Two 30mg tablets vs One 60mg tablet?

[Auriel619]

Hey Everyone,

I had a patient come in today who was absolutely insistent that two of her 30mg tablets were equal to one 60mg tablet. Our 60mg tablet was on back order and her MD gave her some samples to tide her over. I know if pharmacy school we're taught that technically two 30mg tablets does not equal one 60mg tablet, but I'm never sure of the reason why.

Anybody know of how I can explain to this patient that two 30mg tablet is not necessarily equivalent to one 60mg tablet? Is there any study you've seen that looked at the PK or Cmax values between something similar?

Even if we don't exactly know why two 30mg is not = 60mg, it'd be nice to see something more concrete.

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[awval999]

Not sure if serious....

And you're a pharmacist?

They ARE equivalent.

 

[BidingMyTime]

They are equivalent and legally interchangeable (at least in my state.) Most people have learned that 30 + 30 = 60 by 2nd/3rd grade.

 

[Auriel619]

Not sure if serious....

And you're a pharmacist?

They ARE equivalent.

Hmm maybe it is a basic question but do you know of anything concrete that confirms two tabs of one is equivalent to 1 tablet? Like for Zantac 150mg, there's no information in the labeling to show that it's bioequivalent to one tablet of the 300mg. I'm confident that therapeutically it's not an issue.

 

[Auriel619]

They are equivalent and legally interchangeable (at least in my state.) Most people have learned that 30 + 30 = 60 by 2nd/3rd grade.

heh must've missed that class.

 

[awval999]

Hmm maybe it is a basic question but do you know of anything concrete that confirms two tabs of one is equivalent to 1 tablet?

Yes, the mathematical law of addition.

http://en.m.wikipedia.org/wiki/Addition

 

[BidingMyTime]

Hmm maybe it is a basic question but do you know of anything concrete that confirms two tabs of one is equivalent to 1 tablet? Like for Zantac 150mg, there's no information in the labeling to show that it's bioequivalent to one tablet of the 300mg. I'm confident that therapeutically it's not an issue.

What confirms it for me, is that its legally substitutable. If the 2 weren't equivalent, then the FDA would not let them be substituted for each other, the FDA is overly strict on this stuff (just like Cheratussin is not legally substitutable for Robitussin AC and phenazopyridium is not legally substitutable for Pyridium.....even though we all know they are basically the same thing.)

 

[awval999]

Addition is a mathematical axiom, one of peanos axioms, which defines arithmetic. It cannot be proven.

Addition
Addition is a function that maps two natural numbers (two elements of N) to another one. It is defined recursively as:

For example,

a + 1 = a + S(0) = S(a + 0) = S(a).
The structure (N, +) is a commutativesemigroup with identity element 0. (N, +) is also a cancellative magma, and thus embeddable in a group. The smallest group embedding N is theintegers.

 

[PharFromNormal]

Be forewarned...

2 Asacol 400s =/= Asacol 800

Different pk values occur.

 

[ancienbon]

Hey Everyone,

I had a patient come in today who was absolutely insistent that two of her 30mg tablets were equal to one 60mg tablet. Our 60mg tablet was on back order and her MD gave her some samples to tide her over. I know if pharmacy school we're taught that technically two 30mg tablets does not equal one 60mg tablet, but I'm never sure of the reason why.

Anybody know of how I can explain to this patient that two 30mg tablet is not necessarily equivalent to one 60mg tablet? Is there any study you've seen that looked at the PK or Cmax values between something similar?

Even if we don't exactly know why two 30mg is not = 60mg, it'd be nice to see something more concrete.

The patient was right.I hope you did not argue with him

 

[fauxden]

Be forewarned...

2 Asacol 400s =/= Asacol 800

Different pk values occur.

I don't think the 400's are made anymore?

 

[Mcat14]

Be forewarned...

2 Asacol 400s =/= Asacol 800

Different pk values occur.

Correction......... 2 Asacol 400 mg =/= Asacol HD 800 mg

 

[owlegrad]

Sue your pharmacy school for teaching you that 30 mg + 30 mg =/= 60 mg. For curiosity sake, what is the medication?

 

[TheGoatBoyy]

So changing from something like citalopram 20mg 1 qd to citalopram 10mg 2 qd without any consultation of the physician is legal in some/all states? I always thought it was one of those things that was in an inconvenient grey area because therapeutic equivalence is defined as "contain the same active ingredient(s); dosage form and route of administration; and strength."

 

[zelman]

So changing from something like citalopram 20mg 1 qd to citalopram 10mg 2 qd without any consultation of the physician is legal in some/all states? I always thought it was one of those things that was in an inconvenient grey area because therapeutic equivalence is defined as "contain the same active ingredient(s); dosage form and route of administration; and strength."

Not legal in many states. Therapeutically equivalent in most cases.

 

[zelman]

Be forewarned...

2 Asacol 400s =/= Asacol 800

Different pk values occur.

Marketing BS. They could not be deemed to be equivalent because the mechanism of action is as a topical agent, so blood levels are meaningless. It was a garbage patent extension.

