One day last week I was talking to a doctor of physical therapy and he asked a most interesting question that I had to think about before attempting an answer.

He said that he had a patient who could not take her oral pain medication because it upset her stomach and she asked him if she could crushed the tablet, mix in a hand cream and then apply it to the skin.

The patient wondered if the drug would be absorbed adequately for pain relief that way since commercial pain relief creams seemed to be popular with arthritic patients. He told her that he didn’t know if that would work but that he’d find out. He posed the question to me since I’m a pharmacist and he knew of several analgesic patches presently available that effectively deliver pain relief drugs through the skin.

Truly, I had never given much thought to a “do-it-yourself-at-home” drug delivery system such as that. Human skin has a barrier layer of stratum corneum (the outer-most part of the epidermis) that is lipid-rich and penetration of large drug molecules through that layer without expert preparation into a cream would be difficult.

For centuries, poultices, gels, ointments, creams and bath salts have been applied to skin for both cosmetic and health benefits. However, these types of applications are primarily intended for their topical effects with no regard to absorption through the skin’s barrier layers.

As a long distance runner, though, I often soak in a hot Epsom Salt bath (magnesium sulfate) to relieve the soreness in my tired, restless legs and believe that the magnesium absorbs to give a beneficial effect.

In the last couple of centuries, certain botanical medications were incorporated into emulsions (intricate water and oil mixtures that literally wrap water and oil molecules around each other) to create a delivery system that provided some systemic action if the drugs were adequately dissolved in the water or oil before the emulsion was compounded.

The idea of a topical drug delivery system has been expanded by the modern pharmaceutical industry and transdermal technology to deliver drugs into the body is a reality today.

Transdermal patches now deliver a wide variety of medications: male and female hormone therapy, both narcotic and non-narcotic pain relieving drugs, contraceptives, motion sickness drugs, smoking cessations drugs, and even medications for Parkinson’s disease.

The first transdermal drug patch was launched in 1979, and presently about 20 drugs are available in transdermal drug patch therapies.

The technology has limitations, however, in that the drug to be absorbed from the patches must be of a particularly small molecule size, they must be soluble in oils and be therapeutically effective in low doses. At one time, research teams attempted to administer insulin to diabetics in this manner, but the insulin molecule is too large to penetrate the skin’s barrier layers.

So the ultimate answer to this patient’s question about crushing and mixing her pain medication into a hand cream would not work well since the pure drug would need to be dissolved into the basic emulsion components (the water, the oil, or a chemical emulsion compound) before actually making the cream. The same principle would apply to an ointment, gel or lotion.

I also joked with my physical therapist friend about using such transdermal technology to poison someone. Although I’ve blogged in the past about several poison compounds that absorb readily through the skin, adulteration of transdermal patch technology was one specific method of murder I had not considered.

Contaminating a drug patch with a poison to either acutely or chronically poison a victim is certainly possible. People have been murdered with various drug patch medications via overdosing on nicotine patches or fentanyl narcotic patches by applying several at a time.

It’s conceivable that someone could discreetly inject a poison into a prescription drug patch to kill a victim. The poison, however, would have to be lethal in minute quantities to do this effectively and have the ability to be absorbed through the skin. I think the concept would make for an interesting and unique murder weapon.

The possible poisons that could taint a prescription drug patch in this way might include anthrax, polonium, various snake and insect venoms, jellyfish and fugu compounds, botulin and various heavy metals (such as dimethyl mercury), and various liquid nerve agents.

There are new transdermal technologies on the horizon that would make transdermal poisoning even more conceivable. Second-generation transdermal technology uses micro-ultrasound systems to increase skin permeability and iontophoresis (breaking down a drug molecule into its ion components) to increase absorption rates of drugs.

Third-generation transdermal technology includes thermal ablation (outer layer tissue destruction with micro-bursts of heat) and micro-needles imbedded into transdermal patches to not only increase absorption rates, but also to include classes of drugs (or poisons) previously unable to be absorbed through the skin with traditional drug patch technology.

These enhanced transdermal options increase the potential of drug patch technology being used as dramatic alternatives to oral delivery and hypodermic injections as a method of poisoning the villain in your next thriller.

Thoughts? Comments? I’d love to hear them!