creatinine(out) + H(+)(in) => creatinine(in) + H(+)(out)
creatinine(out) + h(+)(in) => creatinine(in) + h(+)(out)
creatinine(out) + H(+)(in) => creatinine(in) + H(+)(out)
creatinine(out) + h(+)(in) => creatinine(in) + h(+)(out)