In IPA usage and also when a language uses both U+0061 LATIN SMALL LETTER A and U+0251 LATIN SMALL LETTER ALPHA or both U+0069 LATIN SMALL LETTER I and U+0269 LATIN SMALL LETTER IOTA it is important to design the italic in such a way so that there is no confusion between the characters. One solution for that could be to slant the "a" or "i" characters rather than design them in a true italic style. In the example below the USV is shown in the first row, the regular style characters are shown in the 2nd row, standard italic is shown in the 3rd row (where they are easily confused) and the 4th row shows "a" and "i" in a slant italic style (which helps differentiate between the characters).
Although all the "a" and "i" characters are not demonstrated here, they should all be slanted (such as U+00E0 LATIN SMALL LETTER A WITH GRAVE, U+00E1 LATIN SMALL LETTER A WITH ACUTE, U+00E2 LATIN SMALL LETTER A WITH CIRCUMFLEX, U+00E3 LATIN SMALL LETTER A WITH TILDE, U+00E4 LATIN SMALL LETTER A WITH DIAERESIS, etc.).