What Changes the Drug, and What Changes the Teaching

1 · Food, timing Levothyroxine, a thyroid hormone, is taken on an empty stomach with water, separated from calcium and iron by several hours. Alendronate, a bisphosphonate, is taken on waking with a full glass of plain water while the patient stays upright and takes nothing else by mouth for the next half hour.

2 · Food, chelation Tetracyclines and fluoroquinolones bind calcium, magnesium, aluminum and iron. Dairy, antacids, and mineral supplements are separated from the dose or the antibiotic never reaches the bloodstream.

3 · Food, enzyme Grapefruit juice inhibits intestinal CYP3A4 and raises blood levels of certain statins and of dihydropyridine calcium channel blockers. The teaching point is to avoid the juice, not to change the dose.

4 · Food, consistency Vitamin K intake is kept consistent on warfarin rather than eliminated, because the target is a stable international normalized ratio and not a low one. A patient who suddenly stops eating greens destabilizes just as surely as one who suddenly starts.

5 · Lab, and what the nurse does with it Rising creatinine on an angiotensin-converting enzyme inhibitor: report. Falling platelets on heparin: hold and report. Rising transaminases on a statin: report and clarify. Serum creatinine reviewed before metformin is given around iodinated contrast: clarify before administering. Every entry ends in a verb.

6 · Herbal and over-the-counter St. John's wort induces CYP3A4 and reduces the effect of oral contraceptives, warfarin, cyclosporine and several antiretrovirals. Ginkgo, garlic, ginger, and high-dose fish oil add bleeding risk to anticoagulants and antiplatelets. An over-the-counter nonsteroidal anti-inflammatory drug added to an angiotensin-converting enzyme inhibitor and a diuretic raises acute kidney injury risk sharply. Acetaminophen hidden inside combination cold and sleep products pushes patients past the daily maximum without their knowing.

7 · Lifespan and pregnancy Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers carry a boxed warning for fetal toxicity and are stopped when pregnancy is detected. Warfarin is teratogenic, so heparin or a low molecular weight heparin is used in pregnancy instead. Tetracyclines discolor developing teeth and are avoided in pregnancy and in young children. Aspirin is avoided in febrile children because of Reye syndrome. In older adults, reduced renal clearance and cumulative anticholinergic burden change the choice before the dose does. The old pregnancy letter categories were retired and replaced by narrative pregnancy and lactation labeling, so no letter appears in this book.

Watch outherbal products are drugs. They belong on the medication reconciliation, and the patient will not volunteer them unless asked by name.

Margin noteask what else they're swallowing. → BOOK 05 · P10

No creatinine, transaminase, platelet, or international normalized ratio value is printed → BOOK 07. No maximum daily dose is calculated → BOOK 06. Psychotropic interactions, including any serotonin-related syndrome → BOOK 14.

TakeawayA safe order becomes unsafe through food, a lab result, a supplement, or a life stage, and all four are asked about at intake.