Child-Resistant Closures: Is a Revolution in Design Imminent?

CPSC requirements that closures be both senior friendly and childproof haven't led to radical new designs—yet.


by Greg Erickson, Contributing Editor

ALso in this article: Design and Analysis of Plug and Gasketed Closures

Awakened at midnight by a headache, you stumble to the medicine chest for a new bottle of analgesic. Then it gets worse. You have to struggle with a frustrating child-resistant closure. The packaging appears to have been designed to exacerbate rather than alleviate your discomfort.

Not anymore. All that has changed, or should soon, now that manufacturers and users of drug container closures have been required by the Consumer Product Safety Commission (CPSC) to introduce improved systems. The time is certainly ripe. Older consumers in particular, contending with reduced hand strength and diminished eyesight, have for years complained loudly about pharmaceutical packages. Some senior citizens found opening medicine containers so frustrating, even painful, that they took shortcuts. Common tricks have included leaving a cap loose or transferring pills to plastic sandwich bags.

Rexam Closures' CR cap for pharmaceutical tubes employs a push-and-turn mechanism. An audible �click� indicates that the tube has been securely resealed.


If consumer convenience were the only issue here, CPSC would never have stepped in. But difficult-to-use packages for pharmaceutical products represent a literally life-or-death situation. The issue is not that senior citizens can't get to their medicines easily enough; it is that children get into them far too easily. Says Ken Giles, spokesperson for CPSC, "Poisonings have happened when youngsters have visited homes where no children live . . . [and they] have happened when older persons carried medicines into homes that have small children." Overall, says the commission, 17% of medicines ingested in recent years by children under the age of 5 belonged to a grandparent or great-grandparent.

The good news is that the number of children poisoned this way each year has been falling steadily. CPSC estimates that child-resistant (CR) packaging for aspirin and oral prescription medicine has saved the lives of about 700 youngsters in the 26 years since the Poison Prevention Packaging Act mandating CR packaging was passed. In 1972, deaths of children under 5 involving all household products (drugs and non-drugs combined) totaled 216; in 1994 the number was 34. Child deaths from ingested aspirin dropped during that period from 46 to 1.

Giles says he fully expects this desirable trend to continue as CR drug packages become increasingly easy for senior citizens and other adults to use properly. This follows a change in protocol—the way CR closures are tested and approved by CPSC. The deadline for compliance with the new protocol was January 21, 1998.

CPSC submits all CR drug closures to testing by adults as well as children. To help ensure that seniors would use such closures correctly, the age of the adults involved in the testing has been raised. "It used to be the 18-to-45 age group we tested," Giles says. "Now we test with adults aged 50 to 70. The big difference is that now an approved closure requires cognitive skills instead of physical strength."

As any parent knows, kids can be cognitively skillful. CPSC acknowledges this in a recent document: "Children are going to investigate several different ways of opening a container. If their fingers don't work, their teeth might. It would be impossible to manufacture a package or closure that would prevent every single child from getting into the contents under all possible circumstances." Therefore, CPSC requires a CR closure to prevent 80% of children 5 and under from opening a container during a 10-minute test. (The government allows drug manufacturers to offer a regulated nonprescription product in one size or package that is not child resistant. It must be labeled as such. If a prescription is involved, the purchaser or prescribing physician can request non-CR packaging.)

Richard Ward, director of consumer product testing at Perritt Laboratories (Hightstown, NJ), an independent third-party testing lab for the pharmaceuticals industry, says there's much new design work going on. "It will probably be the end of June [1998] before we see a lot of brand-new stuff," he says. "The bulk of what's going on is fine-tuning. Right now closures look much the same as they did in years past. But as time goes on they'll keep getting better."

One reason the alterations haven't been revolutionary so far: A major change in the configuration of a drug closure could require use of new materials, and that would send the closure through FDA's time-consuming package qualification process. This process has to do not with ease of use or child resistance, but rather with the possible interaction between product and container. John Ames, director of product development at closure manufacturer The West Co. (Lionville, PA), says, "You want to change the way a closure works without changing the material that it's made of. The idea is to make as few changes as possible. That way you don't need to requalify the package."

The West Co. makes the closure used on the Aleve analgesic bottle—a design that Ward says has really taken hold. A similar closure is being marketed by Weatherchem Corp. (Twinsburg, OH). Called the Top-Squeeze, it opens with a half-turn and closes with an audible click, which lets users know they have resealed the container securely.

Jeff Minette, vice president of marketing for Rexam Closures (Evansville, IN), says his company now has at least eight different closure systems that can pass the new CPSC protocol. Some of these are alterations of existing designs; others make use of brand-new technology. Bristol-Myers products Bufferin, Excedrin, and Nuprin use Rexam push-and-turn CR closures. Another of Rexam's designs is called the Squeeze-Lok Low Profile. Minette calls the closure "torque independent," which means it requires little strength on the part of the adult consumer. Yet the combined action of pushing and turning can stymie most children.

Rexam has also introduced the CR-SF (senior-friendly) closure for tubes. There's a need. Many available topical ointments for treatment of muscle pain and hemorrhoids come in tubes. Some of the active ingredients contained in the formulations are toxic if taken internally.

