Čak i da osip nestane do sutra, želi vidjeti nalaz prije nego što promijeni lijek.

Čak i da means even if.

In this sentence, it introduces a hypothetical situation: even if the rash disappears by tomorrow...

Compared with čak i ako:

• čak i da often sounds a bit more hypothetical, more tentative, or slightly more stylistic
• čak i ako is often a more straightforward even if

So both can often be translated the same way, but čak i da can feel a little more like even if that were to happen.

Nestane is the 3rd person singular present form of the perfective verb nestati.

After da, Croatian often uses this kind of form to talk about a future or hypothetical event:

• da osip nestane = if the rash disappears / were to disappear

So even though the form looks like present tense, here it refers to a possible future outcome, not a habitual present action.

Because osip is the subject of nestane.

It is the thing that may disappear, so it stays in the nominative:

• osip nestane = the rash disappears

If you are looking for the basic structure, it is simply:

• subject: osip
• verb: nestane

Here do sutra means by tomorrow.

Literally, do often means until / up to, but in this kind of context English usually prefers by tomorrow:

• nestane do sutra = disappears by tomorrow

That means the disappearance happens at some point before tomorrow arrives, or by the deadline of tomorrow.

Croatian often leaves out subject pronouns when they are clear from the verb form or from context.

• želi = he/she wants

So the sentence does not need on or ona unless the speaker wants extra emphasis or contrast.

The same applies to promijeni later in the sentence: the implied subject is usually the same person.

Because Croatian commonly uses željeti + infinitive, just like English uses want + to + verb.

So:

• želi vidjeti = wants to see

This is a very common pattern:

• želim jesti = I want to eat
• želi doći = he/she wants to come

In a medical context, nalaz usually means something like:

• test result
• medical report
• finding
• lab result

The best English translation depends on context. In everyday medical English, report or test result is often the most natural choice.

So here vidjeti nalaz means seeing the medical result/report before changing the medication.

Prije nego što is a fixed expression meaning before when it introduces a full clause.

So:

• prije nego što promijeni lijek = before he/she changes the medication

It is best learned as one unit.

Croatian often uses:

• prije nego što + verb

when English would use:

• before + clause

For example:

• Prije nego što ode, nazvat će me.
• Before he/she leaves, he/she will call me.

Because promijeni comes from the perfective verb promijeniti, which focuses on a single completed change.

Here the sentence is talking about the point at which the person changes the medication, not an ongoing process or a habit. That is why perfective is natural:

• promijeni lijek = changes the medication / makes the change

If you used mijenja, it would sound more like an ongoing or repeated action.

Also, after expressions like prije nego što, Croatian often uses a perfective present form when referring to a future completed action.

It is accusative, but for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: lijek
• accusative: lijek

Here it is the direct object of promijeni, so it is in the accusative, even though the form does not visibly change.

Because the sentence begins with a subordinate clause:

• Čak i da osip nestane do sutra, ...

That opening clause is separated from the main clause by a comma. This is standard Croatian punctuation.

So the structure is:

• subordinate clause: Čak i da osip nestane do sutra
• main clause: želi vidjeti nalaz prije nego što promijeni lijek

Yes, you could say:

• Čak i ako osip nestane do sutra...

That would still be natural and would mean basically the same thing.

The difference is mostly in nuance:

• čak i ako = more neutral, straightforward even if
• čak i da = often a bit more hypothetical or stylistically softer

In many real situations, both are possible.