This can be due to combination of;
1) The antibiotics are secreted in the saliva. That are common reason to coat the tongue.
2) Phlegm can coat the tongue.
3) Gastroesophageal reflux disease; this can precipitate due to the chest cold or due to antibiotics.
This should resolve on its own (spontaneously), when the chest cold gets better and antibiotics are stopped. No active treatment is required for it.
Please feel free for your follow up questions.
Usually three days are sufficient. But sometimes if the symptoms are inadequately relieved, you may need additional three days of azithromycin. If the symptoms are same in the severity, a culture of phlegm may be considered.
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