Principles of pharmacology and pharmacokinetics - delivery techniques, such as oral, intravenous, transdermal

Routes

Drug delivery route (oral, intravenous, intramuscular, subcutaneous, transdermal, inhaled, and others) determines onset speed, bioavailability, and practical administration considerations - route selection should match the clinical urgency, required reliability of absorption, and patient-specific factors (swallowing ability, venous access, adherence considerations)
A fundamental prescribing decision made for essentially every medication, with route selection sometimes as clinically important as the drug and dose chosen

Intravenous administration provides immediate, complete bioavailability given direct systemic delivery, appropriate for emergencies requiring rapid onset; oral administration is convenient but subject to absorption variability and first-pass metabolism; transdermal/depot formulations provide sustained, steady-state delivery over extended periods, useful for chronic conditions requiring consistent drug levels without frequent dosing

Route selection should be explicitly reconsidered as clinical circumstances change (e.g. a patient unable to swallow requiring conversion from oral to an alternative route, with appropriate dose adjustment for bioavailability differences)
Emergency/critical situations favour IV administration for speed and reliability; chronic stable conditions may favour longer-acting depot/transdermal formulations for adherence and steady-state benefits; patient-specific factors (swallowing difficulty, cognitive impairment affecting reliable oral dosing) should inform route selection
Route change requires dose adjustment reflecting bioavailability differences between routes for the same drug

Depot antipsychotic/contraceptive formulations for adherence support, transdermal opioid patches for chronic stable pain, enteral vs parenteral nutrition route selection, route conversion dose adjustment
Depot and transdermal formulations offer a specific adherence advantage in patients with unreliable daily oral dosing (e.g. some patients with severe mental illness on depot antipsychotics) by removing the need for daily patient action - route selection can therefore be as much an adherence strategy as a pharmacokinetic one

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