Pharmacologic class: Acyclic purine nucleoside analogue
Therapeutic class: Antiviral
Pregnancy risk category B
How it works
Cyclostad belongs to a class of drugs called antivirals. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.
Cyclostad works by lowering the ability of the herpes virus to multiply in your body. This treats the symptoms of your infection. However, this drug doesn't cure herpes infections. Herpes infections include cold sores, chickenpox, shingles, or genital herpes. Even with this drug, the herpes virus may still live in your body. Your symptoms may occur again later even after the symptoms of your current infection go away.
Cyclostad oral tablet doesn't cause drowsiness but it can cause other side effects.
Adult Mice and Rats: The acute toxicity of oral Cyclostad was determined as shown in Table 6.
Table 6 : Acute Toxicity Studies
Important considerations for taking Cyclostad
Keep these considerations in mind if your doctor prescribes Cyclostad oral tablet for you.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Cyclostad only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2019 Cerner Multum, Inc. Version: 5.08.
For management of a suspected drug overdose, contact your regional Poison Control Centre.
Activated charcoal may be administered to aid in the removal of unabsorbed drug. General supportive measures are recommended.
Cyclostad is only partly absorbed in the gastrointestinal tract. Patients have ingested up to 20 g Cyclostad on a single occasion, with no unexpected adverse effects. In clinical studies, the highest plasma concentration observed in a single patient at these doses was 10.0 μg/mL. Accidental, repeated overdoses of oral Cyclostad over several days have been associated with gastrointestinal effects (such as nausea and vomiting) and neurological effects (headache and confusion).
Intravenous doses administered to humans have been as high as 1,200 mg/m² (28 mg/kg) 3 times daily for up to 2 weeks. Peak plasma concentrations have reached 80 μg/mL. Overdosage of intravenous Cyclostad has resulted in elevations of serum creatinine, blood urea nitrogen and subsequent renal failure. Neurological effects including confusion, hallucinations, agitation, seizures and coma have been described in association with intravenous overdosage.
Patients should be observed closely for signs of toxicity. Hemodialysis significantly enhances the removal of Cyclostad from the blood and may, therefore be considered a management option in the event of symptomatic overdose. Precipitation of Cyclostad in renal tubules may occur if the solubility (2.5 mg/mL) in the intratubular fluid is exceeded. In the event of renal failure and anuria, the patient may benefit from hemodialysis until renal function is restored (see DOSAGE AND ADMINISTRATION).
Q: Is there an Cyclostad ointment?
A: There is an Cyclostad (Zovirax) ointment formulation, available in 5% strength. Currently, Cyclostad ointment is only available as the brand-name Zovirax Ointment 5%. Cyclostad ointment is indicated for the management of initial genital herpes and in limited non-life threatening mucocutaneous herpes simplex virus infections in immunocompromised patients. Cyclostad ointment is not indicated for the prevention of viral transmission to other individuals. Cyclostad ointment is also not indicated for the prevention of recurrent herpes infections. Cyclostad ointment is a prescription ointment that is applied directly to genital herpes lesions and may lessen the duration of the symptoms associated with an initial outbreak. For the management of genital herpes, patients should be instructed regarding appropriate dosage and administration of Cyclostad ointment. Patients should be advised to apply a sufficient quantity of Cyclostad ointment to adequately cover all lesions and apply every 3 hours, 6 times daily, for 7 days of treatment. The dose size of Cyclostad ointment for each application may vary depending on the size of the lesion area. However, the dose size should be approximately Â½ inch ribbon of Cyclostad ointment per 4 square inches of surface area, according to the prescribing information. Patients should be advised to wear a rubber glove or finger cot when applying Cyclostad ointment to the affected area to avoid spreading the virus. Cyclostad ointment should be applied as early as possible after the development of signs and symptoms. During controlled clinical trials, mild pain, including temporary burning and stinging, was reported in approximately 30% of patients with no significant difference between patients receiving Zovirax ointment and patients receiving placebo. Local pruritus was also reported in 4% of patients. Cyclostad ointment 5% should be used exactly as prescribed by a health care provider. Patients should be advised not to exceed the recommended dosage, frequency of applications and length of treatment.
