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Severe acute gastrointestinal side-effects following high oral doses of metronidazole (6 g/m2) could be avoided by a combined oral and rectal application. With tablets and an enema (1 g metronidazole/2 ml) in a ratio 1:4 and an increased dosage of 10 g/m2, maximal serum concentrations of about 200 micrograms/ml are obtained like after an oral dosage of 6 g/m2. The maximal radiosensitizing effect on hypoxic tumor cells is seen five hours after oral application and seven hours after the combined oro-rectal application. No longterm toxicity was found following six high doses of metronidazole.

In a quantitative study we have compared the serum levels, the time course and the photosensitizing capacity of a conventional crystalline 8-methoxypsoralen brand and an investigational liquid formula. Evidence is presented showing that the liquid preparation is superior to the crystalline form: it peaks earlier after ingestion, it produces higher and more constant degree of photosensitization, it is eliminated more rapidly from the blood, and it requires a lower UV-A dose for eliciting photosensitivity reactions aiming at a reduction of the total cumulative UV-A dose required for clearing psoriasis.