In Jainism, the practice of Ekashana (eating once a day) is a form of austerity (tapa) that emphasizes discipline, self-control, and non-attachment to food. Traditionally, during Ekashana, one eats only once during the day, typically before sunset, and abstains from food and sometimes water at other times.

Regarding medicine:

• If the medicine is essential for health and prescribed by a doctor, Jain teachings allow its consumption, as preserving life (prāṇa) is important. However, Jains are encouraged to use medicine with care, choosing those that involve the least amount of himsa (violence), and to avoid unnecessary medication.
• Timing: Strict practitioners may try to take necessary medicine during the time of their meal (during the Ekashana) to maintain the austerity's purity. However, if the medicine is needed at night and delaying it might harm health, most Jain teachers and traditions permit taking it, as health and ahimsa (non-violence, including towards oneself) are given priority.
• Intent: The intention (bhava) behind taking the medicine matters. If it is taken purely for health reasons and not as a food or pleasure, it is generally acceptable.

In summary: If you must take medicine at night for health reasons before Ekashana, it is allowed in Jainism, but you should do so mindfully and with the intention of maintaining health, not for enjoyment or breaking the austerity. If possible, consult your spiritual teacher (guru) for guidance according to your tradition.