A fixed set always takes the dative, whatever is happening: mit, nach, bei, seit, von, zu, aus. That is why it is zum Arzt, bei der Ärztin, mit dem Rezept, seit einer Woche. Learn them as a block and half of German case choice is settled.
Examples
- Ich gehe morgen zum Arzt.
- I am going to the doctor tomorrow.
- Mit dem Rezept bekommst du die Tabletten.
- With the prescription you can get the tablets.
- Ich habe seit einer Woche Husten.
- I have had a cough for a week.
The mistake to avoid
Zu plus dem contracts to zum, and zu plus der to zur - the full forms sound wrong.
Where this fits in
Body, health & feelings, German A2: Talk about your body, common illnesses, and how you feel. Visit a doctor or pharmacy and describe symptoms.