Bel direct bij zwelling of zeldzame bijwerkingen.

Bel is the imperative form of bellen (to call).

In Dutch, commands often use just the verb by itself, without a subject:

• bellen = to call
• ik bel = I call
• u belt = you call
• Bel! = Call!

So Bel direct ... means Call immediately ...

Dutch often leaves out je or u in instructions, especially in medical, official, or practical language.

Yes. In this sentence, direct means immediately / right away.

English often uses an -ly adverb (directly, immediately), but Dutch very often uses the same form as the adjective:

• een direct antwoord = a direct answer
• Kom direct! = Come immediately!

So here direct functions like an adverb, even though it does not change form.

Not literally. In this kind of medical instruction, bij usually means:

• in case of
• if there is
• when experiencing

So bij zwelling of zeldzame bijwerkingen means something like in case of swelling or rare side effects.

This is a very common use of bij in warnings and instructions.

Dutch often omits articles in short instructions, warnings, and labels.

So instead of something fuller like:

• Bel direct bij een zwelling of bij zeldzame bijwerkingen

you often get the more compact style:

• Bel direct bij zwelling of zeldzame bijwerkingen

This style is common in medicine packaging, manuals, and notices. It sounds brief and practical.

Zwelling is singular, meaning swelling.

In this type of warning, Dutch often uses a singular noun in a general sense:

• bij koorts = in case of fever
• bij pijn = in case of pain
• bij zwelling = in case of swelling

It does not necessarily mean only one single swelling. It refers to the condition in general.

Because zeldzame is an adjective placed before a noun, and in Dutch that adjective usually takes -e.

Here:

• zeldzaam = rare
• bijwerkingen = side effects
• zeldzame bijwerkingen = rare side effects

This -e ending is very common before nouns, especially in plural noun phrases like this one.

Bijwerkingen is the plural of bijwerking, meaning side effect.

It is a compound noun:

• bij- = secondary / additional / side-
• werking = effect / working

So:

• bijwerking = side effect
• bijwerkingen = side effects

Dutch uses compounds very often, and they are written as one word.

Yes. Of here is simply the conjunction or.

So:

• zwelling of zeldzame bijwerkingen = swelling or rare side effects

Be careful not to confuse this with other uses of of in Dutch, such as in indirect yes/no questions:

• Ik weet niet of hij komt = I don’t know whether he is coming

In your sentence, it just means or.

That is normal in Dutch instructions when the context is already clear.

In a medical leaflet or on packaging, Bel direct ... usually means:

• call your doctor
• call the pharmacy
• call emergency services
• call the contact number already mentioned nearby

Dutch often leaves this unstated when the surrounding text makes it obvious.

Yes. This sentence is very compact and typical of medical or official instructions. In fuller everyday Dutch, you might see something like:

• Bel direct als u zwelling of zeldzame bijwerkingen krijgt.
• Bel onmiddellijk bij zwelling of zeldzame bijwerkingen.

These versions make the situation more explicit. The original is shorter and more leaflet-like.