External, topical treatments include the anesthetic benzocaine, the antihistamine diphenhydramine, and the corticosteroid hydrocortisone. Other similar compounds are procaine and benzocaine. Hexoralettene N contains benzocaine, menthol and chlorhexidine hydrochloride. The esters include benzocaine, procaine, tetracaine, and chloroprocaine. Lozenges may contain benzocaine, an anaesthetic, or eucalyptus oil. Local anesthetics such as benzocaine, however, are contraindicated. This may include paracetamol (acetaminophen), ibuprofen, benzocaine ear drops, or opioids. Other Chloraseptic formulas are based on benzocaine. Topical agents shown to be effective include antipyrine and benzocaine ear drops. A bath solution of benzocaine has been used to anesthetize amphibians for surgery. Benzocaine is generally well tolerated and non-toxic when applied topically as recommended. Treatment of benzocaine with hydrazine leads to aminostimil - a compound related to isoniazid. Benzocaine is the ethyl ester of "p"-aminobenzoic acid (PABA). Benzocaine can be prepared by esterification using 4-aminobenzoic acid and ethanol. Substances involved may include benzocaine, nitrates, or dapsone.