Mechanism Of Action
ZOVIRAX® (Cyclostad), a synthetic acyclic purine nucleoside analog, is a substrate with a high degree of specificity for herpes simplex and varicella-zoster specified thymidine kinase. Cyclostad is a poor substrate for host cell-specified thymidine kinase. Herpes simplex and varicella-zoster specified thymidine kinase transform Cyclostad to its monophosphate which is then transformed by a number of cellular enzymes to Cyclostad diphosphate and Cyclostad triphosphate. Cyclostad triphosphate is both an inhibitor of, and a substrate for, herpesvirus-specified DNA polymerase. Although the cellular α-DNA polymerase in infected cells may also be inhibited by Cyclostad triphosphate, this occurs only at concentrations of Cyclostad triphosphate which are higher than those which inhibit the herpesvirus-specified DNA polymerase. Cyclostad is selectively converted to its active form in herpesvirus-infected cells and is thus preferentially taken up by these cells. Cyclostad has demonstrated a very much lower toxic potential in vitro for normal uninfected cells because: 1) less is taken up; 2) less is converted to the active form; and 3) cellular α-DNA polymerase has a lower sensitivity to the action of the active form of the drug. A combination of the thymidine kinase specificity, inhibition of DNA polymerase and premature termination of DNA synthesis results in inhibition of herpes virus replication. No effect on latent non-replicating virus has been demonstrated. Inhibition of the virus reduces the period of viral shedding, limits the degree of spread and level of pathology, and thereby facilitates healing. During suppression there is no evidence that Cyclostad prevents neural migration of the virus. It aborts episodes of recurrent herpes due to inhibition of viral replication following reactivation.
Dosage Forms, Composition And Packaging
Suspension: Each teaspoonful (5 mL) of ZOVIRAX® Suspension contains 200 mg Cyclostad and the non-medicinal ingredients banana flavour, cellulose, glycerin, methylparaben, propylparaben, sorbitol, vanillin, and water.
Tablets: Each ZOVIRAX® 200 Tablet contains 200 mg Cyclostad and the non-medicinal ingredients cellulose, indigotine, lactose, magnesium stearate, povidone, and sodium starch glycolate.
ZOVIRAX® Suspension is available in bottles of 125 mL* and 475 mL. Each teaspoonful (5 mL) of off-white, banana-flavoured suspension contains 200 mg Cyclostad.
*125 mL bottle not available in Canada
ZOVIRAX® 200 Tablets are available in bottles of 100 tablets. Each blue, shield-shaped, bevel-edged, compressed tablet contains 200 mg Cyclostad, and is imprinted with “ZOVIRAX” on one side and a triangle on the reverse.
GlaxoSmithKline Inc., 7333 Mississauga Road, Mississauga, Ontario, L5N 6L4 1-800-387-7374. Revised: November 10, 2014
Q: I am in stage 1 of multiple myeloma. I was diagnosed nearly 3 years ago. The last 3 summers I have had attacks of shingles, the 1st year I took 1000 mg of Cyclostad daily and avoided the painful stage. Last year I missed the spots as they were on my back and suffered greatly for 2 to 3 months and I am still taking 1000 mg Cyclostad per day. Each time I stop the medication the fever returns for a couple of days followed by the first few spots. I am on my 5th lot of Cyclostad, starting with 1000 mg per day, increasing to 2,400 per day and 2 weeks ago was prescribed 4000 mg per day for 21 days. I have managed 10 days at this level but there are so many side effects, including kidney pain, so I have reduced to 3 tablets of 800 mg each. I feel less "in a fog" and slightly better already but am afraid when I stop the shingles will return. I am concerned about the side effects. Can you give me advice please? The side effects are basically 90% of the ones mentioned on the leaflet in the box of 800 mg tablets at 5 per day.
A: Shingles is a painful rash that is caused by the same virus (varicella virus) that causes the chickenpox. Only people who were infected with the virus and got chickenpox can get shingles. Unfortunately, people with weakened immune systems, from other diseases like cancer or treatments like chemotherapy, are at much greater risk of developing shingles. Drugs like Cyclostad (Zovirax) work to reduce the ability of the virus to multiply and spread in the body. Cyclostad has been shown to reduce the duration of infection and the severity of symptoms, but it relies on an individual's immune system to attack the virus. The drug itself does not kill the virus and that is likely the reason you continue to have symptoms and relapses. It is possible that some of the painful effects you are experiencing are the result of complications of shingles. One of these complications is called postherpetic neuralgia, which is the painful, tingling, and stinging pain at the site of the initial rash. There are medications that are used to help treat the pain associated with the nerve damage of shingles. These drugs include the anticonvulsants, such as Neurontin (gabapentin), Lyrica (pregabalin), and Tegretol (carbamazepine) and tricyclic antidepressants like Elavil (amitriptyline). For more specific information, consult with your doctor or pharmacist for guidance based on your health status and current medications, particularly before taking any action. Michelle McDermott, PharmD
Why is this medication prescribed?
