rx perspective
Cost-Effectiveness 101
The cost of a medication isn't the same as the cost of successful treatment.
By Thomas Bournias, M.D.

Despite conventional wisdom telling us that "you get what you pay for," we know that a higher price doesn't always mean a better product. That's why smart consumers don't just look at the cost of a given item; they weigh a variety of factors against its price -- quantity, quality, durability, practicality, comfort, even aesthetic appeal -- in order to determine its true value.

When buying medicine, however, consumers typically don't take such considerations into account. For the most part, in spite of direct to consumer advertising, consumers trust their prescribing physician to make decisions about which medication they should be taking.

But how does the physician choose, when several medications are available to treat a condition? In most situations, the doctor must weigh multiple factors, and those factors go beyond formulary and the price of the drug. They include the efficacy, safety and side effects of the drug, the patient's physical condition, health and lifestyle, and to a lesser extent, factors such as whether the drug is on the health plan formulary or whether the patient will have to pay for it out of pocket.

All of these factors can affect whether a drug will achieve the desired long-term therapeutic results. And using a formula to compare these factors can tell us how much (on average) it will cost to achieve a successful treatment using each medication. In other words, it can help us determine which medication is most cost-effective.

Although comparing the cost-effectiveness of drugs is a new concept to many physicians, it's a useful way to understand -- and explain to patients -- the true value of their medications. For example, even though a patient may be more likely to buy and use a medication that's less expensive, you can show the patient that it isn't cost-effective if it doesn't work consistently. The cost of failed therapy nearly always outweighs early savings. So calculating the cost-effectiveness of a medication -- i.e., the cost per successful treatment -- is an excellent way to gauge its true value in comparison to other options.

The idea of comparing the cost-effectiveness of medications isn't new to managed care organizations. They recognize that cost-per-treatment success is a more relevant measure of cost than acquisition costs alone, and they request this kind of data before adding a medication to their formularies.

How can a physician make evidence-based decisions about the cost-effectiveness of a medication? In simplest terms, cost-effectiveness is calculated by dividing a medication's price by its success rate.

For example, if drug A costs $150 and drug B costs $100, and both drugs are 100% successful every time they're used to treat patients, drug A's cost-per-success is $150; B's cost-per-success is $100, and B is the more cost-effective medication. However, if drug B is only 50% successful, then drug B's cost-effectiveness ratio is $100/50%, or $200. In the latter scenario, drug A is the more cost-effective of the two medications -- despite having a higher price than drug B. (See chart, facing page.)

Comparing Glaucoma Medications

For a real-life example of this cost-effectiveness model at work, we can apply it to glaucoma medications frequently prescribed in daily clinical practice.

Bimatoprost is a prostamide that effectively lowers intraocular pressure (IOP) in patients with glaucoma or ocular hypertension (OHT). Clinical trials have demonstrated that bimatoprost monotherapy is significantly more effective than either timolol(1, 2) or latanoprost(3, 4, 5) at reducing IOP. Evidence also shows that bimatoprost monotherapy lowers IOP as well as the combination of latanoprost with timolol(6) and better than the fixed combination of timolol and dorzolamide.(7)

Beta blockers may seem more appealing to some glaucoma patients because they're available in generic form. However, two-thirds of patients on beta blocker monotherapy have to change therapy within 2 years.(8)

Furthermore, about 50% of patients on beta blockers require additional concomitant therapy,(9) and when adjunctive medications are added, they're usually brand-name drugs that increase the cost of treatment. In short, the least expensive generic is not always the most cost-effective solution.

These points are supported by efficacy data from an ocular hypo-tensive study I participated in that evaluated the clinical effectiveness of bimatoprost in the treatment of glaucoma and OHT in community-based practice.(10) Economists ap-plied cost-effectiveness methodolo- gies to the data from this study.(11)

Participating physicians enrolled patients who needed additional IOP lowering. A subset of patients participating in the trial switched from a regimen that included latanoprost 0.05% plus one adjunctive medication, to bimatoprost 0.03% monotherapy.

Treatment success rates (used as the denominator of the cost-effectiveness ratio) were derived from a
2-month naturalistic effectiveness trial. This trial evaluated the percentage of patients achieving target IOPs in the group that switched from latanoprost in combination with adjunctive therapies to bimatoprost monotherapy.(12)

Researchers calculated the direct costs and cost-effectiveness of treatment to achieve a range of clinically relevant target pressures, from 13 mm Hg to 20 mm Hg. The percentage of patients who achieved (or were lower than) modeled target pressures was greater among patients on bimatoprost monotherapy than among patients treated with latanoprost dual therapy. For example, at study entry 44 out of 147 patients (30%) whose original regimen included latanoprost plus one adjunctive medication achieved an IOP ¾17 mm Hg at baseline. Two months after switching to bimatoprost, 59% of patients achieved this target.

