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In clinical practice and in most ongoing studies in adult and pediatric tumours, daily short-time infusions of ifosfamide (IFO) on 2-5 consecutive days with cycle doses between 6 g/m2 and 12 g/m2 are used at present. The continuous i.v. infusion of IFO/mesna over 1-5 days is still experimental. Since mesna prevents IFO-induced urotoxicity, the IFO dose could be increased to 16 g/m2 per cycle. As the dose and schedules of IFO/mesna were increased and varied, CNS and renal toxicity became more evident. CNS toxicity seems not to be dependent on i.v., but on oral dosing of IFO. Renal dysfunction and previous administration of cisplatinum predispose for CNS toxicity. The incidence or severity of CNS toxicity does not increase with subsequent courses of IFO i.v. The nephrotoxicity of IFO is dependent on IFO dose, diuresis, mesna dose and whether there has been previous cisplatinum and seems to involve preferentially the tubulus system, leading to 25 cases of Fanconi renal syndrome as published in 1988-1990. Fanconi's syndrome depends on the cumulative IFO dose, the previous administration of nephrotoxic drugs such as cisplatinum and the age of the children. Studies are continuing to determine the least nephrotoxic dose and schedule of IFO plus mesna. Leucopenia and thrombopenia are well-known dose-dependent side-effects of IFO, with similar incidence after i.v. short-time and continuous infusion.

Antitumor activity (increase in lifespan and cure) was greater for ifosfamide (IFO) in several experimental tumors, some of which were primarily resistant to cyclophosphamide (CYC). IFO has been shown to be active in anthracycline-resistant and in adriamycin/cisplatin-resistant sublines of an Ehrlich ascites tumor, as well as in tumor cells primarily resistant to CYC. The few comparative controlled clinical trials available suggest superior single-agent activity of IFO compared with CYC in soft tissue sarcoma and ovarian cancer. Combination chemotherapy with IFO has been effective in second-line treatment of sarcomas, malignant lymphomas, lung cancer, and testicular cancer, most of them pretreated with or refractory to CYC. Although it is difficult to obtain clinical proof that there is no cross-resistance between IFO and CYC, IFO has been shown to be active in multirefractory malignant lymphomas, in small cell lung cancer not responding to adriamycin, vincristine, and etoposide, and in soft tissue and bone sarcomas. Testicular cancer and pancreatic cancer are some of the tumors in which IFO activity is currently being evaluated and in which CYC has so far failed to show sufficient clinical activity. More comparative controlled clinical trials are needed in ovarian cancer, breast cancer, malignant lymphomas, sarcomas and cervical cancer, in which IFO has already shown sufficient single-agent activity. Due to its lower level of cross-resistance with a variety of heterocyclic products, but also with other alkylating agents, in addition to its use in induction chemotherapy, IFO is an important second-line agent in many clinical situations.

The intravenous injection of the lighter lanthanide ions Pr(III), Nd(III), and Sm(III) in doses of 35 mumoles/kg inhibits, and isoosmolar doses of the heavier lanthanide ions Gd(III), Dy(III), and Er(III) stimulate rat liver nuclear in vitro RNA synthesis catalyzed by RNA polymerase B 24 h after their application, while nuclear RNA synthesis, catalyzed by RNA polymerase A, was inhibited by the same isoosmolar doses of Pr(III), Nd(III) and not influenced by Sm(III), Gd(III), Dy(III), or Er(III). The effect of in vivo applied Pr(III) and Nd(III) on rat liver in vitro nuclear RNA synthesis shows a similar time and dose-dependent pattern. The decreased rat liver nuclear in vitro RNA synthesis 24 h after intravenous injection of Pr(III) as well as after Nd(III) was accompanied by a decreased nuclear in vitro 3H-acetate uptake by the chromatin-bound histone fractions, F 2a2, F 3, and F 2al. At the same time after the Pr(III) injection, the capacity and number of initiation sites of the rat liver nuclear template for homologous nuclear RNA polymerases, prepared from control rat liver nuclei, was lower than the corresponding control template. A decreased activity of endogenous free nuclear RNA polymerases, as determined with the aim of the synthetic poly(dA-dT) template 24 h after Pr(III), may further contribute to the decreased nuclear RNA synthesis. The results indicate a primary ionic size-correlated interference of lanthanides with the nuclear control mechanisms of RNA synthesis.

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