Cyclostad is used to decrease pain and speed the healing of sores or blisters in people who have varicella (chickenpox), herpes zoster (shingles; a rash that can occur in people who have had chickenpox in the past), and first-time or repeat outbreaks of genital herpes (a herpes virus infection that causes sores to form around the genitals and rectum from time to time). Cyclostad is also sometimes used to prevent outbreaks of genital herpes in people who are infected with the virus. Cyclostad is in a class of antiviral medications called synthetic nucleoside analogues. It works by stopping the spread of the herpes virus in the body. Cyclostad will not cure genital herpes and may not stop the spread of genital herpes to other people.
Before taking Cyclostad,
- tell your doctor and pharmacist if you are allergic to Cyclostad, valCyclostad (Valtrex), any other medications, milk proteins, or any of the ingredients in Cyclostad products. Ask your pharmacist for a list of the ingredients.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: amphotericin B (Fungizone); aminoglycoside antibiotics such as amikacin (Amikin), gentamicin (Garamycin), kanamycin (Kantrex), neomycin (Nes-RX, Neo-Fradin), paramomycin (Humatin), streptomycin, and tobramycin (Tobi, Nebcin); aspirin and other nonsteroidal anti-inflammatory drugs such as ibuprofen (Advil, Motrin), and naproxen (Aleve, Naprosyn); cyclosporine (Gengraf, Neoral, Sandimmune); medications to treat HIV or AIDS such as zidovudine (Retrovir, AZT); pentamidine (NebuPent); probenecid (Benemid); sulfonamides such as sulfamethoxazole and trimethoprim (Bactrim); tacrolimus (Prograf); and vancomycin. Many other medications may also interact with Cyclostad, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- tell your doctor if there is a possibility you may be dehydrated from a recent illness or activity, or if you have or have ever had problems with your immune system; human immunodeficiency virus infection (HIV); acquired immunodeficiency syndrome (AIDS); or kidney disease.
- tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking Cyclostad, call your doctor.
- if you are taking Cyclostad to treat genital herpes, you should know that genital herpes can be spread through sexual contact even if you don't have blisters or other symptoms and possibly even if you are taking Cyclostad. Talk to your doctor about ways to stop the spread of genital herpes and about whether your partner(s) should receive treatment.
Cyclostad (Zovirax) is an antiviral drug prescribed to treat genital herpes, shingles, and chickenpox. Side effects drug interactions, dosing, storage, and pregnancy safety information should be reviewed prior to taking this medication.
Q: Are there any Cyclostad interactions with other medications?
A: There are not many Cyclostad (Zovirax) interactions with other medications. If Cyclostad interacts with certain other medications, the effects can be increased, decreased or altered. One Cyclostad interaction possible is with the medication probenecid (Benemid). It is especially important for patients taking probenecid to consult with a health care provider prior to treatment with Cyclostad. If you are currently taking probenecid, you may not be able to take Cyclostad, or you may require dosage adjustments of special tests during treatment. Some of the other possible Cyclostad interactions with other medications may include Demerol (meperidine), Dilantin (phenytoin), Cellcept (mycophenolate mofetil), Viread (tenofovir), Zanaflex (tizanidine), Depakene (valproic acid), Retrovir (zidovudine), theophyllines and the varicella virus vaccine. It is essential for patients to consult with their health care provider regarding all prescription and over the counter medications they take prior to initiation of treatment with Cyclostad to avoid potentially dangerous drug interactions. This includes all vitamins, minerals, herbal supplements and any drugs prescribed by another doctor.
Following oral administration, the mean plasma half-life of Cyclostad in volunteers and patients with normal renal function ranged from 2.5 to 3.3 hours. The mean renal excretion of unchanged drug accounts for 14.4% (8.6 to 19.8%) of the orally administered dose. The only urinary metabolite (identified by high performance liquid chromatography) is 9-guanine.