October 2000
HALIFAX, Nova Scotia - Topical lidocaine 2.5% and prilocaine 2.5% (eutectic mixture of local anesthetics, EMLA, AstraZeneca), does not cause a diminution in the antibody response to the measles-mumps-rubella vaccine (MMR, M-M-R II, Merck), according to researchers here who examined the effect of EMLA on a live viral vaccine.
"It was already known EMLA patches decrease pain associated with needles; our study just confirmed that," said Scott Halperin, MD, director of the Clinical Trials Research Center, Dalhousie University in Halifax, Nova Scotia.
"The new part is that physicians are starting to use the patch for immunization and no one had information whether it would interfere with what we're giving immunizations for - to raise antibodies so kids are protected. Our study is the first study to show that at least for the MMR vaccine, there's no change in the levels of antibodies. So the EMLA patch does not interfere with what we're giving the vaccine for."
According to the study published in The Journal of Pediatrics, a total of 160 healthy infants 12 months and older were enrolled in the randomized, double-blind, placebo-controlled trial. Infants were randomized to receive EMLA or placebo patches prior to immunization and venipuncture. While previous studies showed EMLA decreases pain associated with minor medical procedures, including pain from intramuscular and subcutaneous injections, it was not known if it would diminish the immunogenicity of vaccine, therefore, decreasing efficacy.
EMLA patches are circular shaped and measure 9.6 cm2. Study participants were randomized to receive the EMLA patch or placebo, applied to the mid-thigh muscle and left in place for 60 to 180 minutes, and removed no longer than 10 minutes prior to immunization.
A single lot of MMR vaccine was used in the study, administered subcutaneously with a 25-gauge, 15-mm needle into patients' lateral mid-thigh. EMLA has a subcutaneous penetration of <5 mm - less than the depth of deposition of subcutaneous vaccines.
The vaccination process was videotaped beginning 10 seconds prior to and continuing two minutes after immunization. Baseline recordings were taken before immunization, after parents had time to calm their children. Infants in the study were observed for 15 minutes following immunization. Venipuncture was performed following immunization after videotaping was completed.
Infants were seen one month after receiving MMR, when postimmunization blood specimens were obtained. The researchers measured rubella and mumps antibodies by enzyme immunoassay and measles antibodies by plaque reduction neutralization. Pain was measured with the Modified Behavioral Pain Scale, hence the use of the video recorder. Videotapes were scored in a blind fashion by trained researchers not involved in the clinical aspects of the study.
Levels of measles, mumps and rubella antibodies were similar between the EMLA and placebo groups both before and following immunization.
Between 94.8% and 97.5% of the infants had a fourfold or more increase in antibody titer. EMLA and placebo patients had measles antibody titers of 120 reciprocal dilution (89.7% and 91.1%, respectively), mumps antibody levels of >231 EU/mL (88.3% and 94.9%) and rubella antibody levels of >8 IU/mL (92.3% and 93.7%).
According to the researchers, the study lent additional support that EMLA is effective in reducing pain associated with subcutaneous immunization.
"There's a measurable difference. Is it a large enough difference? That's a difficult question. A parent might say if there's any difference, they want to use it. We didn't really assess that. We're really talking small differences because the bottom line is immunizations are not very painful," said Halperin.
Halperin said they also studied the EMLA patch with the diphtheria-tetanus-acellular pertussis-polio-Haemophilus influenzae type b vaccine (Pentacel, Aventis Pasteur), which is not approved for use in the United States, and with the hepatitis B vaccine (Recombivax, Merck).
"We also studied [the EMLA patch] with other childhood vaccines," said Halperin. "The results were quite similar. Basically the patch decreased the pain associated with immunization and had no effect on the antibody response."
For more information:
- Halperin S, McGrath P, Smith B, et. al. Lidocaine-prilocaine patch decreases the pain associated with the subcutaneous administration of measles-mumps-rubella vaccine but does not adversely affect the antibody response. J Pediatr. 2000;136(6):789-93.
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