| Class | Cholinergic |
|---|---|
| Chemistry |
Imidazole drivative alkaloid |
| Routes of administration |
Eyedrops, but also orally |
| Absorption |
Probably good oral bioavailability, as it undergoes little hepatic metabolism; whereas ocular bioavailability is supriringly poor for a predominantly ocular agent (1-3%) |
| Solubility |
pKa 6.6, good water solubility, poor lipid solubility |
| Distribution |
VOD = 2.3L/kg, minimally protein-bound |
| Metabolism |
Minimal hepatic metabolism; mostly metabolised to pilocarpic acid by serum esterases and acetylcholinesterase in the synaptic cleft |
| Elimination |
minimal renal elimination |
| Time course of action |
Elimination half-life of approximately 0.76–1.3 h |
| Target receptor |
Muscarinic receptors (M1-M5), which are mainly Gq-coupled receptors |
| Mechanism of action |
Mostly an eye drop, and so mostly seen to act on the pupil to cause miosis and to reduce anterior chamber pressure by causing trabecular meshwork to open, allowing the aqueous humor to drain from the eye. |
| Clinical effects |
If taken systemically, has many cholinergic side effects, including salivation, bronchorrhoea, bradycardia, lacrimation, urinary incontinence and diarrhoea |
| Literature reference |
Al-Badr et al, 1983 |
| CICM details of understanding | Not specifically listed in the CICM syllabus |
| Mentioned around Deranged Physiology | |
| Related SAQs |