The photocatalytic degradation of the antiviral drug Isoprinosine (inosine pranobex, IPN) by TiO2 P─25, ZnO and SnO2 was investigated in two different aquatic matrices, i.e. milli-Q-water (MQ) and tap water (TW) under solar irradiation of 500 W/m2. The changes in concentration of IPN during all experiments were monitored using HPLC at a wavelength of 260 nm, and the photocatalytic degradation of IPN followed pseudo-first-order kinetics. The highest value of the pseudo-first-order rate constant of IPN photodegradation (k) was obtained by the presence of 20 mg/l TiO2─P25, (k=0.0483 min-1) in MQ water with the value of the coefficient of determination (R2) equal to 0.9268. The study also assessed the impact of photocatalyst doses and initial IPN concentrations on the efficacy of IPN photodegradation. The results showed that IPN was resistant to degradation under only sunlight (without any photocatalysts addition), with a degradation rate of 9% after 2 hours in milli-Q water and 16% after 2 hours in tap water. However, the addition of selected photocatalysts resulted in the breakdown of the IPN molecule. TiO2-P25 was particularly promising among the tested photocatalysts. The research also discovered that IPN partially adsorbed to TiO2 particles (33% after 2 hours), ZnO particles (26% after 2 hours), and SnO2 (4% after 2 hours). Based on the findings, solar-light-driven photocatalysis could be a promising technique for the degradation of certain antiviral drugs in environmental matrices after optimizing the process.