Symposium on Critical Thinking and Consumer Chemistry
Rating Antacids in Consumer Reports Geoffrey Martin Consumers Union. 256 Washington Street, Mt.Vernon, NY 10553 The consumer who shops for an antacid might well get an ulcer from trying to decide among the variety of brands and products available. But even if you are a chemist, you will he hard put to tell which one works best. Consumer advocates have urged that an antacid package display some measure of the strength or effectiveness of the product. Most reasonably, this would seem to be the Acid Neutralizing Capacity (ANC), expressed as the number of milliequivalents (meq) of acid (as HCI) that can he neutralized by one standard dose of the antacid. Manufacturers have determined those values for their products and will reveal them on request. Keeping the ANC off the packaging might seem a clear case of drug manufacturer obstructionism, hut some among them claim that the ANC is an oversimplified quantity that expresses only part of an antacid's value. For example, a coating action may play a soothing role unrelated to the acid neutralizing action. Likewise, the buffering ability of an antacid is also r e l e v a n t a f t e r all, sodium hydroxide will neutralize HCI. When we tested antacids at Consumer Reports, we considered that a titration should mimic the in vivo action of an antacid as much as possible. We were looking for a measure of antacid effectiveness more useful than ANC alone. The titration graph in Figure 1is that of baking soda (% tsp.) vs. added HCI. This familiar curve quickly reaches an initial maximum nH of 6.4. then slowly decreases until it drops sharply near the equivalence point. The traditional analysis of weak bases by neutralizing with excess strong acid and hack-titrating the acid excess with sodium hyroxide is a useful way of obtaining the acid neutralizing capacity. But one loses information about intermediate pH values and buffering capacity of the weak base in that kind of titration. Our titration is a simulation of the challenge faced by an antacid in actual use; in effect, it is a direct titration stretched out over a 30-min period, with a very slow approach to the equivalence point. In this method, 20 meq of antacid (determined from the ANC) is to be neutralized by 20 meq of 0.1 N HCI.
0
10
20
Figure 1. Titration of baking soda vs. HCi.
214
Journal of Chemical Education
30 min
To begin, 10 meq of HC1 is placed in a beaker, all the antacid is added at once (with magnetic stirring), and the remaining 10 meq of acid is added dropwise so that the equivalence point is reached after 30 min. The horizontal axis of the titration graph is in units of time (as well as in milliequivalents of acid). The slow addition of HCI simulates the secretion of stomach acid. From a chemist's view, the extended time allows insoluble hydroxides to dissolve, gases to evolve, and suspensions to break up. Antacid Tablets Two tablets of Alka-Seltzer Gold (citrate-buffered sodium bicarbonate without aspirin) yield a straight-line titration graph sloping down from an initial pH of 5.2; after 30 min, the pH is 4.0 (Fig. 2). Though equivalent amounts of baking soda and Alka-Seltzer are being titrated, the latter is huffered a t 1.5 pH units lower than baking soda during the titration. An antacid should not upset the acid balance in the digestive system too extremely, lest digestive enzymes be deactivated. By this reasoning, sodium bicarbonate is amore desirable antacid when buffered. A buffered antacid nearly identical to Alka-Seltzer can be obtained by stirring half a teaspoon of baking soda into 120 mL of orange juice (Fig. 3). Figure 4 compares, on a 20-meq (approx 2 tablets) basis, the titration of three chewable tablets: Tums (calcium carbonate), Rolaids (sodium bicarbonate, aluminum hydroxide), and Maalox #1 (Al and Mg hydroxides). Tums maintains a pH of greater than 3 for the full 30-min period, while the other two products do so for only 20 and 8 min, respectively. In our project, we used pH 3 as the limit below which an acid-antacid mixture would he considered ineffective. The time above that limit, the "duration", is a measure of effectiveness. On this basis, Tums appears the better product. But there is a problem, at least for us at Consumer Reports. One of the tablet products, Maalox #1, has a recommended dose twice that of the other brands tested, that is,
0
10
20
30 rnin
Figure 2. Titration ot baking soda (unbuffered) and Aika-Seltzer (buffered baking soda).
two t o four tablets rather than one to two. When Maalox #1 is titrated a t its higher dose level (four tablets), i t maintains a pH above 3 for 20 min, compared with 8 min a t the lower (two-tablet) dose (Fie. 5).. A chemist should balk a t comoaring nonequimolar samples for neurraliing ability; bur a manufacturer will wish to have label directions to determine the conditions of use.
..
Let us compare the liquid ("suspension") antacids by referrine to Figure 6. Of the reoresentative brands titrated as a 20-me; doseU(typically1.5 to 2 tsp), the duration above p H 3 ranees from 30 min (Riooan) down to 9 rnin (Maalox). But here again, Maalox recommends twice the dose level of the other brands. When titrated ar that 3 - r s level. ~ Maalox hasa duration of nearly 30 min. Armed with these data and the unit cost of the ~ r o d u c t s . we then set about rating theanurcids in some sort 0.f order of recommendation. The discussion that follows apuroximates the process that leads to a Consumer Reports ratings table.
