LMM coefficient difference

I try to use MixedModels and GLM for binary data outcome analysis. So I have model:

@formula(resp ~ pred1 + pred2)

where pred1 and pred2 are continuous predictors. I fit model with Bernoulli() distribution and LogitLink() link function. After that I have coef vector with 3 coefficients.

So, I want to get difference: pred1 - pred2 and interpret this like exp(OR*). For that I make contrast vector l = [0, 1, -1], than get difference diff = l'*coef(glm_model) and SD: diff_sd = sqrt(dot(l, vcov(glm_model), l)).

Does that calculations meaningful?

*OR = p1 * (1 - p2)/ p2 / (1 - p2)