Se a infeção piorar, talvez eu precise de outro antibiótico.

In this sentence, se is a conjunction meaning if.

So Se a infeção piorar means If the infection gets worse.

This is different from the other very common se, which can be a reflexive pronoun, as in ele lavou-se (he washed himself). Portuguese uses the same word for several functions, so you have to identify it from context. Here, it clearly introduces a condition, so it means if.

Here, piorar is the future subjunctive, not a plain infinitive in function.

After se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation:

• Se chover, fico em casa. = If it rains, I’ll stay home.
• Se a infeção piorar... = If the infection gets worse...

The confusing part is that for many -ar verbs, the future subjunctive form looks exactly like the infinitive in the singular:

• infinitive: piorar
• future subjunctive: piorar

So the form is the same, but the grammar is different.

A useful comparison:

• se for from ir/ser
• se tiver from ter

Those make it easier to see that Portuguese is really using a special tense here.

Because talvez often triggers the subjunctive when it expresses uncertainty or possibility.

So:

• talvez eu precise = correct here
• talvez eu preciso = not natural in standard Portuguese in this meaning

The verb precise is the present subjunctive of precisar.

This happens because talvez means maybe/perhaps, and the speaker is not presenting the need for another antibiotic as a fact, only as a possibility.

Compare:

• Eu preciso de outro antibiótico. = I need another antibiotic.
  This is presented as a fact.
• Talvez eu precise de outro antibiótico. = Maybe I need / may need another antibiotic.
  This is uncertain, so subjunctive is used.

Precise is the present subjunctive form of precisar for eu.

A quick comparison:

• indicative: eu preciso
• subjunctive: que eu precise

In this sentence, the subjunctive appears because of talvez:

• talvez eu precise

So even though English says maybe I need or maybe I may need, Portuguese uses a special verb form to show uncertainty.

That is true: Portuguese often omits subject pronouns because the verb ending already shows who the subject is.

So both of these are natural:

• talvez eu precise de outro antibiótico
• talvez precise de outro antibiótico

Including eu can make the sentence slightly clearer or more explicit, especially in longer sentences or when the speaker wants to keep the subject clearly in focus. It is not wrong or unusual; it is just more explicit than necessary.

Because the verb precisar is commonly used with the preposition de in European Portuguese.

So:

• precisar de alguma coisa = to need something

Examples:

• Preciso de ajuda.
• Precisamos de mais tempo.
• Talvez eu precise de outro antibiótico.

In some varieties of Brazilian Portuguese, especially in informal speech, you may hear precisar without de, but in European Portuguese, precisar de is the normal choice and the safest one for learners.

Because outro can work by itself as a determiner meaning another or other.

So outro antibiótico is completely natural and usually the most straightforward choice here:

• de outro antibiótico = of another antibiotic / another antibiotic

You can also hear um outro antibiótico, but that can sound a bit more emphatic or stylistically heavier depending on context.

For a learner, the important point is:

• outro + noun is normal
• you do not need um before outro

Portuguese uses articles more often than English, and here a infeção refers to a specific infection already known in the situation.

So the article a is natural because the sentence is talking about the infection in question, not infection in general.

Compare:

• A infeção piorou. = The infection got worse.
• Uma infeção pode ser grave. = An infection can be serious.

Here, it is clearly a specific infection, so a infeção is the expected form.

Yes, infeção is the modern standard spelling in Portugal under the current orthographic rules.

Older spelling:

• infecção

Current standard spelling:

• infeção

So if you come across infecção, it is usually an older spelling or a spelling kept in older materials. In modern European Portuguese, infeção is what you should learn and use.

Yes. Portuguese allows several natural word orders here.

For example:

• Se a infeção piorar, talvez eu precise de outro antibiótico.
• Talvez eu precise de outro antibiótico se a infeção piorar.
• Se a infeção piorar, eu talvez precise de outro antibiótico.

The original version is very natural. It starts with the condition and then gives the possible result.

A punctuation note:

• If the se clause comes first, a comma is normal: Se a infeção piorar, ...
• If the se clause comes after the main clause, the comma is usually omitted: Talvez eu precise de outro antibiótico se a infeção piorar.

A native speaker would normally process it like this:

• Se a infeção piorar = conditional clause, using the future subjunctive
• talvez = marker of uncertainty
• eu precise = present subjunctive, because the statement is only a possibility
• de outro antibiótico = complement of precisar

So the sentence combines two ideas:

1. a possible future condition
2. an uncertain possible result

That is why you see two different subjunctive-related forms in the same sentence:

• piorar after se
• precise after talvez