Some clinical questions

[GravityBeetle]

Haven't posted these in a while. Here we go...

1. This came up a while ago. Are there any dosing strategies for initiating diltiazem with an IV bolus followed by po? From what I know it's supposed to be IV bolus -> second IV bolus if needed -> IV infusion -> start PO 1 hr before stopping infusion. Also is there a max dose for weight based dosing of the IV bolus (0.25 mg/kg actBW)?
2. In the new 2019 CAP guidelines, for outpatient without comorbidities, doxycycline is recommended over macrolides it seems unless your area has low macrolide resistance rates. However for outpatient with comorbidities and inpatients, macrolides are preferred over doxycyclines in combination with a beta lactam (strong recommendation vs conditional). Why is this?
3. Another ID question. Would you say if viral bronchitis or influenza symptoms do not get better after a week or get worse, would it be appropriate to initiate antibiotics for pneumonia even without a positive chest xray?
4. Any guidelines or recommendations for treating superficial vein thrombosis? Uptodate says NSAIDS for uncomplicated cases but does not list a specific agent, dose, duration
5. Why is the max dose for IV ondansetron higher than PO? It is 24 mg/day for PO and 48 mg/day for IV (up to 16 mg/kg/dose x 3 doses/day). Usually it is the other way around...

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[Rockinacoustic]

Good questions:

1. For rate control, you can do a max repeat Diltiazem bolus of 0.35mg/kg if the first bolus was ineffective. You are correct when transitioning from IV infusion to oral start your PO dose 1 hour before you start titrating down the infusion rate (i.e. you wouldn't just have someone go from 15mg/hr to nothing in that hour). There's a well published formula for IV infusion to PO conversion but it's not evidence based.
2. There is no-where in the US where macrolide S. pneumoniae resistance rates are <25%, therefore Doxycycline/high-dose amoxicillin is a better empiric option for you're healthier outpatients. Adding a beta-lactam adds that additional S. pna coverage to macrolide therapy, and from what I remember most of the clinical trials compared that combo to fluoroquinolones. Theoretically, Doxycycline should be equally as effective in combination but there's not as must randomized data to support it for inpatients.
3. I'm never making this decision but I would say this is reasonable if the patient is not getting better and still has signs/symptoms of an infection
4. Not aware of any guidelines, but I would look at what primary literature uptodate is referencing for that recommendation
5. I also don't know this but would hazard to guess you're using higher IV doses for pre-treatment in chemotherapy patients where PO would not be appropriate.