<p>There is no absolute contraindication but the risk of anaphylaxis is increased by repeated parenteral administration.&nbsp;Mild allergic phenomena, such as sneezing or mild asthma are warning signs that further may give rise to anaphylactic shock. To avoid this possibility it is advisable to start a second course of injection with a dose considerably lower than that previously used. Because of the above, vitamin B1 injection should not be given intravenously except in the case of comatose patients. Once thiamine deficiency is corrected there is no need for parenteral administration or for the administration of amounts in excess of daily requirement.</p>