A Cochrane review included 3 studies with a total of 148 subjects. One poor quality trial (23 people), compared intravenous glycyrrhizin and intravenous procaine. It found no significant difference between the two interventions for treating symptoms and rash.
One fair quality trial (85 people), compared the oral antihistamine dexchlorpheniramine (4 mg), the oral steroid betamethasone (500 mcg), and a combination of betamethasone (250 mcg) and dexchlorpheniramine (2 mg). It found no significant difference in itch resolution at two weeks, as rated by the participants, between dexchlorpheniramine and betamethasone, and the combination of dexchlorpheniramine and betamethasone. However, both dexchlorpheniramine and betamethasone alone seem to be better at clearing rash than the combination of dexchlorpheniramine and betamethasone. These interventions were not compared with placebo.
The small good quality trial (40 people) that compared oral erythromycin and placebo found that erythromycin was more effective than placebo in terms of rash improvement, as rated by the trialists, after two weeks (RR 13.00; 95% CI 1.91 to 88.64). It was also more effective in decreasing the itch score (difference of 3.95 points, 95% CI 3.37 to 4.53).
No serious adverse effects were reported for the interventions. Two out of 17 people on oral erythromycin and 1 out of 17 on placebo reported minor gastrointestinal upset.
Comment: The quality of evidence is downgraded by imprecise results; few patients and wide confidence intervals.