Para-aminobenzoic acid esters drugs

The sulfonamides have a bacteriostatic rather than a bactericidal action. Many local anesthetics used in the eye are esters of para-aminobenzoic acid, and such drugs will interfere with the action of sulfonamides. Thus, to obtain the maximum effect from instillation of sulfonamide eye-drops, these drugs should not be used until the effect of the local anesthesia disappears. 

Procaine (novocain), the first synthetic local anesthetic, is an amino ester (see Figure 14-1) with low potency, slow onset, and short duration of action. Its use now is confined to infiltration anesthesia and occasionally for diagnostic nerve blocks. Its hydrolysis in vivo produces para-aminobenzoic acid which inhibits the action of sulfonamides. Thus, large doses should not be administered to patients taking sulfonamide drugs. 

The occurrence of photoallergy to esters of / -aminobenzoic acid was described in the discussion of photoallergic topical drugs (Sect. P.IX). Ordinary contact sensitization is more frequent, described as early as 1949 by Meltzer and Baer (1949). Cross-reactions to other para compounds such as paraphenylenediamine-de-rived hair dyes, azo and aniline dyes, local anesthetics (procaine, benzocaine), sulfonamides, and / -aminosalicylic acid occur. The spectrum of cross-reactions varies from patient to patient (Fisher et al. 1958). Fisher (1977) has emphasized the importance of recognizing impurities in a compound as responsible for certain crossreactions, i.e., benzocaine in glyceryl-/7-aminobenzoic acid (Escalol 106),... 

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