Please stop giving the current medication; promethazine is generally not recommended for infants under two years old due to safety risks. For a six-month-old, over-the-counter cough and cold medicines are usually avoided. Instead, you can safely use paracetamol drops to manage her fever, dosed strictly according to her weight. To relieve her cold, use saline nasal drops and a bulb syringe to clear her nose, and ensure she stays well-hydrated with breast milk or formula. Since her symptoms have lasted a week, please consult a paediatrician for a safe, hands-on evaluation.

Promethazine syrup can help relieve symptoms of dry cough and cold by reducing allergy-related irritation and helping with sleep. It is generally safe when taken in the correct dose as prescribed by a doctor, but it can cause side effects like drowsiness, dizziness, or dry mouth, so it should be used with caution, especially in children, elderly people, or those with certain medical conditions. It should not be used for long periods, and activities requiring alertness (like driving) should be avoided after taking it. For most mild cases, simple measures like rest, fluids, steam inhalation, and basic medicines may be enough, and it is best to consult a doctor before using promethazine to ensure it is appropriate for your condition.

Persistent cough with weight loss should not be ignored, as it may be due to infection (like tuberculosis), allergy, asthma, or other lung conditions. Phenergan may help with allergy-related cough, but it will not treat the underlying cause. It is important to see a doctor for proper evaluation and treatment.