Table 1.
0
10
20
Acid Neutratlzlng Capaclty (ANC) per Recommended
Rating (1-5 scale)
ANC per dose (mequiv)
5 4
3
40 30 24 22 20
2
18 15 14
30 min
Figure 3. Baking soda buffered In orange juice behaves like Alka-Seltzer.
Antacids Maalax (liq. 3 tsp) Maaiax (4 tab) Gelusil Riopan Di-Gel baking soda Maalox (liq, 1.5 tsp) Mylanta Maalox (2 tab) Turns Alka-Seltzer Rolaids
10 a
1.5 to 2 top far ligulds or 2 tablela, unless noted.
Table 2.
I 0
10
20
Duration (minutes above pH 3) per Recommendei Dose
Rating
Duration (min)
Antacid
5
50 36 34 32
4 3
28 26 20
2
18 10
Alka-Seltzer Maalox (liq. 3 tsp) Riopan Turns baking soda Gelusii Mylanta Rolaids Maalox (4 tab) Di-Gel Maalox (liq, 1.5 tsp) Maalox (2 tab)
30 rnin
Figure 4. Comparison of threetablet products(tihation of two tablets of each).
8
51
Mvlanta
Maalox
0
10
20
Figure 5. Titration of Maalox #1 tablets at two doses.
30
mln
0
10
20
30 min
Figure 6. Tltration of three liquid antacids.
Volume 65 Number 3 March 1988
215
~ANC~rrsmmmendsdWU.
Figure 7. Consumer Repomstyle rating table for antacids.
Rating the Antacids
First, let us consider ranking the products in ways that do not involve price; we typically look for criteria of quality regardless of cost. Table 1 ranks several products according to ANC per average recommended dose. Not surprisingly, the higher dose levels of the two Maalox products lead the list. So we find suitable breaks in the ranking and, with the firm guidance of our statistical staff, assign scores from 5 (excellent or best) to 1(poor or worst). Second, consider ordering the antacids by their duration above pH 3 when recommended doses are titrated by our method (Table 2). By this standard, Tums moves up to the top gruup, wen though its AN(: per dose is low. h t the picture, \Vhen cuniideratiuns of cost are h r ~ ~ g into
216
Journal of Chemical Education
baking soda is by far the cheapest at less than a penny per dose. The ratinas chart in FLure 7 lists the cost per average recommended Gose for each antacid. Looking i t cost per ANC of 20 (Fig. 71, all of the products except Alka-Seltzer and baking soda are clustered in the 5- to 7-cents range. Cost per recommended dose shows a little more spread among the antacids. Tums is on the low end at 5 cents oer dose. while Alka-Seltzer and the Maalox products are a t least 10 cents per dose. Note that here is where the relatively higher cost of Maalox's larger dose shows up. Figure 7 lists the products with all of the ranking hases compared. Cost per ANC of 20 is the only one that is independent of the dose level the manufacturer chooses to recbmmend on the package. Duration (per dose) and ANC per dose are independent of price; these two are therefore the only quantities that could he printed on a package. Those two values are also the best hases for a ratings table in Consumer Reports. Figure 7 lists antacids in order of decreasing duration per dose, and, for products of equivalent duration.. thev. are listed in order of decreasine ANC per dose. In our must rrcrnt report on antacid9 (Consumer lilrporrs 19113, (Auguitl, 4121 nu rating order was employed; the products were listed alphabetically with R graphical presentation of duration along with a limited discussiun. Alaheling standard could he implemented in several ways. ANC per dose could he printed on the product label; that single nunher w0u.d gi\,e at least some measure of re1atiL.e acid neutralizing ahilits, but would indicate nuthing of buffering capacity. A typical lahel might read: "On the basis of an ANC per dose of 20, this bottle contains 24 doses." The duration, on the other hand, would indicate the uverall strength as well az the effect at' bufterina. In pr~nciple, each manufacturer could adjust the recommended dose so that the duration-as measured by a standard laboratory analysis-would match the upper limit possible; in this discussion, 30 minutes. A manufacturer might choose not to meet the 30-minute mark. In any case, the lahel could also indicate the number of doses in the container. A tvoical lahel com~arisonbetween eaual-weight bottles duration of two products might'read as follows: " ~ i o d u c i t , 30 minutes. 16 doses in this bottle": "Product B. duration 26 minutes, 24 doses in this b o t t l e " . ~ i t h comparable durations, the number of doses and the relative urices could help the consumer decide which antacid to buy. Development uf an acceptable titration prcrtocol nmuuld he subject tu discussions among standard-setting organizations and industry representati\,es. In R product category where such variation in potency is the norm, it seems to us necessary to agree on a basis by which consumers can make a meaningful choice among antacids.
Originally presenred at a symposium on consumer cnemisrry at the ACS Meet ng. Anaheim. CA. on September 9. 1986.
