Grapefruit: why this class is not the class that cares

Grapefruit: why this class is not the class that cares Writing it up because I had to work it out twice and would rather nobody else did.

Practical question with the units stated, because I have seen how quickly these go wrong without them.

I have a 2 mg vial of semaglutide and I am working to a 0.25 mg step. My syringes are U-100 insulin syringes, 1.0 mL barrel.

I can do the arithmetic and I have done it twice, getting the same answer both times, but I would like someone to check the reasoning rather than the number — specifically whether I have thought about the residual volume correctly, and whether the graduation I am landing on is one a person can actually read.

Worth separating two things that the opening post runs together.

SGLT2 inhibitors: frequently co-administered and relevant to renal and cardiovascular discussion, not to interactions. There is no pharmacokinetic interaction of concern.

post #47 answers the question as asked. The question underneath it is different.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

On post #48 — agreed on the reasoning, with one qualification.

Separation timing versus clinically important interaction: a separation timing inconvenience (taking one medication 2 hours before or after another) is not the same as a clinically important interaction. Both can reduce absorption of one or the other, but only true interactions require active management.

Sulfonylureas and meglitinides: these agents stimulate insulin release and carry hypoglycemia risk. Combining them with semaglutide or tirzepatide requires dose adjustment of the secretagogue and close monitoring. The combination is not contraindicated but requires active management.

post #94 answers the question as asked. The question underneath it is different.

Anticoagulants: no direct interaction with the compounds in this class. Weight loss and body composition changes might affect the clearance or effect of warfarin if you are on it; monitoring INR more frequently during weight loss is reasonable.

Separation timing versus clinically important interaction: a separation timing inconvenience (taking one medication 2 hours before or after another) is not the same as a clinically important interaction. Both can reduce absorption of one or the other, but only true interactions require active management.

Food interactions: most interactions are absorption interactions. Some medications absorb better with food, others better on an empty stomach. With an incretin agonist that already slows gastric emptying, food effects interact with the drug effect as well.

Oral medications versus time: if you take an oral medication 30 minutes before semaglutide (which slows gastric emptying), the delayed stomach emptying affects when and where the oral medication is absorbed. Separating by a larger interval (1 to 2 hours) usually resolves this.