Minor Determinants of Penicillin and Amoxicillin Are Still Key Components of Penicillin Skin Testing.

BACKGROUND

The positive rate and pattern of penicillin skin test (PST) has been reported to be decreasing and changing. Previous studies differ about which penicillin component is the dominant component in positive PST result.

OBJECTIVE

To characterize past and current PST patterns to determine whether different determinants in PST have changed over time.

METHODS

A retrospective review of electronic medical records (January 2001-December 2017) was performed for patients who underwent PST. Data were divided into 4 cohorts to see whether trends occurred over time. The cohorts were divided as follows: cohort 1 (2001-2005), cohort 2 (2006-2010), cohort 3 (2011-2015), and cohort 4 (2016-2017).

RESULTS

A total of 30,883 patients underwent PST with the following breakdowns per cohort: cohort 1, 6,536; cohort 2, 10,372; cohort 3, 10,640; and cohort 4, 3,335. Of these, 329 patients (1.0%) had a positive PST result with a wheal of 3 × 3 mm or greater, with 110 in cohort 1, 130 in cohort 2, 67 in cohort 3, and 22 in cohort 4, whereas 170 patients (0.5%) had a positive PST result with a wheal of 5 × 5 mm or greater, with 54 in cohort 1, 72 in cohort 2, 34 in cohort 3, and 10 in cohort 4. When the positive PST rates of cohort 2 (1.25%), cohort 3 (0.6%), and cohort 4 (0.6%) were compared with those of cohort 1 (1.7%), there was a significant decrease in positive PST rates (P = .0278; P < .0001; P < .0001, respectively). When cohort 1 positive rate to benzylpenicillin polylysine among the positive PST (wheal of 3 × 3 mm or greater) was compared with those of the other cohorts (cohorts 2-4), the percent positive of benzylpenicillin polylysine in PST was 27% compared with 21% (P = .38), 34% (P = .5), and 18% (P = .6), respectively. When the positive PST result was defined as a wheal of 5 × 5 mm or greater, the positive rate for benzylpenicillin polylysine in PST increased over time (cohort 2: 22%, P = .8; cohort 3: 32%, P = .3; cohort 4: 40%, P = .264) compared with cohort 1 (19%).

CONCLUSIONS

Positive PST rate is decreasing. We demonstrate that despite benzylpenicillin polylysine solely positive rates remaining relatively stable, the minor penicillin determinants and amoxicillin play an important role in PST and their adoption into standard protocol for routine PST should be considered.