I would preferably use famotidine or other H2-receptor blockers icompared to proton pump inhibitors (PPI) in severe or critical COVID-19 patients because H2RB have immune modulatory properties (1-3). Furthermore, PPI can increase the risk of pneumonia (4), and fatality in COVID-19 pneumonia (5).

1. Article Possible role of histamine receptors in the central regulati...

2. Article Famotidine use and quantitative symptom tracking for COVID-1...

3. Article Famotidine against SARS-CoV2: A hope or hype?

4. Article Meta-analysis: Proton pump inhibitor use and the risk of com...

5. Preprint Network-Based Analysis of Fatal Comorbidities of COVID-19 an...

Recent evidence indicates proton pump inhibitors (PPI) are related to increased COVID-19 risk, therefore Histamine 2 receptor blockers (H2RB) should be preferred in the times of COVID-19 pandemic.

Proton Pump Inhibitors Tied to COVID-19 Risk

https://www.medscape.com/viewarticle/933645

No drug is non-harmful when the patient don't need it. Drug use in general MUST be rational.Otherwise, one might do empirical study, but not clinical practice.

While the use of famotidine (and others in category) may be helpful and useful for COVID-19 the question is incorrect as there is really almost no data to support the effectiveness, dosage, time length, and other pathology factors in COVID-19. Therefore the use of this (and most other drugs) is not based on 'empiracal' data for treating COVID-19 but simply our best 'guesses.'

I also must agree with Iman Hassan Ibrahim that there is not any drug which may be completely harmless (even our foods can have risks) especially when we are now finding out that PPI's seem to increase the risk of infections from SARS-CoV-2 and this may also include this acid blocker category. The lack of acid may increase the risk that some of the viruses survive the stomach and infect the intestines.