Tonic water: A rare cause of exanthema

Introduction

To the Editor, Tonic water (or Indian tonic water) is a carbonated soft drink in which quinine is dissolved. Quinine is an alkaloid extracted from cinchona's bark.¹ Originally used as a prophylactic drink against malaria, nowadays it has significantly lower quinine content and is drunk for its distinctively bitter taste. In Europe, the European Food Safety Authority limits quinine's concentration in tonic water to 100mg/L,² 0.25–0.50% of the concentration used in original therapeutic tonic water. Quinine is also a flavour component of bitter lemon, carbonated chinotto beverages and some traditional flavoured wines. Nowadays, tonic water containing quinine is added to many jello shot recipes to make the shot fluorescent. Reported cases of exanthemas caused by quinine contained in tonic water are rare. Suspected allergy to quinine has to be studied, especially if the patient is planning to travel to a malaria endemic region. This allergy confirmation is still so important because, even nowadays, quinine is a mainstay in the treatment of severe malaria.³ Other antimalarial medicines, used extensively in the treatment and prevention of malaria, such as chloroquine and mefloquine,³ share a common quinoleine core with quinine which may explain the possibility of cross reactivity,⁴ although this process has not been clearly demonstrated. This evidence emphasises, even more, the importance of quinine allergy investigation. We report the case of a 37-year-old man who was sent to our outpatient clinic by the traveller's health clinic for suspicion of quinine allergy. The patient mentioned that more than 20 years ago he had a maculopapular exanthema...