If the extent of bioavailability is equivalent with the two routes, the oral route will likely provide the longest duration of action. The reason for this is that drug from the intramuscular site will be slowly absorbed. Since the elimination doesn't differ between the two routes, the slower absorption of the intramuscular route will produce a lower peak concentration than that seen after the oral route of administration. Therefore, the time during which the drug concentration exceeds the minimum needed for pharmacologic effect is generally going to be less for the intramuscular administration. This means that duration will be greater for oral administration.

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