
- Confusion or agitation (especially in elderly or renal impairment)
Serious — seek immediate care
- Nephrotoxicity — acute kidney injury; risk with dehydration, renal impairment, or high doses. Maintain adequate hydration during therapy.
- Neurological toxicity — tremor, seizures, encephalopathy; almost exclusively in renal impairment. Dose adjustment is critical.
- Thrombotic microangiopathy — very rare; reported in severely immunocompromised patients on high doses
Hydration is important: Acyclovir can crystallise in renal tubules if fluid intake is inadequate — particularly at higher doses (800mg for shingles). Drink at least 2 litres of water daily during acyclovir therapy, especially in hot weather or during physical activity.
Contraindications and Precautions
- Hypersensitivity to acyclovir, valacyclovir, or any excipient
- Renal impairment — dose adjustment mandatory. Risk of neurological and nephrotoxic adverse effects without adjustment.
- Elderly patients — age-related decline in renal function increases risk of toxicity; start at lower end of dose range
- Pregnancy — oral acyclovir is used in pregnancy when the clinical benefit outweighs risk (e.g. severe primary genital herpes, HSV in the third trimester). Discuss with your obstetrician or midwife.
- Dehydration — risk of acyclovir crystallisation in kidneys. Ensure adequate hydration throughout therapy.
- Concurrent nephrotoxic drugs — use with caution; monitor renal function
Drug Interactions
- Probenecid (gout medication) — reduces renal excretion of acyclovir, increasing blood levels. May require dose reduction.
- Cimetidine (H2 blocker) — reduces acyclovir renal clearance; monitor for toxicity
- Mycophenolate mofetil (transplant) — both drugs compete for renal tubular secretion; monitor renal function
- Nephrotoxic drugs (aminoglycosides, NSAIDs, cyclosporine) — additive risk of kidney injury; avoid concurrent use where possible
- Zidovudine (AZT) — combination with high-dose acyclovir may increase neurological side effects in HIV patients; monitor carefully
Frequently Asked Questions — Acyclovir Tablets in Canada
Should I take acyclovir with food? Acyclovir tablets can be taken with or without food. Unlike many medications, food does not significantly affect acyclovir absorption. However, taking it with a meal may reduce nausea — a common side effect particularly with the higher 800mg shingles dose.
Why is the shingles dose 800mg but the herpes dose is 200mg? Varicella-Zoster Virus (VZV — the shingles virus) requires higher acyclovir concentrations to achieve therapeutic inhibition than Herpes Simplex Virus (HSV). VZV thymidine kinase is less efficient at activating acyclovir than HSV thymidine kinase — requiring approximately 10× higher drug levels for equivalent antiviral effect. The 800mg dose for shingles is not an error; it reflects this pharmacological difference.
Is it safe to take acyclovir long-term for suppressive therapy? Yes — acyclovir has been used continuously for up to 10 years in clinical studies with no significant cumulative toxicity identified in patients with normal renal function. Annual reassessment with your physician is recommended to evaluate whether suppressive therapy remains warranted. Renal function should be monitored periodically in patients on long-term therapy, particularly the elderly.
Does acyclovir reduce the risk of transmitting herpes to my partner? Yes — daily suppressive acyclovir reduces asymptomatic viral shedding (the main mechanism of transmission) by approximately 50–60%, and clinical studies show reduced transmission risk. However, it does not eliminate shedding completely. Consistent condom use combined with suppressive therapy provides the best protection.
Why must I start acyclovir within 72 hours for shingles? Antiviral therapy for shingles is most effective when the virus is in its early rapid replication phase — before maximum nerve damage occurs. After 72 hours from rash onset, the virus has largely completed its acute replication burst, and antiviral therapy provides diminishing returns. The 72-hour window also corresponds to the period when acyclovir most reliably reduces post-herpetic neuralgia (PHN) — the chronic nerve pain that can persist for months or years after shingles resolves.
Do I need a prescription for acyclovir tablets in Canada? Yes. Acyclovir tablets are a prescription-only medication in Canada. Your family physician, nurse practitioner, or pharmacist (in provinces with prescribing authority) can prescribe them.
How long does delivery take to my province? Standard delivery to all Canadian provinces and territories takes 4–9 business days. All orders ship in neutral packaging with no external reference to the pharmacy name or medication type.
Related Products
- Aciclovir Cream 5% (Zoviclovir) — topical formulation for cold sores and localised herpes lesions
- Anti-Viral Category — full guide including Acyclovir mechanism, cream vs tablets comparison, and Vermox Generic
The content on this page is for educational purposes only and does not constitute medical or pharmacological advice. Acyclovir tablets are a prescription medication in Canada. Consult a licensed Canadian healthcare provider before starting antiviral therapy. Patients with renal impairment must have their acyclovir dose adjusted by a physician — standard doses can cause serious neurological and kidney toxicity in patients with reduced kidney function. If you have shingles, seek medical attention promptly — the 72-hour treatment window is clinically significant.
