OBJECTIVES: I. Compare the efficacy of heme arginate, singly or in combination with tin mesoporphyrin, in lowering porphyrin precursors in patients with asymptomatic acute intermittent porphyria.

II. Evaluate and compare the safety and tolerability of these treatment regimens in this patient population.

PROTOCOL OUTLINE: This is an unblinded, dose ranging study. Patients receive heme arginate alone or in combination with tin mesoporphyrin.

Patients receive tin mesoporphyrin IV as a single dose. Heme arginate is administered as a single intravenous infusion.

Patients are entered in cohorts of 4. Subsequent cohorts of 4 patients each receive escalating doses of tin mesoporphyrin in combination with 1 of 2 different dosages of heme arginate. Subjects must maintain a constant diet.

Patients experiencing adverse reactions are followed as clinically indicated.

PROTOCOL ENTRY CRITERIA:

--Disease Characteristics--

• Documented acute intermittent porphyria in remission for at least 1 month
• Increased excretion of porphyrin precursors
• Absence of neurovisceral symptoms due to porphyria for at least 1 month

--Prior/Concurrent Therapy--

• At least 1 month since prior heme preparation therapy
• Concurrent medication for coexisting condition is allowed, as long as dose and pattern of administration is held constant during study

--Patient Characteristics--

• Renal: Urinary porphobilinogen excretion of at least 20 mg every 24 hours
• Other: Not pregnant Fertile female patients must use effective contraception during and at least 6 months before study At least 1 month since any symptoms of disease No concurrent acute hemorrhagic disorder such as: Gastrointestinal bleeding Intracerebral hemorrhage No known hypersensitivity to heme arginate, tin mesoporphyrin, another heme preparation, or related heme analogue No other condition that may increase risk to patient