Successful oral desensitization to i.v. para-aminosalicylic acid (PAS) using encapsulated PAS dry substance.

para-Aminosalicylic acid (PAS) is commonly used in the treatment of drug-resistant tuberculosis, including multidrug-resistant tuberculosis. Since its first use in the 1940s, hypersensitivity reactions frequently limit its use in clinical practice. Cases of successful desensitization against PAS using orally administered ascending doses are described in the literature. A 25-year-old patient with severe pulmonary multidrug-resistant tuberculosis developed drug fever with rash, acral cyanosis, and shivering immediately after the intravenous application of PAS. Hard gelatine capsules containing PAS dry substance were prepared in order to desensitize this patient. Encapsulated PAS was applied orally in rising doses starting with 10 mg/day and doubling the dose every 2 days until the half-maximal dose of 5,120 mg was reached. Desensitization covers a period of 21 days. Subsequent intravenous application of PAS at the full dose was well tolerated. In a 12-month follow-up period, no more allergic reactions appeared. PAS dry substance encapsulated in hard gelatine capsules and administered orally in rising concentrations may be useful to archive a successful desensitization for subsequent intravenous applications.