Intravesical chemotherapy: studies on the relationship between osmolality and cytotoxicity

The effectiveness of intravesical chemotherapy for the treatment of superficial bladder cancer may be influenced by the conditions of administration, such as the osmotic strength of the instillate. Urine from patients with bladder cancer before treatment had osmolalities in the range 187 to 852 mOsm./kg. and these had decreased by an average of 135 mOsm./kg. at the completion of intravesical chemotherapy. Clinical preparations of drugs used for intravesical chemotherapy had osmotic strengths ranging from 65 to 1,038 mOsm./kg. The antitumor activities of the drugs most frequently used intravesically (doxorubicin, epodyl, mitomycin C and thiotepa), and of cisplatin and epirubicin in media of 6 different osmolalities were measured with a human bladder cancer cell line by inhibition of colony-forming ability. Reducing osmotic strength from 590 to 125 mOsm./kg. significantly increased the in vitro cytotoxicities of thiotepa, mitomycin C, cisplatin and epirubicin but not those of doxorubicin and epodyl. We conclude that the use of an instillate at the lowest achievable osmotic strength probably will be optimal for the intravesical administration of chemotherapeutic drugs.