The cost of treatment (the numerator of the cost-effectiveness ratio) was calculated to include average expected annual treatment costs for physician visits and medications. (The model assumed that if the hypothetical patient in either treatment group didn't achieve the pre-established target IOP at month two, the physician would prescribe adjunctive medication.) The projected cost of treatment, based on a target pressure of 17 mm Hg or less for bimatoprost monotherapy, was $1,131. The projected cost of treatment for latanoprost plus one adjunctive medication was $1,544. Using the 2-month study drug costs (and the same success percentages) as mathematical factors in the cost-effectiveness ratio, the cost-per-treatment-success (i.e., cost-effectiveness) comes out to $319 for bimatoprost vs. $861 for latanoprost plus one adjunctive medication.

These findings strongly suggest that patients who don't do well on latanoprost plus an adjunctive may benefit from switching to bimatoprost monotherapy, both in terms of efficacy and overall cost.

The Numbers that Count

When prescribing medications, physicians should consider the cost-effectiveness factor, particularly when treating a chronic disease like glaucoma. After all, the cost of achieving the desired clinical result may be quite different than the purchase price of the medications.

Dr. Bournias is director of the Northwestern Ophthalmic Institute and assistant professor of clinical ophthalmology at Northwestern University Medical School in Chicago.

The numbers above were calculated using data from a subgroup of patients in a clinical trial (Bournias et al., 2003) who switched to bimatoprost monotherapy from a regimen that included latanoprost plus one adjunctive medication.

References

1. Higginbotham EJ, Schuman JS, Goldbert I, et. al. "One-year Randomized Study Comparing Bimatoprost and Timolol in Glaucoma and Ocular Hypertension." Archives of Ophthalmology. 2002; 120(10): 1286-1293.

2. Sherwood M, Brandt J. "Six-Month Comparison of Bimatoprost Once-Daily and Twice-Daily with Timolol Twice-Daily in Patients Elevated Intraocular Pressure." Survey of Ophthalmology. 2001; 45 (suppl 4): S361-368.

3. Dubiner H, Cooke D, Dirks M, Stewart WC, Van Denburgh AM, Felix C. "Efficacy and Safety of Bimatoprost in Patients with Elevated Intraocular Pressure: A 30-Day Comparison with Latanoprost." Survey of Ophthalmology. 2001; 45 (suppl 4): S353-360

4. Gandolfi S, Simmons ST, Sturm R, Chen K, Van Denburgh AM. "Three-Month Comparison of Bimatoprost and Latanoprost in Patients with Glaucoma and Ocular Hypertension." Advanced Therapeutics. 2001; 18 (3):110-121.

5. Noecker RS, Dirks MS, Choplin NT, Bernstein P., Batoosingh AL, Whitcup SM. "A Six-Month Randomized Clinical Trial Comparing the Intraocular Pressure-Lowering Efficacy of Bimatoprost and Latanoprost in Patients with Ocular Hypertension of Glaucoma." American Journal of Ophthalmology. 2003; 135 (1): 55-63.

6. Dirks M (2002). "Bimatoprost as Monotherapy in Patients Previously Treated with Timolol/Latanoprost Dual Therapy." Poster presentation at the annual meeting of the American Glaucoma Society, San Juan, Puerto Rico.

7. Coleman AL, Lerner L, Bernstein P, Whitcup S. "A Three-Month Randomized Clinical Trial of Bimatoprost (LUMIGAN(r)) Versus Timolol/Dorzolomide (Cosopt (r)) in patients with Glaucoma or Ocular Hypertension." Ophthalmology. 2003 (in press).

8. Glaucoma Laser Trial Research Group: The Glaucoma Laser Trial. Ophthalmology. 1990:97:1403-13.

9. Physician Drug & Diagnosis Audit (PDDA), Verispan.

10. Bournias T, Lee D, Gross RL, Matox C. "Ocular Hypotensive Efficacy of Bimatoprost When Used as a Replacement for Latanoprost in the Treatment of Glaucoma and Ocular Hypertension." Journal of Ocular Pharmacology and Therapeutics. 2003; 19(3):193-203.

11. Walt JG, Spalding JR, Habib L. "Cost Effectiveness of Bimatoprost versus Latanoprost Plus Adjunctive Products for Glaucoma Treatment." Poster presentation at the annual meeting of the Association for Research in Vision and Ophthalmology, May 4-9 2003, Ft. Lauderdale, FL.

12. Walt JG, Spalding JR, Habib L. "Cost Effectiveness of Bimatoprost versus Latanoprost Plus Adjunctive Products for Glaucoma Treatment." Value in Health. 2003;6(3): 237-238.