Obese individuals are also likely to have a degree of heart failure which further decreases blood flow. This makes their fat a large compartment of potential distribution for lipophilic drugs which fills gradually, and then becomes a slowly emptying reservoir.
How does obesity affect volume of distribution?
In obese compared with normal weight individuals, the total volume of distribution (Vd) is moderately increased (aminoglycosides, caffeine) or similar (H2-blockers, neuromuscular blockers), but the Vd corrected by kilogram of actual bodyweight is significantly smaller.
How does obesity affect drug absorption?
Obesity also has an effect on the gastric emptying and gut permeability, meaning that drugs are absorbed at different rates to normal. Drug penetration into tissue is also affected, meaning that a higher dose may be needed in order to reach effective concentrations.
How does weight affect drug action?
Changes in body weight can influence the amount of medicine you need to take and how long it stays in your body. The circulatory system may slow down, which can affect how fast drugs get to the liver and kidneys.
Does body weight affect drug absorption?
The distribution of a drug between fat and lean tissues may influence its pharmacokinetics in obese patients. Thus, the loading dose should be adjusted to the TBW or IBW, according to data from studies carried out in obese individuals.
What happens when an obese person is given with a lipophilic drug?
After redistribution, lipophilic drugs tend to accumulate in the fat mass. As a result, volume of distribution (Vd) for lipophilic drugs will increase in the obese. The loading dose of these drugs should therefore be based on TBW. Hydrophilic drugs will be primarily distributed to the muscle mass.
Does obesity increase VD?
Paracetamol Vd is increased in obesity and in males relative to females. Clearance increases with body weight and therefore is much greater in obese patients and males.
How does obesity affect drug half life?
Increased half life of lipid-soluble drugs
For some (as mentioned above) the hepatic clearance rate increases as well, which keeps the half life relatively stable over a range of BMIs. For others the clearance rate actually decreases because of extensive distribution into fat.
Which drugs are dosed by ideal body weight?
In general, lean body weight is the most appropriate dose for most anesthetic drugs, with the exception of NDMB, where ideal body weight may be more appropriate. Succinylcholine should be dosed to total body weight.
What drugs accumulate in fat?
Drugs that dissolve in fat (fat-soluble drugs), such as the antianxiety drug clorazepate, tend to concentrate in fatty tissues.
What is weight based dosing?
Weight-Based Dosing Errors
Medication dosing is often calculated on the basis of a patient’s weight, particularly for pediatric patients, who require individualized dose calculations based on their size.
Does Weight Affect ibuprofen?
Ibuprofen volume of distribution was increased in obese subjects, and this increased distribution correlated positively with body weight (r = 0.82; P less than 0.001).
Why are drugs harmful at all ages?
Adolescents who flood their brains with chemicals do lasting damage at a very critical age of neurodevelopment. These drugs are powerful neuromodulators that modify the function of brain circuits. These changes take root even after the drugs themselves are cleared from the body.
When do you use ideal body weight and actual body weight?
If a patient’s actual body weight was less than his or her ideal weight, then actual weight should be used. However, if the patient is obese, then a correction is used.
How do you calculate ideal body weight?
Ideal body weight is computed in men as 50 + (0.91 × [height in centimeters − 152.4]) and in women as 45.5 + (0.91 × [height in centimeters − 152.4]). A simple alternative would be to compute ideal body weight as the weight corresponding to an ideal body mass index of 22 kg/m2.
How does age affect drug action?
In general, as we age, total body water and muscle mass decrease while percentage of body fat increases. These changes can lead to drugs having a longer duration of action and increased effect. Drugs that were effective may become compounded and overexceed their therapeutic threshhold causing increased side effects.