Partial agonist

Short description: Agonist drug having partial efficacy at a receptor

Relationship between percentage activity and concentration of full agonists and partial agonists

In pharmacology, partial agonists are drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist. They may also be considered ligands which display both agonistic and antagonistic effects—when both a full agonist and partial agonist are present, the partial agonist actually acts as a competitive antagonist [citation needed], competing with the full agonist for receptor occupancy and producing a net decrease in the receptor activation observed with the full agonist alone.[1] Clinically, partial agonists can be used to activate receptors to give a desired submaximal response when inadequate amounts of the endogenous ligand are present, or they can reduce the overstimulation of receptors when excess amounts of the endogenous ligand are present.[2]

Some currently common drugs that have been classed as partial agonists at particular receptors include buspirone, aripiprazole, buprenorphine, nalmefene and norclozapine. Examples of ligands activating peroxisome proliferator-activated receptor gamma as partial agonists are honokiol and falcarindiol.[3][4] Delta 9-tetrahydrocannabivarin (THCV) is a partial agonist at CB2 receptors and this activity might be implicated in ∆9-THCV-mediated anti-inflammatory effects.[5] Additionally, Delta-9-Tetrahydrocannabinol (THC) is a partial agonist at both the CB1 and CB2 receptors, with the former being responsible for its psychoactive effects.

## See also

* Competitive antagonist
* Intrinsic sympathomimetic activity of beta blockers
* Inverse agonist
* Mixed agonist/antagonist

## References

1. ↑ Calvey, Norman; Williams, Norton (2009). "Partial agonists". Principles and Practice of Pharmacology for Anaesthetists. John Wiley & Sons. p. 62. ISBN 978-1-4051-9484-6. https://books.google.com/books?id=lnRlU12Q4h8C&pg=PA62.
2. ↑ "Mechanistic explanation for the unique pharmacologic properties of receptor partial agonists". Biomedicine & Pharmacotherapy 59 (3): 76–89. April 2005. doi:10.1016/j.biopha.2005.01.010. PMID 15795100.
3. ↑ "Honokiol: a non-adipogenic PPARγ agonist from nature". Biochimica et Biophysica Acta (BBA) - General Subjects 1830 (10): 4813–9. October 2013. doi:10.1016/j.bbagen.2013.06.021. PMID 23811337.
4. ↑ "Polyacetylenes from Notopterygium incisum--new selective partial agonists of peroxisome proliferator-activated receptor-gamma". PLOS ONE 8 (4): e61755. 2013. doi:10.1371/journal.pone.0061755. PMID 23630612. Bibcode: 2013PLoSO...861755A.
5. ↑ "PHARMACOLOGICAL PROPERTIES OF THE PHYTOCANNABINOIDS ∆9-TETRAHYDROCANNABIVARIN AND CANNABIDIOL - Phd thesis of: Dr. Daniele Bolognini - PDF". 2010. http://insubriaspace.cineca.it/bitstream/10277/269/1/Phd_thesis_bolognini_completa.pdf.

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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

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* 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)

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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)

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* Compartment
* Bioequivalence

Related
fields|

| Neuroscience and psychology|

* Neuropsychopharmacology
* Neuropharmacology
* Psychopharmacology
* Electrophysiology

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Medicine|

* Clinical pharmacology
* Pharmacy
* Medicinal chemistry
* Pharmacoepidemiology

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Biochemistry and genetics|

* Pharmacoinformatics
* Pharmacogenetics
* Pharmacogenomics

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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)
* Polypharmacology
* Chemotherapy
* List of drugs
* WHO list of essential medicines

| Tolerance and resistance|

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

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Antimicrobial pharmacology|

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

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