KD values for drugs

[myliham]

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I have an assignment due for Dynamics and I was wondering if anyone know where I can find KD values (Constant Disassociation) values for various drugs.

 

[patmcd]

Something like the USP might or it might be in the drug's monograph.

 

[sdn1977]

Are you referring to Kd? which is the elimination rate constant?

This is a fraction per unit of time & represents the fraction of the volume of distribution which will be cleared per unit of time.

In first order elimination kinetics, the ellmination rate constant (Kd) is the rate of elimination at an instant in time & if the plasma level is decaying, the amount of drug removed per day will become less & less, altho the fraction of the total amount of drug remaining in the body which is removed will remain constant.

Not all drugs follow first order elimination rate kinetics.

Sometimes, the Kd needs to be adjusted similarly to the clearance for renal failure patients. Because clearances by various routes are additive, so are the elimination rate constants.

Kd (adjusted) = Kmetabolic + (Krenal x fraction of normal renal funtion remaining)

You generally calculate the Kd after observing a few half lives then use literature values for Vd & calculate Cl

Cl = Kd x Vd

The clearance of most drugs is constant over the range of concentration in plasma or blood. This means that elimination is not saturated & the rate of elimination is directly proportional to it concentration. For drugs that exhibit dose dependent elimination, clearance will vary with concentration:

This is similar to the Michaelis-Menten equation for enzyme kinetics. Some dosage regimens are more complex, particularly if they show multicompartment volumes of distribution.

So....I'm not sure there is an actual table....you can find usual Vd, Cl & t1/2 & therefore calculate Kd in the normal pt...but if the pt does not show normal kinetics, you have to calculate that pts Kd.

 

[myliham]

Are you referring to Kd? which is the elimination rate constant?

This is a fraction per unit of time & represents the fraction of the volume of distribution which will be cleared per unit of time.

In first order elimination kinetics, the ellmination rate constant (Kd) is the rate of elimination at an instant in time & if the plasma level is decaying, the amount of drug removed per day will become less & less, altho the fraction of the total amount of drug remaining in the body which is removed will remain constant.

Not all drugs follow first order elimination rate kinetics.

Sometimes, the Kd needs to be adjusted similarly to the clearance for renal failure patients. Because clearances by various routes are additive, so are the elimination rate constants.

Kd (adjusted) = Kmetabolic + (Krenal x fraction of normal renal funtion remaining)

You generally calculate the Kd after observing a few half lives then use literature values for Vd & calculate Cl

Cl = Kd x Vd

The clearance of most drugs is constant over the range of concentration in plasma or blood. This means that elimination is not saturated & the rate of elimination is directly proportional to it concentration. For drugs that exhibit dose dependent elimination, clearance will vary with concentration:

This is similar to the Michaelis-Menten equation for enzyme kinetics. Some dosage regimens are more complex, particularly if they show multicompartment volumes of distribution.

So....I'm not sure there is an actual table....you can find usual Vd, Cl & t1/2 & therefore calculate Kd in the normal pt...but if the pt does not show normal kinetics, you have to calculate that pts Kd.

I am actually refering to the rate of disassociation

 

[imperial frog]

I'f I'm not mistaken, I believe that Goodman and Gillmans has constant tables for most of the common drugs in one of the appendixes.

 

[sdn1977]

I'f I'm not mistaken, I believe that Goodman and Gillmans has constant tables for most of the common drugs in one of the appendixes.

I think you're thinking of the % urinary excretion & clearance values for drugs - thats different from the dissociation constant.

There is a small table of dissociation constants in water @ 25 C for weak acids & bases in Remingtons (at least my edition).....for what its worth. For example...the dissociation constant for K2PO4 is the sum of the dissociation constants for each successive ionization of all its possible forms, all of which can exist at the same time in blood.

 

[imperial frog]

So what you're saying is that I was mistaken.

 

[calrx]

myliham- I'm having the same problem. This is turning out to be quite a pain in the butt. Let me know if you find a good source.🙄