Effect of herbal medication on amoxicillin activity

Journal of Dental Hygiene, Fall, 2004 by Truc Nguyen, Aubrey Yost

Purpose. This study investigated whether three herbal medicaments had any effects on amoxicillin activity.

Methods and Materials. Streptococcus mitis was the indicator microorganism. The following were placed on 10mm filter paper discs using a pipette:

T1) St. John's Wort extract (15 M-BM-5l) and amoxicillin solution (15 M-BM-5l)

T2) Echinacea extract (15 M-BM-5l) and amoxicillin solution (15 M-BM-5l)

T3) Ginkgo Biloba extract (15 M-BM-5l) and amoxicillin solution (15 M-BM-5l)

T4) Amoxicillin, positive control (15 M-BM-5l prepared solution at concentration of 125 mg/5 ml)

T5) Sterile water, negative control (30 M-BM-5l)

The series was repeated 5 times (25 times). Plates were incubated for 24 hours at 37M-BM-:C. Zones of inhibition (mm) were measured and analyzed using the Kruskal-Wallis Ranks and Mann-Whitney U-Tests. Zones of inhibition, areas of no microbial growth, are produced on bacteria-inoculated agar whenever an antimicrobial is diffused into the medium from the paper disc. The effect of the antimicrobial is negative if no zone of inhibition develops, while a moderate or large zone indicates that the bacterium would not grow in the presence of that medication. This test is used routinely to determine clinical microbial sensitivity or resistance to many antimicrobials.

Results. The mean inhibition zone was determined for each treatment. For T1, the value was 74.40 mm (SD=6.82). T2 averaged 55.3 mm (SD=15.49), while T3 measured 60.67 mm (SD=1.84). T4 value was 73.87 (SD=6.49), and T5 measured 0 (SD=0). T1 was greater than both T2 and T3 (p=0.008), but T1 showed no significant difference from T4 (p=0.841). T2 showed no significant difference from T3 (p=0.841), and T2 and T3 was less than T4 (p=0.008). All treatments were greater than T5 (p<0.0001).

Conclusion. Results showed that echinacea extract and gingko biloba extract reduced the zone of inhibition of amoxicillin at a significant level. St. John's wort appeared to increase amoxicillin zone of inhibition.

Clinical Significance. It is imperative that patients disclose use of all medications and herbal supplements because antibiotic efficacy may be negatively affected.

Truc Nguyen and Aubrey Yost

Dental hygiene students at Loma Linda University School of Dentistry, Loma Linda, CA. James D. Kettering, PhD, and Rhonda Hammerslough, RDH, MA, EdS, faculty advisors