But according to Mike Meyer, U.S. sales manager at Europack (Medfield, MA), developing CR tubes is a difficult proposition. One of the companies he represents is Switzerland-based Pressta, a marketer of aluminum tubes. End-users, says Meyer, "are all looking for a tube closure that satisfies the new CPSC protocol." One problem is that many closure designs used on rigid containers don't work with semirigid containers. For example, push-down-and-turn closures function poorly on a tube, which lacks the stability and wall strength of a bottle or jar. Another problem: children can bite or otherwise break through the wall of an aluminum or plastic tube, bypassing the closure altogether.

The tablet blister pack, too, faces difficult challenges. Daniel Gerner is president of Packaging Coordinators Inc. (Philadelphia), a contract packager specializing in blisters. He's also vice chairman of the Healthcare Compliance Packaging Council, a group that promotes use of blister-based unit-dose packaging. "It's still a constant battle," he says. "The harder you make it for kids to open a blister, the harder you make it for adults." However, Gerner says his company has developed a configuration it believes to be a breakthrough.

Called Slide Pack, it's a unit-dose package comprising a traditional blister card and an additional piece of plastic that covers the die-cut openings. Once the secondary sheet of springy plastic has been slid off to one side, the push-through lidding is exposed and the tablets can be accessed easily. Gerner says, "You have to slide something over to one side with one hand while the other hand is doing something else." Children don't catch on to that so readily.

Wouldn't it be nice—from the consumer's point of view—if some sort of standardization came into the field of pharmaceutical closures? All analgesics could have identical push-and-turn tops; all cough syrups could have squeeze-and-turn ones. Nice, maybe, but highly unlikely.

Says Ward, "There is no move toward standardization. Even simple moves toward narrowing down the types of things drug manufacturers would be able to use don't really seem to be going that well. There is no avenue for standardization to speak of."

There is, however, a definite move in the other direction, as pharmaceutical manufacturers strive not only to meet CPSC's new protocol but also to differentiate their products as much as possible from the competition's. Truly revolutionary new CR-SF closure designs are undoubtedly just around the corner.

Rexam Closures' CR cap for pharmaceutical tubes employs a push-and-turn mechanism. An audible "click" indicates that the tube has been securely resealed.Squeeze & Turn CR closures from Owens-Brockway (Toledo, OH) are easy for adults to open.


Design and Analysis of Plug and Gasketed Closures for Medical and Pharmaceutical Applications

by Clint Haynes

Billions of injection-molded plastic closures are produced each year for the medical and pharmaceutical industries. Although the packaging generally plays second fiddle to the product it contains, the seal between the bottle and closure represents the primary boundary for patient safety and product efficacy.

The main attributes of a successful medical or pharmaceutical closure are a microbial or liquid seal, acceptably low removal torque, and low cost. Two sealing systems commonly used to achieve these goals are closures with plug seals and closures that use a second material as a gasket or liner.

The plug seal has gained popularity because of its sealing robustness and low cost. The two critical dimensions for this type of radial-sealing closure system are the outside diameter (OD) of the plug and the inside diameter (ID) of the bottle finish. These dimensions and their variability establish the sealing performance, application torque requirements, and removal torque characteristics. The integrity of the sealing surface generally depends on the process that was used to produce the bottle. For containers molded on a wheel or shuttle machine, a secondary reaming operation is generally needed to improve the contact surface.

Plug seals are particularly versatile because they offer a great deal of axial compliance. Once contact is made between the plug and the bottle ID, sealing can be achieved over a broad range of axial travel or cap rotation for a relatively low application torque. The magnitude of the local contact stress and pressure caused by the interference of the cap and bottle is also very important to a successful design.

Figure illustrates predicted contact pressure distribution in a gasket seal at completion of assembly.


For extrusion-blow-molded bottle finishes, where the dimensional variability can be as much as ±0.010 in. on the diameter, selecting the appropriate dimensions can be a challenging task. The recommended process for selecting dimensions is to calculate the OD of the plug and ID of the bottle based on the yield stress of the material for the minimum interference condition. The performance at the nominal and maximum interference conditions is then determined using nonlinear finite-element analysis methods.

EVA, thermoplastic elastomers (TPEs), silicone, and paper-based materials are commonly used as gaskets and liners for medical and pharmaceutical packaging. If a microbial seal is required, injection-molded or extruded TPEs are typically used. Given the appropriate material selection and design, liners and gaskets offer very robust sealing systems. However, compared to gasketless sealing systems, these designs can be significantly more expensive to produce because they require higher-cost materials and additional material handling and assembly. These designs may also require higher removal torque.

The performance of liners can vary dramatically depending on the material used and the environmental conditions they will experience. When designing sealing systems using TPE, the primary technical hurdles include potentially high removal torque values and significant material relaxation at elevated temperature, often as a result of autoclave sterilization. The specific design performance can be simulated and optimized before prototypes are manufactured using nonlinear finite-element analysis techniques.

Clint Haynes is vice president of Stress Engineering Services (Mason, OH).

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