Аптека уже закрылась, поэтому я не купил лекарство.

Закрылась is the past tense of закрыться, which means to close in the sense of becoming closed.

• закрыть = to close something
• закрыться = to close / to become closed

So:

• Аптека закрыла... would mean The pharmacy closed something
• Аптека закрылась means The pharmacy closed

In English, we often use close both transitively and intransitively:

• She closed the door
• The store closed

In Russian, that difference is often shown by using -ся.

Because the subject аптека is feminine singular, and the verb is in the past tense.

Past tense in Russian agrees with gender and number:

• masculine: закрылся
• feminine: закрылась
• neuter: закрылось
• plural: закрылись

Since аптека is feminine, we get закрылась.

Уже means already.

So Аптека уже закрылась = The pharmacy had already closed / The pharmacy was already closed depending on context.

Its position is fairly flexible, but placing it before the verb is very common:

• Аптека уже закрылась
• Уже аптека закрылась — possible, but less neutral
• Аптека закрылась уже — possible, but sounds more marked or conversational

In this sentence, уже emphasizes that by the time the speaker wanted to buy the medicine, it was too late.

Because поэтому here introduces the result: therefore / so / that’s why.

The sentence has two parts:

• Аптека уже закрылась
• поэтому я не купил лекарство

Russian normally puts a comma between these clauses.

So the structure is:

[Cause], therefore [result].

No, they are different.

• поэтому = therefore / so / that’s why
• потому что = because

Compare:

• Аптека уже закрылась, поэтому я не купил лекарство.
  The pharmacy had already closed, so I didn’t buy the medicine.

• Я не купил лекарство, потому что аптека уже закрылась.
  I didn’t buy the medicine because the pharmacy had already closed.

They express the same basic idea, but from different directions:

• поэтому introduces the result
• потому что introduces the reason

Не купил uses the perfective verb купить, which focuses on a single completed result — or, with negation, the fact that the result did not happen.

Here the idea is: I didn’t manage to buy it / I ended up not buying it.

Compare:

• Я не купил лекарство = I didn’t buy the medicine
  Focus: the purchase did not happen.

• Я не покупал лекарство = I wasn’t buying medicine / I didn’t buy medicine (as a repeated or ongoing action)
  This sounds different and would usually be used in another context.

In this sentence, не купил is the natural choice because we are talking about one specific failed purchase.

Лекарство is in the accusative case, because it is the direct object of купил.

The dictionary form is:

• лекарство = medicine / a medicine

For neuter inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: лекарство
• accusative: лекарство

That is why the form looks unchanged.

Because Russian has no articles.

Russian does not have direct equivalents of English a/an and the. Whether something is definite or indefinite is usually understood from context.

So:

• аптека can mean the pharmacy or a pharmacy
• лекарство can mean the medicine, a medicine, or just medicine

In this sentence, context makes it natural to translate them as the pharmacy and the medicine or medicine.

Yes. Russian word order is more flexible than English word order, though different orders can change emphasis.

The neutral version is:

Аптека уже закрылась, поэтому я не купил лекарство.

Other possible versions include:

• Я не купил лекарство, потому что аптека уже закрылась.
• Поэтому я не купил лекарство: аптека уже закрылась.
• Лекарство я не купил, потому что аптека уже закрылась.

These all express roughly the same core meaning, but the emphasis shifts.

Russian often uses word order to highlight:

• what is new information
• what is contrastive
• what the speaker wants to stress

Аптека usually means pharmacy.

Depending on context, English might translate it as:

• pharmacy
• drugstore

But the Russian word mainly refers to the place where medicines are sold. It is not automatically as broad as some English uses of drugstore, which can sometimes include many other everyday items.

So for most learners, pharmacy is the safest basic translation.