PABA MAY INCREASE SERUM LEVELS. URINARY ALKALISERS, ANTACIDS, CORTICOSTEROIDS MAY INCREASE EXCRETION, MAY POTENTIATE THE EFFECTS OF ANTICOAGULANTS, HYPOGLYCAEMICS, METHOTREXATE, PHENYTOIN, VALPROIC ACID, TRICYCLIC ANTIDEPRESSANTS. MAY ANTAGONISE URICOSURICS, SPIRONOLACTONE AND TETRACYCLINES.