 

[Ackj]

Are you thinking about how 30ml + 30ml =/= 60ml when mixing products? That is true due to the molecular forces.

For plain IR doses, there is no doubt that they are the same. For weird XL forms, like OROS, you probably will have some variation in PK parameters, but unlikely to be clinically significant.

In practice, you will need some form of documentation, regardless of how you feel about it. I don't know of any system that will let you switch to a non-matching strength during a refill, and simply keeping the old label and giving 2x lower strength leads to bypassing accuracy scans and misbranding.

 

[zelman]

Hey Everyone,

I had a patient come in today who was absolutely insistent that two of her 30mg tablets were equal to one 60mg tablet. Our 60mg tablet was on back order and her MD gave her some samples to tide her over. I know if pharmacy school we're taught that technically two 30mg tablets does not equal one 60mg tablet, but I'm never sure of the reason why.

Anybody know of how I can explain to this patient that two 30mg tablet is not necessarily equivalent to one 60mg tablet? Is there any study you've seen that looked at the PK or Cmax values between something similar?

Even if we don't exactly know why two 30mg is not = 60mg, it'd be nice to see something more concrete.

What you're saying is rarely true. I think you memorized the exception, rather than the rule. The only case that comes to mind is Procardia XL 90mg has different PK than 3 of the 30mg tablets taken together. I believe that's in the package insert. However, 2 of the 30's are close enough to a 60 mg tablet that they don't mention it as being a problem.

 

[Auriel619]

Are you thinking about how 30ml + 30ml =/= 60ml when mixing products? That is true due to the molecular forces.

For plain IR doses, there is no doubt that they are the same. For weird XL forms, like OROS, you probably will have some variation in PK parameters, but unlikely to be clinically significant.

In practice, you will need some form of documentation, regardless of how you feel about it. I don't know of any system that will let you switch to a non-matching strength during a refill, and simply keeping the old label and giving 2x lower strength leads to bypassing accuracy scans and misbranding.

Hey I appreciate the posts. The more I think about it, the more I think it was something an previous preceptor told me and I just internalized it, never really questioned it.

 

[Carboxide]

Not legal in many states. Therapeutically equivalent in most cases.

Right. If your state is an Orange Book state then it's not legal. If it's not, and your state (like mine) just says you can make an "equivalent generic" substitution, then it's legal.

 

[PharFromNormal]

Marketing BS. They could not be deemed to be equivalent because the mechanism of action is as a topical agent, so blood levels are meaningless. It was a garbage patent extension.

Blood levels are meaningless until systemic effects of a topical agent are meaningful.

 

[zelman]

Blood levels are meaningless until systemic effects of a topical agent are meaningful.

They may be clinically meaningful, but serve little purpose in the generic approval process.

 

[sakigt]

Pharmacy school taught me 4x 200mg ibuprofen were not equal to the 800mg prescription but this was due to the labeling problem. If a doc writes for 200mg x4 TID etc then its fine for them to get the OTC....

But yeah, we have to double up tabs all the time (hospital)

 

[Carboxide]

Pharmacy school taught me 4x 200mg ibuprofen were not equal to the 800mg prescription but this was due to the labeling problem. If a doc writes for 200mg x4 TID etc then its fine for them to get the OTC....

But yeah, we have to double up tabs all the time (hospital)

There is a huge difference between 'legally substitutable' and 'therapeutically equivalent.'

 

[PharFromNormal]

They may be clinically meaningful, but serve little purpose in the generic approval process.

That's great tell me about the brand approval process.

 

[zelman]

That's great tell me about the brand approval process.

I'll tell you that most "new" brand name drugs (besides biologics) are overpriced versions of current drugs modified just enough to give them a new patent life. See Delzicol or Minastrin as examples.

 

[BidingMyTime]

In practice, you will need some form of documentation, regardless of how you feel about it. I don't know of any system that will let you switch to a non-matching strength during a refill, and simply keeping the old label and giving 2x lower strength leads to bypassing accuracy scans and misbranding.

In states where it is legal, of course you can't just keep the old label, you would document on the script that you are filling with 2x30mg to equal 60mg, then change the qty & directions accordingly, ie 60mg QD #30 would become 30mg 2 tablets QD #60.
I generally don't change refills, because there is usually a reason it was filled that way originally (ie pt finds swallowing 2 smaller tablets easier than 1 larger tablet, or the pt is really taking 1 -2 tablets QD even though the RX was written just for 2 tablet QD. If a refill did need to be changed, then the original RX would be reentered, again documenting the change, and documenting the actual number of refills left on the RX>

 

[maria1oh]

What med are you talking about? I do not thunk it is legal for c2s. Two Oxy 15s will nit be a legal substitute for 1 Oxy 30

 

[BidingMyTime]

What med are you talking about? I do not thunk it is legal for c2s. Two Oxy 15s will nit be a legal substitute for 1 Oxy 30

CII's would be a completely different issue, with different laws there. I'm talking about regular medicines, like when a doctor writes 2x40mg for Lasix or changing a 40mg Prozac to 2x20mg Prozac (this one I change a lot because IL public aid will pay for 2x20mg, but not 40mg Prozac.)