Inosine pranobex (Isoprinosine or Methisoprinol) is a combinatinon of inosine, acetamidobenzoic acid, and dimethylaminoisopropanol used as an antiviral drug. Inosine pranobex has no effect on viral particles itself. It acts as a immunostimulant, an analog of thymus hormones.It is most commonly used to treat the rare measles complication subacute sclerosing panencephalitis in conjunction with intrathecal interferon therapy

Pharmacodynamic Studies: The in vivo antiviral and antitumour effects of inosine pranobex are secondary to the immunomodulating activity of the drug. Although reports of poor in vitro antiviral activity of inosine pranobex are often in conflict with the reported in vivo antiviral activity of the drug, synergistic antitumour activity has been reported both in vitro and in vivo when the drug was used in combination with fluorouracil.
In vitro exposure of cells to inosine pranobex induces T-lymphocyte differentiation and potentiation of induced lymphoproliferative responses. The drug has been shown to modulate T-lymphocyte and natural killer cell cytotoxicity, suppressor and helper cell functions, as well as to increase the number of IgG and complement surface markers. Interleukin-1 and -2 production, and neutrophil, monocyte and macrophage chemotaxis and phagocytosis are also potentiated by inosine pranobex.
Some of the immunomodulating effects listed above have also been demonstrated in cells from patients administered the drug. In a double-blind comparison in patients with Herpes zoster, inosine pranobex produced a significantly greater restoration of E-rosette activity than placebo, and in 3 of 5 double-blind comparisons in patients with initial or recurrent Herpes simplex genitalis or labialis the drug significantly improved one or two of several immunological responses tested (phytohaemagglutinin response, lymphotoxin production, lymphocyte transformation response, skin test reactivity). Although open studies in patients with subacute sclerosing panencephalitis showed some immunological indices to vary during long term treatment with inosine pranobex, it is difficult to ascertain whether these were effects of the drug or manifestations of the disease process. Open studies in patients with Hodgkin’s or non-Hodgkin’s lymphoma and several studies in irradiated or post-surgery cancer patients (in which full details were not given) have reported that inosine pranobex may induce positive immunomodulating effects. However, further study is needed in this area. As compared with placebo, inosine pranobex has significantly increased the graft versus host response (an indicator of T-lymphocyte competence) in irradiated or chemotherapy-treated patients with cancer of the stomach, colon and/or rectum.
In male patients with persistent generalised lymphadenopathy, who received inosine pranobex 3 or 4g daily for 28 days, several studies reported an improvement in natural killer cell number and function and some of them also reported a concomitant increase in total T-lymphocytes and helper T-lymphocytes; however, significant immunomodulation in patients with clinically apparent acquired immunodeficiency syndrome (AIDS) has not been reported. Two controlled studies have shown that long term treatment with inosine pranobex is associated with an increased rate of clearance of hepatitis B antigen from the serum of patients with acute hepatitis, and open studies in asymptomatic carriers and patients with chronic aggressive infection suggest a similar effect. In patients with autoimmune disease (alopecia totalis, universalis or areata, rheumatoid arthritis or aphthous stomatitis), small open studies intimate some positive inosine pranobex immunomodulating effects, but further study is needed.
The mechanism of action of inosine pranobex remains unknown. However, the drug may act to restore depressed T-lymphocyte function to normal by increasing lymphokine (interleukin-1 and -2) elaboration, or alternatively by increasing cell ribosomal RNA and protein synthesis while simultaneously inhibiting the use of cell ribosomal RNA for viral replication.