Onset of action

Short description: Duration of time between drug administration and effect

Onset of action is the duration of time it takes for a drug's effects to come to prominence upon administration. With oral administration, it typically ranges anywhere from 20 minutes to over an hour, depending on the drug in question. Other methods of ingestion such as smoking or injection can take as little as seconds to minutes to take effect. The determination of the onset of action, however, is not completely dependent upon route of administration. There are several other factors that determine the onset of action for a specific drug, including drug formulation, dosage, and the patient receiving the drug.

## Effect of Administration Route on the Onset of Action

A drug's pharmacological effects can only occur once it has been fully solubilized and has entered the blood stream. For most drugs administered orally, the drug must be ingested, pass through the stomach, and into the small intestine, where the drug molecules enter the blood stream through the villi and microvilli.[1] A few drugs such as alcohol are absorbed by the lining of the stomach, and therefore tend to take effect much more quickly than the vast majority of oral medications which are absorbed in the small intestine. Gastric emptying time can vary from 0 to 3 hours,[2] and therefore plays a major role in onset of action for orally administered drugs. For intravenous administration, the pathway is much shorter because the drug is administered (usually already in solution) directly to the bloodstream.

## References

1. ↑ Pang, K. Sandy (2003). "Modeling of Intestinal Drug Absorption: Roles of Transporters and Metabolic Enzymes (For the Gillette Review Series)". Drug Metabolism and Disposition 31 (12): 1507–1519. doi:10.1124/dmd.31.12.1507. PMID 14625347. http://dmd.aspetjournals.org/content/31/12/1507.full.
2. ↑ Bummer, Paul (2012). Gastro Intestinal Tract and Oral Drug Absorption. University of Kentucky.

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Pharmacology

Ligand (biochemistry)|

| Excitatory|

* Agonist
* Endogenous agonist
* Irreversible agonist
* Partial agonist
* Superagonist
* Physiological agonist

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Inhibitory|

* Antagonist
* Competitive antagonist
* Irreversible antagonist
* Physiological antagonist
* Inverse agonist
* Enzyme inhibitor

|

* Drug
* Neurotransmitter
* Agonist-antagonist
* Pharmacophore

Pharmacodynamics|

| Activity at receptor|

* Mechanism of action
* Mode of action
* Binding
* Receptor (biochemistry)
* Desensitization (pharmacology)

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Other effects of ligand|

* Selectivity (Binding, Functional)
* Pleiotropy (drugs)
* Non-specific effect of vaccines
* Adverse effects
* Toxicity (Neurotoxicity)

|

Analysis|

* Dose–response relationship
* Hill equation (biochemistry)
* Schild plot
* Del Castillo Katz model
* Cheng-Prussoff Equation
* Methods (Organ bath, Ligand binding assay, Patch-clamp)

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Metrics|

* Efficacy
* Intrinsic activity
* Potency (EC50, IC50, ED50, LD50, TD50)
* Therapeutic index
* Affinity

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Pharmacokinetics|

| Metrics|

* Loading dose
* Volume of distribution (Initial)
* Rate of infusion
* Onset of action
* Biological half-life
* Plasma protein binding
* Bioavailability

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LADME|

* (L)ADME: (Liberation)
* Absorption
* Distribution
* Metabolism
* Excretion (Clearance)

|

* Compartment
* Bioequivalence

Related
fields|

| Neuroscience and psychology|

* Neuropsychopharmacology
* Neuropharmacology
* Psychopharmacology
* Electrophysiology

|

Medicine|

* Clinical pharmacology
* Pharmacy
* Medicinal chemistry
* Pharmacoepidemiology

|

Biochemistry and genetics|

* Pharmacoinformatics
* Pharmacogenetics
* Pharmacogenomics

|

Toxicology|

* Pharmacotoxicology
* Neurotoxicology

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Drug discovery|

* Classical pharmacology
* Reverse pharmacology

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* Photopharmacology
* Immunopharmacology
* Cell biology
* Physiology

Other|

* Coinduction (anaesthetics)
* Combination therapy
* Functional analog (chemistry)
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* Chemotherapy
* List of drugs
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| Tolerance and resistance|

* Drug tolerance
* Tachyphylaxis
* Drug resistance
* Antibiotic resistance
* Multiple drug resistance

|

Antimicrobial pharmacology|

* Antimicrobial pharmacodynamics
* Minimum inhibitory concentration
* Bacteriostatic
* Minimum bactericidal concentration
* Bactericide

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