When a drug takes effect?

[nurselove757]

By looking at a drug book, how can I tell when a drug takes it effect? For example, I'm curently using iPhones Micromedex drug book. I'm currently looking at the pharmacokinetics section and I have this information on Seroquel:

Absorption: Oral, regular-release tablets: time to peak concentration, 1.5 h

Elimination Half-Life: regular-release tablet: approximately 6 h

I remember back in nursing school we talked about onset of drug also.

I feel as if I need validation on this.

What is the difference between Onset of drug and Absorption as far as the effect of the drug is concerned on the patient? This drug book does give me information about Absorption, but no information about the onset. Please help me understand!

[Esme12, ASN, BSN, RN]

On set is the beginning of absorption. Onset begins as quickly as digestion occurs when take PO which varies according to when they last ate. A full stomach will have a slower inset than an empty one. Onset for an IV drug is immediate.

Whether or not a drug is sustained release or enteric coated for a delayed absorption

The rate and extent of drug absorption from the small intestine are related to the release of the active ingredient from a dosage form, its solubility in the liquid phase of gastrointestinal contents, and the transport of the dissolved compound or the intact dosage form from the stomach into the duodenum. With pharmaceutical preparations releasing the active compound within the stomach, and enteric-coated "micro"-formulations (micropellets), gastric emptying is possible during the interdigestive and the digestive period. Potential differences of drug absorption between fasting administration and intake during the digestive period are unpredictable, because they are related to the release characteristics of the dosage form. However, larger enteric-coated preparations like tablets can leave the stomach only with a phase 3 contraction of fasting motility; intake during the digestive period will result in gastric retention of this type of dosage form until all food has left the stomach and fasting motility is restored. Consequently the onset of drug absorption is delayed. This interaction between food and large enteric-coated dosage forms is predictable from pyloric function in relation to the gastric motility. As it occurs regularly, it can be taken into account when prescribing enteric-coated dosage forms. If concomitant intake of food and enteric-coated drugs is unavoidable, but a rapid onset of drug absorption is necessary, micropellets are the dosage form of choice. When the therapeutic effect is insufficient, drug dosage form and timing of drug administration should be checked before prescribing a different active compound.

http://www.ncbi.nlm.nih.gov/pubmed/11036435

[classicdame, MSN, EdD]

the rate at which a drug takes affect depends on many factors including hydration status, any intestinal disorders, NPO status, glucose level----so the drug mfg. probably gives a range or simply states "peak" time. In this case, you would expect the drug to be absorbed sooner than 1.5 hours for it to peak. Some drugs begin absorption in the mouth while others have to travel around to get therapeutic. Sulfa, for instance, has slower absorption which is why it is effective in kidney and bladder infections.