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En excerpt from the book : 

by Ross, R.Ph. Pelton, Lee Overholser

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ISOPRINOSINE,® a registered trademark of SysteMed, Inc., has demonstrated strong antiviral activity and is an important agent for restoring and strengthening the immune system. It is marketed in over fifty countries around the world under the trade names of Methisoprinol and Inosiplex. In Europe, Mexico, and other areas Isoprinosine is also prescribed for patients who have compromised immune systems due to conditions like AIDS. Unfortunately, it is not approved by the FDA for distribution in the United States, although it can be imported from other countries.


In many cancer patients chemotherapy and radiation suppress the immune system. The immunodepressed patient frequently develops viral infections and other complications that increase mortality. Isoprinosine is often given to these patients because of its antiviral action (7) and its ability to activate natural killer (NK) cells and stimulate the production of T- and B-cell lym-phocytes. (8, 9)

Clinical Studies

In one study Isoprinosine was used to treat viral infections in patients with acute leukemia, chronic leukemia, and Hodgkin's disease. Favorable results were seen in 75 percent of the acute leukemias, in 80 percent of the chronic leukemias, and in each of three Hodgkin's cases. (13)

In another study Isoprinosine was tested as both a curative and a prophylactic treatment for viral infections in patients with leukemia. In twenty-five schoolchildren with leukemia and at high risk for viral infections, 76 percent showed very good response to Isoprinosine therapy. In another group of twenty-five high-risk leukemia patients, none developed viral infections. (12)

Studies have shown that the use of Isoprinosine along with relatively low doses of interferon enhances the antitumor effect of interferon. The best results were obtained when both interferon and Isoprinosine were injected three times a week for one month. (2)

Gastrointestinal Cancers

Gastrointestinal cancers account for a large number of diagnosed malignancies. Surgically removing the tumor is the most widely accepted treatment throughout the world. However, the surgical procedure itself often suppresses the host immune system and may cause metastatic spreading of the disease.

Besides the body's reaction to the surgery itself, the immune system can be depressed by general anesthesia, the cortisol produced by the body under stress, transfusions, and many of the drugs commonly used in association with surgery, such as sedatives, analgesics, sleep medications, and broad-spectrum antibiotics.

Because spreading of the cancer is frequently the primary cause of failure in surgery for gastrointestinal cancer, patients are often treated postoperatively with chemotherapy and radiation. Of course, chemotherapy and radiation both decrease immune-system activity in patients, who are already immuno-suppressed.

At the surgical clinics at the University of Rome, a group of thirty patients underwent surgery for gastrointestinal cancer and then received chemotherapy and radiation. In a controlled trial, the test patients were given 4 grams of Isoprinosine per day. The treatment began fourteen days after surgery and continued for twenty-eight days. The immunological scores in the Isoprinosine-treated patients nearly doubled with respect to the controls. (4) Improvement was seen by day seven of the treatment and persisted through day forty-two, with best results observed after fourteen days of treatment.

Isoprinosine and Radiation

In a double-blind study, Isoprinosine was used to evaluate the immune function in cancer patients receiving pelvic radiation. Within three months of treatment, Isoprinosine-treated patients showed a much more rapid return of immune function. By the third month, 54 percent of the patients receiving Isoprinosine showed immune restoration, compared with only 13 percent in the control group. (6) By the fifth month, the number of patients with restored immune systems was equal, indicating that the control group had caught up with the treatment group.

A similar study treated twenty-nine patients with uterine cancer, forty-six patients with breast cancer, and thirty-one patients with cancers of the ear, nose, and/or throat. In all cases, cellular immunity restoration occurred significantly earlier in the Isoprinosine-treated group. On day 105 of the study, 62.5 percent of the patients receiving Isoprinosine showed immunorestoration, compared with 33.3 percent of the controls, and 70.8 percent of the breast cancer patients showed immunorestoration, versus only 22.7 percent of the controls. (1)

Isoprinosine is an immunorestorative agent that is effective in preventing and/or curing a wide range of the opportunistic secondary infections that often occur in cancer patients undergoing traditional forms of chemotherapy and radiation treatment. Its effectiveness in cancer therapy has not been fully evaluated.

Isoprinosine and Melanoma—Pulse Therapy

The pattern of administration appears to affect the effectiveness of Isoprinosine. A group of melanoma patients who received surgery was divided into three groups. Group I received only surgery; groups II and III received Isoprinosine according to different schedules after their surgery. (11)

Group II received Isoprinosine for five days, alternating with ten days without the drug. The patients stayed on this schedule throughout the period of the study. Group III took Isoprinosine on the schedule of five days on and ten days off for two months. The participants then took the drug for five days once every two months. These intermittent schedules for taking drugs are called pulsed therapy.

Group II experienced an initial improvement in surgery-induced immune deficiency, but subsequently developed a slight immunodepression. Group III had a prolonged restoration in immune response. The authors emphasize that immunological follow-ups during Isoprinosine therapy are needed and that the research is continuing to determine what the best pulsed dosage schedule will be.

Negative Studies

Some studies indicated that Isoprinosine was ineffective in clearing up infections or restoring the immune system in cancer patients. However, examination of these trials shows that the patients failed to respond due to one or more of the following reasons:

  • a) duration of treatment was too short (5, 10)
  • b) dosage administered was too small (5)
  • c) patients treated were already too critical to respond to treatment (3)

In one study (14), the immune restorative effect of Isoprinosine was studied in sixty patients with various types of cancer. Forty patients received Isoprinosine, and twenty served as controls. The authors report that 50 percent of the immunodepressed patients showed restoration of immune function. Even though half of the patients did not respond to treatment with Isoprinosine, the authors state, "These results demonstrate an im-munomodulatory effect of Isoprinosine in cancer patients and lend further support to the use of this drug as an immunomod-ulating therapy among cancer patients."

In another study with a negative outcome, the authors point out that Isoprinosine's antiviral effect is attributed to stimulation of lymphocytes. In some cases, Isoprinosine's failure could be related to selection of patients who are already deficient in lymphocytes due to previous chemotherapy or irradiation. (5)

Side Effects and Toxicity

Isoprinosine is virtually without side effects and toxicity. All published studies report excellent drug tolerance. Only a very few patients reported gastric distress. In a few patients there is a temporary rise in serum uric acid. Uric acid levels should be monitored for patients who have gout, kidney disease, or kidney stones. There appears to be no gastrointestinal or blood toxicity associated with the administration of Isoprinosine. (4)


Isoprinosine is most frequently administered at the rate of 4 gm per day or at 50 mg/kg/day, administered orally in three or four equal doses during waking hours. It is marketed as a 500-mg tablet.

The pulsed dosage therapy mentioned in this chapter was very interesting, but it was mentioned in only one study. At this time pulsed administration should be considered experimental, and, therefore, a recommended dosage cannot be given.

Although AIDS is not the topic of this book, it seems appropriate to point out that many studies have been published showing that Isoprinosine's antiviral and immunostimulatory effects can benefit AIDS patients. In fact, Isoprinosine is being used in Scandinavian countries for the treatment of AIDS.